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  • Articles  (392)
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  • Springer  (392)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of space flight on GLUT-4 content in rat plantaris muscle (1998)
    Springer
    International journal of biometeorology 41 (1998), S. 101-104 
    Details
    ISSN: 1432-1254
    Keywords: Key words Space flight ; Rat ; Plantaris muscle ; GLUT-4 ; Citrate synthase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  The effects of 14 days of space flight on the glucose transporter protein (GLUT-4) were studied in the plantaris muscle of growing 9-week-old, male Sprague Dawley rats. The rats were randomly separated into five groups: pre-flight vivarium ground controls (PF-VC) sacrificed approximately 2 h after launch; flight groups sacrificed either approximately 5 h (F-R0) or 9 days (F-R9) after the return from space; and synchronous ground controls (SC-R0 and SC-R9) sacrificed at the same time as the respective flight groups. The flight groups F-R0 and F-R9 were exposed to micro-gravity for 14 days in the Spacelab module located in the cargo bay of the shuttle transport system – 58 of the manned Space Shuttle for the NASA mission named ”Spacelab Life Sciences 2”. Body weight and plantaris weight of SC-R0 and F-R0 were significantly higher than those of PF-VC. Neither body weight nor plantaris muscle weight in either group had changed 9 days after the return from space. As a result, body weight and plantaris muscle weight did not differ between the flight and synchronous control groups at any of the time points investigated. The GLUT-4 content (cpm/µg membrane protein) in the plantaris muscle did not show any significant change in response to 14 days of space flight or 9 days after return. Similarly, citrate synthase activity did not change during the course of the space flight or the recovery period. These results suggest that 14 days of space flight does not affect muscle mass or GLUT-4 content of the fast-twitch plantaris muscle in the rat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004840050060
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  • 2
    Electronic Resource
    Electronic Resource
    Porous-silicon microcavities (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1213-1223 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Other solid inorganic materials ; Electron states in low-dimensional structures (superlattices, quantum well-structures and multilayers) ; Quantum optics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The properties and preliminar applications of porous-silicon (p-Si) microcavities are here reported. These structures are based on a planar resonator formed by two narrow-band high-reflectance distributed Bragg reflectors separated by a thin active optical layer, all of which are made of p-Si layers. The accurate control of the electrochemical dissolution of Si lets us realize p-Si multilayers with the desired refractive indices sequence. Large improvements of the emission properties of p-Si microcavities with respect to standard p-Si samples are observed: 1) increased emission intensity, 2) spectral narrowing of the emission band, and 3) high directionality in the emission pattern. Resonant-cavity light-emitting diodes with higher efficiencies and stabilities with respect to standard p-Si/metal devices are demonstrated. Reflectivity changes due to absorption saturation have been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464699
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  • 3
    Electronic Resource
    Electronic Resource
    The optical transition in porous Si: The effects of quantum confinement, surface states and hydrogen passivation (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1121-1129 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present a theoretical study of two infinite wires of Si with a different lateral size. The analysis is based on the linear muffin tin orbitals method in the atomic sphere approximation (LMTO-ASA). We consider free, partially and totally H-covered [001] Si quantum wires with rectangular cross-section. The results of this investigation prove the quantum wire nature of porous Si and interpret many of its physical features. In particular we show thata) as expected quantum confinement originates the opening of the LDA gap;b) the gap opening effect is asymmetric: 1/3 of the widening is in the valence band, while 2/3 in the conduction band;c) the near band gap states originate from Si atoms located at the center of the wire;d) the confinement is enhanced in the case of free surfaces;e) the imaginary part of the dielectric function shows a low-energy side structure strongly anisotropic, identified as responsible of the luminescence transition;f) the presence of dangling bonds destroys the luminescence properties;g) in spite of featurec), all Si atoms are collectively involved in the luminescence transition;h) the shift detected by the Si L2, 3VV Auger signal is due to H-interaction effect and is not a measure of the quantum confinement effect;i) the Si atoms probed by the Si L2, 3VV Auger are bonded with H and H2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464690
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  • 4
    Electronic Resource
    Electronic Resource
    Erbium doping of crystalline and amorphous silicon for optoelectronic applications (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1131-1148 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this work we demonstrate that efficient light emission at 1.54 μm can be achieved when Er ions are incorporated into crystalline Si or in heavily oxygen-doped amorphous and polycrystalline Si films (SIPOS). We have found that temperature quenching of photo- and electroluminescence, which is the major limitation towards the achievement of room temperature luminescence, can be strongly reduced by codoping these films with oxygen. This impurity is already present in as-prepared SIPOS and it is introduced by ion-implantation in crystalline Si. Er luminescence is obtained under both optical and electrical excitation and we demonstrate that excitation occurs through a carrier-mediated process. Electrical excitation is obtained by incorporating Er in properly designed device structures. It is found that this excitation can occur both through the recombination of hole-electron pairs and through impact excitation of the Er ions by hot electrons. These two mechanisms have different efficiencies and impact excitation is shown to prevail at room temperature. These data are presented and possible future developments are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464691
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum confinement and disorder in porous silicon: Effects on the optical and transport properties (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1111-1119 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The striking optical properties of porous silicon (PS) show a twofold aspect typical of an ordered and a disordered material, respectively. Raman, electron microscopy, and resonant photoluminescence studies indicate that the light emission originates from crystalline regions. On the contrary, several features, like the non-exponential decay of photoluminescence (PL), the broad emission spectrum, the photoluminescence fatigue under light exposure etc. are typical of a disordered material and reminiscent of similar effects founde.g. in amorphous semiconductors. These twoapparently conflicting aspects have for a long time hindered the understanding of the basic light emission mechanism. In this paper we report new optical data showing that disorder in porous silicon leads to strong carrier localisation. Light emission in PS is suggested to occur through transitions involving localized states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464689
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  • 6
    Electronic Resource
    Electronic Resource
    Light-emitting nanocrystalline silicon by low-pressure chemical-vapor deposition of disilane (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1159-1165 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Porous silicon is an attractive material for silicon optoelectronics. The great advantage of porous silicon lies on the simple way of production which makes silicon nanostructures easily available. After several papers have been published on this topic, we are able to identify some disadvantages connected to the porous nature of the material and to the method of fabrication. Other dry processes can be used to produce Si nanostructures. In this paper we present a method fully compatible with the standard semiconductor technology. The optical and structural properties of the nanocrystalline films so far obtained are presented, together with some promising results indicating good electrical properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464693
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  • 7
    Electronic Resource
    Electronic Resource
    Photoluminescence studies of Si nanocrystals (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1167-1177 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report room temperature time-resolved photoluminescence (PL) and temperature dependence of continuous wave (cw) PL studies of high fluence (from 3·1016 to 3·1017 cm−2) Si+-implanted thermal SiO2 layers after annealing at high temperature (T=1000°C). Such measurements were related to TEM analysis of samples. Nancocrystals were observed at TEM only a samples implanted at higher fluence. In these samples a near infrared PL signal peaked at approximately 1.5 eV with decay time of about 100 μs is present. Besides, in all samples a light emission is present in the green region of the spectrum. The intensity of the emission shows large variations with ion fluence, and is characterized by 0.4, 2 and 7 ns decay times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464694
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  • 8
    Electronic Resource
    Electronic Resource
    Changes in magnetic properties induced by heavy-ion irradiation in magnetic insulators as seen by Mössbauer spectroscopy (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 337-340 
    Details
    ISSN: 0392-6737
    Keywords: Atoms and molecules ; Magnetic ordered materials: other intrinsic properties ; Magnetomechanical and magnetoelectric effects, magnetostriction ; Mössbauer effect: other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The high-energy heavy-ion irradiation of magnetic materials induces not only amorphous matter in the ion tracks but also improvement or even creation of new magnetic properties in a stressed shell surrounding the track core. Two examples are presented in this paper: magnetization creation in the spinel ZnFe2O4 after Kr, Xe and Pb irradiations and trapping of magnetic domains in another spinel, the magnetite Fe3O4, after lead irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458914
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of hematin and Mössbauer gamma-radiation on human osteosarcoma cell lines (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 359-363 
    Details
    ISSN: 0392-6737
    Keywords: X- and γ-rays instruments and techniques ; γ-rays ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In the present work we report an investigation on cultures of the human osteosarcoma cell line «MG-63» and the human osteoblastic cell line «HOBIT». We have examined the combined effects of hematin and 14.4keV gamma-radiation from a Mössbauer source. Preliminary results seem to confirm the trend already observed for the bone marrow system. Different degrees of growth inhibition were observed when hematin alone and hematin plus gamma-rays were administered to the cultures. It was previously found that hematin has no toxic effects on normal cells up to a concentration of 10−4 M, but the same concentration produces various degrees of inhibition on cultures of tumor cells. While no significant effect could be attributed to irradiation alone, hematin plus irradiations show a larger inhibition than that expected for pure additive effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458918
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature dependence of phonon energy spectra with nuclear resonant scattering of synchrotron radiation (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 381-384 
    Details
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Phonons and vibrations in crystal lattices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The phonon energy spectra of a polycrystalline α-Fe foil were observed at 150 K and 300 K by using the nuclear resonant scattering of synchrotron radiation. In each spectrum, inelastic scattering was observed at both sides of the elastic peak. It was found that the ratio of the elastic-scattering component and the asymmetry of the intensity of the side bands observed at 150 K are larger than those observed at 300 K, respectively. The observed temperature-dependent spectra are in good agreement with the spectra calculated from the phonon energy distribution function. One of the advantageous features of this method is that the excitation of only a specific element is possible. Our results show that this method is applicable to the study of lattice dynamics and opens a new field of the nuclear resonant scattering spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458922
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  • 11
    Electronic Resource
    Electronic Resource
    Nanoparticles (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 163-180 
    Details
    ISSN: 0392-6737
    Keywords: Fine particle systems ; PACS 76.80 ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Mössbauer spectroscopy is well known to be a very sensitive technique for studying small magnetic particles: small variations in the dynamic properties often manifest themselves as rather large changes in the spectra. However, anay detailed investigation is limited by the complexity of the phenomena and also by the line shape problem. As a result, variations in Mössbauer features between samples can always be interpreted in several ways. Utilization of other techniques to support the conclusions in indispensable. This will be emphasized in the case of γ-Fe2O3 nanoparticles, the dynamic properties of which have been studied over a very wide time range using measurements of the zero-field-cooled magnetization, thermoremanent magnetization, and a.c. susceptibility at various frequencies, in addition to Mössbauer spectroscopy. After a survey of the basic laws of superparamagnetic relaxation and the effects of interparticle interactions, this paper will show how the approximations usually made for interpreting Mössbauer data can lead to misinterpretation of the phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458890
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  • 12
    Electronic Resource
    Electronic Resource
    Mössbauer study on the gamma-radiolysis of tetralithium iron(III) trioxalate chloride nonahydrate (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 221-225 
    Details
    ISSN: 0392-6737
    Keywords: Radiolysis, dissociation and ionization by X-ray, γ-ray and particle radiation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The final product of the gamma-radiolysis of tetralithium iron (III) trioxalate chloride nonahydrate has been identified by Mössbauer spectroscopy as FeC2O4·2H2O. The radiolytic decomposition proceeds as a first-order process due to the original compound depletion and to the radiolytic stability of the ferrous compound. Chemical calibration of the relative peaks areas of the two iron species indicates that the correspondingf-factors ratio is unaffected by the radiolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458894
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  • 13
    Electronic Resource
    Electronic Resource
    57Fe Mössbauer study of ternary alloy systems Fe(Sb1−x Te x )2 for 0.5≤x≤1.0 at 4.2K (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 243-246 
    Details
    ISSN: 0392-6737
    Keywords: Mösbauer effect ; other γ-ray spectroscopy ; Fe and its alloys ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report on low-temperature (4.2 K)57Fe Mössbauer studies of the ternary alloy system Fe(Sb1−x Te x )2 for 0.5≤x≤1.0. The Mössbauer spectra are electric-quadrupole doublets for all the specimens, indicating a non-magnetic character. The quadrupole splitting decreases with the increase in tellurium concentration. FeTe2 has also been studied in external magnetic fields up to 6T. These experiments show that the electric-field gradient in this alloy is negative and has an asymmetry parameter of η ≈0.7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458898
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  • 14
    Electronic Resource
    Electronic Resource
    Mössbauer studies related to the solid-state dynamics of C60 (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 227-230 
    Details
    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Mössbauer effect ; other γ-ray spectroscopy ; Crystalline state (including molecular motions in solids) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary C60 (Buckminsterfullerene) is isolated from organic solvents above 260 K as an f.c.c. solid with complete orientational disorder. The rotational dynamics are diffuse and isotropic, with a short (12 ps) correlation time at 300 K. Below 260 K, the solid forms in a simple cubic lattice withPa3 symmetry. The librational motion occurs by activated jumps with a correlation time of about 60 ns at 200 K. To gain further insight into the dynamics of C60, the compound C60Fe(CO)4 (I) (generously made available to us by A. Stephens and M. Green of Oxford University) has been studied by57Fe Mössbauer spectroscopy. As expected, the resonance at 90 K consists of a doublet with an isomer shift (relative to metallic iron) of 0.034(1) mm s−1 and a quadrupole splitting of 1.607(5) mm s−1. There is no significant temperature-dependent, intensity asymmetry of the doublet. The temperature dependence of the effect magnitude is well fit by a linear regression over the range 85〈T〈210 K. To elucidate the relationship of these results to the effect of the C60 moiety in I, further lattice dynamical Mössbauer studies have been carried out on (maleic anhydride) Fe(CO)4 (II), one of the few isolatable tetracarbonyl complexes of iron. For (II), the quadrupole splitting is 1.371(5) mm s−1 at 90 K, and the temperature, dependence of the isomer shift is smaller than it is for (I), while the temperature dependence of the recoil-free fraction is significantly larger in (I) than in (II).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458895
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  • 15
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    Electronic Resource
    A Mössbauer-effect investigation of some electrochemically inserted lithium thiospinels (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 237-241 
    Details
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Electrochemical devices ; Crystal symmetry: models, space groups and crystalline systems and classes ; Electron microscopy and other methods ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present here a study carried out on In16Sn4S32 and In16Fe8S32 spinels. Electronic and local environment changes of Sn and Fe are discussed from recorded Mössbauer parameters. In the case of the tin thiospinel, a reduction process from SnIV to SnII is obvious till an amount of 8 inserted Li. For the iron thiospinel a migration of iron atoms from the octahedral to the tetrahedral sites is observed. In the region of higher lithium amounts (10– Li), in both spinels a further environment appears indicating an increase of covalency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458897
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  • 16
    Electronic Resource
    Electronic Resource
    Red- and blue-light emission from free-standing porous silicon (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1149-1157 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Other solid inorganic materials ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Interfaces ; heterostructures ; nanostructures ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report the observation of strong red- and blue-light emission in free-standing porous-silicon samples prepared fromn + substrates at different anodization current densities. The surface morphology of the free-standing samples has been analyzed by means of atomic-force microscopy. Upon excitation with nanosecond pulses at room temperature, both blue and red luminescence bands appear, peaked around 3.2 and 2.0 eV, respectively. An extensive study of the time-resolved behavior of the photoluminescence signal reveals different dynamical features for the two spectral regions. The observed long decay time (several μs) of the red band reflects the predominant effect of non-radiative processes and is consistent with models based on excition diffusion through the interconnected silicon nanocrystals (quantum dots) skeleton. The relatively fast blue-band decay time (≈400 ns) is shown to be related to non-radiative recombination through trap states at the silicon nanocrystal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464692
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  • 17
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    Electronic Resource
    Effect of surfactants in the electrochemical preparation of porous silicon (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1179-1186 
    Details
    ISSN: 0392-6737
    Keywords: Methods of deposition of films and coatings ; film growth and epitaxy ; Electrochemistry and electrophoresis ; Surface and interface chemistry ; Infrared and Raman spectra and scattering ; Photoluminescence ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Porous-silicon layers were prepared by anodic oxidation of mono- and multi-crystalline Si substrates,n + andp-doped, in aqueous HF solutions containing surfactants. The resulting samples show a bright red-orange photoluminescence: PL spectra and uniformity are analysed as a function of surfactants kind and concentration. Moreover, the results of Raman spectroscopy are discussed in terms of current theories.
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    URL: http://dx.doi.org/10.1007/BF02464695
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  • 18
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    Electronic Resource
    Porous-silicon coatings for photovoltaic devices (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1225-1232 
    Details
    ISSN: 0392-6737
    Keywords: Methods of deposition of films and coatings ; film growth and epitaxy ; Surface treatments ; Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity ; Photoelectric conversion: solar cells and arrays ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Porous silicon was formed on multicrystalline Si substrates by stain etching in aqueous HF/HNO3 solutions. In this work optical and electrical properties of the resulting films are discussed as a function of process parameters. Porous-Si films have been shown to be able to reduce surface reflectance to 3% in 350–700 nm wavelength range and their application in anti-reflection coating of photovoltaic solar cells has been demonstrated, obtaining (10×10) cm2 multicrystalline Si solar cells with efficiency approaching 12% under standard AM 1.5 simulated sunlight.
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    URL: http://dx.doi.org/10.1007/BF02464700
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  • 19
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    TEM and photoluminescence characterization of porous-silicon layers from 〈111〉-orientedp + silicon substrates (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1233-1239 
    Details
    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A first structural investigation, carried out by transmission electron microscopy on porous-silicon samples fromp +, 〈111〉-oriented substrates is presented. The samples, which show intense visible room temperature luminescence, are composed by an interconnected network of crystalline nanostructures. Evidences of the pores propagation along the 〈100〉 directions are provided. The optical and morphological characteristics of the investigated samples are found to be much similar to those of samples coming fromp-type, non-degenerate, 〈100〉-oriented substrates rather than those obtained from 〈100〉 substrates with comparable resistivity. This striking effect is explained by invoking different etch-limiting mechanisms during pore formation. Their relative weights are proposed to depend on the crystallographic orientation of the silicon specimen subjected to etching.
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    URL: http://dx.doi.org/10.1007/BF02464701
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  • 20
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    Identification of a spin-glass and a cluster-glass by Mössbauer measurements: Fe0.5Mn0.5TiO3 and Fe0.2Mg0.8TiO3 (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 263-268 
    Details
    ISSN: 0392-6737
    Keywords: Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) ; Critical-point effects, specific heats short-range order ; Antiferromagnetics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Mössbauer measurements have been made on two kinds of spin-glass (SG) systems: one is the magnetically non-diluted mixed compound Fe0.5Mn0.5TiO3 with the SG-freezing temperatureT SG=21.5K, and the other is the diluted one Fe0.2Mg0.8TiO3 withT SG=6K. We have shown that the temperature variation of the Mössbauer spectrum of Fe0.2Mg0.8TiO3 above and around itsT SG is essentially different from that of Fe0.5Mn0.5TiO3: the former is typical of a cluster-glass and the latter of an ordinary spin-glass. The present work has clearly demonstrated that the Mössbauer spectroscopy is the most useful and unique technique to distinguish a cluster-glass from an ordinary spin-glass.
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    URL: http://dx.doi.org/10.1007/BF02458902
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  • 21
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    Mössbauer, X-ray fluorescence and paleomagnetic studies of deep-sea sediments from the Peru Basin: two million years of sedimentation history (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 341-345 
    Details
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Sediment cores with different sub-bottom depths (I: 45 cm and II: 700 cm) from the Peru Basin have been investigated. From the depth profile of the relative amount of Fe(II) a redox zone is obtained which correlates with the organic carbon flux into the sediment (core I). Mössbauer parameters suggest that the iron in the sediments is mainly contained in clay minerals and to varying extent also in goethite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458915
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  • 22
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    Reyleigh scattering of Mössbauer radiation in hyaluronate oriented fibres (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 371-374 
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    ISSN: 0392-6737
    Keywords: X-ray ; Mössbauer and other γ-ray spectroscopic analysis methods ; Molecular biophysics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The Rayleigh scattering of Mössbauer radiation has been measured on highly oriented fibres of Na-hyaluronate at different hydration levels. The elastic-and inelastic-scattering intensities, measured as a function of the scattering vectorQ, have provided information on the dynamic structuring of the water molecules to the polysaccharidic chains.
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    URL: http://dx.doi.org/10.1007/BF02458920
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    Time-dependent absorption of gamma-radiation under high-frequency magnetic excitation of57Fe (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 385-388 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other ψ-ray spectroscopy ; Strong field excitation of optical transitions in quantum systems multiphonon processes ; dynamic Stark shift ; Effects of internal magnetic fields ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have studied the time dependence of Mössbauer absorption in a magnetically soft sample of Fe18Ni82 permalloy under the influence of a radio-frequency (r.f.) magnetic field. Absorption was measured as a function of the r.f. field phase at specific gamma-ray energies. We have shown that measuring the time dependence of absorption makes it possible to differentiate between purely magnetic and magnetoacoustic modulation mechanisms even in cases where clear distinction is not visible in conventional energy domain spectra.
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    URL: http://dx.doi.org/10.1007/BF02458923
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    Selected studies of magnetism at high pressure (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 145-161 
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    ISSN: 0392-6737
    Keywords: Metal-insulator transitions ; High-pressure and shock-wave effects in solids ; Mössbauer effect ; other γ-ray spectroscopy ; Transition-metal compounds ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Most previous studies of magnetism in various compounds under extreme conditions have been conducted over a wide pressure range at room temperature or over a wide range of cryogenic temperatures at pressures below 20 GPa (200 kbar). We present some of the most recent studies of magnetism over an extended range of temperatures and pressures far beyond 20 GPa,i.e. in regions of pressure-temperature (P-T) space where magnetism has been largely unexplored. Recent techniques have permitted investigations of magnetism in selected 3d transition metal compounds in regions ofP-T where physical properties may be drastically modified; related effects have often been seen in selected doping studies at ambient pressures. We present57Fe and129I Mössbauer isotope studies covering the range 300–4 K to sub-megabar pressures in compounds such as Sr2FeO4, LaFeO3 and FeI2, representative of a broad class of 3d transition metal compounds. At ambient pressure the electronic structure of the transition metal atom in these antiferromagnetic insulators extends from 3d 4 to 3d 6 and has a distinct influence on the pressure evolution of their magnetic properties. Mössbauer studies of these compounds are considered in conjunction with available structural and electrical transport data at pressure.
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    URL: http://dx.doi.org/10.1007/BF02458889
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    Magnetic properties of57Fe/Ir(100) superlattices (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 299-304 
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    ISSN: 0392-6737
    Keywords: Layer structures: multilayers, and superlattices (growth structure, and nonelectronic properties) ; Magnetism in interface structures (including layer and superlattice structures) ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The synthesis of a new BCT Fe phase was performed in Fe/Ir(100) superlattices grown by MBE. Magnetic properties of57Fe/Ir(100) superlattices with 4 ml Fe and variable Ir thickness (2–30 Å) are investigated by57Fe conversion electron Mössbauer spectroscopy in the 4.2–300 K temperature range. Two spectral components are evidence, related, respectively, to Fe atoms involved in the central part of the iron layers and at the interface between iron and iridium layers. The appearance of a high magnetic hyperfine splitting in the iron BCT structure above a volume threshold of 12 Å3 is evidenced. Marked differences are observed between the mean magnetic properties and the local ones suggesting strong relaxation effects.
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    URL: http://dx.doi.org/10.1007/BF02458908
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    Spinodal decomposition of Fe−Cr−Ni alloys studied by Mössbauer spectroscopy (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 259-262 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect, other γ-ray spectroscopy ; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) ; X-ray Mössbuer and other γ-ray spectroscopic analysis methods ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A thermodynamic calculation of the Fe−Cr−Ni phase diagram suggests that the composition 30 at.%Cr-5 at.%Ni is expected to be found inside the spinodal line, whereas 16 at.%Cr-5 at.%Ni is expected outside at 723 K. These two alloys have been thermally aged for time periods up to 40 minutes at 723K. A significant broadening of the magnetic-hyperfine-field distribution indicates that Fe-30 at.%Cr-5 at.%Ni undergoes typical spinodal decomposition in agreement with the calculation. Spinodal decomposition is distinguished from nucleation-growth by a detailed analysis of the magnetic-hyperfine-field distribution.
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    Man-made materials—an exciting area for hyperfine-interaction investigations (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 137-144 
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    ISSN: 0392-6737
    Keywords: Intrinsic properties of magnetically ordered materials ; Magnetic films and multilayers ; Nuclear magnetic resonance and relaxation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Man-made low-dimensional magnetic systems including surfaces, interfaces and multilayers, have attracted a great amount of attention in the past decade because, as expected, the lowered symmetry and coordination number offer a variety of opportunities for inducing new and exotic phenomena and so hold out the promise of new device applications. Local spin density functional (LSDF)ab initio electronic-structure calculations employing the full-potential-linearized augmented-plane-wave (FLAPW) method have played a key role in the development of this exciting field by not only providing a clearer understanding of the experimental observations but also predicting new systems with desired properties. One of the striking successes of theory in the last decade has been the calculation of hyperfine fields at surfaces and interfaces. Concurrently, several groups have followed the pioneering work of Korecki and Gradmann and have measured hyperfine fields at surfaces and interfaces. In this paper, we review new features of hyperfine-interaction investigations in man-made materials which emphasizes how the close interplay of theoretical determinations and experiment are essential because the hyperfine field is not proportional to the magnetization and so interpretations of experiment are totally dependent on theory.
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    URL: http://dx.doi.org/10.1007/BF02458888
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    Donor-hydrogen complexes in crystalline silicon (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 181-198 
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    ISSN: 0392-6737
    Keywords: Impurities: concentration, distribution, and gradients ; Doping and impurity implantation in germanium and silicon ; Interaction between different crystal defects ; gettering effect ; Calculations of total electronic binding energy ; Elemental semiconductors ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing119Sb→119Sn source Mössbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the Mössbauer intensity associated with the trapping of hydrogen, even at low temperatures. This is interpreted as the formation of a component with a negligible recoilless fraction. The different Mössbauer components were studied as a function of H dose, H-implantation temperature and annealing temperature. The data show that the visible component is associated with the well-known SbH complex, whereas the invisible component is associated with the formation of SbH n (n≥2) complexes. We show that these complexes are in thermal equilibrium with a larger hydrogen reservoir (H 2 * ), which governs their thermal stability. No Sb-H complexes are observed inp-type Si after H-implantation, in agreement with the current belief that hydrogen has a deep donor level in the gap. The microscopic structure of the various Sb-H and Sn-H complexes was studied with first-principles calculations using the pseudopotentialdensity-functional approach. The structure of the Sb-H complex is found to be similar to the P-H complex, with the H in an antibonding site of a Si atom neighbouring the Sb impurity. For SbH2 three configurations are found with energies differing by less than ≈ 0.1 eV. We find that the reaction SbH+H≠SbH2 is exothermic. We argue that the SbH2 complexes are shallow donors, irrespective of the structure. Therefore, the formation of SbH2 may depassivate the sample.
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    URL: http://dx.doi.org/10.1007/BF02458891
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    AC conductivity of porous silicon: A fractal and surface transport mechanism? (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1187-1196 
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    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In this paper we report on the frequency dependence of the AC conductivity of porous silicon in the range 10 Hz-100 kHz. Two types of testing devices have been fabricated on three different series of samples formed electrochemically using as a starting materialptype,n −-type andn +-type silicon substrates. For frequencies less than 20-40 kHz the conductivity is found to follow a sublinear frequency dependence. This behaviour is typical of a carrier transport mechanism determined by an anomalous diffusion process. At higher frequencies we find that surface states influence the transport mechanism. This suggests a double-channel transport mechanism: one related to porous-silicon “volume” properties and the other more connected to the “surface” itself.
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    URL: http://dx.doi.org/10.1007/BF02464696
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    Current-voltage characteristics of porous-silicon structures (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1197-1204 
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    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary I–V DC characteristics have been measured on metal/ porous-silicon structures. In particular, the measurements on metal/ free-standing porous-silicon film/metal devices confirmed the result, already obtained, that the metal/poroussilicon interface plays a crucial role in the transport of any device. Four-contacts measurements on free-standing layers showed that the current linearly depends on the voltage and that the conduction process is thermally activated, the activtion energy depending on the porous silicon film production parameters. Finally, annealing experiments performed in order to improve the conduction of rectifiyng contacts, are described.
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    White-light emission from porous-silicon-aluminum Schottky junctions (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 1205-1212 
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    ISSN: 0392-6737
    Keywords: Optoelectronic devices ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Porous-silicon-based white-light-emitting devices are presented. The fabrication process on different substrates is described. The peculiarities of technological steps for device fabrication (porous-silicon formation and aluminum treatment) are underlined. Doping profile of the porous layer, current-voltage characteristics, time response, lifetime tests and electroluminescence emission spectrum of the device are presented. A model for electrical behaviour of Al/porous silicon Schottky junction is presented. Electroluminescence spectrum of the presented devices showed strong similarities with white emission from crystalline silicon junctions in the breakdown region.
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    Point defects in FeAl (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 329-336 
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    ISSN: 0392-6737
    Keywords: Kinetics of defect formation and annealing ; Alloys ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Point defects in annealed B2-phase FeAl samples in the range 47–53 at.% Fe were studied using57Fe Mössbauer spectroscopy. Spectra were analyzed using local environment models according to which point defects in atomic shells close to probe atoms induce shifts in the nuclear monopole interaction. For well-annealed samples, better results were obtained assuming only the presence of FeAl antisite and VFe vacancy defects, and not of AlFe antisite defects. Monopole interactions of57Fe probes on the Fe and Al sublattices having no defects in the first two shells were about +0.27 and −0.03 mm s−1, respectively, with respect to Fe in alpha-Fe metal. The shifts induced by FeAl and VFe defects in the first shells of Fe probes on the Fe and Al sublattices were −0.15 and −0.24 mm s−1, respectively, and, in the second shells, +0.06 and +0.011 mm s−1. In addition to structural defects needed to accommodate deviations from stoichiometry, annealed samples were found to contain several percents of FeAl and VFe defects due to lattice disorder, with greater disorder in Fe-deficient alloys.
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    Photodissociation of carbonmonoxy-porphyrin complexes (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 353-357 
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    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Spectra ; photodissociation and photoionization of biomolecules ; bioluminescence ; Measurement of rate constants ; reaction cross-sections and activation energy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Partial photodissociation of two carbonmonoxy-porphyrin complexes, a bridged and a fenced one, has been achieved. The results from monitoring the recombination point to an important influence of the solvent matrix on the recombination rates.
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    Nuclear-resonance beamline at ESRF (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 375-379 
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    ISSN: 0392-6737
    Keywords: Phonons and vibrations in crystal lattices ; Nuclear resonance fluorescence ; Synchrotrons ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The Nuclear-Resonance Beamline at ESRF is dedicated to the excitation of nuclear levels by synchrotron radiation. The source of radiation and optical elements are optimized to provide an intense, highly monochromatic, collimated and stable X-ray beam of small cross-section at the Mössbauer transition energies between 6 keV and 30 keV. The set-up of the beamline allows to perform studies in diffraction, small-angle scattering, forward scattering and incoherent scattering. Equipment is available to maintain the sample at variable temperature and magnetic field. Fast detectors and timing electronics serve to separate the delayed nuclear scattering from the «prompt» electronic scattering and to measure the time spectra of nuclear radiation with sub-nanosecond resolution. The general layout and the parameters of the beamline are reported. Typical domains of applications are discussed and illustrated by first experimental results.
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    The active center of superoxide dismutase fromPropionibacterium shermanii (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 199-212 
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    ISSN: 0392-6737
    Keywords: Molecular biophysics ; Nuclear quadrupole resonance (NQR) ; Mössbauer spectra ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A self-consistent description of the EPR spectra and of the Mössbauer spectra of the natural superoxide dismutase fromPropionibacterium shermanii with ferric iron as an active centre is presented. The spectra were measured atpH 6.5, 7.8 and 9.4. The theoretical approach is based on the use of the complete crystal field Hamiltonian for the high-spin ferric complexes with due regard for the terms of the fourth power of the electronic spin. It is shown that a SOD molecule can exist in two conformations. The low-pH conformation has predominantly trigonal symmetry, while the high-pH conformation has the symmetry close to the «extreme rhombic». This interpretation is in full agreement with EXAFS structural data.
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    Structure and composition of iron-containing langmuir-blodgett films (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 305-311 
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    ISSN: 0392-6737
    Keywords: Magnetic properties of monolayers and overlayers ; X-ray, Mössbauer and other γ-ray spectroscopic analysis methods ; Mass spectrometry (including, SIMS, multiphoton ionization and resonance ionization mass spectrometry) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The composition of differently prepared Langmuir-Blodgett multilayers of ferric arachidate has been investigated by means of absorption Mössbauer spectroscopy and heavy-ion-induced mass spectrometry. We found that the iron concentration in qualitatively good films is 3.5 times higher than the stoichiometric value. Antiferromagnetic ordering in this two-dimensional model substance can be observed when the Fe−Fe distance in the layers is about 0.3 nm or below. The area density of the iron atoms in the planes decreases with decreasingpH values of the subphase which also leads to a disappearance of the long-range magnetic ordering and to a decrease of the Debye temperature of the films which is linearly dependent on the iron concentration in the films.
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    How to do resonant nuclear experiments with synchrotron radiation (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 213-220 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; X- and γ-ray instruments and techniques ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The use of synchrotron radiation to excite low-lying nuclear resonances is a rapidly developing field showing great promise for hyperfine spectroscopy, phonon spectroscopy and kinetic studies, crystallography, and fundamental physics experiments. Recent technical advances in synchrotron sources, optics, and fast detectors have drastically increased signal rates and expanded the range of samples that can be studied. A typical experiment today uses a high-brightness synchrotron source having X-ray pulses well-separated in time, a meV-bandpass monochromator using perfect crystals of silicon or germanium, a sample containing resonant nuclei, and an avalanche photodiode timing detector. Both coherent and incoherent scattering can be observed; the coherent scattering is used for hyperfine spectroscopy and studies of diffraction interference phenomena, and the incoherent-scattering signal promises to be very useful for phonon spectroscopy and other studies of excitations in condensed systems. At this point seven nuclear isotopes have been used to resonantly scatter synchrotron radiation, but the number is rapidly increasing.
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    Application of61Ni Mössbauer spectroscopy to chemical problems (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 231-235 
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    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Structure, bonding, conformation, configuration and isomerism of biomolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Using the possibility to produce61Co sources at the MAinz MIcrotron,61Ni Mössbauer spectroscopy was applied to different kinds of chemical problems. Measurements of isomer shifts andV zz values in some common compounds and compounds with unusual chemical bonding for comparison with band structure calculations, measurement of61Ni Mössbauer parameters in model compounds for hydrogenase and dehydrogenase with an active [NiS4] centre, and study of novel binary NiF3 compounds at helium temperature are presented.
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    57Fe Mössbauer study of Fe nitrides (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 253-257 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Fe and its alloys ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Magnetic properties of Fe nitrides have been re-examined by57Fe Mössbauer spectroscopy. Hyperfine magnetic fields for α″-Fe16N2 are 30, 31 and 39T at 298K, but the averaged hyperfine field is 33T and nearly equal to the value of pure α-Fe. σ-Fe2 N is an antiferromagnet below 9K having a small magnetic moment less than 0.1 μB, although γ′-Fe4N and ε-Fe3–2N are ferromagnets. ZnS-type FeN is non-magnetic at 4.2K. Mössbauer spectra obtained from NaCl-type FeN are complex and some Fe atoms in this nitride show a surprisingly large hyperfine magnetic field of 49T.
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    Harmonic analysis of Mössbauer spectra and its applications (1996)
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    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 269-273 
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    ISSN: 0392-6737
    Keywords: Spin density waves ; Antiferromagnetics ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A new iterative procedure for a numerical analysis of Mössbauer spectra in terms of higher-order harmonics is used to study spin-and charge-density waves in single-crystal and polycrystalline samples of chromium and chromium-vanadium alloys.
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    Iron nanoparticles grown in a carbon arc discharge (1996)
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    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 281-285 
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    ISSN: 0392-6737
    Keywords: Fine particle systems ; Mössbauer effect ; other γ-ray spectroscopy ; Structural acoustics and vibration ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Iron particles, encapsulated by graphite layers, were produced by means of the Kratschmer arc discharge method in an iron pentacarbonyl atmosphere. The Mössbauer effect is dominated by the vibration of the particles as a whole. Superparamegnetism is dominant for iron oxide particles. No endohedral iron fullerenes were observed, contrary to a previous report.
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    A non-magnetic Fe probe of multiple magnetic phase transitions in RMn2Si2−x Ge x , R=rare earth (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 275-280 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Magnetically ordered materials: other intrinsic properties ; Magnetic phase boundaries (including magnetic transitions, metamagnetism etc) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Dilute57Fe Mössbauer-spectroscopy studies of RMn2X2 (X=Si and/or Ge, R=La, Ce, Pr, Nd, Sm, Eu and Gd) at 4.2 to 650 K yield the following results: Fe in RMn2X2 does not carry a magnetic moment. It reveals the magnetic order in the Mn and R sublattices through transferred hyperfine fields (∼100 kOe). The compounds LaMn2Si2, LaMn2Ge2, CeMn2Ge2, PrMn2Ge2, NdMn2Ge2 and SmMn2Ge2, known to be ferromagnets withT c=300–350 K, are antiferromagnetically ordered above their correspondingT c. TherT N values extend from 385 K (SmMn2Ge2) to 470 K (LaMn2Si2). At the ferromagnetic-antiferromagnetic phase transition, a sharp reorientation of the Mn magnetic moments relative to the crystalline axes occurs. In RMn2Si2−x Ge x with intermediatex values, the Ge is much more dominant in determining the magnetic properties of the Mn sublattice. While PrMn2Si2 is an antiferromagnet (T N=365 K) and PrMn2Ge2 is a ferromagnetantiferromagnet (T c=328 K,T N=415 K), we find that in PrMn2SiGe, the magnetic behaviour is similar to that in pure PrMn2Ge2,T c=305 K andT N=395 K.
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    Mössbauer spectroscopy, intracluster atomic mobility and thermodynamics of ultrafine oxide clusters (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 287-292 
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    ISSN: 0392-6737
    Keywords: Phonons and vibrations in crystal lattices ; Solid-liquid transitions ; Thermodynamic properties and entropy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Dynamic properties of ultrafine clusters of γ-Fe2O3 (ferric oxide, FO) were studied by Mössbauer spectroscopy and by thermodynamic analysis. The data obtained for FO clusters allowed the conclusion that dynamic properties of clusters as well as the decrease of melting point and the appearance of a gap between freezing and melting points depend on intracluster atomic mobility. Intracluster atomic mobility in FO clusters was shown to increase by the action of surfactants which decrease intercluster interactions. The increase in intracluster atomic mobility was suggested to proceed via formation of a solid-liquid state.
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    Mössbauer spectroscopy on bent Si crystals (1996)
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    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 293-297 
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    ISSN: 0392-6737
    Keywords: Doping and impurity implantation in germanium and silicon ; Elasticity, elastic constants ; Crystal morphology and orientation ; Point defects (vacancies, interstitials, colour centres, etc.) and defect clusters ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have shown through Mössbauer spectroscopy that the electric field gradient (EFG), associated with an atomic defect, is sensitive to the bending of ultrathin Si crystals. The changes in the EFG depend on the bending direction. A direct application is the derivation of the orientation of defects that are located in the crystal’s surface region. We have used this observation for determining the configuration of Co dimers in Si. Based on the bending experiments, the pair axis is found to point in the 〈110〉 direction with respect to the host lattice.
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    URL: http://dx.doi.org/10.1007/BF02458907
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    Emission Mössbauer studies of57Co2+ and119Sb5+ adsorbed on γ-Fe2O3 and NiFe2O4 surfaces (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 313-317 
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    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Magnetism in interface structures (including layer and superlattice structures) ; Superface and interface chemistry ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Surface chemical states of57Co2+ and119Sb5+ ions adsorbed on γ-Fe2O3 and NiFe2O4 were studied in the presence of the aqueous phase using the magnetic interaction between the substrates and57Fe2+ or119Sn4+ arising from the adsorbed species. Two chemical forms were observed for the57Co2+ adsorbed on γ-Fe2O3; one giving a peak in the high-field region and another giving a broad distribution in the lower fields, which were attributed to57Co2+ at surfaceB sites of the spinel structure of γ-Fe2O3 and57Co2+ species weakly bonded to the substrate, respectively. In case of the NiFe2O4 substrate, the latter species was dominant and was converted to the former by heating. Most of the119Sb5+ ions adsorbed on the γ-Fe2O3 and NiFe2O4 particles were found to have a certain magnetic interaction with the magnetically ordered ions of the substrates.
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    Mössbauer studies of ultrathin Fe/Pt multilayers (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 319-323 
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    ISSN: 0392-6737
    Keywords: Magnetism in interface structures (including layer and superlattice structures) ; Magnetic properties of monolayers and overlayers ; Interfacial magnetic properties ; Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A series of ultrathin Fe/Pt multilayers, prepared by magnetron sputtering, were studied by CEMS and transmission MS. The Fe-layer thickness varied from 3 to 12.5 Å and that of Pt from 5 Å to 39 Å. The 3 Å/9 Å Pt sample displays magnetic hyperfine structure at RT, while the 3 Fe/19 Pt sample is paramagnetic at RT, demonstrating the effect of interlayer interaction. Both samples display out-of-plane magnetic anisotropy with 39° angle with respect to the vertical for the former and nearly 0° angle for the latter. The analysis of the spectra of samples with thickness larger than one monolayer of Fe is done with components assigned to individual Fe monolayers. In all these cases a component appears with a hyperfine field larger by ∼ 10% at RT and 17% at L.He than the corresponding values of α-Fe. This component is attributed to the first monolayer below the Fe/Pt interface in accordance with similar results in the Fe/Pd system and with theoretical predictions.
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    57Fe-DCEMS studies of thin corrosion layers (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 325-328 
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    ISSN: 0392-6737
    Keywords: X-ray Mössbauer and other γ-ray spectroscopic analysis methods ; Metals and alloys ; Composition and phase identification ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The characterization of the corrosion products formed on an57Fe film onto a low alloy steel disc after 4 h and 8 h exposure to an artificially SO2-polluted atmosphere has been carried out by ICEMS/DCEMS. The corrosion products found are FeSO3·3H2O, FeSO4·nH2O, a third unidentified Fe2+ species, an amorphous Fe3+ oxyhydroxide and a second Fe3+ species which could correspond to superparamagnetic α-FeOOH or ferrihydrite. Although the DCEM spectra recorded at different electron energies do not show dramatic differences in the relative concentrations with depth, the results suggest that FeSO3·3H2O is preferentially located in the inner part of the corrosion layer whilst the outer part is richer in FeSO4·nH2O and Fe3+ species.
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    URL: http://dx.doi.org/10.1007/BF02458912
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    Iron(III) species formed during iron(II) oxidation and iron-core formation in the bacterioferritin ofEscherichia coli (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 347-352 
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    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Other topics in biophysics and medical physics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary This paper describes a preliminary investigation of the mechanisms of Fe(II) oxidation and storage of Fe(III) in the bacterioferritin ofEscherichia coli (EcBFR). Using Mössbauer spectroscopy to examine the initial oxidation of iron by EcBFR we have confirmed that this ferritin exhibits «ferroxidase» activity and have shown that dimeric and monomeric iron species are produced as intermediates. We compare the characteristics of ferroxidase activity in EcBFR with those of human H-chain ferritin (HuHF) and discuss the different Mössbauer parameters of their dimeric iron with reference to the structures of their di-metal sites. In addition, we present preliminary findings suggesting that after an initial «burst», the rate of oxidation is greatly reduced, possibly due to blockage of the ferroxidase centre by bound iron. A new component, not found in HuHF and probably representing a small cluster of Fe(III) atoms, is reported.
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    URL: http://dx.doi.org/10.1007/BF02458916
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    Dynamics of polyglutamic acids in α-helical and coil states. Comparison with dynamics of some globular proteins. Rayleigh scattering of Mössbauer radiation (RSMR) data (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 365-369 
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    ISSN: 0392-6737
    Keywords: Molecular dynamics and conformational changes ; Mössbauer effect ; other γ-ray spectroscopy ; Brillouin and Rayleigh scattering ; other light scattering ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The classical model system poly-L-glutamic acid (poly-Glu), was investigated in a disordered coil state (atpH=7.0) and in helix state (atpH=2.0) by the RSMR technique. By considering that the coil state of poly-Glu models unfolded (random coil) state and α-helix state models the fluctuating secondary structure (during consequent folding of protein), a comparative analysis of the dynamical properties of poly-Glu in different states with the dynamical properties of different proteins in the native state (α-helical myoglobin and HSA, partially β-sheet lysozyme) and in intermediate (molten globule) state (α-lactalbumin) was performed. This comparison brings some unpredicted results: native α-helical proteins behave close to random coil, native partially β-sheet proteins behave close to fluctuating secondary structure (α-helix) and the dynamic behaviour of molten-globule state (partially β-sheet α-lactalbumin) is not different from the behaviour of lysozyme and much more rigid than that of native α-helical proteins.
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    URL: http://dx.doi.org/10.1007/BF02458919
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    Fascinating electronic games in iron complexes (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 107-136 
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    ISSN: 0392-6737
    Keywords: Crystal and ligand fields ; Mossbauer effect ; other γ-ray spectroscopy ; Visible and ultraviolet spectra ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Coordination compounds of transition metal ions with open-shell electron configurations may exhibit dynamic electronic-structure phenomena, depending on the nature of the coordinating ligand sphere. The change of spin state with temperature («thermal spin-crossover»), light-induced electron transfer processes leading to long-lived metastable charge and spin states (e.g., «LIESST» effect), are some of the fascinating electronic games encountered in transition metal compounds, which are presently under extensive study by chemists and physicists. Mössbauer spectroscopy plays a dominant role in the investigation of such phenomena in iron compounds, as will be demonstrated in this paper. This work will focus on selected examples of «thermal spin-crossover» in iron(II) complexes and switching between different spin states by irradiation with light of different wavelength (LIESST effect), demonstrating that Mössbauer spectroscopy besides other physical techniques proves to be a highly elegant tool for following the spin state conversion and the concomitant changes of molecular and crystal structure properties. Finally, Mössbauer emission spectroscopy, both time integral and time differential, has been employed to generate and identify long-lived excited spin states by making use of the nuclear disintegration of57Co as an intrinsic molecular light source (NIESST=nuclear decay-induced excited-spin-state trapping). Lifetime measurements by optical techniques on LIESST states and by time-differential Mössbauer coincidence spectroscopy on NIESST states prove that the relaxation pathways in the mechanisms for LIESST and NIESST are identical.
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    URL: http://dx.doi.org/10.1007/BF02458887
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    «Self-organized» InAs/GaAs quantum dots (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1285-1293 
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    ISSN: 0392-6737
    Keywords: Localized single-particle electronic states (excluding impurities) ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss some specific properties of self-organized InAs-GaAs quantum dots grown by Molecular Beam Epitaxy. We report on the optical spectra obtained under resonant excitation, where both a Raman contribution and a resonant emission of the dots are evidenced. We show that the emission of single dots can easily be isolated by processing measas on samples with a graded indium content, and finally discuss the temporal and temperature behaviour of the emission.
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    URL: http://dx.doi.org/10.1007/BF02457200
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    Coherence and correlation in laser excitation of semiconductor quantum wells (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1315-1322 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Time resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The concept of coherence due to optical excitation of an ensemble of two-level atoms is relatively simple and well established. For the laser-excited electron-hole pairs or excitions in a semiconductor, the Pauli exclusion and the Coulomb interaction lead to the necessary evolution of the theory of coherence to incorporate the spin degree of freedom, the filling of phase space, the excitons and particularly, their correlation. We have developed two theoretical approaches: one using the Feynman diagrams and one in terms of a force-force correlation function. The former gives us a pictorial way to describe the optical processes and the latter gives us a prescription for computation beyond the perturbative approach. In this paper, we will attempt to use simple physical pictures based on our theory to describe the time development of the coherence, the role of correlation, the dependence on the polarization of light, and the nonlinear time-resolved optical experiments which measure the coherence.
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    New hexagonal structures for two-dimensional photonic band gap materials (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1401-1405 
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    ISSN: 0392-6737
    Keywords: Electromagnetic wave propagation ; radiowave propagation ; Developments in band-structure calculation techniques ; Other topics in optical properties of condensed matter and other interactions of matter with particles and radiations ; Other topics in electromagnetic technology ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Recently, periodic dielectric structures have been proposed to inhibit spontaneous emission in semiconductors. From this suggestion, the new concepts of photonic band gap and photonic crystal have been developed. Zero-threshold lasers, wave guides and polarizers are promising applications. A new class of twodimensional periodic structures with hexagonal symmetry is investigated in order to obtain photonic band gap materials. This set has the hexagonal symmetry and contains, in particular, several structures previously discussed. The photonic band gap structure is related to the basic properties of the materials and some features of the opening of the gaps are explained. By varying the crystal pattern, we show how band gaps common toE andH polarizations appear for a new design of two-dimensional periodic dielectric structures. The dependence of the widths of these gaps on the filling patterns is studied and potential application for the creation of photonic crystals in the optical domain is discussed.
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    Exciton dynamics in ZnSe/ZnS x Se1−x superlattices (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1429-1433 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Localised single-particle electronic states (excluding impurities) ; Photoluminescence ; II–VI semiconductors ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Time-resolved photoluminescence experiments in a wide carrier density range up to and beyond the threshold for stimulated emission in ZnSe/ZnS x Se1−x superlattices are presented. Different localisation mechanisms of free excitons are identified giving rise to different radiative recombination channels. At high carrier density localised energy states merge into miniband that allows for exciton-exciton interaction, such as screening of the free-exciton absorption and inelastic exciton-exciton scattering.
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    URL: http://dx.doi.org/10.1007/BF02457222
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    Size-dependent electron-hole exchange interaction in CdSe quantum dots (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1407-1412 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Surface and interface electron states ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have investigated the fine structure of luminecence of CdSe nanocrystals observed with size-selective excitation. We show that the luminescence line closest to the laser arises from the recombination of the optically forbidden A-exciton. Radiative recombination occurs via a phonon-assisted virtual transition to theB-exciton state. The electron-hole exchange energy obtained from the experimental results strongly increases with decreasing nanocrystal size as expected from the increasing overlap of the electron and hole wave functions. The size dependence is in good agreement with the theoretical predictions.
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    Exciton states in In x Ga1−x As/GaAs double quantum wells: Normalized reflection spectra (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1423-1427 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Surface and interface electron states ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Normalized reflection spectra in GaInAs/GaAs quantum wells are shown for two sets of samples with different alloy concentration (x=9% and 18.5%) and well thickness ranging from 1.5 nm to 25 nm. All samples were grown on (001) GaAs surface by Molecular Beam Epitaxy and characterized by RHEED and X-ray reflection diffraction. Exciton envelope function in effective mass approximation and optical response in polaritonic schema are computed. Normalized reflection spectroscopy has shown itself to be a well suited technique in order to study structural and electronic properties of confined quantum structures.
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    Two-dimensional wannier excitons. Effects of a random adiabatic potential (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1447-1452 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Optical properties of thin films, surfaces, and layer structures (superlattices, heterojunctions, and multilayers) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We investigate the absorption spectrum and the distribution of radiative decay times for two-dimensional excitons in semiconductor quantum wells, as affected by an adiabatic white-noise random potential. Such a potential could result from atomic-scale fluctuations in the composition of an alloy semiconductor, or in quantum well thickness. We find in general that the shortest radiative decay time is directly proportional to the inhomogeneous width of the exciton line in absorption, itself proportional to the correlation parameter for the random potential.
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    Experimental evidence of the exciton centre-of-mass quantization in Zn1−x Cd x Se/ZnSe multiple quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1473-1479 
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    ISSN: 0392-6737
    Keywords: Surface and interface electron states ; Excitons and related phenomena (including electron-hole drops) ; Polaritons (including photon-phonon and photon-magnon interactions) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report the evidence of exciton-polariton centre-of-mass quantization in II–VI quantum wells consisting of ternary alloy. Absorption and photoluminescence studies on Zn0.89Cd0.11Se/ZnSe quantum wells, covering the intermediate region between two- and three-dimensional exciton behaviour, exhibit distinct optical resonances in the high-energy tail of the free-exciton structure. We reproduce the well width dependence of the centre-of-mass states by modeling the optical response of the QWs with a thin-slab variational wave function, which takes into account non-adiabatic terms.
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    Modulation spectroscopy study of an InGaAs/GaAs-strained asymmetric triangular quantum well heterostructure (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1499-1503 
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    ISSN: 0392-6737
    Keywords: Optical properties of thin films, surfaces, and thin layer structures (including superlattices, heterostructures, and intercalation compounds) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have studied modulation spectra related to the intersubband transitions at 300 K and 20 K from an In GaAs/GaAs-strained asymmetric triangular quantum well (ATQW) heterostructures fabricated by molecular beam epitaxy using the digital alloy compositional grading (DACG) method. A careful analysis of the spectra has led to the identification of various excitonic transitions,mnh(1), between them-th conduction band state to then-th, heavy (light)-hole band state. Comparison of the observed intersubband transitions with a theoretical calculation based on the envelope, function model, including the effects of strain provided a self-consistent verification that the DACG method produced the intended ATQW composition profile.
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    Ellipsometric investigations and luminescence properties of semiconductor microcavities (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1519-1526 
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    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; III–V compounds and systems ; III–V semiconductors ; Polarimeters and ellipsometers ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Luminescence investigations on MBE-grown AlAs/AlGaAs microcavities reveal position-dependent spectra from embedded GaAs quantum wells and from the reflector material. Because of their uniform energetic shifts they should be connected with the spatial distribution of strain. The spectra themselves are related to the radiative recombination of confinement-shifted free-electron-hole pairs, free and bound excitons and to the intrinsic luminescence of AlGaAs. Ellipsometric investigations in the range of the resonator stop band around 1.5 eV accentuate the one-dimensional behaviour as a 1D singularity within the effective joint density of states. The resonator mode and the stop band are dependent on the angle of incidence. The effective dielectric function is metal-like with the maximum imaginary part above 103,i.e. as it is typical for a pure metal in the FIR. Analogous investigations between 2.5 and 3.5 eV determined the critical pointsE 0 andE 1 of the energy band structure of AlAs and AlGaAs, respectively.
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    Interparticle interaction in spin-aligned and spin-degenerate exciton systems in II–VI quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1543-1547 
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    ISSN: 0392-6737
    Keywords: Studies of specific magnetic materials ; Optical properties of thin films surfaces and layer structures (superlattices, heterojunctions and multilayers) ; Excitons and related phenomena (including electron-hole drops) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Two qualitatively different e-h systems have been investigated in undoped CdTe/Cd0.88Mn0.12Te and Cd0.97Mn0.03 Te/Cd0.75Mn0.25 Te QWs at 2 K and magnetic fields up to 14 T, namely a strongly spin-depolarized system in the CdTe QW and a highly spin-polarized one in the Cd0.97Mn0.03 Te QW. The interaction of the spin-aligned excitons is repulsive. In contrast, in the spectra of a dense spin-depolarized excitonic system an additional well pronounced emission lineM was observed at approximately 5 meV below the excitonic line. This line is assigned to the emission of molecules consisting of excitons with opposite spins of both electrons and holes.
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    Coherent dynamics of excitonic and biexcitonic wave packets in semiconductor superlattices (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1573-1578 
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    ISSN: 0392-6737
    Keywords: Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Excitons and related phenomena (including electron-hole drops) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report on the observation of an electric-field-induced electric-dipole moment of biexcitonic molecules in a GaAs/Al0.3Ga0.7As superlattice. The macroscopic oscillating electric field, associated with the microscopic wave packet dipole moments, is monitored by time-resolved transmittive electro-optic sampling. The field dependence of the biexcitonic binding energy is detected by transient four-wave mixing. From these experiments, an ultrafast non-resonant excitation mechanism of biexcitons is inferred.
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    Transfer dynamics from an interface type-II heavy-hole exciton to a type-I light-hole exciton in a ZnSe/(Zn, Mn) Se heterostructure (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1567-1571 
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    ISSN: 0392-6737
    Keywords: Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Photoluminescence ; II–VI compounds and other chalcogenides ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Resonant photoluminescence and excitation spectroscopy and time-resolved photoluminescence are performed on a 50 Å thick ZnSe/(Zn, Mn) Se strained quantum well. From these experiments, the existence of a relaxation from a type-II heavy-hole bound interface exciton to a type-I light-hole exciton is demonstrated. The time transfer from the heavy-hole exciton to the light-hole exciton is found to be of the same order of magnitude as the recombination time of the heavy-hole exciton. This transfer is enhanced when temperature increases.
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    Bipolariton in quantum wells (1995)
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    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1255-1264 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Polaritons (including photon-photon and photon-magnon interactions) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We develop the bipolariton concept for a quasi-2D excitonic molecule (m) in quantum wells (QWLs). The bipolariton wave equation, which includes both the exciton-exciton (x-x) attraction and thex-photon (γ) coupling, is analysed. In the 2D bipolariton model, a quasi-2Dm exists in QWLs mainly as two quasi-boundsurface polaritons and, consequently, decays mainly into two outgoing surface polaritons. In quasi-2D GaAs QWLs the polariton renormalizations give rise to a «Mexican hat» structure in them dispersion at small momenta together with a considerable increase of both them effective binding energy ɛ m and the inversem radiative lifetimeГ m . A van Hove singularity in the joint density of polariton states is responsible for this effect.
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    Phonon-polariton interaction in a microcavity (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1657-1662 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Polaritons (including photon-phonon and photon-magnon interactions) ; Dynamics of nonlinear optical systems ; optical instabilities, optical chaos, and optical spatio-temporal dynamics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The linewidth of the microcavity exciton polariton is studied by onresonant and off-resonant photoluminescences. The two main contributions to the linewidth are caused by radiative loss and phonon scattering. The oscillator strength is found to be unmodified by the exciton-phonon coupling. Comparison is made between theory and experiment.
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    URL: http://dx.doi.org/10.1007/BF02457259
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    Linear and non-linear optical properties of semiconductor superlattices: Excitonic and field-induced effects (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1693-1697 
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    ISSN: 0392-6737
    Keywords: High-field and nonlinear effects ; Theory of electronic transport ; scattering mechanism ; Ultrafast optical techniques ; Optical properties of thin films, surfaces and layer structures (superlattices, heterojunctions, and multilayers) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effective dimensionality of excitons can be drastically changed by applying an alternating electric field. On the basis of a full three-dimensional description of both coherent and incoherent phenomena in anisotropic structures it is found that appropriate applied oscillating fields change the exciton wave function from anisotropic three dimensional to basically two dimensional. This effective-dimension change is caused by dynamic localization which leads to an increase of the exciton binding energy and of the corresponding oscillator strength.
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    URL: http://dx.doi.org/10.1007/BF02457265
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    Fast exciton and free-carrier kinetics in semiconductors: a Monte Carlo simulation (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1717-1722 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The coupled dynamics of free carriers and excitons after non-resonant excitation with short laser pulses is investigated by means of an Ensemble Monte Carlo method which includes phonon-assisted formation and dissociation of free excitons. Simulations for bulk GaAs reveal that excitonic binding under participation of LO phonons is a very fast and effective process. The temporal rise of exciton luminescence depends on the particular excitation conditions and is determined by all interaction mechanisms in the system.
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    URL: http://dx.doi.org/10.1007/BF02457269
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    Quantum grating reflectivity and grating polariton lifetimes (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1743-1746 
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    ISSN: 0392-6737
    Keywords: Wave propagation transmission and absorption ; Optical properties of thin films, surfaces, and layer structures (superlattices, heterojunctions, and multilayers) ; Polaritons (including photon-phonon and photon-magnon interactions) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary An analysis of the optical properties of an array of quantum wires of cylindrical shape is presented. Effects of the electromagnetic coupling between the wires are found to be given by additional energy shifts and modified oscillator strengths of the reflectivity peaks with respect to the single-wire exciton polariton ones previously calculated. Numerical values for realistic structures show the importance of these effects. Changes of the lifetimes of the single-wire excitations produced by this electromagnetic coupling are also put into evidence. In particular, the short lifetimes of the two-dimensional exciton-polariton are recovered when the interwire distanceD is smaller than the wavelength λ of light. Stationary, or non-radiative electromagnetic modes are also expected in this close-packed case. These radiative and non-radiative modes therefore show some analogies with those found in two-dimensional systems such as quantum wells.
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    URL: http://dx.doi.org/10.1007/BF02457273
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    Exciton-photon coupling in GaAs bulk microcavities (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1747-1751 
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    ISSN: 0392-6737
    Keywords: Polaritons (including photon-phonon and photon-magnon interactions) ; Excitons and related phenomena (including electron-hole drops) ; Quantum optics ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A great interest in the study of exciton-photon coupling in resonant optical media such as semiconductor microcavities is currently developing both in experiments and in theory. We investigate the spectral response of a new semiconductor quantum system in which the cavity material itself is the active medium. If the Fabry-Perot quasi-mode is carefully tuned on the excitonic transition of the cavity bulk material, strong exciton-photon coupling takes place and produces new features such as a Rabi-like splitting as large as that observed in quantum well microcavities and comparable optical absorption. In addition, the polaritonic spatial dispersion and the quantization of the centre-of-mass motion introduce remarkable fine structures which are absent in the quantum well case. We demonstrate the above effects from a spectroscopic analysis of GaAs cavities, using standard reflectance and photoluminescence techniques. The experimental results are further clarified with theoretical calculations performed with an adapted transfer-matrix approach. The case of semi-cavities is finally considered and a new way to control the exciton-photon interaction in our system is achieved tailoring the photonic wave function with a change in the reflectivity phase of the mirrors.
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    URL: http://dx.doi.org/10.1007/BF02457274
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    Stark ladders in piezoelectric superlattices (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1775-1779 
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    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Dielectric, piezoelectric, and ferroelectric materials ; Electrooptical effects ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We describe an experimental and theoretical investigation of Wannier-Stark ladders in the optical spectra of (111)B InGaAs/GaAs piezoelectric superlattices. A unique feature of these structures is that an external electric field can be used to produce a flat superlattice—that is zero overall potential drop per period—in which there are large, opposing fields in the well and barrier. These fields cause a spatial separation of the electron and hole wave functions in the axial direction, leading to Stark ladderss which are intermediate between Type I (electrons and holes together) and Type II (electrons and holes separated by half a period) in character.
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    URL: http://dx.doi.org/10.1007/BF02457279
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    Theory of resonant rayleigh scattering of excitons in semiconductor quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1801-1805 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Electron states in low-dimensional structures (including quantum wells ; superlattices ; layer structures ; and intercalation compounds ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Disorder-induced Rayleigh scattering of excitons in quantum wells is investigated theoretically. For classical excitions (long-range spatial correlation), the disorder average can be performed exactly. For the full problem, a kinetic equation with «weak memory» for the excition distribution is derived which coincides with the classical result in the appropriate limit. The theoretical results are compared with recent experimental data on femtosecond time-resolved luminescence explaining well the finite rise time and the heavy-light-hole beating.
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    URL: http://dx.doi.org/10.1007/BF02457284
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    Information flow in sensory neurons (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 733-741 
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    ISSN: 0392-6737
    Keywords: General, theoretical, and mathematical biophysics (including logic of biosystems, quantum biology, and relevant aspects of thermodynamics, information theory, cybernetics, and bionics) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Recent experiments show that the neural codes at work in a wide range of creatures share some common features. At first sight, these observations seem unrelated. However, we show that all of these features of the code arise naturally in a simple threshold crossing model when we choose the threshold to maximize the transmitted information. This maximization process requires neural adaptation to not only the d.c. signal level, as in conventional light and dark adaptation (for example), but also to the statistical structure of the signal and noise distributions. Interestingly, if we fix the threshold level, we can observe a peak in the transmitted information at a finite value of the input signal-to-noise ratio. However, when we allow the threshold to adapt to the statistical structure of the signal and noise, the transmitted information is always monotonically increasing with increasing input signal-to-noise ratio.
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    URL: http://dx.doi.org/10.1007/BF02451830
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    Fluctuations, stochastic resonance and noise-protected heterodyning in bistable optical systems (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 743-754 
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    ISSN: 0392-6737
    Keywords: Optical bistability, multistability, and switching ; optical computers ; Fluctuation phenomena, random processes and Brownian motion ; Optical resonantors ; Probability theory, stochastic processes and statistics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Statistical distributions, power spectra and susceptibilities of an all-optical bistable system subject to noise are considered. In the presence of an additional small periodic signal, a stochastic-resonance phenomenon for additive noise is found to occur, and has been investigated theoretically and experimentally. A new form of optical heterodyning related to stochastic resonance, in which two high-frequency signals (an input signal and a reference one) are applied to an all-optical bistable system, is reported. A noise-induced enhancement of the heterodyne signal has been investigated theoretically, by means of analogue electronic simulation and in experiments in which a optical system was driven by two modulated laser beams at different wavelengths.
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    URL: http://dx.doi.org/10.1007/BF02451831
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    Neural encoding in invertebrate neurons (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 725-731 
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    ISSN: 0392-6737
    Keywords: General, theoretical, and mathematical biophysics (including logic of biosystems, quantum biology, and relevant aspects of thermodynamics, information theory, cybernetics, and bionics) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The effect of a weak periodic perturbation on the firing activity of two different types of neurons is investigated. Post-stimulus and interspike interval histograms are built up from the times of occurrence of the action potentials and a comparative analysis is performed between the two preparations. A discussion of how the leaky integrate-and-fire model can mimic the experimental data is included.
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    On the effect of the noise in dynamical systems (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 653-660 
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    ISSN: 0392-6737
    Keywords: Chaos ; Theory and models of chaotic systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We discuss the complexity in dynamical systems with a random perturbation by considering the rateK of divergence of nearby orbits evolving under two different noise realization. This quantity has a clear meaning in the context of the information theory and it has physical relevance for the analysis of experimental data. Our definition of complexity becomes crucial for strongly intermittent systems whereK is very different from the Lyapunov exponent.
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    URL: http://dx.doi.org/10.1007/BF02451824
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    Randomly rattled ratchets (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 685-697 
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    ISSN: 0392-6737
    Keywords: Active transport processes ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Ratchets are anisotropic periodic potentials. Particles subject to ratchet forces and simultaneously to thermal and nonthermal fluctuations can rectify the nonequilibrium noise, thereby extracting energy from incoherent and otherwise symmetric random forces. In this paper I describe some simple models which illustrate this phenomenon, highlighting two particular mechanisms leading to fluctuation-induced current.
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    Sensitivity of non-linear dynamical systems to fluctuations: Hopf bifurcation and chaos (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 709-723 
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    ISSN: 0392-6737
    Keywords: Nonlinear theories (including bifurcation theory) ; Fluctuation phenomena, random processes, and Brownian motion ; Theory and models of chaotic systems ; Computational modeling: simulation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The statistical properties of non-linear dynamical systems are studied using the master equation approach. Detailed analysis of a model system undergoing a Hopf bifurcation reveals a non-trivial interference between macroscopic behaviour and microscopic dynamics in spatially extended systems. The effect of intrinsic fluctuations in the regime of homogeneous deterministic chaos is also analysed and the robustness of the macroscopic description is confirmed.
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    URL: http://dx.doi.org/10.1007/BF02451828
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    Dynamics controlled by additive noise (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 855-861 
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    ISSN: 0392-6737
    Keywords: Chaos ; Theory and models of chaotic systems ; Instability and shear flows ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Analysis is presented of a system, derived previously as a low-order model for the shear instability of convection, whose dynamics are dramatically simplified by tiny amounts of additive noise. The dynamics divide naturally into two phases. In the slower phase, trajectories are close to an invariant manifold; this allows small random disturbances to exert a controlling influence. A map is derived which provides an accurate description of the trajectories.
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    Fundamental sources of noise in sensory transduction (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 883-891 
    Details
    ISSN: 0392-6737
    Keywords: General, theoretical, and mathematical biophysics (including logic of biosystems, quantum biology, and relevant aspects of thermodynamics, information theory, cybernetics, and bionics) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The contribution of chemical steps in trasduction chains to the output noise of a receptor cell (as opposed to the noise inherent in the stimulus,e.g., a dim light flash) has been evaluated both analytically and by a computer simulation study on a simple model, using a Monte Carlo technique. The noise deriving from chemical reactions (chemical shot noise, CSN) is shown to add to the source noise thereby increasing significantly the output variation coefficient. It is proposed that this noise contribution should be taken into account in interpreting the sensitivity of a sensory system and in particular the dose-response curves at low levels of the stimulus.
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    Non-linearity of the interactions between bottom-up and top-down signals in multistable visual perception (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 941-947 
    Details
    ISSN: 0392-6737
    Keywords: Physiological optics: vision ; General, theoretical, and mathematical biophysics (including logic of biosystems, quantum biology, and relevant aspects of thermodynamics, information theory, cybernetics, and bionics) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Both bottom-up sensory information and top-down influences contribute to the perception processes. We studied the perceptual alternations of a multistable ambiguous pattern. We observed that it is possible to interfere on the process of the perception alternance by means of subliminal visual stimuli, which either contrast or second the previous perception. We investigated also the effect of the top-down volitional factor on the perceptual alternation. By using a combination of such top-down factor and bottom-up stimulation, we ascertained that a non-linear type of interaction occurs between the two above factors.
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    Ballistic transport of electronic excitations and coherent light propagation in semiconductor quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1265-1276 
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    ISSN: 0392-6737
    Keywords: Polaritons (including photon-phonon and photon-magnon interactions) ; Optical properties of thin films, surfaces, and layer structures (superlattices, heterojunctions, and multilayers) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The transport of radiative and electronic excitations in coherently driven semiconductor quantum wells is analysed. On ultrashort time scales the spatial dynamics is determined by light propagation only, whereas for longer times the propagation of light and electronic excitations may be coupled. The theory is applied to the propagation of electronic excitations in the plane of a single quantum well and to polariton propagation in quantum well wave guides.
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    Excitons in microcavities: Cavity polariton photoluminescence (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1323-1332 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Polaritons (including photon-phonon and photon-magnon interactions) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present an extensive set of absorption and PL measurements on semiconductor microcavities in the strong-coupling regime. We observe strong coupling from 110 K to room temperature. We look at the behaviour of the photoluminescence for different exciton-photon detuning. We discuss this data using two different pictures, the first is a non-interacting (uncoupled) picture of an exciton in a cavity filter. The second model is that of a cavity polariton and this explains the observed dynamics in the strong-coupling regime. We show how the opposing needs of strong coupling and high photoluminescence extraction efficiency can be reconciled.
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    Binding energies of excitons in ionic quantum well structures (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1343-1347 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Polarons and electron-phonon interactions ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; III-V compounds and systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have calculated the binding energies of excitons in quantum well structures based on ionic semiconductors by including the electron-hole interactions with the longitudinal-optical-phonon field. We have taken into account these interactions by using different effective interaction potentials between the electron and the hole as derived by Haken, Aldrich and Bajaj, and Pollman and Buttner. We have calculated the binding energies of excitons in several ionic quantum well structures as functions of well width using these effective potentials following a variational approach. We find that the values of the exciton binding energies calculated using these potentials are always larger than those, obtained using a Coloumb potential screened by static dielectric constant.
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    External-field-dependent enhancement of internal Coulomb interactions in time-resolved four-wave mixing (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1355-1358 
    Details
    ISSN: 0392-6737
    Keywords: Time-resolved optical phenomena (including electron-hole drops) ; Optical properties of thin films surfaces, and layer structures (superlattices, heterojunctions and multilayers) ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We show that a detailed understanding of the influence of the exciton-exciton interaction on the non-linear excitonic response in a GaAs/AlGaAs superlattice can be obtained by changing the external applied field. In time-resolved four-wave mixing this implies a change from a third-order polarization signal dominated by phase space occupation to a Coulomb interaction-induced signal when the bias is increased at high excitation densities. The experimental data are compared with theoretical results based on the numerical solution of the semiconductor Bloch equations.
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    Carrier recombination dynamics in self-ordered InAs quantum dots (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1371-1375 
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    ISSN: 0392-6737
    Keywords: III–V semiconductors ; III–V compounds and systems ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A photoluminescence study of self-ordered InAs quantum dots grown by molecular beam epitaxy on a GaAs substrate is reported. Short pulses and high excitations have been used in order to observe emission from higher states of the quantum dots. The energy spacing between adjacent transitions seems to be of the order of 40–50 meV for dot diameters around 20 nm. The photoluminescence decay time from the ground state is of the order of 650–700 ps and decreases down to roughly 100 ps for the highest confined states. A cascade-like mechanism for the carrier relaxation in these structures is strongly suggested by the time-resolved data.
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    Relaxation of polarized excitons in asymmetric double quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1453-1458 
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    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells superlattices, layer structures, and intercalation compounds) ; Other semiconductor-to-semiconductor contacts,p-n junctions, and heterojunctions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We consider the intrawell and interwell relaxation of circularly polarized excitons in an asymmetric double-quantum-well structure. For the intrawell case (photocreated light excitons coupled to the detected heavy excitons by an optical-phonon emission) the polarization changes sign after a fast relaxation. For the interwell case (transfer of polarization from the ground heavy exciton of the narrow well towards the ground heavy exciton of the wide well) we observe that the initial polarization is recovered after energy relaxation only if a fast-relaxation path is available which involves only intermediate heavy exciton states.
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    Exciton states and relaxation dynamics in shallow quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1493-1498 
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    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; III-V semiconductors ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Optical properties of GaAs/Al x Ga1−x As shallow quantum wells have been studied in the 2–200K range, both by c.w. and time-resolved experiments. The results agree with a variational calculation of the excitonic transitions. The LO-phonon-assisted carrier relaxation and a temperature-activated non-radiative channel are evidence.
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    Some new fundamental properties of GaN single-crystal films on SiC and sapphire substrates (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1509-1512 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; III-V Compounds and systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The reflectance spectra of GaN/6H-SiC, films and the absorption spectra of GaN/Al2O3 films were studied and several fundumental parameters of GaN-energy positions of exciton, resonances ω0, damping constants⩾s, longitudinal-transverse splittings ωLT and the oscillator, strengthsf of the exciton states were determined. A blue shift and broadening of the luminescence band were observed in the luminescence spectra of GaN quantum dots. The mean dot radius in the sample was estimated to be about 4.5nm.
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    Exciton dynamics within growth islands of GaAs/Al x Ga1−x As single quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1531-1536 
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    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The localization dynamics of excitons within growth islands of GaAs/Al x Ga1−x As single quantum wells (SQW) have been investigated by time-resolved photoluminescence spectroscopy (TRPL). Several samples with different substrate misorientation and growth interruption times are compared with regard to the photoluminescence (PL) emission dynamics. For monolayer (ML) islands larger than the exciton radius,i.e. long growth interruption, the time evolution of the different PL peaks reflects the transfer of free excitons between growth islands as well as the localization within a single growth island. The samples with shorter growth interruption reveal a much less pronounced PL splitting due to ML islands. The dynamics appears to be mainly determined by exciton localization to thicker ML islands. The density of localization centres is larger for the sample grown on misoriented substrates.
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  • 90
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    Non-linear optics of hybrid excitons in organic-inorganic nanostructures (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1555-1559 
    Details
    ISSN: 0392-6737
    Keywords: Nonlinear optics ; Optical properties of thin films, surfaces, and thin layer structures (including superlattices, heterostructures, and intercalation compounds) ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Excitons and related phenomena (including electron-hole drops) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In a system comprising an organic layer coupled to a semiconductor layer, if the energy of the Frenkel exciton in the first is close to that of the Wannier exciton in the second, the lowest electronic excitations can be described as hybrid resonances. These new excitons give rise to very pronounced optical non-linearities because they have at the same time large oscillator strengths, typical of Frenkel excitons, and large radii, typical of Wannier excitons. The results of a microscopic calculation of the optical properties of such a system are presented and discussed: compared with the usual semiconductor quantum wells, enhancements of two orders of magnitude both in the size of the susceptibility (linear part) and in its relative change with increasing excitation density (Kerr non-linearity) are predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457243
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  • 91
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    Excitonic states of biased InAs quantum dots (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1579-1583 
    Details
    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Other semiconductor-to-semiconductor contacts,p-n junctions, and heterojunctions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report on the calculation of electron and hole states in InAs/GaAs quantum dots. The latters are modelled by cones floating on a wetting layer. The calculations include the effect of an electric field applied parallel to the cone axis as well as the evaluation of the electron-hole correlation and exchange (short-range part) energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457247
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  • 92
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    Excitation energy dependence of the optical properties of InGaAs/GaAs quantum well heterostructures (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1383-1387 
    Details
    ISSN: 0392-6737
    Keywords: III–V semiconductors ; Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Excitons and related phenomena (including electron-hole drops) ; III–V compounds and systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report an experimental study on a large set of InGaAs/GaAs quantum well structures by means of continuous-wave photoluminescence and photoluminescence excitation. The luminescence spectrum at low temperature systematically exhibits a doublet structure whose lineshape is very sensitive to the excitation energy. Accordingly, the excitation spectra detected by monitoring the emission at the two different luminescence peaks have very different profiles, with peaks and/or dips which are not directly related to absorption resonances. As a matter of fact, the anomalies disappear when increasing the temperature or when using an optical bias with energy above the GaAs energy gap. In these cases, the excitation profiles recover the behaviour typical of 2D systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457214
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  • 93
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    Exciton recombination mechanism and binding energies in MOCVD-grown Zn1−x Cd x Se−ZnSe single quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1585-1593 
    Details
    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; Optical properties of thin films surfaces and layer structures (superlattices, heterojunctions and multilayers) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report here on the study of the optical properties of ZnCdSe−ZnSe quantum structures elaborated by metalorganic chemical vapour deposition (MOCVD). The band structure is experimentally investigated by means of photoluminescence and photoreflectance. We have computed the exciton binding energies for heavy- and light-hole excitons in the context of a self-consistent two-parameter trial function. As a complement, we study the temperature dependence of the photoluminescence intensity under both direct and indirect photoexcitation in graded-index separate confinement heterostructures based on these materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457248
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  • 94
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    Screening effects in piezoelectric strained [111]-Grown (In, Ga) As/(Al, Ga) As quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1595-1599 
    Details
    ISSN: 0392-6737
    Keywords: Optical properties of thin films, surfaces, and thin layer structures (including superlattices, heterostructures, and intercalation compounds) ; III-V semiconductors ; Surface and interface electron states ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The optical nonlinearities produced by screening of the piezoelectric field byphotogenerated carriers in a [111]-grown (In, Ga)As/(Al, Ga)As single strained-layer quantum well structure are calculated and compared with those in a [001]-grown structure. Nonlinear absorption and refractive index spectra show that screening of the strain-induced electric field by photo-carriers that have escaped from the [111]-grown quantum well produces optical nonlinearities comparable to those in the more conventional [001]-grown quantum well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457249
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  • 95
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    Exciton effects in strain-balanced GaInAs/AlInAs and GaInAs/GaInAs coupled quantum wells (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1607-1612 
    Details
    ISSN: 0392-6737
    Keywords: Optical properties of thin films, surfaces, and thin layer structures (including superlattices, heterostructures, and intercalation compounds) ; Nonlocalized single-particle electronic states ; Collective effects ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary High magnetic and electric fields are used to investigate the excitonic properties of strain-balanced InGaAs coupled quantum wells, providing details of their band structure. The bands are strongly non-parabolic and the heavy in-plane hole mass deduced for a lattice-matched structure is shown to be reduced by either tensile or compressive strain. The different band-offsets on changing from InGaAs to AlInAs barriers modify the interwell coupling and result in the observation of Stark ladder transitions and conventional Stark effect behaviour, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457251
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  • 96
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    Recombination processes in strain-induced InGaAs quantum dots (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1699-1703 
    Details
    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; Localized single-particle electronic states (including impurities) ; III–V compounds and systems ; Photoluminescence ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have performed time-integrated and time-resolved photoluminescence experiments on high-quality stressor-induced InGaAs/GaAs quantum dots. The optical spectra of these dot structures exhibit large quantization effects together with remarkably low inhomogeneous broadenings of the respective excitonic transitions. Thus a detailed investigation of the relaxation and recombination dynamics within the distinct electronic dot states becomes feasible. We find that the initial relaxation of optically generated carriers down to the lowest dot states is very efficient. This fast thermalization is ascribed to Coulomb scattering between carriers confined in dot states and carriers located in the higher-energetic quantum well states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457266
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  • 97
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    Observation of the Wannier-Stark ladders associated to the light-hole ground state and to the heavy-hole first excited state in GaInAs/AlGaInAs superlattices (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1763-1768 
    Details
    ISSN: 0392-6737
    Keywords: Electron states in low-dimensional structures (including quantum wells, superlattices, layer structures, and intercalation compounds) ; III–V and II–VI inorganics ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Photoluminescence excitation experiments have been performed with a non-intentionally doped GaInAs/AlGaInAs superlattice lattice-matched to an InP substrate. The superlattice is the intrinsic part of a p-i-n diode. We have observed the 1s and 2s heavy-hole exciton states and the Wannier-Stark ladder associated to the light-hole exciton. Three other lines in our spectrum are related to the Wannier-Stark ladder associated to the first excited state of the heavy hole. These transitions are weakly allowed from the built-in voltage existing in the superlattice. Calculations based on Airy functions quantitatively support our interpretation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457277
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  • 98
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    Double 2s-1s resonance in LO-phonon-assisted secondary emission of excitions in CdTe/(Cd, Mn) Te MQW structures (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1787-1790 
    Details
    ISSN: 0392-6737
    Keywords: Excitons and related phenomena (including electron-hole drops) ; II–VI compounds and other chalcogenides ; II–VI semiconductors ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We report on the observation of the doubly resonant secondary emission involving 2s and 1s exciton states. The resonance conditions have been realized in CdTe/Cd1-xMnx Te quantum well structures by magnetic-field tuning of the 2s-1s energy spacing to the LO-phonon energy. Theoretical analysis shows the doubly resonant process to be indirect, with hot 1s excitons acting as intermediate states. It is concluded that the resonance width of 2.6 meV gives the 2s-exciton homogeneous linewidth governed by elastic scattering into the hot 1s exciton states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457281
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  • 99
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    Hybridization of excitons in parallel organic and semiconductor quantum wires (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1797-1799 
    Details
    ISSN: 0392-6737
    Keywords: Excitions and related phenomena (including electron-hole drops) ; Electron states in low-dimensional structures (including quantum wells) ; superlattices ; layer structures ; and intercalation compounds ; Optical properties of thin films ; surfaces ; and layer structures ; superlattices ; heterojunctions ; and multilayers ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We demonstrate that a hybridization of Frenkel and Wannier-Mott excitons in parallel neighbouring organic and semiconductor quantum wires may occur due to the resonance dipole-dipole interaction between the wires. The hybridization might be especially efficient for excitons with small wave vectors along the wires when the transition dipole moments of excitons are oriented perpendicular to the wires. The hybrid wire excitons may possess both a large radius and a relatively large oscillator strength which could be important in non-linear optics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02457283
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  • 100
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    Stochastic resonance in a laser with saturable absorber (1995)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 803-810 
    Details
    ISSN: 0392-6737
    Keywords: Nonlinear optics ; Fluctuation phenomena, random processes, and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We have investigated, experimentally and theoretically, the occurrence of stochastic resonance (SR) in a laser with saturable absorber: a non-linear optical system presenting optical bistability and self-pulsed regimes for the laser output intensity. In the optical-bistability regime we have obtained an excellent demonstration of SR by studying Fourier spectra and residence time distributions; operating just below the Hopf bifurcation that originates pulsed periodic regime we have obtained experimental evidence of the SR phenomenon. For operation close to the Hopf bifurcation, the theoretical analysis (performed through numerical simulations) has demonstrated that simultaneous presence of noise and periodic forcing generates excursions far from equilibrium; from the locking between these excursions and periodic forcing the SR phenomenon may arise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02451837
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