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  • 1
    Electronic Resource
    Electronic Resource
    The mechanism of the unimolecular dissociation of trichloroethylene CHCl=CCl2 in the ground electronic state (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7902-7909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unimolecular dissociation of trichloroethylene in its electronic ground state has been investigated using an infrared multiphoton dissociation combined with photofragmentation translational spectroscopy to measure product translational energies. The main reaction channel was found to be HCl elimination on the basis of observed product time-of-flight (TOF) spectra. A center-of-mass translational energy distribution for this channel provides direct evidence for competition between two channels, three- and four-centered HCl eliminations. Cl elimination was found to be a minor but significant channel from observed Cl+ and C2HCl+TOF spectra. The branching ratios were determined as 0.28, 0.55, and 0.17 for the three- and four-centered HCl eliminations and the Cl elimination, respectively. The three-centered channel exhibits a "statistical'' translational energy distribution which is typical for a reaction with no potential energy barrier in the reverse reaction, that is to say, no exit barrier reaction. In contrast, the four-centered channel exhibits a "nonstatistical'' translational energy distribution having a peak at around 2 kcal/mol in energy, indicating that a significant exit barrier exists in the channel. The fraction of potential energy converted to translational energy was estimated to be around 10%. Ab initio calculations at the QCISD(T)/6-311+G**//MP2(FC)/6-31G* level were employed to confirm the reaction mechanism. The agreement in the energetics is quite good. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468989
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  • 2
    Electronic Resource
    Electronic Resource
    Azimuthal ordering in Langmuir monolayers (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1196-1197 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple mean-field model of azimuthal ordering in Langmuir monolayers induced by anisotropic dispersion forces is presented. The approach is removed from previous studies of this interaction in systems of grafted rods insofar as the tilt of amphiphiles is decoupled from azimuthal ordering and treated as an external variable. We examine the phase space of fixed tilt against temperature, finding that azimuthal ordering is second order for most tilts, except in the range 57°–66°, where it is first order. This is related to the existence of three different types of azimuthal order; polar, nematic, and polar–nematic. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476666
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and optical absorption properties of Si nanocrystals fabricated with low-pressure chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4006-4011 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a simple technique for fabricating a layer of isolated Si quantum dots on SiO2 glass substrates. This technique uses conventional low-pressure chemical-vapor deposition for an extremely short deposition time in the early stage of poly-Si film growth. The layer after a deposition time of 60 s has isolated Si nanocrystals 5–20 nm in diameter and 2–10 nm in height. The measurements of optical absorption coefficient α show that the absorption edge for Si nanocrystals shifts to higher energies compared to that of bulk Si, indicating a widening of the energy gap caused by quantum size effects. The linear relationship (αhν)1/2 against hν suggests that the Si nanocrystal, whose diameter is as small as 10 nm, basically maintains the properties of an indirect band-gap semiconductor. Special attention must be paid to the Brownian migration of Si nanocrystals for fabricating Si quantum dots. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363359
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  • 4
    Electronic Resource
    Electronic Resource
    1.3 μm InAsP compressively strained multiple-quantum-well lasers for high-temperature operation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4119-4121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-temperature operation of InAsP-based laser diodes at 1.3 μm has been realized according to guidelines of a large conduction-band-offset material (ΔEc) with a large optical confinement factor (Γ). Using photoluminescence excitation spectroscopy measurements, it was found that the conduction-band offset of InAs0.52P0.48P/InGaAsP is the half of the band-gap energy difference (0.5 ΔEg), which is larger than that of conventional quaternary material systems. A strain-compensation growth technique enabled the fabrication of a large number of wells for large Γ. For broad-area laser diodes, the maximum operating temperature increased as the number of wells increased from 4 to 15. In buried heterostructure lasers with ten wells, with high-reflectivity coating on both facets, continuous-wave lasing operation at temperatures up to 150 °C was achieved with a characteristic temperature of 59 K (30〈T〈70 °C) demonstrating the suitability of InAsP for high-temperature operation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359497
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  • 5
    Electronic Resource
    Electronic Resource
    Conduction type control from n to p type for organic pigment films purified by reactive sublimation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7153-7157 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of purification by reactive sublimation technique and bromine doping on the Fermi level and the photovoltaic properties of n-type perylene pigment films were investigated. Photovoltage arisen from the Schottky junction between n-type perylene pigment film and Au increased significantly by repeating the train sublimation under methylamine gas atmosphere. This phenomenon was revealed to be due to the negative shift of the Fermi level resulting from the effective removal of unknown but specific impurity acting as an acceptor by reactive sublimation. On the other hand, by bromine doping, Fermi level of the pigment film shifted largely to a positive direction and reached the nearby valence band, while the direction of photocurrent flow arising from the Schottky junction with Au was reversed. This result is a clear demonstration of alternating the type of conduction from n type to p type. This means that the pn control of organic semiconductors is possible. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360423
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  • 6
    Electronic Resource
    Electronic Resource
    Electrostatic deformation in band profiles of InP-based strained-layer quantum-well lasers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5180-5184 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the electrostatic deformation in the conduction-band and valence-band profiles of 1.3-μm InP-based strained-layer (SL) quantum-well (QW) lasers in the temperature range of 273–373 K. Electrostatic deformation is analyzed by the self-consistent numerical solution of the Poisson's equation, the scalar effective-mass equation for the conduction band, and the multiband effective-mass equation for the valence band. It is shown that, in InP-based QWs, electrostatic band-profile deformation causes a significant change in effective barrier height for the conduction and valence bands, which has a pronounced influence on the electron and hole distribution throughout the whole QW structure in the temperature range studied. We demonstrate that it is necessary to take into account electrostatic deformation in both band profiles for an analysis of the high-temperature characteristics of InP-based SL-QW lasers. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359265
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature dependence of intrasubband relaxation time and its influence on high-temperature characteristics of InP-based quantum-well lasers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5237-5240 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By taking into account the temperature dependence of the intrasubband relaxation times for electrons and holes, we study the temperature sensitivity of the optical gain and of the gain saturation coefficient for 1.3-μm InP-based strained-layer (SL) quantum-well (QW) lasers. The band structures are obtained by the self-consistent numerical solution of the Poisson equation, the scalar effective-mass equation for the conduction band, and the multiband effective-mass equation for the valence band. The intrasubband relaxation times are then calculated within the fully dynamic random phase approximation including carrier-carrier and carrier-phonon interactions on an equal basis. We demonstrate that the temperature dependence of the intrasubband relaxation times plays a key role in determining the temperature sensitivity of the optical gain and of the gain saturation coefficient of InP-based SL-QW lasers. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359274
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetization of cadmium ferrite prepared by coprecipitation (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1015-1019 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the magnetization of the ultrafine cadmium ferrite particles formed during the coprecipitation method and discussed the origin of enhanced magnetization based on the magnetic properties. A transmission electron microscopy micrograph shows aggregation of fine particles having two kinds of shapes, fibrous and granular. X-ray diffraction patterns of the specimens prepared by the coprecipitation method are composed of peaks corresponding to CdFe2O4, Cd(OH)2, and α-FeO(OH). The pattern indicates that the peaks of CdFe2O4 are fairly broad, suggesting the formation of a very small crystallite, with an average size of ∼8 nm. The ultrafine CdFe2O4 particles exhibit ferromagnetic behavior and have a net magnetization of 89±5 emu/g at 6 K. These results suggest that there must be many ferromagnetic clusters consisting of Fe3+ ions at the B sites around Fe3+ ions at the A site by the A–B interactions. Thus, such a change in the distribution of Fe3+ ions in the ultrafine CdFe2O4 particles results in increasing magnetization with decreasing particle size. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362834
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  • 9
    Electronic Resource
    Electronic Resource
    Dominant mechanism for limiting the maximum operating temperature of InP-based multiple-quantum-well lasers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2192-2197 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the basic mechanism for limiting the maximum operating temperature (Tm) of InP-based multiple-quantum-well (MQW) lasers emitting at a wavelength of 1.3 μm. It is shown that laser operation is characterized in terms of the temperature dependence of threshold gain (gth) by introducing a critical temperature (Tc): gth exhibits a linear relationship with temperature below Tc, while it superlinearly increases with increasing temperature above Tc. This rapid increase in gth leads to a marked increase in threshold current and a significant reduction in differential quantum efficiency above Tc. We indicate that Tc exhibits a direct correlation with Tm: the higher Tc, the higher Tm. In the temperature range above Tc, laser operation moves into a loss-multiplication regime, where a considerable portion of the injected carriers brings about a significant increase in internal loss rather than gain due to their pileup in the separate confinement heterostructure layers. We demonstrate that an anomalous increase in internal loss, which occurs at the final stage in this loss-multiplication regime, determines Tm of 1.3 μm InP-based MQW lasers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361183
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  • 10
    Electronic Resource
    Electronic Resource
    Discrimination of product isomers in the photodissociation of propyne and allene at 193 nm (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4363-4368 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of propyne and allene are investigated in two molecular beam/photodissociation instruments, one using electron impact ionization and the other using tunable vacuum ultraviolet (VUV) light to photoionize the photoproducts. The primary dissociation channels for both reactants are C3H3+H and C3H2+H2. Measurement of the photoionization efficiency curves on the VUV instrument shows that the C3H3 product from propyne is the propynyl (CH3CC) radical, whereas the C3H3 product from allene is the propargyl (CH2CCH) radical. The dominant C3H2 product from both reactants is the propadienylidene (H2CCC) radical. We also observe a small amount of secondary C3H2 product from photodissociation of the C3H3 radicals in both cases. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478318
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