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  • 1
    Electronic Resource
    Electronic Resource
    Structural and electrical defects in amorphous silicon probed by positrons and electrons (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5145-5152 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of pure amorphous Si, prepared by ion implantation, has been investigated by variable-energy positron annihilation spectroscopy (PAS) and lifetime measurements of optically generated free carriers. In general, PAS measurements are thought to be sensitive to vacancy-type defects while the carrier lifetime depends on the density of band-gap states (e.g., dangling bonds). The PAS measurements indicate that the density of positron-trapping defects can be reduced by thermal annealing at 500 °C. Concurrent with the removal of structural defects the density of band gap states is reduced as indicated by an increased photocarrier lifetime by a factor of 10. Some material has been implanted with H+ and annealed at a low temperature (150 °C). The hydrogen is expected to passivate electrical defects associated with strained and dangling bonds and indeed the photocarrier lifetime is increased in this material. Moreover, the PAS measurements cannot distinguish this material from 500 °C annealed amorphous Si, indicating that (some of) the electrical defects are associated with positron-trapping, and therefore possibly vacancy-type, structural defects. Finally, both methods have been used to detect small amounts of ion irradiation damage in annealed amorphous Si.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351993
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  • 2
    Electronic Resource
    Electronic Resource
    Positron beam defect profiling of silicon epitaxial layers (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3003-3006 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial layers of silicon grown on a Si(100) substrate by molecular-beam epitaxy (MBE) and solid-phase epitaxy (SPE) have been investigated by slow positron beam analysis methods. Results of Doppler broadening measurements revealed that the S parameter of the SPE material is considerably higher than the value measured for the MBE layer, indicative of a higher concentration of open-volume defects in the former material. This was confirmed by measurements of the positronium fraction at elevated temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349329
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  • 3
    Electronic Resource
    Electronic Resource
    Buried oxide and defects in oxygen implanted Si monitored by positron annihilation (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1179-1187 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One- and two-detector Doppler broadening measurements performed on low (∼1014 to 1015 O+/cm2) and high dose (∼1017 to 1018 O+/cm2) oxygen-irradiated Si using variable-energy slow positrons are analyzed in terms of S and W parameters. After annealing the low-dose samples at 800 °C, large VxOy complexes are formed at depths around 400 nm. These complexes produce a clear-cut signature when the ratio of S to that of defect-free bulk Si is plotted. Similar behavior is found for samples irradiated with 2 and 4×1017 O+/cm2 and annealed at 1000 °C. After irradiation with 1.7×1018 O+/cm2 and anneal at 1350 °C a 170 nm thick almost-bulk-quality Si surface layer is formed on top of a 430 nm thick buried oxide layer. This method of preparation is called separation by implantation of oxygen. S−W measurements show that the surface layer contains electrically inactive VxOy complexes not seen by electron microscopy. A method is presented to decompose the Doppler broadening line shape into contributions of the bulk, surface, and defect. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380411
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  • 4
    Electronic Resource
    Electronic Resource
    Kr incorporation in sputtered amorphous Si layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3467-3478 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Si layers were grown by krypton plasma sputter deposition at 310 °C. By pulsation of the substrate potential between 0 and 50 eV, the Kr concentration in the layers could be varied to a maximum of 5.5 at. %. A model which describes trapping of inert gas atoms in the sputtered layer in terms of implantation and trapping, diffusion, growth, resputtering, and gas sputtering is presented. High-resolution electron microscopy, electrode-probe (x-ray) microanalysis, positron annihilation, Raman spectroscopy, Mössbauer spectroscopy, and bending and hardness measurements were performed on the deposited layers. It turns out that the ion assisted growth leads to a strong reduction of open volume defects. The experiments point to the presence of very small Kr agglomerates. From the Mössbauer experiments a lower limit of 250 K for the Debye temperature of the Kr agglomerates is derived. Molecular-dynamic simulations from which the Debye temperatures of Kr mono-, di-, and trimers in amorphous Si can be derived are presented. The simulations indicate the presence of predominantly Kr monomers and dimers. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358641
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of ion beam assistance on the microstructure of nonhydrogenated amorphous carbon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3121-3129 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonhydrogenated diamondlike carbon films have been prepared by dual ion beam sputtering and ion-beam-assisted magnetron. The assistance parameters—ion energy, ion mass, ion flux/atom flux—have been systematically varied, and the films have been characterized by Rutherford backscattering spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, positron annihilation spectroscopy, Raman spectroscopy, and nanoindentation. It was found that the density and the degree of disorder of the films go through a maximum with ion energy, and the void concentration goes through a minimum. Microstructure analysis shows that the films are mostly sp2 bonded, with a maximum of about 16% concentration of sp3 bonding from the largest values of density. The evolution of density with ion flux and energy is consistent with a combined effect of atomic displacements in the film leading to densification, and damage buildup leading to progressive graphitization as the energy is increased. The large hardness/elastic modulus ratios obtained should lead to excellent friction properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356164
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of positron beam data by the combined use of the shape- and wing-parameters (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9029-9036 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved approach is presented for the analysis of positron beam Doppler broadening data. Instead of analyzing the energy-dependent shape parameter, the so-called S(E) data, we combined the shape S(E) and wing W(E) data by plotting them as a trajectory in the S–W plane, using the implantation energy as a running parameter. It is shown that this plot is of particular interest for the qualitative interpretation of the data. Furthermore, it allows the independent determination of the characteristic shape and wing parameters of the different positron trapping layers without the use of a numerical simulation and fitting program. The method and its advantages and limitations are illustrated for three cases: a silicon sample implanted with helium, a metal–oxide–silicon system subjected to a bias voltage and a bare oxide layer on silicon. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362635
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  • 7
    Electronic Resource
    Electronic Resource
    Positron annihilation study of low pressure chemical vapor deposited silicon nitride films (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1687-1689 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Doppler S-parameter measurements have been performed on low-pressure chemical vapor deposited (LPCVD) Si3N4 samples. Annealing of the samples at 1000 °C for times up to 1 h resulted in a decrease of both the S parameter and the positron diffusion length of the silicon nitride. The diffusion length recovers after reimplantation of deuterium, but the S parameter remains low. The data are discussed using a model also applied to understand some electrical properties of the LPCVD nitride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106218
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  • 8
    Electronic Resource
    Electronic Resource
    Rectangular nanovoids in helium-implanted and thermally annealed MgO(100) (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1110-1112 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cleaved MgO(100) single crystals were implanted with 30 keV 3He ions with doses varying from 1×1019 to 1×1020 m−2 and subsequently thermally annealed from 100 to 1100 °C. Transmission electron microscopy observations revealed the existence of sharply rectangular nanosize voids at a depth slightly shallower than the helium-implantation range. Monitoring of the defect depth profile and the retained amount of helium was performed by positron-beam analysis and neutron depth profiling, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125954
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  • 9
    Electronic Resource
    Electronic Resource
    Natural community bioassays to determine the abiotic factors that control phytoplankton growth and succession (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 20 (1988), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. The successional patterns of the dominant phytoplankton species in Lake Maarsseveen (The Netherlands) were very similar in 1980 and 1981. In December/January the diatoms Stephanodiscus hantzschii Grun., Stephanodiscus astraea (Ehr.) Grun. and Asterionella formosa Hass. dominated the algal community (A. formosa had several further population increases during the year). Fragilaria crotonensis Kitt. came to dominance in March/April, followed by the chrysophyte Dinobryon divergens Imhof and the diatom Cyclotella comta (Ehr.) Kütz in May/June. A second appearance of D. divergens was observed in July/August, followed in 1980 by F. crotonensis and a third small increase of D. divergens. In both years S. astraea and S. hantzschii started to grow again in November/December. Cryptophyceae and Chlorophyta were present throughout the year, but did not show a distinct succession.2. Natural community bioassays, performed under natural light and temperature conditions in a newly developed outdoor bioassay apparatus, showed that phosphate was the major nutrient limiting the growth rate of the phytoplankton. From January till June, during the decline in phosphorus concentration, the diatoms became successively phosphate limited in the sequence: S. hantzschii, S. astraea, F. crotonensis, A. formosa and C. comta. Light limitation was probably the major cause of the relatively late start of F. crotonensis in early spring.3. D. divergens, increasing after the diatoms from June till September, was stimulated by the addition of a chelator (EDTA). The chelator might stimulate the formation of trace metal species favouring their uptake (e.g. iron).4. The patterns of succession of the diatoms observed from January till June and from July till December were to a large extent symmetrical. The controlling factors followed opposite trends: declining phosphorus concentrations with increasing irradiance from winter till spring and increasing phosphorus concentrations with decreasing irradiance from summer till late winter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1988.tb00443.x
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  • 10
    Electronic Resource
    Electronic Resource
    Nutrition (1942)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biochemistry 11 (1942), S. 391-414 
    Details
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.bi.11.070142.002135
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