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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the water bound to a polymer matrix by infrared spectroscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5431-5437 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article focuses on the interaction of water with solid polymers. A portion of the water adsorbed in hydrophilic materials is strongly bound to individual sites (bound water), while an additional amount is bound less firmly to the polymeric chain (free water). Both free and bound water have been the subject of many studies that have uncovered, in some cases, qualitative evidence of the presence of water directly bound. In this article, we report a method to determine the different fractions of water adsorbed in hydrophilic materials. One fraction corresponds to the first layer in contact with the adsorbing solid and the other corresponds to the remaining water absorbed layers. We were able to determine said quantification by means of measuring the change in the natural vibration frequency brought about by the interaction of water molecules with the solid. The measurement was done on films of methylcellulose exposed to humid environments using infrared spectroscopy and gravimetric static microclime sorption methods. Theoretical predictions for bound water were developed using multilayer adsorption models. The experimental concentration of bound water as a function of relative humidity was compared with these predictions, allowing us to judge the applicability of different adsorption models employed in the study of gas condensation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1365427
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  • 2
    Electronic Resource
    Electronic Resource
    Electron transverse energy distribution in GaAs negative electron affinity cathodes: Calculations compared to experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1809-1815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transverse momentum of photoelectrons released from a negative electron affinity GaAs cathode is small compared with other thermonic or field emission electron sources. A low photoelectron transverse momentum in vacuum promises highly focused, low-energy beams useful for numerous applications. A simplified theory for electron emission from GaAs predicts much lower electron transverse momentum than those previously measured experimentally. To address this theory–experiment mismatch, Monte Carlo based calculations were compared with experimental data. We checked the possibility of there being electron scattering in the Cs,O layer; however, none of the scattering checked (isotropically distributed, cosine distributed, and Rutherford scattering) properly fit the experimental results. The assumption of conservation of the parallel component of the crystal momentum k during the emission is mainly believed to be responsible for the calculation-theory disagreement. The best simulation-experiment fit was obtained through a relaxation of the conditions imposed on the transverse momentum inside and outside of the semiconductor when an ideal interface is considered. We obtained the best results by assuming that the effective mass of the electron inside GaAs is equal to the effective mass of the electron in vacuum. Two independent experiments confirmed that in both cases, this same-mass approximation gives the best fit. The physical meaning of this is not clear, but it seems to be related to the amorphous nature of the Cs,O layer. We conclude that the way to get lower electron transverse energy spread cathodes is to study alternative activation methods and new materials with smaller effective electron masses. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362992
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  • 3
    Electronic Resource
    Electronic Resource
    Physics of high-intensity nanosecond electron source: Charge limit phenomenon in GaAs photocathodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7318-7323 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaAs negative electron affinity cathodes are used as high-intensity, short-time electron source at the Stanford Linear Accelerator Center. When the cathodes are illuminated with high-intensity laser pulses draw peak currents that are extremely high, typically of tens of Amperes. Because of the high currents, some nonlinear effects are present. Very noticeable is the so-called charge limit (CL) effect, which consists of a limit on the total charge in each pulse; that is, the total bunch charge stops increasing as the light pulse intensity increases. The CL effect is directly related to a photovoltage built up in the surface as a consequence of the photoelectrons coming from the bulk. We discuss possible ways to minimize the formation of the surface photovoltage. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361448
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  • 4
    Electronic Resource
    Electronic Resource
    Photoemission from the Sr/Si(001) interface (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6070-6072 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of Sr on n-type Si(001) was studied in detail for coverages between 0 and 1 monolayer (ML) using core level photoemission spectroscopy. In a similar manner, the Sr saturation coverage was studied in the 600–925 °C temperature range. Data analysis was carried out by a method that allows accurate determination of the band-bending shifts. Using this method it is possible to pinpoint the formation and destruction of chemical species from bungled core level photoemission data without needing to know details of the chemical composition of the spectra. Through this analysis it was established that the interaction between Sr and Si breaks down the binding energy difference between upward and downward Si dimer atoms. In addition, it was found that the saturation coverage exhibits a clear plateau at 1 ML around 650 °C, and a slope change at 1/3 ML around 850 °C. The surface band bending suffers a discontinuous increase as the Sr coverage surpasses 〈fraction SHAPE="CASE"〉12 ML and as the low energy electron diffraction symmetry changes from [2×3] to [2×1]. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415758
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  • 5
    Electronic Resource
    Electronic Resource
    Evolution of the crystallographic position of As impurities in heavily doped Si crystals as their electrical activity changes (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3090-3092 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Arsenic impurities in silicon can be electrically activated beyond their electrical solubility to as high as 4×1021/cm3 by ion implantation and laser melting; further annealing decreases this activity to its equilibrium saturation level. To characterize the deactivation process, we used x-ray standing-wave spectroscopy. Hall effect, and secondary-ion-mass spectroscopy. Our results indicate that the As impurities remain in substitutional positions even after 85% of the activation has been lost, so deactivation cannot be due to As migration to interstitial sites or to large precipitates. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116432
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  • 6
    Electronic Resource
    Electronic Resource
    Chemical depth profile of ultrathin nitrided SiO2 films (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 1014-1016 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin nitrided SiO2/Si(001) films were studied using angle-resolved x-ray photoemission spectroscopy. The structure of the oxynitride depended on the nitridation process. Under one type of nitridation the film kept the structure of the SiO2, with N assuming O sites. By taking advantage of the nonuniformity on the chemical depth profile, the Si 2p chemical shift was determined for those Si atoms bonded to three O and one N atom, and for those bonded to two O and two N atoms. The stoichiometry depth profile was recognized through a simple method that allowed the input of physical constrains. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1494121
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  • 7
    Electronic Resource
    Electronic Resource
    Lattice compression of Si crystals and crystallographic position of As impurities measured with x-ray standing wave spectroscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1429-1437 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an earlier letter [Appl. Phys. Lett. 68, 3090 (1996)] we reported results about heavily arsenic doped silicon crystals, where we unambiguously showed, based on x-ray standing wave spectroscopy (XSW) and other techniques, that electrically deactivated As remains essentially substitutional. In this article we present the analysis methodology that led us to said conclusion, and show how from further analysis it is possible to extract the compression or expansion of thin epitaxial layers. We report the evolution of the compression of highly As doped Si epitaxial layers as deactivation takes place. The XSW measurements required a very small thickness of the doped layer and a perfect registry between the substrate and the surface layer. We found larger values for compression than previously reported, which may be explained by the absence of structural defects on our samples that relax the interface stress. Our results show a saturation on the compression as the electron concentration increases. We also report an estimation of the small displacement from perfect substitutional positions suffered by deactivated As. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369274
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