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  • 1
    Electronic Resource
    Electronic Resource
    Extraction of kinetic parameters in temperature programmed desorption: A comparison of methods (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6725-6732 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An investigation of the temperature programmed desorption (TPD) of CO and D2 from Ni(111) has been carried out. It has been shown that a differential method for the extraction of the kinetic parameters, threshold temperature programmed desorption (TTPD), can be applied with accuracy near the limit of zero coverage. In this limit, agreement is found between integral and differential methods for kinetic parameter evaluation. The factors which limit the applicability of TTPD are explored and a method to verify its proper application is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453409
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  • 2
    Electronic Resource
    Electronic Resource
    Decomposition mechanisms of SiHx species on Si(100)-(2×1) for x=2, 3, and 4 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7493-7503 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Silane adsorption at a surface temperature of 150 K and the surface decomposition of SiH3 and SiH2 have been investigated on the Si(100)-(2×1) surface using static secondary ion mass spectrometry (SSIMS) and temperature programmed desorption (TPD). Silane dissociatively chemisorbs at 150 K to form SiH3 and H. At saturation, the combined coverage of these two is approximately 0.4 groups/1st layer Si atom (0.2 SiH4 adsorbed/1st layer Si atom). Using SiH4, the surface coverage of SiH3 species is varied, and the coverage-dependant kinetics of SiH3 decomposition are examined using temperature programmed SSIMS. Changes in SiH4 exposure and source of SiH3 (di- vs monosilane) cause changes in surface SiH3 stability. The stability changes are interpreted as due to blocking of empty sites (dangling bonds, db) required for SiH3 decomposition to SiH2 and H. It is shown here that the decomposition temperature of SiH3 can vary from 200 to 600 K, depending on the dangling bond coverage (θdb). Subsequently, evidence for a coverage dependant change in the decomposition mechanism of SiH2 is presented. Two mechanisms for SiH2 decomposition are experimentally distinguished, and competition of these is governed by θdb. We conclude that both the mechanism and rate of decomposition of surface SiH3 and SiH2 are dependant on the local surface environment near these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459424
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  • 3
    Electronic Resource
    Electronic Resource
    Decomposition of silane on Si(111)-(7×7) and Si(100)-(2×1) surfaces below 500 °C (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3144-3153 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using static secondary ion mass spectrometry (SIMS) to observe the silicon hydride species formed by silane adsorption on atomically clean single crystal silicon surfaces, two distinct adsorption mechanisms are identified. Dissociation to SiH3 plus H occurs on the Si(100)-(2×1) surface, which contains pairs of dangling bonds located on Si dimers (with Si–Si distance ≈2.4 A(ring)). In contrast, SiH2 formation in the adsorption step is indicated on the Si(111)-(7×7) surface, where adjacent dangling bonds are separated by more than 7 A(ring). Lower limits on the silane reactive sticking coefficient (SR) are evaluated using hydrogen coverage (aitch-thetaH) measurements after calibrated SiH4 exposures, and this limit is ≈10−5 for 25 °C gas and 100–500 °C surface temperatures. Within experimental error, SR is the same for both mechanisms on the two clean surfaces (aitch-thetaH near zero). Dependence of SR on aitch-thetaH is reported at 400 °C for both surfaces, and differences appear as aitch-thetaH exceeds 0.1 H/Si. Silane adsorption is weakly activated on Si(111)-(7×7), as evidenced by enhanced adsorption as TS is increased between 50 and 400 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457912
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrogen on polycrystalline diamond films: Studies of isothermal desorption and atomic deuterium abstraction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 992-1002 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Studies of hydrogen isothermal desorption and abstraction from polycrystalline diamond surfaces are presented. The surface H and D coverages (θH and θD) are measured in real time by mass analyzing the recoiled ions generated in a time-of-flight scattering and recoil spectroscopy (TOF-SARS) experiment. For surface temperatures (Ts) from 825 and 920 °C, isothermal H2 desorption is 1st order in θH with a measured activation energy, ET, of 69±6 kcal/mol and a pre-exponential factor, ν, of 1010.5±0.9 s−1. For H2 desorption from diamond, the estimated ΔET based on bond energy calculations is ≈88 kcal/mol, substantially higher than the experimentally measured ET. This difference suggests π-bonding of the surface after H2 desorption is involved. Using a simple bond order argument, the π-bonding contribution is estimated to be ≈21 kcal/mol. The abstraction and replacement of absorbed H by atomic deuterium (Dat) is explained by three first-order reactions. Under a constant Dat flux, the rate of abstraction of adsorbed H by Dat is 1st order in θH, with an "apparent activation energy'' (Ea) of 0.8±0.2 kcal/mol and ν=(1.3±0.2)10−3 s−1. The low Ea and 1st order kinetics imply that H is abstracted from the surface by a generalized Eley–Rideal or direct mechanism. Using the relative rate of Dat abstraction of H to Dat adsorption on clean diamond, we estimate an upper limit for the abstraction activation barrier of 16 kcal/mol. Under identical reaction conditions, the rate for Hat abstraction of D is ≈1/3 the rate for Dat abstraction of H. We interpret this isotope effect using momentum transfer arguments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469167
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  • 5
    Electronic Resource
    Electronic Resource
    Atomic H abstraction of surface H on Si: An Eley–Rideal mechanism? (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3301-3309 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The abstraction kinetics for atomic hydrogen (Hat) removal of chemisorbed D and atomic deuterium (Dat) removal of chemisorbed H are studied on single crystal Si surfaces. The surface H and D coverages are measured in real time by mass analyzing the recoiled H+ and D+ ion signals. On both Si(100) and Si(111) surfaces, the abstraction reactions are efficient, and have very low activation energies (approximately-equal-to)0.5–1 kcal/mol. For abstraction from surfaces containing only monohydride species, the abstraction reaction probability is (approximately-equal-to)0.36 times the adsorption rate of Hat or Dat. For the same Hat and Dat exposures, the reaction rates for Hat removal of adsorbed D and Dat removal of adsorbed H are nearly identical. All observations are consistent with a generalized Eley–Rideal abstraction mechanism, and a two-dimensional quantum-mechanical model is used to calculate reaction probabilities for these reactions. According to the model, the activation energies are due to enhanced abstraction rates from excited vibrational states of the adsorbed Si–H or Si–D bond. With SiH2 and SiH3 species present on the surface, the removal rate of H using Dat is decelerated, suggesting that the higher hydrides have a lower cross section for abstraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467577
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  • 6
    Electronic Resource
    Electronic Resource
    Isotope effects in hydrogen adsorption on Ni(111): Direct observation of a molecular precursor state (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6792-6802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nature of the interaction of hydrogen with Ni(111) is probed by comparing the adsorption and desorption kinetic behavior of H2 and D2. Pure H2 and pure D2 adsorbed on Ni(111) at 140 K exhibit identical desorption behavior. The adsorption rate law depends upon (1-θ) rather than (1-θ)2, suggesting that the rate determining step involves the interaction of an H2 molecule with a single Ni site. The temperature programmed desorption spectra show two desorption features, β1 and β2, which have maxima in desorption rate at 290 and 370 K. When either pure H2 and pure D2 or a mixture of H2 and D2 interact with the Ni(111) surface at 87 K, evidence for kinetic retardation of D2 adsorption is observed. When the H2:D2 mixture is exposed to the Ni(111) surface, held at 87 K, an additional desorption feature, α, is uniquely observed at 100 K for D2. α-D2 desorbs with first order kinetics exhibiting Ed =11.1 kJ/mol and a preexponential factor of 1.2×105 s−1. It may be due to desorption from an intrinsic molecular precursor state. The observed differences between hydrogen and deuterium adsorption indicate the presence of an activation energy barrier for dissociative chemisorption, and a sensitivity of the adsorption process to differences in zero point vibrational energies. A molecular precursor state is proposed to describe the H2+Ni(111) interaction. Dissociative adsorption of hydrogen on intentionally produced surface defects has been shown to destabilize α-D2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451411
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  • 7
    Electronic Resource
    Electronic Resource
    Growth of Si on Si(100) via H/Cl exchange and the effect of interfacial boron (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4073-4082 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using alternating exposures of Si2H6 and Si2Cl6, very thin Si layers have been grown on the Si(100) surface at temperatures (T) as low as 475 °C. Although this growth method is not truly self-limiting, some of the desired features for Si atomic layer epitaxy (ALE) are retained, as discussed here. The growth rate of new Si on Si(100) using this method is limited by the thermal desorption of H2 and HCl. Doping the surface with boron atoms can lower the growth temperature, due to a weakening of the Si—H and Si—Cl bonds on the surface as observed in the temperature programmed desorption results from H2, HCl, and SiCl2 desorption from the clean and the boron-doped Si(100) surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352261
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  • 8
    Electronic Resource
    Electronic Resource
    Atomic layer epitaxy of Si on Ge(100) using Si2Cl6 and atomic hydrogen (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 884-886 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface composition is measured during atomic layer epitaxy (ALE) growth of Si on Ge(100) using Si2Cl6 and atomic hydrogen (Hat) at TS=400 °C. During each Si2Cl6 exposure, Si is adsorbed until Cl fully terminates the surface, making the Si deposition step self-limiting. The terminating Cl layer is removed by Hat exposure. At 400 °C, H2 rapidly desorbs from Ge(100) and Si/Ge alloy surfaces, regenerating the surface dangling bonds for the next Si2Cl6 adsorption cycle. A thin alloy is grown epitaxially on the Ge(100) substrate, which displays a linear increase in Si content and a linear decrease in Ge content, measured over 1–20 Si ALE cycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110984
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  • 9
    Electronic Resource
    Electronic Resource
    Nanocrystal seeding: A low temperature route to polycrystalline Si films (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3569-3571 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method is presented for growth of polycrystalline silicon films on amorphous substrates at temperatures of 540–575 °C. Grain nucleation and grain growth are performed in two steps, using Si nanocrystals as nuclei ("seeds''). The nanocrystal seeds are produced by excimer laser photolysis of disilane in a room temperature flow cell. Film (grain) growth occurs epitaxially on the seeds in a separate thermal chemical vapor deposition (CVD) step, with growth rates 10–100 times higher than similar CVD growth rates on crystal Si. Grain size and CVD growth rates are dependent on seed coverage, for seed coverage 〈0.2 monolayers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111200
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  • 10
    Electronic Resource
    Electronic Resource
    Atomic layer epitaxy of Si on Ge(100): Direct recoiling studies of film morphology (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1615-1621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two Si atomic layer epitaxy schemes based on Cl/H exchange chemistry are compared by deposition of Si on Ge(100). Time-of-flight direct recoiling and reflection high-energy electron diffraction are used to characterize the very thin Si layers. It is shown that alternating exposure to SiCl2H2 and atomic hydrogen deposits Si in a process that is self-limiting. Growth of Si by this method results in either alloy formation or Si island growth as low as 465 °C on Ge(100), which prohibits a simple measurement of Si thickness/cycle. In contrast, alternating exposure to Si2Cl6 and Si2H6 below 500 °C results in Si deposition with uniform thickness. Plots of direct recoil intensity versus incident angle (with respect to the surface plane) are a sensitive probe of the thin layer morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357741
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