π-bonded dimers, preferential pairing, and first-order desorption kinetics of hydrogen on Si(100)–(2×1)

D'Evelyn, Mark P.; Yang, Yu-Chu; Sutcu, L. F.

doi:10.1063/1.462417

Cited by 143 publications

(89 citation statements)

References 49 publications

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“…4 1 " 45 As previously, for hydrogen adsorbed alone, 43 ,4 6 we attribute the near-first-order kinetics to preferential pairing of adsorbed atoms on surface dimers driven by the weak nt bonds on clean surface dimers. The presence of two types of atoms (H, X), three types of pairing (H+H, H+X, X+X), and three desorption channels necessitates a generalization of the doubly-occupied dimer model that we developed to explain the desorption kinetics of hydrogen from Si(100)2x143 and is described below.…”

Section: Competitive Pairing Modelsupporting

confidence: 72%

“…53 The available experimental evidence seems to favor a sequential 32 ' 5 1 desorption mechanism between H atoms paired on a single dimer. 42 -4 6 , 4 9 ,51,54 The near-first-order kinetics can be explained by preferential pairing of adsorbed hydrogen, 4 3 "46, 54 which is driven by the nt bond 55 on "unoccupied" surface dimers and has been observed directly by scanning tunneling microscopy (STM).54 Fitting the deviation from first-order kinetics at low coverage to the predictions of our doubly-occupied dimer model 4 3 leads to estimates of 5-7 kcal/mol and = 5 kcal/mol for the pairing energies of hydrogen on Si(100) 43 - 4 5 and Ge(100), 46 which is also a measure of the it bond strength on the clean surface. 4 3 ,4 6 These estimates of the pairing energy for hydrogen on Si(100) are also in reasonable agreement with values implied by recent Si-H bond strength calculations.…”

Section: Introductionmentioning

confidence: 92%

“…For the present we assume that the dimers are non-interacting as in the original model. 43 We consider the effects of interactions between dimers for H on Si (100)2xI elsewhere. 69 , 70 For simplicity let us assume that in the (degenerate) ground state of the system, all 2 NH hydrogen atoms are paired on NH dimer sites and all 2NX halogen atoms are paired on Nx dimer sites.…”

Section: Competitive Pairing Modelmentioning

confidence: 99%

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Adsorption, desorption, and decomposition of HCl and HBr on Ge(100): Competitive pairing and near-first-order desorption kinetics

D'Evelyn

Yang

Cohen

1994

The Journal of Chemical Physics

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We have investigated the surface chemistry of coadsorbed hydrogen and halogen atoms on Ge(100), produced by dissociative chemisorption of HCl and HBr, by temperature-programmed desorption. The initial sticking probability S0 for HCl decreases from 0.6 at a substrate temperature of 270 K to 0.05 at 400 K, indicative of a precursor state to adsorption. For HBr S0 is constant at 0.7 over the same temperature range. A fraction f of adsorbed hydrogen atoms desorb associatively as H2 near 570 K, while the remaining (1−f) H atoms recombine with adsorbed halogen atoms and desorb as the hydrogen halide (HX) near 580–590 K. The activation energies for desorption of H2, HCl, and HBr are all approximately 40 kcal/mol. For both HCl and HBr f is 0.7 at low initial coverage and decreases slightly to 0.6 at saturation. The fraction f of adsorbed halogen atoms left on the surface following the competitive desorption of H2 and HX desorb as the dihalides GeCl2 and GeBr2 near 675 and 710 K, respectively. Desorption of H2, HCl, and HBr occurs with near-first-order kinetics, similar to the behavior of hydrogen adsorbed alone, which we attribute to preferential pairing induced by the π bond on unoccupied Ge dimers. We introduce and solve a generalized doubly occupied dimer model incorporating competitive pairing of H+H, H+X, and X+X on Ge dimers to explain the near-first-order kinetics. The model quantitatively accounts for both the desorption kinetics and the relative yields of H2 and HX with pairing energies of ≊3 kcal/mol. Implications of the present results for surface thermochemistry, chemical vapor deposition, and atomic layer epitaxy of Ge and Si(100)2×1 surfaces are discussed.

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Section: Competitive Pairing Modelsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 92%

Section: Competitive Pairing Modelmentioning

confidence: 99%

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Adsorption, desorption, and decomposition of HCl and HBr on Ge(100): Competitive pairing and near-first-order desorption kinetics

D'Evelyn

Yang

Cohen

1994

The Journal of Chemical Physics

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“…The nearly constant peak temperatures, Tp, together with the asymmetric peak shape at high initial coverage, indicate near first-order desorption kinetics [9]. However, the slight increase in Tp and the more symmetric peak shape at lower initial coverages demonstrate a slight departure from first-order kinetics, as also occurs for hydrogen on Si(100) [10][11][12]. The dependence of Tp on 0 is shown in Fig.…”

Section: Resultsmentioning

confidence: 83%

“…The 71 bonds on clean surface dimers provide a driving force for pairing of adsorbates on the dimers [12,15]. For hydrogen the pairing enthalpy is approximately equal to the ii-bond strength [12,16].…”

Section: Discussionmentioning

confidence: 99%

Hydrogen-Halogen Chemistry on Semiconductor Surfaces

Cohen¹,

Hukka²,

D'Evelyn³

1992

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REPORT DOCUMENTATION PAGE OMB No 0704-o188PuDhIC reoor ng Curden for this coilection of intormatiOn is estimated to average I hour per response, including the time for reviewing instructions. searching exlstlng dat& a . gathering an" maintaining the data needed. and omiletifg and revieing the collection of information. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(Ei) 10. SPONSORING/MONITORING AGENCY REPORT NUMBEROffice of Naval Research 800 N. Quincy Street Arlington, VA 22217-5000 SUPPLEMENTARY NOTES Prepared for publication in:Thin Solid Films. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODEApproved for public release; distribution is unlimited. ABSTRACT (Maximum 200 words)The chemistry of coadsorbed H and X (X=CI, Br) on semiconductor surfaces is important in epitaxial growth of silicon from chlorosilanes and of SixGe.x alloys, in hydrogenating/ halogenating cycles in atomic layer epitaxy, and also provides an interesting model system, yet has received little attention to date. We have investigated the interaction of H, HCl,. and HBr with Ge(100) by temperature-programmed desorption, and find that H 2 , HCl, and HBr each desorb with near-first-order kinetics near 570-580 K, and that GeCl2 and GeBr2 desorb with second-order kinetics near 680 K and 710 K, respectively. Trends in the chemistry and kinetics can be rationalized by viewing the dimer atoms on clean Ge(100)-(2xl) as being linked by a strained double bond and adsorption, decomposition, and desorption as being analogous to addition, rearrangement, and elimination reactions of molecular germanium compounds. The near-first-order desorption kinetics are attributed to pairing on surface dimers induced by the t bond on unoccupied dimers. We infer a pairing enthalpy for H+H (-the t bond strength of dimerized Ge(100) surface atoms) of 4-5 kcal/mol. SUBJECT TERMS 15. NUMBER OF PAGES 77251-1892 AbstractThe chemistry of coadsorbed H and X (X--C1, Br) on semiconductor surfaces is important in epitaxial growth of silicon from chlorosilanes and of SixGej-x alloys, in hydrogenating/ halogenating cycles in atomic layer epitaxy, and also provides an interesting model system, yet has received little attention to date. We have investigated the interaction of H, HC1, and HBr with Ge(100) by temperature-programmed desorption, and find that H2, HC1, and HBr each desorb with near-first-order kinetics near 570-580 K, and that GeC12 and GeBr2 desorb with second-order kinetics near 680 K and 710 K, respectively. Trends in the chemistry and kinetics can be rationalized by viewing the dimer atoms on clean Ge(100)-(2xl) as being linked by a strained double bond and adsorption, decomposition, and desorption as being analogous to addition, rearrangement, and elimination reactions of molecular germanium compounds. The near-first-order desorption kinetics are attributed to pairing on surface dimers induced by the n bond on unoccupied dimers. We infer a pairing enthalpy for H+H (= the n bond strength of dimerized Ge(100) surface atoms) of 4-5 kcal/mol.

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Adsorption–Desorption of H2/Si: A 5-D Dynamical Model

Brenig

Groß

Höfer

et al. 1997

phys. stat. sol. (a)

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Several theoretical and experimental results on the dynamics of dissociative adsorption and recombination desorption of hydrogen on silicon are reviewed. Theoretically a 5‐D model is presented taking lattice distortion, corrugation and molecular vibrations into account besides the translational motion of the molecule. The properties of this model are investigated within the framework of coupled channel calculations. While the temperature dependence of sticking is dominated by lattice distortion, the main effect of corrugation is a reduction of the pre‐exponential factor by about one order of magnitude per lateral degree of freedom. Molecular vibrations have little effect on the adsorption–desorption dynamics itself but lead to vibrational heating in desorption with a strong isotope effect. Ab initio calculations for the H2 interaction with the dimers of Si(100) 2×1 show properties of the potential surface in qualitative agreement with the model, but its dynamics differs quantitatively from the experimental results. Experimentally extremely small sticking probabilities in the range 10−9 to 10−5 could be measured using optical second‐harmonic generation (SHG) for H2 and D2 on Si(111) 7×7 and Si(100) 2×1. Strong phonon‐assisted sticking was observed for gases at 300 K and surface temperatures between 550 and 1050 K. The absolute values as well as the temperature variation of the adsorption and desorption rates show surprisingly little isotope effect and differ only little between the two surfaces. These results indicate that tunnelling, molecular vibrations, and the structural details of the surface play only a minor role for the adsorption dynamics. Instead, they appear to be governed by the localized H–Si bonding and Si–Si vibrations. These results together with previously measured energy and angular distributions of desorbing molecules can be described very well with the theoretical model.

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π-bonded dimers, preferential pairing, and first-order desorption kinetics of hydrogen on Si(100)–(2×1)

Cited by 143 publications

References 49 publications

Adsorption, desorption, and decomposition of HCl and HBr on Ge(100): Competitive pairing and near-first-order desorption kinetics

Adsorption, desorption, and decomposition of HCl and HBr on Ge(100): Competitive pairing and near-first-order desorption kinetics

Hydrogen-Halogen Chemistry on Semiconductor Surfaces

Adsorption–Desorption of H2/Si: A 5-D Dynamical Model

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