First principles calculation of prepairing mechanism for H2 desorption from Si(100)−2×1

Pai, Sharmila V.; Doren, Douglas J.

doi:10.1063/1.469834

Cited by 42 publications

(23 citation statements)

References 44 publications

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“…One of the principal reasons that defect models have been suggested to explain the first-order kinetics is that the energetics of desorption from some ab initio cluster calculations 4 -6 was found to be larger than experimental measurements. While these calculations did allow some substrate relaxation, other ab initio cluster calculations employing more substrate relaxation 9 as well as several ab initio slab calculations [10][11][12] are in agreement with experimental desorption energies, so that this argument must be viewed with some caution. It should also be pointed out, however, that both of the latter sets of calculations are based on density functional theory, while the former are all based on configuration interaction so that this may also play a significant role in the contradictory results.…”

Section: Introductionmentioning

confidence: 90%

“…These include both cluster 9 and slab models 10-12 of the surface. There is no way in general to guarantee that the GGA approximation in DFT produces a qualitatively correct PES without going beyond this level of approximation, which is currently impossible for surface calculations.…”

Section: Possible Sources Of Disagreementmentioning

confidence: 99%

“…[9][10][11][12]23 The lowest energy pathway between the adsorbed ͑monohydride͒ and gas phase H 2 or D 2 is via an asymmetric transition state. This transition state occurs for a Si dimer buckling angle intermediate between that of the free surface and the flat dimer appropriate for the monohydride surface.…”

Section: Introductionmentioning

confidence: 99%

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D2 dissociative adsorption on and associative desorption from Si(100): Dynamic consequences of an ab initio potential energy surface

Luntz

Kratzer

1996

The Journal of Chemical Physics

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Dynamical calculations are reported for D 2 dissociative chemisorption on and associative desorption from a Si͑100͒ surface. These calculations use the dynamically relevant effective potential which is based on an ab initio potential energy surface for the ''pre-paired'' species. Three coordinates are included dynamically; the distance to the surface, the D-D bond length and a Si phonon coordinate. Other coordinates ͑multidimensionality͒ have been included via a static approximation. Both an asymmetric and symmetric reaction paths are considered. While energetics favors the asymmetric path, phase space favors the symmetric one. Under the conditions of many experiments, either could dominate. The calculations show quite weak dynamic coupling to the Si lattice for both paths, i.e., weak surface temperature dependences to dissociation and small energy loss to the lattice upon desorption. These calculations do not support previous suggestions that either a strong coupling to the lattice or ''entropic'' effects can reconcile the apparent violation of detailed balance obtained by comparing experimental dissociation to desorption barriers. In fact, the results reported here do not agree with several experimental findings. We discuss several possibilities for this disagreement, including experimental artifact, limitations in the dynamical model and even the possibility that electronically adiabatic dynamics involving the ''pre-paired'' species is not relevant to experiments on real systems.

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Section: Introductionmentioning

confidence: 90%

Section: Possible Sources Of Disagreementmentioning

confidence: 99%

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D2 dissociative adsorption on and associative desorption from Si(100): Dynamic consequences of an ab initio potential energy surface

Luntz

Kratzer

1996

The Journal of Chemical Physics

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“…The only cluster-based support to direct desorption via the pre-pairing mechanism comes from the DFT calculations by Pai and Doren 13 . Using the non-local Becke-Lee-Yang-Parr (BLYP) functional 20,21 , they find E des a = 64.9 kcal/mol (2.8 eV) including a zero-point energy (ZPE) correction.…”

Section: Introductionmentioning

confidence: 99%

“…The intriguing experimental result that the H 2 desorption from Si(001) follows first-order kinetics [2][3][4] has triggered an intense theoretical activity in this field mainly concentrated on the mechanism(s) leading to such an unusual behavior. The available first principles calculations address the latter question on the basis of two different models: (i) the cluster approximation using either configurationinteraction (CI) methods [5][6][7][8][9][10][11][12] or density-functional theory (DFT) 8,13 to describe the exchange and correlation effects or (ii) extended slab models for the Si(001)-2×1 surface using DFT [14][15][16] .…”

Section: Introductionmentioning

confidence: 99%

Effect of the cluster size in modeling the H2 desorption and dissociative adsorption on Si(001)

Penev¹,

Kratzer²,

Scheffler³

1999

The Journal of Chemical Physics

164

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Three different clusters, Si9H12, Si15H16, and Si21H20, are used in density-functional theory calculations in conjunction with ab initio pseudopotentials to study how the energetics of H2 dissociative adsorption on and associative desorption from Si(001) depends on the cluster size. The results are compared to five-layer slab calculations using the same pseudopotentials and high quality planewave basis set. Several exchange-correlation functionals are employed. Our analysis suggests that the smaller clusters generally overestimate the activation barriers and reaction energy. The Si21H20 cluster, however, is found to predict reaction energetics, with E des a = 56 ± 3 kcal/mol (2.4 ± 0.1 eV), reasonably close (though still different) to that obtained from the slab calculations. Differences in the calculated activation energies are discussed in relation to the efficiency of clusters to describe the properties of the clean Si(001)-2×1 surface.

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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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First principles calculation of prepairing mechanism for H2 desorption from Si(100)−2×1

Abstract: Density functional calculations show that H2 desorption from Si(100)−2×1 via a ‘‘prepaired’’ state is consistent with energetic and dynamic measurements. The corresponding adsorption process is discussed and comparisons are made to earlier theoretical studies.

Cited by 42 publications

References 44 publications

D2 dissociative adsorption on and associative desorption from Si(100): Dynamic consequences of an ab initio potential energy surface

D2 dissociative adsorption on and associative desorption from Si(100): Dynamic consequences of an ab initio potential energy surface

Effect of the cluster size in modeling the H2 desorption and dissociative adsorption on Si(001)

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

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