H2 adsorption/desorption at Si(111)-(7 × 7): a density functional study

Abstract

The interaction of H 2 with the Si( 111 )-(7 x 7) surface is investigated by means of density functional slab calculations on a (4 x 2) reconstructed model surface. A viable mechanism for fll desorption is identified, which involves thermally activated Sill 2 units at adatom sites. This mechanism leads to adsorption and desorption barriers of 1.0 and 2.4 eV, respectively, in agreement with experiment. An explanation for the two components observed in the ~ peak of temperature-programmed desorption spectra is proposed. The lattice deformation energy at the transition state for desorption is large (~ 0.6 eV ). If we assume that this remains in the surface after H 2 desorption, the low translational energy of desorbing molecules which has been observed experimentally can in part be explained. © 1997 Elsevier Science B.V.

Molecular beam investigation of hydrogen dissociation on Si(001) and Si(111) surfaces

“…Detailed calculations show, that adsorption via a direct reaction pathway almost leads to braking of one of the backbonds of the adatoms [62]. Also a reaction path via a dihydride state has been considered [61]. Since both mechanisms may be operative on the surface, a more complex superposition of the potential energy surfaces might be necessary.…”

“…The interdimer pathway which has been treated only sporadically in earlier theoretical work [50,58] is indeed energetically favoured over the simpler intra-dimer pathway according to the most recent calculations [59,60]. On Si(111)7×7, H 2 is likely to interact with both the rest-atoms and the ad-atoms dangling-bonds [16,61,62].…”

Effect of beam energy and surface temperature on the dissociative adsorption of H2 on Si(001)

“…Ab initio calculations for Si(111)7ϫ7 have identified the dominant surface excitation as a strong distortion of adatom back bonds. 25,26 We hope that the presence of a consistent data set will lead to renewed theoretical efforts also for the H 2 -Si(001) system which is considered to be prototypical for our understanding of the reaction dynamics on semiconductor surfaces.…”

Diffusion of Single Hydrogen Atoms on Si(111)-(7×7) Surfaces

“…Although its lifetime is much shorter, this state can be directly observed below 320 ± C. Above that, the lifetime is too short to be imaged by STM. From thousands of continuous-time STM images taken below 320 ± C, we can estimate the binding energy difference between A and R sites using the relation P R ͞P A 1 2 exp͑E A 2 E R ͒͞k B T , where the statistical weight 1 2 accounts for the fact that the number of the available A sites is twice that of the R sites. On the 7 3 7 surface, E A 2 E R is found to be ϳ0.2 eV for both the faulted and unfaulted halves.…”

“…One of the fundamental issues is the role of surface diffusion of hydrogen atoms. For example, it has been speculated that surface diffusion plays a crucial role in the recombinative desorption of hydrogen from silicon surfaces [1]. Surface diffusion of chemisorbed species is, of course, an important process in catalysis.…”