Dissociative adsorption ofNH3onSi(001)−(2×

Abstract

Using the first-principles pseudopotential-local-density-approximation approach, we have studied the dissociative molecular adsorption of NH 3 on Si(001)-(2ϫ1). We find that upon adsorption the Si dimer becomes symmetric and somewhat elongated. We also find that the Si-N bond is inclined at 10°with respect to the surface normal, the N-Si bond length is 1.75 Å, and the N-H bond length is 1.05 Å. Finally, our electronic structure calculations suggest that the adsorption of ammonia almost completely passivates the silicon surface.

Comparative study of the adsorption and dissociation of vinylacetic acid and acrylic acid on silicon (001)

“…When the dissociated model is considered, the H adsorbed by the other Si dimer component is at a distance of 1.51 Å, exactly the same value obtained by us for this bond length when the adsorption of the ammonia molecule is considered. 30 The same level of agreement was observed for the Siu H bond tilt: = 20.7°with respect to the surface normal. Our structural data are also consistent with the theoretical findings by Kim and Cho 25 for the adsorption of acetic acid with the silicon surface.…”

The mechanism of amine formation on Si(100) activated with chlorine atoms

“…These Cl activated reactions at 348 K are consistent with first principles studies on a Si surface terminated with dangling bonds, which is experimentally equivalent to annealing at high temperatures, above 1100 K. The ab initio results show that NH 3 dissociatively adsorbs into Si-NH 2 and Si-H on bare dimers with an activation energy of $0.6-1.0 eV relative to physisorbed NH 3 , depending on the surface coverage [50,52]. Dissociation produces an almost symmetric dimer containing Si-NH 2 and Si-H with a tilt angle of 1-2° [50][51][52]. First principles calculations for gas phase reactions between NH 3 and SiH 2 Cl 2 [54] provide an analog for reactions between NH 3 and a H-terminated or a Cl-terminated Si surface.…”

“…7, has been observed experimentally on clean Si(1 0 0)-(2 · 1) below room temperature [19,21]. First principles studies of ammonia reacting with clean Si(1 0 0)-(2 · 1) show that NH 3 bonds with the electron deficient down Si atom of an asymmetric Si-Si dimer, which has a 16-18°tilt angle on the clean surface, producing a molecularly adsorbed state, which is stable at low temperature and is tilted by 13° [50][51][52]. The electronegativity of Cl polarizes the Si-Cl bonds and makes dative bond formation possible by donation of the lone pair of electrons on N to an electropositive Si dimer atom.…”

Role of surface strain in the subsurface migration of adsorbates on silicon

“…14,15 Since silicon atoms on the surface remain unsaturated even after the ͑2 ϫ 1͒ reconstruction, this surface is very reactive. For example, ammonia ͑NH 3 ͒ and water ͑H 2 O͒ adsorb dissociatively, even at cryogenic temperatures, to form ͑Si͒NH 2 and ͑Si͒H moieties in the former case [16][17][18][19][20][21][22][23][24][25][26] and ͑Si͒OH and ͑Si͒H species in the latter. [27][28][29][30] Dissociated species may occupy the same dimer or neighboring dimers, known respectively as intradimer and interdimer dissociations.…”