Adsorption and Decomposition of NH3 on Si(100)-Detection of the NH2(a) Species.

摘要

The dissociative adsorption of Ammonia on Silicon(100) -(2x1) has been studied using accurate surface coverage measurements, temperature programmed desorption, Auger spectroscopy and digital ESDIAD/LEED methods. It has been found that NH2 surface species (amino species) are produced to a saturation coverage of 1 NH2/Si dimer at 120 K. This is accompanied by the production of a Si-H surface species. Digital ESDIAD measurements of the H(+) angular distribution from NH2(a) species indicate that torsional oscillations about the Si-NH2 bond are responsible for the characteristic elliptical H(+) pattern whose long axis is perpendicular to the Si-Si dimer bond direction. It has been shown that NH3 dissociatively adsorbs with unity sticking probability at 120 K up to 86% of full coverage, indicative of a mobile precursor adsorption mechanism. The preadsorption of atomic H onto the Si dangling bond sites reduces the adsorptive capacity of the Si(100) surface, and 1 H/Si completely passivates the surface for NH3 chemisorption. The NH2(a) species, produced by adsorption at 120 K are stable up to about 600 K, where decomposition occurs to produce N(a) and H(a). A minor reaction channel involving NH2(a) + H(a) to produce recombined NH3(g) is observed in the temperature range 600-700 K. Above 700 K, surface N(a), produced from NH2(a) decomposition, enters into the Si(100) lattice. Keywords: Thermal decomposition, Single crystals, Reprints. (aw)