New Mechanism for Hydrogen Desorption from Covalent Surfaces: The Monohydride Phase on Si(100)

Abstract

A new mechanism for the thermal desorption of molecular hydrogen from the monohydride phase on Si(100) has been identified. The unusual first-order desorption kinetics that are observed are due to the irreversible excitation of a hydrogen adatom into a delocalized, two-dimensional band state on the surface with an activation energy of 47 kcal/mol. The desorption reaction occurs between this excited hydrogen adatom and a second, localized hydrogen adatom.

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

“…An example which attracted considerable experimental and theoretical interest over the last years is the H dissociative adsorption and associative desorption on the Si(001)-2×1 surface 1 which is a subject of this study. 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] .…”

Photoreactivity of Si(111)−H in Ambient

“…The small temperature change (5 K) indicates that laser-induced thermal desorption of H is not responsible for the SH signal change. Temperatures in excess of 700 K are required for significant desorption from Si(111)-H. 37 ) (s) and intermittent laser irradiation, i.e., sampled on average every 3 days after H termination (9). Each data point in the intermittent experiment received less than 20 s of illumination (7 mJ/cm 2 ).…”

The adsorption of silane, disilane and trisilane on polycrystalline silicon: a transient kinetic study

“…This is not much of a problem as long as the reactions after the adsorption step are so fast that in the time interval between two pulses, which is mainly of the order of a second, the free surface can be regenerated. It is known, however, that hydrogen desorption, whether first-order as on Si(001) [3,4,[23][24][25][26] or second-order as on Si(11l) [4], is a slow process with a characteristic time of about 1 s even at 850 K. This is consistent with the results obtained by Holleman and Verweij [27] and by Weerts [13]. These kinetic modelling studies showed that the desorption of molecular hydrogen from the hydrogenated polysilicon surface occurs with a similar characteristic time.…”

“…Hydrogen desorption is accounted for through reaction $5. As discussed by various authors [3,4,[24][25][26], the desorption reaction is of first order in hydrogen adatom coverage on Si(001). Also, in studies on the growth mechanism of polycrystalline silicon under LPCVD conditions [13,27] a first-order desorption reaction for hydrogen is found.…”

“…[1,2]), laserinduced thermal desorption (LITD) [3,4], modulated molecular beam scattering (MMBS) [5,6] and reflection high-energy electron diffraction (RHEED) [7]. These studies all have been performed under UHV conditions on well-defined single-crystalline surfaces.…”