Adsorption, Isomerization, and Decomposition of HCN on Si(100)2 × 1:  A Computational Study with a Double-Dimer Cluster Model

Abstract

The adsorption, isomerization, and decomposition of HCN on Si(100)-2 × 1 surface have been investigated by means of a density functional theory calculation using a double-dimer cluster model. The results revealed that both HCN and its HNC isomer can be readily adsorbed on a Si−Si dimer either dissociatively or molecularly in an end-on and a side-on configuration. Side-on adsorption occurs by the cycloaddition of the C⋮N group on to the Si−Si dimer, whereas dissociative adsorption gives rise to H(a) and CN(a) adspecies initially via the end-on configuration on the same dimer or across the two dimers. Adsorbate−adsorbate interactions and reactions have also been studied with two HCN molecules. For the end-on adsorption, the first HCN(a) exerts a significant effect on the adsorption geometry of the second HCN. In particular, a synergetic effect has been observed for the parallel adsorption of two HCNs with their CN groups bridging across the two dimers. For the side-on adsorption, the adsorbate−adsorbate interaction is negligible with minor effects on the adsorption geometry. H-migration between the two neighboring, side-on HCN admolecules can occur readily, leading to the formation of HCNH(a) and NC(a) surface species. The calculated vibrational frequencies of the HCNH(a) and NC(a) adspecies are in good agreement with the experimental HREELS data of the HCN/Si(100) system.

Theoretical investigations on CH2CH–CH2OH on the Si(100)-2×1 and Ge(100)-2×1 surfaces

“…Although B3LYP has a tendency to underestimate barriers with a typical error of about 4.0 kcal/mol [41], B3LYP has been used extensively to calculate unsaturated hydrocarbon compounds and alcohols on the Si(1 0 0)-2 · 1 surface with the cluster approximation. These results are generally in good agreement with the experiments [25,30,[34][35][36]42,43]. Therefore, it is expected that B3LYP is reasonable for the present system.…”

“…A Si 15 H 16 and Ge 15 H 16 two-dimer cluster model is used to model the Si(1 0 0)-2 · 1 surface. This model includes the four silicon atoms representing the surface atoms and the eleven silicon atoms composing subsurface bulk atoms as described in previous theoretical investigations [34][35][36]. The dangling bonds of the subsurface atoms are terminated by hydrogen atoms.…”

Adsorption and Decomposition Pathways of Cyanogen Halides on Si(100)−(2×1)

“…For HCN, a stable side-on structure surrounded by transition state barriers larger than the adsorption energy is predicted. 7,17 The stronger HC bond with respect to the HSi bond gives the analogous HCN structure greater stability than that of XCN2. For XCN2, a low barrier reaction pathway driven by the formation of a strong XSi bond destabilizes this structure.…”

“…[24][25][26][27][28] However, the initial dative bonding geometry for ammonia and HCN is sensitive to the cluster size. 17,26 Size-dependent effects on both the resulting stable structures and selective transition states are investigated using the larger Si 21 H 20 cluster.…”

Comprehensive Study of Methylation on the Silicon (100)-2 × 1 Surface: A Density Functional Approach

“…In our work, a two-atom-modeled surface is sufficient, as there is no dative bond beyond the two atom surface space in the adsorption process and in reaction mechanisms and, second, all the reactions adopted here are involved in either one bond dissociation or a one to one substitution process on the silicon surface. The cluster 33−48 has also been proved to be best represented as a single dimer cluster for observing the surface mechanisms especially adsorption and dissociation processes and gave satisfactory results comparable with the experimental values for small molecules like CO, 34 HCN, 35 Lewis acids, 37 alcohols, 36,46 amines, 46 cyclic systems, 40 organosulfurs, 41 metal oxide, 43 amino acids, 47 etc. Very recently, Raghavachari et al 48 have also used the cluster to observe the hydrogen abstraction mechanism on the silicon surface.…”