Co-adsorption patterns of NH3 on Si(001): Comment on “The ordering of the adsorbed NH3 molecules across the Si dimer rows on the Si(001) surface”

Competing interactions in molecular adsorption: NH3on Si(001)

“…Stemming from the proposed appearance of the ID structure, the authors of the low-coverage study suggested that the linear OD feature, identified in the high-coverage STM data, and shown in figure 6, should be reinterpreted as ID features [40]. As we have argued previously [61], this suggestion leads to a logical contradiction and can be dismissed. If we imagine a group of three (10) dimers, arranged (10), (10), (01).…”

“…The basic physics would suggest that the NH 2 group would be higher than the H group; the physical height difference in an atomic model matched the measured height difference in STM at −2 V sample bias, and the lone pair on the N atom would appear bright relative to the H atom. However, this interpretation has been disputed [59][60][61].…”

“…For example, strong contrast effects around defects are seen in clean silicon [62,63] in this voltage range. For any structure, therefore, such a low voltage is inappropriate for the simulation of experimental images taken at bias voltages, such as −2 V, which are far from the band edge [61]. Secondly, DFT is a ground state theory, and notably does not calculate the width of the band gap correctly; calculations of filled states are therefore more reliable than those of empty states, and simulations of filled states images are in general much more reliable than those of empty states images.…”

“…Dissociation into an OD structure would lead to the NH 2 group adsorbed on this same atom; the brighter end must therefore be the NH 2 group. • Analysis of correlations between dimer rows shows a positive correlation of the bright ends of the dimers [59,61,65], and shown below in figure 17. This can be explained naturally by a H-bonding interaction between NH 2 groups, if the bright end of the dimer is the NH 2 .…”

Coadsorption of Ethylene and Nitrobenzene on Si(100)-2 × 1: Toward Surface Patterning at the Molecular Level

“…In fact, this propensity has been used before to investigate the properties of this surface as a molecular template. For example, ammonia adsorption and the following dissociation on a Si(100)-2 × 1 surface can be thermally controlled to produce two different kinds of predominant surface structures: in one case the NH 2 fragments following the NH 3 dissociation could line up on the same side of the silicon dimer row, and in another they would follow the alternating buckling of surface dimers to ultimately produce the zigzag configuration. − Another example of selective dissociation is the reaction of BF 3 to form Si−BF 2 and Si−F. , BF 3 , upon reacting with the silicon surface, dissociates into BF 2 and F fragments, but precovering the surface with trimethylamine (TMA) alters the electron density of the surface dimer and creates a nucleophilic site on the Si u atom where BF 3 adsorbs intact . These coadsorption studies used the Si(100)-2 × 1 surface as a template utilizing the redistribution of electronic density within the same silicon surface dimer upon the initial chemical modification; however, controlling the long-range pattern with this approach is rather difficult.…”