Direct dimer-by-dimer identification of clean and monohydride dimers on the Si(001) surface by scanning tunneling microscopy

Abstract

Atomic resolution images of clean Si(001)-(2×1) and the monohydride phase, Si(001)-(2×1)H were investigated using scanning tunneling microscopy at various sample-tip bias voltages. At a sample-tip bias of −1.9 V, each dimer of the monohydride phase shows two protrusions 3.3 Å apart separated by a minimum 0.12 Å deep, while clean dimers show a single protrusion per unit cell. Monohydride dimers appear lower than ‘‘clean’’ dimers, with apparent height differences ranging from 1.9 Å at −1.6 V to 0.65 Å at −3.0 V sample bias. An analysis of the apparent height and spatial distribution of tunneling current within each dimer can be used to unambiguously discriminate between clean dimers, monohydride dimers, and vacancy defects. This methodology is applied to study the distribution of hydrogen on Si(001) surfaces during chemical vapor deposition using disilane, revealing segregation of the monohydride into nearly isotropic islands.

Cycloaddition Chemistry on Silicon(001) Surfaces: The Adsorption of Azo-tert-butane

“…Previous studies of hydrogen on Si(001) have found that bonding of a single H atom to a SiSi dimer yields a “hemihydride” (db-Si−Si−H) moiety with one dangling bond (“db”) per dimer. STM images of the hemihydride moiety show a single bright protrusion (corresponding to the dangling bond) in an off-center position that is very similar to the appearance of the B features in Figure , while infrared spectra show a single vibrational line near 2087 cm -1 , close to the 2086 cm -1 line observed here for ATB adsorbed on Si(001) at 300 K. The appearance of the A features suggests that they correspond to ATB molecules or molecular fragments. The fact that the molecules appear similar on dimer rows that are running perpendicularly (i.e., on the upper and lower terraces) indicates that the appearance of the molecules in the image is not dominated by the shape of the tip, but is instead a true reflection of the symmetry of the molecules.…”

The impact of stochastic incorporation on atomic-precision Si:P arrays

“…However, we also observe two feature categories that aren't associated with successful incorporation. The first is a set of features with a relative height of 1 Å that was previously assigned to depassivated Si atoms [37], consistent with height measurements of the pre-dose surface. The second set of features have relative heights greater than 1.8 Å, which we ascribe to either background contamination in the UHV chamber or ejected Si adatoms adsorbed on H [38,39].…”

Cycloaddition Chemistry of 1,3-Dienes on the Silicon(001) Surface: Competition between [4 + 2] and [2 + 2] Reactions

“…Indeed, in repeated experiments we find that the amount of surface hydrogen varies from sample to sample while the C−H region remains identical; this suggests that the small amount of surface hydrogen detected in the FTIR arises from trace contaminants in the chamber or, more likely, in the reactants themselves. We additionally note that neither the A nor the B species has the proper symmetry to be accounted for by individual H atoms, paired H atoms on a single dimer, − or methyl group, all of which have been studied previously via STM. Thus, we conclude that the vast majority of impinging DMBD molecules adsorb without C−H or C−C bond cleavage and that adsorption occurs primarily through interaction of one or more of the CC bonds with the surface dimers.…”