Communication: Fully alignment-specified O2 chemisorption on vicinal Si(100)

Abstract

A fully alignment-resolved O2 sticking experiment on a single domain Si(100)-(2×1) surface is presented. This provides the first experimental evidence that the reactivity of O2 depends on both the polar and azimuthal angles of the molecular axis relative to a surface. It has been found that, in case of side-on collision, an O2 molecule perpendicular to the dimer on Si(100) is about 40% more reactive than that parallel to the dimer. Comparison of the O2 sticking on flat and vicinal Si(100) surfaces indicates that barrierless dissociation channels exist at the double layer step.

Supersonic Molecular Beam Experiments on Surface Chemical Reactions

“…They measured the O2 sticking probability on a Si(100)-(2 × 1) surface while modulating the O2 geometries, and observed clear differences among them. [76] The helicopter geometry results in the highest sticking probability, showing the preference for the side-on collision. The difference in the two cartwheel geometries indicates that O2 is more reactive when its axis is perpendicular to the Si dimer.…”

“…The difference in the two cartwheel geometries indicates that O2 is more reactive when its axis is perpendicular to the Si dimer. [76] They also applied the alignment-resolved sticking experiment to the analysis of O2 adsorption on Al (111). [77] The dynamics of O2 adsorption on Al(111) remained unclear despite many years of research.…”

“…Alignment is defined as the second moment and accounts for the importance of the difference between the long‐side (either the head or tail) and broad‐side approaches of the molecule. The alignment effects in surface chemical reactions were extensively studied by Rocca's group[73] and by Kurahashi and Yamauchi [74–77]…”

“…Kurahashi et al., combining a supersonic O 2 beam with a magnetic hexapolar field, have developed a single spin‐rotational state selected O 2 beam, for which both the molecular alignment and the spin direction relative to the magnetic field ( H ) are well defined [74–77]. Since the O 2 axis is mainly perpendicular to the H direction, the three different geometries depicted in Figure can be realized by controlling the H direction at the sample.…”

“…Since the O 2 axis is mainly perpendicular to the H direction, the three different geometries depicted in Figure can be realized by controlling the H direction at the sample. They measured the O 2 sticking probability on a Si(100)‐(2 × 1) surface while modulating the O 2 geometries, and observed clear differences among them [76]. The helicopter geometry results in the highest sticking probability, showing the preference for the side‐on collision.…”