New Oriented-Molecular-Beam Machine for Surface Stereochemistry with X-ray Photoemission Spectroscopy

Abstract

The stereochemical control of surface reactions is one of the ultimate goals of surface scientists. An oriented-molecular-beam technique based on the Stark effect of a molecule in an inhomogeneous hexapole electrostatic field is a potential tool for achieving this goal. This technique allows us to select a specific rotational quantum state and also an orientation of a reagent molecule. We have designed, built, and tuned a new UHV-compatible oriented-molecular-beam machine for the elucidation of surface chemical reactions and their related surface modifications. This apparatus is equipped with the components for Xray photoemission spectroscopy (XPS) in order to detect the surface-reaction products. In the dissociative adsorption of NO on a Si{111} surface, we found a steric effect in the reactivity by monitoring the products on the surface with the new machine. The N-end collision is more reactive than the O-end collision at an incident energy of 58 meV. To our knowledge, this is the first measurement of the steric effect appearing in the reaction products on a surface.

Supersonic Molecular Beam Experiments on Surface Chemical Reactions

“…Thus, we perform the direct observation of the surface products created by the oriented NO beam. [91,102,103] Figure 14 shows the orientation dependence of the O-1s and N-1s XPS spectra, measured at ΘTotal ≈ 0.28 ML for the 58 meV oriented NO |0.5 0.5 0.5〉 beam at Ts = 400 K. It is clear that an N-end collision is more reactive than an O-end collision. Figure 15 shows the total coverage ΘTotal dependence of the stereo-asymmetric factor R. Here, we define R as follows where Si(t), with i = N or O, is the reactive sticking probability for the N-or O-end collision, respectively.…”

“…Therefore, we can expect that the molecular‐orientation dependence found in the scattered NO need not be reversed in the surface products. Thus, we perform the direct observation of the surface products created by the oriented NO beam [91,102,103]…”

Surface chemical reactions induced by well-controlled molecular beams: translational energy and molecular orientation control

“…The quantitative degree of orientation has also been studied [126,127]. The principles of focusing and orientation by the electrostatic hexapole and a uniform field in front of the crystal surface were reported for CH 3 Cl [128] and NO [77,129]. At Osaka University, we performed the evaluation of the sticking probability using the King-Wells method [128,130], and also surface-scattering experiments for the oriented molecular beam incidences [109,110].…”

“…At Osaka University, we performed the evaluation of the sticking probability using the King-Wells method [128,130], and also surface-scattering experiments for the oriented molecular beam incidences [109,110]. At SPring-8, we measured steric effects appearing on the surface products using XPS for the oriented molecular beam incidences [129].…”

Stereodynamics in Surface Chemical Reactions with Oriented Molecular Beams

“…1 大阪大学科学教育機器リノベーションセンター(〒567 0047 大阪府茨木市美穂ヶ丘 8 1) Orientation distribution function (full line) for NO 13) . Dotted circle at the center corresponds to random orientation.…”