Reactive scattering of Cs + from chemisorbed molecules on a Ni(100) surface. Secondary neutral mass spectrometry with a hyperthermal ion beam

Abstract

Reactive scattering of hyperthermal Cs + ions is studied from a Ni(100) surface chemisorbed with CO, OH, and benzene. The products of reactive scattering, CsCO +, CSOH +, and CsC 6H 6 +, reflect molecular identity of the chemisorbed species. It is demonstrated that this method can be used to monitor adsorption kinetics of the adsorbates in real-time. The reaction dynamics is investigated through measurement of reaction yields as a function of adsorbate surface coverage, Cs + beam exposure, and beam incidence angle. Cs + collision induces desorption of CO from a CO-covered surface, with a desorption cross section of 2.4(± 1.4) × 10 −15 cm 2 molecule −1 for a 30 eV beam incident at 45°. The desorbing CO molecules are combined to the scattered Cs + ions with an association probability of 1.0(± 0.6) × 10 −3. This number indicates that a hyperthermal Cs + ion provides an efficient means of cationizing a collisionally desorbed neutral molecule. From angular dependence study, it is suggested that Cs + ions scatter from a Ni(100) surface to a specular direction with a sharp angular distribution. The desorbing CO molecules have an angular distribution that is peaked more probably toward a specular direction than the surface normal.