A SIMPLE MOLECULAR-BEAM SYSTEM FOR SURFACE REACTIVITY STUDIES

A simple design for a thermal molecular beam system is described, which can be added as a bolton to a conventional vacuum system. It provides a beam of well-defined spatial distribution, which can be heated or cooled, and used for a variety of applications. These include the accurate and rapid determination of sticking probabilities and their coverage dependence, the gas temperature dependence of sticking, and reactive scattering measurements. The use of the beam is exemplified for the dissociative sticking of oxygen on Cu(110) and the reaction of a beam of methanol with a predeposited patch of oxygen. The initial 02sticking probability is determined to be 0.21 (+ 0.01) independent of substrate temperature (300–600 K). Methanol is dehydrogenated by preadsorbed O atoms, but by different mechanisms at high and low substrate temperatures. © 1990, American Vacuum Society. All rights reserved.