A novel single-crystal adsorption calorimeter and additions for determining metal adsorption and adhesion energies

Abstract

A new microcalorimeter for measuring heats of adsorption on clean single-crystal surfaces is described, and its operational characteristics are presented. The principle is similar to that pioneered by David King's group: A pulse of gas from a molecular beam adsorbs on an ultrathin single crystal's surface, causing a measurable transient heat input and temperature rise. Our novel heat detector is a 9 μm thick pyroelectric polymer ribbon, which is mechanically driven to make a gentle mechanical/thermal contact to the back of the single-crystal sample during measurements. Advantages include use of thicker samples (1 μm), sample preparation at very high temperatures, and potential measurements at cryogenic temperatures. A novel chopped molecular beam of metal vapor and a method of correcting for absorbed radiation from the hot effusion cell are also described. This system is applied to study the heats of adsorption of metals on clean, well-defined and single-crystalline surfaces as a detailed function of coverage, from which metal/substrate adhesion energies can also be extracted. We obtain pulse-to-pulse standard deviations of <2% in the heat of adsorption for pulses containing <0.03 ML of Cu and Pb, and absolute accuracy to within a few percent. © 1998 American Institute of Physics.