Three-dimensional view of the thermal desorption reaction: copper on rhenium(0001)

The application of the Polanyi-Wigner equation to describe the rate R-des o f a thermal desorption process from a homogeneous surface is common practic e in surface science temperature-programmed desorption (TPD) studies. Curre nt evaluation methods (known as line-shape analyses) deduce from series of thermal desorption traces [coverage (Theta)-dependent] energetic and kineti c parameters such as desorption energy, desorption order or frequency facto r. The TPD spectra themselves, i.e., the function R-des(T), as well as the output of such an analysis (e.g., the remaining coverage Theta (res) as a f unction of T for a given initial coverage), represent parametrized two-dime nsional (2D) graphs. It will be shown in this work by means of selected exa mples [taken from noble metal desorption from a Re(0001) surface] that the 2D graphs are nothing but projections of R-des on to either a rate-temperat ure or a rate-coverage plane. By using the three-dimensional (3D) represent ation of R-des in T, Theta space, valuable information on phase transitions occurring during the desorption process, on multiple TPD states and interl ayer interactions can easily be visualized and exploited. (C) 2000 Elsevier Science B.V. All rights reserved.