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

The application of the Polanyi–Wigner equation to describe the rate Rdes of a thermal desorption process from a homogeneous surface is common practice in surface science temperature-programmed desorption (TPD) studies. Current evaluation methods (known as line-shape analyses) deduce from series of thermal desorption traces [coverage (Θ)-dependent] energetic and kinetic parameters such as desorption energy, desorption order or frequency factor. The TPD spectra themselves, i.e., the function Rdes(T), as well as the output of such an analysis (e.g., the remaining coverage Θres as a function of T for a given initial coverage), represent parametrized two-dimensional (2D) graphs. It will be shown in this work by means of selected examples [taken from noble metal desorption from a Re(0001) surface] that the 2D graphs are nothing but projections of Rdes on to either a rate–temperature or a rate–coverage plane. By using the three-dimensional (3D) representation of Rdes in T, Θ space, valuable information on phase transitions occurring during the desorption process, on multiple TPD states and interlayer interactions can easily be visualized and exploited.