Thermal desorption of PTCDA on Cu(111)

Organic molecules often show very complex thermal desorption spectra. If there is an ordered structure the activation energy for desorption Edes will decrease for the first few layers because of the decreasing van der Waals interaction of the layers to the substrate. This is especially true for the system 3,4,9,10 perylene-tetracarboxylic-dianhydride on Cu(111). The spectra consist of three different signals which can be attributed to the second layer, the multilayer and a crystal phase. The numerical algorithm sketched in this paper gives a desorption energy of 2.35eV for the second layer and 2.2eV for the multilayer.