Layer Growth, Thermal Stability, and Desorption Behavior of Hexaaza-triphenylene-hexacarbonitrile on Ag(111)

The layer growth, thermal stability, and desorption kinetics of ultrahigh vacuum (UHV)-grown organic discoid molecules (hexaaza-triphenylene-hexacarbonitrile (HATCN)) on Ag(111) have been studied by atomic force microscopy (AFM), thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED). X-ray drift action (XRD), and X-ray photoelectron spectroscopy (XPS) In the initial growth stage (<= 0 24 tun mean film thickness) a strongly bonded monolayer of face-on oriented molecules is formed which does not desorb upon heating to 900 K, probably due to the formation of paracyanogen With increasing film thickness the monolayer of face-on oriented molecules transforms at room temperature into a monolayer built up of edge-on oriented molecules, which saturates at a mean film thickness of around 0 8 nm This layer partially decomposes during heating. and C2N2 fragments desorb between 650 and 900 K On the monolayer of standing molecules a second, metastable, layer forms, which saturates at I 36 nm. With further increase of the coverage, this metastable layer dewets abruptly upon heating at about 350 K, and all molecules, besides those in the first monolayer, get incorporated into the island-like bulk phase. The formed three-dimensional (31)) islands, which are thermally stable up to 400 K. possess bulk crystal structure, as verified by XRD measurements, but the crystallites are randomly oriented