STM and STS investigation of ultrathin tin phthalocyanine layers adsorbed on HOPG(0 0 0 1) and Au(1 1 1)

The initial adsorption of tin phthalocyanine (SnPc) on graphite and gold surfaces was studied by low-temperature UHV-STM. At submonolayer coverages on highly oriented pyrolytic graphite (HOPG), SnPc forms substrate-defined molecular chains, while SnPc monolayers reveal dense packed structures with the molecules symmetry. A comparitive study with CuPc on HOPG reveals similar chains in the submonolayer regime. No chains were found upon SnPc adsorption onto Au(1 1 1). At ordered SnPc/HOPG films with thickness around one monolayer, local I(V) curves were collected with high reproducibility. Their wide energy gap shows the semiconductive properties of the SnPc monolayers. A strongly increased differential conductivity was observed at distinct energy values.