Observation of a temperature-dependent transition of a copper-phthalocyanine thin film adsorbed on HOPG

We have studied the temperature-dependent electronic states of a copper-phthalocyanine (CuPc) monolayer film adsorbed on a graphite substrate by using metastable-atom electron spectroscopy and ultraviolet photoelectron spectroscopy. The CuPc molecules, which are flat-lying at room temperature, become tilted and condensed at temperatures below 130 K. Taking the temperature-dependent transition reported in the literature into account, we conclude that the transition observed in the present study originates from the change in the correlation between the molecule–substrate and the intermolecular interactions.