Abstract
The temperature-dependent adsorption behavior of fourfold symmetric metal phthalocyanines (MPcs) on metals with commensurate and incommensurate symmetries was investigated by scanning tunneling microscopy. On the fourfold symmetric Cu(100) surface, planar and fourfold molecular structures in two equivalent orientations were found for MPcs when prepared at room temperature. In addition, two metastable orientations were identified when prepared at low temperature, which can be depopulated upon annealing. MPcs adsorbed on the sixfold symmetric Cu(111) surface showed a disturbed molecular appearance. The symmetry of molecular structures changed from fourfold to twofold, which is discussed in terms of molecule-substrate interaction. © 2008 The American Physical Society.