Molecular Ordering and Dipole Alignment of Vanadyl Phthalocyanine Monolayer on Metals: The Effects of Interfacial Interactions

Abstract

We present an <i>in situ</i> low-temperature scanning tunneling microscopy (LT-STM) study to elucidate the effects of interfacial interactions on the molecular ordering and dipole alignment of dipolar vanadyl phthalocyanine (VOPc) monolayer on metal surfaces, including Cu(111), Ag(111), Au(111), and graphite. The adsorption of VOPc on the relatively inert graphite surface leads to the formation of well-ordered molecular dipole monolayer with unidirectionally aligned O-up configuration. In contrast, VOPc on Cu(111), Ag(111), and Au(111) adopts both O-up and O-down configurations. The VOPc strongly chemisorbs on Cu(111), leading to the formation of one-dimensional molecular chains, and two-dimensional molecular islands comprising pure O-down adsorbed VOPc molecules at low and high coverage, respectively. In contrast, VOPc physisorbs on Au(111) and results in an orientation transition from flat-lying to inclined molecular islands. Regarding the interfacial interaction strength, the Ag(111) represents an intermediate case (weak chemisorption), which enables the formation of disordered phase and ordered islands, as well as the orientation transition within the disordered phase