Copper phthalocyanine on hydrogenated and bare diamond (001)-2 x 1: influence of interfacial interactions on molecular orientations.

The molecular orientations of copper phthalocyanine (CuPc) organic semiconductor molecules on hydrogenated and bare diamond (001)-2 x 1 surfaces are studied using synchrotron-based photoemission spectroscopy (PES) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Angular-dependent NEXAFS reveals that the CuPc molecular assemblies are orientationally ordered and lying down on hydrogenated diamond, whereas they undergo a molecular reorientation on bare diamond from lying down at submonolayer coverage to standing up in multilayers. The molecular film on bare diamond also exhibits an order-disorder-order transition in the molecular orientations. The distinct molecular orientation within the CuPc films on both diamond (001) surfaces is explained in terms of the interplay between intermolecular interactions and molecule-substrate interactions.