Paper Title
Phase Transition and Electronic Properties at the COPC-Au(110) Interface

Abstract
The structural and electronic properties at the CoPc-Au(110) interface have been studied with the scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy (UPS). At low coverage and room temperature, CoPc molecules tend to adsorb in a random fashion. At the monolayer (ML) coverage and elevated temperature (~540K), long range patterns of square and hexagonal packing is observed. The brightest center spot, characteristic shape, internal structure, and orientation of each CoPc molecule is attributed to the Co ion and the benzene rings in the CoPc molecule with a flat lying geometry. Beyond ML coverage, the formation of molecular clusters is noticed. Our ultraviolet-PES results reveal organic emission features from 1 to 12 eV below the Fermi level. These features started to emerge at the early coverage, i.e. 1ML and continue to grow till the terminal coverage of 10 ML. However, the features shift in binding energy with increasing the thickness of the organic films indicating a strong molecule-substrate interaction. Our angle integrated-UPS measurements suggest that the molecular plane is nearly parallel to the substrate in the case of ML. Our calculated work functions for the clean Au(110) and thick molecular layer are 4.35 eV and 4.27 eV, respectively. The estimated ionization potential is circa 6.47eV. With incident angle-dependent photoelectrons collected at various emission angles (0-600), a quite intense modification of the electronic structures of CoPc molecules at the interface with Au (110) with respect to the bulk phase has also been observed; which probably is due to the local charge transfer from the Au(110) substrate to the molecule. Keywords - Electronic Structure, Electronic Properties, CoPc, UPS, STM