Heteroepitaxial metallo-phthalocyanine (MPc, M = cobalt, nickel, copper) thin films on gold: Atomic and interfacial electronic structures

Organic semiconductors have become a hot topic for research within the past few years. This work describes research into a family of organic semiconductors known as metallo-phthalocyanine (MPc) in which the electronic and optical properties can be easily tuned by the systematic modification of the metal cations and ligands. More specifically, thin films of CoPc, NiPc, and CuPc have been evaporated onto a "5 x 20" reconstructed Au(001) substrate and have been investigated by employing low energy electron diffraction and ultraviolet photoelectron spectroscopy. Low energy electron diffraction reveals that thin films of CuPc and NiPc are highly ordered with a square unit cell aligned along the substrate <110> and <11¯0> axes. In addition, deposition of CuPc onto the Au(001) substrate when at room temperature and elevated temperatures reveal that the square unit cell is larger when the substrate is heated. On the other hand, CoPc thin films are not well ordered as evidenced by multiple rotationally equivalent square domains, which are separated by 16°. Even more interesting is that the contrast between NiPc and CoPc on Au(001) is further found in the interfacial electronic structure. Ultraviolet photoelectron spectroscopy studies of the interfacial layers of NiPc deposited on the reconstructed gold substrate indicate that NiPc physisorbs on the gold surface as verified by a uniform molecular orbital (MO) shift. However, similar studies of the interfacial layers of CoPc depict an interaction between the CoPc 13a1g MO and the Au surface suggesting a charge transfer between the two.; In addition to the research into MPc thin films, this work also describes the development of a Low Energy Electron Diffraction Intensity versus Voltage (LEED-IV) system for the Laboratory for Surface Analysis and Modification. This development involved the merging of various hardware and software systems by means of LabVIEW environment. Characterization of the system performance was carried out through the use of a MoS2 sample with known LEED-IV characteristics. The results of the system characterization revealed that the fully operational and ready to be applied to other samples.