Preparation and Characterization of Cuprous Oxide Thin Films using Low-Temperature Scanning Tunneling Microscopy

Hanna Fedderwitz, PhD, University of Oldenburg, Germany

Cu₂O thin films of up to 5nm thickness were prepared by evaporating copper in an oxygen atmosphere of 10-6 mbar. Gold and Molybdenum were used as chemically inert and reactive substrates respectively. The samples were analysed in a Scanning Tunneling Microscope (STM) showing the structure of the Cu₂O surface at an atomic level. Scanning Tunneling Spectroscopy (STS) has been used to explore the electronic structure. Additionally X-ray Photoelectron Spectroscopy (XPS) was used to determine the chemical composition of the films. On Au(111) flat and homogeneous Cu₂O films with a variety of surface structures have been obtained. The electronic and stoichiometric results have been compared to calculations from Density Functional Theory (DFT). The most common surface structure (called the hexagonal phase) resembles the bulk Cu₂O(111) termination. The preparation on a Mo(001) substrate yielded well ordered Cu nano-particles. In this case the decrease in surface energy from Mo(001) to MoOx was found to be responsible for Cu particle growth according to the Wulff-Theorem.