Cu_2O/MgO band alignment and Cu_2O-Au nanocomposites with enhanced optical absorption

Abstract

Single crystalline Cu2O film has been successfully synthesized on MgO(100) surface through laser molecular beam epitaxy. In situ reflection high-energy electron diffraction was employed to study the epitaxial growth of Cu2O. The composition and structure of the Cu2O were studied in detail by in situ X-ray photoelectron spectroscopy and transmission electron microscopy. Valence band structures of Cu2O/MgO heterojunction were investigated by in situ X-ray photoelectron spectroscopy and in situ ultraviolet photoemission spectroscopy. The valence band offset was found to be 0.54 eV. By alternative deposition, Cu2O-Au nanocomposites were prepared, which were characterized by in situ reflection high-energy electron diffraction, in situ X-ray photoelectron spectroscopy and transmission electron microscopy. Interestingly, below some critical content of Au, the epitaxial growth of Cu2O recovered after the deposition of Au. Due to the surface plasmon resonance of formed Au colloids, enhanced optical absorption at the wavelength from 600 nm to 800 nm was observed, which is in well agreement with the Mie theory. Depending on the pulses of Au, the position and the width of the absorption peaks can be easily changed.