Formation by ion mixing of almn thin films in amorphous and quasi-crystalline phases: Comparison of their electronic structure as determined by optical measurements

Abstract

Alternate layers of aluminium and manganese were deposited by sputtering on amorphous silica substrates. The ratio of aluminium to manganese layer thicknesses was adjusted in order to vary the total manganese concentration. The layers were ion beam mixed with a 500 keV Xe + beam to a fluence of 10 16 Xe cm −2. The mixing efficiency was checked using Rutherford backscattering spectrometry analysis. Amorphous or quasi-crystalline phases are obtained, depending on the substrate temperature during the mixing. The atomic structure was controlled by transmission electron microscopy. For manganese concentrations from 15% to 20%, ion beam mixing at 150 °C results in the icosahedral phase; mixing at 77 K provides samples in the amorphous state. It is emphasized that all samples in this concentration range are single phase. The optical conductivity was determined from reflectance and/or ellipsometric measurements in the energy range from 0.5 to 6 eV. All spectra are strongly dominated by the manganese d states. No drastic differences are observed between the amorphous and the icosahedral states for manganese concentrations between 15% and 20%.