Characterization of cobalt-diamond (100) interfaces: Electron affinity and Schottky barrier

UV photoemission measurements were used to relate the electron affinity and Schottky barrier of thin Co layers on diamond (100) surfaces. Cobalt films of 2 Angstrom thickness were deposited on natural single crystal diamond (100) substrates by hot filament evaporation in ultra-high vacuum (UHV). The surfaces were characterized with auger electron spectroscopy and atomic force microscopy. The study explores the properties of the cobalt-diamond interface as a function of different surface cleaning procedures. Prior to deposition the diamond samples have been cleaned by UHV anneals at either 500 degrees C or 1150 degrees C. Following either of these anneals a positive electron affinity was deduced from the ultraviolet photoemission measurements. The measurements indicate that the surface annealed at 500 degrees C is terminated with oxygen while the surface annealed at high temperature is free of adsorbates. Upon deposition of Co on the surface heated to 1150 degrees C, a negative electron affinity (NEA) was detected, and a Schottky barrier height of 0.35 eV was measured. However, for Co films deposited on substrates annealed to 500 degrees C a positive electron affinity and a Schottky barrier height of 1.45 eV were observed. The results are discussed in terms of a model that relates the electron affinity to the metal workfunction and the Schottky barrier.