Growth mode and electronic structure of copper films on aluminium substrates

Abstract

The growth mode, geometric and electronic structure of thin copper films deposited onto aluminium single crystal substrates have been studied by LEED, AES, angle-resolved UPS and work function changes. Growth occurs in a quasi-layer-by-layer fashion on Al(111). Temperature dependent interdiffusion leads to formation of a mixed Cu/Al interface upon which ordered epitaxial films eventually grow. The ordered structure is rotationally commensurate with the Al(111) substrate with an interatomic distance typical of bulk Cu. Electronic structure of films grown at 300 K converges to that of a bulk Cu single crystal, convergence being essentially complete at a coverage of 10 monolayers. In contrast, growth occurs in a long-range disordered fashion up to relatively high coverages on Al(100) probably in the form of densely packed Cu clusters above a mixed Cu/Al interfacial region. For submonolayer coverages the work function remains close to the clean Al values, increasing to 4.7 and 4.5 eV for (111) and (100) faces, respectively, in the range from 1 to 4 monolayers. Additional studies carried out at elevated (375 K) and low temperature (120 K) allow postulation of a fully coherent model of the complex growth and electronic properties of this particular metal-on-metal system.