Work function changes in the (111)Pd/(111)Cu and CO / (111)Pd / (111)Cu systems

• Published in: Applied surface science 1988-09, Vol.33, p.220-237
• Main Authors: Vook, R.W., Swirbel, T.J., Chao, S.S.
• Format: Article
• Language: English
• Subjects: Analysing. Testing. Standards; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Measurement of properties and materials state; Metals, semimetals and alloys; Metals. Metallurgy; Nondestructive testing; Physics; Specific materials; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/0169-4332(88)90310-8

Work function changes in the initial stages of growth of bilayer films in the epitaxial (111)Pd/(111)Cu/mica system were measured along with changes that occurred on annealing. The films were characterized using the Kelvin probe work function (WF) method, reflection high energy electron diffraction (RHEED), Auger electron spectroscopy (AES) sputter depth profiles, angle resolved X-ray photoelectron spectroscopy (ARXPS), transmission electron microscopy (TEM) and via CO adsorption. The results show that as Pd was deposited on the (111)Cu film, the WF decreased approximately 250 meV in the range 0 to 0.5 monolayer (ML) Pd. Between 0.5 and approximately 3.5 ML, the WF increased more or less linearly before leveling off at the value for bulk Pd. Room temperature CO exposures showed no change in adsorption until more than a quarter ML of Pd had been deposited, as indicated by a negligible WF change. The CO saturation WF change then increased almost 800 meV as approximately 4.5 ML Pd were deposited before decreasing and leveling off at a net increase of around 605 meV for a thick Pd overgrowth. Annealing the bilayers at various temperatures up to 315°C decreased the work function. AES depth profiles together with ARXPS indicated Pd-Cu interdiffusion had taken place. A review of previous results by others on similar systems is presented and compared with those obtained in the present work. This work provides important new information on how the electronic and chemical properties of epitaxial (111)Cu films can be modified by the deposition of thin (111)Pd overlayers.