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30 nm thick Gold films were deposited by electron beam gun onto a room temperature native oxide (SiOx) covered Si(100) wafer in a UHV evaporator (Varian VT 460) at an evaporation speed of around 10 nm/s. The surface morphology was determined by atomic force microscopy (AFM).
Angularly integrated- and resolved photoemission spectra were recoded, using conventional light sources as well as synchrotron radiation, the latter at MAX-lab beamline 41. The as deposited Au film was cleaned and thinned by Ar ion sputtering. After these treatments photoemission measurements were carried out as a function of the layer thickness. The thicknesses and surface morphologies were investigated by Atomic force microscopy and Rutherford backscattering after the photoemission measurements, and the layers were found to be in the range 5-30 nm. Reference data (photoemission and surface roughness as well) were also obtained on a 100 nm thick Au layer.
The photoemission data were correlated to calculated valence band data for polycrystalline bulk Au. At the 30 nm thick Au film the valence band data quite markedly differed from the bulk ones. A peak maximum was detected at 0,5 eV binding energy with a 0.5 eV half width. This peak increased in intensity as the thickness of the layers decreased to 7 nm.
This effect was correlated to the electron confinement, even though the thickness of the film was quite large compared to the electron wavelength of the states at the Fermi level. This peak was quite sensitive for the angle of the emission in the range 0°-10°, which is remarkable, as angular dependence is not expected for a polycrystalline sample. However, since the experimental uncertainties could be excluded, it may be related to a real effect and a possible source is the surface roughness. Naturally this explanation should still be supported with further studies.
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