AVS 53rd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS-ThP

Paper AS-ThP20
Ordered Au(111) Surfaces Grown on Si(111)

Thursday, November 16, 2006, 5:30 pm, Room 3rd Floor Lobby

Session: Aspects of Applied Surface Science Poster Session
Presenter: K. Pedersen, Aalborg University, Denmark
Authors: K. Pedersen, Aalborg University, Denmark
A. Silva, Aalborg University, Denmark
P. Morgen, University of Southern Denmark
Z.S. Li, University of Aarhus, Denmark
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Gold surfaces are the primary choice as substrate in studies of organic structures on surfaces since they are stable in various biochemical environments and allow attachment of biomolecules through thiol groups. Typically, surfaces of bulk Au crystals or thin films on Mica are used. However, formation of well-ordered thin Au films on Si would be a step in the direction of direct integration of biosensors on wafers containing Si electronics. Deposition of Au directly on Si leads to formation of a disordered surface layer containing a mixture of Si and Au that floats on top of the Au layer even for relatively thick Au films. In the present work the properties of thin Au films grown on top of a thin (7 layers) Cu film as a buffer between the Si substrate and the Au overlayer are described on the basis of photoemission spectroscopy and AFM. Previous investigations have shown that the Cu buffer layer improves the growth of Ag and Al relative to direct growth on clean Si(111)7x7. For both Ag and Al the Cu buffer layer leads to improved sharpness of quantum well (QW) peaks and surface states. The present experiments demonstrate that also in the case of Au deposition a thin Cu layer improves the film properties. A sharp Au(111) LEED pattern is observed even for films that are only a few layers thick. The Shockley surface state characteristic of Au(111) surfaces appears at a binding energy of 0.5 eV. Furthermore, structures appear that disperses toward the sp-band edge 1.1 eV below the Fermi level as the film thickness grows. This is characteristic of QW levels. The energy window for observing QW effects is narrow in Au compared to for instance Ag and Al where the sp bands extend over ~4 eV. In Au the window from the sp- band edge to the onset of the d-bands is less than 1 eV. The appearance of QW levels indicates flat domains on the atomic monolayer level. This is supported by AFM and STM investigations performed ex situ on the samples investigated by photoemission.