Screening waves from steps and defects on Cu(111) and Au(111) imaged with STM: Contribution from bulk electrons

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Abstract
By studying two-dimensional (2D) Fourier transforms of scanning tunneling microscopy (FT-STM) images, we obtain information about the role of surface states versus bulk states in the screening of defects and step edges at the close-packed Cu and Au surfaces. The STM images, obtained at low temperature and low bias voltage, exhibit wave interference patterns originating from the energy-resolved Friedel oscillations of surface- state electrons created by the screening of surface defects. The FT-STM pictures directly yield images of the 2D surface Fermi contour. Here we present results for Cu(111) and Au(111) surfaces, which reveal the existence of an additional contour in the FT-STM power spectrum. This contour is related to the “neck” of the bulk Fermi surface as accounted for by a simple model. The results give information about the role that both bulk and surface-state electrons play in the screening of defects at or near the surface. We find that the surface-state electrons dominate the screening of step edges on Au(111).

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