Atomic-scale variations in contact potential difference on Au/Si(111) 7 X 7 surface in ultrahigh vacuum

The results of contact potential difference (CPD) imaging on Au-deposited p-type and n-type Si(lll) 7 X 7 surfaces are discussed. The scanning Kelvin probe microscopy (SKPM) technique based on the gradient of the electrostatic force was used under ultrahigh vacuum (UHV) conditions to acquire the data presented. The CPD images of Au deposited on the Si(lll) 7 X 7 surface show virtually identical features, irrespective of whether the Si is n- or p-type. In these images, it is believed that the atomically resolved potential difference does not originate from the intrinsic work function of the materials but reflects the local electron density on the surface. On the other hand, the average potentials corresponding to the DC levels in each CPD image reflects the work function value on the surface. The work function of p-type Si(lll) 7 X 7 is found to be higher than that of n-type by about 0.45 eV, where both samples had the same resistivity of about 0.5 Omega cm and the same Au coverage. If the Au coverage is increased, the work function increases. (C) 2000 Elsevier Science B.V. All rights reserved.