Surface diffusion of Sb on Ge(111) monitored quantitatively with optical second harmonic microscopy

K. A. Schultz, E. G. Seebauer

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Surface diffusion of Sb on Ge(111) has been measured with the newly developed technique of optical second harmonic microscopy. In this method, concentration profiles at submonolayer coverage are imaged directly by surface second harmonic generation with 5 μ spatial resolution. A Boltzmann-Matano analysis yields the coverage dependence of the diffusivity D without parametrization. Experiments were performed at roughly 70% of the bulk melting temperature Tm. In the coverage range 0<θ<0.6, the activation energy Ediff remains constant at 47.5±1.5 kcal/mol, but the pre-exponential factor D0 decreases from 8.7×10 3±0.4 to 1.6×102±0.4 cm2/s. Both Ediff and D0 are quite large, which is consistent with high-temperature measurements in other systems. The inadequacies of current theories for high-temperature surface diffusion are outlined, and a new vacancy model is proposed for low-coverage diffusion. The model accounts semiquantitatively for the large values of Ediff and D0, and suggests that these quantities may be manipulated using doping levels and photon illumination. An islanding mechanism is proposed to explain the decrease in D0 with θ.

Original languageEnglish (US)
Pages (from-to)6958-6967
Number of pages10
JournalThe Journal of Chemical Physics
Issue number9
StatePublished - 1992

ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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