Calculation of Diffracted Laser Beam Intensities from Non-Sinusoidal Periodic Surface Profiles Extending in the [001]-Direction on Pt(110)

Abstract

Laser beam diffraction is a very sensitive and useful method in measuring amplitudes and shapes of periodic surface profiles in the μm-region. The measurements of diffracted laser beam intensities can be performed in situ even if the specimen is in UHV and at high temperature. For sinusoidal profiles these diffracted laser beam intensities have been calculated and tabulated for the fixed laser beam wavelength λ = 0.6328 μm and for profiles with a periodicity length d = 4–7 μm and amplitudes A < 0.4 μm. These were used in surface self-diffusion measurements on Pt(110) in the [001] surface direction and at several other crystals [1,2]. The diffusion coefficient was obtained from the slope of the linear part of the amplitude decay curve plotted logarithmically. The surface diffusion theory implies sinusoidal surface profiles and the linear decay of the amplitudes. However in the region of large profile amplitudes, the decay was curved. In this range of large amplitudes non-sinusoidal surface profiles having (111) facets were assumed. Computer simulatiohs, which use surface diffusion theory, showed the same curved and linear amplitude decay as in experiment. This implies special assumptions for the angular dependence of the surface free energy γ [3, 4]. However, the measured diffracted laser beam intensities were not yet compared with calculated ones from these non-sinusoidal surfaces. That is the purpose of this paper.