SIMPLE ANALYSIS OF SPOT SPLITTING DUE TO DIFFRACTION AT SURFACES WITHATOMIC STEPS

Probing surface morphology by diffraction techniques is well establish ed, especially for atomic steps on bare surfaces or on adlayer covered surfaces. The diffuse scattering contains information about the terra ce size distribution. The sharpness of this distribution determines th e shape of the spot profiles. While one observes a single broad should er for broad distributions, the shoulder splits into satellites for sh arp distributions. For sharp distributions the average terrace size de termines mainly the satellite position while the half-width of the sat ellites is governed by the standard deviation of the distribution. For broad distributions the situation is vice versa. Generally the should er can be fitted very well by two satellites with Lorentzian shape so that one can easily obtain the two prominent parameters of the terrace size distribution (average terrace size and standard deviation) from the splitting of the shoulder and the half-widths of the satellites. A dditionally, this model is extended to two-dimensional surfaces with s tep trains. For a single step train with fluctuating steps the diffrac tion pattern shows a weak diffuse shoulder besides the strong satellit es due to the average step-step distance. This effect is also predicte d for crossing step trains which mimic mounds on the surface. Therefor e equivalent to the one-dimensional case, the average terrace size and the local slope of the surface can be analysed from the satellite pos ition and their half-width. (C) 1997 Elsevier Science B.V.