Roughening and smoothing behavior of single crystal Si by low energy Ar + ion bombardment

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We examined the dependence of smoothing or roughening behavior on the initial surface roughness of single crystal Si. An atomically flat cleaved Si surface of roughness 0.038 nm rms and a Si wafer substrate roughness of 0.12 nm rms were sputtered by 0.2–3 keV Ar + ion beam at normal ion incidence. Surface morphology was observed by atomic force microscope (AFM) under DFM mode. Result shows that the rough surface ( R = 0.12 nm rms) becomes smooth ( R = 0.068 nm rms) and the smooth surface ( R = 0.038 nm rms) becomes rough ( R = 0.068 nm rms) due to low energy Ar + ion beam sputtering process and both finally saturates at 0.068 nm rms. The saturated roughness R sat depends on ion beam energy and increases with increasing beam energy. To understand the roughening mechanism, we studied the dynamic scaling theory and measured the roughness exponent α and growth exponent β. The values of α = 1.03 and β = 0.28 are in agreement with the Cuerno’s one dimensional simulation of the Linear diffusion equation with noise, that corresponds to the initial stage of dynamic scaling of ion bombardment.