Effect of surface roughness on the measurement of electron impact inner-shell ionization cross sections using thick-target method

The effect of surface roughness on the measurement of electron impact inner-shell ionization cross sections in the thick-target method has been studied by using Monte Carlo simulations. The surface roughness structures were described by a series of hemispheres, which were produced randomly on the smooth surface of a thick Ni target. The characteristic X-ray yields of K-shell ionization for Ni element by electron impact near threshold energy were obtained by Monte Carlo simulations for the target with smooth surface and the targets with various surface roughnesses. The Tikhonov regularization method was applied to treat the inverse problem involved and obtain the K-shell ionization cross sections for Ni element. The comparisons between K-shell ionization cross sections of Ni element obtained for the target with smooth surface and the targets with various surface roughnesses were made. The results show that the effect of surface roughness increases as the roughness increases and the surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%.