Rutherford backscattering analysis of thin films and superlattices withroughness

Abstract

Knowledge on the thickness, composition, and interfaces of thinfilms and multilayers is, in many systems, fundamental for the understandingand optimization of their properties. One of the techniques often applied tosuch studies is Rutherford backscattering (RBS). However, it has been verydifficult to account for the effects of interface roughness in the dataobtained, and the alternative has been to develop dedicated data analysiscodes for particular problems where roughness plays a determinant role. Inthis work, the effect of roughness is taken into account in the data analysisby calculating the effect of roughness on the apparent energy resolution as afunction of depth. This depends on the exact type of roughness, and threedifferent models have been implemented: inhomogeneous layer thickness,corrugated sample, and rough substrate surface. Interfacial mixing inmultilayers can also be analysed with the method developed. Automatic fits tothe data can be performed in this way, where the roughness parameters arederived during the fit, providing a new tool for RBS analysis. The code isapplied to several systems in order to test its validity and applicability.Systems which are hard to analyse by RBS have been chosen: Si/VS/ Si0.65Ge0.35300 nm/ Si0.2Ge0.8 4nm/ Si0.65Ge0.35 15 nm/Si 3 nm thin films, where VSstands for a linearly composition-graded virtual substrate; and MgO/( Fe 25 Å/Co 20 Å)10 multilayers.