The distribution of elements in sequentially prepared MgB2 on SiC buffered Si substrate and possible pinning mechanisms

MgB2 thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg-B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15 nm and 50 nm) of stoichiometric MgB2 final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film. X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15 nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of T-C of the film to 20 K. We register different slope of the H-C2 (T) dependence - the lowest temperature value of H-C2 for the 15 nm thick film exceeds the one for the 50 nm thick film in spite of lower T-C. We suppose that delta l pinning mechanism is dominant for the 15 nm thick film. (C) 2012 Elsevier B. V. All rights reserved.