Ion beam analysis techniques have been used to probe for carbon contamination in high temperature superconductor thin films. These techniques provide a powerful tool to detect C with limit of detection close to 0.01 at.% and to measure carbon depth profiles on the nanometer scale with a depth resolution of 10 nm at the surface. In the present study, a series of YBa2Cu3O7-delta (YBCO) films have been formed on MgO substrates by a sol-gel method. Different film thicknesses and heat treatments were studied. Typical formation temperatures were 770-850 degreesC resulting in thicknesses from 50 to 600 nm. It was found that, depending on the sample preparation conditions, carbon was incorporated in the films at a concentration of 0.5-4.6 at.%. Carbon was homogeneously distributed throughout the films. (C) 2003 Elsevier B.V. All rights reserved.