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A method for determining both the thickness and the average stoichiometry of thin films is presented. The method is based on implanting radioactive -sources in the substrate prior to layer growth and measuring the energy loss of the -particles as they traverse the layer. Information about the stoichiometry is obtained through the comparison of the energy loss of -particles of different initial energies. Experimental examples for the utilization of this method are presented, in which Sb was grown on Si substrates, GaAs, InAs and AlAs on GaAs and YBCO on YSZ. The experimental precision which can be expected using the method is discussed, together with specific scenarios in which it could be advantageously applied.

The (a, b)-plane infrared and visible conductivity (30-30000 cm −1 ) of a 40% praseodymium-substituting yttrium YBa2Cu3O7 film displays a loss of spectral weight over two separate energy ranges when lowering the temperature. A first loss of spectral weight is present in the range 300-800 cm −1 from room temperature down to 40 K (Tc = 35 K). A further distinct spectral weight diminution appears in the superconducting phase at frequencies below 200 cm −1 . This diminution can be observed due to the high signal-to-noise ratio allowed by the large area of the thin film. We propose that the lower energy loss of spectral weight reflects the formation and the properties of the superconducting condensate.