This paper describes a new technique to quantitatively extract the number of unoccupied d states in a material utilizing measurements of the L X-ray absorption edge spectra. A correlation between the area under each of the L2 and L3 X-ray absorption edges and d-band vacancies in platinum-containing materials which exhibit white lines is given for the first time. The technique is demonstrated with a platinum catalyst supported on silica as an example. The quantity determined is the fractional change of the d-band occupancy for the sample from that of bulk platinum.

Criteria for terminating smoothing to remove a cubic spline background from the x-ray absorption coefficient are stated in terms of three parameters obtained from the k3 weighted Fourier transform of the resulting x-ray absorption fine structure data. The three parameters are HR, the average value of the transform magnitude between 0 and 0.25 Å, HM, the maximum value in the transform magnitude between 1 and 5 Å, and HN, the average value of the transform magnitude between 9 and 10 Å. The termination criteria are HR−HN ⩾0.05HM; or if HN ≳0.1HM, then HR ⩾0.1HM. The incorporation of the criteria into a computer program to facilitate automatic background removal is discussed. Examples of application of the technique to copper, β-PtO2, and ferritin samples are presented.

The design of optoelectronic devices fabricated from III-nitride materials is aided by knowledge of the refractive index and absorption coefficient of these materials. The optical properties of GaN, AlN and AlGaN grown by MOVPE on sapphire substrates were investigated by means of transmittance and reflectance measurements. Thin (less than 0.5 μm) single crystal films were employed to insure that transmission measurements could be obtained well above the optical band gap. The influence of alloy broadening on the absorption edge was investigated by using a series of AlGaN alloy samples with a range of Al compositions. The optical absorption coefficient above the band gap was obtained for AlGaN having up to 38% Al composition. The refractive index below the band gap was determined for the same series of samples. These properties provide information critical to the optimal design of solar blind detectors or other optoelectronic devices.

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