The use of Fourier transform infrared spectroscopy for alpha determination of quartz

The use of a Fourier Transform Infrared (FTIR) spectrometer, for the determination of the infrared extinction coefficient (alpha) in quartz has been examined. Alpha is used as a quality factor in quartz. Sawyer has developed the alphagraph as our standard method of infrared measurement. The alphagraph is a measurement of alpha as a function of the position along the major growth direction (Z) of the crystal. The FTIR essentially looks at the entire spectrum (about 400 cm^-1 to 4000 cm^-1) in one pass. Since the measurement is not instantaneous, the sample cannot be moved during the measurement. An alphagraph is made by measuring the entire spectrum at a point, moving the sample a small amount, and repeating. The wavenumbers of interest are then plotted versus position. A custom sample handling and data collection system has been developed to perform these alphagraphs. The optimal settings, including aperture size and step size, have been determined. Results have been compared at the three wavenumbers most typically used in alpha determination. The spectrometer has been calibrated versus the standards from the International Round Robin in Infrared Alpha Measurements. The spectrometer shows good agreement with the standards and good reproducibility over long periods of time