SR-FTIR Microscopy and FTIR Imaging in the Earth Sciences

Abstract

Infrared spectroscopy was developed at the beginning of the 20th century for analytical chemical purposes and it is remarkable that the first contribution of the first issue of Physical Review, one of the first and among the most important physical magazines, published in 1883, was devoted to “a study of the transmission spectra of certain substances in the infrared” that included also a plate of a quartz rock crystal (Nichols 1883). In 1905, William W. Coblentz released the very first database of IR spectra where the characteristic wavelength at which various materials absorbed the IR radiation were listed. For more than a century IR spectroscopy has been considered as a powerful analytical tool for phase identification and to characterize the structural features and quantify molecules or molecular arrangements in solids, and also in liquids and gases. This technique has been used extensively by organic chemists, and since the 1950s it has been recognized as a fundamental technique in mineralogical and Earth sciences in conjunction with X-ray diffraction (Keller and Pickett 1949, 1950; Launer 1952; Adler and Kerr 1965). The first “encyclopedia” of IR spectra of minerals appeared in 1974 (Farmer 1974) and is still a primary reference for those using infrared spectroscopy as a tool in material science. In the late ‘60s and beginning of ‘70s a new IR technique, Fourier-transform infrared (FTIR) spectroscopy, was developed and later a new class of spectrometers was commercially available, based upon the combination of a FFT (Fast-Fourier-Transform) algorithm and computers. The advantage of these instruments over the previously used wavelength-dispersive spectrometers is fully described in several books, e.g., Griffiths and de Haseth (1986) and Smith (1996). Briefly, in FTIR spectrometers IR light is focused through an interferometer and then through the sample. A moving mirror inside the apparatus …