Infrared Spectroscopy

Abstract

Infrared spectroscopy is one of the most popular spectroscopic techniques in solid-state physics. The simple reason for this is that nearly all materials exhibit a more or less expressed structure of the absorption in the IR spectral range. The origin of these structures has already been discussed to some extent in Chap. 7. Absorption processes due to transitions across the energy gap, from excitons or from impurity states, are found in the visible spectral range as well as in the IR. Important additional sources for absorption and reflection are the IR active phonons or vibrational modes which can give valuable supplementary information to results from Raman scattering. In Chaps. 8 and 9 we have already discussed under which conditions vibrational modes are observable in an IR spectrum and in Sect. 6.3 we have even given a mathematical description of the response function in the form of the Kramers—Heisenberg dielectric function. In the preset chapter particular attention will be paid to special instrumentation not discussed previously, to advanced problems and to several examples from solid-state physics. The first two sections elucidate the characteristic difference between radiation sources, optical components, spectrometers, and detectors for the visible and the IR spectral ranges. To do this it is useful to divide the spectral range into three sections:

• near infrared (NIR) 0.8–10 µm,

• middle infrared (MIR) 10–40 µm,

• far infrared (FIR) 40–1000 µm,