Fourier transform spectroscopy

About: Fourier transform spectroscopy is a research topic. Over the lifetime, 5418 publications have been published within this topic receiving 134133 citations.

Degree of dissociation measured by FTIR absorption spectroscopy applied to VHF silane plasmas

Abstract: In situ Fourier transform infrared (FTIR) absorption spectroscopy has been used to determine the fractional depletion of silane in a radio-frequency (rf) glow discharge. The technique used a simple single-pass arrangement and was implemented in a large-area industrial reactor for deposition of amorphous silicon. Measurements were made on silane plasmas for a range of excitation frequencies. It was observed that, at constant plasma power, the fractional depletion increased from 35% at 13.56 MHz to 70% at 70 MHz. With a simple model based on the density continuity equations in the gas phase, it was shown that this increase is due to a higher dissociation rate and is largely responsible for the observed increase in the deposition rate with the frequency.

High pressure crystal phases of solid CH4 probed by Fourier transform infrared spectroscopy

Abstract: High pressure infrared spectra of solid CH4 are reported in the range 0.8–30 GPa at room temperature, coupling a Fourier transform infrared spectrometer to a membrane diamond–anvil cell by means of a high efficiency beam condensing optical system. Two crystal phases, A and B, have been investigated. The phase transition is affected by hysteresis and occurs at 9±0.5 GPa during compression and at 7±0.5 GPa during expansion. Due to hysteresis, the transition has been studied as a function of time at higher pressures and found to undergo a first‐order kinetics, with rate constant increasing with pressure. Since our experimental apparatus allows us to perform high pressure Raman measurements too, structural properties of both A and B phases have been proposed from the analysis of the infrared and Raman data. Within the framework of the widely used three‐site model, the A phase structure is consistent with a D4h unit cell symmetry. On the contrary, the analysis of the ω1 infrared and Raman multiplets in phase B as a function of pressure suggests quite plausibly a single site, well‐ordered crystal structure. By means of group‐theoretical arguments it is concluded that CH4 molecules occupy sites of Cs symmetry, while the unit cell symmetry must be chosen among D4h, D6h, Th and Oh groups. Qualitative considerations point to D6h as the more favored unit cell symmetry for phase B.

Subsurface Layer Studies by Attenuated Total Reflection Fourier Transform Spectroscopy

Abstract: In total reflection spectroscopy the effective sampled depth increases as the angle of incidence approaches the critical one. At each angle of incidence, successive layers within the sample are weighed differently in the overall spectrum, and the manner of this weighing changes with angle. It is thus possible in principle to deconvolute a set of spectra taken at different angles into spectra corresponding to successive depth invervals. As this angular effect is particularly marked near the critical angle, where attenuated total reflection spectra are severely distorted, the spectra usually require inversion into optical constant spectra. This has been done by a new technique that measures spectra twice at each angle with different prism materials to give the necessary data sets. Examples of such subsurface spectra are shown.