Raman thin films

Physical Properties. Raman spectroscopy is an excellent tool for investigating stress and strain in many different materials (see Materlals reliability). Lattice strain distribution measurements in siUcon are a classic case. More recent examples of this include the characterization of thin films (56), and measurements of stress and relaxation in silicon—germanium layers (57). 

Stress in crystalline solids produces small shifts, typically a few wavenumbers, in the Raman lines that sometimes are accompanied by a small amount of line broadening. Measurement of a series of Raman spectra in high-pressure equipment under static or uniaxial pressure allows the line shifts to be calibrated in terms of stress level. This information can be used to characterize built-in stress in thin films, along grain boundaries, and in thermally stressed materials. Microfocus spectra can be obtained from crack tips in ceramic material and by a careful spatial mapping along and across the crack estimates can be obtained of the stress fields around the crack. ... 

Levels of carotenoids are much lower in the skin relative to the macula of the human eye, but higher light excitation intensities and longer acquisition times can be used in Raman detection approaches to compensate for this drawback. Since the bulk of the skin carotenoids are in the superficial layers of the dermis, and since the concentrations are relatively low, the thin-film Raman equation given above, Equation 6.1, should still be a good approximation. 

Finally, as in macro-Raman experiments, orientation-insensitive spectra can also be calculated for spectromicroscopy. A method has been developed recently for uniaxially oriented systems and successfully tested on high-density PE rods stretched to a draw ratio of 13 and on Bombyx mori cocoon silk fibers [65]. This method has been theoretically expanded to biaxial samples using the K2 Raman invariant and has proved to be useful to determine the molecular conformation in various polymer thin films [58]. 

Kitahara, K. Yamazaki, R. Kurosawa, T. Nakajima, K. Moritani, A. 2002. Analysis of stress in laser-crystallized polysilicon thin films by Raman scattering spectroscopy. Jpn. J. Appl. Phys. 41 5055-5059. 

Nanu, M. Schoonman, J. Goossens, A. 2004. Raman and PL study of defectordering in CuInS2 thin films. Thin Solid Films 451—452 193-197. 

Raman samples were prepared by peeling SiNW thin films off the silicon wafers to avoid Raman signals from the silicon substrate. A razor blade was used to shave the thin films on top of the silicon wafers. The thin films were mounted on a carbon tape for SEM and Raman inspection, or on a transparent Mylar film for Raman measurements. 

FIGURE 10.13a. Raman measurements of the SiNW thin film on the Mylar thin film. A peak at 700 nm was found. The intensity was nearly twice the regular Raman intensity at 520 cm for silicon The Inset shows the weak peak at 520 cm . ... 

EDX-SEM results measured on a thin-film sample on a carbon tape showed that the nanowires contained Si and O (Fig. 10.15). The ratio of Si to O was approximately 1.5-2 1, suggesting that the nanowires were made of Si02 with O vacancies. This also agreed with the results from the PL and Raman experiments. No carbon signal from the carbon tape was observed because the film was too thick for the e-beam to penetrate. 

J. Palm, S. lost, R. Hock and V. Probst, Raman spectroscopy for quality control and process optimization of chalcopyrite thin films and devices. Thin Solid Films, 515, 5913-5916 (2007). 

Thin film electrodes have made feasible thermal jump kinetic measurements of extremely fast electrode reactions [26], by illuminating a thin electrode film by a very rapid laser pulse and monitoring the relaxation process on a nanosecond time scale. Thin films of silver have also been deposited on electrode materials such as carbon to enable surface-enhanced Raman spectroscopic investigation of surface-bound species [27]. 

Analysis of Surfaces and Thin Films by IR, Raman, and Optical Spectroscopy... 

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