Spectroscopy Solutions for Materials Analysis

R aman images constructed from hyperspectral cubes recorded under well-defined confocal conditions show high-quality chemical contrast. Careful studies are required to determine the optimum measurement conditions and limiting spatial resolution of the technique. Calculations and measurements of the laser spot size for the high numerical aperture (n.a.) objectives indicate that spatial resolution of a wavelength (р 0.5 m) is achievable under good conditions. What does that mean in terms of the quality of a Raman image? Preliminary measurements have been made on polystyrene microspheres of the order of 8 m in diameter, dispersed on silicon. The spectrum from the center of one of the beads is shown in Raman chemical images of one of these beads are shown in These micrographs have the silicon and polystyrene intensities superimposed. What is curious is the "hot spots" on the sides of the spheres. What we have noticed is that rather than the sphere shadowing the silicon intensity, the presence of the sphere in fact intensifies it, presumably because of the focusing properties of the sphere. To explore this phenomenon, an xz profile was recorded and is shown in The second set of measurements were made with polystyrene spheres of uniform dimension, dispersed from solution also on a silicon substrate. Monodispersed polymer beads make ideal samples for this type of test. When Raman Imaging: Defining the Spatial Resolution of the Technology Chemical images of polystyrene beads on silicon acquired using Raman mapping and image processing are reviewed. The effects of the objective on the quality of the final image, particularly its magnification and numerical aperture, and the step size of the map, are discussed as well. Fran Adar, Eunah Lee, Sergey Mamedov, and Andrew Whitley deposited from aqueous solutions onto a silicon substrate, it is possible to find isolated spheres, small clusters, and close-packed films. In line with the results and conclusion of the measurement shown earlier, and from our previous report (1), the maps from these spheres were recorded with intervals considerably smaller than the expected spatial resolution. Using polystyrene microspheres of sizes of 5.2 m, Raman images were generated with objectives 100x/n.a. ϭ 0.9, 50x/n.a. ϭ 0.75, and 20x/n.a. ϭ 0.4. By using objectives with different magnifications and numerical apertures, it is possible to explore the predicted role of the numerical aperture on the properties of the Raman chemical image. The Raman images were acquired on the Aramis using a 1200 g/mm grating, the 532-nm laser (approximately 10 mW at the sample after the OD 0.6 neutral density filter), slit and confocal hole sizes of 100 and 400 m, respectively. The motorized xy stage was incremented by 0.2 m per data point. This value is considerably smaller than the nominal spot size -of the order of a wavelength of the light. The images were collected with two 1-s integrations, which enables the cosmic ray removal routine. Conclusions The results of this study and our previous report (1) show that the use of the highest numerical aperture objective coupled with a step size 5-10 times smaller than the laser spot size will provide the highest quality chemical images. This is of particular relevance and importance for Raman imaging of biological material such as bacteria and subcellular organelles, where the features of interest push the spatial resolution of the technique to its limit. The introduction of faster detectors, advanced spectral imaging software, and new mapping stages capable of stepping with nanometric precision and reproducibility has taken Raman imaging to a new level of capability useful to both spectroscopists and microscopists alike. © Reprinted from SPECTROSCOPY Supplement: Reference

Study of crystallographic properties and elemental migration in two-stage prepared Cu(In,Al) Se2

CuInAl metallic precursor films were selenised at different temperatures and the migration of the elements investigated. GD-OES was used to determine the elemental depth profiles, and XRD analysis gave an insight into the phase transformations taking place. These combined techniques made it possible to study the diffusion and reaction processes taking place during the selenisation stage. Post selenisation annealing was also investigated, which led to partial incorporation of the Al into the CuInSe2 lattice