The optical properties of homoepitaxial GaN layers deposited by organometallic vapor phase epitaxy on stripe-patterned GaN films on 6H-SiC substrates have been investigated. Analysis of the spatiallyresolved Raman scattering spectra indicate an improvement in material quality of the overgrown region. Room-temperature color cathodoluminescence imaging and low-temperature photoluminescence measurements indicate that a donor and an acceptor, different from those detected in the underlying GaN/AlN/SiC substrate, have been incorporated in the epitaxial layer. Detailed photoluminescence studies of the near band-edge emission strongly suggest that Si is the additional donor detected in the homoepitaxial GaN layer. Its occurrence, along with that of an acceptor-related defect which is primarily found in the laterally overgrown region, is discussed.Recently it was demonstrated that the usual high threading dislocation density in heteroepitaxial layers can be significantly reduced using a patterned GaN film for selective homoepitaxial deposition 1,2 . In this work we report the optical and electronic properties of GaN layers selectively overgrown by metalorganic vapor phase epitaxy (MOVPE) on GaN/AlN/6H-SiC substrates.Each of the initial 1.5-2.0 µm thick GaN films was deposited on a 100 nm AlN buffer layer prepared by deposition on 6H-SiC(0001) substrates 3 . These films were subsequently covered with a 100 nm SiO 2 film which were patterned by standard lithography and chemical etching 2 . The stripe patterns included both 3 µm and 5 µm wide stripe openings oriented along 1100 and etched through the SiO 2 film. Different areas had different stripe separations which range from 3 µm to 40 µm. The patterned substrates were reinstalled in the MOVPE reactor. The amount of vertical and lateral epitaxial overgrowth (LEO) showed a strong dependence on stripe orientation and growth conditions 5 . Under optimized growth conditions rectangular crosssectional stripes were deposited on both 3 µm and 5 µm wide stripes 2 . Cross-sectional and plan view transmission electron microscope TEM micrographs of isolated stripes show that the threading dislocations originating at the GaN/AlN interface are confined to the vertical growth region (window regrowth: WR) 2 . Continuous films were achieved for both 3 µm and 5 µm wide stripes; however, we will present and discuss only the results related to isolated stripes where adjacent overgrowth regions had not coalesced.The samples were initially characterized by spatially-resolved room temperature Raman scattering (RS) using the 514 nm line of an Ar ion laser focused to a 1 µm spot size 4 . The 325 nm line of a HeCd laser which was incident either normal to or at 60 degrees from normal was the exciting source for the low-temperature PL experiments. An 0.85 m double-spectrometer with 1800 gr/mm gratings, a low noise photomultiplier, and a photon counting system were used to analyze the light emitted by the samples 5 . The PL experiments were conducted with comparable or higher spectral resolution t...

From a colourimetric point of view, colour has two independent aspects: brightness and chromaticity. In black and white images, all elements are of the same chromaticity and can be distinguished only by brightness contrast. In the colour image, elements of the same brightness can be discriminated by chromaticity (colour) contrast. Generally, colour image elements can be discriminated both by brightness and by chromaticity. As the human eye can distinguish a number of hues two orders of magnitude larger than the number of grey levels, it is safe to say that the colour image is much more informative than the black and white image. There are some peculiarities of the colour image and methods of its formation in SEM. Two principles of image formation are used. The first consists of the formation of a real colour image in the cathodoluminescence mode. In this case the colour of an image element is determined by the spectrum of the luminescence emission excited in the corresponding point of an object by the electron beam. The second principle is that of colour coding (quasicolour, pseudocolour), when a video signal in colour (either digital or analog) corresponds to a video signal (amplitude, frequency, phase, etc.) produced by any mode in the scanning electron microscope. We present a review of the methods of colour display of video information in scanning electron microscopy and their applications to physics, geology, soil science, biology, and medicine.

Summary:The application of color cathodoluminescent scanning electron microscopy (CCL-SEM) for qualitative luminescence analysis of cholesterol, bilirubin, and protein in human gallstones was demonstrated. Images of these deposits (cholesterol, bilirubin, and protein) were formed in real colors (blue-cholesterol, red, orange-bilirubin, yellow, green-protein) in accordance with the cathodoluminescent spectrum for each control material. The other method described for transmission electron microscopy (TEM) of ultrathin sections provides more detailed characterization of the ultrastructure of cholesterol-containing regions and their spatial interrelations with bilirubin-containing regions. Using CCL-SEM combined with TEM permits the receipt of more complete information about the chemical composition and ultrastructure of gallstones and may lead to more effective understanding of the pathogenesis of cholesterol cholelithiasis.

Summary:The polytype transformation in SiC-epitaxial layers grown by the sublimation "sandwich method" have been studied by means of a real color SEM cathodoluminescence (CL) technique. The variation of polytypes grown on 6H-, 4H-, 15R-, and 21R-polytype substrates is demonstrated. Different spectral composition of local CL emission is observed on smooth and profiled substrate surfaces. The double polytype transformation effect was fixed. The nature of the polytype transformation in S i c epitaxial layers is discussed.