Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption by an elliptic pore nucleated at the boundary of a foreign polytype inclusion. It is shown that depending on the inclusion distortion, the pore can either be a separate micropipe, or grow up to a certain length, or occupy the whole facet of the inclusion.

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We reveal a correlated reduction in the cross sections of two neighboring micropipes ͑MPs͒ in the crystal growth of silicon carbide using computer simulation of phase contrast images. The correlated reduction is explained by the exchange of full-core dislocations in a contact-free reaction between two parallel MPs. We develop a theoretical model that describes the energetics of this process.Nowadays research pertaining to silicon carbide ͑SiC͒ power electronics has been hampered by insufficient quality and size of SiC ingots. Seeded sublimation growth techniques produce large-area SiC wafers; however, the sublimation growth is accompanied by the formation of cylindrical pores called micropipes ͑MPs͒. As a rule, they represent the hollow cores of superscrew dislocations with giant Burgers vectors. MPs have deleterious effect on the properties of SiC such as large breakdown electric field strength, high thermal conductivity, etc. Therefore, the problem of growing bulk SiC crystals with low MP density is of special importance. [1][2][3][4][5] The MP evolution during the crystal growth is a complex process that involves the formation of new MPs, 6-17 the overgrowth of the existing MPs due to their various reactions with one another, 18,19 and the coalescence of MPs resulting in micropore formation. 3,15,20,21 In this letter we discuss one more form of MP evolution, namely, a correlated reduction in the cross sections of two neighboring MPs along their axes ͑generally parallel to the growth direction͒. Such variations in MP cross sections can lead to MP healing. We provide experimental evidence of this effect and discuss its reasons and a possible mechanism. Our main idea is that MPs can remotely interact with each other by the exchange of full-core dislocations. We propose a theoretical model describing the energetics of this process.SiC sample was an axial-cut slice along the growth direction ͓0001͔ obtained from 4H-SiC boule. The boule was grown in Ar by the sublimation sandwich method 9 at the growth temperature of 2100°C and with the growth rate of 0.5 mm h −1 . The sample contained MPs of Ϸ0.5-10 m in diameter located almost parallel to the surface. MPs were examined with the white beam phase contrast imaging method 3,14,18,20 at the 7B2 X-ray Microscopy Beamline of the Pohang Light Source, Korea. The source with effective sizes of 160 ͑H͒ and 60͑V͒ m was located at a distance of 34 m from the sample. The sample ͑rotated to have a horizontal position of the MP axis for better edge enhancement in a more coherent vertical direction͒ was sequentially placed at different distances from the detector. We obtained nine images for the distances from 5 to 45 cm starting with the first image registered at 5 cm from the sample. Three MPs forming a group were examined: two in contact and the third lying remotely. The phase contrast image of the MP group is shown in Fig. 1͑a͒, while Fig. 1͑b͒ demonstrates the optical micrograph of the remote MP, taken on a Zeiss universal microscope equipped with a charge coupled device.For ...

The natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and lactic acid (LA) was used for the preparation of chitosan (CS) films by the solution casting method. The content of NADES in films was from 0 to 82 wt%. The impact of NADES on the morphology and crystalline structure of films was investigated using scanning electron microscopy as well as wide-angle and small-angle X-ray scattering. The experimental results allow to propose CS chains swelling in NADES. FTIR spectroscopy confirms the interactions between CS and NADES components via the formation of hydrogen and ion bonds. The thermal properties of the composite films were studied by simultaneous thermogravimetric and differential thermal analysis. Thermomechanical analysis demonstrated appearance of two transitions at temperatures between −23 and −5 °C and 54–102 °C depending on NADES content. It was found that electrical conductivity of film with 82 wt% of NADES reaches 1.7 mS/cm. The influence of the composition and structure of films on the charge carriers concentration and their mobility is discussed.

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Successive molecular assembling in polymer chains furnished a series of the comb shaped copolymers of 4 aminostyrene containing side styrylquinoline chromophore groups. Thermal, thermomechanical, spectroscopic, and luminescent properties of the polymers and low mo lecular weight model chromophores were studied.

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