Abstract: Polycrystalline CuInSe2 semiconductors are efficient light absorber materials for thin film solar cell technology, whereas printing is one of the promising low cost and non-vacuum approaches for the fabrication of thin film solar cells. The printed precursors are transformed into a dense polycrystalline CuInSe2 semiconductor film via thermal treatment in ambient selenium atmosphere (selenization). In this study, the effect of the selenium content in high purity mechanically synthesized CuInSex (x = 2, 1.5, 1 or 0.5) alloy precursors on the recrystallization of the CuInSe2 phase during the selenization process was investigated. The nanostructure and phase variation of CuInSex nanopowders were investigated by different characterization techniques. The recrystallization process of the 12 μm thick CuInSex coatings into the CuInSe2 phase during selenization in selenium vapor was investigated via in-situ high temperature X-ray diffraction. The CuInSex precursors with lower selenium content showed a more pronounced phase conversion into CuInSe2 compared to the higher selenium content CuInSex precursors. Moreover, the CuInSex (x = 0.5 and 1) precursor resulted in a denser polycrystalline CuInSe2 semiconductor film with larger crystals. This could be attributed to a more intensive atomic interdiffusion within the CuInSex precursor system compared to a CuInSe2 phase precursor, and the formation of intermediate CuSe and CuSe2 fluxing phases during selenization.

Abstract: The compositional influence of Cr and Y on the microstructure of Mg―Cr―O, and Mg―Y―O films synthesized by reactive magnetron sputtering has been investigated by transmission electron microscopy, X-ray diffraction and molecular dynamics simulations. A decrease in crystallinity is observed in these films as the M (Cr or Y) content is increased. It is found that M forms a solid solution with MgO for metal ratios up to ~ 70% and ~ 50% for Cr and Y respectively. Above ~ 70% Cr metal ratio the Mg―Cr―O films are found to be completely amorphous. The Mg―Y―O films are composed of Mg(Y)O and Y2O3 nano crystallites, up to ~ 50% Y metal ratio. Above this ratio, only Y2O3 nano crystallites are found. The preferential < 111> MgO grain alignment is strongly affected by the increase in M content. For M metal ratios up to ~ 50%, there is a selective promotion of the < 100> MgO grain alignments and a decline in the < 111> grain alignments.

Abstract: Highly effective IR light-emitting diodes operating at the wavelength 1.66 mu m and based on the buried heterostructure In0.88Ga0.12As0.26P0.74/ In0.72Ga0.28As0.62P0.38/In0.53Ga0.47As/InP have been grown by liquid-phase epitaxy (LPE) and characterized in detail by means of transmission electron microscopy (TEM), high-resolution electron microscopy (HREM),electron diffraction (ED), X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS) and electroluminescence measurements. The InGaAsP epilayers are found to be well lattice matched and of good structural quality. A tentative explanation is presented for the spinodal decomposition observed in InGaAsP alloys. A new type of selective CK, gas sensor has been developed and fabricated an the basis of the IR light-emitting diode mentioned above. Especially designed for the remote control of CH4 gas via fibre optics, an integrated optoelectronic readout scheme has been developed and tested, It is shown that the proposed type of sensor can be used for the quantitative remote control of CH4 gas concentration (0.2-100%) via a fibre glass line up to a distance of 2 x 1 km. (C) 1997 Elsevier Science S.A.

Abstract: Ti6Al4V sheet material is subjected to simple shear deformation with strain ratio's of 10%, 30% and 50%. Optical microscopy, transmission electron microscopy and electron backscatter diffraction techniques are applied to study the presence and morphology of deformation twins. Only the View the MathML source type of twins seems to be present with a volume fraction below 1%. These View the MathML source twins show a high density of basal stacking faults of the ABABACAC type identified using atomic resolution transmission electron microscopy. A resolved shear stress analysis shows that twins most often occur on those planes with the highest resolved shear stresses, but that the starting texture is not beneficial for the occurrence of twins. It is further suggested that a transitory strain hardening regime observed around 530 MPa might be related with the onset of twinning.

Abstract: The anion-excess fluorite-like solid solutions with general composition Bi1−xTex(O,F)2+δ (x > 0.5) have been synthesized by a solid state reaction of TeO2, BiF3 and Bi2O3 at 873 K with following quenching. The homogeneity areas and polymorphism of the I ↔ IV Bi1−xTex(O,F)2+δ phases were investigated. The crystal structure of the low temperature IV-Bi1−xTex(O,F)2+δ phase has been solved using electron diffraction and X-ray powder diffraction (a = 11.53051(9) Å, S.G. Ia-3, RI = 0.046, RP = 0.041). Glass formation area in the Bi2O3BiF3TeO2 (10% TiO2) system was investigated. IVBi1−xTex(O,F)2+δ phase starts to crystallize at short-time (0.53 h) annealing of oxyfluoride glasses at temperatures above Tg (600615 K). The ionic conductivity of the crystalline Bi1−xTex(O,F)2+δ phase and corresponding glass-ceramics was investigated. Activation energy of conductivity Ea = 0.41(2) eV for the IV-Bi1−xTex(O,F)2+δ crystalline samples and Ea = 0.73 eV for the glass-ceramic samples were obtained. Investigation of the oxyfluoride samples with a constant cation ratio demonstrates essential influence of excess fluorine anions on the ionic conductivity.

Abstract: When studying photocatalysis it is important to consider, beside the chemical approach, the engineering part related to process optimisation. To achieve this a fixed bed photocatalytic set-up consisting of different catalyst placings, in order to vary catalyst distribution, is studied. The use of a fixed quantity of catalyst placed packed or randomly distributed in the reactor, results in an almost double degradation for the distributed catalyst. Applying this knowledge leads to an improved performance with limited use of catalyst. A reactor only half filled with catalyst leads to higher degradation performance compared to a completely filled reactor. Taking into account this simple process optimisation by better distributing the catalyst a more sustainable photocatalytic air purification process is achieved. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: The rational synthesis, comprehensive characterization, and mechanical and micromechanical properties of a calcium phosphate cement are presented. Hydroxyapatite cement biomaterial was synthesized from reactive sub-micrometer-sized dicalcium phosphate dihydrate and tetracalcium phosphate via a dissolution-precipitation reaction using water as the liquid phase. As a result nanostructured, Ca-deficient and carbonated B-type hydroxyapatite is formed. The cement shows good processibility, sets in 22 ± 2 min and entirely transforms to the end product after 6 h of setting reaction, one of the highest conversion rates among previously reported for calcium phosphate cements based on dicalcium and tetracalcium phosphates. The combination of all elucidated physical-chemical traits leads to an essential bioactivity and biocompatibility of the cement, as revealed by in vitro acellular simulated body fluid and cell culture studies. The compressive strength of the produced cement biomaterial was established to be 25 ± 3 MPa. Furthermore, nanoindentation tests were performed directly on the cement to probe its local elasticity and plasticity at sub-micrometer/micrometer level. The measured elastic modulus and hardness were established to be Es = 23 ± 3.5 and H = 0.7 ± 0.2 GPa, respectively. These values are in close agreement with those reported in literature for trabecular and cortical bones, reflecting good elastic and plastic coherence between synthesized cement biomaterial and human bones.

Abstract: A seriesof [TiN/TiAlN]nmultilayer coatingswith different bilayer numbers n=5, 10, 25, 50, and 100 were deposited on stainless steel substrate AISI 304 by a lateral rotating cathode arc technique in a flowing nitrogen atmosphere. The composition and microstructure of the coatings have been analyzed by using energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), and conventional and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows that the preferential orientation growth along the (111) direction is reduced in the multilayer coatings. TEM analysis reveals that the grain size of the coatings decreases with increasing bilayer number. HRTEMimaging of the multilayer coatings shows a high density misfit dislocation between the TiN and TiAlN layers. The cross-plane thermal conductivity of the coatings was measured by a pulsed photothermal reflectance technique. With increasing bilayer number, the multilayer coatings' thermal conductivity decreases gradually. This reduction of thermal conductivity can be ascribed to increased phonon scattering due to the disruption of columnar structure, reduced preferential orientation, decreased grain size of the coatings and present misfit dislocations at the interfaces.

Abstract: Optical properties, spectral dependence of photoconductivity and photoconductivity decay in nanocrystalline indium oxide In2O3 are studied. A number of nanostructured In2O3 samples with various nanocrystals size are prepared by sol-gel method and characterized using various techniques. The mean nanocrystals size varies from 7 to 8 nm to 39-41 nm depending on the preparation conditions. Structural characterization of the In2O3 samples is performed by means of transmission electron microscopy and X-ray powder diffraction. The combined analysis of ultraviolet-visible absorption spectroscopy and diffuse reflectance spectroscopy shows that nanostructuring leads to the change in optical band gap: optical band gap of the In2O3 samples (with an average nanocrystal size from 7 to 41 nm) is equal to 2.8 eV. We find out the correlation between spectral dependence of photoconductivity and optical properties of nanocrystalline In2O3: sharp increase in photoconductivity was observed to begin at 2.8 eV that is equal to the optical bandgap in the In2O3 samples, and reached its maximum at 3.2-3.3 eV. The combined analysis of the slow photoconductivity decay in air, vacuum and argon, that was accurately fitted by a stretched-exponential function, and electron paramagnetic resonance (EPR) measurements shows that the kinetics of photoconductivity decay is strongly depended on the presence of oxygen molecules in the ambient of In2O3 nanocrystals. There is the quantitative correlation between EPR and photoconductivity data. Based on the obtained data we propose the model clearing up the phenomenon of permanent photoconductivity decay in nanocrystalline In2O3. (C) 2015 Elsevier B.V. All rights reserved.

Abstract: Diamond is a promising material for a number of bio-applications, including the fabrication of platforms for attachment and investigation of neurons and of neuroprostheses, such as retinal implants. In the current work ultrananocrystalline diamond (UNCD) films were deposited by microwave plasma chemical vapor deposition, modified by UV/O-3 treatment or NH3 plasma, and comprehensively characterized with respect to their bulk and surface properties, such as crystallinity, topography, composition and chemical bonding nature. The interactions of insect circadian pacemaker neurons with UNCD surfaces with H-, O- and NH2-terminations were investigated with respect to cell density and viability. The fast and strong attachment achieved without application of adhesion proteins allowed for advantageous modification of dispersion protocols for the preparation of primary cell cultures. Centrifugation steps, which are employed for pelletizing dispersed cells to separate them from dispersing enzymes, easily damage neurons. Now centrifugation can be avoided since dispersed neurons quickly and strongly attach to the UNCD surfaces. Enzyme solutions can be easily washed off without losing many of the dispersed cells. No adverse effects on the cell viability and physiological responses were observed as revealed by calcium imaging. Furthermore, the enhanced attachment of the neurons, especially on the modified UNCD surfaces, was especially advantageous for the immunocytochemical procedures with the cell cultures. The cell losses during washing steps were significantly reduced by one order of magnitude in comparison to controls. In addition, the integration of a titanium grid structure under the UNCD films allowed for individual assignment of physiologically characterized neurons to immunocytochemically stained cells. Thus, employing UNCD surfaces free of foreign proteins improves cell culture protocols and immunocytochemistry with cultured cells. The fast and strong attachment of neurons was attributed to a favorable combination of topography, surface chemistry and wettability. (C) 2016 Elsevier B.V. All rights reserved.

Abstract: The adsorption of CO2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe atoms, are investigated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, neglecting the heat effects. Fe ad-atoms are more stable when they are dispersed on hollow sites. They introduce a large density of states at the Fermi level (N-F); where keeping such density low would help in gas sensing. Furthermore, the Fe ad-atom can weaken the C=O double bonds of the chemisorbed CO2 molecule, paving the way for oxygen atoms to drain more charges from Fe. Consequently, chemisorption of CO2 molecules reduces both N-F and the conductance while it enhances the sensitivity with the increasing gas dose. Conducting armchair CNTs (ac-CNTs) have higher sensitivity than graphene and semiconducting zigzag CNTs (zz-CNT5). Comparative study of sensitivity of ac-CNT-Fe composite towards various gases (e.g., O-2, N-2, H-2, H2O, CO and CO2) has shown high sensitivity and selectivity towards CO, CO2 and H2O gases. (C) 2016 Elsevier B.V. All rights reserved.