Abstract: Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids.

Abstract: The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on ​palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as ​palladium membranes for hydrogen applications.

Abstract: The novel synthesis of a polymeric interface grown from the surface of bright fluorescent nanodiamonds is reported. The polymer enables bioorthogonal attachment of various molecules by click chemistry; the particles are resistant to nonspecific protein adsorption and show outstanding colloidal stability in buffers and biological media. The coating fully preserves the unique optical properties of the nitrogen-vacancy centers that are crucial for bioimaging and sensoric applications.

Abstract: Strong granularity-correlated and intragrain modulations of the superconducting order parameter are demonstrated in heavily boron-doped diamond situated not yet in the vicinity of the metal-insulator transition. These modulations at the superconducting state (SC) and at the global normal state (NS) above the resistive superconducting transition, reveal that local Cooper pairing sets in prior to the global phase coherence.

Abstract: The removal of secondary phases from the surface of the kesterite crystals is one of the major challenges to improve the performances of Cu2ZnSn(S,Se)(4) (CZTSSe) thin film solar cells. In this Contribution, the KCN/KOH Chemical etching approach, originally developed for the removal of CuxSe phases in Cu(In,Ga)(S,Se)(2) thin films) is applied to CZTSe absorbers exhibiting various chemical compositions. Two distinct electrical behaviors were observed on CZTSe/CdS solar cells after treatment: (i) the improvement of the fill factor (FF) after 30 s of etching for the CZTSe absorbers showing initially a distortion of the electrical characteristic; (ii) the progressive degradation Of the FF after long treatment time for all Cu-poor CZTSe solar cell samples. The first effect can be attributed to the action of KCN on the absorber, that is found to clean the absorber free surface from most of the secondary phases surrounding the kesterite grains (e.g., Se-0, CuxSe, SnSex, SnO2, Cu2SnSe3 phases, excepting the ZnSe-based phases). The second observation was identified as a consequence of the preferential etching of Se, Sn, and Zn from the CZTSe surface by the KOH solution, combined with the modification of the alkali content of the absorber. The formation of a Cu-rich shell at the absorber/buffer layer interface, leading to the increase of the recombination rate at the interface, and the increase in the doping of the absorber layer after etching are found to be at the origin of the deterioration of the FF of the solar cells.

Abstract: Tetrahedral chain ordering in the Sr2MnGaO5 structure is studied using electron diffraction (ED) and high-resolution electron microscopy. The ED patterns show the presence of satellite reflections, which indicate a commensurately modulated structure with a = 5.4056(8) Angstrom b 16.171(3) Angstrom, c = 5.5592(7) Angstrom, q – 1/2c*, superspace group Immma(00gamma,)s00. The Superstructure arises due to ordering of the two types of symmetry related tetrahedral chains (L and R) according to a ... LRLR ... sequence, where L and R chains alternate along the c-axis within the same (GaO) layer. Numerous defects at different structural levels were observed, comprising interleaving L and R chains, violation of the ... LRLR ... chain sequence within one layer, different stacking modes of the ... LRLR ... ordered layers with subsequent alternation of blocks of different width along the h-axis of the brownmillerite subcell and island fragmentation of the modulated superstructure. By in situ heating ED experiments it is found that the long-range ordering of the tetrahedral chains is stable tip to 665degreesC and is completely suppressed at 905degreesC. (C) 2003 Elsevier Inc. All rights reserved.

Abstract: The three-dimensional size, morphology and distribution of Ni4Ti3 precipitates in a Ni50.8Ti49.2 polycrystalline shape memory alloy with a heterogeneous microstructure have been investigated using a focused ion beam/scanning electron microscopy slice-and-view procedure. The mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured and/or calculated. The morphology of the precipitates was quantified by determining the equivalent ellipsoids with the same moments of inertia and classified according to the Zingg scheme. Also, the pair distribution functions describing the three-dimensional distributions were obtained from the coordinates of the precipitate mass centres. Based on this new data it is suggested that the existence of the heterogeneous microstructure could be due to a very small concentration gradient in the grains of the homogenized material and that the resulting multistage martensitic transformation originates in strain effects related to the size of the precipitates and scale differences of the available B2 matrix in between the precipitates.

Abstract: The properties and applications of metallic nanoparticles are inseparably connected not only to their detailed morphology and composition but also to their structural configuration and mutual interactions. As a result, the assemblies often have superior properties as compared to individual nanoparticles. Although it has been reported that nanoparticles can form highly symmetric clusters, if the configuration can be predicted as a function of the synthesis parameters, more targeted and accurate synthesis will be possible. We present here a theoretical model that accurately predicts the structure and configuration of self-assembled gold nanoclusters. The validity of the model is verified using quantitative experimental data extracted from electron tomography 3D reconstructions of different assemblies. The present theoretical model is generic and can in principle be used for different types of nanoparticles, providing a very wide window of potential applications.

Abstract: Nanoparticle assemblies can be investigated in 3 dimensions using electron tomography. However, it is not straightforward to obtain quantitative information such as the number of particles or their relative position. This becomes particularly difficult when the number of particles increases. We propose a novel approach in which prior information on the shape of the individual particles is exploited. It improves the quality of the reconstruction of these complex assemblies significantly. Moreover, this quantitative Sparse Sphere Reconstruction approach yields directly the number of particles and their position as an output of the reconstruction technique, enabling a detailed 3D analysis of assemblies with as many as 10 000 particles. The approach can also be used to reconstruct objects based on a very limited number of projections, which opens up possibilities to investigate beam sensitive assemblies where previous reconstructions with the available electron tomography techniques failed.

Abstract: Chalcopyrite semiconductors are of considerable interest for application as absorber layers in thin-film photovoltaic cells. When growing films of these compounds, however, they are often found to contain CuAu-like domains, a metastable phase of chalcopyrite. It has been reported that for CuInS2, the presence of the CuAu-like phase improves the short circuit current of the chalcopyrite-based photovoltaic cell. We investigate the thermodynamic stability of both phases for a selected list of I-III-VI2 materials using a first-principles density functional theory approach. For the CuIn-VI2 compounds, the difference in formation energy between the chalcopyrite and CuAu-like phase is found to be close to 2 meV per atom, indicating a high likelihood of the presence of CuAu-like domains. Next, we calculate the spectroscopic limited maximum efficiency (SLME) of the CuAu-like phase and compare the results with those of the corresponding chalcopyrite phase. We identify several candidates with a high efficiency, such as CuAu-like CuInS2, for which we obtain an SLME of 29% at a thickness of 500 nm. We observe that the SLME can have values above the Shockley-Queisser (SQ) limit, and show that this can occur because the SQ limit assumes the absorptivity to be a step function, thus overestimating the radiative recombination in the detailed balance approach. This means that it is possible to find higher theoretical efficiencies within this framework simply by calculating the J-V characteristic with an absorption spectrum. Finally, we expand our SLME analysis to indirect band gap absorbers by studying silicon, and find that the SLME quickly overestimates the reverse saturation current of indirect band gap materials, drastically lowering their calculated efficiency.

Abstract: The electronic phase behavior and functionality of interfaces and surfaces in complex materials are strongly correlated to chemical composition profiles, stoichiometry and intermixing. Here a novel analysis scheme for resonant X-ray reflectivity maps is introduced to determine such profiles, which is element specific and non-destructive, and which exhibits atomic-layer resolution and a probing depth of hundreds of nanometers.

Abstract: Using the four-band continuum model we derive a general expression for the infinite-mass boundary condition in bilayer graphene. Applying this new boundary condition we analytically calculate the confined states and the corresponding wave functions in a bilayer graphene quantum dot in the absence and presence of a perpendicular magnetic field. Our results for the energy spectrum show an energy gap between the electron and hole states at small magnetic fields. Furthermore the electron (e) and hole (h) energy levels corresponding to the K and K' valleys exhibit the E-K(e(h)) (m) = E-K'(e(h)) (m) symmetry, where m is the angular momentum quantum number. (C) 2014 Elsevier Ltd. All rights reserved.

Abstract: The Ni(1+)/Ni(2+) states of nickelates have the identical (3d(9)/3d(8)) electronic configuration as Cu(2+)/Cu(3+) in the high temperature superconducting cuprates, and are expected to show interesting properties. An intriguing question is whether mimicking the electronic and structural features of cuprates would also result in superconductivity in nickelates. Here we report experimental evidence for a bulklike magnetic transition in La(4)Ni(3)O(8) at 105 K. Density functional theory calculations relate the transition to a spin density wave nesting instability of the Fermi surface.