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In this paper, first‐principles calculations are performed to investigate the elastic constants, structural stability, electronic properties, and optical properties of ideal BiVO4 and BiVO4 with oxygen vacancy (Vo‐BiVO4) under equivalent hydrostatic and z‐axial pressure. It is found that the structural stability of the material is not affected and the indirect band‐gap is well kept in BiVO4 and Vo‐BiVO4, independent of the applied pressure. Essentially, as the equivalent hydrostatic and z‐axial pressure is increased, the hybridization of O 2p, V 3d, and Bi 6s orbitals will be enhanced in the ideal BiVO4, while the hybridization of O 2p, V 3d, and Bi 6p orbitals is enhanced in Vo‐BiVO4. Moreover, the band edges are shifted to lower energies under pressure, resulting in substantially reduced band gap, which might facilitate the photocatalytic performance. The shape of the optical spectrum of ideal BiVO4 displays an exponential form while that of Vo‐BiVO4 shows leaf‐like form in the low energy range, although they have similar shapes in the whole energy range. The absorption amount increases with the increase of z‐axial pressure, which might improve the visible light absorption. [ABSTRACT FROM AUTHOR]

Core–shell nanostructures are predicted to highly improve the efficiency of deep‐UV light emitting diodes (LEDs), owing to their low defect density, reduced quantum‐confined Stark effect, high‐quality non‐polar growth and improved extraction efficiency. In this paper, we report on the nanofabrication of high‐quality AlN nanorod arrays using a hybrid top‐down/bottom‐up approach for use as a scaffold for UV LED structures. We describe the use of Displacement Talbot Lithography to fabricate a metallic hard etch mask to allow AlN nanorod arrays to be dry etched from a planar AlN template. In particular, we investigate the impact of etching parameters on the nanorod etch rate, tapering profile and mask selectivity in order to achieve vertical‐sided nanorod arrays with high aspect ratios. AlN facet recovery is subsequently explored by means of regrowth using Metal Organic Vapor Phase Epitaxy. Low pressure and high V/III ratio promote straight and smooth sidewall faceting, which results in an improvement of the optical quality compared to the initial AlN template. The promising results open new perspectives for the fabrication of high‐efficiency deep‐UV‐emitting core–shell LEDs. [ABSTRACT FROM AUTHOR]

Among metal disilicide materials, α‐MoSi2 exhibits high thermal conductivity and high oxidation resistance at high temperatures, making it an attractive option for high temperature applications. In the present study, we fabricate α‐MoSi2 pellets with a density of 96% theoretical density (TD) and quantify the thermal properties (thermal conductivity and thermal expansion heat capacity), mechanical properties (Vickers hardness and fracture toughness), and electrical properties (Seebeck coefficient and electrical resistivity). In this paper, we evaluate the experimental data, and present a review of the literature. In addition, we attempt to correlate the heat capacity measurement obtained experimentally with the results of our theoretical calculations to identify their relationship. [ABSTRACT FROM AUTHOR]

Chiral metastructures consisting of ring (polygonal or cubic) nodes and elastic bending ligaments exhibit excellent design flexibility for compliant structures. In this paper, based on rigid cubic node rotation and the kinematic geometrical relations of a three‐dimensional (3D) isotropic anti‐tetrachiral structure, an analytical expression for the modulus of the 3D isotropic anti‐tetrachiral structure is derived from strain energy analysis. The nylon powder Selected Laser Sintering (SLS) additive manufacturing technique is employed for fabricating two types of 3D isotropic anti‐tetrachiral specimens with different geometrical parameters; then comparison between experiments, finite element analysis (FEA), and theoretical studies is performed for verifying the analytical formula. The mechanical properties of 3D isotropic anti‐tetrachiral structures can be tuned with two independent dimensionless geometrical parameters. The proposed 3D anti‐tetrachiral structures can be employed for designing advanced structures against impact damages, realizing flexibility of industrial components, and optimizing the vibration attenuation abilities of engineering structures. [ABSTRACT FROM AUTHOR]

In this paper, first principles calculations based on density functional theory were used to study the electronic properties and adsorption behavior of modified rutile surfaces with neutral element dopants (Si, Ge, Sn). The results showed that Sn doped surface has the smallest work function (7.07 eV) and Ge doped surface has the lowest conduction band edge (1.28 eV). Furthermore, the adsorption behavior of H2O and Arg‐Gly‐Asp (RGD) molecules on modified rutile surfaces was calculated to estimate the biocompatibility of modified dental implant surfaces. For the purpose of simulating the real solution environment, the free energy of solvation for adsorbates, calculated by Gaussian 09 program code, was taken into account. The results of the adsorption calculations of H2O indicate that Sn doped surface has a more negative adsorption energy (−3.15 eV) and a higher charge transfer (−0.1) than any other modified surface, which is consistent with its low work function. The results of the adsorption calculations of Arg‐Gly‐Asp demonstrate that Ge doped surface also has a shorter distance (1.95 Å) between Ti atom and O atom in RGD, which is similar with the partial density of states results. All of the results show that the electronic structure of an implant surface has a significant influence on its bioactivity and is also useful for the design of modification methods on dental implant surfaces. [ABSTRACT FROM AUTHOR]

This paper presents a study on structural and electronic properties of bulk polypropylene – one of the fastest growing engineering plastics – based on density‐functional calculations. The use of recently developed non‐local van der Waals functionals to approximate the exchange–correlation energy is crucial for a good description of structural properties. Various types of chemical imperfections, their impacts on electronic properties of polypropylene are also studied. [ABSTRACT FROM AUTHOR]

In the present paper, we review the recent research on the physics of magnetocaloric materials aiming to define a coherent theoretical framework in which hysteresis and kinetic effects can be appropriately discussed and interpreted in relation to intrinsic and extrinsic factors. We dedicate our efforts to introduce a thermodynamic description of the material, including the out‐of‐equilibrium aspects which are necessary to understand hysteresis, heat flux avalanches and thermal relaxation effects. In particular we show how intrinsic and extrinsic factors, contributing to define the energy landscape of the system, influence the resulting hysteresis and how different kinetic effects are expected depending on the phase transformation mechanisms, here described either as an out‐of‐equilibrium domain boundary motion or as a thermally activated process associated to energy barriers. Several applications of the theoretical models are discussed in relation with experiments on La(Fe‐Si)13‐based compounds and Mn–Bi. [ABSTRACT FROM AUTHOR]

Despite the intensive development of the terahertz technologies in the last decade, there is still a shortage of efficient room‐temperature radiation detectors. Carbon nanotubes (CNTs) are considered as a very promising material possessing many of the features peculiar for graphene (suppression of backscattering, high mobility, etc.) combined with a bandgap in the carrier spectrum. In this paper, we investigate the possibility to incorporate individual CNTs into devices that are similar to Schottky diodes. The latter is currently used to detect radiation with a frequency up to 50 GHz. We report results obtained with semiconducting (bandgap of about 0.5 eV) and quasi‐metallic (bandgap of few meV) single‐walled carbon nanotubes (SWNTs). Semiconducting CNTs show better performance up to 300 GHz with responsivity up to 100 V W−1, while quasi‐metallic CNTs are shown to operate up to 2.5 THz. [ABSTRACT FROM AUTHOR]

Lightweight materials for efficient electromagnetic interference shielding over a wide range of frequency are of great interest. Aerogels of multi‐walled carbon nanotubes (MWCNTs) distributed in a dielectric matrix may interact effectively with electromagnetic radiation. Moreover, being arranged in specific patterns, they can also provide metamaterial characteristics (e.g., negative refractive index). In the present paper, we have studied the interaction between two spheres of the carbon nanotube aerogels in order to obtain a comprehensive basis for producing periodic 2D and 3D structures of such aerogel spheres in a dielectric matrix. We have extended the open resonator technique to the case of two units of MWCNT aerogels in order to reveal the interaction between them. The performance of the system depends on the orientation of the electric field to the axis of the aerogel cluster: MWCNT aerogel spheres (d = 4.5 mm) interact considerably at the gap between spheres ∼0.2λ (11.6 GHz) for perpendicular orientation, while, in case of axial orientation, the interaction is negligible even at the distances close to the contact between aerogels (∼0.02λ). Additionally, the cluster of two carbon nanotube aerogel spheres provides the polarizability close to that of copper spheres while having only 1% of their weight. [ABSTRACT FROM AUTHOR]

This paper is devoted to the influence of the multi‐walled carbon nanotube (MWCNT) spatial distribution within a polymer matrix on the electrophysical properties of the composite. We have studied composites with MWCNT concentrations close to the percolation threshold upon variation in (i) the morphology of the reinforcing material using MWCNTs with different aspect ratio and nanotube aggregate size (up to the average size of ≈300 µm) that were isolated from each other by thin polymer layers, and (ii) the type of the polymer matrix. The composites obtained have been characterized using optical and scanning electron microscopy, and DC conductivity measurements. A study of the electromagnetic response in microwave (0.01–18 GHz) and terahertz (100–200 GHz) ranges was performed. In the region close to and above the percolation threshold, the electrophysical properties of the composites were found to be strongly affected by the spatial distribution of MWCNTs in the composite matrix. The effect of conductive fillers (NTs) size on the EMI reflectance of the composites was different for microwave and terahertz ranges. [ABSTRACT FROM AUTHOR]

The present paper is devoted to the influence of the growth temperature of multi‐walled carbon nanotubes (MWCNTs) on their defective structure. The MWCNTs obtained within the range of 610–750 °C have been studied using two methods: Raman spectroscopy and the analysis of the temperature dependence of conductivity. This approach allows us to obtain independent data on the concentration of the defects within the MWCNTs via the intensity ratio of 2D and D bands, on one hand, and charge carrier concentration, on the other hand. The results obtained using Raman spectroscopy and the analysis of the conductivity have provided asymptotic and volcano‐like curves, respectively, of defect concentration within the temperature range studied. This can be attributed to the difference in the probing depth of each method (∼50 nm for Raman spectroscopy, and ∼2–3 nm for conductivity measurements) providing different sensitivity to surface impurities or defects. The secondary factors (the size of the active component, the amount of the lateral carbon deposits) have been shown to mask the influence of the growth temperature. Nevertheless, as these secondary factors and the synthesis temperature independently affect the effective nanotube defectiveness, we have shown the defect concentration to fall with increasing MWCNT growth temperature. [ABSTRACT FROM AUTHOR]

X‐ray refractive lenses are widely used optical devices at today synchrotron X‐ray sources. In the present paper we demonstrate negative influence of the X‐ray diffraction on optical properties of monocrystalline X‐ray refractive lenses in operation. Several types of single‐crystal diamond lenses were studied in X‐ray spectroscopy mode at the European Synchrotron Radiation Facility. X‐rays were propagating through individual lenses, stacked together in a row, and the transmitted intensity was measured at different energies. While using the stack of crystallographically co‐aligned lenses, we obtained the strong maximal reduction of 35% in an intensity of the outgoing signal. The effect was caused by diffraction losses in the single‐crystal diamond and also called “X‐ray glitch.” The magnitude of the effect was then minimized down to ∼10% by use of stacks with different crystallographic orientation of individual lenses inside. At the same time, X‐ray glitches did not affect any focal spot's size or shape while only arousing the darkening of the focal spot at exact energies of X‐ray glitches. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of tensile and deformation behavior of an auxetic plied yarn structure. The basic configuration of the plied structure formed with two soft yarns and two stiff yarns was firstly introduced. Based on this 4-ply helix structure, six kinds of yarn samples were made by different combinations of soft yarns, stiff yarns and twist levels. These yarn samples were first tested and the effects of different design parameters were analyzed. Apart from the tensile test, changes in the internal structure of two samples upon stretching were also studied through microscopic examination. Finally, double helix yarn and 6-ply auxetic yarn were made for a comparative purpose to investigate the effect of helical structure. The study shows that all of the 4-ply auxetic yarn samples exhibit negative Poisson's ratio (NPR) throughout the entire tensile process, and the magnitude of NPR gets larger with a smaller soft yarn diameter, a higher tensile modulus of stiff yarn and a lower twist level. The study also shows that auxetic behavior inside the 4-ply structure is generated by the interplay between the soft yarns and stiff yarns and 4-ply auxetic yarns have the advantages to produce immediate auxetic effect upon stretching. [ABSTRACT FROM AUTHOR]

This paper proposes an in-plane negative area compressibility (NAC) material not due to Lifshitz mode, but due to all around in-plane pressure. The NAC system consists of an array of two-dimensional material in the form of n-sided polygon with n/2 number of connecting rods, where n is an even number. Two types of NAC microstructural geometries are introduced herein: 8-sided polygon in square array and 6-sided polygon in hexagonal array. The polygons are permitted to change in shape - and hence change in area - at constant side lengths with accompanying translational motion of the connecting rods, thereby changing the overall area of the cell. Results reveal that negative compressibility is observed in the square array NAC when the material shape is in between a regular octagon and a square, and in the hexagonal array NAC when the material shape is in between a regular hexagon and an equilateral triangle. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-dimensional (3D) cellular structure with negative Poisson's ratio was designed by alternating cuboid surface indents on the vertical ribs of the unit cells. The Poisson's ratio and Young's modulus of structures with different geometric parameters were determined using the finite element method (FEM) as a function of these parameters. Samples with identical geometric variables were fabricated via 3D printing, and their through-thickness direction Poisson's ratios were measured and compared with simulation results. Results showed that the Poisson's ratio of the 3D cellular structures can be tuned from positive to negative and can reach a minimal value of −0.958. Good agreement was found between the experimental results and the simulation. This lattice structure is considerably stiffer than re-entrant negative Poisson's ratio foam with the same solid phase. The design concept developed here can be optimized for specific applications via geometric parameters manipulation. [ABSTRACT FROM AUTHOR]

Scattering type scanning near-field optical microscopy (s-SNOM) is an effective tool for the nanoscale examination of nano-objects. In this paper, we present a modified device setup that enables spectroscopic measurements with a tunable laser, even without an FTIR (Fourier Transform Infrared) spectroscopy add-on. We demonstrate the effectiveness of this setup by measurements on boron nitride nanotubes (BNNTs). In far-field absorption measurements, BNNTs have a characteristic peak around 1375 cm−1 due to a phonon polariton mode. This peak is also visible in near-field measurements along with several other peaks that are not present in the far-field spectrum. As these peaks are caused by local defects, their spatial distribution reveals the defect structure of individual nanotubes. [ABSTRACT FROM AUTHOR]

The transport properties of phonons in a nanocomposite have been investigated in this paper. In our model, the nanocomposite consists of nanoparticles embedded in a host dielectric material. The phonon dispersion relation of the nanocomposite is characterized in terms of a defined phonon refractive index and a filling factor parameter. This phonon refractive index depends on its velocity whereas the filling factor is determined by the diameter of the nanoparticles. Consequently, at zero filling, only the host material is present. Our model calculations also include point defects such as impurities, vacancies and the mass and size variations of nanoparticles. The phonon conductivity is determined by employing the Kubo formulism. We also report our calculated results for the phonon relaxation rates due to point defects and boundaries scattering where the latter is due to phonons interacting with the surface boundaries of nanoparticles and the host material. The thermal conductivity, dispersion relation, velocity, density-of-states and relaxation rates of phonons are determined by the filling factor and phonon refractive indices of the nanoparticles. There is a good agreement between our numerical results and the data obtained experimentally for the conductivity of AlN-polyimide nanocomposite. Our results also demonstrate that as the filling factor is increased the phonon conductivity also increases. Possible applications are new types of nanocomposites with variable thermal conductivity by adjusting the filling factor and refractive indices of the nanoparticle and host material. These nanocomposites may be important components in the fabrication of thermal nanodevices used for heating and cooling. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a reaction graph-based analysis method to study the mathematical structure and dynamical behavior of thin-film deposition reaction network models. Using this approach, we identify reaction network invariants and determine the chemical significance of these conserved modes for thin-film deposition reaction mechanisms. Furthermore, the species-reaction graphs can be used to distinguish “proper” from problematic reaction networks during the initial stages of reaction kinetic modeling studies. Results are presented in the context of a titania deposition process where the transition from atomic layer deposition to chemical vapor deposition growth modes is observed. [ABSTRACT FROM AUTHOR]

Neutron reflectivity (NR) was used to study the sorption of Eu(III) by graphene oxide (GO) films exposed to ethanol solution of EuCl3. Most of the earlier sorption studies have been performed using GO dispersed in solution. In contrast, layered structure of GO films imposes limitations for penetration of ions between individual sheets. The analysis of NR data recorded before and after sorption under vacuum demonstrates an increase of GO film thickness due to sorption by 35–40%. The characterization of chemical state of Eu(III) sorbed by GO films by X‐ray absorption near‐edge structure (XANES) in high‐energy resolution fluorescence detection (HERFD) method at the Eu L3 edge reveals that it remains the same as in anhydrous EuCl3. Analysis of all collected data including reference experiments with bulk GO samples allows to conclude that EuCl3 penetrates into GO interlayers with ethanol solution and remains trapped in interlayers after evaporation of ethanol. Sorption of EuCl3 results in nearly complete amorphization of film and likely formation of voids, thus making NR models based on specific volume of unit cell not valid for quantitative evaluation of Eu sorption. Limitations of NR method must be taken into account in future studies of sorption by thin films. [ABSTRACT FROM AUTHOR]

We report on single walled carbon nanotubes (SWCNTs) used as a filler material for polycarbonate (PC) composites in this paper. Thin flexible composite films were prepared by solvent casting with a viscous dispersion of SWCNTs in a polymer matrix. The interaction of SWCNTs with PC was studied by Raman spectroscopy. Our investigations focus on the electrical conductivity and thermopower of the carbon nanotube network formed within the matrix. In this paper, we demonstrate that the incorporation of carbon nanotubes in the polymer composite profoundly modifies the electrical properties of the polymer composite in proportion with the SWCNT concentration. Although, the electrical conductivity of the composite increases by 16 orders of magnitude upon adding 1 wt% of SWCNTs, the Seebeck coefficient, which characterizes the thermoelectric properties, appears to be dominated by the type of polymer matrix and decreased slightly throughout the tested filler loading. A reasonable Seebeck coefficient of 65 µV K−1 was determined for these SWCNT composite films and, thus, suggests that thermoelectric power generation would be a good application for them. We also demonstrated that both the electrical conductivity and the Seebeck coefficient of SWCNTs embedded in a polymer can be efficiently modified by means of chemical treatments. In this way, flexible composite films exhibiting positive and negative Seebeck coefficients were fabricated. Assembling these films into a sandwich structure with alternating p/n junctions should produce a higher potential difference when a temperature gradient is applied across a multilayer thermoelectric device. [ABSTRACT FROM AUTHOR]

A basic understanding of the physical composition of historic works of art, such as Old Master paintings, is essential for their long-term preservation. Such a broad understanding has largely been obtained over the last fifty years. However, a more sophisticated understanding of paintings' complex structures can also provide evidence of their modes of production. Such research can offer insights into historic technologies, of which surviving paintings are some of the finest products. This paper is an overview that uses a few examples to illustrate the sophisticated scientific and technological infrastructures that supported the creation of European art up to the 17th century. It briefly indicates how knowledge about material behaviour was transmitted and then lost. It treats great paintings as engineered structures made to the most exacting specifications and suggests that the physical nature of artworks offers researchers significant challenges. [ABSTRACT FROM AUTHOR]

This paper presents the results of the high pressure (up to 7 GPa) effect on the diluted magnetic semiconductor (DMS) CdGeAs2: Mn with x = 0.06-030. The normal R0 and anomalous RS portions of the Hall coefficients have been determined from the magnetic field dependencies of the Hall resistance. Pressure ranges related to the anomalies of the electric and magnetic properties have been found and studied. It has been shown that structural phase transitions are observed on the baric dependencies and their transition point shifts depending on the Mn content. The first- and second-order phase transitions (ferromagnetic-paramagnetic and paramagnetic-paramagnetic) have been identified on the magnetic susceptibility dependence in the pressure areas of P > 1.3 GPa and P ≈ 4 GPa which can be explained by occurrence of the second phase of MnAs in the basic structure of CdGeAs2. Positive (PMR) and negative magnetoresistance (NMR) induced by high pressure also takes place in all the compounds studied. [ABSTRACT FROM AUTHOR]

It has been recently shown that the addition of Ga to Lu3Al5O12 garnet (LuAG) removes the electron trapping associated with cation antisite defects. In this paper, we show via atomic scale simulations that the replacement of Al with Ga in LuAG actually lowers the energy of the antisite disorder process. Thus, we predict that Ga additions will lead to an increase of the antisite defect concentration and, in the absence of the electronic structure changes, would actually degrade the performance of the material. Since there are two crystallographically distinct Al sites in the garnet structure, we not only present results for complete replacement of Al with Ga, but also partial replacement for 40% (on 16a) and 60% (on 24d) of the Al with Ga. Our results support the explanation for Ga-doping leading to improvement in garnet scintillator performance that relies on variations of the electronic structure rather than reduction of the antisite defect concentration. [ABSTRACT FROM AUTHOR]

The paper studies radiation-induced modification of energetic spectra of excitons in CdTe quantum dots (QDs) in a (Cd, Mn)Te matrix. Exciton levels in such system are very sensitive to the changes in Mn concentration due to the exchange interaction between magnetic Mn ions and charge carriers (the giant splitting effect). Radiation-enhanced diffusion causes Mn penetration into the QD that leads to the changes in the exciton level energy. We found the spatial distribution of Mn ions for different durations of the irradiation and performed quantum calculations of the energy of exciton states with the obtained Mn concentration profiles. The dependences of the position of the exciton levels and the splitting between the energy of exciton states with σ+ and σ- polarizations on the irradiation parameters and the QD's radius have been investigated. The calculations show that the irradiation causes a large shift of exciton levels. The splitting between levels with σ+ and σ- polarizations may be increased in the order of value due to the irradiation. The radiation effects are stronger for QD with smaller radius. [ABSTRACT FROM AUTHOR]

In this paper, we report on the diameter distribution of boron-doped single-walled carbon nanotubes grown from triethyl borate with high vacuum chemical vapor deposition, using multi-frequency Raman resonance spectroscopy. The nanotube yield is higher than in previously reported material produced with the same method. Our results suggest that the amount of as-grown material and the range of diameters are directly correlated with feedstock used in the synthesis. The ID/ IG ratio shows that the morphology of the samples is critically affected by the temperature. The population of diameters in the optimal conditions shows a Poisson distribution with a mean value at ∼1.15 nm. [ABSTRACT FROM AUTHOR]

With the adsorption of larger molecules being increasingly tackled by surface scientists, the aspect of chirality often plays a role. This paper gives a topical review of molecular chirality at surfaces and gives a phenomenological overview of different aspects of adsorption and self-assembly of chiral and prochiral molecules and the principles of mirror-symmetry breaking at a surface. After a brief introduction into the history of molecular chirality and the important role it played for understanding the spatial structure of molecules, definitions of chirality are presented. Topics treated here are principle ways to create single chiral adsorbates, chiral ensembles, and monolayers by achiral molecules, adsorption of intrinsically chiral molecules at achiral and chiral surfaces, long-range symmetry breaking in two-dimensional (2D) crystals due to additional chiral bias, chiral restructuring of solid surfaces under the influence of chiral molecules, switching the handedness of adsorbates, and chirality at the liquid/air interface. An outlook onto further potential research directions and recommendations for further reading, including nonsurface-related sources of chiral topics completes this paper. [ABSTRACT FROM AUTHOR]

We formulate a general method to analyze hybridization modes in metamaterials by employing electrical circuit models. By rewriting circuit equations for coupled inductor-capacitor circuit networks in the bra-ket notation, we show that there exists a good analogy between circuit models and quantum tight-binding models in solid-state physics. Our picture is also applicable to transmission systems that do not have tightly bound eigenmodes. This analogy enables the synthesis of various electromagnetic metamaterials having dispersion relations similar to those for electrons in solids and consequently allows the systematic construction of metamaterials with desired characteristics. In this paper, we focus on the formation of flat bands in metamaterials with specific symmetries. The flat band, which corresponds to a slow group velocity of light or a heavy photon, is useful in designing functional metamaterials. [ABSTRACT FROM AUTHOR]

In the nearly 45 years since Stan Ovshinsky's original publication [Phys. Rev. Lett. 21, 1450 (1968)] announcing the discovery of electric-field-induced threshold switching in chalcogenide alloy semiconductor glass thin films, the field of amorphous semiconductor physics has developed remarkably. Many commercial applications of these materials have been developed, including X-ray image intensifiers, photocopier photoreceptors, and optical and electrical phase change memory devices. Despite these developments, a universally agreed upon, comprehensive model for the Ovshinsky Effect threshold switch still has not emerged. This paper is a brief review of the present state of understanding of this fascinating solid state physics phenomenon. [ABSTRACT FROM AUTHOR]

Phase-change materials are of intense research interest due mainly to their use in phase-change memory (PCM) devices that are emerging as a promising technology for future non-volatile, solid-state, electrical storage. Electrically driven transitions from the amorphous to the crystalline phase in such devices exhibit characteristic threshold switching. Several alternative electronic explanations for the origins of this characteristic behaviour have been put forward, for example Poole-Frenkel effects, delocalisation of tail states, field emission processes and space charge limited currents [for a full discussion, see Radielli et al., J. Appl. Phys. 103, 111101 (2008) and Simon et al., MRS Proc. 1251, H01-H011 (2010)]. However, an alternative to these conventional electronic models of threshold switching is based on electric field induced lowering of the system free energy, leading to the field induced nucleation of conducting crystal filaments. In this paper we investigate this alternative view. We present a detailed kinetics study of crystallisation in the presence of an electric field for the phase-change material Ge2Sb2Te5. We derive quantitative crystallisation maps to show the effects of both temperature and electric field on crystallisation and we identify field ranges and parameter values where the electric field might play a significant role. Then we carry out physically realistic simulations of the threshold switching process in typical phase-change device structures, both with and without electric field dependent energy contributions to the system free energy. Our results show that threshold switching can be obtained by a mechanism driven purely by electric field induced nucleation, but the fields so required are large, of the order of 300 MV m−1, and significantly larger than the experimentally measured threshold fields. [ABSTRACT FROM AUTHOR]

The present paper reports on our recent achievements including the photoalignment achieved of liquid crystals (LCs) using amorphous chalcogenide semiconductors (AChS) glassy films and the creation of optically addressed spatial light modulators (OASLMs). The photoalignment in this case is based on the phenomenon of photoinduced anisotropy, essentially found to be efficient in the nano-dimentional (ND, <50 nm) AChS films while the OASLM action is based on their photosensitivity. [ABSTRACT FROM AUTHOR]

Velocity undershoot in zinc blende (ZB) and wurtzite (WZ) InN is investigated by ensemble Monte Carlo (EMC) calculation. The results show that velocity undershoot arises from the relatively long energy relaxation time compared with momentum. Monte Carlo transport simulations over wide range of electric fields is presented in the paper. The results show that velocity undershoot impacts the electron transport greatly, compared with velocity overshoot, when the electric field changes quickly with time and space. A comparison study between WZ and ZB InN shows that WZ InN has more advantages in device applications due to its excellent electron transport properties. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic behavior of hexagonal rare-earth diboride RB2 are studied using ab initio density-functional theory in the DFT + U approach. The effect of the spin-orbit coupling is also investigated and it is found to be a necessary requirement for the accurate description of the magnetic moment. In this paper, we study the magnetic phase stability of RB2 compounds; the band structure and the density of state (DOS) results prove that the coulomb potential and the spin-orbit interaction are keys factors to understand the magnetic properties of these series of materials. In addition, we also explain the behavior of a chemical bond of RB2 compounds through the analysis of the DOS and of the charge density. [ABSTRACT FROM AUTHOR]

Previously, a sandwich structure in which the Poisson ratios of the core and facesheets possess opposite signs has been shown to exhibit overall conventional and auxetic behavior depending on the loading mode - axial loading or bending - for an intermediate range of relative core thickness. In addition to these two loading modes, sandwich structures in aerospace applications encounter torsional loads. In this paper, the effective Poisson's ratio for torsional loading is proposed. Results show that, depending on the loading mode and the relative core thickness, there can be up to four levels of overall auxeticity, namely (i) full auxeticity (FA) if the structure behaves as an auxetic structure under all three modes of loading, (ii) high auxeticity (HA) if the structure behaves as an auxetic structure in two of the loading modes, (iii) low auxeticity (LA) if the structure behaves as an auxetic structure in only one of the loading modes, and (iv) no auxeticity (NA) if the structure behaves as a conventional structure under all of the three loading modes. These results indicate that by selecting the Poisson's ratios and the thickness of the cores and facesheets, the sandwich structure can be made to respond differently under different external loading conditions. [ABSTRACT FROM AUTHOR]

Physical properties of a nano structure are dramatically affected by its surface reconstruction and quantum confinement. For a core/shell structured nanowire (NW), the core/shell interface also plays a key role. The effects induced solely by the surface reconstruction can be estimated by using a reference model in which the dangling bonds on the NW's surface are saturated by a number of pseudo hydrogen atoms with fractional charge. We present in this paper a first principles study on the role of the surface reconstruction in several series of gallium nitride/aluminum nitride core/shell structured NWs. We also show that the model of pseudo hydrogen atoms does suppress the effects of surface reconstruction on both structural and electronic properties of the NWs, thus the model can be used to estimate the role of surface reconstruction. [ABSTRACT FROM AUTHOR]

In our previous paper [Phys. Rev. B 89, 165430 (2014)] we have found that in graphene, in distinction to the four occupied bands, which can be described by the simple tight-binding model (TBM) with four atomic orbitals per atom, the two lowest lying at the [ABSTRACT FROM AUTHOR]

GaN/AlN is a promising material system for the development of an ultrafast intersubband technology operating at telecommunication wavelengths, thanks to the large conduction band offset and sub-picosecond intraband relaxation time. In this paper, we explore short wavelength infrared intersubband transitions occurring in the conduction band of GaN/AlN heterostructures in both planar and nanowire (NW) geometries. We study the effect of Si and Ge doping in both quantum wells and NW heterostructures using the same active region thickness and dopant concentration. We demonstrate that both Si and Ge are suitable dopant candidates at a concentration of mid-1019 cm−3 for the fabrication of intersubband devices based on planar and NW heterostructures. [ABSTRACT FROM AUTHOR]

Interaction of high energy electrons with spacecraft materials, such as polyimide (PI, Kapton®), is known to cause their physical degradation. In this paper, we investigated chemical and optical changes in Kapton® during and after irradiation with high energy (90 keV) electrons. Several complimentary characterization techniques were utilized to qualify and quantify radiation induced property changes in the material, including directional-hemispherical reflectance (DHR) coupled with Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR), and the surface potential decay method. It was found that the conductivity of radiation-damaged PI is significantly increased compared to that of the pristine material. This change is attributed to the creation of radicals during irradiation, which could play a critical role in the transport of electrons through the bulk of the damaged material. Excessive radicals are likely originating from a radiation-induced breakage of phenyl rings and/or ether bridges forming a metastable carbonyl. [ABSTRACT FROM AUTHOR]

The present paper examines the influence of a nonlinear relationship between the local oxygen-vacancy concentration and the local resistivity on resistive switching effects in complex oxides. The continuity equation has been used as a model for the motion of oxygen vacancies when a periodic time-dependent electrical current is applied. The question of endurance of the switching cycles is discussed. It is found that nonlinearity of the resistivity-concentration dependence enhances the endurance. [ABSTRACT FROM AUTHOR]

Most of the detailed studies have been directed toward III-V semiconductors based type-I and type-II heterostructures. But, the transformations between type-I and type-II heterostructures have not been well studied so far. In this paper, it is reported that the proper doping in a specific region of well known type-II InAs/AlSb nanoscale heterostructure can transforms it into the type-I heterostructure. Moreover, this doping also improves the interband optical gain of the transformed type-I heterostructure as compared to the original type-II structure. The eight band k · p model based self-consistent calculations have been performed to calculate the band structure and the carrier's wavefunctions. On the basis of outcomes from the calculations, it is reported that the optimized interband optical gain (within TM mode) of the transformed heterostructure is almost ten times as compared to the other heterostructures operating in mid-infrared (MIR) region. Thus, the transformed heterostructure may be an important heterostructure made of InAs/AlSb material system for MIR wavelength region. Hence, the proper doping can transform type-II heterostructure made of an optically inactive material system into type-I structure, a very efficient optically active heterostructure (referred to as gain structure), which can provide technologically important MIR wavelength range. [ABSTRACT FROM AUTHOR]

authoren This paper investigates the effects of an intense laser field and electric field on the optical properties of quantum well represented by Morse potential. The non-resonant, high-frequency intense laser effects upon the system are treated within the framework of non-perturbative approach, modifying the confinement potential associated to the heterostructure. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. The results for a typical GaAs quantum well correspond to several configurations of the structural parameter, the strengths of the intense laser radiation, and the static electric field. Numerical results reveal the striking influence of the external fields on the magnitude and resonant peak energy positions of the optical absorption coefficients and refractive index changes. Besides, the control of intersubband optical transitions by the structure parameter seems feasible. [ABSTRACT FROM AUTHOR]

The recent developments of electron quantum optics in quantum Hall edge channels have given us new ways to probe the behavior of electrons in quantum conductors. It has brought new quantities called electronic coherences under the spotlight. In this paper, we explore the relations between electron quantum optics and signal processing through a global review of the various methods for accessing single- and two-electron coherences in electron quantum optics. We interpret electron quantum optics interference experiments as analog signal processing, converting quantum signals into experimentally observable quantities such as current averages and correlations. This point of view also gives us a procedure to obtain quantum information quantities from electron quantum optics coherences. We illustrate these ideas by discussing two-mode entanglement in electron quantum optics. We also sketch how signal processing ideas may open new perspectives for representing electronic coherences in quantum conductors and understand the properties of the underlying many-body electronic state. [ABSTRACT FROM AUTHOR]

Recently, a fabricated two-dimensional (2D) Bi2Te3 single quintuple layer (BiTe-1QL) has demonstrated great potential in the application of electronics. However, detailed research of the deformation effect on this material is still lacking. In this paper, the deformation effects on the crystal lattice and electronic band structure of BiTe-1QL were studied by first-principle methods. It was found that tensile and compressive deformations in the x- or y-direction on BiTe-1QL caused both the movements of Bi and Te1 atomic layers along the x-direction, which can be explained by minimizing the deformation-introduced symmetry breaking. The position of the valence-band maximum of BiTe-1QL experienced a shift among critical points near the band edge with the applied strain. Moreover, −8% deformation in the x-direction causes the BiTe-1QL be a direct-bandgap semiconductor. The theoretical investigations clarify the structural and electronic properties of quasi-2D BiTe-1QL, and pave the way for its potential application in electronics. [ABSTRACT FROM AUTHOR]

The possibility of combining both optical transparency and high electrical conductivity in the same material makes transparent conducting oxides one of the most sought after materials in transparent electronics. This paper presents the investigations done on the conductivity mechanisms of n-type transparent conducting silver indium oxide thin films in different temperature ranges varying from 6 to 333 K. X-ray diffraction indicates the films to be amorphous, and the morphology of the films from scanning electron microscopy and atomic force microscopy shows agglomerations with average particle size ∼30 nm. X-ray photoelectron spectroscopy and energy-dispersive analysis of X-rays establish the films to be nearly stoichiometric with In/Ag at.% ratio in the range 1.1-1.2. The transmittance percentage obtained from optical transmittance and absorbance spectra is moderately high and the bandgap energy of the thin films is ∼3.5 eV. Transport parameters, such as carrier mobility ∼103 cm2/V s and carrier concentration ∼1018/cm3, are elucidated from Hall and thermopower data. [ABSTRACT FROM AUTHOR]