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Helical arrangements are very common both in nature and in artificial structures. In this paper, an analysis of a prismatic composite bar is presented. The cross-sectional shape of the bar is described by a regular polygon. The composite is built of two homogeneous isotropic materials characterised by different Poisson's ratios one of which can be negative. Spatial distribution of materials in the composite is based on helical shape. Both materials are connected with the use of a transition zone of assumed width. The bar is subjected to torsional loading and its behavior is investigated by means of FEM method. Both material properties and the parameters of helical shape are investigated and the result of numerical analysis is presented. [ABSTRACT FROM AUTHOR]

The present paper concerns two methods: IMD (isotropic material design) and YMD (Young modulus material design) concerning Pareto optimal distributions of the material and its isotropic properties. The merit function is the weighted sum of compliances corresponding to n independent loading conditions. The unit cost of the design is assumed as equal to the trace of the elastic moduli tensor C. In the IMD method, the design variables are the bulk and shear moduli. In the YMD method, the Poisson ratio is assumed as given, possibly non-uniformly distributed in the design domain, the Young modulus being the only design variable. Both the methods reduce to the auxiliary minimization problem involving statically admissible stress fields corresponding to the subsequent loading conditions. The integrand is expressed by a norm of the collection of these stresses, hence has linear growth. The numerical method proposed refers to the primal formulation: it is based on piece-wise polynomial approximation of the set of statically admissible stresses. The exemplary Pareto optimal solutions show that admitting negative values of Poisson's ratio may contribute to a decrease of the total compliances. [ABSTRACT FROM AUTHOR]

The contact problem between two bodies: plate and semi-cylindrical bar is studied in this paper. The analysis concerns the contact pressure distribution along the contact region, as well as the deflection of the plate. Furthermore, the case of a composite plate covered with the auxetic layer is also considered. The influence of the Poisson's ratio of the layer on the behavior of the plate is studied. The contact pressure distribution along the contact area is analyzed using finite element analysis. [ABSTRACT FROM AUTHOR]

We propose in this paper analytical and numerical models that describe the in-plane uniaxial elastic properties (Young's moduli and Poisson's ratios) of a honeycomb structure with curved walls. We perform a parametric analysis of the mechanical performance of this honeycomb also by taking into account the different types of deformations acting inside the cell walls. The curved wall honeycomb possesses higher magnitudes of the Poisson's ratio ν12 in the auxetic configuration compared to classical center symmetric configuration with straight cell wall. The presence of the curvature also allows creating configurations with positive Poisson's ratio even for negative internal cell angles, and makes this honeycomb design attractive for mechanical tailoring. [ABSTRACT FROM AUTHOR]

The self-assembly of simple building blocks to complex superstructures is significant for engineering materials with enhanced and synergistic properties. In this work, black phosphorus quantum dots (BPQDs) showing quantum confinement effects were prepared. The BPQDs are hierarchically self-assembled to paper-like membranes as large as in the centimeter range in two main stages: aggregation driven by Brownian motions due to minimization of the surface free energy and an interfacial self-concentrating process by capillary interactions. Moreover, from the absorption band edges, the band gap of BPQDs is estimated to be about 1.3 eV, which is evidently larger than the 0.8 eV of bulk black phosphorus. The remarkable extension of the band gap indicates the quantum confinement effects of the electrons. The Raman spectrum of BPQDs shows that all the phonon modes shift to lower frequencies and broaden dramatically compared with that of the bulk BP, which suggests phonon confinement effects. [ABSTRACT FROM AUTHOR]

In this paper, we introduce methods of constructing structures with rigid sliding units that exhibit auxetic behavior, namely, have negative Poisson's ratio. First, we illustrate how we can construct 2-dimensional (2D) auxetic structures with bow-tie shaped rigid sliding hexagonal units. Next, we show that we can construct 3-dimensional (3D) auxetic structures by arranging hourglass shaped rigid sliding units in regular triangular configuration or in regular square configuration. Also, we show, through theoretical and numerical analysis, that these structures indeed exhibit auxetic behaviors. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including the Poisson's ratio, auxetics and textile fabrics.

A sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff layers to a lightweight but thick core. Composites analyzed in this paper consist of two different materials: auxetic and structural steel. The optimization criterion is minimum compliance for the load case where the frame's top boundary is downward loaded. Outer layers are made of steel while the middle layer is two-phase solid material composite. Only the middle layer is optimized by means of minimization of the objective function defined as the internal strain energy. In the first part of this paper we study the application of the solid isotropic material with penalization (SIMP) model to find the optimal distribution of a given amount of materials in sandwich-structured composite. In the second part we propose a multilayered composite structure in which internal layers surfaces are wavy. In both cases the total energy strain is analyzed. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue including the auxetics, conventional foams, and negative Poisson's ratio.

The 80 years since Zachariasen's famous paper, 20 years before Stephen Elliott was born, on the random network theory of glass structure have seen remarkable progress in our understanding of the structure of glassy materials through the construction of models and comparison with experiment. In the early days, models were hand‐built with plastic units and had free boundary conditions. Today, very much larger computer models have periodic boundary conditions. We recount the progress that has been made in the last 80 years, and discuss the current agreement between models and experiments that remains imperfect. Stephen Elliott's work on medium range order forms an important part of the history of this subject. [ABSTRACT FROM AUTHOR]

Materials with unusual mechanical properties can be potentially used as matrices to create high-performance lightweight composites. The appearance of materials with negative Poisson's ratio (auxetics), has led to the evaluation of auxetic composites for possible engineering applications. Because the experimental evaluation of composites with specific properties is expensive and time consuming, computational modelling and simulation provide efficient alternatives to predict the parameters of the composites. In this paper a finite element method was used to find the engineering constants (Young's modulus and Poisson's ratio) of auxetic composites consisting of concentric cylindrical inclusions made of combinations of auxetic and classic (non-auxetic) materials. It has been observed that not only the mechanical properties of the different composite phases influence the effective mechanical properties of the whole composite, but also the location of the same material phases do matter. [ABSTRACT FROM AUTHOR]

This special issue of I physica status solidi (b) i contains 21 original papers, which are based on presentations at the Compound Semiconductor Week (CSW) 2019 held in Nara, Japan, May 19-23, 2019. The CSW2019 is a joint venue for the 46th International Symposium on Compound Semiconductors (ISCS) and the 31st International Conference on Indium Phosphide and Related Materials (IPRM). CSW2019 covered a wide range of recent progress in material sciences, fabrication technologies, and physics of compound semiconductors. [Extracted from the article]

In the paper, the luminescence processes in CeO2 nanocrystals have been investigated and several types of luminescent centers were revealed. For CeO2 nanocrystals treated in oxidation atmosphere two possible pathways of relaxation of the charge transfer excitation led to intrinsic charge transfer (CT) luminescence and luminescence of F0-centers. Treatment in reducing atmosphere leads to formation of additional luminescent centers formed by Ce3+ ions which charge is compensated by oxygen vacancies in first coordination sphere of Ce3+ ion. Shallow defects related to F+-centers present near edge of 4f0 band modify sufficiently the processes of excitation relaxation forming excitation traps that provide a series of trapping-retrapping acts during excitation lifetime. [ABSTRACT FROM AUTHOR]

Using hybrid density functional calculations, this paper systematically investigated the common defects in m-HfO2 and [ABSTRACT FROM AUTHOR]

Iron-gallium alloy (galfenol) is a body centered cubic (BCC) magnetostrictive alloy that, like many other BCC metals, is auxetic in the h110i{100} directions. For compositions of 12- 33 at.% gallium, Poisson ratio (n) values as low as 0.7 are observed along these directions in response to a uniaxial elastic force (tensile tests, resonant ultrasound spectroscopy, etc.). In 2014, Raghunath and Flatau first reported that galfenol also exhibits positive strain in both these directions when the uniaxial force applied along the h110i{100} directions is provided solely by a magnetic field, i.e., with no external mechanical/elastic force or stress being applied to the alloy [Raghunath and Flatau, IEEE Trans. Magn. 50(11), 1-4 (2014)]. The observed response is a result of the intrinsic, atomic-scale, bi-directionally coupled magnetoelastic properties of these alloys. In this paper, we advance the understanding of the intrinsic atomic-scale magnetoelastic coupling of the alloy that leads to the observed magnetoelastic auxetic-like behavior by presenting simulations developed based on density functional theory, which we show match the experimental findings and energy-based simulations. The elastic anisotropy and the electronic mechanisms that lead to magnetoelastic auxetic-like behavior in galfenol are discussed. [ABSTRACT FROM AUTHOR]

Negative stiffness elements (elements with direction of the force opposite to the direction of the deformation) are unstable as the energy is no longer positive definite. Nevertheless, materials and structures with negative stiffness elements can exist when the element negative energy is compensated by the energy of the rest of the system or an encompassing system that provide stabilisation. In this paper, we study stability of twodimensional square packing discrete mass-spring systems with some spring stiffnesses being negative. Each mass (particle) in the system has three degrees of freedom. The particles are connected by normal, shear and rotational springs to simulate all possible elastic interactions between the masses. The stability is investigated by considering three simple problems: (i) a system consisting of only one particle, (ii) a "channel" of two particles, (iii) two-by-two and three-by-three systems of particles. The particles are connected to rigid external boundary. We found that two-dimensional square packing systems with fixed boundary particles consisting of positive and negative stiffness springs can be stable when the total number of negative stiffness springs does not exceed the total number of degrees of freedom of the system. This necessary condition is also generalised to three-dimensional cubic packing systems. The presence of negative stiffness springs leads to a decrease in the eigenfrequencies: the smallest eigenfrequency becomes zero when the absolute value of the negative stiffness spring reaches its critical value. [ABSTRACT FROM AUTHOR]

The torsion of a prismatic beam has been a classic problem of structural mechanics since the famous works of Saint-Venant. In this paper, an analysis is extended on a composite beam with elliptical cross-section. We consider a beam in which the elliptical cross-sectionis split into sectors inwhichtwo materials, one of which is auxetic, are distributed alternately. The influence of auxetic phase on the total elastic strain energy is analyzed as well as geometrical parameters representing both the shape of the cross-section, and the arrangements of sectors. An unexpected behavior of a beam with strong auxetic phase is presented as, in the case of selected parameters, the beam with elliptical crosssection is more rigid than the beam with a circular one. [ABSTRACT FROM AUTHOR]

This special issue "Interdisciplinary Research in Materials Science" contains a culmination of FRIMS research activities to date as well as a selection of the papers presented at the above symposium. The Frontier Research Institute for Materials Science (FRIMS) was established in 2016 as a Center of Excellence at Nagoya Institute of Technology (NITech). In this symposium that 116 scientists and students attended, FRIMS members presented their research results as the culmination of the last six years of research at FRIMS. [Extracted from the article]

The paper describes the magnetoelectric (ME) effect in a gradient laminate structure consisting of a LiNbO3/Ni/metglas multilayer based on a bidomain lithium niobate single crystal with a Y + 128° cut. The main purpose of the work is to obtain a self‐biased structure. A theoretical and experimental study is conducted to determine the optimal thickness of the Ni film for creating such a structure. The application of self‐biased structures based on gradient bidomain crystals in ME devices can significantly reduce their weight and dimensions as well as improve their electrical characteristics. [ABSTRACT FROM AUTHOR]

Herein, a ternary system of TeO2–ZnO–Na2O (TZN) with competitive roles of covalent Zn–O and ionic Na–O bonds in tellurite glassy network is examined for high‐temperature in situ X‐ray diffraction (XRD) and Raman spectroscopy. TZN glasses are doped with Nd2O3 and the effects of Nd doping on the crystallization of glasses are also written. In situ high‐temperature XRD permits the assignment of each of the differential scanning calorimetry (DSC) crystallization peaks (the first crystallization peak (Tc1) is related to sodium‐based crystalline phases, while the second crystallization peak (Tc2) is correlated with tellurium‐/zinc‐based crystalline phases). The study of in situ high‐temperature Raman spectroscopy shows that Tc1 shows γ‐TeO2 crystallized phase‐like peaks while Tc2 crystallization has more α‐TeO2‐crystallized phase‐like peaks. Comparison at the same temperature (430 °C) permits a first understanding of the structural changes of the glasses in terms of the evolution first to α‐TeO2, ZnO, ZnTeO3, and Zn2Te3O8 crystalline phases compared with Na10Zn4O9 phase. The ZnTeO3 and Zn2Te3O8 crystallization evolution is also compared between the Nd‐doped and nondoped glasses, which gives more insight into the tellurite glass structures. [ABSTRACT FROM AUTHOR]

The superconductor to normal metal phase transition induced by the in-plane magnetic field is studied in free-standing Pb(111) nanofilms. In the considered structures, the energy quantization induced by the confinement leads to the thickness-dependent oscillations of the critical field (the so-called 'shape resonances'). In this paper, we examine the influence of the orbital effect on the in-plane critical magnetic field in nanofilms. We demonstrate that the orbital term suppresses the critical field and reduces the amplitude of the thickness-dependent critical field oscillations. Moreover, due to the orbital effect, the slope [ABSTRACT FROM AUTHOR]

The paper moves from a technological process developed in previous works to produce chiral honeycombs made of thin composite laminates. Such approach is applied in this work to manufacture the morphing ribs for a variable camber wing-box. The specifications for such components are obtained by developing a finite element model of a demonstrator, which is designed taking into account aeroelastic performances, structural, and technological issues. In the first part of the paper, the design of such a demonstrator is presented and the role of composite chiral ribs with auxetic behavior is outlined. Production, testing, and numerical studies of manufacturing trials are performed to assess the technological process applied to small-sized chiral units made of different materials, to investigate their mechanical properties, and to validate a numerical approach for design and analysis. A complete chiral composite rib is then produced and tests are carried out to verify the overall structural response and to validate the numerical approach. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including the dilational materials, the auxetic lattices and the polymorph of silica.

In this paper the history of ellipsometry is described with emphasis on the 19th century. The understanding of polarized light and its interaction with matter is tightly connected to the development of the electromagnetic theory and thus optics. While some effects of polarized light were already known to the Vikings, a reasonable starting is the work of É. Malus, who first defined light polarization. First instruments were likely built in the first half of the 19th century. However, ellipsometry became an optical characterization technique only after the optical response was formulated within the Maxwell equations at the beginning of the 20th century. In this paper the history of ellipsometry is described with emphasis on the 19th century. The understanding of polarized light and its interaction with matter is tightly connected to the development of the electromagnetic theory and thus optics. After É. Malus first defined light polarization, the first instruments were likely built in the first half of the 19th century. [ABSTRACT FROM AUTHOR]

This paper describes a theoretical model which takes into account charge injection by thermally stimulated hopping (HP), as proposed by Arkhipov, and Fowler-Nordheim tunneling (FNT), for steady-state response of a metal/organic semiconductor hetero-junction in a polymeric light-emitting diode (PLED). The reason for combining these two models is that both injection processes are usually observed in metal/organic semiconductor hetero-junctions. The present model takes into account the material disorder and the escape probability introduced by Arkhipov et al. for both injection processes. The proposed model was tested with experimental results obtained from a PLED ITO/MEH-PPV/Al. Analysis of the experimental results took into account the well-known characteristic of the MEH-PPV in which the charge transport is dominated by holes. Because of this, the electronic current component is assumed to be negligible compared to that for holes. Considering that the device is composed of two different metal/semiconductor junctions, that is, ITO/MEH-PPV and MEH-PPV/Al, the heights of the different potential barriers could be determined. The injection potential barrier, for holes, was determined as 0.4 eV for direct bias (ITO as anode), and as 0.8 eV for reverse bias (aluminum as anode). It was verified that the FNT process is preferable to the HP process in the following situations: (i) high interface potential barrier, (ii) high electric field, and (iii) low temperatures. On the other hand, that is, for a low interface potential barrier, low electric field and high temperatures, the HP process is dominant. With the application of the proposed model, which combines HP and FNT, it was possible to fit the current versus voltage curves for the studied PLED in a wide range of temperatures and electric fields, for direct and reverse bias. Additionally, it was shown that the condition where the HP injection probability is neglected, the non-linearity in FNT plots [ABSTRACT FROM AUTHOR]

In this paper, we propose a model that combines a Landau free energy part and a micromagnetic free energy part aimed at describing a magnetostructural multiferroic.We show that in the limit of high-elastic anisotropy and strong magnetostructural interplay, the model is able to reproduce characteristic strain and magnetization configurations typical of magnetic shapememory materials. For low-elastic anisotropy, in the presence of disorder arising from compositional fluctuations giving rise to a distribution of local transition temperatures, the model is able to reproduce strain glass behaviour. In this case, the temperature dependence of the magnetization measured after zero magnetic field cooling deviates from the magnetization measured after magnetic field cooling protocol, which proves that the strain glass behaviour induces non-ergodicity in the magnetic degrees of freedom as well. [ABSTRACT FROM AUTHOR]

The paper reviews the interplay of Rashba/Dresselhaus spin splittings in various two-dimensional systems made of zinc-blende III-V, wurtzite, and SiGe semiconductors. We discuss the symmetry aspects of the linear and cubic in electron wavevector spin splitting in heterostructures prepared on (001)-, (110)-, (111)-, (113)-, (112)-, and (013)- oriented substrates and address the requirements for suppression of spin relaxation and realization of the persistent spin helix state. In experimental part of the paper, we overview experimental results on the interplay of Rashba/Dresselhaus spin splittings probed by photogalvanic spectroscopy: The method based on the phenomenological equivalence of the linear-in-wavevector spin splitting and several photogalvanic phenomena. [ABSTRACT FROM AUTHOR]

This paper reports a development of bi-stretch auxetic woven fabrics by using non-auxetic yarns and weaving technology. The fabric structure is first designed based on a re-entrant hexagonal geometry by combination of loose weave and tight weave in a woven fabric structure, and then fabricated on a rapier weaving machine by using both non-elastic and elastic yarns. Two variations of the fabric are produced by using different elastic yarn arrangement in weft direction. The designed auxetic geometry is finally achieved after a washing process due to creation of non-uniform contraction or shrinkage profiles within the fabric structural unit cell. The testing results showed that the developed fabrics exhibit negative Poisson ratio effect in both weft and warp directions in a large range of tensile strain. [ABSTRACT FROM AUTHOR]

Materials and structures are exposed to simultaneous fluctuations in temperature, pressure, and moisture in the environment, which result in additional stresses and strains in addition to mechanical loadings. This paper develops the effective coefficient of thermal expansion (CTE), coefficient of moisture expansion (CME), and compressibility for the interconnected array of ring and sliding rod structures made from conventional materials, wherein conditions that lead to negative thermal expansion (NTE), negative moisture expansion (NME) and negative compressibility (NC) -- and hence the negative environmental expansion (NEE) -- are established. The above-mentioned coefficients shift toward negative values as the ratio of ring-to-rod expansivity increases. The established effective CTE, CME, and compressibility not only permit the requirements for NTE, NME, and NC to be ascertained, but also allow the less restrictive condition of zero environmental expansion to be implemented in the design of materials and structures, without requiring zero CTE, CME, and compressibility. [ABSTRACT FROM AUTHOR]

This paper reports a new type of auxetic yarn made with circular braiding technology to overcome the yarn slippage problem in the conventional helical auxetic yarn structure. Various auxetic yarn structures are firstly produced on a vertical circular braiding machine with 16 yarn carries by changing the number and arrangement of stiff yarn as well as diameter of elastic yarn and core yarn, and then tested under single and repeating tensile conditions. The results show that not only yarn slippage problem could be overcome in the newly developed auxetic yarn structure, but also an early activation and a higher magnitude of negative Poisson's ratio could be achieved. The results also show that all structural parameters including stiff yarn number and arrangement, core yarn, and elastic yarn diameter have an influence on the auxetic effect of the novel yarn structure. Since the new auxetic yarn is produced by using standard braiding manufacturing technique and conventional non-auxetic yarns, there are few technological barriers for its largescale manufacture for practical application. [ABSTRACT FROM AUTHOR]

This work describes the identification of the shear modulus of open cell polyurethane thermoformed auxetic foams from 3- and 4-point bending tests. The foams are incorporated in sandwich beams with carbon fibre/epoxy face skins, and benchmarked against similar sandwich structures made with the conventional counterpart open cell foam. Three types of beams are tested: one with auxetic foams, another type related to a conventional foam core with the same thickness of the auxetic porous materials, and a third type of beam consisting in conventional foam with a thickness corresponding to an iso-weight configuration to the auxetic specimen. The auxetic foam has a shear modulus 7% lower than the one of the bulk conventional specimens, but higher shear stresses at large deformations and a smoother strain stiffening response compared to the beams with the conventional thinner core. The paper also highlights the low shear wave speed of these auxetic foams compared to other porous polymers used in helmet and head protection applications, as well as potential uses of the quasi-zero-stiffness behavior here observed for the auxetic foam sandwich beam. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new numerical method to find the ground state energy of a given physical system within the Kohn–Sham density functional theory. The h‐adaptive finite element method is adopted for spatial discretization and implemented with matrix‐free operator evaluation. The ground state energy is found by performing unconstrained minimization with non‐orthogonal orbitals using the limited memory Broyden–Fletcher–Goldfarb–Shanno (BFGS) method. A geometric multigrid preconditioner is applied to improve the convergence. The clear advantage of the proposed approach is demonstrated on selected examples by comparing the performance to other methods such as preconditioned steepest descent minimization. The proposed method provides a solid framework toward O(N) complexity for the locally adaptive real‐space solution of density functional theory with finite elements. [ABSTRACT FROM AUTHOR]

Incubation of strain technology in the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) arena by developing heterostructure layers combined of Si and SiGe layers within the channel is employed widely. Development of a fully depleted novel device featuring a distinguished tri‐layer heterostructure channel consisting of mobility enriched double strained Si (s‐Si) layers sandwiching strained SiGe (s‐SiGe) in between has been the crux of this paper. The channel with s‐Si/s‐SiGe/s‐Si significantly enhances electron mobility in comparison to conventional device of s‐Si on relaxed SiGe channel, leading to improved device performance without implementing additional scaling. The tri‐layered channel and the conventional device are compared and eloquent drain current enhancement of 49% attained with minimal value of threshold voltage roll‐off with increased strain infusion within the channel region, which augments electron mobility in the s‐Si layers. Augmented maximum transconductance for sub‐50 nm channel length due to velocity overshoot enhancement of 119% in comparison to conventional device acquired lead to ≈25% decrease in threshold voltage by band structure lowering with the instigation of the strain technology in the short channel device attained. Hence, with higher carrier mobility and improved drive current double strained Si heterostructure on insulator (HOI) MOSFET device is designed and developed. [ABSTRACT FROM AUTHOR]

The paper, as the third in a series, presents the complete formulas for the crystal field splitting third moment of free ion states as functions of the relevant crystal field parameters in the case of the trigonal and hexagonal crystal fields. The additive structure of the expressions consists of 21 independent components for the trigonal symmetry, 12 for the hexagonal one and only 4 components for the ideal hexagonal coordination. The two scalar characteristics of the crystal field Hamiltonian HCF – the crystal field splitting second and third moments – enable us to verify the HCF parametrizations solely in an algebraic way. Such verification concerns the multipolar structure of the parametrizations as well as the signs of the crystal field parameters. Both the crystal field splitting moments can ensure us in what degree the comprehensive HCF parametrizations are adequate with respect to the individual ionic states of the electron configuration. As an example two chosen HCF parametrizations, one for the hexagonal system Nd3+:LaCl3 of the C3h symmetry, and the second for the trigonal system Tb3+:Y2O2S of the C3v symmetry are subjected to in depth analysis. The presented approach provides a critical insight into the crystal field parametrizations from a different point of view, i.e., omitting the conventional fitting procedure. After the extended verification the studied classical HCF parametrizations withstand, in principle, the test of time. [ABSTRACT FROM AUTHOR]

Recently, chalcopyrite compounds have been extensively studied as the absorber for solar cells. Inserting an intermediate band in the main band gap of the absorber has been proposed to exceed the Shockley–Queisser limit on single band solar cells. In this paper, the group‐IV elements Si, Ge, and Sn substituting at Al site in AgAlSe2 to form an intermediate band in the main band gap has been studied by first‐principles calculations. The half‐filled intermediate bands from the antibonding state of group‐IV s state and Se‐p state show delocalized characteristics and just shift from each other in Si, Ge, and Sn‐doped AgAlSe2. Based on the analysis on the position of the intermediate band and defect formation energy, Si‐doped AgAlSe2 has been excluded and Ge and Sn‐doped AgAlSe2 have been suggested as promising absorber for the intermediate band solar cell. A heterojunction based on CuAlTe2, AgAlSe2:Sn, and CdS has been proposed as a suitable device for intermediate band solar cells after considering the lattice mismatch and band alignment. [ABSTRACT FROM AUTHOR]

The deep level E3 is a commonly observed defect in bulk crystals and thin films of ZnO independently of the method of growth. Its chemical origin is still not finally understood. In this paper, previous research on the E3 level is reviewed and recent experimental results acquired by optical deep level transient spectroscopic (DLTS) methods are presented for the temperature range from 4 to 350 K, for photon energies between 0.25 and 4 eV, and for emission rates ranging from 10−3 to 104 s−1. The capture cross section of the optical transition of E3‐trapped electrons into the conduction band is described. Additionally, a second optical transition occurs for photon energies higher than 1 eV, which accounts for the lowering of the E3 DLTS signal at low temperatures under illumination. Further, it is unambiguously shown that the E3 defect can bind up to two electrons and that it has the properties of a negative‐U center. Photoluminescence measurements reveal that the E3 defect is directly connected to a radiative recombination channel at 2.09 eV. Further, electron paramagnetic resonance (EPR) measurements were performed with optical excitation in dependence on the temperature and photon energy. Interestingly, the temperature‐dependent EPR signal of V O + is similar to that of the photo‐ionization cross‐section of the E3 defect. These experimental findings are discussed in comparison with published EPR results and results obtained by first‐principle calculations of native point defects in ZnO. [ABSTRACT FROM AUTHOR]

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]

Molecular dynamics simulations is used to investigate the mechanical properties of three‐dimensional (3D) graphene under uniaxial tensile loading. The results show that the tensile deformation of 3D graphene exhibits size dependence along both armchair and zigzag directions. By analyzing the atomic von Mises stress and structural evolution, compared to the 3D graphene with smaller in‐plane cell size, the larger 3D graphene exhibits two typical deformation events, i.e., transverse structural shrinkage and axial elastic deformation. The fracture stress of 3D graphene is much smaller than that of 2D graphene because of its porous structure. However, the fracture strain of 3D graphene is larger than that of 2D graphene due to the larger transverse structural shrinkage along both armchair and zigzag directions. Effects of temperature, strain rate, and thickness of 3D graphene on the tensile behavior is investigated. The simulation results indicate that the fracture stress and the fracture strain decrease with increasing temperature and with decreasing strain rate. However, the fracture stress and the fracture strain is not dependent on the thickness of 3D graphene. The results in this paper suggest that 3D graphene with higher stretchability tunable by in‐plane cell size can be promising multifunctional materials for many engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigations of the electronic structure and optical properties of the GdSn1.1Ge0.9 and TbSn1.1Ge0.9 compounds. Employing the local spin density approximation accounting for strong electronic correlations in the 4f‐shell of rare‐earth ions, that is the LSDA + U method, we carry out the spin‐polarized calculations of band structure. In a broad range of wavelengths the optical constants of the compounds are measured by an ellipsometry method. A number of spectral and electronic characteristics are calculated. Based on the calculated density of states the structural features of optical conductivity for the investigated intermetallic compounds are interpreted in the region of interband absorption. [ABSTRACT FROM AUTHOR]

Twenty years ago Heinz Bässler published in this journal the seminal review article on charge transport in disordered organic semiconductors [Phys. Status Solidi B 175, 15 (1993)], which has become one of the most popular references in this research field. Thanks to this paper, our understanding of charge transport in disordered organic materials has been essentially improved in the past two decades. New theoretical methods have been developed and new results on various phenomena related to charge transport in disordered organic materials have been obtained. The aim of the current review is to present these new theoretical methods and to highlight the most essential results obtained in their framework. While theoretical consideration in the article by Bässler was based on computer simulations, particular attention in the current review is given to the development of analytical theories. Dependences of charge carrier mobility and diffusivity on temperature, electric field, carrier concentration and on material and sample parameters are discussed in detail. Schematic behaviour of charge carriers within the Gaussian density of states (DOS) [ABSTRACT FROM AUTHOR]

This paper reports an experimental investigation on the effect of auxeticity towards impact loads. Both conventional and auxetic polyurethane (PU) foams were subjected to impact drop tests, and the damaged surfaces were visually inspected. Although it is known that auxetic materials resist indentation due to densification along the load line, experimental impact tests on conventional and auxetic PU foams reveal that auxetic foams are not necessarily advantageous over conventional ones for very high impact. This paper proposes a geometrical model that resembles the microstructure of auxetic foams, as well as elucidates both the auxetic behavior and the limiting strength at high impact. [ABSTRACT FROM AUTHOR]

This paper examines a novel approach to designing auxetic textiles. Knit design techniques are used to create auxetic weft-knitted textiles. Development of the appropriate fabrics addresses aesthetic, tactile and subjective design qualities alongside questions of auxetic functionality and testing considerations. The auxetic fabrics produced exhibit expansion in the X- or Y-axis (aligning axes to direction of knitting). The results range from neutral Poisson's ratio to those with a marked expansion in relation to their extension. The fabric discussed uses relief stitch structures and transferred stitches. Variant auxetic knitted fabrics have been produced including related stitch structures and spacer fabrics using the same design processes. The auxetic effects are inspired by common auxetic geometries from the literature. This research aims to combine the methodologies used in knit design and knit engineering to create functional auxetic textiles by using the methods innate to a more traditionally aesthetic design subject. Using quantitative methods to measure the auxetic effect in the samples and qualitative personal reflections on samples, results are kept simple in order to promote dissemination amongst practitioners in different fields. Utilising focus groups with practitioners from various design fields it is also possible to assess the visual, tactile and commercial appeal of the auxetic fabrics whilst they are still in the developmental stage. Using these different methods of feedback into the design stage the theoretical outcome remains simple in terms of language and results stated. The importance of knowledge transfer between disciplines of design and engineering is key to this study. Data capture is imperative encompassing qualitative and quantitative perspectives in conjunction with the use of generically specified terminology. The knowledge transfer afforded by these collaborations is a key output to support the methods chosen for fabric development, those which cross disciplines and appeal to a wide market. Along with an open and experimental approach to conceiving product applications, this will help to place auxetic materials in public view in areas that are novel to the field of auxetic research. [ABSTRACT FROM AUTHOR]

The paper deals with the extended thermodynamical model of thermoelastic interactions in nonlinear elastic solids of anomalous mechanical properties (negative Poisson's ratio materials) including energy dissipation during the thermoelastic damping phenomenon. The model has been based, among others, on Murnaghan's free energy. Numerical simulations show unconventional effects occurring in such materials. [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]