Search

Paper is an important material for many applications. During the centuries, it has been the most widely used writing support and therefore paper degradation is a major issue for cultural heritage. The main component of paper is cellulose, one of the most abundant biomaterials on Earth. Cellulose oxidation is mainly responsible for the yellowing of the ancient samples, through the formation of chromophores. In order to investigate this issue and the chromophores' role, we exploit the optical properties combining non-destructive experiments and theoretical calculations based on ab-initio techniques. In this paper, we illustrate the method and show its application to three ancient paper samples. The procedure we describe is a precious tool for cultural heritage preservation: indeed, the approach we present is based on non-invasive and non-destructive measurements that allows a microscopic understanding of cellulose-based artifacts degradation. [ABSTRACT FROM AUTHOR]

The objective of this research is to understand more fully the out-of-plane auxetic behavior of paper. In the reported research, initial characterization of the auxetic properties of common, commercially available papers is described. The results of these experiments suggest that the auxetic response seen in paper structures is related to the cellulose fiber network structure, as previously suggested, and is related to inter-fiber bonding and fiber organization in the sheet. These results also indicate that further study is needed to understand how materials and processing variables influence auxetic behavior. A mathematical model, attempting to explain auxetic response in an idealized arrangement of fibers is included. Ultimately, the fundamental understanding resulting from this research should lead to new product development opportunities for forest product-based paper materials as well as to the establishment of predictive structure-property relations for auxetic materials using paper as a model system. [ABSTRACT FROM AUTHOR]

In this paper, the authors consider the processes that occur at the interfaces during nanowires (NWs) growth by the vapor→droplet liquid→solid mechanism (VLS), and how that leads to the faceting of the sidewall surface of the NWs. It is shown that faceting is possible only when the wetting scenario of the VLS growth of the NWs is accomplished due to the exit of the oblique closed‐packed faces to the sidewall surface of the NWs. Those oblique closed‐packed faces emerge at the crystallization front near the triple phase line. The faceting of the sidewall surface of the NWs can be controlled (i) by changing the contact angle of the catalyst droplet on the top of the NWs with the appropriate catalysts; (ii) by introducing the impurities into the gas phase, which decreases the free surface energy of the catalyst droplet; or (iii) by changing the temperature. [ABSTRACT FROM AUTHOR]

In this article, we investigate the nanocomposite material formation, particularly the deposition of nanocrystalline diamond and carbon nanowalls (CNWs) on single-wall carbon nanotubes buckypaper (BP). One part of the buckypaper substrate was nucleated by nanodiamond powder. The growth was carried out in a hot filament chemical vapor deposition (HFCVD) system. Contact angle measurements, scanning electron microscopy, and Raman spectroscopy were used for the surface morphology analysis and characterization of carbon phases. Due to a different surface pretreatment, different carbon nanostructures were formed: diamond film was grown on the nucleated BP area; non-treated area of the BP was covered with a dense field of CNWs. Covering a part of the BP surface prevented an access of the HF-plasma and so the growth of any carbon structures. [ABSTRACT FROM AUTHOR]

Electrochemical water‐splitting, sustained by renewable energy, is aimed at green H2 production. Efficient and sustainable electrocatalysts are required for a proper energy transition. Oxygen evolution reaction (OER) in alkaline electrolyte can be pursued by using earth‐abundant elements‐based catalysts, such as Ni oxyhydroxides. A proper optimization of intrinsic properties and synthesis procedure is still needed. Herein, the synthesis of Ni/NiO nanoparticles (NPs) through a physical and green technique, pulsed laser ablation in liquid (PLAL), is presented. Ablating a Ni target in deionized water, at different ablation times, leads to NP dispersions used for realization of OER electrode onto graphene paper. Ion‐beam analysis of catalysts amount and homogeneity of NP‐based electrode is performed for the electrode optimization in terms of electrochemical performances. An overpotential at 10 mA cm−2 of 306 mV is achieved for 40 μg cm−2 of catalyst, while lowering the catalyst amount to 8 μg cm−2, unprecedented turnover frequency of 0.20 s−1 and mass activity of ≈1.3 A mg−1 are reached. These data show that Ni/NiO NPs produced by PLAL are highly effective for OER in alkaline media and encourage the use of PLAL as a green and efficient technique for electrocatalyst production. [ABSTRACT FROM AUTHOR]

In order to achieve the attenuation of low‐frequency sound, in this paper, a hybrid metamaterial structure with a complete band gap below 500 Hz is proposed, which is subjected to second‐order fractal, series fusion, and whether the structure is framed or not to form 8 different structures. Based on the finite element method and Bloch's theorem, the bandgap and transport properties of all model structures are evaluated, and the bandgap and propagation properties of metamaterial structures with different fractal levels are elucidated in terms of band structure and group velocity. In addition, the third‐order fractal structure and the dependence of the band gap on the material are also studied. The results show that the structure has a superior band gap width, and the complete band gap of its tandem fusion structure accounts for up to 45.502% in the range of 500 Hz, and the second‐order fractal has a complete band gap of 45.588% in the range of 1000 Hz. Compared with other structures, it can produce lower and better band gap. The research in this paper provides a new strategy for realizing acoustic metamaterial structures with low frequency band gaps. [ABSTRACT FROM AUTHOR]

Silver nanowires (AgNW) mixed with nanocellulose nanowires (NCNW) are deposited in photolithgraphed gratings of varying depth. The nanocellulose onto which the AgNWs are mixed is of varying length. It is found that the recirculation flow is larger when the length of the NCNW is longer, and the grating used is deeper. The electrical properties of the resulting quasi‐1D electrode is tested both before it is transferred into the nanocellulose paper and after, and it is observed that it retains the same order of magnitude for the conductivities as the 0.3 and 0.2%wt concentrations for the bare AgNW. This is attributed to the use of the NCNW, at high concentrations. Using the NCNW in the mixtures allows for the AgNW to be transferred from the gratings to any substrate. Using the NC paper allows to obtain a nearly transparent or translucent nearly 1D electrode, where 1D refers to the fact the length of the obtained electrode far exceeds its width. [ABSTRACT FROM AUTHOR]

To improve the electron collection efficiency of gallium nitride (GaN) nanorod array photocathode, external electric field is used to assist collect photoelectrons and a theoretical model of field‐assisted photoelectric emission for GaN nanorod array is established herein. The results indicate that inclined incident light can improve the photoelectron collection efficiency on the side surface of the nanorod and that external electric field can promote the drifting of the photoelectron to the top surface of the nanorod. The square array with a filling fraction of 0.7 reaches its maximum photoelectron collection efficiency at the incident angle of 5° and field intensity of 0.1 V μm−1. This paper might play a theoretical guiding role in the fabrication of photodetectors with high photoelectric conversion efficiency. [ABSTRACT FROM AUTHOR]

To facilitate the calculation of the fourth‐order crystal‐field (CF) splitting moment, which in a complex way depends on the split state |J⟩, a time saving formula is elaborated, which is positively verified for several cubic systems RE3+: Cs2NaLaCl6. The appropriate crystal‐field parameters (CFPs) have to be substituted to the presented formula. However, the question is which ones. The clear answer proven in the paper is that single‐state CFPs should necessarily be used. To test the approach, a few cubic systems, for which such single‐state CFPs are available, have been studied. Conventionally fitted CFPs, averaged over the entire electron configuration, do not satisfy the equation, which contradicts the fundamental principle of the CF theory. Such verification significantly limits the physical meaning and applicability of the conventional HCF fitted parameterizations. [ABSTRACT FROM AUTHOR]

A more accurate synaptic modeling based on oxygen vacancy conductive mechanism is presented in this paper. Two internal state variables, that is, the length and area of conductive region, are used to describe the vertical and lateral growth/dissolution dynamics of the region, based on the physical mechanisms of ion drift and two different diffusion effects. Since the effect of length on the electric field is not negligible, it is introduced into the modeling. In addition, the Fick and Soret diffusions are considered, because they cause the model to produce a "forgetting" property and a "memory" retention. By the comparisons, this modeling captures the actual device better than others. In addition, the previous models can be derived from this one. Some rough analysis suggests that the modeling possibly captures different memristors by adjusting the parameters, and the effects of oxygen concentration and temperature on synapse can also be considered. Therefore, this modeling is more comprehensive and generalized. Several important synaptic functions are simulated, including excitatory postsynaptic current, paired‐pulse facilitation, spike‐rate‐dependent plasticity, and spike‐timing‐dependent plasticity, which may provide a theoretical basis for some potential applications such as artificial neural networks and artificial intelligence. [ABSTRACT FROM AUTHOR]

This is the fifteenth volume of I Physica Status Solidi B i focussed on materials and models showing negative Poisson's ratio (PR), which are often called auxetics, and other systems of unusual, e.g., "negative", characteristics. SP [ sp [1] SP ] sp This time it contains 19 papers which are grouped into three sections. This non-classical effect cannot occur in classical thermo-elasticity but is allowable in Cosserat solids. SP [ sp [17] SP ] sp Next, I Elena Pasternak and Arcady Dyskin i propose a mechanism to control the constriction of elastic rod modulus by lateral compression. This, amongst other things, opens a way to design materials ensuring vibration isolation. SP [ sp [18] SP ] sp I Haifeng Ruan and Dong Li i propose a hierarchical acoustic metamaterial with a spider-web-like structure. [Extracted from the article]

Obtaining a reliable positive‐type (p‐type) GaN semiconductor is difficult because of the unipolarity of GaN. This difficulty is one of the bottlenecks restricting the development of GaN‐based optoelectronic devices. To address this problem, this paper adopted the method of generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential based on the framework of density functional theory to construct Ga35MN36, Ga34MN36, and Ga34MHiN36 (M = Be/Mg/Ca; Hi = interstitial hydrogen) models. Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models were also constructed. Results of our calculations indicated that the Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models cannot achieve a p‐type doping system. Furthermore, the formation energy of Ga34MN36 and Ga34MHiN36 (M = Be/Mg/Ca) systems was greater under Ga‐rich conditions than that under N‐rich conditions, indicating that both doping systems more readily formed and had a more stable structure under N‐rich conditions. Moreover, the formation energy of Ga34MHiN36 (M = Be/Mg/Ca) system was lower than that of Ga34MN36 (M = Be/Mg/Ca) system, and the existence of interstitial H proved to be beneficial to the improvement in system stability. The Ga34CaHiN36 system had the largest hole mobility and the best conductivity. Therefore, the Ga34CaHiN36 system is an ideal material for the application of conductive GaN devices. This study provides guidance into the preparation of p‐type conductive GaN materials. [ABSTRACT FROM AUTHOR]

Measuring the electrical surface resistance of 2D materials without contact can provide a method for obtaining their intrinsic characterization. Herein, the aim is to show that a rutile dielectric resonator (RDR) can be used to measure the electrical surface resistance of conducting coatings deposited on substrates, at the resonance frequency. Moreover, it is known that the substrate exerts a strong influence capable of intrinsically modify the properties of 2D materials, as found in graphene. The RDR method is used for different samples of metals (Cu, Mo, Ti, and brass), carbon nanotubes (bucky paper), a film of compacted graphene flakes, a film of compacted graphene oxide flakes, and graphene obtained by chemical vapor deposition (CVD) on different substrates (SiO2/Si, quartz, and polyethylene terephthalate [PET]). The results show that reasonable values can be obtained for thin conducting materials with a thickness of not less than a few micrometers. In the case of graphene grown on a substrate, the presence of graphene is clearly detected but the resistivity value cannot be extracted. [ABSTRACT FROM AUTHOR]

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]

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]

In this paper, the dynamic behavior of a three-layered sandwich beam with a metal foam core is investigated. Outer layers of the sandwich beam are made of AlSi12 alloy and the core is metal porous foam made of AlSi12. Numerical analysis is made for different parameters of the core -- average damping loss factor, densities, Young modulus, and Poisson's ratio of core foam. The simulations are used to determine the mechanical impedance for a sandwich beam with the applied harmonic load. Numerical calculations are made with the use of finite element method. The results imply that the auxetic core of the composite beam can have a great impact on the dynamic behavior (mobility) of the system. Furthermore, it appears that there are ranges of frequencies in which the mobility of the system can be minimized by using the auxetic foam core. [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]

The paper discusses the problem of recovery of the microstructure of the least compliant bodies of non-homogeneous optimal isotropic properties predicted by the Isotropic Material Design method. The three-dimensional microstructure is assumed as constructed by a subsequent lamination process in which two isotropic materials of ordered properties are used, the process being repeated three or six times, subsequently. The Hooke tensors closest to the optimal ones are found by making use of the analytical Francfort--Murat formulae for effective moduli of third and sixth rank sequential laminates. The ability to model an auxetic behavior within the subdomains where the optimal Poisson's ratio assumes negative values is also shown. [ABSTRACT FROM AUTHOR]

In this paper, the entropy change and the caloric effects induced by charge transfer are discussed. According to the general discussion based on simple physical arguments in the framework of itinerant electrons, large caloric effects can be induced by the charge transfer mechanism even in non‐magnetic materials. This fact, which can be very important to build solid state refrigerators with high performance, opens a new horizon in this area of research. We also suggest some compounds which are good candidates to exhibit caloric effects induced by the physical mechanism of charge transfer in a wide range of temperatures. [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]

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]

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]

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]

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]

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]

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]

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]

The ICPS series traditionally encompasses a variety of topics spanning device physics, quantum technologies, spin physics, wide bandgap materials, light-matter interactions, and other branches of materials science, physics and engineering. It is my pleasure to write this preface to the Special Section in the May 2023 issue of I pss(b) i , dedicated to the collection of selected works presented during the 35 SP th sp International Conference on Physics of Semiconductors (ICPS) held in Sydney, Australia in 2022. As we are preparing for the next meeting in Ottawa, Canada, the collection of papers should inspire our junior colleagues, that not only semiconductor physics is here to stay, but in fact, it is a multi-disciplinary and burgeoning field of research. [Extracted from the article]

The valence and conduction band offset in FeNiO/CuNiO bilayer film are studied utilizing X‐ray photoelectron spectroscopy and UV–vis spectroscopy. The bilayer film is grown on Si substrate employing ion beam sputtering technique using a mixture of argon and oxygen gases at 25% oxygen partial pressure. From the precise knowledge of the valence band maxima energies and core‐level energy positions in the single‐layer film and the corresponding shifts in the bilayer film, the valence and conduction band offsets are estimated to be 0.8 and 0.3 eV, respectively. From the computed band offset data, a type‐I band alignment is identified at the interface of the grown bilayer film, which facilitates the knowledge of carrier transport mechanism and is highly attractive for the realization of efficient room‐temperature optoelectronic device. [ABSTRACT FROM AUTHOR]

In the paper, an analysis of the spectral characteristics of the MFCA (modulated free-carrier absorption) signal for silicon 3-5 Ω cm, n-type is presented. During the change of the wavelength of a probe light, three distinctive regions are observed in the amplitude and the phase characteristics. In the first region ( λprobe << hc/ Eg), only the PCR (photocarrier radiometry) signal exists. The second region ( λprobe > hc/ Eg) is typical for the MFCA signal. The nature of the third region ( λprobe near hc/ Eg), characterized by a long relaxation time is being studied here. The spectroscopy approach to the MFCA technique provided an opportunity to explain the type of free-carrier scattering mechanism that dominates in the NIR region. In the paper, an attempt was also undertaken to estimate the recombination parameters of the sample. [ABSTRACT FROM AUTHOR]

In this work we investigate the growth of diamond film on a porous single-wall carbon nanotubes (SWNT) paper by employing three different Chemical Vapour Deposition (CVD) systems: plasma-assisted hot filament, focused microwave plasma and linear antenna microwave plasma. We observe that the diamond growth is strongly affected by the different conditions in each of the CVD processes resulting in different SWNT/diamond composite structures. It is also found that only the linear antenna microwave plasma CVD process allows penetration of the activated growth species into the volume of the SWNT paper, whereas using the other methods, the diamond grains are formed on the SWNT paper surface only. Moreover, the growth of diamond structures within the substrate volume is strongly influenced by the CH4/CO2/H2 gas content ratio. A key factor influencing the formation of a compact SWNT/diamond composite is keeping the equilibrium between two competitive processes: establishing conditions where the diamond structure can grow while etching/damage of the SWNT paper is still kept at a minimum. The morphology and chemical composition of formed composite materials were characterized by scanning electron microscopy and Raman spectroscopy. [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]

In the present paper, the evolution over time of flat nanowires (NWs) with different widths and at different temperatures is simulated by computer modeling and analyzed. The results can be applied to a wide range of physical systems as the NWs could be parts of nanoelectronic devices or nanosystems, e.g., nanofractals, which can be created during the deposition of nanoparticles on surfaces. The present paper deals with the initial stages of nanowire evolution aiming at the elucidation of the essential features of the fragmentation process. It is demonstrated that the breakup of NWs is driven by the diffusivity of the particles at periphery. The microscopic parameters characterizing the fragmentation are established. The dependence of the time required for the first fragmentation on the nanowire width is presented. The temperature dependence of the nanowire fragmentation is also examined. The dependences of the maximum number of islands created in the fragmentation process on the nanowire width and the temperature are derived. Examination of the temperature dependence of the first fragmentation instant and number of islands as well as the dependence of these quantities on the nanowire width gives the possibility to establish the relationships between experimental observations and microscopic parameters of the system. [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]

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]

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]

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]

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]

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]

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]

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]