Using density functional theory calculations, the structural and electronic properties of the melt-castable energetic materials of bis-oxadiazole-bis-methylene dinitrate (BODN) were studied. The calculated lattice parameters, molecular geometry and band gap by the semi-empirical dispersion (Grimme) corrected generalized gradient approximation functional of Perdew-Burke-Ernzerhof (GGA-PBE-G06) are in good agreement with experimental and theoretical results. Also, the pressure effect on BODN was studied in this work. It is found that although the calculated lattice parameters a, b and c are all decreased monotonically with pressure up to 25 GPa, the b-axis is the easiest compressible. The compression behaviors of geometry were investigated, and found the bond C1-N1 and C3-O2 respective in the oxadiazole and alkyl nitric ester groups were more compressible than the others. The molecular interactions were examined by the Hirshfeld surface and 2D-fingerprint analysis. Moreover, the predicted band gap under high-pressure conditions was discussed as well.

In this paper, photoresistive properties in pristine and homogeneously boron and nitrogen doped semiconducting single-walled carbon nanotubes is studied. The calculations are based on density function theory in combination with Non-Equilibrium Greens Function formalism. The resistance in the SWCNT models is found to decrease with the increasing flux levels. At low electrode voltages, nitrogen doped model shows more photoresistive effect while at high electrode voltages, the most significant photoresistive effect is found in boron doped model. The study reveals that the resistance of the proposed SWCNT systems is dependent on the light intensity, and the conventional boron and nitrogen doping increases the photoresistance by manifold. The models are promising for wide range of applications in the future electronic industry.

A ferrimagnetic mixed spin square Blume-Capel Ising nanowire system on spin-1 core and spin-3/2 outer shell have been investigated. The general formula for the temperature dependence of the equilibrium magnetization of the system is presented. The ferrimagnetic core-shell nanosystem shows a compensation point when the exchange interactions are changed for different values of the single-ion anisotropies of shell sublattices and core ones, respectively. So, one can examine interesting phenomena are compensation behaviors and the free energy of the nanosystem, where these phenomena found that the mixed-spin square Blume-Capel Ising nanosystem which is being considered has two compensation temperatures in the range of −0.8≤DB|J1|≤−0.4, respectively.

The study of half-metallic behavior, thermoelectric properties and thermodynamic stability of the new quaternary PdZrTiAl Heusler were carried out based on the Density Functional Theory (DFT) calculations. The generalized gradient approximation with Tran-Blaha potential (GGA + mbJ) was utilized to treat the exchange-correlation energy for the calculations of electronic structures. More accurate results of the dynamic stability investigation of the intended Heusler compound were obtained by using and Quantum Molecular Dynamic (QMD) simulation. Calculation of the electronic structure indicates that the PdZrTiAl compound has an indirect band gap 0.69eV (from GGA + mbJ) in the down spin and therefore is a ferromagnetic half-metal with 3.00μB magnetic moment. The investigation of the thermodynamic phase diagram showed that this material is stable in all thermodynamic conditions. Furthermore, the phonon positive frequencies and the results of QMD, confirms the sustainability of this structure in XX΄YZ stoichiometric compound. The elastic constants reveal that the PdZrTiAl are mechanically stable and the Poisson's ratio confirmed that the alloys considered are ductile. Also, thermoelectric properties of this compound were studied using transport quasi-classical theory. It was observed that in two majority and minority spin states, this combination shows an utterly distinct thermoelectric behavior. This compound has a good merit coefficient at dn spin at all temperature ranges, especially at low temperatures and the negative sign of the Seebeck coefficient indicates that electrons are charge carriers.

The thermal entanglement in the spin-1 two-dimensional Heisenberg antiferromagnetic chain, with ion-single anisotropy, square lattice and in the neighborhood of critical anisotropy Dc is studied employing Schwinger bosons. In particular, we discuss the effect of the variation of the critical anisotropy Dc that separates the topological order of vortices for DDc, on thermal entanglement. Furthermore, we analyze the effect of quantum phase transition described in the diagram Dc vs. J2 (second neighbors interactions ) on entanglement for a particular class of two-dimensional Heisenberg models which presents different exchange interactions Jx and Jy on x and y directions on square lattice.

Transport properties of irradiated graphene (electrical conductivity and mobility) are numerically investigated using the real-space Kubo formalism. A micrometer-sized system consisting of millions of atoms with nanopores of various sizes and concentrations is described. Electrical conductivity and mobility as a function of carrier (hole) density are calculated to provide possible comparisons with experiments.

GaAsSb based materials have become the promising system for infrared semiconductor lasers and detectors. In this article, the strain, energy band structures and photoluminescence (PL) of GaAs0.92Sb0.08/Al0.3Ga0.7As strained quantum wells (QWs) grown with molecular beam epitaxy are systematically analyzed both theoretically and experimentally. The theoretical results are derived by Kane’s model and k⋅p method, and the optical properties of a high-quality GaAs0.92Sb0.08/Al0.3Ga0.7As strained QWs sample are thoroughly investigated by excitation- and temperature-dependent PL measurements. The theoretical results show the strain has significant influence on the band structure of QWs. In experimental part, it is found that the light-hole exciton emission coexists with the heavy-hole exciton line in the temperature range of 50 K to 300 K. However, the emission of localized excitons, which is caused by the nonuniformity of component in the GaAsSb well layer, takes over the light-hole exciton emission at lower temperatures (<50 K).

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in doped both armchair and zigzag nanotubes. The effects of both gap parameter and electron doping on RKKY interaction have been addressed. RKKY interaction for traverse components of localized spins as a function of distance between localized moments has been analyzed. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain transverse static spin susceptibility of graphene like nanotubes in the presence of gap parameter and electron doping. The spin susceptibility components are calculated using the spin dependent Green's function approach for tight binding model Hamiltonian. The effects of tube diameter on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show the influences of electron doping on the spatial behavior of transverse RKKY interactions are different for zigzag and armchair types of nanotube.

There are lots of efforts on the investigate for high-temperature superconductors in hydrogen-rich system, since the LaH10 (250–260 K) and SH3 (203 K) compounds smashed the record for superconducting temperatures above 200 K. In this study, as a result of extensive simulations, we propose several unreported thorium hydrides under pressures, using our in-house developed CALYPSO structure searching method in combination with density functional theory. New ThH3 and Th2H7 structures are found as thermodynamically stable phases at atmospheric pressure. As a result of the analysis of the electronic properties in those predicted structures, it is found that the f electrons of Th and the s electrons of H mainly contribute to the fermi level, thus leading to the superconductivity. Our results enrich the knowledge in the Th–H system and provide insights into designing superconducting hydrides under high pressure.

We present theoretical and experimental investigations on the electronic and magnetic properties of the Mn2+δCo0.5-δV0.5Al (δ = 0 ÷ 0.08) and Mn2+zCo0.5V0.5-zAl (z = −0.14 ÷ 0.08) Heusler alloys. The electronic band structure calculations by the Korringa-Kohn-Rostoker (KKR) Green's function method show the dependence of the total spin moment on the preferential site occupation for different crystal sites and predict compensated ferrimagnetic behavior for the compounds obtained from Mn2Co0.5V0.5Al by slight variation of composition. Experimental investigations by tuning the Mn content in Mn2Co0.5V0.5Al alloys have been performed in order to achieve the fully compensated ferrimagnetic behavior which is of particular importance for spintronics. The thermo-magnetic measurements show different types of ferrimagnetic behavior with the threshold influenced by Mn content: N-type of ferrimagnetic behavior for Mn2+δCo0.5-δV0.5Al, while for the Mn2+zCo0.5V0.5-zAl Heusler alloys a combined N/P-type of behavior, depending on z, is observed: N-type for Mn excess/P-type for Mn deficiency. The Curie temperatures of the investigated alloys show high sensitivity on the Mn content. The results of our study may give an insight on the influence of the composition on the magnetic properties of the Mn2Co0.5V0.5Al alloys in order to adjust their properties and make them suitable for spintronic applications.

The effect of hydrostatic pressure on the martensitic transformation and magnetocaloric effect has been systematically studied in Mn44.7Ni43.5Sn11.8 ribbons. The melt-spun ribbons crystallize along the [400] direction, which is perpendicular to the surface of the ribbon. The martensitic transformation temperatures shift from 266.5 K to 281.0 K by applying hydrostatic pressure of 0.75GPa. Under the magnetic field of 30 kOe, the value of is about 19.3 K GPa-1, indicating a broadening of working temperature span for magnetic refrigeration at room temperature. At ambient pressure, a relatively large entropy change value of 35.9 J kg-1 K-1 is obtained under a magnetic field of 30 kOe, which would be related to the orientation of crystal structure.

Spin polarization, when induced in a non-ferromagnetic material, can change the underlying material behavior especially if the spin diffusion length is of the same order as the sample dimension such as thickness. In this study, we experimentally demonstrate thermal hysteretic behavior induced by spin polarization in Ni80Fe20 (10 nm)/Au (100 nm) bilayer freestanding sample. The thermal hysteresis behavior is uncovered using magneto thermal characterization based on self-heating 3ω method. The third harmonic voltage shows diverging behavior and thermal hysteresis during cooling and heating of the sample under an applied magnetic field, which is attributed to the spin accumulation. The spin accumulation and thermal hysteresis in Au occurs due to ferromagnetic proximity polarization from Ni80Fe20 layer. The observed hysteresis behavior is also attributed to freestanding thin film structure and absence of substrate effects leading to longer spin diffusion length. This study demonstrates experimental evidence of ferromagnetic proximity polarization and resulting changes in thermal transport behavior in Au thin films.

Coupling effects among spin, charge, and lattice in a strongly correlated system are critical for next generation spintronic and data storage devices. However, the complex effects are elusive and difficult to distinguish their contributions to polarization modulation. Here we tailored the polarization by co-doping of non-magnetic Y and Eu at A-sites in DyMn2O5. The structure, specific heat, magnetism, and ferroelectricity of the polycrystalline Dy1-x(Eu0.24Y0.76)xMn2O5 ceramics were comprehensively explored. Interestingly, the co-doping does not cause lattice distortion of DyMn2O5, and all the ceramics are orthorhombic structures, while the independent Dy3+ spin order and the Dy3+-Mn3+ coupling can be suppressed. With increasing the co-doping content x, the spins related properties associated with the Dy3+-Mn4+-Dy3+ sub-lattice are progressively inhibited, while they keep less disturbance in the Mn3+-Mn4+-Mn3+ block. Moreover, the spin coupling of Dy3+-Mn3+ ions is stronger again the magnetic field than that of Dy3+-Mn3+. Our results enhance the understanding of ferrielectricity in DyMn2O5, and provide a method for controlling the polarization in the multiferroic manganite coexisting 3d and 4f elements.

In this study, we show that fine manipulation of sound waves can be achieved through lossy acoustic gradient-index metasurfaces by utilizing the energy losses. This work, provides a practical route for achieving independent and arbitrary modulation of the amplitude and phase of sound. We demonstrate this mechanism by producing broadband high-quality airy beams. Furthermore, we realize the multifocal focusing based on this lossy acoustic gradient-index metasurfaces. Our findings increase the freedom and flexibility of the control of sound transmission.

Transition metal silicides which have low band gap or semimetallic states have gained huge interest due to enhanced thermoelectric efficiency. We present high resolution photoemission studies on two such systems like MnSi1.75 a low band gap semiconductor and CoSi a semimetal to understand the inherent electronic properties. Valence band studies on these systems reveal that there are both localized and delocalized 3d states present where as in the pure transition metals more localized states present near the Fermi level. In both MnSi1.75 and CoSi, the localized 3d states are found to shifted to higher binding energy due to the strong hybridization with the Si 3s−3p states that gives rise to the hybridization gap in these systems. The delocalized 3d states in both the systems has much lower electronic density near the Fermi level than the pure transition metals that contributes to the conduction. Supporting evidences of delocalized screening in MnSi1.75 and weak correlated satellite in CoSi have been observed in the 2p core-level spectra. We find that the presence of both hybridization gap and the finite carrier concentration at the Fermi level in these transition metal silicides are necessary to have the enhanced thermoelectric properties.

Systematic density functional theory calculations were carried out to study the structural, electronic, magnetic and optical properties of vacancy and antisite defects in marcasite FeS2 (m-FeS2). Five types of point defects were considered, that is S vacancy, Fe vacancy, FeS divacancy, Fe substitute S site and S substitute Fe site. The results show that Fe substitute S, S vacancy and Fe vacancy are the dominant defects in m-FeS2. The defects remarkably affect the electrical, optical performances of the m-FeS2, and even induce magnetism. All the considered point defects have defect states in the band gap of perfect m-FeS2. We estimated the stability of magnetic state and found that the m-FeS2 with point defects shows magnetic ground state except S vacancy case. Detailed analysis shows that m-FeS2 with S vacancy is a nonmagnetic semiconductor, with Fe vacancy, FeS divacancy and Fe substitute S site become magnetic metal while with S substitute Fe site is a magnetic semiconductor. In addition, compared with perfect m-FeS2, the static dielectric constants and static refractive indexes of m-FeS2 with defects are all increased significantly, the absorption coefficients show red shifts and enhancements in the infrared region due to the defect states.

The new melting curve of cobalt (Co) was determined to be 12 GPa using the in situ high-pressure temperature measurement method (HPTM) in a high-volume cubic press using two melting criteria: first, plateaus in the temperature vs power functions in situ experiments, and second, the texture changes in the samples before and after high-pressure high-temperature (HP-HT) treatments with a scanning electron microscope (SEM). The slope of the melting point with increasing pressure was approximately 33 K/GPa in our experimental pressure range and progressively decreased under further compression. Our new melting curve of Co under high pressure is reasonably consistent with the simulation results using one-phase and two-phase calculations and has a similar trend with the reported melting curves of Fe and Ni.

Using ab-initio methods we study atomic and electronic properties of few-layers of two-dimensional honeycomb boron. Our study shows that structures built of 3 or 4 layers are stable, with significant binding energy. Also, such structures are semiconductors with band gaps susceptible to strain. We also show that deposition of 3 or 4 layers of boron on SiC substrate may modify the band gap depending on the hydrogenation of the topmost layer.

The electronic structure and spin properties of Titanium (Ti) or Iron (Fe) doped hexagonal boron nitride (h-BN) nanosheet have been studied by using ab initio study based on density functional theory (DFT). GGA + U calculations show that one Ti or Fe atom can introduce local magnetic states into the system. Impurity levels will be generated in band gap, and this will lead to spin polarization. The calculated magnetic moments are 1.0 μB and 2.9 μB for Ti and Fe, respectively. Furthermore, the magnetic moments are all contributed by the d orbitals of doped atoms in h-BN monolayer. The studies of magnetic coupling reveal that two Ti atoms are mainly coupled antiferromagnetically at different distances between Ti atoms in h-BN monolayer. The Ti-doped system is coupled ferromagnetically only when Ti-Ti distance is 6.625 Å. While the magnetic coupling exhibits regular oscillation characteristics in the system with two Fe atoms doping at different distances. This novel property in Fe-doped h-BN nanosheet provides a new way to control the spin property of material. Our research is beneficial to the development of spintronics.

PdAs2 monolayer, a new pentagonal two-dimensional (2D) material, greatly attracts widely research interest due to its extremely high carrier mobility with a direct band gap. We have systematically studied the electronic structure, elastic, optical and thermal transport properties of monolayer PdAs2 from first-principles calculations. Our electronic structure calculations show that the monolayer PdAs2 is a semiconductor with a direct band gap of 0.78 eV. Tensile strain has a good regulating effect on the band gap, which can be adjusted from 0.01 eV to 0.84 eV. The calculated elastic constants of monolayer PdAs2 confirm that the PdAs2 monolayer is mechanically stable. The calculated optical properties reveal that the energy range of the absorption spectrum is 1 eV–15 eV. The absorption range of PdAs2 monolayer is mainly visible and ultraviolet light. Under the tensile strain, the absorption spectrum shows obvious redshift. With the increase of strain, the reflectivity and refractivity increase. The calculated thermal conductivity of the monolayer PdAs2 at 300 K is 1.04 W/(mK), which is lower than that of known pentagonal monolayer. In addition, the effects of phonon free path, group velocity and phonon scattering rate on lattice thermal conductivity are analyzed.

We systematically investigate the structural, electronic properties of bulk CeO2, its H-phase and T-phase monolayers, studied using first-principles calculations based on density functional theory (DFT). The calculated electronic bandgap is 2.02 eV, 0.86 eV and 2.52 eV for CeO2 bulk, H-phase and T-phase, respectively. Here, the bandgap is tuned by applying triaxial tensile strain up to 28%. Using strain engineering, the bandgap further increases and behaves as a metal at about 28% for the bulk as well as its monolayers. It is found that for bulk CeO2, initially, the bandgap increases for strains up to 16% and then decreases. Similarly, for H-phase the bandgap increases initially at 4% strain and then decreases. Whereas, for T-phase, on applying strain the band gap decreases. Here, the bandgap is in visible range due to that it will be used in optoelectronic devices such as solar cells and LEDs. The result also shows that the CeO2 nanostructures have diverse electronic properties, tunable by strain engineering and have wide applications in nanoelectronics and nanodevices.

We report on the systematic normal and superconducting states microwave absorption studies in polycrystalline samples of SmFeAsO1−xFx using an electron spin resonance (ESR) spectrometer. In the normal state, we observed two absorption spectra; at high fields (∼3500 G) and low fields (around 0 G). The high field spectrum is in principle a resonance spectrum corresponding to a saturated state. It was observed that this signal broadens and its peak to peak intensity decreases on cooling the sample from room temperature. Ultimately, the signal becomes ESR ‘silent’ in the superconducting state. On the other hand, the low field microwave absorption (LFMA), centered around zero field, was observed for the first time, in a superconducting material. Based on the line-width, hysteresis and peak to peak signal intensity, we have shown that this spectrum is distinctively different from the already known LFMA signal that occurs in the superconducting state. These results present a system that shows LFMA spectrum in both normal and superconducting state thus providing an excellent platform to analyse the elusive LFMA phenomenon.

In the present communication, the conductivity of the single crystal methylammonium lead bromide as a function of temperature is studied. As a result, the activation energies for the dark/light conditions were determined. Interestingly, when the light illumination is applied, depending of the applied bias voltage, the complex conductivity response on the temperature changes was observed. Depending on the electrical field applied, the material follows two behaviors: first is typical of semiconductors and the second one and non-Arrhenian behavior, which is distinctive for metals. This is, for the best of our knowledge, the first observation of this unique property of single crystal methylammonium lead bromide perovskite.

We study the superconducting state of a strip under an transport current Ja and an external magnetic field H. We show that the value of the critical currents at which the vortex-antivortex (V-Av) pair penetrates the sample, the number of phase-slip lines, and their average velocities and dynamics strongly depend on the size of the sample L. Our investigation was carried out by numerically solving the two-dimensional generalized time-dependent Ginzburg-Landau equations (GTDGL).

The Ba1-xCaxTi1-ySnyO3 (abbreviated as BCxTSy, x = 0.01, y = 0.01; x = 0.03, y = 0.015; x = 0.05, y = 0.02; and x = 0.07, y = 0.025 mol) electroceramics were synthesized by solid-state reaction method and investigated their structural, dielectric, ferroelectric and piezoelectric properties. Rietveld refinement for X-ray diffraction data for the composition x = 0.03, y = 0.015 reveals the phase co-existence of two non-centrosymmetric orthorhombic (Amm2) (7.71%) + tetragonal (P4mm) (92.29%) lattice symmetries respectively near room temperature which is also evidenced by temperature-dependent Raman and dielectric studies. All compositions reveal the dense microstructure having relative density ∼92%–96% and average grain size ∼10.7–22.5 μm -The phase diagram based on dielectric studies suggests that the composition x = 0.03, y = 0.015 reveals T(R–O) ∼ −60 °C, T(O-T) ∼ 19 °C and TC ∼ 126 °C with higher Pr = 11.80 μC/cm2, Ec = 3.5 kV/cm, Pmax = 21.92 μC/cm2, d33* = 505.5 pm/V, d33 = 287 pC/N and electrostrictive coefficient (Q33) = 0.036 m4/C2 properties which could be useful for developing the piezoelectric Ac device application. Here, we have achieved the phase-coexistence of two non-centrosymmetric lattice symmetries near room temperature to invoke the reliable ferroelectric and piezoelectric properties and discussed the results with the structure-property-composition relation.

We have studied collective spin density excitation of fractional quantum Hall effect (FQHE) in rotating Bose–Einstein condensation for the three filling fractions of first series of Jain’s composite fermion sequences. We have considered short-ranged contact interactions between the Bose atoms as well as long range Coulomb interactions to compare the nature of the spectra with FQHE of electrons. Using Monte-Carlo method for finite but large number of particles, the lowest order collective modes of spin-reversed sectors is calculated here, by computing the energy differences of the respective excitons from the fully polarized ground states.

We have investigated the ferromagnetic properties of MoS2 thin film doped by iron using chemical vapour deposition. The structure of film was determined to be poly-crystalline with various phases. The iron doped MoS2 film shows that the ferromagnetic hysteresis appears at room temperature, and also indicated two Curie temperatures. The remnant magnetization and coercive field at room temperature are 36 emu/cm3 and 44 Oe. The elemental atomic concentration of iron doped MoS2 measured by x-ray photoelectron spectroscopy was 0.69 at.%.

The mechanism of not diverging Grüneisen parameter in the quantum critical heavy-fermion quasicrystal (QC) Yb15Al34Au51 is analyzed. We construct the formalism for calculating the specific heat CV(T), the thermal-expansion coefficient α(T), and the Grüneisen parameter Γ(T) near the quantum critical point of the Yb valence transition. By applying the framework to the QC, we calculate CV(T), α(T), and Γ(T), which explains the measurements. Not diverging Γ(T) is attributed to the robustness of the quantum criticality in the QC under pressure. The difference in Γ(T) at the lowest temperature between the QC and approximant crystal is shown to reflect the difference in the volume derivative of characteristic energy scales of the critical Yb-valence fluctuation and the Kondo temperature. Possible implications of our theory to future experiments are also discussed.

Existing defect models for Co-doped ZnO with O vacancy (VO) are controversial in explaining the origin of the magnetism. To address this issue, we investigated the effects of Co doping and VO on the magnetic properties of ZnO through first-principles calculations by using generalized gradient approximation + U under the density functional theory. The total density of states of co-doping of one Co and one VO shows half-metallic behavior, which is highly beneficial when using dilute magnetic semiconductors (DMSs) as a hole injection source. The ferromagnetism for co-doping of one Co and one VO is derived from the double exchange effects among the spin polarized electrons of O–2p, Co–3d, and Zn–4s states as mediated by the electron carriers from VO, which is consistent with the mean field approximation theory and the double exchange mechanism theory. The co-doping of two Co and two VO causes the ZnO crystal undergo transition from anti-ferromagnetism (AFM) to ferromagnetism (FM) with the change of Co-Co distance. Zn34Co2O35d (the Co-Co distance is 6.136 Å) can achieve Curie temperature higher than room temperature. In the same doping mode, increased concentrations of Co and VO increase the net magnetic moments.

Using density functional theory calculations, we studied the electronic and energetic properties of –F, –NH2, and –NO2 functionalized Hexa-peri-hexabenzocoronene (HBC, C42H18) nanographene and their potential application in Li-ion batteries (LIBs). We found that Li/Li+ preferably adsorbs above the center of peripheral six-membered rings of HBC with adsorption energy about -53.7 kcal/mol. After the Li+ adsorption, the work function of HBC is increased by about 84.5%, while the atomic Li decreases it by about 36.0%. After functionalization, –NO2 increases the HBC work function from 3.45 to 4.00 eV, and the –NH2 decreases it to 3.28 eV. Also, –NO2 strongly and –NH2 weakly reduces the HOMO-LUMO gap of HBC. Our calculated cell voltage for LIB when an HBC nanographene is used as the anode is about 1.70 V. Based on the results, –NH2 group increases the cell voltage by about 0.25 V and reversely, –NO2 group decreases it from 1.70 to 1.16 eV. This indicates that the NH2-HBC is much more appropriate material for application in the anode of LIBs compared to the F-HBC, NO2-HBC, and pristine HBC.

Molecular dynamics simulation is used to systematically investigate mechanical properties of tungsten-hydrogen system and hydrogen diffusion in tungsten. It is found that the tensile strength of tungsten is decreased seriously by the formation of hydrogen bubbles, and the intrinsic mechanism is discussed by deformation dislocations. The present calculation also reveals that the hydrogen clusters in tungsten would be hard to diffuse, and may finally accumulate and form bubbles. In addition, the uniaxial and isotropic tensile strains have different effects on the diffusivity of hydrogen clusters, and the mean square displacements of H clusters diffusing along several directions under uniaxial and isotropic tensile strains are derived and compared with each other. The simulated results agree well with experimental evidence and calculated data available in the literature.

The heterojunction diode using Sn doped In6Se7 and CuInSe2 thin films are fabricated on FTO coated glass substrates using reactive evaporation technique. The structure of CuInSe2 film is studied using XRD analysis and the film exhibits polycrystalline nature. XPS result confirms that the prepared sample is nearly stoichiometric. The I-V measurements of FTO/n-In6Se7:Sn/p-CuInSe2/Ag heterojunction diode, in dark condition, shows rectification behavior. The knee voltage and ideality factor of the diode are observed to be 1.52 V, 3.09 V and 5.57, 16.16 respectively when the Sn dopant concentration varied from 0.47 at% to 1.57 at%. The absence of photoresponse from the diodes under illumination condition is explained using the energy band structure of the heterojunction.

Extraordinary optoconductance (EOC) devices with symmetric leads have been shown to have a symmetric positional dependence when exposed to focused illumination. While advantageous for a position sensitive detector (PSD), this symmetric positional dependence, when the device is uniformly illuminated, leads to a minimization of the output voltage. Here, with the aid of a previously employed point charge model, we address two ways to break the symmetry and recover the output signal. The first is to impose uniform illumination but only on half the sample. This method has practical limitations as the device is miniaturized to the nanoscale. The second is via asymmetric placement of the voltage probes in a four-probe measurement. Crucial to the discussion is the effect of the surface charge density. Several ways of modeling the induced surface charge density are presented. Utilizing the above described approach, optimal asymmetric lead positions are found.

Alloying elements play an important role in the design of plasma facing materials with good comprehensive properties. Based on first-principles calculations, the stability of alloying element W and its interaction with vacancy defects in Ta–W alloys have been studied. The results show that W tends to distribute dispersedly in Ta lattice, and is not likely to form precipitation even with the coexistence of vacancy. The aggregation behaviors of W and vacancy can be affected by their concentration competition. The increase of W atoms has a negative effect on the vacancy clustering, as well as delays the vacancy nucleation process, which is favorable to the recovery of point defects. Our calculations are in consistent with the defect evolution observed in irradiation experiments in Ta–W alloys. The results suggest that W is a potential repairing element that can be doped into Ta-based materials to improve their radiation resistance.

With the help of the McMillan formula and virtual crystal model, we predict Tc may exceed 34 K in a beryllium-based alloy with a specific composition, reminiscent of Tc=35 K in the first cuprate superconductor. This may similarly inspire research efforts to seek high temperature superconductors in ambient.

Designing new two-dimensional (2D) materials with novel band structures has continuously attracted research interest because of their fundamental science and potential applications. Here we report a unique 2D hexagonal structure of calcium chloride (h-CaCl2) monolayer featuring quasi-planar hexa-coordinate calcium and chloride. In this paper, structural, electronic and optical properties of the h-CaCl2 have been studied. We determine the most stable site for halogens on the h-CaCl2. The calculations are performed on a single layer 3 × 3 × 1 supercell h-CaCl2 within the framework of density functional theory (DFT) to have the maximum computation accuracy. The results show that the h-CaCl2 is a semiconductor with a relatively wide band gap of 5.78 eV. Real and imaginary parts of the dielectric function for an isolated single-layer h-CaCl2 are investigated. Adsorption and reflection calculation results reveal optical blindness of the system within the visible range of the electromagnetic spectrum and prove its suitability for ultraviolet (UV) detection applications.

The inherent unsatisfactory configurational and poor chemical stability of colloidal quantum dots (CQDs) are the main impediments hindering their broad device operation. In this work, we synthesized colloidal quantum dots-silica monolith (CQDs-SM) solid-state luminophores with different emission colors through a simple sol-gel method. The synthetic method, the morphologies of the composites and optical properties measurement in our work is in a new regime not studied before. Thermostability test indicated that the encapsulated CQDs-SM composites samples had excellent stability against elevated temperature compared with that of fresh CQDs. Furthermore, the as-prepared CQDs-SM displays excellent photoluminescence stability in the air atmosphere for several months. The light emission also efficiently sustained stable with no measurable decrease for over 100 h under continuous UV laser illumination, which can be attributed to the SiO2 capping layer protecting the CQDs from degradation and agglomeration. It is quite obvious that the remarkable optical performances and novel synthesis method used here will offer CQDs-SM composites a new platform for applications in light sources and displays.

Multiferroics have attracted research interest for decades due to their potential applications. Multiferroics are relatively scarce due to the mutual exclusivity between magnetic and ferroelectric properties. New room-temperature multiferroics are looking forward to be exploited. Room-temperature multiferroic properties have been observed in a new rare-earth iron garnet (REIG), Nd3Fe5O12 (NdIG). The dielectric properties of NdIG over a wide temperature range (300 K to 650 K) at different frequencies (100 Hz to 1 MHz) and in the temperature range from 70 K to 300 K at 100 Hz are investigated herein. The results show that this material has two dielectric relaxations in the temperature range from 290 K to 525 K and a dielectric anomaly around the magnetic ordering temperature (565 K). The first dielectric relaxation in the temperature range from 290 K to 500 K is attributed to the conduction with an activation energy of 0.75 eV. The other dielectric relaxation in an elevated temperature range has an activation energy of 0.87 eV, which originates from the inhomogeneous structure. Furthermore, the ferroelectric polarization of approximately 28 μC/m2 at 77 K is determined by the positive-up-negative-down method and induced by the effective magnetic field created by the iron sublattice magnetic ordering and electric-dipole moments of the neodymium ions.

Recent experiments have shown that Fe doping to the SnO2 system can increase the magnetic moment and induce a remarkable red shift of the absorption spectrum. However, the valence state of Fe is not strictly controlled in the experiment, and the relationships between the magneto-optical properties and the Fe valence state are lacking. Therefore, the electronic structures and magneto-optical properties of pure SnO2 and Fe2+/3+-doped SnO2 systems were theoretically studied. First-principles calculations revealed that Fe2+/3+ doping significantly redshifts the absorption spectral, induces spin-polarized impurity bands near the Fermi level, and leads to evident spin polarization phenomenon. Fe2+ and Fe3+ exhibit different effects on the electronic structures and magneto-optical properties of the doped system. Specifically, Fe3+ doping enhances the dominant role of p–d exchange interaction and the Fe3+ doped systems are likely to obtain high Curie temperature and magnetic moment at the same doping concentration and position; moreover, the imaginary part and absorption spectrum of the dielectric function of Fe2+-doped SnO2 systems have large new peaks in the low-energy region, which are attributed to electronic transitions from the spin-polarized impurity levels to the conduction band.

A Series of LuMn1−xRuxO3 (0≤x≤0.3) samples were prepared by traditional solid-state reaction method. The interactions between Ru3+ (with 4d electrons) and Mn3+ (with 3d electrons) on the structure and magnetic properties of LuMn1−xRuxO3 were investigated. The results of structural investigation reveal that samples crystallize in a single hexagonal structure with P63cm group for LuMn1−xRuxO3 samples with x≤0.1. The change of Mn-O bond lengths and Mn-O-Mn bond angles indicates the trimerization of Mn3+ ions is weakened and the tilting angle of MnO5 bipyramids is decreased. The temperature dependence on magnetization M(T) curves prove that weak ferromagnetism (FM) exists in the samples. Meanwhile, the antiferromagnetic (AFM) transition temperature TN of LuMn1-xRuxO3 samples is enhanced by the Ru doping. The weak FM is resulted from the alteration of frustrated magnetic structure, while the enhancement of AFM coupling is ascribed to the strong super-exchange Ru3+-O2—Ru3+ and Ru3+-O2—Mn3+ interaction by Ru3+ doping. This paper provides an important reference of 4d ion doping in LuMnO3.

Magnetic spinel oxides, including CoFe2O4 (CFO), have crucial applications in spintronics. They have excellent magnetic properties, such as high spin polarization and high Curie temperature, which enables the operation of spintronic devices at room temperature. Some interesting phenomena have also been discovered for interfaces consisting of spinel oxides and heavy metals. However, the magnetic properties of ultrathin CFO films have not been investigated sufficiently. In this report, a characterization of the magnetic properties of an ultrathin CFO film was performed by using the magnetic proximity effect (MPE) to observe the anomalous Hall effect (AHE) in Pt. The result was consistent with the measurement performed with magneto-optical effects. By fitting AHE with the Langevin function, it was concluded that these ultrathin films (tCFO<3.4 nm) showed superparamagnetism, and the magnetic moment was estimated to be 3000μB. The results provided the novel method to evaluate the magnetic properties of ferromagnetic insulators by using MPE and AHE, thus providing a better understanding of interface magnetism.

'There is an interest in growing N-polar GaN on bulk GaN for high electron mobility transistors (HEMTs). Current N-polar HEMT technology is dominated by devices grown on non-native substrates which possess a high density of dislocations due to lattice mismatch. N-polar GaN films grown directly on non-miscut GaN substrates have displayed a high density of pits and depressions on the surface. This work demonstrates that surface impurities play a major role in the formation of surface-pits in epitaxially grown film. By subjecting the GaN substrate to an ultra-violet (UV) O3 (ozone) clean prior to growth and initiating growth with a 2 nm coherently strained AlN layer, grown under metal-rich conditions, we have demonstrated N-polar GaN films with a nearly pit-free surface. This AlN initiation layer (AIL) likely captures impurities on the substrate surface thus decoupling the substrate surface from the epitaxially grown film. It is demonstrated that utilizing thicker AILs, up to 8 nm, further improves film quality and surface morphology. The methods employed in this study to produce high-quality N-polar GaN grown on bulk GaN will pave the way for future GaN devices with an order of magnitude or more lower threading dislocation density (TDD).

3C–SiC is a promising platform for semiconductor spintronics because it consists of light group-IV elements and has a zinc blende structure. To demonstrate spin transport in this attractive semiconductor, we conducted an experiment of spin-pump-induced spin transport through n-type 3C–SiC. A spin current is injected from Ni80Fe20 into the SiC channel under ferromagnetic resonance of the Ni80Fe20. The DC electromotive force caused by the inverse spin Hall effect in an adjacent metal detector attached to the SiC is detected as a manifestation of the spin current transport. This indicates 1.2-μm-long spin transport through the n-type 3C–SiC at room temperature. This achievement is the first step in the investigation of the physics of 3C–SiC for further spintronics study and its application.

Thermoelectric materials are attracting increasing attention for their ability to convert heat into cleaner electricity. In this work, we have systematically studied the thermoelectric properties of strontium sulfide (SrS) in the rock-salt structure based on first-principle calculations together with Boltzmann transport theory. The phonon spectra of the rock-salt structure SrS have no imaginary frequency modes, indicating the dynamic stability of SrS. The room-temperature lattice thermal conductivity κι of SrS is calculated to be 10.70 W/mK. We also calculated the phonon-mode contribution to κι, scattering rate, and mean free path (MFP). It is found that the acoustic branches have obvious contribution to the total lattice thermal conductivity, and the MFP can provide guidance for designing thermoelectric nanostructures. The ZT values of SrS with respect to carrier concentration n and temperature T are also obtained. It is found that, when temperature is from 300 K to 700 K, for p-type, the highest ZT value calculated by PBE varies from 0.15 to 0.41, and the highest ZT value by HSE varies from 0.10 to 0.30; For n-type, the highest ZT value by PBE varies from 0.08 to 0.26, and the highest ZT value by HSE varies from 0.09 to 0.28. In general, the p-type SrS has the better thermoelectric property than the n-type SrS.

1T-TaS2 is a material that belongs to the family of transition metal dichalcogenides and features a rich phase diagram including different charge density wave states. So far, most techniques used to study this material focus on either very local properties on the atomic scale or use global measurements of the whole sample like the electrical resistance. Here, we report on the influence of micrometer scale laser illumination on the global electric properties of a bulk sample. Thermoelectric effects are found to be responsible for a large electric response to the laser illumination. This effect is used to develop a method that allows to spatially map the thermoelectric properties of a 1T-TaS2 sample on the millimeter scale with micrometer resolution. We show that a specific temperature sweep can impede the phase transition, allowing to study long-lived mixed states, consisting of two phases. With this method we are able to image metastable states occurring in the transition between the nearly commensurate and commensurate charge density wave state in bulk 1T-TaS2 and compare the results to Raman spectroscopy.

A new property of Heusler alloys known as shell-ferromagnetism is observed predominantly in NiMn-based Heusler alloys with X as Ga, Al, In and Sn. An antiferromagnetic-matrix/shell-ferromagnetic precipitate dual-phase generates from an anti-ferromagnetic initial structure with temper-annealing in an external magnetic field. The present study focuses on the magnetic and structural instabilities in CuMn-based Cu50Mn45Al5 Heusler alloy when temper-annealed under a magnetic field, as in NiMn-based Heusler alloys. The ternary Cu50Mn45Al5 Heusler alloy exhibits a cubic mictomagnetic structure in its initial state. Structural decomposition occurs during temper-annealing under a magnetic field from the initial state to a triple-phase composite alloy. The decomposed phases are identified to be cubic L21 Cu2MnAl, cubic L10 Cu50Mn50 and A13 β-Mn. As observed in shell-ferromagnetism, the ferromagnetic Cu2MnAl precipitates form in a mictomagnetic CuMn matrix with an additional β-Mn component.

In this study, the vibrational, electronic and optical properties of graphene-like structure of boron carbide were investigated by density functional theory and the results were compared to the calculated properties of graphene. By investigating the phonon dispersions and vibrational properties, the BC monolayer found stable and revealed lower group velocity and higher specific heat capacity than graphene. In contrast to graphene, metallic characteristic of graphene-like boron carbide was confirmed by analyzing the total density of states and band structure which could be responsible for the observed different optical properties compared to graphene particularly at low energy region of electromagnetic waves spectrum.

We present a theory and a computational tool, Silicon-Qnano, describing atomic scale quantum dots in silicon. The developed methodology is applied to model dangling bond quantum dots (DBQDs) created on a passivated H:Si-(100)-(2 × 1) surface by removing a hydrogen atom. The electronic properties of the DBQD are computed by embedding it in a computational box of silicon atoms. The surfaces of the computational box were constructed by using density functional theory as implemented in the Abinit package. The top layer was reconstructed by the formation of Si dimers passivated with H atoms while the bottom layer remained unreconstructed and fully saturated with H atoms. The computational box Hamiltonian was approximated by a tight-binding (TB) Hamiltonian by expanding the electron wave functions as linear combinations of atomic orbitals and fitting the bandstructure to ab-initio results. The parametrized TB Hamiltonian was used to model large finite Si(100) boxes (slabs) with number of atoms exceeding present capabilities of ab-initio calculations. The removal of one hydrogen atom from the reconstructed surface resulted in a DBQD state with a wave function strongly localized around the Si atom and the energy in the silicon bandgap. The DBQD could be charged with zero, one, and two electrons. The Coulomb matrix elements were calculated and the charging energy of a two electron complex in a DBQD obtained.

The synthesis, characterization and magneto-transport investigations on the single crystals of semimetal NbAs2 in a temperature range varying from 300 K to 2.5 K with a magnetic field up to 14 T are reported. The temperature dependence of resistivity that exhibits a metallic behavior without a magnetic field is seen to show an upturn as the magnetic field is applied resulting in a very large magneto-resistance. The upturn temperature displays a systematic increase with increasing fields. It is shown that this behavior of magneto-resistance can be understood in terms of the Kohler's scaling relation rather than in terms of the existence of a critical magnetic field inducing a metal to insulator transition. Through careful experiments, including angular dependence of magneto-resistance, it is verified that NbAs2 does not show negative longitudinal magneto-resistance, a characteristic of Weyl semimetal.

MXenes, transition metal carbides and nitrides, are a bourgeoning class of two-dimensional (2D) materials due to their tunable electronic and magnetic structures, rich surface chemistry and thermal stability. Here, we perform structural, electronic, vibrational and thermal properties of six transition-metal carbides (Re2C, Tc2C, Mo2C, W2C, Os2C, Ru2C) both 2H and 1T phases by first-principle calculations within density functional theory. Although physical and thermal properties of some pristine MXenes put forward to understanding tunable electronic and magnetic properties, many of 1T-phase and almost never of 2H-phase are not investigated in detailed. Firstly, the atomic structure of six MXenes both 1T and 2H phases are optimized, and their respective dynamical stabilities are discussed. Secondly, electronic band structure calculations reveal that the pristine MXenes are metallic. Finally, phonon calculations of pristine MXenes are computed with the density functional perturbation theory and reported. Raman-active modes are predicted and to assign them to specific atomic motions. Ab-inito molecular dynamic simulations (AIMD) are also performed to check the thermal stability of these MXenes. Our results clearly proved that while 2H-W2C, 2H-Mo2C, 2H-Re2C and 1T-W2C can keep the stabilities at very high temperature (1500 K). The results suggest that these pristine MXenes combining with outstanding properties such as non-magnetic metallic state and high-temperature thermal stability would provide promising candidates for using from energy storage to spintronic applications.

The structural, electronic, elastic and vibrational properties of boron nitride (BN) were analyzed using ab initio computational methods based on density functional theory. The exchange-correlation energy functional was evaluated using the local density approximation (LDA) under pressure. BN crystallizes in hexagonal structure (h-BN) with symmetry . The structural transform was obtained at the BN from h-BN transformed into wurtzite (w-BN) with symmetry at 12.5 GPa. During this phase transformation, intermediate states with space group and P3m1were observed. Besides, the electronic properties for the obtained stable phases of BN were calculated. Both structures have a semiconductor character with a direct band gap. We also made elastic and phonon calculations to understand the mechanical and dynamically stability of the obtained phases of BN. BN is stable in both phases. As a result of the literature searches, the obtained intermediate states were first predicted in this study. Thus, we believe that this study will guide the experimental studies to be conducted.

Thermal expansion of α-rhombohedral boron (α-B12) and two isostructural boron-rich pnictides (B12P2 and B12As2) has been studied between 298 and 1280 K by high-temperature synchrotron X-ray diffraction. For all studied phases no temperature-induced phase transitions have been observed. The observed temperature dependencies of the lattice parameters and unit cell volumes were found to be quasi-linear. Variation of the thermal expansion coefficients in the group of boron-rich pnictides (B13N2 – B12P2 – B12As2) was analyzed.

CuZr intermetallic has attracted wide attention because it exhibits a reversible martensitic transformation above 100 °C and could expand the application field of high temperature shape memory alloys. The relationship between the stacking fault energy (SFE) and conductivity of CuZr with different alloying elements (Al, Fe, Ni and Zn) is investigated by first-principles calculations. For <001> slipping direction, the values of unstable SFE for different alloys are predicted and conclude that adding Ni or Fe atom decreases SFE and improves the ductility. Moreover, the addition of Ni atom reduces the unstable SFE of CuZr even by 50%. Meanwhile, both CuZr–Ni and CuZr–Fe have larger conductivity than CuZr, CuZr–Zn and CuZr–Al. Consequently, the lower the unstable SFE of alloy, the better the conductivity. In this way, we can obtain CuZr–Ni or CuZr–Fe with good toughness and conductivity, which has potential applications to manufacture antennas and parabolic radars in aerospace.

We consider a hybrid heterostructure containing an inorganic quantum well in close proximity with an organic material as overlayer. The resonant optical pumping of Frenkel exciton can lead to an efficient indirect pumping of Wannier excitons. As organic material in such hybrid structure we consider crystalline tetracene. In tetracene diffusion length of singlet exciton diffusion is strongly dependent on temperature. We have obtained the exact analytical solution of diffusion equation for exciton in organics at different temperatures defining different diffusion lengths of excitons. Then we have included in consideration Coulomb interaction between organics and QW. It was shown that this interaction multiple increases effectiveness of transfer from organics to QW in the same way as it was predicted early in our publications for inverse transfer from QW to organics. The effectiveness of energy transfer in hybrid with tetracene was calculated by definite method for two selected temperatures that opens possibility to operate in full region of temperatures. Temperature dependence of energy transfer in organics opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic subsystem to the inorganic subsystem. This varying pumping may be used for experimental investigating of different nonlinear effects.

Using a combination of reflectivity and ellipsometry, we determined the far-infrared dielectric functions of molecular beam epitaxy-grown Hg1−xCdxSe thin films between 85 cm−1 and 8, 000 cm−1. Spectroscopic ellipsometry, performed between 400 cm−1 and 8000 cm−1, recovered the dielectric function and the thickness of our Hg1−xCdxSe films. Ellipsometry results were then used to model the reflectivity data allowing us to obtain absolute reflectance values and map the dielectric function from reflectivity between 85 cm−1 and 8, 000 cm−1, and to obtain the absorption due to free electrons, phonons, and band electrons. Specifically, our models find two transverse optical modes for Hg1−xCdxSe, where the HgSe-like mode blue-shifts and the CdTe-like mode red-shifts with increasing Cd concentration.

The electronic and transport properties of BeSiPn2 (Pn = P, As) with chalcopyrite type semiconductor, are studied using the full-potential linear augmented plane wave method (FP-LAPW). The estimated structural properties such as cell parameters a and c, c/a ratio and internal parameters are in reasonable agreement with the measured one. The calculated band structures reveal that the BeSiP2 and BeSiAs2 are semiconductors with a direct bandgap of approximately 1.84 eV and 1.64 eV, respectively. Moreover, the calculated thermoelectric properties show that these materials exhibit a high Seebeck coefficient for the hole and electron doping and interesting values of the figure of merit at high temperature (0.93 at 1019 cm−3 hole concentration). These results, confirming that the BeSiPn2 (Pn = P, As) materials can be promising candidates for high temperature thermoelectric applications.

In this letter, we report an unusual crossover in the current-voltage characteristics of forming-free titanium oxide-based memory bits. The voltage at which crossover between high and low resistance states take place, Vcr gradually shifts to lower bias values with either decreasing sweeping rates, increasing maximum scan voltage or increasing current compliance. Interestingly, the crossover effect is not pronounced for reduced-oxide based memory bits. The mechanism behind these changes in the I-V curves is discussed.

We examine the influence of inter-qubit distances and reservoir temperature on the dynamics of the parameter estimation for the qubit systems considering the interaction of dipole-dipole and collective damping effect. We find that the dynamical behaviour and preservation of the parameter estimation-precision is greatly dependent on the qubits distances and the temperature of the reservoir. Moreover, we study the effect of the qubits-distance and temperature of the reservoir on the dynamics of the fidelity and squeezing entropy for atomic systems. The obtained results show how the considered physical model in the quantum measurement theory can be useful to describe and implement realistic experiments with optimal conditions.