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Optoelectronic functional materials with flexible and in-plane anisotropic properties has been a significant development direction of nanotechnology due to wearable and polarized optoelectronic applications. Herein, the elasticity, global band dispersion, optical dielectric properties of environmentally friendly IVB-VIA layered transition metal trichalcogenides (MX3, M = Zr, Hf; X = S, Se) are investigated systematically by density functional theory with different kinds of van der Waals correction and hybrid functional. The low elastic modulus suggests that they are appropriate for the design of flexible optoelectronic devices. Originating from the effect of d states of chalcogens and s states of transition metals, the dispersion of the valence band edge of monolayer MX3 shows that the effective mass of carriers along the wave vector kx is much heavier than that of carriers along the wave vector ky. This means that the mobility of carriers exhibits obvious in-plane anisotropy. Meanwhile, the optical dielectric properties of monolayer MX3 as well as absorbed photon flux (Jabs) of the related heterostructures display noteworthy in-plane anisotropy in the visible-IR region. The ratio of Jabs from different direction reaches up to 1.7. This work could not only promote understanding of rich photophyiscal properties of transition metal trichalcogenides, but also provide a theoretical reference for the invention of high-performance optoelectronic devices with high flexibility and anisotropy. [ABSTRACT FROM AUTHOR]

This study describes the fabrication of hybrid two-dimensional (2D)-quantum dot (QD) MoS2–AgInS2 photoconductive devices through the mechanical pressing of a MoS2 flake onto an AgInS2 QD film. The devices exhibit an enhanced photoresponse at both continuous and modulated optical excitations, compared with the bare MoS2 or AgInS2 layer, due to the formation of a built-in electric field near the MoS2/AgInS2 interface. The continuous wave photoresponse is significantly higher due to the effective photoconductive gain when electrons flow freely through the MoS2 flake, whereas holes are effectively trapped in AgInS2 QDs. The study highlights the potential of hybrid 2D-QD MoS2–AgInS2 devices for photovoltaic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) have attracted momentous scientific attention because of their intriguing properties, such as high optical transparency, high charge mobility, self-passivating surfaces, adjustable bandgap values, and work function and chemical stability. These TMDC materials have been incorporated into third-generation perovskite solar cell (PSC) devices to boost their solar harvesting and conversion performance. Herein, we provide an overview of the dominant PSC configurations and various modifications that have been carried out on TMDCs that are geared toward the enhancement of the performance of the PSC devices. The integration of TMDCs and their effects on various parts of the PSC devices have been pointed out. Furthermore, the utilization of computational tools in the deep understanding of the TMDC materials and PSC devices has been elucidated. Finally, the challenges and prospects of integrating TMDC materials in the PSC devices have been discussed. [ABSTRACT FROM AUTHOR]

In this study, we synthesized VSx transition metal chalcogenides by the hydrothermal method and changed some parameters (reaction time, synthesis temperature, and adding surfactant) in the synthesis process. In this work, the structure of samples has been analyzed (by x-ray diffraction, ultraviolet–visible, Fourier-transform infrared, field-emission scanning electron microscopy). The vanadium sulfide structure phase altered from VS4 to VS2 by increasing the time and temperature of the reaction. Based on Kramers–Kronig equations, the effect of changing synthesis parameters and sheet dimensions on optical and dielectric parameters was investigated. Different components of the complex refractive index and complex dielectric function are increased by decreasing sheet dimensions. Also, the position of transversal and longitudinal optical modes is shifted to lower wavenumbers by increasing sheet dimensions. Moreover, the real part of the dielectric function alters from negative to positive by sheet dimension's alteration. This study demonstrates the great potential of vanadium sulfide compounds for optoelectronics applications. [ABSTRACT FROM AUTHOR]

There are a lot of problems with the conventional fusion welding process, so ultrasonic welding has been used for about 20 years and has helped a lot of manufacturing industries, including aviation, medicine, and microelectronics. Ultrasonic welding takes less than one second, making it suitable for mass production. Poor weld quality and joint strength are common issues that industries encounter as a result of this process. Actually, the success and quality of the welding are determined by its control parameters. This research examines the impacts of weld time, vibrational amplitude, and weld pressure on the welding of 0.6 mm thick sheets of two different metals, specifically copper and aluminum (AA2024). Responses, including tensile shear stress, weld area, and T-peel stress, are acquired through experiments that follow a full factorial design including four replicas. The highest recorded tensile shear stress was 4.34 MPa, the maximum weld area measured was 63.6 mm2, and the peak T-peel stress reached 1.22 MPa. A second-order non-linear regression model was constructed using all of these data points, which related the responses to the predictors. Due to the importance of quality in the production sector, the process parameters were determined by the combination of genetic algorithm (GA) and fuzzy logic (FL) approaches. The impact of the weld zone temperature on various quality characteristics has been investigated through experiments. It has been noted from the confirmatory test that FL produces superior output outcomes compared to the genetic algorithm, with FL achieving a fuzzy multi-performance index of 0.94 compared to 0.61 for GA. By conducting microstructural analysis, weld quality levels, including "under-weld," "good weld," and "over-weld," were established. [ABSTRACT FROM AUTHOR]

The magnetoimpedance effect allows us to estimate the extent of spin dependent scattering in disordered solids. The change in impedance with respect to applied magnetic field manifests through local change in permeability on the surface and it amplifies at defect sites. The local electrical inhomogeneities are expected to aid this effect through spin dependent scattering. The organic conjugated electrical networks provide scope for producing such inhomogeneities formed by path defects and protonic charge accumulation leading to spin dependent scattering. This hypothesis is investigated in the present work taking polyaniline as a prototype network. The electrical inhomogeneities in the network were controlled by selective oxidation and aging in polyaniline. The Giant Magnetoimpedance (GMI) was observed in the electrically inhomogeneous network with the change in electrical impedance of the order of 50%–60% for lower frequencies with prominent capacitive coupling and a change of the order of 200% at higher frequencies with prominent inductive coupling with the application of magnetic field. However, no spin accumulation was observed in the insulating networks formed by a modified oxidative process. This study is expected to serve as a tool to develop frequency selective spin accumulation based magnetic field sensors and oscillator networks. [ABSTRACT FROM AUTHOR]

We show that the integral cross sections for state-to-state quantum scattering of cold molecules in a magnetic field can be efficiently computed using the total angular momentum representation despite the presence of unphysical Zeeman states in the eigenspectrum of the asymptotic Hamiltonian. We demonstrate that the unphysical states arise due to the incompleteness of the space-fixed total angular momentum basis caused by using a fixed cutoff value Jmax for the total angular momentum of the collision complex J. As a result, certain orbital angular momentum (l) basis states lack the full range of J values required by the angular momentum addition rules, resulting in the appearance of unphysical states. We find that by augmenting the basis with a full range of J-states for every l, it is possible to completely eliminate the unphysical states from quantum scattering calculations on molecular collisions in external magnetic fields. To illustrate the procedure, we use the augmented basis sets to calculate the state-to-state cross sections for rotational and spin relaxation in cold collisions of 40CaH(X2Σ+, v = 0, N = 1, MN = 1, MS = 1/2) molecules with 4He atoms in a magnetic field. We find excellent agreement with benchmark calculations, validating our proposed procedure. We find that N-conserving spin relaxation from the highest-energy to the lowest-energy Zeeman state of the N = 1 manifold, | 11 1 2 〉 → | 1 − 1 − 1 2 〉 is nearly completely suppressed due to the lack of spin–rotation coupling between the fully spin-stretched Zeeman states. Our results demonstrate the possibility of rigorous, computationally efficient, and unphysical state-free quantum calculations on cold molecular collisions and on near-threshold energy levels of strongly anisotropic atom-molecule collision complexes in an external magnetic field. [ABSTRACT FROM AUTHOR]

Bandgap engineering plays a vital role in material development and device optimization due to its significant impact on the photovoltaic and photoelectricity properties of materials. Nevertheless, it is still a great challenge to accurately control the bandgap of semiconductors to achieve the targeted properties of materials. Recently, pressure-induced bandgap regulation has emerged as a novel and effective tool to regulate bandgap, reveal the intrinsic band nature, and construct the in-depth structure–property relationships therein. In this review, the unique techniques of microscopic in situ steady-state UV–Vis absorption spectroscopy and high-pressure diamond anvil cell are introduced. This technique provides a powerful method to monitor the bandgap behaviors at high pressure. Then, the pressure-triggered bandgap responses are outlined based on several typical semiconductors, including metal halide perovskites, inorganic quantum dots, piezochromic molecular compounds, and two-dimensional semiconductor materials. The summarized structural effects on bandgap evolution and the general principles for bandgap engineering under high pressure are expected to provide guidance for further material design under ambient conditions. Microscopic absorption spectroscopy detection under high pressure is proven to be an ideal platform for developing functional materials and high-performance devices. [ABSTRACT FROM AUTHOR]

Cemented carbide (WC-Co), the widely used tool-die material, is difficult to be machined by conventional and nonconventional techniques. This inspired exploring additive manufacturing (AM) of this material. However, porosity, brittleness due to cobalt depletion, etc. have been reported in the literature with rare success. For the AM of WC-Co, the current work focuses on directed energy deposition, which can be implemented with existing laser cutting-welding workstations, with modifications. To ensure the retention of cobalt even after inevitable vaporization of some of its initial content during deposition, 20 wt. % of Co was mixed with WC powder by low-energy ball milling. Laser power, scan speed, and powder flow rate were varied following a full-factorial design of experiments. The analysis of variance revealed that the experimental model and most of the parameters were significant. Only the laser power came out to be insignificant for the contact angle. The track height and width increased with the laser power and reduced with the scan speed. The contact angle increased with the scan speed and reduced with the powder flow rate. Cross sections of the deposited track showed no pores or cracks. Multiobjective optimization with gray relational analysis was conducted to get the parameter combination giving high values of the contact angle, track height, and width simultaneously. The optimum parameter combination, thus, obtained is 700 W laser power, 5 mm/s scan speed, and 5 g/min powder flow rate. This yielded 305 ± 40 μm track height, 2132 ± 33 μm width, and 152° ± 2° contact angle. [ABSTRACT FROM AUTHOR]

Quantum confinement effects can induce the formation of discrete nanostructures with well-defined preferred heights in thin metallic films. In most systems, such electronic growth modes are weak and limited to cryogenic conditions. Recently, however, we have discovered that metals grown upon van der Waals surfaces can exhibit electronic growth at, or even above, room temperature to spontaneously form well-defined and highly stable nanostructures. Here, we explore the initial stages of room temperature deposition of Pd onto MoS2. We found that, even for minimal thicknesses, Pd spontaneously formed discrete islands with three atomic layers. The islands maintained this preferred height for nominal coverages below three atomic layers. At higher coverages, the preferred height switched abruptly to six atomic layers. Unlike previous studies using Au or Ag, the islands did not increase laterally with coverage but rather increased in number with lateral size remaining about the same. The preferred heights in Pd/MoS2 correlate to the Pd Fermi surface topography and are also consistent with thicknesses showing minima in the density of states at the Fermi level, which suggest that the electronic growth modes are the driving factors in these self-assembled Pd nanostructures. The Pd system shows a preference for island nucleation compared to Au and Ag which grow laterally with increasing coverage. This is likely related to differences in bonding at the interface as Pd is typically much more reactive than Ag or Au. [ABSTRACT FROM AUTHOR]

We explore a new glassy material for radiation shielding applications. Novel transparent and non-toxic Bi2O3–B2O3 glasses including different concentrations of CdO were prepared by the conventional melt quenching method. The prepared samples were characterized and analyzed by using various analytical tools (XRD, FTIR, Raman, DSC, and UV-Vis-NIR). Ab initio molecular dynamics simulations were carried out to create structural models of the materials, and these were compared to our measurements. To the best of our knowledge, this is the first study to compare the vibrations obtained experimentally with the vibrational density of states obtained from an ab initio computer model for these materials. The radiation shielding properties were measured for the photon energy range (10−3–105 MeV): both mass attenuation coefficient (μ/p) and effective atomic number (Zeff) showed a gradual increase with an increase in the CdO content. The mean-free-path, tenth value layer, half-value layer, and electron density for all prepared glasses were estimated. Promising results were achieved with the new glasses for radiation shielding purposes such as nuclear reactor and medical applications. The structural, electronic, and vibrational properties of the computer models revealed a topologically disordered, but chemically ordered network, and our vibrational computations provide direct insight into several Raman peaks observed for the materials. [ABSTRACT FROM AUTHOR]

Field-induced superconductivity has been observed on the surfaces of various materials; however, the underlying mechanism of this two-dimensional superconductivity remains elusive. While tunneling spectroscopy measurements provide valuable insights into the microscopic nature of the superconducting state, there is a scarcity of tunneling spectroscopy measurements specifically focused on field-induced superconductivity when compared to transport measurements. In this study, we present a novel approach for tunneling spectroscopy using top metal contacts on field-induced superconducting MoS2. Our experimental findings, including the energy gap values, are consistent with those of a previous study conducted using a different device configuration. The observed energy-dependent density of states cannot be explained by the conventional BCS mechanism. We address the impact of inhomogeneity within the superconducting phase and discuss potential methods for its suppression. The proposed tunneling spectroscopy technique offers simplicity and ease of implementation, making it applicable for investigating other two-dimensional superconducting systems. [ABSTRACT FROM AUTHOR]

Artificial intelligence plays a very prominent role in many fields, and of late, this term has been gaining much more popularity due to recent advances in machine learning. Machine learning is a sphere of artificial intelligence where machines are responsible for doing daily chores and are believed to be more intelligent than humans. Furthermore, artificial intelligence is significant in behavioral, social, physical, and biological engineering, biomathematical sciences, and many more disciplines. Fractional-order modeling of a real-world problem is a powerful tool for understanding the dynamics of the problem. In this study, an investigation into a fractional-order epidemic model of the novel coronavirus (COVID-19) is presented using intelligent computing through Bayesian-regularization backpropagation networks (BRBFNs). The designed BRBFNs are exploited to predict the transmission dynamics of COVID-19 disease by taking the dataset from a fractional numerical method based on the Grünwald–Letnikov backward finite difference. The datasets for the fractional-order mathematical model of COVID-19 for Wuhan and Karachi metropolitan cities are trained with BRBFNs for biased and unbiased input and target values. The proposed technique (BRBFNs) is implemented to estimate the integer and fractional-order COVID-19 spread dynamics. Its reliability, effectiveness, and validation are verified through consistently achieved accuracy metrics that depend on error histograms, regression studies, and mean squared error. [ABSTRACT FROM AUTHOR]

We report high resolution electronic spectroscopy of cold magnesium monofluoride (MgF) molecules in the gas phase, which are created by a combination of laser ablation, chemical reaction, and 6 K helium buffer-gas cooling. Thanks to the sufficient population in the low-lying rotational states, the P, Q, and R branches in the electronic transition of the X2Σ+ to A2Π state are able to be measured unambiguously by in-cell absorption spectra. For the first time, we show that the A 2 Π state of MgF is actually a normal state, not an inverted one. The laser cooling relevant transitions X 2 Σ + v = 0,1 , N = 1 → A 2 Π 1 / 2 (v = 0 , J ′ = 1 / 2) are also identified, along with the hyperfine structure of the X 2 Σ + (v = 0, N = 1) state. This study provides an important step for ongoing laser cooling experiments of MgF molecules. [ABSTRACT FROM AUTHOR]

Rigorous coupled-channel quantum scattering calculations on molecular collisions in external fields are computationally demanding due to the need to account for a large number of coupled channels and multiple total angular momenta J of the collision complex. We show that by restricting the total angular momentum basis to include only the states with helicities K ≤ Kmax, it is possible to obtain accurate elastic and inelastic cross sections for low-temperature He + CaH, Li + CaH, and Li + SrOH collisions in the presence of an external magnetic field at a small fraction of the computational cost of the full coupled-channel calculations (where K is the projection of the molecular rotational angular momentum on the atom-diatom axis). The optimal size of the truncated helicity basis set depends on the mechanism of the inelastic process and on the magnitude of the external magnetic field, with the minimal basis set (Kmax = 0) producing quantitatively accurate results for, e.g., ultracold Li + CaH and Li + SrOH scattering at low magnetic fields, leading to nearly 90-fold gain in computational efficiency. Larger basis sets are required to accurately describe the resonance structure in the magnetic field dependence of Li + CaH and Li + SrOH inelastic cross sections in the few partial wave-regime as well as indirect spin relaxation in He + CaH collisions. Our calculations indicate that the resonance structure is due to an interplay of the spin-rotation and Coriolis couplings between the basis states of different K and the couplings between the rotational states of the same K induced by the anisotropy of the interaction potential. [ABSTRACT FROM AUTHOR]

By combining the exclusive characteristics of a two-dimensional MoS2 layered material with a conventional key material, aluminum nitride (AlN), a flexible supercapacitor electrode can be realized. We present a bendable electrode that is straightforwardly grown on stainless-steel foil via a binder-free sputtering route. The inherent merits of good conductive pathways among MoS2 nanolayers and enriched pseudocapacitive and dielectric activity from AlN nanoflowers enable synergism of the intermixed porous structure. This unique surface morphology facilitates sulfur and nitrogen edges to make insertion/de-insertion of Li-ions more feasible to store electrochemical energy. The MoS2-AlN@SS hybrid working electrode achieves a gravimetric capacitance of 372.35 F/g at a 5 mV/s scan rate with a wide potential window of 2 V in a 1 M Li2SO4 electrolytic aqueous solution. The composite thin film of better adhesion with the current collector exhibits a remarkably high specific power of 28.05 W h/kg at a specific power of 0.26 kW/kg, simultaneously an advanced cycling lifespan of 93% over 5000 charge–discharge cycles. The capacity of the hybrid electrode is almost unperturbed under bending from 0° to 175°, while only ∼5% degradation in capacitance was noticed at a flexing angle of 175°. These distinctive features of this electrode material elucidate the practical applicability and recommend it as a promising candidate in wearable bendable supercapacitors. [ABSTRACT FROM AUTHOR]

The emergence of supramolecular aggregates from simple microscopic interaction rules is a fascinating feature of complex fluids which, besides its fundamental interest, has potential applications in many areas, from biological self-assembly to smart material design. We here investigate by Monte Carlo simulation the equilibrium structure of a two-dimensional mixture of asymmetric dimers and spheres (disks). Dimers and disks are hard particles, with an additional short-range attraction between a disk and the smaller monomer of a dimer. The model parameters and thermodynamic conditions probed are typical of colloidal fluid mixtures. In spite of the minimalistic character of the interaction, we observe--upon varying the relative concentration and size of the two colloidal species--a rich inventory of mesoscale structures at low temperature, such as clusters, lamellæ (i.e., polymer-like chains), and gel-like networks. For colloidal species of similar size and near equimolar concentrations, a dilute fluid of clusters gives way to floating lamellæ upon cooling; at higher densities, the lamellæ percolate through the simulation box, giving rise to an extended network. A crystal-vapour phase-separation may occur for a mixture of dimers and much larger disks. Finally, when the fluid is brought in contact with a planar wall, further structures are obtained at the interface, from layers to branched patterns, depending on the nature of wall-particle interactions. [ABSTRACT FROM AUTHOR]

We investigate the structure of a dilute mixture of amphiphilic dimers and spherical particles, a model relevant to the problem of encapsulating globular "guest" molecules in a dispersion. Dimers and spheres are taken to be hard particles, with an additional attraction between spheres and the smaller monomers in a dimer. Using the Monte Carlo simulation, we document the low-temperature formation of aggregates of guests (clusters) held together by dimers, whose typical size and shape depend on the guest concentration X. For low X (less than 10%), most guests are isolated and coated with a layer of dimers. As X progressively increases, clusters grow in size becoming more and more elongated and polydisperse; after reaching a shallow maximum for X ≈50%, the size of clusters again reduces upon increasing X further. In one case only ( X = 50%and moderately low temperature) the mixture relaxed to a fluid of lamellae, suggesting that in this case clusters are metastable with respect to crystal-vapor separation. On heating, clusters shrink until eventually the system becomes homogeneous on all scales. On the other hand, as the mixture is made denser and denser at low temperature, clusters get increasingly larger until a percolating network is formed. [ABSTRACT FROM AUTHOR]

We use accurate quantum scattering calculations to elucidate the role of short-range molecule-field interactions in atom-molecule inelastic collisions and abstraction chemical reactions at low temperatures. We consider two examples: elastic and inelastic scattering of NH(3Σ) molecules with Mg(1S) atoms in a magnetic field; reactive scattering LiF + H→Li + HF in an electric field. Our calculations suggest that, for non-reactive collision systems and abstraction chemical reactions, the molecule-field interactions cannot generally be neglected at short range because the atom-molecule potential passes through zero at short range. An important exception occurs for Zeeman transitions in atom-molecule collisions at magnetic fields ≲1000 G, for which the molecule-field couplings need only be included at large ρ outside the range of the atom-molecule interaction. Our results highlight the importance of an accurate description of ρ-dependent molecule-field interactions in quantum scattering calculations on molecular collisions and chemical reactions at low temperatures. [ABSTRACT FROM AUTHOR]

A heterostructure of MoS2/SnO2 has been fabricated. A SnO2 film was deposited by Sn sputtering followed by oxidation of a Sn film in the ambient. Later, a MoS2 film was deposited on SnO2 by pulsed laser deposition. The built-in electric potential generated at the SnO2/MoS2 interface facilitates self-powered broadband photodetection ranging from the ultraviolet-visible to near-infrared (NIR) wavelength. Under NIR illumination, the device exhibits excellent photoresponse with a responsivity of 0.35 A W−1 and a detectivity of 1.25 × 1011 Jones at 0 V. Moreover, the device shows faster response with rise/fall times as 153/200 ms. The excellent performance of the device is attributed to the high electron transport behavior of SnO2 and a built-in electric field at the interface. [ABSTRACT FROM AUTHOR]

Ultracold molecules offer unprecedented opportunities for the controlled interrogation of molecular events, including chemical reactivity in the ultimate quantum regime. The proliferation of methods to create, cool, and confine them has allowed the investigation of a diverse array of molecular systems and chemical reactions at temperatures where only a single partial wave contributes. Here we present a brief account of recent progress on the experimental and theoretical fronts on cold and ultracold molecules and the opportunities and challenges they provide for a fundamental understanding of bimolecular chemical reaction dynamics. [ABSTRACT FROM AUTHOR]

Reddish orange-emitting 0.948(K0.5 Na 0.5)NbO3-0.052LiSbO3-xmol%Sm2O3 (KNN-5.2LS-xSm2O3) lead-free piezoelectric ceramics with good piezoelectric properties were fabricated in this study, and the photoluminescence and electrical properties of the ceramics were systematically studied. Results showed that Sm2O3 substitution into KNN-5.2LS induces a phase transition from the coexistence of orthorhombic and tetragonal phases to a pseudocubic phase and shifts the polymorphic phase transition (PPT) to below room temperature. The temperature stability and fatigue resistance of the modified ceramics were significantly improved by Sm2O3 substitution. The KNN-5.2LS ceramic with 0.4 mol. % Sm2O3 exhibited temperature-independent properties (25-150 °C), fatigue-free behavior (up to 106 cycles), and good piezoelectric properties (d 33 *= 230 pm/V, d 33 = 176 pC/N, k p = 35%). Studies on the photoluminescence properties of the samples showed strong reddish-orange emission upon blue light excitation; these emission intensities were strongly dependent on the doping concentration and sintering temperature. The 0.4 mol. % Sm2O3-modified sample exhibited temperature responses over a wide temperature range of 10-443 K. The maximum sensing sensitivity of the sample was 7.5 × 10-4 K at 293 K, at which point PPT occurred. A relatively long decay lifetime t of 1.27-1.40 ms and a large quantum yield η of 0.17-0.19 were obtained from the Sm-modified samples. These results suggest that the KNN-5.2LS-xSm2O3 system presents multifunctional properties and significant technological potential in novel multifunctional devices. [ABSTRACT FROM AUTHOR]

Nonlinear optical absorption and optical power limiting properties of Fe2O3 hexagonal nanomorphotype are investigated using open aperture Z-scan technique with the 5 ns and 100 fs laser pulses, at 532nm and 800 nm excitation domains. At relatively low pulse energies (below 5 μJ), sample shows saturable absorption (SA), but on going to the higher energies an interesting switchover from saturable absorption to effective two photon absorption is observed in both excitation domains. The magnitude of effective two photon absorption coefficients is calculated to be in the range of 10-10 m/W for nanosecond and 10-15 m/W for femtosecond laser pulse energies, respectively. XRD and TEM study reveals the polycrystalline nature, hexagonal morphology, and size of the nanostructure. The luminescence emission property is examined by photoluminescence spectroscopy (PL). It is found that some strange features exist in the luminescence spectra that are consistent with the nanoparticles size distribution. The PL emission lines are explained as originated from various optical band edges due to the size induced quantum confinement and band gap resonant PL absorption/emission behavior of semiconductor nanostructures. [ABSTRACT FROM AUTHOR]

Generally, sheet thickness plays a significant role in the selection of appropriate process parameters in order to produce high quality weld joint in the laser welding process. The heat sink capacity and weld penetration are known as two criteria that are mainly influenced by sheet thickness. In this study, the effect of sheet thickness, welding speed, nozzle distance, and laser power were investigated in order to determine the temperature distribution near the melt pool, dimensions of molten pool through experimental and numerical analysis. The weld joint mechanical characterization was determined via elongation rate and tensile strength. The highest value of tensile strength is about 80% of the typical base metal and the elongation of the welded samples achieved about 40% of the base metal. The thinner sheets showed more sensitivity related to the elongation of the joint by increasing the welding speed. Also, the temperature rise with increasing laser power near the melt pool for the thinner sheet was about 200 °C in comparison to the 3 mm sheet, which is about 90 °C. The obtained simulation results for the maximum temperature discrepancy at near the melt pool was 12 °C and 4 °C for 1 and 3 mm thickness orderly, which depicts good agreement with the temperature experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we explore the capabilities of MoS2 and WS2 2D monolayers to produce radiation in the terahertz range by the generation of high-order harmonics. This phenomenon, which is a result of the non-linear response of the electronic carrier population to the applied electric field, is studied by using a particle ensemble stochastic simulation approach based on the Monte Carlo method. The power of the produced harmonic signals is studied against the electric field amplitude, the external temperature, and the frequency of the excitation. Additionally, the stochastic nature of the simulation tool enables us to discern the purely discrete harmonic signal from the background spectral noise that comes from intrinsic carrier velocity fluctuations in the diffusive regime, permitting to set bandwidth thresholds for harmonic extraction. It was found that both TMDs showed similar bandwidth thresholds when compared to the III–V semiconductor at low temperatures, while WS2 would be a far better choice over MoS2 for exploitation of the seventh and ninth harmonic generation. [ABSTRACT FROM AUTHOR]

Alkali atoms trapped in solid hydrogen matrices have demonstrated ultralong electron spin coherence times and are promising as quantum sensors. Their spin coherence is limited by magnetic noise from naturally occurring orthohydrogen molecules in the parahydrogen matrix. In the gas phase, the orthohydrogen component of hydrogen can be converted to parahydrogen by flowing it over a catalyst held at cryogenic temperatures, with lower temperatures giving a lower orthohydrogen fraction. In this work, we use a single cryostat to reduce the orthohydrogen fraction of hydrogen gas and grow a solid matrix from the resulting high-purity parahydrogen. We demonstrate the operation of the catalyst down to a temperature of 8 K, and we spectroscopically verify that orthohydrogen impurities in the resulting solid are at a level <10−6. We also find that, at sufficiently low temperatures, the cryogenic catalyst provides isotopic purification, reducing the HD fraction. [ABSTRACT FROM AUTHOR]

We report the ultrafast carrier dynamics of an SnSe2–SnSe composite thin film (∼150 nm thick) deposited using thermal evaporation of in-house synthesized SnSe2 powder. Raman and UV–visible spectroscopy supports the optical properties (direct and indirect bandgaps of 1.86 eV and 0.96 eV, respectively). Ultrafast transient spectroscopy is used to study the charge excited state dynamics in the SnSe2–SnSe composite thin film in the femtosecond to nanosecond interval. An energy model has been proposed based on the ultrafast transient absorption and the thin film's steady-state absorption studies. This article provides comprehensive knowledge about the excited carriers and their relaxations in 0.9 ps–31.1 ns via different trap states. [ABSTRACT FROM AUTHOR]

Two-dimensional materials are gaining more and more attention in the field of electronic devices because of their unique advantages, such as high crystalline quality and clean and flat contact planes; compared to traditional materials, the use of two-dimensional materials as the working layer of a resistive random-access memory (RRAM) has the potential to further reduce the device size and enhance its performance. Herein, a black phosphorus (BP) single crystal flake passivated by hafnium oxide is used as the working layer for an RRAM. The devices show a switching on/off ratio of 102 in more than 100 cycles, and others can even be as high as 106. We speculated the working mechanism of the BP RRAM based on the results of serial experiments and transport analysis. [ABSTRACT FROM AUTHOR]

Grand-canonical transition-matrix Monte Carlo and histogram reweighting techniques are used herein to study the vapor-liquid coexistence properties of two-dimensional (2D) flexible oligomers with varying chain lengths (m = 1-8). The phase diagrams of the various 2D oligomers follow the correspondence state (CS) principle, akin to the behavior observed for bulk oligomers. The 2D critical density is not influenced by the oligomer chain length, which contrasts with the observation for the bulk oligomers. Line tension, calculated using Binder's formalism, in the reduced plot is found to be independent of chain length in contrast to the 3D behavior. The dynamical properties of 2D fluids are evaluated using molecular dynamics simulations, and the velocity and pressure autocorrelation functions are investigated using Green-Kubo (GK) relations to yield the diffusion and viscosity. The viscosity determined from 2D non-equilibrium molecular dynamics simulation is compared with the viscosity estimated from the GK relations. The GK relations prove to be reliable and efficient for the calculation of 2D transport properties. Normal diffusive regions are identified in dense oligomeric fluid systems. The influence of molecular size on the diffusivity and viscosity is found to be diminished at specific CS points for the 2D oligomers considered herein. In contrast, the viscosity and diffusion of the 3D bulk fluid, at a reduced temperature and density, are strongly dependent on the molecular size at the same CS points. Furthermore, the viscosity increases and the diffusion decreases multifold in the 2D system relative to those in the 3D system, at the CS points. [ABSTRACT FROM AUTHOR]

We report on the strong red emission properties of lead-free perovskite ferroelectric Pr3+-doped Na0.5Bi0.5TiO3 (NBT: Pr3+) thin films without the need of charge compensation. The thin films were prepared by a chemical solution deposition method combined with a rapid thermal annealing process at 700 °C. The strong red emission assigned to prominent 1D2→3H4 transitions of the Pr3+ ions at 611 nm was observed together with a very weak blue-green emission, indicating the commercial use potential of the lead-free perovskite NBT: Pr3+ ferroelectric thin film materials. The energy transfer from the host lattice to the Pr3+ ions should be responsible for the strong red emission, while the weak blue-green emission might be due to the quenching of 3P0 induced by a low-lying Pr3+/Ti4+↔Pr4+/Ti3+ intervalence charge transfer state. The lead-free NBT: Pr3+ thin films also exhibit good ferroelectric and dielectric properties. [ABSTRACT FROM AUTHOR]

The interpretation of the linear character of the observable classic rectilinear diameter law and the linear character of the Zeno-line (unit compressibility line Z=1) on the basis of global isomorphism between Ising model (lattice gas) and simple fluid is proposed. The correct definition of the limiting nontrivial Zeno state is given and its relation to the locus of the critical point is derived within this approach. We show that the liquid-vapor part of the phase diagram of the molecular fluids can be described as the isomorphic image of the phase diagram of the lattice gas. It is shown how the position of the critical points of the fluids of the Lennard-Jones type can be determined based on the scaling symmetry. As a sequence, the explanation of the well-known fact about “global” cubic character of the coexistence curve of the molecular fluids is proposed. [ABSTRACT FROM AUTHOR]

Spatial updating grand canonical Monte Carlo algorithms are generalizations of random and sequential updating algorithms for lattice systems to continuum fluid models. The elementary steps, insertions or removals, are constructed by generating points in space either at random (random updating) or in a prescribed order (sequential updating). These algorithms have previously been developed only for systems of impenetrable spheres for which no particle overlap occurs. In this work, spatial updating grand canonical algorithms are generalized to continuous, soft-core potentials to account for overlapping configurations. Results on two- and three-dimensional Lennard–Jones fluids indicate that spatial updating grand canonical algorithms, both random and sequential, converge faster than standard grand canonical algorithms. Spatial algorithms based on sequential updating not only exhibit the fastest convergence but also are ideal for parallel implementation due to the absence of strict detailed balance and the nature of the updating that minimizes interprocessor communication. Parallel simulation results for three-dimensional Lennard–Jones fluids show a substantial reduction of simulation time for systems of moderate and large size. The efficiency improvement by parallel processing through domain decomposition is always in addition to the efficiency improvement by sequential updating. [ABSTRACT FROM AUTHOR]

A theory for concentration fluctuations in binary polymer blends is developed using field-theoretic techniques. The theory provides a simple, unified framework for addressing a number of important issues. First, consideration of the fluctuation and correlation effects on different length scales leads to a clarification of three different X parameters and their interrelationship. By incorporating interaction (modeled by the bare χ[sup b]) and packing effects up to the polymer size, an effective χ[sup e] emerges as the natural parameter for characterizing the molecular compatibility of the two polymer species. The measured quantity in small-angle neutron scattering (SANS) experiments is an apparent χ[sup a] that includes long wavelength critical and spinodal fluctuations, and is related to χ[sup e] through a self-consistent equation. χ[sup a] exhibits the typical upward parabolic composition dependence observed in experiments and computer simulations. Second, a unified Ginzburg criterion involving both the composition and temperature (or temperaturelike variable) is derived that is applicable to both the critical and the off-critical spinodal regimes. The common characterization of the Ginzburg criterion in terms of a range of temperature (or temperaturelike variable) alone is generally inadequate. The molecular weight scaling proposed by de Gennes and Binder in the respective critical and off-critical spinodal regimes are recovered as special cases in the limit of large molecular weights. For typical molecular weights used in experiments the Ginzburg region is larger than commonly believed. Finally, the nature of the thermodynamic spinodal is examined. It is shown that a true off-critical thermodynamic spinodal does not exist in spatial dimensions less than 4. In its place, a pseudo-spinodal can be defined where the susceptibility reaches a finite maximum. The pseudo-spinodal precedes the mean-field spinodal but approaches the latter in the... [ABSTRACT FROM AUTHOR]

Investigates the phase diagram of the four-dimensional Lennard-Jones fluid using the Gibbs ensemble Monte Carlo (GEMC) method. Influence of particle numbers and their distribution between the liquid and gas phases; Simulation parameters for GEMC of the four-dimensional Lennard-Jones fluid.

Reports that the thermodynamic properties of model structurally symmetric polymer blends were calculated using a theory that is a generalization of the optimized cluster theories for atomic mixtures and single component molecular systems. Optimized cluster theory of binary polymer blends; Diagrammatically proper integral equation theory.

Reports on fluctuation effects in diblock copolymer fluids. Analytic Polymer Reference Interaction Site Model (PRISM) theory of structurally and interaction symmetric Gaussian diblock copolymer fluids; Estimated location of the order-disorder transition; Numerical applications of PRISM theory.

Reports on the development of a quasi-two-dimensional Stockmayer model in which the center of mass of the molecule is confined on a plane while the dipole of the molecule can rotate freely in three dimensional space. Use of the Gibbs ensemble Monte Carlo technique to determine the vapor-liquid equilibria of the model fluids; Systems with different reduced dipole moments studied.

Details a theory for the thermodynamic properties of binary polymer blends to predict the compositional dependence of the effective chi parameter X(sub s) in isotopic polyethylene mixtures. Generalization of the optimized cluster theory for single component molecular fluids; Exact cluster expansions for the Helmholtz free energy and pair-correlation functions.