Applications In Optoelectronic Devices Research Articles

High-performance flexible photodetectors based on CdTe/MoS2 heterojunction.

Flexible photodetectors have attracted escalating attention due to their pivotal role in next-generation wearable optoelectronic devices. This work presents high-performance photodetector devices based on CdTe/MoS2 heterojunctions, showcasing outstanding photodetecting and distinctive mechanical properties. The MoS2 film was exfoliated from bulk layered MoS2 and covered by a sputtered ultrathin CdTe film (∼8.4 nm) to form a heterojunction. Benefitting from the photovoltaic effect induced by the built-in electrical field near the high-quality interface, the fabricated CdTe/MoS2 heterojunction photodetector can operate as a self-powered photodetector without any external bias voltage, especially showing a high photodetectivity of 5.84 × 1011 Jones, remarkable photoresponsivity of 270.3 mA W-1, fast photoresponse with a rise/fall time of ∼44.8/134.2 μs and excellent bending durability. These results demonstrate that the CdTe/MoS2 heterojunctions could have significant potential for future applications in optoelectronic devices.

Synthesis of Hybrid Tin-Based Perovskite Microcrystals for LED Applications.

Considerable focus on tin-based perovskites lies on substitution to leadhalide perovskites for the fabrication of eco-friendly optoelectronic devices.The major concern related to tin-based perovskite devices are mainly thestability and the efficiency. However, thinking on the final commercializationscope, other considerations such as precursor stability and cost are majorfactors to carry about. In this regard, this work presents a robust and facilesynthesis of 2D A2SnX4 (A = 4-fluorophenethylammonium(4-FPEA); X = I, Br, I/Br) and 3D FASnI3 perovskite microcrystals followinga developed synthesis strategy with low-cost starting materials. In thisdeveloped methodology, acetic acid is used as a solvent, which helps to protectfrom water by making a hydrophobic network over the perovskite surface, andhence provides sufficient ambient and long-term inert atmosphere stability ofthe microcrystals. Further, the microcrystals are recrystallized in thin filmsfor LED application, allowing the fabrication of orange, near-infrared and purered emitting LEDs. The two-step recrystallized devices show better performanceand stability in comparison to the reference devices made by using commercialprecursors. Importantly, the developed synthesis methodology is defined as ageneric method for the preparation of varieties of hybrid tin-based perovskitesmicrocrystals and application in optoelectronic devices.

Accelerated Discovery of Halide Perovskite Materials via Computational Methods: A Review

Halide perovskites have gained considerable attention in materials science due to their exceptional optoelectronic properties, including high absorption coefficients, excellent charge-carrier mobilities, and tunable band gaps, which make them highly promising for applications in photovoltaics, light-emitting diodes, synapses, and other optoelectronic devices. However, challenges such as long-term stability and lead toxicity hinder large-scale commercialization. Computational methods have become essential in this field, providing insights into material properties, enabling the efficient screening of large chemical spaces, and accelerating discovery processes through high-throughput screening and machine learning techniques. This review further discusses the role of computational tools in the accelerated discovery of high-performance halide perovskite materials, like the double perovskites A2BX6 and A2BB′X6, zero-dimensional perovskite A3B2X9, and novel halide perovskite ABX6. This review provides significant insights into how computational methods have accelerated the discovery of high-performance halide perovskite. Challenges and future perspectives are also presented to stimulate further research progress.

Optically Mediated Nonvolatile Resistive Memory Device Based on Metal-Organic Frameworks.

Metal-organic frameworks (MOFs), characterized by tunable porosity, high surface area, and diverse chemical compositions, offer unique prospects for applications in optoelectronic devices. However, the prevailing research on thin-film devices utilizing MOFs has predominantly focused on aspects such as information storage and photosensitivity, often neglecting the integration of the advantages inherent in both photonics and electronics to enhance optical memory. This work demonstrates a light-mediated resistive memory device based on a highly oriented porphyrin-based MOFs film, in which the resistance state of the memristor is modulated by light, realizing the integration of the perception and storage of optical information. The memristor shows excellent performance with a wide light range of 405-785nm and a persistent photoconductivity phenomenon up to 8.3 × 103 s. Further mechanistic studies have revealed that the resistive switching effect in the memristor is primarily associated with the reversible formation and annihilation of Ag conductive filaments.

First principle investigations of opto-electronic and thermoelectric response of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds

We have investigated the structural, electronic, optical, and thermoelectric behavior of halide-based double perovskites A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds to reveal their potential in various opto-electronic and thermoelectric applications using first-principle calculations. For the computation of the various properties of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds, we have used approximations available within density functional theory (DFT). The energy bands and density of states have been used to elucidate the electronic response of the studied compounds, while the interpretation of optical properties is presented in terms of dielectric tensor, absorption coefficient, reflectivity, refraction and energy loss spectra. The investigated compounds exhibit a direct band gap within the energy range of 1.36 to 2.24 eV, indicating the promising nature of these compounds for diverse optoelectronic applications. Moreover, thermoelectric properties such as the figure of merit, power factor, Seebeck coefficient, specific heat, electric and thermal conductivity have also been computed for the studied compounds. Our investigation unveils the remarkable optoelectronic characteristics of the studied perovskites, which can be attributed to their advantageous bandgap and highly effective light absorption capabilities. Furthermore, these perovskites showcase exceptional thermodynamic stability, elevated electrical conductivity, favorable figure of merit (ZT) values, and reduced thermal conductivities. These findings suggest their suitability for applications in optoelectronic devices and thermoelectric applications. In this study, it is found that A2TlAsBr6 compounds exhibit significant absorption in the visible spectrum, rendering them more favorable for optoelectronic applications compared to A2TlAsCl6 compounds. Conversely, for thermoelectric applications, the Cl-based perovskites studied show greater promise than their Br-based counterparts. The modified Becke–Johnson (mBJ) potential emerges as the most precise approach for analyzing the electronic, optical, and thermoelectric characteristics of A2TlAsX6 (where A = K, Rb; X = Cl, Br) perovskites, surpassing other approximations utilized in present study.

A systematic first-principles investigation of the structural, electronic, mechanical, optical, and thermodynamic properties of Half-Heusler ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) for spintronics and optoelectronics applications.

This paper is the first to look at the structural, electronic, mechanical, optical, and thermodynamic properties of the ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) half-Heusler (HH) using DFT based first principles method. The lattice parameters that we have calculated are very similar to those obtained in prior investigations with theoretical and experimental data. The positive phonon dispersion curve confirm the dynamical stability of ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The electronic band structure and DOS confirmed that the studied materials ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) are direct band gap semiconductors. The investigation also determined significant constants, including dielectric function, absorption, conductivity, reflectivity, refractive index, and loss function. These optical observations unveiled our compounds potential utilization in various electronic and optoelectronic device applications. The elastic constants were used to fulfill the Born criteria, confirming the mechanical stability and ductility of the solids ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The calculated elastic modulus revealed that our studied compounds are elastically anisotropic. Moreover, ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) has a very low minimum thermal conductivity (Kmin), and a low Debye temperature (θD), which indicating their appropriateness for utilization in thermal barrier coating (TBC) applications. The Helmholtz free energy (F), internal energy (E), entropy (S), and specific heat capacity (Cv) are determined by calculations derived from the phonon density of states.

(Ge2S8)100-xTex chalcogenide glasses: Physico-mechanical study for NIR optical devices

To better understand the variations in physical, mechanical, and electrical properties, (Ge2S8)100-xTex chalcogenide glasses have been synthesized. These glasses encompass a composition range of 0 ≤ x ≤ 12. The mechanical properties have been studied by determining the longitudinal (νL) and transverse (νT) ultrasonic velocities. A network structure evaluation with composition has been performed via parameters like coordination number (<Nr>), crosslinking density (DCL), glass transition temperature (Tg), etc. Also, the elastic parameters trend values have been associated with the decrease in the cohesive energy value of the system. An overall physical analysis of the Ge-S-Te systems reveals that the system's rigidity and the cross-linking density are decreasing. Within the temperature range of 300–420 K, the temperature dependency of the dark conductivity and photoconductivity has been investigated. The intensity-dependent photoconductivity is governed by a power law, with intensity (Iph = Gδ) with δ lying between 0.5 and 1. The photosensitivity values reveal that the glassy system may be suitable for applications in optoelectronic devices. A correlation among the parameters has been established by calculating elastic parameters and conductivity measurements and evaluating the network structure theoretically. The present efforts clarify the composition-structure dependence and relationship in the Ge-S-Te glass series.

Covalent Bond Torsion-Enabled Unique Crystal-Phase Transformation of an Organic Semiconductor for Multicolor Light-Emitting Transistors.

High-mobility and color-tunable highly emissive organic semiconductors (OSCs) are highly promising for various optoelectronic device applications and novel structure-property relationship investigations. However, such OSCs have never been reported because of the great trade-off between mobility, emission color, and emission efficiency. Here, we report a novel strategy of molecular conformation-induced unique crystalline polymorphism to realize the high mobility and color-tunable high emission in a novel OSC, 2,7-di(anthracen-2-yl) naphthalene (2,7-DAN). Interestingly, 2,7-DAN has unique crystalline polymorphism, which has an almost identical packing motif but slightly different molecular conformation enabled by the small bond rotation angle variation between anthracene and naphthalene units. More remarkably, the subtle covalent bond rotation angle change leads to a big change in color emission (from blue to green) but does not significantly modify the mobility and emission efficiency. The carrier mobility of 2,7-DAN crystals can reach up to a reliable 17 cm2 V-1 s-1, which is rare for the reported high-mobility OSCs. Based on the unique phenomenon, high-performance light-emitting transistors with blue to green emission are simultaneously demonstrated in an OSC crystal. These results open a new way for designing emerging multifunctional organic semiconductors toward next-generation advanced molecular (atomic)-scale optoelectronics devices.

Dichloro-tin (IV) hexadeca-fluoro-phthalocyanine (F16PcSnCl2) thin film on porous silicon layers by ultrasonic spray pyrolysis, for possible application in optoelectronics devices.

Abstract Phthalocyanines represent a significant class of organic semiconductors that have garnered attention for their potential applications in conducting polymers and organic electronics. The unique structural characteristics of phthalocyanines, coupled with their chemical behavior and the possibility of variations in their bandgap associated with different substitution sites, offer exciting prospects for designing novel device applications. In this study, we have successfully fabricated a heterostructure incorporating dichloro tin (IV) hexa deca fluoro phthalocyanine (F16PcSnCl2) on both porous (PS) and crystalline (c-Si) silicon. The PS substrate was prepared using metal-assisted chemical etching (MACE). To explore the optoelectronic applications, we thoroughly characterized the optical, electrical, and morphological properties of the heterostructures. F16PcSnCl2 exhibits the lowest reflectance within the visible light spectrum, making it highly advantageous for photosensitive applications that demand efficient light absorption, diffusion, or scattering. The morphological analysis of the F16PcSnCl2 film using FE-SEM reveals the presence of nanosphere-type structures with diameters range from 62 ± 5 to 48 ± 5 nm and 151 ± 5 to 108 ± 5nm uniformly distributed on both PS and c-Si substrates, respectively, at different substrates temperatures (100 and 70 ºC). The absorbance spectrum exhibits the Soret, Q1 and Q2 bands at wavelength ranges from 330 to 358 nm, 566 to 588 nm and 620 to 652 nm, respectively, which serve as typical indicators of the F16PcSnCl2 complex. Al/c-Si/F16PcSnCl2/Ni-70°C and Al/c-Si/PS/F16PcSnCl2/Ni-70°C hybrid heterostructures fabricated for electrical characterization, displayed a better rectifying ohmic behavior and demonstrating a major photocurrent effect with current values of 300 µA and 30 µA, respectively, at white light conditions. Overall, the integration of organic and inorganic materials in heterostructures holds great promise for innovative applications in optoelectronics.

Investigations on structural and opto-electrical characterization of Ag-TCNQ (metal-organic frameworks) as complex thin films for potential device applications

The silver- (7, 7, 8, 8-tetracyanoquinodimethane (Ag-TCNQ) organometallic complex was synthesized chemically as a nano-powder and thereafter deposited as a thin film by thermal evaporation. The monoclinic, needle-like, polycrystalline structure of the Ag-TCNQ complex was analyzed employing x-ray diffraction (XRD) and a scanning electron microscope (SEM). Whereas their chemical structure and stability were explored using Fourier transformation infrared (FTIR) techniques. The findings imply a charge transfer of degree −0.5 between TCNQ° and TCNQ−, as revealed by the shift of the bands of the C≡N stretching and the (C═C-H) bond positioned at 2198 and 824 cm−1, respectively. As well as the optical properties of Ag-TCNQ thin film were studied using spectrophotometric measuring in the wavelength ranging 200 to 2500 nm. The measurement of transmittance and reflectance spectra were employed to calculate the refractive index (n), dielectric constant, absorption index (k), surface and volume energy loss functions, and optical conductivity. In the normal dispersion zone, optical characteristics such free charge carrier concentration, infinity dielectric constant (ε ∞), lattice dielectric constant (ε L), oscillator energy (Eo), and dispersion energy (Ed) were estimated. Furthermore, the optoelectronic nonlinear optical features and electronic transitions for the Ag-TCNQ thin film were assessed. Finally, these findings are promising milestones on the path to providing convincing evidence for the synthesis of stoichiometric thermally stable Ag-TCNQ thin film by conventional thermal evaporation technique that is potential to be utilized in optoelectronic devices applications.

PbI2 Passivation of Three Dimensional PbS Quantum Dot Superlattices Toward Optoelectronic Metamaterials.

Lead chalcogenide colloidal quantum dots are one of the most promising materials to revolutionize the field of short-wavelength infrared optoelectronics due to their bandgap tunability and strong absorption. By self-assembling these quantum dots into ordered superlattices, mobilities approaching those of the bulk counterparts can be achieved while still retaining their original optical properties. The recent literature focused mostly on PbSe-based superlattices, but PbS quantum dots have several advantages, including higher stability. In this work, we demonstrate highly ordered 3D superlattices of PbS quantum dots with tunable thickness up to 200 nm and high coherent ordering, both in-plane and along the thickness. We show that we can successfully exchange the ligands throughout the film without compromising the ordering. The superlattices as the active material of an ion gel-gated field-effect transistor achieve electron mobilities up to 220 cm2 V-1 s-1. To further improve the device performance, we performed a postdeposition passivation with PbI2, which noticeably reduced the subthreshold swing making it reach the Boltzmann limit. We believe this is an important proof of concept showing that it is possible to overcome the problem of high trap densities in quantum dot superlattices enabling their application in optoelectronic devices.

The physical characteristics of Zintl TeRhCl for renewable applications: A DFT approach

Due to their adaptable electronic and structural attributes, Zintl phases play a crucial role in customizing materials for a wide range of applications. We utilized DFT to examine the optoelectronic, structural transport response of TeRhCl Zintl phase. Structural stability is established by analyzing the optimization curve and determining the formation energy through calculations. The band structure has been calculated, revealing an indirect bandgap of 0.75 eV when employing GGA and 1.43 eV with the mBJ approach. The TDOS and PDOS graphs support the band structure's characteristics. Based on their optical properties, TeRhCl exhibit optical activity in the visible region. The optical characteristics suggest that this compound is feasible for the application in optoelectronic devices. The thermoelectric properties are investigated by employing electronic structure analysis and Boltzmann transport theory. At elevated temperatures, a significant ZT value of 0.83 is attained. The thermoelectric and optical response indicate its potential utility in forthcoming applications for both thermoelectric and optoelectronics devices.

Pressure and atomic size effects of IV cation on mechanical and electronic properties of Zn-IV-N2 (IV=Si, Ge and Sn): first principles calculation

Zn-IV-N2 compounds, incorporating Si, Ge, and Sn, have emerged as pivotal materials for their mechanical and electronic properties, influencing optoelectronic devices and photovoltaic applications. Employing density functional theory (DFT), we comprehensively investigate the structural, elastic, mechanical, and electronic characteristics of ZnIVN2 (IV=Si, Ge, Sn) under ambient and pressure conditions up to 20 GPa. Our findings suggest that a larger atomic size of the group IV cation can be more easily compressed than a smaller size. The mechanical stability criteria and the phonon dispersion show mechanical and dynamic stability in both ambient pressure and under high pressure up to 20 GPa. The ZnSiN2 and ZnGeN2 exhibit linear increments in bulk modulus (B), shear modulus (G), and Young's modulus (E) under pressure, while ZnSnN2 experiences a decrease in G and E. Notably, the energy gap of ZnSiN2, ZnGeN2, and ZnSnN2 (4.62 eV indirect, 2.82 eV, 1.16 eV, respectively) increases with pressure due to higher N s orbital energy, approaching the UV region. In the valence band, a hybridization of N p and Si/Ge/Sn p orbitals is observed, offering opportunities to tailor the band gap for optimal applications in optoelectronic devices. Preferentially adjusting group-IV elements over group-II elements is recommended for optimizing band gap modulation. The correlation between larger atomic size and decreased band gap energy highlights the potential to fine-tune material properties through controlled variations in group-IV elements.

Structural and optical properties of In-doped CdS nanostructures: A comprehensive study

This research offers a comprehensive exploration of the effects of In-doping on the characteristics of CdS nanopowders (NPs). The structural and morphological properties of In-doped CdS nanostructures were investigated, revealing significant changes induced by In-doping. X-ray diffraction (XRD) analysis verified the formation of CdS phase. Determination of crystallite size (D) demonstrated a decrease from 27.0 nm for undoped CdS to 23.0 nm for CdS doped with 12% In-doped. Field-emission scanning electron microscopy (FESEM) imaging showed grain-like structures with sizes of 20 – 35 nm, showing variations in particle size distribution with increasing In-dopant concentration. Photoluminescence (PL) analysis illustrated changes in PL intensity and emission peak wavelengths due to In-doping. PL intensity decreased after In-doping. Additionally, a blue-shift in emission peak wavelengths indicated changes in the bandgap energy of CdS induced by In-doping. UV-Vis spectroscopy assessed the optical properties, revealing shifts in absorption and transmission spectra du to In-doping. In-doping enhanced absorption within the 400 – 500 nm range while decreasing absorption within 600 – 1000 nm. Transmission spectra displayed increased transparency after In-doping, attributed to modifications in band structure and morphology. Reflectance spectra initially increased with In-dopant concentration within 400 – 500 nm, followed by a decrease, suggesting alterations in electronic and structural properties. Estimation of band gap energy (Eg) unveiled an increase in Eg for In-doped CdS nanostructures compared to undoped CdS, likely due to reduced crystallite size and the Burstein-Moss effect induced by In-dopant ions. Raman analysis revealed a shift in peak positions and changes in intensity after In-doping, with a decrease in the 2LO/LO ratio indicating a deterioration in crystalline quality after In-doping. Overall, this comprehensive investigation provides valuable insights into the structural, morphological, optical, and electrical properties of In-doped CdS nanostructures, pivotal for their promising applications in optoelectronic devices and photovoltaics.

Morphological, structural, and electronic properties of green synthesized ZnO nanoparticles by experimental and DFT+U method – A review

In these decades, researchers have paid much attention to green synthesis methods because of their low cost and eco-friendliness. Among all other semiconductors, ZnO nanoparticles have huge applications in optoelectronics devices, solar cells, photocatalysis, transistors, etc. This review article explains the green synthesis methods and factors affecting the morphology of ZnO nanoparticles. The morphology shows different structures such as nanowires, cubic, hexagonal, flower-like structures, etc. The XPS peaks Zn-2p1/2, Zn-2p3/2, and O-1S suggest that the synthesized nanoparticles are ZnO. The theoretical review part explains the electronic and structural properties of wurtzite ZnO nanoparticles. The implementation of the Hubbard-U scheme in the d and p shells using Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) shows the drastic change in the electronic and structural properties of ZnO nanoparticles. The optimized lattice parameters and band gap using Hubbard parameters by different DFT codes are tabulated. Also, we compared computational and experimental results.

Computational study to investigate effectiveness of titanium substitution in CaFeH3 perovskite-type hydride: An approach towards advanced hydrogen storage system

In recent years, there has been increased interest in hydrogen storage due to the numerous advantages hydrogen offers as an energy source. This study explores the structural, hydrogen storage, electronic, elastic, mechanical, and optical properties of Ca1-xTixFeH3 through DFT. After Ti substitution in the host material, structure phase transformation occurs: cubic → pseudo-cubic → cubic. Study compounds are thermodynamically stable and experimentally synthesizable according to the calculated negative formation energies. Gravimetric hydrogen storage capacities for different concentrations of Ti (x = 0, 0.11, 0.33, 0.55, 1) were calculated as 2.963, 2.938, 2.843, and 2.753 wt%, respectively. The investigation focuses on understanding the material's BS, Fermi level, and DOS, elucidating its metallic characteristics, and non-zero DOS at the Fermi level contributing to electrical and thermal conductivity. Elemental partial density of states reveals hybridization effects with Ti doping, affecting the valence band's atomic contributions. Using cubic symmetry, C11, C12, and C14 elastic constants were used to describe mechanical characteristics, and the Born criteria were met. Thus, mechanical stability was demonstrated for these compounds. Optical analyses exhibit changes concerning Ti concentrations and energy levels, including absorption spectra, conductivity, reflectivity, dielectric function, refractive index, energy loss function, and extinction coefficient. These findings shed light on the material's response to incident radiation and potential applications in hydrogen storage and optoelectronic devices.

A comprehensive first-principles investigation of structural, electronic, vibrational, optical, thermodynamic and thermoelectric properties of LiZnAs

The structural, electronic, vibrational, optical, thermodynamic and thermoelectric properties of Nowotny–Juza filled tetrahedral semiconductor LiZnAs under high pressure is investigated using the plane-wave pseudo-potential approach in the frame work of density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated lattice constant (a0) and bulk modulus (B0) at ambient pressure are consistent with earlier reported experiment and theoretical results. The variation in Lattice constant, Bulk modulus (B0), Young modulus (Y), Shear modulus (G), Elastic anisotropy factor (A), Poission ratio (μ), Paugh (B/G) ratio and Elastic constants with pressure is analyzed and concluded. Electronic band structure calculations reveal that with applied pressure direct band gap increases and the indirect band gap decreases. Thermodynamic properties reveals thermodynamically stability with pressurize conditions. The real and imaginary parts of the Dielectric function (ε), Refractive index (η), Extinction Coefficient (k), Optical Conductivity (s), Electron/Optical Energy Loss Function (L), Absorption Coefficient (α), Reflectivity (R) at different pressure conditions are correspondingly studied. With applied pressure the absorption spectra shows a blue shift which makes LiZnAs as potential candidates for the application of optoelectronic devices in ultraviolet frequency range. The thermoelectric properties like Seebeck coefficient (S), Electrical conductivity (σ), and Electronic thermal conductivity (k) and Power factor (PF) have been studied as a function of temperature and chemical potential. Positive value of calculated Seebeck coefficient with temperatures ensures the p-type semiconducting nature of LiZnAs. Results provides theoretical guidance for future experimental investigations and industrial applications of LiZnAs.

Synthesis of multilayered h-BN film on the molten Ni–B and the influence of underneath W substrate

High-quality two-dimensional hexagonal boron nitride (h-BN) film with tens of layers has been used as a universal substrate and capping layer for the van der Waals devices. Various approaches have been carried out for the synthesis of multilayered h-BN. Among them, the metal flux method is reliable in yielding h-BN crystals with high crystalline quality. However, this time- and energy-demanding method hinders its scale application. Herein, inspired by the metal flux method, we reported the time-effective growth of high-quality multilayered h-BN film (ca. 20 nm) on a molten Ni–B layer wetting on W substrate with chemical vapor deposition method. The film exhibits an excellent stacking sequence and a full-width at half maximum of the Raman E2g peak narrow to 9.5 cm−1. Cross-sectional high-resolution transmission electron microscopy and in-situ x-ray diffraction spectroscopy were carried out to investigate the crystal structure evolution of Ni–B layer wetting on W substrate. It is found that the low surface tension caused by the spreading of Ni–B alloy on the W substrate and the presence of the Ni subsurface may be responsible for the formation of multilayered h-BN with excellent crystalline quality. Meanwhile, the W diffusion in Ni–B-based melt can hinder the formation of h-BN under certain growth conditions. The approach demonstrates the feasibility of large-scale growth of multilayered h-BN, paving the way to future applications in van der Waals electronic and optoelectronic devices.

Electronic and optical properties of As/Bi2Se3 van der Waals heterostructure: Ab initio insights

In this study, based on the first-principles calculations, we theoretically studied the electronic and optical properties of two dimensional (2D) As/Bi2Se3 van der Waals (vdW) heterostructure. The results show that all the materials exhibit semiconducting behavior with calculated band gaps of Eg = 1.71, 1.0, and 1.65 eV without spin-orbit coupling (SOC), for As monolayer, Bi2Se3 monolayer, and As/Bi2Se3 heterostructure respectively. Notably, the As/Bi2Se3 heterostructure demonstrates a type-II band alignment, facilitating the effective spatial separation of photogenerated carriers. This characteristic offers exciting opportunities for applications in efficient optoelectronic devices, photocatalysis, and solar energy conversion. The optical properties studies show that the heterostructure exhibits significant light absorption across the visible to ultraviolet light spectrum, making it a promising candidate for a wide array of optoelectronic devices.

Dependence of Ultrafast Electron Emission Characteristics of Graphene Cold Cathode on Femtosecond Photoexcitation Polarization Angle.

Ultrafast electron pulses, generated through femtosecond photoexcitation in nanocathode materials, introduce high-frequency characteristics and ultrahigh temporal-spatial resolution to vacuum micro-nano electronic devices. To advance the development of ultrafast electron sources sensitive to polarized light, we propose an ultrafast pulsed electron source based on a vertical few-layer graphene cold cathode. This source exhibits selective electron emission properties for varying polarization angles, with high switching ratios of 277 (at 0°) and 235 (at 90°). The electron emission of the graphene evolves from cosine to sine as the polarization angle increases from 0° to 90°. The variation of electron emission current with polarization angle is intrinsically related to light absorption, local field enhancement, and photothermal conversion efficiency. A physical mechanism model and semiempirical expression were presented to reveal the MPP and PTE mechanisms at different polarization angles. This tunable conversion between mechanisms indicates potential applications in tunable ultrafast optoelectronic devices.