Search Results (184)

AlGaN-based high-electron-mobility transistors are critical for next-generation power electronics and radio-frequency applications, yet achieving stable enhancement-mode operation with a high threshold voltage remains a key challenge. In this work, we designed p-AlGaN superlattices with different structures and performed energy band structure simulations using the device simulation software Silvaco. The results demonstrate that thin barrier structures lead to reduced acceptor incorporation, thereby decreasing the number of ionized acceptors, while facilitating vertical hole transport. Superlattice samples with varying periodic thicknesses were grown via metal-organic chemical vapor deposition, and their crystalline quality and electrical properties were characterized. The findings reveal that although gradient-thickness barriers contribute to enhancing hole concentration, the presence of thick barrier layers restricts hole tunneling and induces stronger scattering, ultimately increasing resistivity. In addition, we simulated the structure of the enhancement-mode HEMT with p-AlGaN as the under-gate material. Analysis of its energy band structure and channel carrier concentration indicates that adopting p-AlGaN superlattices as the under-gate material facilitates achieving a higher threshold voltage in enhancement-mode HEMT devices, which is crucial for improving device reliability and reducing power loss in practical applications such as electric vehicles. Full article

Epitaxial growth of β-Ga₂O₃ nanowires on silicon substrates was realized by the low-pressure chemical vapor deposition (LPCVD) method. The as-grown Si/Ga₂O₃ heterojunctions were employed in the Underwater DUV detection. It is found that the carrier type as well as the carrier concentration of the silicon substrate significantly affect the performance of the Si/Ga₂O₃ heterojunction. The p-Si/β-Ga₂O₃ (2.68 × 10¹⁵ cm⁻³) devices exhibit a responsivity of up to 205.1 mA/W, which is twice the performance of the devices on the n-type substrate (responsivity of 93.69 mA/W). Moreover, the devices’ performance is enhanced with the increase in the carrier concentration of the p-type silicon substrates; the corresponding device on the high carrier concentration substrate (6.48 × 10¹⁷ cm⁻³) achieves a superior responsivity of 845.3 mA/W. The performance enhancement is mainly attributed to the built-in electric field at the p-Si/n-Ga₂O₃ heterojunction and the reduction in the Schottky barrier under high carrier concentration. These findings would provide a strategy for optimizing carrier transport and interface engineering in solar-blind UV photodetectors, advancing the practical use of high-performance solar-blind photodetectors for underwater application. Full article

The low-symmetry Weyl semimetallic Td-phase WTe₂ exhibits both a distinct out-of-plane damping torque (${\tau }_{\mathrm{DL}}$) and exceptional charge–spin interconversion efficiency enabled by strong spin-orbit coupling, positioning it as a prime candidate for spin–orbit torque (SOT) applications in two-dimensional transition metal dichalcogenides. Herein, we report on thickness-dependent unconventional out-of-plane ${\tau }_{\mathrm{DL}}$ in chemically vapor-deposited (CVD) polycrystalline Td-WTe₂ (t)/Ni₈₀Fe₂₀/MgO/Ti (Td-WTN-t) heterostructures. Angle-resolved spin-torque ferromagnetic resonance measurements on the Td-WTN-12 structure showed significant spin Hall conductivities of σ_SH,y = 4.93 × 10³ (ℏ/2e) Ω⁻¹m⁻¹ and σ_SH,z = 0.81 × 10³ (ℏ/2e) Ω⁻¹m⁻¹, highlighting its potential for wafer-scale spin–orbit torque device applications. Additionally, a detailed examination of magnetotransport properties in polycrystalline few-layer Td-WTe₂ films as a function of thickness revealed a marked amplification of the out-of-plane magnetoresistance, which can be ascribed to the anisotropic nature of charge carrier scattering mechanisms within the material. Spin pumping measurements in Td-WTN-t heterostructures further revealed thickness-dependent spin transport properties of Td-WTe₂, with damping analysis yielding an out-of-plane spin diffusion length of λ_SD ≈ 14 nm. Full article

Experiences in the production, transportation and preparation of crude oil for transportation have shown that specific problems arise related to their mixing, including water contamination. In recent years, interest in studying these problems has significantly increased, mainly due to the development of extraction technologies for heavy oil samples and bitumen. Along with various difficulties encountered during the pipeline transportation of complex rheological crude oil blended with each other and with light oil, including condensate (such as sedimentation, etc.), imbalances are also observed during storage, as well as in the processes of delivery and reception. During the dehydration of oil mixtures, a synergistic effect is observed in the consumption of demulsifier. The article investigates, in accordance with international standards and based on laboratory tests, how the physico-chemical properties (density, viscosity, freezing point, saturated vapor pressure, chemical composition) of mixtures formed by blending various grades and compositions of Azerbaijani oil examples with each other and with condensate change and how the efficiency of dehydration of oil mixtures is affected by the mixing ratio of the oil involved. It was found that the quality indicators (physico-chemical parameters) of oil mixtures differ non-additively from the initial parameters of the blended products and in some cases, this difference is even observed with anomalies. Moreover, depending on the mixing ratio of the oil, variations in the consumption of demulsifier were also identified. Full article

Two-dimensional (2D) materials are regarded as key foundational materials for next-generation optoelectronic devices. As a promising new type of 2D layered semiconductor, Bi₂O₂Se has emerged as a strong candidate for high-performance opto-electronic devices due to its high carrier mobility, tunable bandgap, and excellent environmental stability. However, achieving precise control over Bi₂O₂Se growth to obtain high-quality Bi₂O₂Se remains a challenge in the field. In this study, we employed chemical vapor deposition (CVD) to grow thin-layer 2D Bi₂O₂Se flakes. We further used a transport model and thermodynamic Arrhenius fitting to analyze the relationship between vapor flux and the properties of the flakes. Density functional theory was used to study the electronic structure of the as-grown samples. The electrical and optoelectronic results demonstrate that Bi₂O₂Se-based FETs exhibit good performance in terms of mobility (129 cm²V⁻¹s⁻¹), on/off ratio (4.51 × 10⁵), and photoresponsivity (94.98 AW⁻¹). This work provides a new way to study the influence of vapor flux on the sizes and shapes of Bi₂O₂Se flakes for photodetectors. Full article

Chemical vapor deposition (CVD) is a highly adaptable manufacturing technique used to fabricate high-quality thin films, making it essential across numerous industries. As materials fabrication processes progress, CVD has advanced to enable the precise deposition of both inorganic 2D materials, such as graphene and transition metal dichalcogenides, and high-quality polymeric thin films, offering excellent conformality and precise nanostructure control on a wide range of substrates. Conjugated conducting polymers have emerged as promising materials for next-generation electronic, optoelectronic, and energy storage devices due to their unique combination of electrical conductivity, optical transparency, ionic transport, and mechanical flexibility. Oxidative CVD (oCVD) involves the spontaneous reaction of oxidant and monomer vapors upon their adsorption onto the substrate surface, resulting in step-growth polymerization that commonly produces conducting or semiconducting polymer thin films. oCVD has gained significant attention for its ability to fabricate conjugated conducting polymers under vacuum conditions, allowing precise control over film thickness, doping levels, and nanostructure engineering. The low to moderate deposition temperature in the oCVD method enables the direct integration of conducting and semiconducting polymer thin films onto thermally sensitive substrates, including plants, paper, textiles, membranes, carbon fibers, and graphene. This review explores the fundamentals of the CVD process and vacuum-based manufacturing, while also highlighting recent advancements in the oCVD method for the fabrication of conjugated conducting and semiconducting polymer thin films. Full article

The two-dimensional semiconductor material MoS₂, grown via chemical vapor deposition, has shown significant potential to surpass silicon in advanced electronic technologies. However, the mass transfer and chemical reaction processes critical to the nucleation and growth of MoS₂ grains remain poorly understood. In this study, we conducted an in-depth investigation into the mass transfer and chemical reaction processes during the chemical vapor deposition of MoS₂, employing a novel multi-physics coupling model that integrates flow fields, temperature fields, mass transfer, and chemical reactions. Our findings reveal that the intermediate product Mo₃O₉S₄ not only fails to participate directly in MoS₂ film growth but also hinders the diffusion of MoS₆, limiting the growth process. We demonstrate that increasing the growth temperature accelerates the diffusion rate of MoS₆, mitigates the adverse effects of Mo₃O₉S₄, and promotes the layered growth of MoS₂ films. Additionally, lowering the growth pressure enhances the convective diffusion of reactants, accelerating grain growth. This research significantly advances our understanding of the mass transport and reaction processes in MoS₂ film growth and provides critical insights for optimizing chemical vapor deposition systems. Full article

As part of crystal growth experiments on transition metal oxidotellurates using chemical vapor transport reactions or hydrothermal conditions, single crystals of Ni^IITe^VIO₄ and Cu^IITe^IV₂O₅ were obtained for the first time in the form of new modifications, as revealed by crystal structure determinations from X-ray data. In the course of these investigations, the crystal structure model of the only phase of Ni^IITe^VIO₄ reported so far (from now on named α-) was corrected. Both α-(space group P2₁/c, Z = 2) and the new β-polymorph of Ni^IITe^VIO₄ (space group I4₁/a, Z = 8) can be considered derivatives (hettotypes) of the rutile structure (aristotype), as shown by detailed symmetry relationships. For CuTe₂O₅ also, only one crystalline phase has been described so far (from now on named α-) that corresponds to the mineral rajite (space group P2₁/c, Z = 2). Its anion comprises two different trigonal-pyramidal TeO₃ groups linked through corner-sharing into a ditellurite unit. The anion part of the new β-CuTe₂O₅ modification (space group P2₁/c, Z = 2), likewise, comprises two Te^IV atoms but is more complex. Here, one Te^IV atom exhibits a coordination number of 4 and is part of a ${}_{\propto }{}^1[$TeO_2/2O_2/1] chain, and the other has a coordination number of 5 and is part of a ${}_{\propto }{}^1[$TeO_2/2O_3/1]₂ dimer. The two types of anions are linked into a tri-periodic framework where both Te^IV atoms are stereochemically active. The α- and β-CuTe₂O₅ modifications show no closer structural relationship, which is also reflected in their clearly different Raman spectra. Data mining for knowledge discovery in a structure database reveals that polymorphism is a rather common phenomenon for the family of inorganic oxidotellurates. Full article

The chemical transport method is a process that occurs naturally; however, it is also very useful in the chemical laboratory environment for the synthesis of inorganic crystals. It was successfully used for the syntheses of simple and complex inorganic compounds, from binary (e.g., ZnS, CdSe) to quaternary (e.g., Cu₂ZnSnS₄) compounds. Many experimental parameters influence the quality of products of chemical transport reactions, and among them, one may distinguish the used precursors and applied temperature gradient. The careful selection of experimental conditions is crucial for the production of high-quality crystals. Mathematical descriptions of the chemical transport phenomena, however, may potentially help in the design of proper conditions. Full article

Incidents involving hazardous materials (HAZMAT incidents) can impact human health and the environment. For the development of risk mitigation strategies, it is essential to understand the circumstances of such incidents. A retrospective study (2016–2023) of acute occupational HAZMAT incidents involving multiple patients (>1, including workers, emergency responders and bystanders) reported to the Dutch Poisons Information Center was conducted. We only included incidents that occurred during the performance of work or as a result of a disruption of a work-related process. Patient characteristics, exposure circumstances (such as the substances involved, chemical phase, and type of release (e.g., spill/release or fire/explosion)) and business classes were analyzed to identify risk factors. From 2016 to 2023, the DPIC was consulted about 516 HAZMAT incidents. Inhalation was the most common route of exposure (89%). Patients were often exposed to chemical asphyxiants (n = 156) and acids (n = 151). Most incidents occurred in fixed facilities (n = 447), while 49 incidents occurred during transport. The primary cause was a spill/release (n = 414), followed by a fire/explosion (n = 65). Most patients were exposed to a gas/vapor (n = 421), followed by a liquid (n = 59) or solid (n = 28). Incidents frequently occurred in industry (20%). The majority of patients reported mild to moderate health effects. Surveillance data on HAZMAT incidents are essential for incident preparedness. Poison Center data can help identify risk factors, which can be used to develop risk mitigation strategies to prevent future incidents. Full article

Graded-interfaces modeling unveils key features of high-power, high-efficiency quantum-cascade lasers (QCLs): direct resonant-tunneling injection from a prior-stage, low-energy state into the upper-laser (ul) level, over a wide (~50 nm) multiple-barrier region; and a new type of photon-induced carrier transport (PICT). Stage-level QCL operation primarily involves two steps: injection into the ul level and photon-assisted diagonal transition. Furthermore, under certain conditions, a prior-stage low-energy state, extending deep into the next stage, is the ul level, thus making such devices injectionless QCLs and leading to stronger PICT action due to quicker gain recovery. Thermalization within a miniband ensures population inversion between a state therein and a state in the next miniband. Using graded-interfaces modeling, step-tapered active-region (STA) QCLs possessing PICT action have been designed for carrier-leakage suppression. A preliminary 4.6 µm emitting STA design of a metal–organic chemical-vapor deposition (MOCVD)-grown QCL led to an experimental 19.1% front-facet, peak wall-plug efficiency (WPE). Pure, diffraction-limited beam operation is obtained at 1.3 W CW power. A low-leakage 4.7 µm emitting design provides a projected 24.5% WPE value, considering MOCVD-growth, graded-interface interface-roughness (IFR) parameters, and waveguide loss (α_w). The normalized leakage-current density, J_leak/J_th, is 17.5% vs. 28% for the record-WPE 4.9 µm emitting QCL. Then, when considering the IFR parameters and α_w values of optimized-crystal-growth QCLs, J_leak/J_th decreases to 13.5%, and the front-facet WPE value reaches 33%, thus approaching the ~41% fundamental limit. The potential of graded-interfaces modeling to become the design tool for achieving room-temperature operation of terahertz QCLs is discussed. Full article

The discovery of two-dimensional (2D) van der Waals ferromagnetic materials opens up new avenues for making devices with high information storage density, ultra-fast response, high integration, and low power consumption. Fe₅GeTe₂ has attracted much attention because of its ferromagnetic transition temperature near room temperature. However, the investigation of its phase transition is rare until now. Here, we have successfully synthesized a single crystal of the layered ferromagnet Fe₅GeTe₂ by chemical vapor phase transport, soon after characterized by X-ray diffraction (XRD), DC magnetization M(T), and isotherm magnetization M(H) measurements. A paramagnetic to ferromagnetic transition is observed at ≈302 K (T_C) in the temperature dependence of the DC magnetic susceptibility of Fe₅GeTe₂. We found an unconventional potential spin glass state in the low-temperature regime that differs from the conventional spin glass states and Griffiths phase (GP) in the high-temperature regime. The physical mechanisms behind the potential spin glass state of Fe₅GeTe₂ at low temperatures and the Griffith phase at high temperatures need to be further investigated. Full article

This review summarized the developments in the field of volatile silver complexes, which can serve as precursors in gas-transport reactions for the production of thin films and metal nanoparticles via chemical vapor deposition (CVD) and atomic layer deposition (ALD). Silver-based films and nanoparticles are widely used in various high-tech fields, including medicine. For effective use in CVD and ALD processes, the properties of silver precursors must be balanced in terms of volatility, thermal stability, and reactivity. In this review, we focus on the synthesis and comprehensive analysis of structural and thermal characteristics for the most promising classes of volatile silver complexes, as well as organometallic compounds. Following the specifics of silver chemistry, some features of the use of precursors and their selection, as well as several key directions to improving the efficiency of silver material deposition processes, are also discussed. Full article

The integration of PbS quantum dots (QDs) with graphene represents a notable advancement in enhancing the optoelectronic properties of quantum-dot-based devices. This study investigated the electrical transport properties of PbS quantum dot (QD)/graphene heterostructures, leveraging the high carrier mobility of graphene. We fabricated QD/graphene/SiO₂/Si heterostructures by synthesizing p-type monolayer graphene via chemical vapor deposition and spin-coating PbS QDs on the surface. Then, we used a low-temperature electrical transport measurement system to study the electrical transport properties of the heterostructure under different temperature, gate voltage, and light conditions and compared them with bare graphene samples. The results indicated that the QD/graphene samples exhibited higher resistance than graphene alone, with both resistances slightly increasing with temperature. The QD/graphene samples exhibited significant hole doping, with conductivity increasing from 0.0002 Ω⁻¹ to 0.0007 Ω⁻¹ under gate voltage modulation. As the temperature increased from 5 K to 300 K, hole mobility decreased from 1200 cm²V⁻¹s⁻¹ to 400 cm²V⁻¹s⁻¹ and electron mobility decreased from 800 cm²V⁻¹s⁻¹ to 200 cm²V⁻¹s⁻¹. Infrared illumination reduced resistance, thereby enhancing conductivity, with a resistance change of about 0.4%/mW at a gate voltage of 125 V, demonstrating the potential of these heterostructures for infrared photodetector applications. These findings offer significant insights into the charge transport mechanisms in low-dimensional materials, paving the way for high-performance optoelectronic devices. Full article

Single crystals of the new modification of copper pyrovanadate, δ-Cu₂V₂O₇, were prepared using the chemical vapor transport reaction method. The crystal structure (monoclinic, P2₁/n, a = 5.0679(3), b = 11.4222(7), c = 9.4462(6) Å, β = 97.100(6)°, V = 542.61(6) ų, Z = 4) was solved by direct methods and refined to R₁ = 0.029 for 1818 independent observed reflections. The crystal structure contains two Cu sites: the Cu1 site in [4 + 2]-octahedral coordination and the Cu2 site in [4 + 1]-tetragonal pyramidal coordination. There are two V⁵⁺ sites, both tetrahedrally coordinated by O atoms. Two adjacent V1O₄ and V2O₄ tetrahedra share the O4 atom to form a V₂O₇ dimer. The crystal structure of δ-Cu₂V₂O₇ can be described as based upon layers of V₂O₇ dimers of tetrahedra parallel to the (001) plane and interlined by chains of the edge-sharing Cu1O₆ and Cu2O₅ polyhedra running parallel to the a axis and arranged in the layers parallel to the (001) plane. The crystal chemical analysis of the three other known Cu₂V₂O₇ polymorphs indicates that, by analogy with δ-Cu₂V₂O₇, they are based upon layers of V₂O₇ groups interlinked by layers consisting of chains of CuO_n coordination polyhedra (n = 5, 6). The crystal structures of the Cu₂V₂O₇ polymorphs can be classified according to the mutual relations between the Cu-O chains, on the one hand, and the V₂O₇ groups, on the other hand. The analysis of the literature data and physical density values suggests that, at ambient pressure, α- and β-Cu₂V₂O₇ are the low- and high-temperature polymorphs, respectively, with the phase transition point at 706–710 °C. The β-phase (ziesite) may form metastably under temperatures below 560 °C and, under heating, transform into the stable α-phase (blossite) at 605 °C. The δ- and γ-polymorphs have the highest densities and most probably are the high-pressure phases. The structural complexity relations among the polymorphs correspond to the sequence α = β < γ < δ; i.e., the δ phase described herein possesses the highest complexity, which supports the hypothesis about its stability under high-pressure conditions. Full article