Search Results (61)

Borophene, a two-dimensional (2D) allotrope of boron, has emerged as a highly promising material owing to its exceptional mechanical strength, electronic conductivity, and diverse structural phases. Unlike graphene and other 2D materials, borophene exhibits inherent anisotropy, flexibility, and metallicity, offering unique opportunities for advanced nanotechnological applications. This review presents a comprehensive summary of recent progress in borophene synthesis methods, highlighting both bottom–up strategies such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE), and top–down approaches, including liquid-phase exfoliation and sonochemical techniques. A key challenge discussed is the stabilization of borophene’s polymorphs, as bulk boron’s non-layered structure complicates exfoliation. The influence of substrates and doping strategies on structural stability and phase control is also explored. Moreover, the intrinsic physicochemical properties of borophene, including its high flexibility, oxidation resistance, and anisotropic charge transport, were examined in relation to their implications for electronic, catalytic, and sensing devices. Particular attention was given to borophene’s performance in hydrogen storage and hydrogen evolution reactions (HERs), where functionalization with alkali and transition metals significantly enhances H₂ adsorption energy and storage capacity. Studies demonstrate that certain borophene–metal composites, such as Ti- or Li-decorated borophene, can achieve hydrogen storage capacities exceeding 10 wt.%, surpassing the U.S. Department of Energy targets for hydrogen storage materials. Despite these promising characteristics, large-scale synthesis, long-term stability, and integration into practical systems remain open challenges. This review identifies current research gaps and proposes future directions to facilitate the development of borophene-based energy solutions. The findings support borophene’s strong potential as a next-generation material for clean energy applications, particularly in hydrogen production and storage systems. Full article

Graphene, a two-dimensional material with remarkable electrical, thermal, and mechanical properties, has revolutionized the fields of electronics, energy storage, and nanotechnology. This review presents a comprehensive analysis of graphene synthesis techniques, which can be classified into two primary approaches: top-down and bottom-up. Top-down methods, such as mechanical exfoliation, oxidation-reduction, unzipping carbon nanotubes, and liquid-phase exfoliation, are highlighted for their scalability and cost-effectiveness, albeit with challenges in controlling defects and uniformity. In contrast, bottom-up methods, including chemical vapor deposition (CVD), arc discharge, and epitaxial growth on silicon carbide, offer superior structural control and quality but are often constrained by high costs and limited scalability. The interplay between synthesis parameters, material properties, and application requirements is critically examined to provide insights into optimizing graphene production. This review also emphasizes the growing demand for sustainable and environmentally friendly approaches, aligning with the global push for green nanotechnology. By synthesizing current advancements and identifying critical research gaps, this work offers a roadmap for selecting the most suitable synthesis techniques and fostering innovations in scalable and high-quality graphene production. The findings serve as a valuable resource for researchers and industries aiming to harness graphene’s full potential in diverse technological applications. Full article

This work presents a comprehensive study of the structural, luminescent, and photoconversion properties of epitaxial composite phosphor converters based on single crystalline films of Ce³⁺-activated Ca_2−xY_1+xMg_1+xSc_1−xSi₃O₁₂:Ce (x = 0–0.25) (CYMSSG:Ce) garnet, grown using the liquid phase epitaxy (LPE) method on single-crystal Y₃Al₅O₁₂ (YAG) and YAG:Ce substrates. The main goal of this study is to elucidate the structure–composition–property relationships that influence the photoluminescence and photoconversion efficiency of these film–substrate composite converters, aiming to optimize their performance in high-power white light-emitting diode (WLED) applications. Systematic variation in the Y³⁺/Sc³⁺/Mg²⁺ cationic ratios within the garnet structure, combined with the controlled tuning of film thickness (ranging from 19 to 67 µm for CYMSSG:Ce/YAG and 10–22 µm for CYMSSG:Ce/YAG:Ce structures), enabled the precise modulation of their photoconversion properties. Prototypes of phosphor-converted WLEDs (pc-WLEDs) were developed based on these epitaxial structures to assess their performance and investigate how the content and thickness of SCFs affect the colorimetric properties of SCFs and composite converters. Clear trends were observed in the Ce³⁺ emission peak position, intensity, and color rendering, induced by the Y³⁺/Sc³⁺/Mg²⁺ cation substitution in the film converter, film thickness, and activator concentrations in the substrate and film. These results may be useful for the design of epitaxial phosphor converters with tunable emission spectra based on the epitaxially grown structures of garnet compounds. Full article

Ultra-high-temperature (>1500 °C) sensors play vital roles in ensuring operational excellence in variety of energy-related applications, such as power plant boilers and gas turbine engines. Crystalline sapphire fibers have enormous potential to replace conventional expensive precious metal (e.g., Pt/Rh)-based high-temperature (>1500 °C) sensors by offering higher environmental robustness and distributed sensing capabilities. However, a lack of proper cladding substantially compromises the performance of the sensor. To overcome this fundamental limitation, we develop a hybrid growing method to fabricate low-loss clad crystalline sapphire fibers. We grow a higher-refractive-index doped crystalline sapphire fiber core using the laser-heated pedestal growth (LHPG) method and lower-refractive-index undoped crystalline sapphire fiber cladding using the liquid-phase epitaxy (LPE) method. Furthermore, due to the existence of this cladding layer, a single mode of operation can be achieved at a core diameter size of 30 μm. The experimental results confirm that the grown clad crystalline sapphire fiber can survive in extremely high-temperature (>1500 °C) harsh environments due to the matched coefficient of thermal expansion (CTE) between the fiber core and the cladding. The numerical results also indicate a temperature sensing accuracy of 3.5 °C. This opens the door for developing point and distributed fiber sensor networks capable of enduring extremely harsh environments at extremely high temperatures. Full article

LiNbO₃ plays a significant role in modern integrated photonics because of its unique properties. One of the challenges in modern integrated photonics is reducing chip production cost. Today, the most widespread yet expensive method to fabricate thin films of LiNbO₃ is the smart cut method. The high production cost of smart-cut chips is caused by the use of expensive equipment for helium implantation. A prospective method to reduce the cost of photonic integrated circuits is to use sputtered thin films of lithium niobite, since sputtering technology does not require helium implantation equipment. The purpose of this review is to assess the feasibility of applying sputtered LiNbO₃ thin films in integrated photonics. This work compares sputtered LiNbO₃ thin films and those fabricated by widespread methods, including the smart cut method, liquid-phase epitaxy, chemical vapor deposition, pulsed laser deposition, and molecular-beam epitaxy. Full article

Narrow-gap InN is a desirable candidate for near-infrared (NIR) optical communication applications. However, the absence of lattice-matched substrates impedes the fabrication of high-quality InN. In this paper, we employed Molecular Beam Epitaxy (MBE) to grow nanostructured InN with distinct growth mechanisms. Morphological and quality analysis showed that the liquid phase epitaxial (LPE) growth of hexagonal InN nanopillar could be realized by depositing molten In layer on large lattice-mismatched sapphire substrate; nevertheless, InN nanonetworks were formed on nitrided sapphire and GaN substrates through the vapor-solid process under the same conditions. The supersaturated precipitation of InN grains from the molten In layer effectively reduced the defects caused by lattice mismatch and suppressed the introduction of non-stoichiometric metal In in the epitaxial InN. Photoluminescence and electrical characterizations demonstrated that high-carrier concentration InN prepared by vapor-solid mechanism showed much stronger band-filling effect at room temperature, which significantly shifted its PL peak to higher energy. LPE InN displayed the strongest PL intensity and the smallest wavelength shift with increasing temperature from 10 K to 300 K. These results showed enhanced optical properties of InN nanostructures prepared on large lattice mismatch substrates, which will play a crucial role in near-infrared optoelectronic devices. Full article

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO₂/Ga₂O₃ core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO₂ core. At temperatures above 530 °C, the thermal reduction of SnO₂ and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga₂O₃ shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO₂ nanobelts, as both structures are likely connected through existing SnO₂/SnO₂ homojunctions comprising thin amorphous layers. Full article

Metal–organic frameworks (MOFs) have drawn intensive attention as a class of highly porous, crystalline materials with significant potential in various applications due to their tunable porosity, large internal surface areas, and high crystallinity. This paper comprehensively reviews the fabrication methods of pure MOF membranes and films, including in situ solvothermal synthesis, secondary growth, electrochemical deposition, counter diffusion growth, liquid phase epitaxy and solvent-free synthesis in the category of different MOF families with specific metal species, including Zn-based, Cu-based, Zr-based, Al-based, Ni-based, and Ti-based MOFs. Full article

In this study, we propose novel three-layer composite scintillators designed for the simultaneous detection of different ionizing radiation components. These scintillators are based on epitaxial structures of LuAG and YAG garnets, doped with Ce³⁺ and Sc³⁺ ions. Samples of these composite scintillators, containing YAG:Ce and LuAG:Ce single crystalline films with different thicknesses and LuAG:Sc single crystal substrates, were grown using the liquid phase epitaxy method from melt solutions based on PbO-B₂O₃ fluxes. The scintillation properties of the proposed composites, YAG:Ce film/LuAG:Sc film/LuAG:Ce crystal and YAG:Ce film/LuAG:Ce film/LuAG:Sc crystal, were investigated under excitation by radiation with α-particles from a ²³⁹Pu source, β-particles from ⁹⁰Sr sources and γ-rays from a ¹³⁷Cs source. Considering the properties of the mentioned composite scintillators, special attention was paid to the ability of simultaneous separation of the different components of mixed ionizing radiation containing the mentioned particles and quanta using scintillation decay kinetics. The differences in scintillation decay curves under α- and β-particle and γ-ray excitations were characterized using figure of merit (FOM) values at various scintillation decay intensity levels (1/e, 0.1, 0.05, 0.01). Full article

Two-dimensional (2D) materials have emerged as a frontier in materials science, offering unique properties due to their atomically thin nature. Among these materials, bismuthene stands out due to its exceptional optical, electronic, and catalytic characteristics. Bismuthene exhibits high charge carrier mobility, stability, and a tunable bandgap (0.3–1.0 eV), making it highly suitable for applications in transistors, spintronics, biomedicine, and photocatalysis. This work explores the so far reported synthesis methods for obtaining 2D bismuthene, including bottom-up approaches like chemical vapor deposition and molecular beam epitaxy, and top-down methods such as liquid-phase exfoliation and mechanical exfoliation. Recent advancements in understanding 2D bismuthene structural phases, electronic properties modulated by spin-orbit coupling, and its potential applications in next-generation photocatalysts are also reviewed. As is retrieved by our literature review, 2D bismuthene shows great promise for addressing significant environmental challenges. For instance, in CO₂ reduction, integrating bismuthene into 2D/2D heterostructures enhances electron transfer efficiency, thereby improving selectivity toward valuable products, such as CH₄ and formic acid. In organic pollutant degradation, bismuth subcarbonate (Bi₂O₂CO₃) nanosheets, obtained from 2D bismuthene, have demonstrated high photocatalytic degradation of antibiotics under visible light irradiation, due to their increased surface area and efficient generation of reactive species. Moreover, bismuthene-based materials exhibit potential in the photocatalytic water-splitting process for hydrogen production, overcoming issues associated with UV-light dependence and sacrificial agent usage. This review underscores the versatile applications of 2D bismuthene in advancing photocatalytic technologies, offering insights into future research directions and potential industrial applications. Full article

In this paper, we demonstrate the potential of the contactless surface photovoltage (SPV) method for fast and reliable control of GaAs-based solar cells directly on epitaxial heterostructures before metallization and photolithography processes. The magnitude of the SPV corresponds to the generated photovoltage in the photoactive region, which is related to the open circuit voltage of the cell. The focus of this investigation is the potential of dilute nitride compounds grown by low-temperature liquid-phase epitaxy (LPE) for application as intermediate cells in multijunction solar cells. First, SPV spectroscopy is used to determine the photosensitivity spectral range and bandgap of the grown dilute nitride compound layers. Further, the photovoltaic quality of the grown solar cell heterostructures is evaluated by comparing the magnitude of their SPV signals with that of a reference GaAs solar cell. A drastic reduction in the measured SPV is observed for nitrogen-containing solar cell structures, which correlates with the lowering of solar cell open-circuit voltage values measured under standard test conditions. Finally, solar cell structures based on nitrogen-free GaAsSb compounds with the same long-wavelength photosensitivity limit as GaAsSbN are grown by LPE. They show one order of magnitude higher SPV signal and, therefore, have a great potential for solar cell application. Full article

Coalescence of nanowires and other three-dimensional structures into continuous film is desirable for growing low-dislocation-density III-nitride and III-V materials on lattice-mismatched substrates; this is also interesting from a fundamental viewpoint. Here, we develop a growth model for vertical nanowires which, under rather general assumptions on the solid-like coalescence process within the Kolmogorov crystallization theory, results in a morphological diagram for the asymptotic coverage of a substrate surface. The coverage is presented as a function of two variables: the material collection efficiency on the top nanowire facet $a$ and the normalized surface diffusion flux of adatoms from the NW sidewalls $b$. The full coalescence of nanowires is possible only when $a=1$, regardless of $b$. At $a>1$, which often holds for vapor–liquid–solid growth with a catalyst droplet, nanowires can only partly merge but never coalesce into continuous film. In vapor phase epitaxy techniques, the NWs can partly merge but never fully coalesce, while in the directional molecular beam epitaxy the NWs can fully coalesce for small enough contact angles of their droplets corresponding to $a=1$. The growth kinetics of nanowires and evolution of the coverage in the pre-coalescence stage is also considered. These results can be used for predicting and controlling the degree of surface coverage by nanowires and three-dimensional islands by tuning the surface density, droplet size, adatoms diffusivity, and geometry of the initial structures in the vapor–liquid–solid, selective area, or self-induced growth by different epitaxy techniques. Full article

In this work, three sets of single crystalline films (SCF) of Al₂O₃:Mn sapphire, YAlO₃:Mn perovskite (YAP:Mn), and Y₃Al₅O₁₂:Mn garnet (YAG:Mn), with a nominal Mn content of 0.1%, 1%, and 10 atomic percent (at.%) in the melt-solutions, were crystallized by the liquid phase epitaxy (LPE) method onto sapphire, YAP and YAG substrates, respectively. We have also calculated the average segregation coefficient of Mn ions for Al₂O₃:Mn, YAP:Mn and YAG:Mn SCFs with Mn content in the melt-solution in the 0.1–10% concentration range, which was equal to 0.1, 0.14 and 0.2, respectively. The main goal of the conducted research was the spectroscopic determination of the preferable valence states of manganese ions which were realized in the SCFs of sapphire, perovskite and garnet depending on the Mn content. For this purpose, the absorption, cathodoluminescence (CL), photoluminescence (PL) emission/excitation spectra and PL decay kinetics of Al₂O₃:Mn, YAP:Mn and YAG:Mn SCFs with different Mn concentrations were studied. Based on the CL and PL spectra, we showed that Mn ions, depending on the Mn content in the melt-solution, are incorporated in Al₂O₃:Mn, YAP:Mn and YAG:Mn SCFs in the different charged states and are located in the different crystallographic positions of the mentioned oxide lattices. We have observed the presence of the luminescence of Mn⁴⁺, Mn³⁺ and Mn²⁺ valence states of manganese ions in CL spectra in all SCFs under study with 0.1 and 1% Mn concentrations. Namely, the Mn⁴⁺ ion valence state with the main sharp emission bands peaked at 642 and 672 nm, related to the ²E → ⁴A₂ transitions, was found in the luminescence spectra of the all studied Al₂O₃:Mn SCFs. The luminescence of the Mn²⁺ valence state was found only in YAP:Mn and YAG:Mn SCFs, grown from melt solution with 1% Mn content, in the emission bands peaked at 525 and 560 nm, respectively, related to the ⁴T₁ → ⁶A₁ transitions. The PL and CL spectra of YAP:Mn and YAG:Mn SCFs with the Mn content in the 0.1–1% range show that the main valence state of manganese ions in these films is Mn³⁺ with the main emission bands peaking at 655 and 608 nm, respectively, related to the ¹T₂ → ⁵E transitions. Meanwhile, higher than 1% Mn content in the melt solution causes a strong concentration quenching of luminescence of all Mn centers in Al₂O₃:Mn, YAP:Mn and YAG:Mn SCFs. Full article

This study investigated a reflective transparent structure to improve the optical efficiency of 850 nm infrared light-emitting diodes (IR-LEDs), by effectively enhancing the number of extracted photons emitted from the active region. The reflective transparent structure was fabricated by combining transparent epitaxial and reflective bonding structures. The transparent epitaxial structure was grown by the liquid-phase epitaxy method, which efficiently extracted photons emitted from the active area in IR-LEDs, both in the vertical and horizontal directions. Furthermore, a reflective bonding structure was fabricated using an omnidirectional reflector and a eutectic metal, which efficiently reflected the photons emitted downwards from the active area in an upward direction. To evaluate reflective transparent IR-LED efficiency, a conventional absorbing substrate infrared light-emitting diode (AS IR-LED) and a transparent substrate infrared light-emitting diode (TS IR-LED) were fabricated, and their characteristics were analyzed. Based on the power–current (L-I) evaluation results, the output power (212 mW) of the 850 nm IR-LED with the reflective transparent structure increased by 76% and 26%, relative to those of the AS IR-LED (121 mW) and TS IR-LED (169 mW), respectively. Furthermore, the reflective transparent structure possesses both transparent and reflective properties, as confirmed by photometric and radial theta measurements. Therefore, light photons emitted from the active area of the 850 nm IR-LED were efficiently extracted upward and sideways, because of the reflective transparent structure. Full article

Microstructure and solute distribution have a significant impact on the mechanical properties of wire and arc additive manufacturing (WAAM) deposits. In this study, a multiscale model, consisting of a macroscopic finite element (FE) model and a microscopic phase field (PF) model, was used to predict the 2319 Al alloy microstructure evolution with epitaxial growth. Temperature fields, and the corresponding temperature gradient under the selected process parameters, were calculated by the FE model. Based on the results of macroscopic thermal simulation on the WAAM process, a PF model with a misorientation angle was employed to simulate the microstructure and competitive behaviors under the effect of epitaxial growth of grains. The dendrites with high misorientation angles experienced competitive growth and tended to be eliminated in the solidification process. The inclined dendrites are commonly hindered by other grains in front of the dendrite tip. Moreover, the solute enrichment near the solid/liquid interface reduced the driving force of solidification. The inclined angle of dendrites increased with the misorientation angle, and the solute distributions near the interface had similar patterns, but various concentrations, with different misorientation angles. Finally, metallographic experiments were conducted on the WAAM specimen to validate the morphology and size of the dendrites, and electron backscattered diffraction was used to indicate the preferred orientation of grains near the fusion line, proving the existence of epitaxial growth. Full article