Properties Of Semiconductors Research Articles

(Invited) In-Situ MOCVD Etching of GaN Using XeF2 for Selective-Area-Epitaxial-Regrowth of p-Type GaN for High Voltage PN Diodes

PN diodes with multi-kilovolt breakdown voltages have been demonstrated to great than 6 kV in GaN, validating the device potential predicted by the intrinsic material properties of III-nitride semiconductors. However, power control circuits also require switching transistors such as junction field effect transistors (JFETs) and practical diodes such as merged PIN Schottky (MPS) diodes. Such devices usually employ selective areas of p-type semiconductor surrounded by n-type material and require the formation of PN junctions with low reverse leakage current. Selective-area p-type doping in Si and SiC based power devices is typically achieved using implantation and thermal annealing to form the p-type areas. Ion implantation of Mg in GaN has demonstrated p-type conductivity, but this process requires specialized equipment for the high-pressure and high-temperature activation of Mg dopants. We have investigated selective-area-regrowth (SArG) to epitaxially grow p-type GaN as an alternative to dopant implantation. Successful PN diode formation by SArG requires a process to remove residual crystalline damage resulting from the ex-situ inductively coupled plasma (ICP) etch typically used to form the p-well, as well as a method to remove the elevated level of Si found at the regrowth interface of a surface that had been exposed to air. For the case of SArG of p-GaN on air-exposed, blanket ICP etched n-type GaN, we present the novel use of a fluorine-based precursor (XeF2) for in-situ etching of GaN in the MOCVD chamber. Unlike chlorine (TBCl and CCl4) and bromine (CBr4) -based precursors we have studied; we obtained a smooth surface following in-situ fluorine etching of air-exposed GaN. Schottky barrier diodes (SBDs) formed by shadow mask evaporation on in-situ fluorine etched n-GaN that had been previously ICP etched showed reverse leakage currents to -40 V that are equal to those of SBDs formed on as-grown n-GaN layers. The in-situ fluorine/ICP etched Schottky diodes had reverse leakage currents more than 3 orders of magnitude lower than those formed on n-GaN layers that had only experienced ICP etching. This suggests that the in-situ fluorine etch was effective at removing the residual damage from the ICP etch process. Furthermore, we discuss the use of in-situ fluorine etching to reduce the concentration of Si at the regrowth interface required to form PN junctions with low reverse leakage current. This work was supported in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under the PNDIODES program directed by Dr. Isik Kizilyalli, and in part by the US Department of Energy (DOE) Vehicle Technologies Office (VTO) under the Electric Drive Train Consortium. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the presentation do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

(Invited) Ferroelectric Nitride Semiconductors: Epitaxy, Properties, and Emerging Device Applications

The incorporation of rare-earth elements such as scandium (Sc) can transform conventional III-nitride semiconductors to be ferroelectric. In this talk I will present recent advances of ferroelectric Sc-III-nitride heterostructures and nanostructures, including epitaxy, properties and emerging device applications. Molecular beam epitaxy and properties of ScAlN and ScGaN with a wide range of Sc compositions will be discussed. Special attention will be paid to the unique ferroelectric properties of these ultrawide bandgap semiconductors. The realization of ultrathin ferroelectric nitride heterostructures and the underlying physics and properties will be discussed, together with their applications in quantum photonics and electronics.

Adaptable nanoparticles as multifunction semi-transparent conductive films and drug delivery system

Adaptable nanoparticles of reduced graphene oxide-curcumin as semi-transparent conductive films and graphene oxide-curcumin as drug delivery system (DDS) were evaluated. The reduced graphene oxide--curcumin nanoparticles showed outstanding organic semiconductor properties as semi-transparent conductive films (semi-TCFs). The optimum conditions for gaining maximum σdc/σop values of rGO-curcumin semi-TCFs were at pH = 11 in the absence of crosslinker, which may be a distinguished option in recent organic electronics. Moreover, the graphene-oxide-curcumin nanoparticles were used to increase water solubility of curcumin. Such nanoparticles could be used to deliver curcumin to delicate positions in human body. Graphene oxide (GO) and reduced graphene oxide (rGO) were synthesized from raw graphite, and characterized using attenuate total reflectance Fourier transform infrared (ATR-FTIR), X-ray pattern (XRD), thermogravimetry (TGA) for chemical structure, crystal structure and thermal stability, respectively. The successful exfoliation process of nanoparticles was also monitored by scanning electron microscope (SEM) technique. Pre-adjusted pH method was used at different pH values (i.e. pH = 4.0–7.4). Power law (ln/ln) constant values like diffusional exponent (n) and proportionality constant (k) demonstrated in-vitro Fickian diffusion mechanism. Successful drug delivery system (DDS) revealed maximum curcumin bioavailability of 97 % compared to 22 % curcumin alone. Conclusively, GO and rGO connected with curcumin could achieve adaptable and potential applications in medical and engineering sectors.

Proton Radiation Effect on Iron Thermal Oxides: Point Defects, Microstructure & Corrosion Electrochemistry

Iron(Fe)-based alloys, such as austenitic stainless steels, form protective surface oxide layers when exposed to oxygen, aqueous electrolyte, and water vapor, which effectively inhibit corrosion [1]. One attribute that underpins the electrochemical reactivity of surface oxide layers is the presence and properties of charged point defects (e.g. vacancies and interstitials charge compensated by electrons or holes), which govern the rate and mechanism of ionic transport when exposed to an oxidizing environment such as an aqueous electrolyte [2,3,4]. However, the effect of radiation on the relationship between point defects, oxide microstructure, and oxidation behavior is poorly understood. Structural materials used in nuclear applications are particularly susceptible to radiation damage, which can degrade the underlying surface oxides. To investigate this phenomenon, thermally oxidized pure Fe was selected as a model material system to study radiation-induced defects in iron oxide scales [3]. Iron oxides were fabricated by thermal oxidation of pure Fe metal in air at 400°C, 600oC, and 800°C for 1 hour. Each oxides layer exhibits an outer hematite (α-Fe2O3) and inner magnetite (Fe3O4)/wüstite (FeO) layers with varying thickness depending on the oxidation conditions. These oxides were then irradiated with 200 keV, 0.03 dpa protons at room temperature. The oxide microstructure and phase compositions were characterized with transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS). These results were corroborated with X-Ray diffraction (XRD) and Raman spectroscopy analysis. The relative vacancy concentrations and size distributions in the oxide layers were investigated using positron annihilation spectroscopy (PAS) and positron annihilation lifetime spectroscopy (PALS) techniques. Lastly, these oxides were exposed to a 0.1 M borate buffer solution (pH 9.2) at applied potential where corrosion reactivity was governed by interfacial reactions and ionic defects to regulate the growth processes observed. The potentials were cycled over the ranges where oxides growth and reduction occurred involving Fe/Fe(II)/Fe(III) reactions at a pH which suppressed chemical reactions at the oxide/electrolyte interface and would lead to solubilization of Fe species. The subsequent oxidation, reduction, and semiconductor properties of the oxides were evaluated using AC and DC electrochemical methods, both with and without prior irradiation. Current results demonstrate that radiation damage can manifest itself in the form of vacancy clustering and possible maghemite (γ-Fe2O3) formation. These phenomena were corroborated with donor density and diffusivity values calculated using Mott-Schottky analysis and electrochemical impedance spectroscopy (EIS) analysis and equivalent circuit model (ECM) interpretation, respectively. Radiation damages to the outer rate-regulating α-Fe2O3 layer correlates with enhanced anodic current density corresponding to Fe/Fe(II)/Fe(III) reactions. However, proton radiation may also interact with the metal/oxide and oxide/oxide interfaces depending on the oxide structure and H+ beam penetration depth, leading to either degradation or improvement in the Fe-oxide corrosion responses. Nevertheless, the damage persists and can continue to impact corrosion mechanisms long after the irradiation source is removed. The multiple techniques adopted, each characterizing a material property of a different length scale (from meso-, micro-, to macroscopic) enable us to hypothesize the roles that point defects played after irradiation and during corrosion and how the radiation-induced changes in the defect characteristics influence corrosion electrochemistry. Acknowledgment Research primarily supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Utilization of the Malvern-Panalytical Empyrean diffractometer were supported by Nanoscale Materials Characterization Facility with National Science Foundation under award CHE-2102156. The TEM sample preparation and characterization was performed at the Analytical Instrumentation Facility at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award number ECCS-1542015). LANL is operated by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. DOE (Contract No. 89233218CNA000001).

(Invited) Heterogeneous Integration of Ultrawide Bandgap III-Nitrides and Diamond

Industry demands for power switching, amplification and photonic applications are continually pushing the limits of semiconductor device technologies leading to increasing applied voltages and, thus, higher electric fields while simultaneously requiring reduction in the size, weight and power consumption. In addition, recent heightened interest in higher temperature (and other extreme environment) applications, while simultaneously maintaining high-voltage and high-power performance, has inexorably led to ultrawide bandgap (UWBG) semiconductor materials. This interest in UWBG materials stems from superior properties that include high material hardness, breakdown strength to withstand large electric fields and mitigation of power dissipation during device switching, deliver high current density while operating at higher junction and ambient temperature. Among these materials are boron nitride in its hexagonal and cubic phases, gallium oxide, diamond, and aluminum gallium nitride. The versatile alloys of wurtzite AlxGa1-xN have long been demonstrated across the full composition range. The variation in Eg with AlGaN composition, along with select WBG and UWBG materials, is shown in Figure 1 versus (in-plane for non-cubic) lattice constant.Premier WBG materials to date for electronics and photonics are SiC (Eg = 3.3 eV) and GaN (Eg = 3.4 eV). The latter has been successfully applied to high-power transistors and near ultraviolet photonics. In both electronics and photonics applications, the polarization fields of the wurtzite crystal structure, generally grown along (0001) direction, produce design challenges. In photonics, for example, the fields and band alignment couple to spatially separate electrically injected electrons and holes to reduce wavefunction overlap in quantum wells. In electronics, the internal fields have contributed to difficulties in the design of logic and bipolar transistor devices based on these materials. Despite this, the inherent polarization field and band offsets were successfully employed in the design of high electron-mobility transistors (HEMTs). The inherent AlGaN/GaN HEMT band offset produces a high electron concentration at the interface that spontaneously forms a two-dimensional electron gas (2DEG). Because charge flow in these devices is restricted to the 2DEG, current crowding results in intense self-heating. The local heating decreases electrical conductivity to produce a runaway scenario for elevating the Joule heating. Dissipating this heat, therefore, is the principal limiting factor in operating at power higher than 40 W/mm.The various temperature dependences of semiconductor device parameters are the principal drivers in the operation of semiconductor devices. The physics has inextricably led to UWBGs for future high temperature applications, > 300 °C, due to their lower intrinsic carrier density and thus the effects of leakage are orders of magnitudes less than Si-based devices. Furthermore, AlGaN and diamond offer superior high temperature mechanical stability due to their structural hardness and chemical inertness. Thermal management is essential for achieving higher power densities. Diamond is highly attractive for many applications due to its high hardness, transparency, chemical inertness, promising semiconductor properties, and its high thermal conductivity (κ) to 2500 W/m·K in natural material. Factors related to the consequences of self-heating in devices have motivated extensive research to improve the properties of diamond and produce better approaches to determine the thermal properties. Laboratory-grown diamond films exhibit significantly poorer κ than natural diamond and, when integrated with other electronic materials, a low thermal boundary conductance (TBC in W/m2·K) that inhibits heat transfer between materials. The former originates from the ubiquitous polycrystalline nature of chemical vapor deposition (CVD) diamond and the presence of non-diamond carbon (NDC) in the layer. The low TBC stems from fundamental barriers to phonon propagation between two materials and from practical issues of poor diamond quality in the initial growth regime. Continued research is needed to improve κ in the polycrystalline diamond and mitigate the negative impact of the initial diamond layer on TBC.The current status of hetero-integration of UWBG AlGaN and diamond will be reviewed. Particular emphasis is given to high Al content AlGaN for near-bandgap matching with diamond. Patterned diamond grown using hot-filament CVD to realize unique three-dimensional lateral device structures in a self-aligned, as-grown fabrication process is employed. Engineering the AlGaN-diamond bandgap alignment is noteworthy at the nonpolar AlGaN – diamond interface including diamond surface terminations that produce either negative or positive electron affinity. The review will focus on improvements in material properties, especially the interfaces, that are critical to both charge and heat transport for UWBG device structures. Figure 1

ОПТИЧНА СПЕКТРОСКОПІЯ ДЕТЕКТОРНИХ ВИСОКООМНИХ МОНОКРИСТАЛІВ CdTe (111) ТА ТВЕРДИХ РОЗЧИНІВ Cd 1-x Zn x Te (х= 0,1)

Cadmium telluride is used for the manufacture of uncooled gamma radiation detectors, and solid solutions of Cd 1-x Zn x Te (x=0.1) are used for the manufacture of X-ray and gamma radiation detectors. The study of the effect of doping on the physical properties of semiconductors is relevant both for experimenters and for the theoretical substantiation of physical processes. This paper presents the results of the study of optical reflection spectra in the spectral range (0,2-1,7) . 10 -6 m and transmittance in the region of the fundamental optical transition E 0 of high-resistivity CdTe single crystals of (111) orientation with resistivity ρ = (2÷5)·10 9 Ohm∙cm doped with chlorine, as well as solid solutions of Cd 1-x Zn x Te (x = 0.1) with resistivity ρ = (5 ÷30)∙10 9 Ohm∙cm. Since the optical reflection coefficient R = f (λ) is related to the optical transmittance T = f (λ) and absorption D = f (λ) by the ratio R+T+D=1 (with the light (electromagnetic) wave scattering in the studied samples not taken into account), the absorption spectra D=1-(R+T) versus the light (electromagnetic) wavelength λ were also constructed in this work. It is determined that the energy of the fundamental optical transition E 0 of the studied materials at T = 300 K is as follows: for CdTe - 1.44 eV; and for Cd 1-х Zn х Te (x = 0.1) - 1.5 eV. The energy relaxation time of free charge carriers τ for p-CdTe (111) single crystals and Cd 1-х Zn х Te (x = 0.1) solid solutions was estimated to be 1.343-10 -14 s and 0,878·10 -14 s, respectively. The effective "optical" mobility for single crystals of p-CdTe (111) and solid solutions of Cd 1-х Zn х Te (x = 0.1) is 274 . 10 -4 ; 179,5 . 10 -4 , respectively. It has been shown that the investigated crystals are of high (detector) quality, which is crucial for the manufacture of highly sensitive and high-resolution ionising radiation sensors. The practical value of the obtained results lies in the determination of electronic and physical parameters of technically important semiconductors CdTe and Cd 1-х Zn х Te (x=0.1).

Electrochemical N2-to-NH3 with high faradaic efficiency on ZrO2/carbon quantum dots catalysts in neutral electrolyte

Electrochemical nitrogen reduction (NRR) to synthesize NH3 is limited by low Faraday efficiency (FE). Developing electrocatalysts that can efficiently adsorb/activate N2 and suppress hydrogen evolution reaction (HER) to enhance FE is needed. In this work, x-ZrO2/CQDs-T series catalysts were successfully prepared. The results demonstrate that: (I) The appropriate introduction of carbon quantum dots (CQDs) effectively enhances the surface adsorption capacity of ZrO2/CQDs for N2. (II) By high-temperature calcination eliminates the alkaline functional group (-NH2) of CQDs, which reduces the basicity of ZrO2/CQDs catalyst and inhibits the adsorption of protons on the catalyst surface. (III) Due to the semiconductor properties of ZrO2, the charge transfer efficiency of ZrO2/CQDs catalyst is significantly reduced, thereby weakening the binding of electrons to the adsorbed protons. As a result, 1-ZrO2/CQDs-750 catalyst appropriately and effectually restricts the accessibility of protons/electrons and promotes more N2 molecules to occupy active sites, thus achieving up to 66.62 % FE, which is superior to most reported NRR catalysts so far. Meanwhile, electrochemical in situ ATR-SEIRAS technique reveals that 1-ZrO2/CQDs-750 catalyst surface occurs in associative alternating reactions. The introduction of CQDs not only effectively affects the adsorption of N2 and N-related intermediates on ZrO2/CQDs catalyst and limits the proton/electron accessibility to improve FE of NRR, but also promotes the exposure of active sites to increase NH3 yield.

Promising Perovskite Solar Cell Candidates: Enhanced Optoelectronic Properties of XSrI3 Perovskite Materials under Hydrostatic Pressure

Density‐functional theory (DFT) has proven to be invaluable for investigating the physical properties of perovskite materials under varying pressure conditions to uncover potential applications in the field of optoelectronics. Herein, lead‐free XSrI3 (X = FA+, MA+, and DMA+ [formamidinium (FA+), methylammonium (MA+), and dimethylammonium (DMA)]) perovskites are designed and utilized using DFT calculations for promising solar cell applications. The application of pressure to these perovskites leads to a reduction in their lattice parameters, thereby enhancing atom interactions within the material. This compression of the crystal lattice also exerts a significant influence on the electronic band structure and the number of available electronic states, providing valuable insights into their semiconducting properties. Moreover, applying pressure results in a narrower bandgap in the perovskite halides, thus broadening the range of light absorption and potentially increasing light‐absorption efficiency. In this work, the feasibility of employing XSrI3 perovskites for enhanced optical performance is highlighted and valuable directions for further exploration in this field are offered. The insights gained from this theoretical study may hold the potential to advance the development of perovskite‐based materials for various optoelectronic applications.

Experimental approval of the working modes of the Sunbrick sun simulator

Commissioning and experimental testing of technical capabilities and modes of operation were carried out, and test measurements of light current-voltage characteristics of solar cells were carried out using a modern measuring complex based on the Sunbrick sun simulator. Automated measurement of the light-voltage-current characteristics of solar cells by the compensation method using the Keithley 2400 measuring device was implemented. During the approbation of the measuring complex based on the Sunbrick sun simulator, the possibility of reproducing different modes of simulator operation was tested and the ability to control radiation in terms of energy in the range from 100 to 1100 W/m2 and by spectral composition. It was established that the spatial unevenness of illumination for the investigated device is less than 2 % with an illumination area of more than 400 cm2. It is shown that the tested measuring complex allows for automated research of solar cells in irradiation regimes corresponding to both terrestrial irradiation conditions and extraatmospheric solar radiation conditions. The possibility of individual adjustment of each of the 36 channels of the emitting element in the range from 400 to 1100 nm has been tested, which adds flexibility in the use of the Sunbrick sun simulator during the study of both solar cells as a whole and the properties of functional semiconductor materials by irradiation with monochromatic or mixed illumination. It is shown that due to the rapidity of conducting research and the ability to immediately visualize the measured current-voltage characteristic on the computer screen, it is possible to significantly speed up the process of researching solar cells. Thus, it is possible to immediately divide the investigated solar cells into groups in relation to their efficiency and determine the presence of possible defects or damage in their structure.

Surface Functionalization of TiO2 Nanotubes Modified with a Thin Film of BiFeO3

The atomic layer deposition method allows for the production of a thin film with a high aspect ratio on the uneven surface of titanium dioxide nanotubes TiO2(Nt). A modified BiFeO3/TiO2(Nt)/Ti (BFOT) structure with controllable electrical characteristics was obtained. BFOT possesses both ferroelectric and semiconductor properties with nonlinear conductivity dependent on the magnitude and duration of the voltage supply. Analysis of the temperature dependence of charge variation showed leakage currents in the BFOT structure due to the capture and release of charge carriers from defect levels. Surface modification of nanotubes with the multiferroic BiFeO3 allows for the creation of semiconductors with adaptive functional properties.

Intrinsically Stretchable and Healable Polymer Semiconductors.

In recent decades, polymer semiconductors, extensively employed as charge transport layers in devices like organic field-effect transistors (OFETs), have undergone thorough investigation due to their capacity for large-area solution processing, making them promising for mass production. Research efforts have been twofold: enhancing the charge mobilities of polymer semiconductors and augmenting their mechanical properties to meet the demands of flexible devices. Significant progress has been made in both realms, propelling the practical application of polymer semiconductors in flexible electronics. However, integrating excellent semiconducting and mechanical properties into a single polymer still remains a significant challenge. This review intends to introduce the design strategies and discuss the properties of high-charge mobility stretchable conjugated polymers. In addition, another key challenge faced in this cutting-edge field is maintaining stable semiconducting performance during long-term mechanical deformations. Therefore, this review also discusses the development of healable polymer semiconductors as a promising avenue to improve the lifetime of stretchable device. In conclusion, challenges and outline future research perspectives in this interdisciplinary field are highlighted.

Antimony Bromide Organic-Inorganic Hybrid Compound with a Long-Chain Diamine Showing Switchable Phase Transition and Second-Harmonic Generation Properties.

Organic-inorganic hybrid metal halides have attracted significant attention in recent years due to their excellent optoelectronic properties and potential applications in solar cells. Herein, the organic-inorganic hybrid molecule [N,N-dimethyl-1,3-propanediamine]SbBr5 (1) was synthesized by reacting a long-chain organic diamine N,N-dimethyl-1,3-propanediamine with SbBr3 as a metal halide precursor in HBr aqueous solution. Compound 1 possesses a one-dimensional chainlike structure with the second-harmonic generation switch and two continuous phase transitions above room temperature. The band gap of compound 1 is about 2.62 eV, exhibiting a semiconductive property, which may have important implications for the development of new optoelectronic devices.

Crystals of 4,7-Di-2-thienyl-2,1,3-benzothiadiazole and Its Derivative with Terminal Trimethylsilyl Substituents: Synthesis, Growth, Structure, and Optical-Fluorescent Properties

Among short donor–acceptor molecules with a central benzothiadiazole fragment, 4,7-di-2-thienyl-2,1,3-benzothiadiazole (T-BTD) is one of the most well-known compounds, valued for its photophysical and semiconductor properties. We have synthesized a derivative of 4,7-di-2-thienyl-2,1,3-benzothiadiazole with trimethylsilyl end-substituents, 4,7-bis(5-(trimethylsilyl)thiophen-2-yl)benzothiadiazole (TMS-T-BTD). The phase transition parameters and thermal stability of T-BTD and TMS-T-BTD were investigated using DSC and TGA methods. The presence of the trimethylsilyl end-groups in TMS-T-BTD significantly enhances solubility, increases the melting temperature, and improves the resistance of TMS-T-BTD to evaporation in the liquid state. Single crystals of T-BTD and TMS-T-BTD were grown from solutions, with the largest sizes being 7 × 2 × 0.5 mm3 and 8 × 1 × 0.45 mm3, respectively. Using single-crystal X-ray diffraction at 293 K, the crystal structure of T-BTD was refined in the rhombic system (sp.gr. Pcab, Z = 8), while for TMS-T-BTD, it was determined for the first time in the monoclinic system (sp.gr. P21/c, Z = 4). The relationship between observed growth anisotropy and molecular packing in the crystals was analyzed. The results of investigations into the spectral-fluorescent properties of solutions in hexane and THF are presented. The solvatochromic effect was studied in a series of solvents, including hexane, THF, dichloromethane, and acetonitrile. The photostability of the compounds in hexane solutions was examined. It was found that the quantum yield of photodestruction for T-BTD is 13 times higher than that of TMS-T-BTD. The fluorescent properties of T-BTD and TMS-T-BTD crystals were investigated.

Probing and controlling oxygen impurity diffusion in h-BN semi-bulk crystals

Combining its unique features of ultrawide bandgap (UWBG) and two-dimensional nature, h-BN has been explored for emerging applications such as deep ultraviolet optoelectronic devices and single photon emitters. One of the unusual applications of h-BN is for solid-state neutron detectors by utilizing the property of high thermal neutron capture cross section of B-10 as well as its UWBG properties. Although a record high detection efficiency of 59% has been attained by h-BN detectors, the understanding/minimization of defects and impurities is still needed to further advance the h-BN material and detector technologies. We report metal organic chemical vapor deposition growth and oxygen (O) impurity diffusion in thick h-BN. The diffusion coefficient (D) of O impurities has been measured via the evolution of an oxygen related emission with the etching depth, providing a value of D of ∼ 2 × 10−13 cm2/s at 1450 °C and supporting the interpretation that oxygen in h-BN is a substitutional donor. A multiple-buffer-layer approach was employed to mitigate to a certain degree the issue of oxygen diffusion from sapphire substrate during growth. It was demonstrated that the performance of h-BN neutron detectors fabricated from the wafer incorporating multiple buffer layers was significantly improved, as manifested by the enhanced thermal neutron detection efficiency. The advancement of the crystal growth technology of h-BN semi-bulk crystals creates applications in optoelectronic and power electronic devices utilizing the UWBG semiconductor properties of h-BN, while high efficiency h-BN neutron detectors have the potential to supplant the traditional He-3 gas detectors in various application areas by offering the obvious advantages of UWBG semiconductor technologies.

MoS2/MoO3 heterojunctions enabled by surface oxidization of MoS2 nanosheets for high-performance room-temperature NO2 gas sensing

Transition-metal dichalcogenides (TMDs) have emerged as ideal candidates for room-temperature gas sensing due to their remarkable semiconductor properties. However, bare TMDs typically exhibit drawbacks such as low sensitivity, slow response, and low recovery speeds, which limit their applicability. In comparison to single materials, enhancing the sensing performance of the material can be achieved through the realization of heterostructures. Therefore, the key to improving the performance of metal-sulfide gas sensors lies in the controlled construction of unique heterostructures. In this work, surface heterostructures composed of molybdenum disulfide (MoS2) nanoflowers loaded with molybdenum trioxide (MoO3) enabled are realized through the surface oxidization of MoS2 nanosheets for high-performance room-temperature detection of NO2 gas. The heterostructures were easily constructed by oxidizing flower-like MoS2 using a hydrogen peroxide aqueous solution. The gas sensor based on the MoS2/MoO3 heterojunction exhibits a response of 18.9 % to 1 ppm NO2, which is nine times higher than that of the MoS2 sensor (2.1 %). Furthermore, even at a NO2 concentration as low as 50 ppb, the sensor response can reach 6.9 %. The sensor displays good repeatability and excellent selectivity. The enhanced gas-sensing performance of the MoS2/MoO3 heterostructure may result from the unique structure of MoS2 and the p-n heterojunction formed at the interfaces. The proposed design strategy and the surface heterostructure constructed in this work can provide guidance for the development of high-performance gas-sensitive materials and devices.

Study on corrosion resistance of passive film promoted by natural rosin-based passive sealant

An eco-friendly Rosin-based passive sealant is prepared, which can seal the micropores and repair the passive film in one-step. Sealing performance of sealants and the growth kinetics of the passive film were analyzed by 3D-XRT tomography, Electrochemistry and XPS. The results showed that the permeation depth of sealant reached more than 150 μm, and the natural rosin effectively prolonged the loss time of sealant. The phosphate conversion layer at the passive film/sealant interface changes the semiconductor properties of the passive film. After immersion for 360 h in 3.5 wt% NaCl solution, the amount of Fe2O3 and Cr2O3 in the passive film increased by 34 % and 20 %, respectively, and the film thickness increased by 257.9 %. Rosin-based passive sealant can directly inhibit the diffusion rate of defects in passive film. This study provides a new theoretical support for the application of rosin sealant.

Study on the semiconductor properties of high entropy alloy FeCoNiCrAl coating prepared by air thermal spraying in 5% NaCl solution

High entropy alloy FeCoNiCrAl coating was prepared using air plasma spraying, and the semiconductor properties of the passivation film were studied in 5% NaCl solution. The element distribution mappings of the coating revealed slight oxidation on the surface of the as-prepared coating, with Al and O combining closely. The Mott-Schottky and XPS measurement showed that the M−S curve of FeCoNiCrAl coating displays an S-type. As the potential increase, the properties of the passivation film also change, which is due to the different properties of the coating formed by different elements, and Fe and Cr dominate the performance of passivation films.

Super-Resolution Exciton Imaging of Nanobubbles in 2D Semiconductors with Near-Field Nanophotoluminescence Microscopy.

Two-dimensional (2D) semiconductors, such as transition metal dichalcogenides, have emerged as important candidate materials for next-generation chip-scale optoelectronic devices with the development of large-scale production techniques, such as chemical vapor deposition (CVD). However, 2D materials need to be transferred to other target substrates after growth, during which various micro- and nanoscale defects, such as nanobubbles, are inevitably generated. These nanodefects not only influence the uniformity of 2D semiconductors but also may significantly alter the local optoelectronic properties of the composed devices. Hence, super-resolution discrimination and characterization of nanodefects are highly demanded. Here, we report a near-field nanophotoluminescence (nano-PL) microscope that can quickly screen nanobubbles and investigate their impact on local excitonic properties of 2D semiconductors by directly visualize the PL emission distribution with a very high spatial resolution of ∼10 nm, far below the optical diffraction limit, and a high speed of 10 ms/point under ambient conditions. By using nano-PL microscopy to map the exciton and trion emission intensity distributions in transferred CVD-grown monolayer tungsten disulfide (1L-WS2) flakes, it is found that the PL intensity decreases by 13.4% as the height of the nanobubble increases by every nanometer, which is mainly caused by the suppression of trion emission due to the strong doping effect from the substrate. In addition to the nanobubbles, other types of nanodefects, such as cracks, stacks, and grain boundaries, can also be characterized. The nano-PL method is proven to be a powerful tool for the nondestructive quality inspection of nanodefects as well as the super-resolution exploration of local optoelectronic properties of 2D materials.

Semiconducting and gas sensing performance of Magnetite nanoparticle systems of different morphologies

Magnetite nanoparticle systems with uniform morphological features were synthesized through co-precipitation and forced hydrolysis without using any surfactants or additives. The selected batches of the synthesized particle systems were calcined at 1200 °C for phase transformation. The as-synthesized and calcined samples were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometry (FTIR), and X-ray Diffraction (XRD). In addition, the as-prepared and commercial magnetite particles were then employed as gas sensors to detect ammonia. Furthermore, the semiconducting properties of the synthesized (magnetite-I magnetite-II & magnetite-III) and commercial magnetite-based sensors were studied in the temperature range from 30 °C to 270 °C which indicated the n-type semiconducting nature of the magnetite particles. While commercial magnetite did not show any response in the employed temperature range. Furthermore, the synthesized magnetite nanoparticle-based sensors showed good and highly reproducible performance toward 10 ppm ammonia with a gas response of 58.44%, 64.39%, and 59.02%, respectively. For instance, magnetite-II and III were more sensitive toward the detection of ammonia with quick response/recovery times of 2s/5.8s and 2.4s/6.2s than 40s/17s for magnetite-I-based sensors. In contrast, the commercial magnetite-based sensor showed a response of 13.59% and significantly longer response/recovery time at room temperature and did not respond to ammonia concentration even at high temperatures. It was attributed to the remarkable uniformity in morphology, porosity, and good crystallinity of the as-prepared nanoparticles compared to the commercial-based sensor. This study unfolds that morphological features of the gas sensor’s material could be the key factors for controlling their sensing properties.

Application of persulfate-assisted graphitic carbon, derived through pyrolysis of waste biomass, driven by visible light, for the removal of tetracycline from water: Mechanisms and performance influencing parameters

Sulfate radical based advanced oxidation process by using carbon-based materials has attracted widespread attention for removal of emerging contaminants in water. This paper reports the study on the efficacy of visible light activated persulfate (PS) – graphitic carbon (GC) system for the removal of tetracycline (TC) from water . Here GCs from residual agricultural biomass were synthesized via a facile and chemical-free pyrolysis route, and their characteristics were analyzed under varying thermal conditions, viz. temperature (550–950 °C) and heating rate (2.5–10 °C min−1). The GCs at high pyrolysis temperatures (> 700 °C) revealed graphitic and condensed aromatic carbon networks with enhanced textural properties, facilitating electron-mediated reactions through interconnected morphology. The methodology is derived from the research that shows certain pyrolysis derived carbon products are known to have transient photocurrent response, indicating semiconductor properties. Here, the visible light-driven GC/PS (950 °C, 5 °C min−1) system resulted in high TC removal efficiency of 91.23% within 180 min compared to other PS/GCs prepred under different conditions. The mass spectroscopy data shows that the GC/PS system successfully degraded TC into simpler products and achieved the highest mineralization efficiency of about 65.43 ± 3.62%. The radical scavenging experiments revealed that 1O2 and •OH were the dominant reactive oxygen species suppressing degradation of TC by 13% and 9%, respectively. It can be surmised that both radical and non-radical pathways facilitate TC degradation via dehydration, demethylation and oxidation of aromatic rings- due to both catalytic and physico-chemical properties of GC/PS .