Crystalline Quality Research Articles

3D Ising Superconductivity in As-Grown Sn Intercalated TaSe2 Crystal.

2D Ising superconductivity emerges in noncentrosymmetric 2D materials, differing from conventional 2D/3D superconductivity. Here, we report the synthesis of a new polymorph of intercalated layered materials, where two layers of Sn are intercalated in between every two layers of TaSe2 (2Sn-2TaSe2), in contrast to the commonly observed single-layer intercalation. Remarkably, the as-grown 2Sn-2TaSe2 single crystals possess a high quality of crystallinity and showcase 3D Ising superconductivity. Transport measurements and theoretical calculations show that the 2Sn-2TaSe2 having C3v point group symmetry induces formation of Ising pairs, which intriguingly exhibits, on one hand, an in-plane upper critical field surpassing the Pauli limit by a factor of 2.6 like a 2D Ising superconductor but, on the other hand, a temperature- and field-dependent conductivity characteristic of conventional 3D superconductivity. Our findings demonstrate the persistent 2D Ising pairing in 3D, paving the way for exploring dimensional physical behaviors by intercalating layered materials.

Spectrally Distinguished Solar-Blind and Visible Photodetector Based on MOCVD-Grown (111) Facet Single-Crystalline ZnGa2O4.

ZnGa2O4 demonstrates excellent crystalline quality, establishing a heteroepitaxial relationship with the sapphire substrate and exhibiting a 6-fold harmonic symmetry corresponding to the sapphire lattice planes. Cross-sectional transmission electron microscopy analysis reveals the single-crystalline nature of ZnGa2O4 films grown on a sapphire substrate using MOCVD. These findings emphasize the critical role of film uniformity in enhancing the performance metrics of unipolar Schottky photodiodes. This unipolar photodiode technique, in which asymmetric Ni/Au and Ti/Au electrodes are on MOCVD-grown single-crystalline ZnGa2O4, provides excellent rectification and high-performance solar-blind detection with a selective nature for the solar-blind and visible spectrum in reverse bias. Its exceptional forward bias operation and robust sensitivity make it excellent for sophisticated UV detection systems in harsh situations, improving security, environmental monitoring, and space applications. The photodiode works in forward bias with a rectification ratio of 1 × 105 (±6 V) for the solar-blind spectrum. The photodiode showed a Schottky behavior with an ultralow dark current of 0.2 pA in the forward direction and exhibited an exceptional dual-band UV-vis response with a photoresponsivity of 370 A/W and -3.6 μA/W, a notable photo-to-dark current ratio of 10, a switching speed of 50 ms, ultralow noisy detection with a noise equivalent power of 2.44 × 10-19 W/Hz1/2, and an ultrahigh detectivity of 1.23 × 1017 Jones observed for the solar-blind spectrum. Additionally, the unipolar photodiode showed a unique dual-mode operation: in forward bias, it exhibits positive photoconductivity (PPC) across the spectrum; in reverse bias, it detects ultraviolet light with PPC and visible light with negative photoconductivity. This unique characteristic enables selective detection with rectification ratios of 105 for UV and 74 for visible light, providing a technique for sophisticated photodetection applications that need accurate solar-blind and visible distinction.

Citrus-Fruit-Based Hydroxyapatite Anodization Coatings on Titanium Implants.

The increasing demand for titanium implants necessitates improved longevity. Plasma-sprayed hydroxyapatite coatings enhance implant osseointegration but are susceptible to delamination. Alternatively, anodized hydroxyapatite coatings have shown greater adhesion strengths. The present study aimed to develop anodized hydroxyapatite coatings on titanium using commercial calcium-fortified fruit juice as a calcium source. Varying the electrolyte compositions enabled the formation of four oxide groups with different predominate calcium compounds. Each oxide's morphology, crystallinity, chemistry, molecular structure, and adhesion quality were compared and contrasted. Nanoscale SEM images revealed a progression from porous surface oxide to white surface deposits to petal-like hydroxyapatite structures with the changing anodization electrolytes. Oxide thickness evaluations showed progression from a single-layered oxide with low Ca-, P-, and Mg-dopant incorporations to bi-layered oxide structures with increased Ca-, P-, and Mg-dopant incorporation with changing electrolytes. The bi-layered oxide structures exhibited a titanium-dioxide-rich inner layer and calcium-compound-rich outer layers. Furthermore, indentation analyses confirmed good adhesion quality for three oxides. For the predominate hydroxyapatite oxides, FTIR analyses showed carbonate substitutions indicating the presence of bone-like apatite formation, and ICP-OES analyses revealed prolonged Ca and Mg release over 30 days. These Mg-enhanced carbonated apatite coatings show much promise to improve osseointegration and future implant lifetimes.

Performance analysis of CdS-based thin films in photovoltaic applications

Cadmium sulfide (CdS) thin films are extensively utilized as a window layer in photovoltaic (PV) devices due to their high transmittance, suitable bandgap, and favorable electrical properties. This work presents a comprehensive performance analysis of CdS based thin films in PV applications, examining key factors such as optical, electrical, and structural properties. The bandgap (approximately 2.42 eV) allows effective photon transmission, reducing energy losses. Critical performance metrics, including film thickness, grain size, crystallinity, and interface quality with the absorber layer, are optimized to enhance charge separation and minimize recombination losses. The study highlights the balance between thin-film transparency and thickness to maximize photon absorption while ensuring film durability and stability in environmental conditions. The findings underscore the potential of CdS thin films to improve PV cell efficiency, offering insights into achieving higher fill factor (FF), short-circuit current (Jsc) and open-circuit voltage (Voc) in CdS-based PV devices.

Chiral anomaly in doped α -Sn films by Fermi level tuning

Gray tin (α-Sn) is an elemental topological material with various topological phases. It is predicted to be a 3D Dirac semimetal when appropriate strain is applied. However, the Dirac semi-metallic properties, such as chiral anomaly, are hard to be observed, probably due to the imperfections in the α-Sn samples. It is even more challenging to manipulate the topological properties in this metastable material without a sacrifice in the crystalline quality. Here, we report a strategy of Fermi level tuning by doping the α-Sn films grown on CdTe (001) substrates by molecular beam epitaxy. The negative magnetoresistance and planar Hall effect, which are attributed to chiral anomaly, are observed in α-Sn when the Fermi level is tuned close to the bulk Dirac point. Detailed analyses of Shubnikov–de Haas oscillations show nontrivial Berry phases for all the samples. Combined with first-principle calculations, these results provide a strong evidence of the three-dimensional Dirac semimetal phase in α-Sn. Furthermore, a clear transition from two-dimensional topological surface states to three-dimensional bulk Dirac cone is demonstrated in α-Sn by precise Fermi level tuning through doping. This study proves the 3D Dirac semimetal phase in α-Sn and provides an effective strategy to manipulate the topological properties for both fundamental studies and device applications.

Effects of polycrystalline AlN layer on the crystalline quality of AlxGa1-xN buffer layer and optimization of growth processes: A molecular dynamics study

Effects of polycrystalline AlN layer on the crystalline quality of AlxGa1-xN buffer layer and optimization of growth processes: A molecular dynamics study

Realizing freestanding single-crystal oriented membranes of ultrawide-bandgap semiconductor ε-Ga2O3 and their prospects in optoelectronic device applications

As an ultrawide bandgap semiconducting material, Ga2O3 has attracted significant attention in providing a foundation for applications in optoelectronic and power devices. The structural incompatibility and/or lattice mismatch of the substrate poses a challenge in preparing vertical devices using Ga2O3. Additionally, the challenges Ga2O3 faces in its epitaxy on a silicon substrate further hinder its integration with other silicon-based advanced electronics. This study demonstrated the use of Sr3Al2O6 as a sacrificial layer to realize single-crystal freestanding ε-Ga2O3 membranes with physical and performance characteristics comparable to those grown epitaxially on rigid substrates. Importantly, these membranes retained integrity after transfer. Observation of sharp diffraction peaks of ε-Ga2O3 (00 l) orientation in x-ray diffraction indicates excellent single-crystalline characteristics and crystalline quality of ε-Ga2O3. High-resolution transmission electron microscopy revealed clear lattice structures belonging to the hexagonal crystal structure of ε-Ga2O3. The dark current of the photodetector made from freestanding ε-Ga2O3 reaches 10−12 A at 5 V, while the photocurrent under 100 μW/cm2 of 254 nm light illumination reaches 10−9 A, with a responsivity of 81.16 mA/W, a detectivity of 2.36 × 1012 Jones, and an external quantum efficiency of 39.67%. Its performance can be compared to or even better than photodetectors made using ε-Ga2O3 directly grown rigid substrates. These results demonstrate that this approach overcomes challenges in fabricating ε-Ga2O3-based vertical devices and their integration with silicon, laying the groundwork for diverse applications with the next generation of semiconductors.

Influence of doping with silver nanoparticles on the molybdenum trioxide gas sensor prepared by spray pyrolysis

By spray pyrolysis method, Molybdenum trioxide films are deposited at 400 °C and doped with silver nanoparticles at different concentrations between (1 and 3) mM. X-ray diffraction (XRD), Atomic force microscopy (AFM), Field-emission scanning electron microscopy (FE-SEM), UV-vis spectroscopy, used to examine the physical properties films. According to XRD data, doping enhances the crystalline quality of deposited MoO3 thin films, which crystallize in an orthorhombic structure with a (021). The enargy gap was found (2.85 - 2.59) eV in films. The performance of gas sensing in the movie CO2 Different ratios of silver nanoparticles (0, 1, and 3 mM) were used for gas measurements. It was discovered that the gas detecting system's performance had greatly increased.

Determination of the Band Gap Energy of SnO2 and ZnO Thin Films with Different Crystalline Qualities and Doping Levels

Determination of the Band Gap Energy of SnO2 and ZnO Thin Films with Different Crystalline Qualities and Doping Levels

Recent Progress of Thin Crystal Engineering for Perovskite Solar Cells.

Metal halide perovskite single crystals hold promise for photovoltaics with high efficiency and stability due to their superior optoelectronic properties and weak bulk ion migration. The past several years have witnessed rapid development of single-crystal perovskite solar cells (PSCs) with efficiency rocketed from 6.5 % to 24.3 %, however, which still lags behind their polycrystalline counterparts. Moreover, the poor device stability under light illumination is contrary to the high ion migration barrier of perovskite single crystals. The key limiting factors should be the low crystalline quality and high surface defect density of solution-grown thin single crystals. Under this circumstance, a review paper summarizing the recent progress and challenges will be instructive for future development of this emerging field. In this manuscript, the crystal engineering used to enhance carrier transport and suppress carrier recombination in vertical single-crystal PSCs will be summarized initially, including crystal growth, component control, surface and interface modification. Subsequently, the application of perovskite single crystals in lateral single-crystal PSCs will be discussed and compared with the conventionally vertical structure. Finally, the challenges and proposed strategies for the development of single-crystal PSCs are provided.

Thermal Annealing Restricts the Rotation Domains of Epitaxial β-Ga2O3 Thin Films on Off-Angle Sapphire Substrates, Enabling Ultrahigh-Sensitivity Solar-Blind Deep UV Photodetector.

β-Gallium oxide (Ga2O3) films with a (-201) preferential orientation were heteroepitaxially grown on aluminum oxide (c/m) substrates at off-angles of 0, 1, 2, 4, and 6° by using metal-organic chemical vapor deposition. The step-flow growth mode inhibited the formation of rotational domains, which were further suppressed by annealing at 1000 °C, resulting in two primary orientations. The crystalline quality, surface morphology, and oxygen vacancy concentration of the β-Ga2O3 films strongly depended on the off-angle of the substrate. Using the 6° tilted substrate and postannealing decreased the full width at half-maximum of the rocking curve of the β-Ga2O3 films to 0.88°, with a root-mean-square roughness of 5.88 nm and a marked reduction in oxygen vacancies. Under a 10 V bias and 254 nm (23.75 μW/cm2) illumination, the β-Ga2O3-based photoconductive-type solar-blind photodetector grown on the 0° substrate exhibited superior responsivity (39.38 A/W), detectivity (4.60 × 1016 Jones), and external quantum efficiency (19074%). The device fabricated on the 6° substrate exhibited faster response times (0.47/4.34 ms) because of the improved film quality, which reduced defect centers and increased the signal feedback speed. This study investigated the growth mechanism of heteroepitaxial β-Ga2O3 films on sapphire substrates with various off-angles and their influence on device performance. This concept may offer insights into the epitaxial growth and device design of other thin films.

ZnGlu MOF-enhanced anthocyanin-gelatin films: A novel approach for monitoring chicken meat freshness through experimental and molecular dynamics insights.

ZnGlu MOF-enhanced anthocyanin-gelatin films: A novel approach for monitoring chicken meat freshness through experimental and molecular dynamics insights.

Influence of aqueous KMnO4 concentration on the structural and optical properties of reduced-graphene oxide nanosheets for enhanced electrical conductivity

Abstract It is reputed that potassium permanganate (KMnO4) powder is a very crucial material used as an oxidant for the preparation of reduced-graphene oxide (rGO) based on Hummer’s method. However, since the oxidant molarity is unknown when using the powder, a new work in which a solution-phased KMnO4 with different concentrations of 0.5 M, 1 M, and 1.5 M was introduced to change the structural, morphological, optical, and electrical properties of rGO. Characterization tools confirmed the formation of rGO nanosheets with different energy gaps depending on the concentrations. Hence, as Raman spectra demonstrated, the crystalline qualities of the nanosheets were highly influenced by the concentrations. The change in the morphological and structural properties of rGO led to a high increase the electric conductivity by lowering the oxidant molarity. In contrast, the maximum value of the dielectric constant was observed at the highest concentration. Moreover, a symmetrical tangent loss was observed in the frequencies less than 100 kHz at a molarity of 1 M. Therefore, 1 M oxidant was selected as the optimal concentration for high-conductivity, high-tangent loss rGO nanosheets. Thus, this modification could improve the rGO features, especially the electrical properties for future electronics.

Direct Syntheses of 2D Noble Transition Metal Dichalcogenides Toward Electronics, Optoelectronics, and Electrocatalysis-Related Applications.

2D noble transition metal dichalcogenides (nTMDCs, PdX2 and PtX2, where X═S, Se, Te) have emerged as a new class of 2D materials, owing to their unique puckered pentagonal structure in 2D PdS2 and PdSe2, largely tunable band structures or band gaps with decreasing the layer thickness at the 2D limit, strong interlayer interactions, superior optoelectronic properties, high edge catalytic properties, etc. Directly synthesizing 2D nTMDCs domains or thin films with large-area uniformity, tunable thickness, and high crystalline quality is the premise for exploring these salient properties and developing a wide range of applications. Hereby, this review summarizes recent progress in the direct syntheses and characterizations of 2D nTMDCs, mainly focusing on the thermally assisted conversion (TAC) and chemical vapor deposition (CVD) methods, by using various metal and chalcogen-contained precursors. Meanwhile, the applications of directly synthesized 2D nTMDCs in various fields, such as high-performance field effect transistors (FETs), broadband photodetectors, superior catalysts in hydrogen evolution reactions, and ultra-sensitive piezo resistance sensors, are also discussed. Finally, challenges and prospects regarding the direct syntheses of high-quality 2D nTMDCs and their applications in next-generation electronic and optoelectronic devices, as well as novel catalysts beyond noble metals are overviewed.

Regulation of superconductivity in Nb thin fllms induced by interstitial oxygen atoms

Abstract The regulation of superconductivity in thin films can provide important information on low-dimensional superconducting properties, and also has important reference values for the application in superconducting devices. Herein, we report the successful regulation of both the superconductivity and normal-state properties of Nb films in a wide range by the controllable introduction of interstitial oxygen atoms. The lattice parameter is enhanced for a extent as large as 4.4%, and the normal-state resistivity ρn is tuned for more than 15 times. The slope of upper critical fleld near Tc shows a close correlation with ρn in a wide range. Importantly, it is found that the suppression of Tc by disorder reveals a linear dependence with ρn in the region with an unchanged crystalline quality, which can be understood based on the picture of three-dimensional ballistic motion.

High performance BAW resonators with improved AlN thin films quality based on BaF2 buffer layer

The quality of AlN thin films has an important effect on the performance of bulk acoustic wave (BAW) resonators. In this work, the low lattice mismatch of BaF2 buffer layer with AlN thin films was employed to improve the crystalline quality of AlN thin films. Furthermore, an ethanol assisted epitaxial liftoff (ethanol-ELO) technique based on the BaF2 buffer layer was proposed to lift off AlN thin films from Si substrate, which reduced surface roughness scattering. The ELO technology reduced the damage of AlN thin films and Si wafer during the ELO process due to the selective etching of AlN and BaF2. Utilizing the BaF2 buffer layer, the as-prepared BAW resonators, based on single-crystalline AlN, displayed Q-factor up to 2857, which was 47% higher than that without the BaF2 buffer layer. This study highlights the significant role of the BaF2 buffer layer in enhancing BAW resonators' performance and reducing fabrication costs.

Crystallographic properties of the HgCdTe layers grown by MBE on CdZnTe(211)B substrates

Crystallographic properties of the HgCdTe layers grown by MBE on CdZnTe(211)B substrates

Study on the Performance of GaN Homoepitaxial Films Grown on Polished Substrates by Different Slurries

Abstract GaN is considered as one of the most promising wide-band-gap semiconductor materials, which has attracted significant attention due to its excellent properties. Here, the performance of the GaN homoepitaxial films grown on different polished substrates by Al2O3 slurry and SiO2 slurry respectively are studied. Atomic force microscope observation shows that the GaN homoepitaxial film grown on polished GaN substrate by the SiO2 slurry could exhibit low-roughness ultra-smooth surface and step-flow growth mode morphology, compared to that grown on the polished GaN substrate by Al2O3 slurry. High-resolution X-ray diffraction，Raman, photoluminescence, and cathodoluminescence measurements are used to investigate the characteristics of the homoepitaxial GaN films on the polished GaN substrates by different slurries. The results indicates that GaN homoepitaxial film grown on the ultra-smooth GaN substrate polished by SiO2 slurry has better crystalline quality, less impurities/defects, lower residual stress, and near stress-free, which has great potential for the further more advanced devices.

Study of Low-Temperature (Al)GaN on N-Polar GaN Films Grown by MOCVD on Vicinal SiC Substrates.

N-polar GaN HEMTs feature a natural back-barrier and enable the formation of low-resistance Ohmic contacts, with the potential to suppress short-channel effects and current collapse effects at sub-100 nm gate lengths, rendering them particularly promising for high-frequency communication applications. In this study, N-polar GaN films were grown on C-face SiC substrates with a 4° misorientation angle via MOCVD. By employing a two-step growth process involving LT-GaN or LT-AlGaN, the surface roughness of N-polar GaN films was reduced to varying degrees, accompanied by an improvement in crystalline quality. The growth processes, including surface morphology at each growth stage, such as the AlN nucleation layer, LT-GaN, LT-AlGaN, and the initial 90 nm HT-GaN, were investigated. The results revealed that a high V/III ratio and low-temperature growth conditions for the low-temperature layers, along with the introduction of a minor amount of Al, influenced adatom migration behavior and facilitated the suppression of step bunching. Suppressing step bunching during the initial growth stages was demonstrated to be critical for improving the surface quality and crystalline quality of N-polar GaN films. An N-polar GaN HEMT epitaxial structure was successfully achieved using the optimized surface morphology with a dedicated Fe-doped buffer process.

Impact of Minimal Silver Incorporation on Chalcopyrite Absorbers—Origins for Improved Open‐Circuit Voltages in (Ag,Cu)(In,Ga)Se2 Solar Cells

The influence of minimal amounts of Ag (0.5–1.4 at%) on elemental distribution and crystalline quality of (Ag,Cu)(In,Ga)Se2 (ACIGSe) absorbers grown by the three‐stage coevaporation without added alkali elements is reported. The elemental ratios affect the amount of Ag to be uniformly incorporated into the chalcopyrite absorber and the open‐circuit voltage (VOC) of the ACIGSe solar cell devices. Ag‐containing absorbers deposited at 530 °C achieve a best photoconversion efficiency of 18.2%. Due to an increased VOC, ACIGSe absorbers perform better than their Ag‐free variants at low deposition temperatures. The factors contributing to this increased VOC of low‐temperature devices are: 1) enhanced elemental Ga and In interdiffusion and hence their spatial distribution across the absorber thickness, leading to an increase in the minimum bandgap, 2) an improved absorber crystalline quality with larger grains resulting in high quasi‐Fermi‐level splitting and lower nonradiative losses. The photoluminescence data obtained on the ACIGSe absorbers reveal the corresponding variations in their bandgap and photoluminescence quantum yield. These material‐level insights into Ag incorporation in chalcopyrite help to advance the development of chalcopyrite‐based tandem solar cells, which—so far—is limited by the requirement of high deposition temperatures.