Transmission Electron Microscopy Studies Research Articles

Transmission Electron Microscopy Study on the Process of Gold Nanoporous Film Formation on AAO Substrate by Thermal Treatment.

Transmission Electron Microscopy Study on the Process of Gold Nanoporous Film Formation on AAO Substrate by Thermal Treatment.

Photocatalytic activities of CTAB assisted ZrO2, V2O5, and ZrO2-V2O5 composite by precipitation process and their studies on structural, morphological and optical properties

Nanocrystalline core/shell structures of cetytrimethylammonium bromide (CTAB)-assisted ZrO2, V2O5, and ZrO2-V2O5 composite was successfully prepared by co-precipitation method calcined at 500 °C. CTAB-assisted ZrO2, V2O5, and ZrO2-V2O5 composite were characterized by different techniques such as, X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Brunauer-Emmett-Teller (BET), Ultra-Violet (UV) and Photoluminescence (PL). The formation of ZrO2, V2O5, and ZrO2-V2O5 composite material has been confirmed by XRD studies. Surface morphology with grain size of CTAB-assisted ZrO2, V2O5, and ZrO2-V2O5 composite was determined by SEM and TEM studies. EDX analysis confirms the presence of compositional elements of ZrO2-V2O5 composites in the lattice such as zirconium, vanadium and oxygen. Optical studies reveal a strong absorption and emission peaks were presented in the UV and visible regions and it useful for optoelectronic device applications. In comparison, ZrO2, V2O5, and ZrO2-V2O5 composite exhibited the higher band gap energies with a significant blue-shift and enhanced UV light absorption compared to bulk counterparts. As-prepared photocatalysts, CTAB-assisted ZrO2, V2O5, and ZrO2-V2O5 composite showed strong photocatalytic activity towards the degradation of Rhodamine B (RhB) dye under UV light irradiation, which can facilitate the efficient separation and migration of photo generated electron-hole pairs. Among result, the ZrO2-V2O5 composite exhibited the synergistic enhanced photocatalytic performance and also the possible photocatalytic mechanism was discussed in detail.

Ocular Delivery of Bimatoprost-Loaded Solid Lipid Nanoparticles for Effective Management of Glaucoma.

Glaucoma is a progressive optic neuropathy characterized by a rise in the intraocular pressure (IOP) leading to optic nerve damage. Bimatoprost is a prostaglandin analogue used to reduce the elevated IOP in patients with glaucoma. The currently available dosage forms for Bimatoprost suffer from relatively low ocular bioavailability. The objective of this study was to fabricate and optimize solid lipid nanoparticles (SLNs) containing Bimatoprost for ocular administration for the management of glaucoma. Bimatoprost-loaded SLNs were fabricated by solvent evaporation/ultrasonication technique. Glyceryl Monostearate (GMS) was adopted as solid lipid and poloxamer 407 as surfactant. Optimization of SLNs was conducted by central composite design. The optimized formulation was assessed for average particle size, entrapment efficiency (%), zeta potential, surface morphology, drug release study, sterility test, isotonicity test, Hen's egg test-chorioallantoic membrane (HET-CAM) test and histopathology studies. The optimized Bimatoprost-loaded SLNs formulation had an average size of 183.3 ± 13.3 nm, zeta potential of -9.96 ± 1.2 mV, and encapsulation efficiency percentage of 71.8 ± 1.1%. Transmission electron microscopy (TEM) study revealed the nearly smooth surface of formulated particles with a nano-scale size range. In addition, SLNs significantly sustained Bimatoprost release for up to 12 h, compared to free drug (p < 005). Most importantly, HET-CAM test nullified the irritancy of the formulation was verified its tolerability upon ocular use, as manifested by a significant reduction in mean irritation score, compared to positive control (1% sodium dodecyl sulfate; p < 0.001). Histopathology study inferred the absence of any signs of cornea tissue damage upon treatment with Bimatoprost optimized formulation. Collectively, it was concluded that SLNs might represent a viable vehicle for enhancing the corneal permeation and ocular bioavailability of Bimatoprost for the management of glaucoma.

Enhanced Photocatalytic Applications of Chitosan Encapsulated Silver Sulphide Quantum Dots

This study explores the synthesis, properties, and applications of chitosan-encapsulated silver sulphide (Ag2S) quantum dots (QDs) for biological applications. The investigation focuses on the fluctuations in the physico-chemical characteristics of chitosan Ag2S QDs, which can be carefully studied due to their environmental activity. X-ray diffraction (XRD) measurements reveal that chitosan-coated Ag2S QDs exhibit higher-intensity peaks. The XRD analysis reports a range of crystallite sizes, with a minimum size of 8 nm and a maximum size of 12 nm. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of chitosan through the detection of functional group peaks. High-resolution transmission electron microscopy (HRTEM) studies indicate that the size of the artificial quantum dots is 6 nm. Energy-dispersive X-ray spectroscopy (EDX) verifies the composition of chitosan-encapsulated Ag2S QDs. Moreover, the chitosan Ag2S quantum dots demonstrate exceptional photocatalytic activity, as evidenced by the degradation of 92% of methylene blue dye within one hour. This research provides valuable insights into the synthesis, properties, and potential applications of chitosan-encapsulated Ag2S quantum dots in diverse fields.

Gold Nanoparticles AuNP Decorated on Fused Graphene-like Materials for Application in a Hydrogen Generation.

The search for a sustainable, alternative fuel source to replace fossil fuels has led to an increased interest in hydrogen fuel. This combustible gas is not only clean-burning but can readily be produced via the hydrolysis of sodium borohydride. The main drawback of this reaction is that the reaction occurs relatively slowly and requires a catalyst to improve efficiency. This study explored a novel composite material made by combining gold nanoparticles and fused graphene-like materials (AuFGLM) as a catalyst for generating hydrogen via sodium borohydride. The novel fused graphene-like material (FGLM) was made with a sustainable dextrose solution and by using a pressure-processing method. Imaging techniques showed that FGLM appears to be an effective support template for nanoparticles. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize and determine the size, shape, and structure of nanoparticles and composites. The TEM study characterized the fused carbon backbone as it began to take on a rounder shape. The TEM images also revealed that the average diameter of the gold nanoparticle was roughly 23 nm. The FTIR study confirmed O-H, C-C, and C=O as functional groups in the materials. The EDS analysis showed that the composite contained approximately 6.3% gold by weight. The crystal structures of FGLM and AuFGLM were identified via P-XRD analysis. Various reaction conditions were used to test the catalytic ability of AuFGLM, including various solution pHs, temperatures, and doses of NaBH4. It was observed that optimal reaction conditions included high temperature, an acidic solution pH, and a higher dose of NaBH4. The activation energy of the reaction was determined to be 45.5 kJ mol-1, and it was found that the catalyst could be used multiple times in a row with an increased volume of hydrogen produced in ensuing trials. The activation energy of this novel catalyst is competitive compared to similar catalysts and its ability to produce hydrogen over multiple uses makes the material an exciting choice for catalyzing the hydrolysis of NaBH4 for use as a hydrogen fuel source.

Chemically assembled 2D-van der Waals WSe2-WC heterostructured photo-anodes for electrochemical devices

Structural, optical, nanomorphological, photoresponsive and electrochemical charge transport characteristics of chemically assembled 2D-layered Tungsten Selenide (WSe2)-Tungsten Carbide (WC) heterostructure were examined. WC exhibited an optical bandgap of ∼3.2 eV, which did not show any optical absorption in the visible spectrum, and WSe2 showed the same in the spectral range of 200 nm-950 nm with an optical bandgap of ∼1.3 eV. Chemical assembly of WSe2-WC heterostructure was made in which the weight fraction of WSe2 was varied to understand its role in WC. Among the 2, 4, 6 and 8 wt% of WSe2 in WC, we observed that 6 wt% exhibited a dominant absorption and fluorescence emission (∼600 nm). High-resolution transmission electron microscopic studies revealed the d-spacing values of 0.24 nm and 0.33 nm for WSe2 and WC, respectively. Further, the presence of W (4f), Se (2d) and C (1 s) were traced out and studied by X-ray photoelectron spectroscopy. Raman modes A1g and EAg1 at 150 cm−1 and 250 cm−1 asserted the presence of WSe2 in WC which exhibited A1g at 150 cm−1. In addition, the individual WSe2 and WC along with WSe2-WC heterostructures were subjected to X-ray diffraction to study the crystallite size and strain-induced broadening due to the lattice deformation that occurred at the WSe2-WC heterostructures. Incorporating WSe2 into WC increased the photo-responsive behaviour and facilitated the charge transport as envisaged from the electrochemical impedance spectroscopic studies.

Fracture Characteristics of Super Duplex Stainless Steel after Hot Tensile Testing

This study’s temperature range of hot tensile testing is 1000–1200 °C, which is consistent with ordinary industrial hot working temperatures. The fractography of super duplex stainless steel S32750 after hot tensile testing is investigated with Optical Microscopy and Scanning Electron Microscopy, and Electron Back-scatter Diffraction and Transmission Electron Microscopy study hot deformation behaviors of the necking area. The results reveal that ~1050–1150 °C is the optimal hot working temperature range regarding hot ductility and cracking sensitivity. The micro-voids nucleate at the ferrite-austenite interphase boundaries following the Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationship at 1000 °C. Therefore, a quasi-cleavage fracture forms along the interphase boundaries. At the temperature range 1050–1150 °C, a uniform distribution of fracture surface is formed, and the highest Reduction in Area appears at 1150 °C. Dynamic phase transformation occurs with the formation of secondary austenite at ferrite grain boundaries at 1200 °C, which results in an intergranular fracture surface morphology.

Dragon fruit peel extract mediated green synthesis of silver nanoparticles and their antifungal activity against Colletotrichum truncatum causing anthracnose in chilli

Plant extracts have been used as reducing and stabilising agents to synthesise various metal-based nanoparticles due to their cost-effective and eco-friendly nature. In the present work, a green and environment-friendly method is adopted for synthesising silver nanoparticles (Ag NPs) using a biowaste of dragon fruit (Hylocereus spp.) peel aqueous extract at 80ºC in an alkaline condition. The Ag NPs were characterised through various analytical and microscopic techniques. The UV-Vis spectra of Ag NPs showed a characteristic peak between 400 - 410 nm. Transmission and scanning electron microscopic studies confirmed spherical monodispersed particles with an average size of 7 nm. Energy-dispersive X-ray spectroscopy (EDX) confirmed the presence of silver and silver chloride among the principal elements. The X-ray powder diffraction (XRD) spectra showed the crystalline nature of synthesised silver and silver chloride nanoparticles. The synthesised nanoparticles showed potential antifungal activity against Colletotrichum truncatum spores in both in vitro conidial germination and spread plate assays. The efficacy of the synthesised NPs confirmed that these NPs could be used as potential antifungal agents against C. truncatum to control anthracnose in chilli.

Structural, Optical, and Dielectric Properties of CuO/CdFe2O4 Nanocomposites Synthesized by the Co-precipitation Method

Abstract In this study, xCuO/(1−x)CdFe2O4 nanocomposites (NCs) were prepared with different weight percentages (x = 0.0, 0.1, 0.3, 0.5, and 1.0) using the co-precipitation method. X-ray powder diffraction patterns revealed the formation of copper oxide (CuO) and cadmium ferrite (CdFe2O4) phases in each NC with hematite as a secondary phase. Transmission electron microscope study confirmed the existence of CuO and CdFe2O4 crystal grains with sizes of 17.86 and 18.45 nm, respectively. Optical analysis indicated that the addition of CuO caused variations in bandgap energy and shifts in the emission wavelength of the NCs. Dielectric measurements were carried out in the frequency range of 1 kHz–5 MHz, and dielectric study was performed by analyzing the frequency, temperature, and composition dependence of the dielectric parameters for the samples. Dielectric results showed the dispersion behavior of the NCs with increasing frequency and composition concentration corresponding to low dielectric losses, which makes them suitable for optoelectronics and high-frequency devices.

Time-resolved imaging and analysis of the electron beam-induced formation of an open-cage metallo-azafullerene.

The visualization of single-molecule reactions provides crucial insights into chemical processes, and the ability to do so has grown with the advances in high-resolution transmission electron microscopy. There is currently a limited mechanistic understanding of chemical reactions under the electron beam. However, such reactions may enable synthetic methodologies that cannot be accessed by traditional organic chemistry methods. Here we demonstrate the synthetic use of the electron beam, by in-depth single-molecule, atomic-resolution, time-resolved transmission electron microscopy studies, in inducing the formation of a doubly holed fullerene-porphyrin cage structure from a well-defined benzoporphyrin precursor deposited on graphene. Through real-time imaging, we analyse the hybrid's ability to host up to two Pb atoms, and subsequently probe the dynamics of the Pb-Pb binding motif in this exotic metallo-organic cage structure. Through simulation, we conclude that the secondary electrons, which accumulate in the periphery of the irradiated area, can also initiate chemical reactions. Consequently, designing advanced carbon nanostructures by electron-beam lithography will depend on the understanding and limitations of molecular radiation chemistry.

Effect of gadolinium doping on the Structural, magnetic, Electrical, Optical, and elastic properties of magnetite nanoparticles

In the present study, Fe3-xGdxO4 nanoparticles (with × varying from 0 to 0.1) were synthesized using the co-precipitation method. Lattice constant and X-Ray density were determined using X-Ray Diffraction (XRD). Transmission Electron Microscopy (TEM) study revealed the formation of rod-like structures along with round-shaped particles after gadolinium doping. Selected Area Electron Diffraction (SAED) showed good crystallinity of nanoparticles. Elastic constants were calculated using FTIR and XRD data. The study of the vibrating sample magnetometer (VSM) revealed that the saturation magnetization increased with Gd3+ doping from 54.3 emu/g at x = 0.0 to 84.8 emu/g at x = 0.04. Coercivity also increased with Gd3+ doping. The value of resistivity has been observed to be 4.02 × 106 Ohm-cm for undoped samples using Keithley’s two-probe method. The dc resistivity of doped samples has been decreased by two orders of magnitude as comparedto the undoped sample. UV–Vis spectroscopy has been used to calculate the band gaps with the help of Tauc plots. The band gap for the undoped particle is 2.46 eV which decreases with Gd3+ doping till 2.08 eV for x = 0.03. Band gaps are correlated to electrical behavior. Young modulus, Bulk modulus, Rigidity modulus, and Poisson’s ratio were found to enhance with gd doping beyond x = 0.03. The increase of elastic constants with doping indicates the strengthening of interatomic bonding. These nanoparticles could have applications as optoelectronic and magnetoelastic sensors.

Designing NbTiTa-Cr/Al refractory complex concentrated alloys with balanced strength-ductility-oxidation resistance properties: Insights into oxidation mechanisms

Limited tensile ductility, poor oxidation resistance, and the ductility-oxidation resistance trade-off are key bottlenecks besetting refractory complex concentrated alloys (RCCAs). Here, in this study, by alloying ductile NbTiTa RCCAs with low content of Cr or Al, we design two novel single-phase RCCAs Nb40Ti40Ta10Cr10 (Cr10) and Nb45Ti30Ta15Al10 (Al10). These two alloys demonstrate excellent tensile strength-ductility combination (∼800 MPa, >20%) and the best oxidation resistance at 800 °C (<7.2 mg/cm2 after 20 h exposure) among all tensile-ductile RCCAs reported by far. Cr10 exhibits much slower oxidation kinetics compared with Al10, attributed to i) the dominant rutile-type Ti1–2x(Nb,Ta)xCrxO2 oxide that has lower volume mismatch with the alloy matrix compared with (Nb,Ta)2O5, as indicated by low Pilling-Bedworth ratio (PBR) values of 1.03–1.76; and ii) the alternative layer structure consisting of dense rutile and porous mixed oxides that is conducive to prohibiting stress cumulation and cracking. A new thermodynamic model connecting the Gibbs free energy of formation of a related oxide to the dynamically varied alloy compositions was proposed and used to unveil the dynamic formation mechanisms of oxides in Cr10 and Al10. The special alternative layer structure, mixed-oxides structure, voids, and/or cracks featured by oxide scales of Cr10 and/or Al10 are well-understood by combining detailed scanning transmission electron microscopy (STEM) studies, thermodynamic simulations, and stress analyses based on PBR evaluations.

A Machine-Vision Approach to Transmission Electron Microscopy Workflows, Results Analysis and Data Management.

Transmission electron microscopy (TEM) enables users to study materials at their fundamental, atomic scale. Complex experiments routinely generate thousands of images with numerous parameters that require time-consuming and complicated analysis. AXON synchronicity is a machine-vision synchronization (MVS) software solution designed to address the pain points inherent to TEM studies. Once installed on the microscope, it enables the continuous synchronization of images and metadata generated by the microscope, detector, and in situ systems during an experiment. This connectivity enables the application of machine-vision algorithms that apply a combination of spatial, beam, and digital corrections to center and track a region of interest within the field of view and provide immediate image stabilization. In addition to the substantial improvement in resolution afforded by such stabilization, metadata synchronization enables the application of computational and image analysis algorithms that calculate variables between images. This calculated metadata can be used to analyze trends or identify key areas of interest within a dataset, leading to new insights and the development of more sophisticated machine-vision capabilities in the future. One such module that builds on this calculated metadata is dose calibration and management. The dose module provides state-of-the-art calibration, tracking, and management of both the electron fluence (e-/Å2·s-1) and cumulative dose (e-/Å2) that is delivered to specific areas of the sample on a pixel-by-pixel basis. This enables a comprehensive overview of the interaction between the electron beam and the sample. Experiment analysis is streamlined through a dedicated analysis software in which datasets consisting of images and corresponding metadata are easily visualized, sorted, filtered, and exported. Combined, these tools facilitate efficient collaborations and experimental analysis, encourage data mining and enhance the microscopy experience.

Novel Bone Void Filling Cement Compositions Based on Shell Nacre and Siloxane Methacrylate Resin: Development and Characterization.

Shell nacre from Pinctada species has been extensively researched for managing bone defects. However, there is a gap in the research regarding using shell nacre powder as a cement with improved biological and physicochemical properties. To address this, bone void filling cement was formulated by incorporating shell nacre powder and an organically modified ceramic resin (ormocer). The shell nacre powder was specifically processed from the shells of Pinctada fucata and analysed using thermogravimetric analysis (TGA), X-ray diffraction spectroscopy, Fourier transform infrared (FTIR), and Raman spectroscopy, confirming the presence of organic constituents and inorganic aragonite. Trace element analysis confirmed the eligibility of shell nacre powder for biomedical applications. Next, the ormocer SNLSM2 was synthesized through a modified sol-gel method. FTIR, Raman, TGA, and transmission electron microscopy studies revealed the presence of a ladder-structured siloxane backbone and methacrylate side chain. To develop chemical curable composite shell nacre cement (SNC), different amounts of shell nacre (24%, 48%, and 72%) were added to the SNLSM2 resin, and the impact on the physicochemical properties of the cement was studied. Among the compositions, SNC 72 exhibited significantly lower linear polymerization shrinkage (0.4%) and higher compressive (>100 MPa) and flexural strength (>35 MPa). SNC 72 was radiopaque, and the exotherm generated during the cement curing was minimal. Cytotoxicity studies with L929 cells revealed the non-cytotoxic nature of the cement. Overall, the findings of this study prove that the shell nacre cement is a promising candidate for managing bone voids.

Bio‐fabrication of Silver Nanoparticles Using Alysicarpus vaginalis Extract: Preparation, Characterization and Comparative in vitro Antibacterial Evaluations

AbstractGreen synthesis of silver nanoparticles (AgNPs) using the Alysicarpus vaginalis alcoholic extract as a reducing agent and a capping ligand was carried out. Notable peaks of λmax 442–602 nm indicated the reduction of silver ions to elemental AgNPs. Particle size (Zavg) was in the range of 32.3±0.76 to 252.3±0.342 nm). The negative Zeta potential (ZP, −2.9±0.31 to −21.7±0.13 mV) and low polydispersity index (PDI, 0.181±0.02 to 0.635±0.02) supported the homogeneous nature of AgNPs. Further, crystalline spherical nature of AgNPs with a smooth surface was confirmed by high‐resolution transmission electron microscopy (HRTEM) studies. The AgNPs showed 1.2 to 1.4‐fold enhanced antibacterial activity than extract (6–10 mm zone of inhibition) against Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes, and Salmonella enterica ser. Typhi by disc diffusion assay. The AgNP formulation F9 showed equal (against Gram‐positive L. monocytogenes) or even better (against Gram‐negative S. enterica Typhi) antimicrobial activity than the positive control, ciprofloxacin. Further investigations on F9 are suggested in order to develop a broad‐spectrum, cost‐effective antibacterial formulation of natural origin. This study represents a significant step forward in the field of bio‐fabrication and presents a promising alternative to traditional chemical synthesis methods for the production of antimicrobial AgNPs.

A highly active additive for magnesium hydride from the MgO–TiO2 mixed oxide family: Magnesium dititanate

This study explores that a promising additive, magnesium dititanate (MgTi2O5), promotes the hydrogen storage behavior of MgH2 by producing active in-situ catalytic species. Due to the creation of active species the dehydrogenation activation energy of MgH2 lowers by 95 kJ/mol. Differential scanning calorimetry (DSC) and hydrogen absorption/desorption kinetics studies provide evidence that MgTi2O5 performs better than the proven additive TiO2 for MgH2. The MgH2/MgTi2O5 composite samples tested by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) studies prove that oxidized Mg and Mg0·56Ti0.44 are the products of interaction between MgH2 and MgTi2O5. Formation of Mg-containing rock salt nanoparticles (MgO and/or MgxTiyOx+y) is identified to be the crucial step in the catalytic dehydrogenation reaction of MgH2/MgTi2O5 hydrogen storage system, which agrees well with the previous observation made for titania additive incorporated MgH2.

Synthesis mechanism and ‘orthodoxy’ test based field emission analysis of hybrid and pristine graphene nanowalls deposited on thin Kovar wires

Graphene nanowalls (GNWs) also known as carbon nanowalls (CNWs) and GNWs‑carbon nanofibers (CNFs) hybrid nanostrucrures are grown on metallic wires using a two-step microwave plasma enhanced chemical vapour deposition (MW-PECVD) process. Here, plasma is generated in two steps (first at lower pressure and then at higher operating pressure) to avoid arcing on the metallic wire during the growth. Combination of Raman and transmission electron microscopy studies revealed presence of herringbone CNFs in the hybrid nanostructures that are grown with −100 V bias compared to pristine GNWs that are grown without any bias. A new approach for field emission (FE) analysis is created by combining FN equation with ‘orthodoxy test’ in a modified approach to avoid spurious results. Here, hybrid nanostructures exhibited higher current and more repeatable field emission characteristics over 4 cycles of operation. Post FE investigations indicate that while pristine GNWs underwent many deformities and structural changes, hybrid structures remain almost unscathed. These investigations point out that a novel synthesis mechanism can be used to grow GNW based hybrid nanostructures for different applications like X-ray sources which involves FE at the core.

Formulation of Piperine-Loaded Nanoemulsion: In Vitro Characterization, Ex Vivo Evaluation, and Cell Viability Assessment.

Piperine is an alkaloid, but its therapeutic efficacy is limited due to poor aqueous solubility. In this study, piperine nanoemulsions were prepared using oleic acid (oil), Cremophore EL (surfactant), and Tween 80 (co-surfactant) using the high-energy ultrasonication approach. The optimal nanoemulsion (N2) was further evaluated using transmission electron microscopy, release, permeation, antibacterial, and cell viability studies based on minimal droplet size and maximum encapsulation efficiency. The prepared nanoemulsions (N1-N6) showed a transmittance of more than 95%, a mean droplet size between 105 ± 4.11 and 250 ± 7.4 nm, a polydispersity index of 0.19 to 0.36, and a ζ potential of -19 to -39 mV. The optimized nanoemulsion (N2) showed significantly improved drug release and permeation compared with pure piperine dispersion. The nanoemulsions were stable in the tested media. The transmission electron microscopy image showed a spherical and dispersed nanoemulsion droplet. The antibacterial and cell line results of piperine nanoemulsions were significantly better than the pure piperine dispersion. The findings suggested that piperine nanoemulsions may be a more advanced nanodrug delivery system than conventional ones.

Extreme Air Sensitivity and Nonself-Limited Oxidation of Two-Dimensional Magnetic Tellurides

The two-dimensional (2D) self-intercalated van der Waals magnets, chromium tellurides (Cr1+δTe2), with room temperature ferromagnetism and exotic topological spin textures, have emerged as an attractive platform for the development of ultrathin spintronic devices. While many prior studies claim Cr1+δTe2 are air-stable, which is crucial for practical applications, we demonstrate that within only minutes of exposure to air dramatic changes occur in the Raman and X-ray photoelectron spectroscopy spectra of nanoplates at room temperature. Time-dependent magnetization measurements and transmission electron microscopy studies suggested the rapid oxidation is not self-limited and has distinct processes on the surfaces and edges. Density functional theory calculations confirmed the spontaneous oxygen adsorption on the surface and the thermodynamically favorable oxidation process. These findings demonstrate unambiguously that the surface of Cr1+δTe2 is extremely air-sensitive, highlighting the necessity of surface protection for fundamental studies of intrinsic 2D magnetism and practical applications of advanced spintronic devices.

Nanostars in Highly Si-Doped GaN.

Understanding the relation between surface morphology during epitaxy of GaN:Si and its electrical properties is important from both the fundamental and application perspectives. This work evidences the formation of nanostars in highly doped GaN:Si layers with doping level ranging from 5 × 1019 to 1 × 1020 cm-3 grown by plasma-assisted molecular beam epitaxy (PAMBE). Nanostars are 50-nm-wide platelets arranged in six-fold symmetry around the [0001] axis and have different electrical properties from the surrounding layer. Nanostars are formed in highly doped GaN:Si layers due to the enhanced growth rate along the a-direction ⟨112̅0⟩. Then, the hexagonal-shaped growth spirals, typically observed in GaN grown on GaN/sapphire templates, develop distinct arms that extend in the a-direction ⟨112̅0⟩. The nanostar surface morphology is reflected in the inhomogeneity of electrical properties at the nanoscale as evidenced in this work. Complementary techniques such as electrochemical etching (ECE), atomic force microscopy (AFM), and scanning spreading resistance microscopy (SSRM) are used to link the morphology and conductivity variations across the surface. Additionally, transmission electron microscopy (TEM) studies with high spatial resolution composition mapping by energy-dispersive X-ray spectroscopy (EDX) confirmed about 10% lower incorporation of Si in the hillock arms than in the layer. However, the lower Si content in the nanostars cannot solely be responsible for the fact that they are not etched in ECE. The compensation mechanism in the nanostars observed in GaN:Si is discussed to be an additional contribution to the local decrease in conductivity at the nanoscale.