Scanning Transmission Electron Microscopy Analysis Research Articles

Environmentally sustainable synthesis of metal nanoparticle clusters and their prospective applications in biomedical and surface enhanced Raman scattering

Abstract In a recent study, gold and silver nanoparticle clusters were successfully synthesized for the first time, to the best of our knowledge, using an environmentally friendly green synthesis method. Both gold and silver nanoparticles exhibit characteristic plasmon resonance peaks at 530 nm and 420 nm respectively with additional peaks at higher wavelengths (620 nm for gold and 580 nm for silver) suggesting the formation of clusters or assemblies of nanoparticles. Scanning Electron Microscopy and Transmission Electron Microscopy analyses reveal that the synthesized gold nanoparticles and silver nanoparticles are predominantly spherical, with average sizes of 10-20 nm for gold nanoparticles and 15-30 nm for silver nanoparticles, along with observable nanoparticle clustering. The Fourier Transform Infrared spectroscopy analysis shows that the functional groups in the Azadirachta indica extract, such as O-H and C-H bonds, participate in the reduction and stabilization of gold and silver nanoparticles. The synthesized gold nanoparticles and silver nanoparticles (showing stronger inhibition) exhibited dose-dependent antibacterial activity against Escherichia coli and antioxidant activity in 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assays, with silver nanoparticles showing higher scavenging efficiency compared to gold nanoparticles. Further, the surface-enhanced Raman spectroscopy analysis of methyl orange showed significant signal enhancement with silver nanoparticles and gold nanoparticles attributed to inter-plasmon coupling and the creation of hot spots in clustered nanostructures.

Novel Quaternary Ammonium Derivatives Based on Apple Pectin.

New quaternary ammonium derivatives (quats) based on apple pectin (PA) were synthesized by the chemical modification of native polysaccharides with various quaternization mixtures containing epichlorohydrin (ECH) and a tertiary amine. Pectin derivatives (QPAs) were studied by elemental analysis, conductometric titration, Fourier-transform infrared spectroscopy (FTIR), and 13C nuclear magnetic resonance (13C NMR). Viscosity measurements enabled the evaluation of the viscosity average molar mass (Mv) for the unmodified polysaccharide, as well as its intrinsic viscosity ([η]) value. Dynamic light scattering (DLS) analysis revealed that the PA and its quats formed aggregates in an aqueous solution with either a unimodal (PA) or bimodal (QPAs) distribution. Scanning transmission electron microscopy analysis (STEM) of the PA and its derivatives demonstrated the presence of individual polymeric chains and aggregates in aqueous solution, with the smallest sizes being specific to amphiphilic polymers. Thermal stability, as well as wide-angle X-ray diffraction (WAXD) studies, generally indicated a lower thermal stability and crystallinity of the QPAs compared with those of the PA. Antipathogenic activity demonstrated that the PA and its derivatives exhibited effectiveness against S. aureus ATCC 25923 bacterium and C. albicans ATCC 10231 pathogenic yeast.

Atomic-Scale Direct Observation on Cation Antisite Intermixing and Identification of Charge Conduction Mechanism in p-Type CuBi2O4 for Photocathodes

Cu-based p-type semiconducting oxides have been investigated for their potential as water-reduction photocathodes in order to enhance energy conversion efficiency in photoelectrochemical cells. Among these oxides, CuBi2O4 has recently gained significant attention as a promising candidate for converting light energy into electrochemical reactions because of its good light absorption property with an adequate bandgap. Despite the importance of identifying the major defect structure to comprehend the electronic conduction behavior, however, no direct experimental analysis has been suggested yet. While the formation of Cu cation vacancies may be discussed as a possible explanation of the p-type conduction behavior, direct evidence regarding the atomic-scale structural and chemical characteristics is still required.In this research, a combination of advanced characterization techniques is employed to figure out a representative defect structure affecting the optoelectronic properties in CuBi2O4. Cs-corrected scanning transmission electron microscopy (STEM) analysis is conducted to identify a noteworthy occurrence of antisite point defects. Atomic-level energy-dispersive X-ray spectroscopy (EDS) analysis is also employed simultaneously, to clearly show the intermixing of BiCu-CuBi antisite cations as a crucial type of point defect in CuBi2O4. Additionally, a combined result of optical and electrical measurement and density functional theory (DFT) calculations demonstrates the presence of local Cu 3d polaron states in the bandgap. A new type of charge conduction mechanism is created by the hopping of hole-polarons between Cu sites, but it is seriously hindered by the BiCu cations occupying Cu sites. A higher degree of intermixing leads to a greater activation energy and decreased electronic conductivity due to the hindrance of hole-polaron hopping, as evidenced in the Arrhenius plot.Overall, this research provides valuable insights into the role of antisite defects in CuBi2O4 and their impact on its potential as a photocathode material. The results highlight the significance of the combination of atomic-scale structure analysis and theoretical calculations to identify the possible existence of defects and gain a comprehensive understanding of the electric characteristics in complex oxides for (photo)electrocatalysis. By understanding how antisite defects affect electronic conductivity, various strategies can be developed by controlling the possible defects to optimize not only CuBi2O4 but also other complex oxides for energy-harvesting applications. Figure 1

Defect induced polar distortion in SrMnO3 thin films

Defect engineering in perovskite oxides enables novel functionalities by inducing and controlling lattice defects, effectively breaking lattice symmetry, stabilizing polar states and inducing ferroelectricity in non-polar/paraelectric or ferro/antiferromagnetic oxide thin films. A polar state can be stabilized in SrMnO3 (SMO) thin films by displacing Mn ions. However, conventional epitaxial strain engineering necessitates deposition on diverse single crystalline substrates with varying misfit strains and optimization of thin film growth conditions, posing challenges in achieving polar states in SMO thin films. In this study, polar distortion was achieved by inducing defects in SMO epitaxial thin films grown on Pb(Mg1/3Nb2/3)O3-PbTiO3 substrates La0.7Sr0.3MnO3 (LSMO) electrode. Scanning transmission electron microscopy analysis revealed that Mn ion displacement and the c/a ratio increased on moving from the SMO/LSMO interface to the top surface of the SMO film. Electron energy loss spectroscopy depth profiles revealed variations in oxygen stoichiometry and Mn3+/Mn4+ ratio across the cross section of the SMO film. Consequently, a polar state was stabilized through strain gradient induced by defect chemistry in SMO thin films. Our study demonstrates that defect engineering can be effectively utilized in the realization of electric field-controlled magnetic devices at room temperature.

Scanning Transmission Electron Microscopy Analysis of the Si(111)–AlN–GaN Nanowire Interface Grown by Polarity‐ and Site‐Controlled Growth Method

In GaN‐on‐Si nanowire integration schemes, where the nanowires are contacted through the substrate, the interfaces between silicon substrate, AlN buffer layer, and GaN nanowire are of high interest. Herein, analysis by scanning transmission electron microscopy (STEM) of GaN nanowires grown on Si(111) by metal–organic vapor phase epitaxy using a polarity‐ and site‐controlled growth method is presented. This method is based on prestructuring the substrate, ex situ oxidation of the surface, and in situ oxide layer desorption. First, an AlN layer is grown to prevent melt‐back etching. Samples are prepared for STEM by focused ion beam cutting. STEM measurements in three different regions reveal that the AlN buffer material is polycrystalline. The degree of polycrystallinity is found to depend on the observed region: the highest degree exists at the field area between nanowires and the lowest at the sidewall of the Si‐pillars. On the sidewall, the ‐direction of the AlN grain is tilted by 30.1° with regard to the Si{111} sidewall plane, leading to reduced lattice mismatch at this location. The growth of GaN is competing with diffusion of Ga atoms through grain boundaries. The dominant mechanism is dependent on the region, leading to site‐controlled growth of nanowires.

Structural disorder Triggered by small organic molecules Boosting δ-MnO2 cathode for Ultra‐Stable aqueous zinc ion batteries

The inferior cycling stability of MnO2-based cathodes, resulting from Mn dissolution and crystal structure transition during Zn-ion insertion/extraction, poses a significant challenge hindering their widespread adoption in aqueous zinc-ion batteries (AZIBs). To mitigate these issues, we propose an approach involving the incorporation of small organic molecules (methylformamide, dimethylformamide, and formamide) to modify the crystalline structure of MnO2. These molecules, characterized by their low orbital energy levels, facilitate the creation of energetically equivalent electron transfer pathways with the unoccupied eg orbitals in Mn4+, as evidenced by the DFT calculations. Furthermore, they modulate the electron cloud density of Mn-O and introduce structural disorder in the MnO2 crystalline lattice, thereby greatly enhancing the structural stability of the Mn-based cathode. In AZIBs tests, the MnO2/methylformamide (MO/NMF) cathode demonstrates a remarkable reversible specific capacity exceeding 270 mAh g-1 at 1 A g-1 and exceptional durability, exhibiting negligible capacity degradation after 2000 cycles at 3 A g-1. In-situ X-ray diffraction, neutron powder diffraction and high-angle annular dark-field scanning transmission electron microscopy analyses confirm the structure stability of MO/NMF during Zn-ion insertion/extraction, attributed to the NMF modification. Additionally, the electrochemical data indicate that modifications with dimethyl formamide and formamide also positively impact the electrochemical performance of the MnO2 cathode. This study offers valuable insights for the development of high-performance Mn-based cathodes.

Epitaxial Thin Film Growth on Recycled SrTiO3 Substrates Toward Sustainable Processing of Complex Oxides.

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high-quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO3 (STO), MgO, LaAlO3, a-Al2O3, and many others. Recent successes in transferring these complex oxides as free-standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost-effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high-resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre-strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y3Fe5O12) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high-quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

Unveiling Nanoscale Ordering in Amorphous Semiconducting Polymers Using Four-Dimensional Scanning Transmission Electron Microscopy.

We present four-dimensional (4D) scanning transmission electron microscopy (STEM) analysis to obtain a high level of detail regarding the nanoscale ordering within largely disordered organic semiconducting polymers. Understanding nanoscale molecular ordering in semiconducting polymers is crucial due to its connection to the materials' important properties. However, acquiring such information in a spatially localized manner has been limited by the lack of a nanoscale experimental probe, weak signal from ordering, and radiation damage to the sample. By collecting nanodiffraction patterns with a high dynamic range pixelated detector, we acquired statistically robust, high signal-to-noise ratio diffraction patterns from semiconducting organic materials, including poly(3-hexylthiophene-2,5-diyl) (P3HT), P3HT/[6,6]-phenyl C61 butyric acid methyl ester, and indacenodithiophene-co-benzothiadiazole (IDTBT), which largely have disordered structures. Real-space images of the ordered domains were reconstructed from the 4D-STEM data set for a variety of scattering vectors and in-plane angles to capture the different molecular stacking distances and their in-plane orientation. These were then analyzed to obtain the average size of the ordered domains within the sample. Such measurements were arranged in a two-dimensional (2D) histogram, which showed a direct relationship between the type and size of molecular ordering. Complementary analyses, such as intensity variance and angular correlation, were applied to obtain ordering and symmetry information. These analyses enabled us to directly characterize the alkyl and π-π stacking of P3HT, as well as the fullerene domains caused by donor segregation in the P3HT sample. Furthermore, the analysis also captured changes in the P3HT domains when the fullerenes are incorporated. Lastly, IDTBT showed a much lesser degree of ordering without much disinclination between the domains within the 2D histogram. The 4D-STEM analysis that we report here unveils new details of molecular ordering that can be used to optimize the properties of this important class of materials.

Solvent-induced modulation of sensitivity and selectivity in the self-assembly of tetracationic cyclophanes with cholesterol sulphate, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate: Observations of significant shifts

Cyclophane CP-1 demonstrates markedly distinct sensitivities toward Cholesterol sulfate (CH-S), Sodium Dodecyl Sulfate (SDS), and Sodium Dodecyl Benzene Sulfonate (SDBS) when the solvent is shifted minimally from a 95 % to a 98 % HEPES-DMSO mixture. In a 98:2 HEPES-DMSO mixture, CP-1 engages in highly selective self-assembly with CH-S, which is characterized by aggregation-induced emission enhancement (AIEE) in contrast to other steroidal sulfates such as pregnenolone sulfate (PRG-S), dehydroisoandrosterone sulfate (DIAND-S), taurocholic acid (TACH-S), and the surfactants SDS and SDBS. This assembly results in an approximate 40-fold increase in fluorescence intensity with three equivalents of CH-S and allows for the detection of concentrations as low as 200 nM under physiological conditions. Dynamic light scattering (DLS) studies illustrate the aggregation of CP-1 and CH-S, with the zeta potential of each shifting from negative values to nearly zero in a 1:2 CP-1:CH-S mixture, indicating self-assembly. This aggregation behavior is reversible, as demonstrated by a corresponding decrease and then increase in fluorescence intensity with temperature variations from 25 °C to 70 °C and back to 25 °C. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses show that CP-1 forms aggregates ranging from 100 to 180 nm, which increase to 150–250 nm upon interaction with CH-S. In a 95:5 HEPES-DMSO mixture, CP-1 exhibits a stronger AIEE response with SDS and SDBS compared to CH-S. Cyclophane CP-2, when dissolved in binary DMSO-water mixtures with water content exceeding 80 %, shows similar AIEE phenomena and undergoes selective fluorescence quenching with SDS and only a 50 % increase in fluorescence intensity with CH-S, irrespective of the HEPES concentration (95 % or 98 %).

5-Fluorouracil adsorption on graphene oxide-amine modified graphene oxide/hydroxyapatite composite for drug delivery applications: Optimization and release kinetics studies

The present study focused on investigation of graphene oxide/hydroxyapatite (GO/HAp) and amine modified graphene oxide/hydroxyapatite (GO-NH2/HAp) composites as potential drug carrier agents for 5-Fluorouracil (5-FU). Incorporation of 5-Fluorouracil drug was performed via adsorption through π-π interactions and electrostatic attractions. Modification of graphene oxide was performed for the production of amine modified graphene oxide/hydroxyapatite composite with the intention of enhancing adsorption performance. The X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and zeta potential/particle size analysis were performed for particle characterization while Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis were used to analyze detailed morphological properties. Experimental design studies were followed out in order to determine the effect of adsorption parameters including graphene oxide amount, pH and initial drug concentration on 5-Fluorouracil adsorption behavior. Adsorption isotherms of both composites with unmodified and modified GO were best fitted to Freundlich model with R2 values of 0.9616 and 0.9682 respectively. The maximum adsorption capacities (qm) were calculated as 47.3 mg/g and 18.4 for graphene oxide/hydroxyapatite and amine modified graphene oxide/hydroxyapatite composites respectively at pH 2.0. The highest adsorption percentage was obtained for amine modified graphene oxide/hydroxyapatite composite as 40.87 % at pH 2.0 condition. In vitro release kinetic studies revealed that compliance with Higuchi and Korsmeyer-Peppas kinetic models were observed for graphene oxide/hydroxyapatite, whereas zero order and Korsmeyer-Peppas kinetic models pointed out as the well-fitted model for amine modified graphene oxide/hydroxyapatite composite. The release period of 5-FU drug from all composites were continued up to 8–10 h in physiological conditions (pH 7.4, 37 °C) indicating an achieved controlled release. Based on the overall findings, graphene oxide/hydroxyapatite and amine modified graphene oxide/hydroxyapatite composites could be suggested as a potential drug delivery agent for 5-FU in clinical applications.

Effects of Gd2O3 additives on microscopical morphology of ZrB2-SiC sintering ceramic system: Insights for electron transpiration cooling

By manipulating the work function, the dissipation of thermal energy on the material surface can be regulated through Electron Transpiration Cooling (ETC) mechanism. The doping of rare-earth oxide serves as an effective approach for reducing the work function, whereas there is still a lack of comprehensive research into the microstructural morphology of the rare-earth oxides and their correlations with the modifications of the work functions. This study investigates the detailed microscopical structure of Gd2O3 in the ultrahigh-temperature ceramic system (ZrB2-20 vol%SiC). Semi-quantitative composition analyses based on X-ray photoelectron spectra indicate that an increased doping concentration of Gd2O3 is beneficial for the formation of a single solid-state Gd0.18Zr0.82O1.91 phase of ZrB2-SiC system. Atomic-scale scanning transmission electron microscopy (STEM) analyses suggest that Gd2O3 is enriched at the interfaces between SiC and ZrB2 matrix with a nanoscale fibrous morphology composed of alternated Gd2O3 crystals and pores, rendering a continuous microstructure throughout the entire system. This peculiar microstructural morphology is anticipated to facilitate its diffusion along the grain boundary and the formation of Gd2O3 nanolayers at the surface region below the melting points of the ceramic matrix, which can efficiently lower the material work function and reduce the emission energy of the surface electrons during thermal emission through ETC mechanism. The composite with 10 vol% Gd2O3 induces a reduction of the averaged work function of ∼0.49 eV before preforming the thermionic emission experiments. Our results provide valuable insights into the impacts of rare-earth oxide on the ZrB2-SiC matrix, as well as shed light on the feasibility of the ETC mechanism through the efficient design of thermal protection materials.

Green Synthesis of Iron-Based Nanoparticles Using Pomegranate Leaf Extracts: Characterization, Biomolecules and Indole Removal

This study investigates the synthesis of iron-based nanoparticles (Fe NPs) using pomegranate leaf extracts and their application in removing indole, a persistent organic pollutant commonly found in wastewater. The physicochemical properties of the synthesized Fe NPs and the active biomolecules in the pomegranate leaf extracts were comprehensively characterized. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses revealed that the Fe NPs exhibited quasi-spherical shapes, with sizes ranging from 75 to 105 nm. Energy-Dispersive X-ray Spectroscopy (EDS) confirmed a homogeneous distribution of elements, including C, O, Fe, and S, on the nanoparticle surfaces, with weight percentages of 43.59%, 42.95%, 12.58%, and 0.88%, respectively. Fourier-transform infrared spectroscopy (FTIR) identified key functional groups like −OH, −COOH, and −C=O, which are essential for the capping and stabilization of the nanoparticles. Biomolecules such as ellagic acid (C14H6O8) and gallic acid (C7H6O5) functioned as reducing agents, improving nanoparticle dispersion and preventing aggregation. The synthesized Fe NPs quickly achieved 45.5% removal of indole within just 20 min and maintained a stable removal efficiency of approximately 51.4% after 90 min. This performance was attributed to the synergetic interaction between the biomolecules and the nanoparticles, with the monolayer adsorption of indole molecules on the Fe NP surfaces likely setting an upper limit on the maximum achievable removal efficiency. It appears from this study that pomegranate leaf extracts can be effectively utilized to synthesize Fe NPs as a novel and eco-friendly approach, demonstrating promising potential for the rapid removal of indole from aqueous solutions.

Demonstration of β-(Al x Ga1−x )2O3/β-Ga2O3 superlattice growth by mist chemical vapor deposition

This study demonstrates the successful growth of a β-(Al x Ga1−x )2O3/β-Ga2O3 superlattice structure with six periods using mist CVD. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis revealed that the superlattice consisted of six periods of β-(Al x Ga1−x )2O3/β-Ga2O3 with an individual layer thickness of 12.9 nm and 9.1 nm, respectively. XRD analysis further confirmed the periodicity of the structure, yielding a period of 22.7 nm, which is in good agreement with the STEM result. Additionally, the Al composition was determined to be x = 0.085 based on XRD peak positions. Both atomic force microscopy and HAADF-STEM observations revealed atomically flat surfaces and sharp interfaces. This achievement highlights the potential of mist CVD for fabricating complex oxide heterostructures, offering a cost-effective and scalable alternative to conventional methods. The findings open new avenues for developing advanced electronic and optoelectronic devices based on wide-bandgap oxides.

Comprehensive characterization of spark plasma sintered ZrB2-SiCp-SiCw composite and its corresponding orthogonal cutting simulation

A composite consisting of 12.5 wt% SiC particles and 12.5 wt% SiC whiskers in a ZrB2 matrix (ZrB2-SiCp-SiCw) was produced using spark plasma sintering. The sintering process was carried out at a temperature of 1900 °C and a pressure of 40 MPa for a duration of 7 minutes. X-ray photoelectron spectroscopy analysis confirmed the presence of C-C, C-Si, O-B, O-Zr, O-Si, and Zr-B bonds. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed the presence of silicon and carbon in the ZrB2 phase. The nano-indentation hardnesses and elastic moduli of ZrB2 and SiC were measured as 2104.58 and 2268.97 Vickers and 397.58 and 394.27 GPa, respectively, under a load of 100 mN and a loading rate of 0.4 mN/sec. The orthogonal cutting process of an Al6061 workpiece with a ZrB2-SiCp-SiCw cutting tool was simulated using DEFORM 2D software. The response surface method was used to develop a model to evaluate the relationship between cutting parameters (tool tip radius, cutting speed, and rake angle), cutting force, feeding force, and maximum temperature. It was found that cutting and feeding forces decrease with increasing cutting speed and rake angle, while increasing the tool tip radius increases these forces. The tool and workpiece endure a higher maximum temperature as the cutting speed and tool tip radius rise, but the maximum temperature drops as the rake angle increases.

Magnetic, structural, and morphological properties behavior of Ni1–xCoxFe2O4 magnetic nanoparticles: Theoretical and experimental study

In this work, we synthesized nanoparticles of the Ni1-xCoxFe2O4 (with x = 0.25, 0.50, and 0.75) inverse spinel by the hydrothermal method. Scanning transmission electron microscopy (STEM) analysis and elemental characterization revealed the formation of nanoparticles of the order of ∼3 nm with a homogeneous distribution of their constituents, denoting the correct material synthesis. The results show that as the content of Co2+ increases, the cell parameter of the structures increases and the crystallite size increases. Besides, the magnetic characterization exhibits an increase in the saturation magnetization as the Co2+ content moves from x = 0.25 to x = 0.75, on the other hand, the coercive field decreases, which is attributed to the superparamagnetic behavior of the structures. By Density Functional Theory (DFT) calculation demonstrates that the inverse spinel is the most favorable configuration for both NiFe2O4 and CoFe2O4 compounds. Besides, by first-principles thermodynamics, we have shown that Co tends to occupy the Ni sites as the most favorable configuration, with an increase in the cell parameter and total magnetization as Co content increases, in excellent agreement with experimental measurements. Our findings demonstrate that Co-Ni-based ferrites are soft magnetic materials, which are suitable candidates to be employed in devices that require rapid magnetization and demagnetization

Influence of High-κ Dielectrics Integration on ALD-Based MoS2 Field-Effect Transistor Performance.

The integration of high-κ dielectrics on MoS2 field-effect transistors (FETs) is essential for the realization of MoS2 in ultrascaled nanoelectronic devices and circuits. Most studies covering this topic are based on exfoliated MoS2 flakes or chemical vapor deposition (CVD) grown MoS2 films, whereas other techniques, such as atomic layer deposition (ALD), are also gaining attention for the growth of MoS2 in recent years. In this work, we grow large-area MoS2 by means of plasma-enhanced (PE-)ALD and evaluate the influence of high-κ dielectrics on the properties of ALD-based MoS2 FETs through electrical characterization combined with surface-chemical and high-resolution scanning transmission electron microscopy (HR-STEM) analyses. We grow HfO x , AlO x , or both by means of PE-ALD or thermal ALD on our fabricated devices and show that, in addition to the dielectric constant, three other major parameters related to the processing of the dielectrics can simultaneously affect the MoS2 FET electrical characteristics and govern its doping. These parameters are the stoichiometry of the dielectric, its carbon impurity content, and the degree to which the MoS2 surface oxidizes upon the dielectric growth. When grown at 100 °C, our HfO x films are oxygen-vacant whereas our AlO x films are oxygen-rich. In addition, carbon impurities are incorporated into the dielectrics at low deposition temperatures, being one of the likely causes of the MoS2 FET overall n-type performance in all of the studied cases. Our investigations also reveal that PE-ALD of HfO x or AlO x oxidizes the MoS2 surface, whereas thermal ALD AlO x leaves MoS2 almost intact. In this respect, if thermal ALD AlO x of proper thickness is grown between MoS2 and HfO x , it can reduce the degree to which the MoS2 surface oxidizes by HfO x and meanwhile improve the total dielectric constant, altogether leading to the most optimal electrical performance in ALD-based MoS2 FETs.

Effective and group refractive index extraction and cross-sectional dimension estimation for silicon-on-insulator rib waveguides.

The accurate determination of the effective and group refractive indices (neff and ng) of optical waveguides as a function of wavelength is of critical importance to the design of photonic integrated circuits (PICs). This paper demonstrates the extraction of the two parameters of silicon-on-insulator (SOI) rib waveguides using the transmission spectra of two racetrack micro-ring resonators (MRRs) with different perimeters. The extracted neff and ng exhibit an uncertainty of approximately 10-3. Based on the extracted neff(λ), we estimate the cross-sectional dimension of the SOI rib waveguide that constitutes the MRR. This waveguide has a nominal rectangular cross section with a width, height, and slab thickness of 450 nm, 200 nm, and 70 nm, respectively. The estimated cross-sectional dimension is in accordance with the findings of the scanning transmission electron microscopy (STEM) analysis, exhibiting a discrepancy of approximately 1%. The proposed methodology offers a universal approach to neff and ng extraction and a non-invasive method for cross-sectional dimension assessment, which can be applied in different PIC platforms.

Investigation of Gamma-Induced Changes to Screening Currents and AC Losses in Mono- Versus Multi-filamentary REBCO Coated Conductors Using DC and AC Magnetometry

REBCO (rare-earth barium copper oxide) coated conductor tapes are a highly attractive option for magnet materials in future tokamak fusion power plants. However, the threat of intense neutron and gamma radiation, together with AC losses during magnet coil ramping, has raised concerns around magnet coil lifetimes. Irradiation-induced changes to flux creep rate has been identified as a key performance-limiting factor in REBCO tapes at low temperatures and high fields post-irradiation with gamma rays; spontaneous flux creep contributes to hysteretic AC loss in REBCO cables under applied AC fields. Knowing that multi-filamentary tapes are under consideration for tokamaks as an AC loss mitigation, magnetic measurements and gamma irradiation experiments are presented here on striated and mono-filamentary YBCO tapes to investigate the differences in post-irradiation screening currents and AC losses. Reduction in AC losses improved magnetisation critical current density (Jc) retention after 1 MGy in the multi- relative to the mono-filamentary samples. After the 5 MGy dose, striations then made the multi-filamentary tape more susceptible to Jc degradation because of the thinner individual filament width. Scanning transmission electron microscopy analysis on an analogous GdYBCO mono-filamentary tape did not indicate the introduction of nm-scale amorphisation to the active GdYBCO layer after gamma irradiation. A potential theoretical explanation for the underlying mechanism altering the flux-pinning landscape across the REBCO layer surface in gamma-irradiated tapes is discussed. This work concluded that gamma effects on screening current capability should be considered in future tokamak REBCO tape qualification studies.

Room‐temperature bulk plasticity and tunable dislocation densities in KTaO3

AbstractWe report room‐temperature bulk plasticity mediated by dislocations in single‐crystal cubic potassium tantalate oxide (KTaO3), contrasting the conventional knowledge that single‐crystal KTaO3 is susceptible to brittle fracture. A mechanics‐based combinatorial experimental approach using cyclic Brinell indentation, scratching, and uniaxial bulk compression consistently demonstrates room‐temperature dislocation plasticity in KTaO3 from the mesoscale to the macroscale. This approach also delivers tunable dislocation densities and plastic zone size. Scanning transmission electron microscopy analysis underpins the activated slip system to be <110> {10}. Given the growing significance of KTaO3 as an emerging electronic oxide and the increasing interest in dislocations for tuning the physical properties of oxides, our findings are expected to trigger synergistic research interest in KTaO3 with tunable dislocation densities.

Lattice strain induced by trace Pt single atoms in nickel for accelerating industrial hydrogen evolution

Strategically designing the electrocatalytic system and cleverly inducing strain is an effective approach to balance the cost and activity of Pt-based electrocatalysts for industrial-scale hydrogen production. Herein, we present a unipolar pulsed electrodeposition (UPED) strategy to induce strain in the Ni lattice by introducing trace amounts of Pt single atoms (SAs) (0.22 wt%). The overpotential decreased by 183 mV at 10 mA cm−2 in 1.0 M KOH after introducing trace amounts of PtSAs. The industrial electrolyzer, assembled with PtSAsNi cathode and a commercial NiFeOx anode, requires a cell voltage of 1.90 V to attain 1 A cm−2 of current density and remains stable for 280 h, demonstrating significant potential for practical applications. Spherical aberration corrected scanning transmission electron microscopy (AC-STEM), X-ray absorption (XAS), and geometric phase analysis (GPA) indicate that the introduction of trace amounts of Pt SAs induces tensile strain in the Ni lattice, thereby altering the local electronic structure and coordination environment around cubic Ni for enhancing the water decomposition kinetics and fundamentally changing the reaction pathway. The doping-strain strategy showcases conformational relationships that could offer new ideas to construct efficient hydrogen evolution reaction (HER) electrocatalysts for industrial hydrogen production in the future.