High-resolution Scanning Transmission Electron Microscopy Research Articles

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.

Morphological Evolution of Atomic Layer Deposited Hafnium Oxide on Aligned Carbon Nanotube Arrays.

Microscopic study of the nucleation and growth of atomic layer deposition (ALD) dielectrics onto carbon nanotubes (CNTs) is an essential while challenging task toward high-performance devices. Here, we capture the morphological evolution and growth behaviors of ALD-HfO2 onto SiO2/Si-supported aligned CNT arrays (A-CNTs) under three ALD recipes via cross-sectional high-resolution scanning transmission electron microscopy. The HfO2 in ALD I (200 °C) preferentially nucleates on the SiO2 substrate in heterogeneous growth mode, resulting in films with considerable pinholes, while ALD II (90 °C) and III (90 °C and extra H2O presoak) exhibit homogeneous growth with nucleation on both SiO2 and CNTs, yielding uniform films. Arrangement defects in A-CNTs exacerbate nonuniformity of HfO2 and tube-tube separation plays deterministic roles affecting the HfO2-CNT interfacial morphology. Electrical measurements from A-CNTs metaloxide-semiconductor devices validate these findings. Our investigation contributes valuable insights for optimizing ALD processes for enhanced dielectric integration on A-CNTs in next-generation electronics.

Automated detection and mapping of crystal tilt using thermal diffuse scattering in transmission electron microscopy

Quantitative interpretation of transmission electron microscopy (TEM) data of crystalline specimens often requires the accurate knowledge of the local crystal orientation. A method is presented which exploits momentum-resolved scanning TEM (STEM) data to determine the local mistilt from a major zone axis. It is based on a geometric analysis of Kikuchi bands within a single diffraction pattern, yielding the center of the Laue circle. Whereas the approach is not limited to convergent illumination, it is here developed using unit-cell averaged diffraction patterns corresponding to high-resolution STEM settings. In simulation studies, an accuracy of approximately 0.1 mrad is found. The method is implemented in automated software and applied to crystallographic tilt and in-plane rotation mapping in two experimental cases. In particular, orientation maps of high-Mn steel and an epitaxially grown La0.7Sr0.3MnO3-SrTiO3 interface are presented. The results confirm the estimates of the simulation study and indicate that tilt mapping can be performed consistently over a wide field of view with diameters well above 100 nm at unit cell real space sampling.

Cu nanoparticles immobilized in mesopores generated in zeolite for high-performing CO2 hydrogenation to methanol

Copper nanoparticles (Cu NPs) are commonly used as catalyst active components in CO2 hydrogenation reactions. However, they often lose their catalytic activity due to sintering in most reaction environments. This study explores a solution for Cu-supported catalysts used for methanol production from CO2 hydrogenation by fixing Cu NPs in the mesopores generated in zeolite. Mesopores were generated in NaY zeolite by partially dealuminating its framework. High-resolution (scanning) transmission electron microscopy (HR(S)TEM) and CO adsorption measurements confirm that the synthesized mesoporous zeolite-supported Cu NPs are highly dispersed and fixed within the mesopores. In comparison with conventional microporous zeolite-supported Cu NPs (2 wt%), Cu NPs (2 wt%, average size of 2.2 nm) in mesoporous zeolite increased methanol production from ∼26 mmolgCu−1h−1 to approximately 56 mmolgCu−1h−1 at 250 °C. By further modifying the mesoporous zeolite with Zr (2 wt%), Cu NPs increased in size, and the methanol production rate increased approximately 2.2 folds to 125 mmolgCu−1h−1 under similar conditions due to zeolite electronic modification and the newly formed Zr-zeolite/Cu interface. However, the addition of Zr significantly increased the Cu NP size and moved part of them out of the mesopores, lowering their stability. In situ DRIFTS experiments reveal CO2 hydrogenation proceeds through the formate route via a direct formation of dominantly carbonate (*CO3), which hydrogenates to formate (*HCOO) and traces of methoxy (*H3CO), and subsequently methanol (CH3OH). This study reports the design of active and stable catalysts for CO2 hydrogenation to methanol by engineering Cu NPs in zeolite pores.

Ageing of commercial austenitic, martensitic and duplex stainless steel surfaces after formation of laser-induced periodic surface structures by fs-laser irradiation

The time-dependent wetting behavior was investigated for commercially available austenitic, martensitic and duplex stainless steel surfaces after femtosecond (fs) laser irradiation. For this purpose, highly regular LIPSS with almost identical geometric properties were generated on the stainless steels in an air environment by near-infrared fs-laser processing (λ = 1025 nm, τ = 300 fs, frep = 100 kHz, v = 0.67 m/s, Δx = 6 μm, F = 1.1 J/cm2) and compared to the polished initial surfaces as reference. The wetting with distilled water was evaluated as a function of aging time by contact angle measurements using the sessile drop method. The laser-induced morphological, topographical and chemical alteration of the surface was characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, glow-discharge optical emission spectroscopy as well as high-resolution imaging and scanning transmission electron microscopy. Despite an almost identical LIPSS-based topography alteration, the stainless steels revealed very different ageing behavior. For permanently used samples, it was shown that the ageing effect is less pronounced than for samples that were stored in ambient air following fs-laser irradiation until the wetting measurement. The results obtained make an important contribution to understanding and controlling the ageing effect of metal surfaces and thus facilitate the transfer of LIPSS-based functional surface engineering and design to industrial processes.

High-Entropy Metal-Organic Frameworks (HEMOFs): A New Frontier in Materials Design for CO2 Utilization.

High-entropy materials (HEMs) emerged as promising candidates for a diverse array of chemical transformations, including CO2 utilization. However, traditional HEMs catalysts are nonporous, limiting their activity to surface sites. Designing HEMs with intrinsic porosity can open the door toward enhanced reactivity while maintaining the many benefits of high configurational entropy. Here, a synergistic experimental, analytical, and theoretical approach to design the first high-entropy metal-organic frameworks (HEMOFs) derived from polynuclear metal clusters is implemented, a novel class of porous HEMs that is highly active for CO2 fixation under mild conditions and short reaction times, outperforming existing heterogeneous catalysts. HEMOFs with up to 15 distinct metals are synthesized (the highest number of metals ever incorporated into a single MOF) and, for the first time, homogenous metal mixing within individual clusters is directly observed via high-resolution scanning transmission electron microscopy. Importantly, density functional theory studies provide unprecedented insight into the electronic structures of HEMOFs, demonstrating that the density of states in heterometallic clusters is highly sensitive to metal composition. This work dramatically advances HEMOF materials design, paving the way for further exploration of HEMs and offers new avenues for the development of multifunctional materials with tailored properties for a wide range of applications.

Unraveling nano-scale effects of topotactic reduction in LaNiO2 crystals

Infinite-layer nickelates stand as a promising frontier in the exploration of unconventional superconductivity. Their synthesis through topotactic oxygen reduction from the parent perovskite phase remains a complex and elusive process. This study delves into the nano-scale effects of the topotactic lattice transformation within LaNiO2 crystals. Leveraging high-resolution scanning transmission electron microscopy and spectroscopy, our investigations uncover a panorama of structural alterations, including grain boundaries and coherent twin boundaries, triggered by reduction-induced transformations. In addition, our analyses unveil the formation of an oxygen-rich disordered transition phase encircling impurities and pervading crystalline domains and the internal strain is accommodated by grain boundary formation. By unraveling these nano-scale effects, our findings provide insights into the microscopic intricacies of the topotactic reduction process elucidating the transition from the perovskite to the infinite-layer phase within nickelate bulk crystals.

Development and Characterization of N2O-Plasma Oxide Layers for High-Temperature p-Type Passivating Contacts in Silicon Solar Cells.

Full-area passivating contacts based on SiOx/poly-Si stacks are key for the new generation of industrial silicon solar cells substituting the passivated emitter and rear cell (PERC) technology. Demonstrating a potential efficiency increase of 1 to 2% compared to PERC, the utilization of n-type wafers with an n-type contact at the back and a p-type diffused boron emitter has become the industry standard in 2024. In this work, variations of this technology are explored, considering p-type passivating contacts on p-type Si wafers formed via a rapid thermal processing (RTP) step. These contacts could be useful in conjunction with n-type contacts for realizing solar cells with passivating contacts on both sides. Here, a particular focus is set on investigating the influence of the applied thermal treatment on the interfacial silicon oxide (SiOx) layer. Thin SiOx layers formed via ultraviolet (UV)-O3 exposure are compared with layers obtained through a plasma treatment with nitrous oxide (N2O). This process is performed in the same plasma enhanced chemical vapor deposition (PECVD) chamber used to grow the Si-based passivating layer, resulting in a streamlined process flow. For both oxide types, the influence of the RTP thermal budget on passivation quality and contact resistivity is investigated. Whereas the UV-O3 oxide shows a pronounced degradation when using high thermal budget annealing (T > 860 °C), the N2O-plasma oxide exhibits instead an excellent passivation quality under these conditions. Simultaneously, the contact resistivity achieved with the N2O-plasma oxide layer is comparable to that yielded by UV-O3-grown oxides. To unravel the mechanisms behind the improved performance obtained with the N2O-plasma oxide at high thermal budget, characterization by high-resolution (scanning) transmission electron microscopy (HR-(S)TEM), X-ray reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) is conducted on layer stacks featuring both N2O and UV-O3 oxides after RTP. A breakup of the UV-O3 oxide at high thermal budget is observed, whereas the N2O oxide is found to maintain its structural integrity along the interface. Furthermore, chemical analysis reveals that the N2O oxide is richer in oxygen and contains a higher amount of nitrogen compared to the UV-O3 oxide. These distinguishing characteristics can be directly linked to the enhanced stability exhibited by the N2O oxide under higher annealing temperatures and extended dwell times.

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.

Investigating Co and Fe Single-Atom (SA) Decorated NS-Doped Reduced Graphene Oxide (Co SA/NS-rGO, Fe SA/NS-rGO) Catalysts for NOx - to NH3 Pulsed Electroreduction

Electrochemical NH3 production has attracted much attention due to its potential to compensate for and supplement the Haber-Bosch process that produces hundreds of billions of kg of NH3 annually.1 One of the proposed electrochemical pathways to produce NH3 is the N2 reduction reaction. However, this reaction suffers from a high bond dissociation energy of 945 kJ mol−1, low NH3 Faradaic efficiency (F.E.) at high overpotentials, and NH3 quantification problems, limiting the extent of its applications.2,3 On the other hand, other N-containing species, NO3 - and NO2 -, that are commonly found in sewages and agricultural water, hold great potential for electrochemical NH3 production owing to their high NH3 yield rate and F.E. as well as building a self-sustaining NH3 production cycle working tandem with denitrification processes.1,4 In this study, we investigated Co and Fe single-atom (SA) decorated NS-doped reduced graphene oxide (Co SA/NS-rGO and Fe SA/NS-rGO) catalysts for nitrate reduction reaction (NO3RR) and nitrite reduction reaction (NO2RR). Both materials have defect-rich properties owing to preserving the nature of doped graphene materials even after the metal incorporation. The presence of the layered structure of graphene and homogenous distribution of Fe and Co SAs in the doped graphene basal plane is shown through High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) measurements. In addition to the Co and Fe SAs on the NS-rGO planes, SEM and X-ray Photoelectron Spectroscopy (XPS) investigations demonstrated that CoS and FeS could be simultaneously formed.We performed NO3RR and NO2RR experiments in 0.1 M KOH + 0.1 M KNO3 and 0.1 M KOH + 0.1 M KNO2 electrolytes with constant Ar purging in a glass H-Cell with a Nafion proton exchange membrane. We obtained NH3 with 65% F.E. at -0.4 V and a maximum of 2 mol s-1 molM -1 yield rate using Co SA/NS-rGO catalyst while with 60% F.E. at -0.5 V and 2.3 mol s-1 molM -1 yield rate using Fe SA/NS-rGO catalyst for NO3RR. Furthermore, the ∼10% NO2 - F.E. that is obtained for NO3RR experiments at -0.3 V and a significant increase in NH3 F.E. after -0.3 V for NO2RR indicates that NO3 - to NO2 - reduction takes place at this potential and our catalysts follow a two-step electron transfer mechanism. Moreover, linear sweep voltammetry (LSV) measurements indicated an onset potential of -0.4 V and -0.5 V for Co SA/NS-rGO and Fe SA/NS-rGO, respectively, for the NO3RR which are in excellent agreement with NO3RR F.E. results. We demonstrate that after prereduction at high negative potentials and with optimizations in experimental conditions, one can obtain >80% NH3 F.E. for NO3RR.To further increase the NH3 yield, three different pulsed electroreduction studies such as applying a potential at (1) the open circuit potential (OCP), (2) NO2 - reduction potential, (3) Co2+ or Fe2+ red-ox potentials and NH3 reduction potentials for 1-5 s intervals were performed. On Co SA/NS-rGO, an increased NH3 F.E. of ∼100% at -0.4 V was obtained under pulsed conditions. Also, by modulating NO3 - to NO2 - conversion to more negative potentials by pulsed electroreduction, significantly higher NH3 F.E. values were obtained for both catalysts. The higher NH3 F.E. and lower overpotential of Co SA/NS-rGO compared to Fe SA/NS-rGO could be attributed to the CoS formation that is more stable than FeS.

Facile preparation of graphene–graphene oxide liquid cells and their application in liquid-phase STEM imaging of Pt atoms

Graphene–graphene oxide (GO) hybrid liquid cells (LCs) for liquid-phase scanning transmission electron microscopy (STEM) were fabricated using a facile method with commercial graphene on a polymethyl methacrylate sheet and GO on a TEM grid. LCs containing Pt nanoparticles (NPs) and pure water were efficiently produced and observed via STEM. Their composition and thickness were characterized by STEM-electron energy-loss spectroscopy. High-resolution (HR) STEM revealed slow-moving Pt NPs’ atomic structures and fast-moving single Pt atoms at the LC’s thin edges. Minimal damage during HR STEM indicated stable LCs because of their excellent electrical and thermal conductivities and radiolysis species scavenging ability.

Unveiling the 3D Morphology of Epitaxial GaAs/AlGaAs Quantum Dots.

Strain-free GaAs/AlGaAs semiconductor quantum dots (QDs) grown by droplet etching and nanohole infilling (DENI) are highly promising candidates for the on-demand generation of indistinguishable and entangled photon sources. The spectroscopic fingerprint and quantum optical properties of QDs are significantly influenced by their morphology. The effects of nanohole geometry and infilled material on the exciton binding energies and fine structure splitting are well-understood. However, a comprehensive understanding of GaAs/AlGaAs QD morphology remains elusive. To address this, we employ high-resolution scanning transmission electron microscopy (STEM) and reverse engineering through selective chemical etching and atomic force microscopy (AFM). Cross-sectional STEM of uncapped QDs reveals an inverted conical nanohole with Al-rich sidewalls and defect-free interfaces. Subsequent selective chemical etching and AFM measurements further reveal asymmetries in element distribution. This study enhances the understanding of DENI QD morphology and provides a fundamental three-dimensional structural model for simulating and optimizing their optoelectronic properties.

Improving the Two-Color Temperature Sensing Using Machine Learning Approach: GdVO4:Sm3+ Prepared by Solution Combustion Synthesis (SCS)

The gadolinium vanadate doped with samarium (GdVO4:Sm3+) nanopowder was prepared by the solution combustion synthesis (SCS) method. After synthesis, in order to achieve full crystallinity, the material was annealed in air atmosphere at 900 °C. Phase identification in the post-annealed powder samples was performed by X-ray diffraction, and morphology was investigated by high-resolution scanning electron microscope (SEM) and transmission electron microscope (TEM). Photoluminescence characterization of emission spectrum and time resolved analysis was performed using tunable laser optical parametric oscillator excitation and streak camera. In addition to samarium emission bands, a weak broad luminescence emission band of host VO43− was also observed by the detection system. In our earlier work, we analyzed the possibility of using the host luminescence for two-color temperature sensing, improving the method by introducing the temporal dependence in line intensity ratio measurements. Here, we showed that further improvements are possible by using the machine learning approach. To facilitate the initial data assessment, we incorporated Principal Component Analysis (PCA), t-Distributed Stochastic Neighbor Embedding (t-SNE) and Uniform Manifold Approximation and Projection (UMAP) clustering of GdVO4:Sm3+ spectra at various temperatures. Good predictions of temperature were obtained using deep neural networks. Performance of the deep learning network was enhanced by data augmentation technique.

The Development and Atomic Structure of Zinc Oxide Crystals Grown within Polymers from Vapor Phase Precursors.

Sequential infiltration synthesis (SIS), also known as vapor phase infiltration (VPI), is a quickly expanding technique that allows growth of inorganic materials within polymers from vapor phase precursors. With an increasing materials library, which encompasses numerous organometallic precursors and polymer chemistries, and an expanding application space, the importance of understanding the mechanisms that govern SIS growth is ever increasing. In this work, we studied the growth of polycrystalline ZnO clusters and particles in three representative polymers: poly(methyl methacrylate), SU-8, and polymethacrolein using vapor phase diethyl zinc and water. Utilizing two atomic resolution methods, high-resolution scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy, we probed the evolution of ZnO nanocrystals size and crystallinity level inside the polymers with advancing cycles─from early nucleation and growth after a single cycle, through the formation of nanometric particles within the films, and to the coalescence of the particles upon polymer removal and thermal treatment. Through in situ Fourier transform infrared spectroscopy and microgravimetry, we highlight the important role of water molecules throughout the process and the polymers' hygroscopic level that leads to the observed differences in growth patterns between the polymers, in terms of particle size, dispersity, and the evolution of crystalline order. These insights expand our understanding of crystalline materials growth within polymers and enable rational design of hybrid materials and polymer-templated inorganic nanostructures.

In2O3-ZnO nanoporous photocatalyst modified with CuOx cocatalyst for enhanced photocatalytic bacterial inactivation and dye degradation

In this study, CuOx surface passivated In2O3 loaded porous ZnO, (CuOx/In2O3(x%)-ZnO)), were synthesized utilizing a solvothermally produced organic–inorganic ZnS(en)0.5 hybrid material. The high-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (TEM) images of the CuOx/In2O3(2.5%)-ZnO nanocomposite reveal a macrosheet-shaped morphology comprising nanosized grains. The photocatalytic behavior of all the synthesized CuOx/In2O3(x = 0,1,2.5, and 5%)-ZnO nanocomposites were examined against aqueous dye solutions of orange II, and bisphenol A, E. coli bacteria under one sun illumination. The CuOx/In2O3(2.5%)-ZnO nanocomposite exhibits enhanced photoactivity for cationic dyes (eosin Y) than that for anionic (orange II). The results indicate that cationic dyes undergo photocatalytic degradation, whereas the anionic dyes adsorb on the CuOx/In2O3(2.5%)-ZnO nanocomposite surface, reducing the removal of organic pollutants. The optimal nanocomposites, CuOx/In2O3(2.5%)-ZnO photocatalyst exhibit maximum photodegradation performance of 99%, 94%, 27% for orange II dye, eosin dye, BPA, and 98% for E. coli inactivation within 180 min, respectively. The CuOx/In2O3(2.5%)-ZnO nanocomposite was successfully demonstrated to be an effective photocatalyst and excellent antibacterial agent. Finally, the charge transfer mechanism during photocatalytic organic decomposition and bacterial inactivation was studied.

The Drosophila blood–brain barrier invades the nervous system in a GPCR-dependent manner

The blood–brain barrier (BBB) represents a crucial interface between the circulatory system and the brain. In Drosophila melanogaster, the BBB is composed of perineurial and subperineurial glial cells. The perineurial glial cells are small mitotically active cells forming the outermost layer of the nervous system and are engaged in nutrient uptake. The subperineurial glial cells form occluding septate junctions to prevent paracellular diffusion of macromolecules into the nervous system. To address whether the subperineurial glia just form a simple barrier or whether they establish specific contacts with both the perineurial glial cells and inner central nervous system (CNS) cells, we undertook a detailed morphological analysis. Using genetically encoded markers alongside with high-resolution laser scanning confocal microscopy and transmission electron microscopy, we identified thin cell processes extending into the perineurial layer and into the CNS cortex. Interestingly, long cell processes were observed reaching the glia ensheathing the neuropil of the central brain. GFP reconstitution experiments highlighted multiple regions of membrane contacts between subperineurial and ensheathing glia. Furthermore, we identify the G-protein-coupled receptor (GPCR) Moody as negative regulator of the growth of subperineurial cell processes. Loss of moody triggered a massive overgrowth of subperineurial cell processes into the CNS cortex and, moreover, affected the polarized localization of the xenobiotic transporter Mdr65. Finally, we found that GPCR signaling, but not septate junction formation, is responsible for controlling membrane overgrowth. Our findings support the notion that the Drosophila BBB is able to bridge the communication gap between circulation and synaptic regions of the brain by long cell processes.

The Defects Genome of Janus Transition Metal Dichalcogenides.

2D Janus Transition Metal Dichalcogenides (TMDs) have attracted much interest due to their exciting quantum properties arising from their unique two-faced structure, broken-mirror symmetry, and consequent colossal polarization field within the monolayer. While efforts are made to achieve high-quality Janus monolayers, the existing methods rely on highly energetic processes that introduce unwanted grain-boundary and point defects with still unexplored effects on the material's structural and excitonic properties Through high-resolution scanning transmission electron microscopy (HRSTEM), density functional theory (DFT), and optical spectroscopy measurements; this work introduces the most encountered and energetically stable point defects. It establishes their impact on the material's optical properties. HRSTEM studies show that the most energetically stable point defects are single (VS and VSe) and double chalcogen vacancy (VS -VSe), interstitial defects (Mi), and metal impurities (MW) and establish their structural characteristics. DFT further establishes their formation energies and related localized bands within the forbidden band. Cryogenic excitonic studies on h-BN-encapsulated Janus monolayers offer a clear correlation between these structural defects and observed emission features, which closely align with the results of the theory. The overall results introduce the defect genome of Janus TMDs as an essential guideline for assessing their structural quality and device properties.

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 3 – Cluster growth and crystal nucleation

This Part 3 focuses on the detailed study of the nanostructures forming in amorphous microwires which were previously received and described in the Part 2. The clustering process was studied at long-term DC Joule heating’s much lower the crystallization temperature. Particular attention is paid to the study of the redistribution of the components of the initial stage of crystallization. The studies were carried out using the Atom Probe Tomography method (APT), which allows for the identification of individually considered atoms. A description and analysis of APT data processing techniques are provided for studying the cluster structure and distribution of elements in the amorphous matrix and crystalline phases. To identify crystalline phases, data obtained using High-Resolution Transmission Electron Microscopy (HR-TEM) and Scanning Transmission Electron Microscopy (STEM), as well as X-Ray Powder Diffraction (XRPD) with synchrotron radiation source were used. The applied techniques made it possible to establish that the formation of nuclei of crystalline phases is preceded by three stages of the amorphous microwire matrix evolution. At the first stage, clusters of the first and second coordination spheres appear. At the second stage, the clusters coagulate and become more than 2 nm in diameter, the stage ends with the predominance of Co-rich and silicide Me-Si clusters. At the third stage, they grow to an average diameter of 4.5 nm, the predominance of clusters of this type remains, and the formation of nuclei of crystalline phases α-Co and Co2Si, with a size of about 8 nm, occurs. This stage is characterized by high stable soft magnetic properties. With a further increase in the heat treatment temperature, a gradual deterioration of the soft magnetic properties and further structural transformation occur – structures of joint crystalline phases from two crystalline phases α-Co and Co2Si are formed in the amorphous matrix, and crystallization occurs with the alternation of these two phases. This leads to a significant redistribution of alloy components. As a result, an amorphous barrier layer is formed in the amorphous matrix near the surface of the growing two-phase substructures, enriched in chromium and silicon; this layer affects the growth of crystalline phases, slowing it down.

Failure of adhesive bonding unveiled by in-situ strain testing by high-resolution scanning transmission electron microscopy

The nano-scale failure behaviors of adhesive interfaces were investigated through in-situ straining testing to observe real-time crack propagations under a scanning transmission electron microscope (STEM). Two different loading modes were applied to thin sections of adhesive interfaces: crack-opening mode applied to pre-cracks made at the interface and shear mode. The failure of aluminum alloy (Al6061) and a second-generation acrylic adhesive (SGA) was examined, enabling observation of the growth of crazing in the adhesive layer, which has a phase-separated structure, preceding the macroscopic failure of the interfaces. Furthermore, the failure of a direct joint of thermoplastic and Al was investigated, with a comparison made to that observed in the adhesive interface. The generation and propagation of cracks near the interface, attributed to the adhesive's phase separation, contribute to the toughness of the adhesive interface. Both the direction of stress acting on the interface and the interface's strength influence the initiation and growth of cracks throughout the adhesive layer.

Improved electrochemical performance of hydrothermally synthesized Zn-Ni-S/rGO nanocomposite as an electrode for supercapacitor application

This present work reports on the hydrothermal synthesis of zinc-nickel sulfide with reduced graphene oxide (Zn-Ni-S/rGO) nanocomposite for supercapacitor applications. The synthesized samples are evaluated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), and high-resolution scanning transmission electron microscopy (HR-TEM), which are employed to examine the structure, morphology, and chemical composition of the Zn-Ni-S/rGO nanocomposite. The XRD results indicates formation of high crystalline Zn-Ni-S/ rGO nanocomposites. FE-SEM equipped with an EDX spectrum, illustrates a spherical morphology of Zn-Ni-S combined with a thin layer of rGO in the form of composite nature. Furthermore, elemental composition of Zinc, Nickel, Sulfur and Carbon presence in the EDS spectra further supports the formation of Zn-Ni-S/rGO nanocomposite. The electrochemcial properties of ZnS and Zn-Ni-S/rGO nanocomposite are studied through cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. High specific capacitance of 284 F/g is obtained at 11 mA g−1 current density. The Zn-Ni-S/rGO nanocomposite demonstrates high capacitance retention of 96 % over 3,000 cycles. The potential application of the Zn-Ni-S/rGO nanocomposite as an efficient electrode material for pseudocapacitors is supported by its favourable performance.