Electron Energy Loss Research Articles

Unveiling the Mechanism in Nickel Loss During the Neutralization of Pregnant Acid Leach Solution by Various Alkaline Chemicals Using Electron Imaging, X-Ray Diffraction, and Electron Energy Loss Spectroscopy Analyses

ABSTRACT Removal of iron and aluminum from nickel-bearing pregnant leach solution is imperative prior to recovering nickel. However, the mechanisms into the loss of both nickel and cobalt in precipitate products during the neutralization process remained unclear and debatable. In this study, the precipitation ratios of nickel, as well as other valuable metals in iron precipitate products, were investigated by examining bulk and surface properties of iron precipitates using X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and electron energy loss spectroscopy. Amorphous ferrihydrite was identified as the major phase for iron precipitates. Over 99% precipitation ratio for iron and aluminum was achieved at pH 3. The loss of nickel in iron precipitates was strongly dependent on solution pHs, and the losses of nickel were found to be 3%, 8%, and 28% at pHs of 3, 4, and 5, respectively. The type of alkaline chemicals impacted the mineralogical composition of iron precipitate products and loss of valuable metals but had a minor impact on iron precipitation ratio. This work revealed three major mechanisms for the loss of nickel and cobalt during iron precipitation process: (1) entrainment of nickel-bearing PLS in filtered products, (2) surface adsorption on iron precipitates, and (3) lattice incorporation of nickel in iron precipitates. Additionally, the result of desorption experiments by H+ and Na+ ions showed that approximately 55–85% of lost nickel was incorporated within the lattice structure of iron precipitates, while the degree of nickel incorporation depends on the type of neutralizing reagents, precipitation conditions, and washing media.

Experimental evidence of magnetism in a 2D electron gas at the CoO/Co3O4 interface by employing EMCD

In the present study we investigate the CoO/Co3O4 interface in order to determine its intriguing magnetic behavior, which can be utilized for tailoring magnetic properties, enabling spin transport, enhancing magnetic coupling, tuning device functionalities, and realizing miniaturized magnetic devices for various technological applications. We decipher the magnetic properties of the CoO/Co3O4 interface from first principles calculations using Wien2k and probe them experimentally by employing electron energy-loss magnetic chiral dichroism (EMCD), which is an electron-energy loss spectrometry (EELS) based technique in the transmission electron microscope (TEM). Both, theory and experiment, are in perfect agreement and result in a ferromagnetic 2D-electron gas of 5Å thickness directly at the interface.

Formation of uranium nitride nanoparticles via mechanical alloying of uranium-molybdenum alloy fuels in gaseous nitrogen

Uranium-molybdenum (U-Mo) alloys show promise as a nuclear fuel system due to their high thermal conductivity and fuel loading capability. However, U-Mo systems are susceptible to irradiation induced swelling ultimately affecting the cladding via mechanical and chemical interactions. To address these shortcomings, this research investigated the formation of uranium mononitride (UN) nanoparticles within a 90 wt% U/ 10 wt% Mo (U-10Mo) matrix to act as a prospective defect sink for fission products at nanometric hetero-interfaces. To promote the formation of UN, U-10Mo powders were mechanically alloyed under a high purity nitrogen atmosphere. Variations of the milling process investigated included media size, duration of milling, and number of times the milling jar was re-aerated with nitrogen gas. Characterization of the fuel microstructure was completed using light element analysis, X-ray diffraction, scanning and transmission-electron microscopy, electron energy loss spectroscopy, and atom probe tomography. UN nanoparticles measuring 1–5 nm in radius were observed in the U-Mo matrix as early as 1 h into the mechanical alloying process. Milling time in excess of 10 h was found to lead to deleterious effects induced by the stainless-steel milling media.

Synthesis of high conformalty Ti-Six-N films using (CH3)3CCl and SiH4; density functional theory simulation and film characterization

The step coverage of the atomic layer deposition (ALD) of Ti-N thin films was improved by the addition of (CH3)3CCl, and Si atoms were added during the Ti-N deposition to form a Ti-Six-N thin film. By ALD, four to eight cycles of the gas (CH3)3CCl/TiCl4/NH3 formed the Ti-N layer and, subsequently, one to two cycles of the gas SiH4/NH3 added Si atoms to formed the Ti-Six-N layer. The ALD process was repeated to form a thin film Ti-Six-N 150 Å (bilayer of (Ti-N) 80 Å + (Six-N) 70 Å) while adjusting the amounts of (CH3)3CCl and SiH4. The crystallinity of Ti-N was studied by X-ray diffraction (XRD), and its composition was studied using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The composition of the Ti-Six-N film was studied using electron energy loss spectroscopy and selected area electron diffraction, and its roughness was confirmed using atomic force microscopy. Transmission electron microscope was used to measures the thickness and composition of the Ti-Six-N film through location in a test pattern with an aspect ratio of 50:1. Step coverage improved to 99.9 % compared to conventional ALD Ti-N when using (CH3)3CCl. Additionally, (CH3)3CCl was more effective at lower temperatures (460 °C compared to 530 °C), and the effect of the (CH3)3CCl flow rate was saturated above 300 sccm.As the amount of (CH3)3CCl increased, the growth per cycle decreased from 0.29 Å/cycle to 0.15 Å/cycle. The addition of Si to the Ti-N film facilitated leakage gain by increasing the difference in the work function between the electrode and the capacitor, material but may have the side effect of pillar bending due to a decrease in crystallinity and hardness. We verified that the XRD (200)/(111) peak ratio decreased as the Si content increased. As a result, the optimal conditions for electrode Ti-Six-N were confirmed as follows: 300 sccm (CH3)3CCl Ti-N, SiH4 10 sccm Six-N combination.Furthermore, the Ti-Six-N layer can serve as the bottom electrode of a capacitor reduce the manufacturing process steps, and be a candidate for a solution for the electrode of the capacitor of a 5 nm node memory device.

Flux pinning dynamics in optimally proton irradiated REBCO coated conductors

Particle irradiation offers a route to incorporating additional flux pinning centres in high-temperature superconducting wires with minimal disruption to the pre-existing defect landscape, thereby further enhancing the critical current in a controllable fashion. This work is a comprehensive study of the fluence-dependence of proton irradiation using protons of two energies, 2.5 and 1.2 MeV, in enhancing the critical current performance in commercially available (Y,Dy)Ba2Cu3O7−δ coated conductors. A sequence of fluences covering the range from 1 × 1015 to 5 × 1016 protons cm−2 was used in the irradiation process to study the flux pinning in this material. The resulting samples were characterized using field angle-dependent transport critical current measurements over a range of temperatures from 20 K to 77.5 K and magnetic fields up to 8 T, thus covering the wide range of operating conditions. Optimisation of fluence for highest performance at each energy resulted in a similar level of isotropic critical current enhancement, a factor 2.6 improvement at 20 K and 8 T, but with a significant difference in the optimised fluence in each case. The lower energy 1.2 MeV protons produce this enhancement at a three-fold lower fluence compared to 2.5 MeV protons, a result of their higher electronic energy loss. The different samples are analysed within the framework of the maximum entropy model, helping to understand the vortex dynamics before and after irradiation.

Self-Modification of Defective TiO2 under Controlled H2/Ar Gas Environment and Dynamics of Photoinduced Surface Oxygen Vacancies.

In recent years, defective TiO2 has caught considerable research attention because of its potential to overcome the limits of low visible light absorption and fast charge recombination present in pristine TiO2 photocatalysts. Among the different synthesis conditions for defective TiO2, ambient pressure hydrogenation with the addition of Ar as inert gas for safety purposes has been established as an easy method to realize the process. Whether the Ar gas might still influence the resulting photocatalytic properties and defective surface layer remains an open question. Here, we reveal that the gas flow ratio between H2 and Ar has a crucial impact on the defective structure as well as the photocatalyic activity of TiO2. In particular, transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS) revealed a larger width of the defective surface layer when using a H2/Ar (50 %-50 %) gas mixture over pure H2. A possible reason could be the increase in dynamic viscosity of the gas mixture when Ar is added. Additionally, photoinduced enhanced Raman spectroscopy (PIERS) is implemented as a complementary approach to investigate the dynamics of the defective structures under ambient conditions which cannot be effortlessly realized by vacuum techniques like TEM.

Feld-induced modulation of two-dimensional electron gas at LaAlO3/SrTiO3 interface by polar distortion of LaAlO3

Since the discovery of two-dimensional electron gas at the LaAlO3/SrTiO3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO3/SrTiO3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO3.

Petrographic and chemical characterization and carbon and nitrogen isotopic compositions of cometary IDPs and their GEMS amorphous silicates

GEMS (glass with embedded metal and sulfides) are the dominant carrier of amorphous silicates in anhydrous interplanetary dust particles (IDPs) and one of the most suitable materials to study early solar system processes. Amorphous silicates in 105 GEMS from eight IDPs were analyzed regarding texture and chemical composition to reassess GEMS formation theories and genetic relationships to amorphous silicate material in meteorites. Petrography of bulk IDPs was investigated to understand GEMS’ relationships to other IDP components. Furthermore, carbon and nitrogen isotopic compositions were measured. Nearly all GEMS are aggregates of several subgrains with variable amount of nanophase inclusions and different Mg- and Si-contents, while single GEMS are rare. The subgrains within aggregates are typically surrounded by one or more carbon rims with high density. The chemical compositions of GEMS amorphous silicates are subsolar for all major element/Si ratios but exhibit wide heterogeneity. This is not influenced by silicon oil from the capturing process of IDPs as assumed before, as a penetration of the silicon oil is excluded by high resolution EELS (electron energy loss spectroscopy) areal density maps of silicon. Furthermore, low Fe-content in GEMS amorphous silicates shows that these are not altered by aqueous activity on the parent body as it is the case for amorphous silicate material in primitive meteorites. The subsolar element/Si ratios and the wide chemical heterogeneity point to a non-equilibrium fractional condensation origin either in the early solar nebula or in a circumstellar environment and are not in agreement with homogenization via sputtering in the ISM. The close association with carbon around GEMS subgrains and as double-rims around GEMS aggregates argue for a multi-step aggregation after formation of the smallest GEMS subgrains in the ISM or the early solar nebula. Carbon acting as matrix material connecting GEMS and other IDP components has lower areal density as seen from carbon EELS areal density maps and isotopic anomalies varying at the nanometer scale, pointing to different origins and processing of materials to varying extent or at changing temperatures.To balance GEMS’ subsolar element/Si ratios, a supersolar component in IDPs was assumed to account for the overall chondritic composition of bulk IDPs. Nevertheless, our bulk IDP analyses revealed subsolar, but variable, element/Si ratios for complete particles as well, depending on type and amount of mineral phases in each particle. Pyroxenes in the investigated particles can occur as elongated euhedral crystals, but are overall rare. The dominant crystalline fraction in the investigated IDP samples are equilibrated aggregates (EAs) that show the same chemical compositions as GEMS, indicating that the EAs are recrystallized GEMS grains and formed after GEMS formation as secondary phases.

Formation processes of iron-based layered hydroxide in acid mine drainage and its implications for in-situ arsenate immobilization: Insights and mechanisms

The immobilization of arsenate in transformed minerals depends on their states in acid mine drainage (AMD). In this study, an iron-based layer hydroxide mineral was derived from the transformation of ferrihydrite under co-existing Mg2+ ions in AMD. The immobilization behavior of arsenate on the mineralized LDHm and pre-prepared LDHad was distinguished. 99 % immobilization efficiency was achieved from the mineralized LDHm, maintaining stability without subsequent releases, across initial arsenate concentrations ranging from 10 to 60 mg/L. LDHm outperformed the pre-prepared LDHad, which was synthesized from AMD for arsenate adsorption. Electron energy loss spectroscopy line profiles revealed predominant incorporation of arsenate in the LDHm structure, supported by higher bulk As signals within LDHm. Density functional theory calculations indicated primary arsenate incorporation into LDHm, forming stable bonds with lower energy activation barriers. Importantly, LDHm exhibited a superior electron rearrangement configuration, resulting in enhanced electron state activity and affinity for arsenate. In contrast, arsenate adsorption predominantly occurred on the pre-prepared LDHad, with notable As signals detected particularly at the edges. Adsorption energy evaluation indicated arsenate preference for bonding to Fe3+ sites on LDHad. These findings provide important insights into the role of stable LDH-like minerals for long-term arsenate immobilization in the natural AMD attenuation processes.

Quantification of the sp3 content in Diamond-Like carbon Films: Effects of Ne plasma addition in Deep Oscillation Magnetron sputtering

Diamond-like carbon (DLC) films are a class of amorphous carbon materials with unique properties, including high hardness and wear resistance, making them attractive for aerospace and automotive applications. Recently, High Power Impulse Magnetron Sputtering (HiPIMS) has emerged as a new route for magnetron-sputtered hard DLC films. The authors have previously demonstrated that adding Ne to the plasma significantly improves the properties of DLC films deposited by Deep Oscillation Magnetron Sputtering (DOMS), a HiPIMS variant. In this study, the sp3 content evolution with DLC film thickness was measured by Electron Energy Loss Spectroscopy (EELS) and Near Edge X-ray Absorption Spectroscopy (NEXAFS). The sp3 content in the top section of the film deposited in Ar + Ne plasma is close to 40 % and remains constant across the film thickness. Conversely, in films deposited in pure Ar plasma, the sp3 content decreases from approximately 30 % to 18 % towards the surface. Ne addition increases the sp3 content by enhancing the carbon ion flux and counteracting the atomic shadowing effect. These findings provide novel insights into the role of Ne in reducing the atomic shadowing effect and improving the overall quality of DLC films, paving the way for their optimized industrial use.

Probing Correlation of Optical Emission and Defect Sites in Hexagonal Boron Nitride by High-Resolution STEM-EELS.

Optically bright emitters in hexagonal boron nitride (hBN) often acting as a source of a single-photon are mostly attributed to point-defect centers, featuring localized intra-bandgap electronic states. Although vacancies, anti-sites, and impurities have been proposed as candidates, the exact physical and chemical nature of most hBN single-photon emitters (SPEs) within the visible region are still up for debate. Combining site-specific high-angle annular dark-field imaging (HAADF) with electron energy loss spectroscopy (EELS), we resolve and identify a few carbon substitutions among neighboring hBN hexagons, all within the same sample region, from which typical defect emission is observed. Our experimental results are further supported by first-principles calculations, through which the stability and possible optical transitions of the proposed carbon-defect complex are assessed. The presented correlation between optical emission and defects provides valuable information toward the controlled creation of emitters in hBN, highlighting carbon complexes as another probable cause of its visible SPEs.

First-principles calculations to investigate effects of strains on structural, electronic, thermodynamic, optical and thermoelectric properties of NaAs3P5 alloy

Herein, the structural, optical, electronic and thermoelectric properties of the NaAs3P5 were investigated by Ab-initio calculations. The electronic results of NaAs3P5 showed that this compound has a metallic characteristic. The optical response of this compound has been studied using optical parameters such as complex dielectric function, refractive index, optical conductivity, electron energy loss, and absorption coefficient. This compound is an n-type material, as determined by thermoelectric experiments because it has a negative Seebeck coefficient when the strain is at 20 %. The highest value of the figure of merit (ZT) is about 0.021. Besides, the obtained value of PF is 7595.5 W−1.K−2.s−1 for 20 % of the strain. As the ZT trend grows, the alloy is being promoted as a potential contender for thermoelectric power production. Applying dilatation strain can improve the mechanical and thermodynamic stability of NaAs3P5 because many solid-state physical characteristics, such as heat capacity, thermal expansion coefficient, and entropy, are related to the Debye temperature.

Probing the Polarization of Low-Energy Excitations in 2D Materials from Atomic Crystals to Nanophotonic Arrays Using Momentum-Resolved Electron Energy Loss Spectroscopy.

Spectroscopies utilizing free electron beams as probes offer detailed information on the reciprocal-space excitations of 2D materials such as graphene and transition metal dichalcogenide monolayers. Yet, despite the attention paid to such quantum materials, less consideration has been given to the electron-beam characterization of 2D periodic nanostructures such as photonic crystals, metasurfaces, and plasmon arrays, which can exhibit the same lattice and excitation symmetries as their atomic analogues albeit at drastically different length, momentum, and energy scales. Because of their lack of covalent bonding and influence of retarded electromagnetic interactions, important physical distinctions arise that complicate interpretation of scattering signals. Here we present a fully-retarded theoretical framework for describing the inelastic scattering of wide-field electron beams from 2D materials and apply it to investigate the complementarity in sample excitation information gained in the measurement of a honeycomb plasmon array versus angle-resolved optical spectroscopy in comparison to single monolayer graphene.

Optical Absorption in Tilted Geometries as an Indirect Measurement of Longitudinal Plasma Waves in Layered Cuprates.

Electromagnetic waves propagating in a layered superconductor with arbitrary momentum, with respect to the main crystallographic directions, exhibit an unavoidable mixing between longitudinal and transverse degrees of freedom. Here we show that this basic physical mechanism explains the emergence of a well-defined absorption peak in the in-plane optical conductivity when light propagates at small tilting angles relative to the stacking direction in layered cuprates. More specifically, we show that this peak, often interpreted as a spurious leakage of the c-axis Josephson plasmon, is instead a signature of the true longitudinal plasma mode occurring at larger momenta. By combining a classical approach based on Maxwell's equations with a full quantum derivation of the plasma modes based on modeling the superconducting phase degrees of freedom, we provide an analytical expression for the absorption peak as a function of the tilting angle and light polarization. We suggest that an all-optical measurement in tilted geometry can be used as an alternative way to access plasma-wave dispersion, usually measured by means of large-momenta scattering techniques like resonant inelastic X-ray scattering (RIXS) or electron energy loss spectroscopy (EELS).

Microstructural and micromechanical characterization of Cr diffusion barrier in ATR irradiated U-10Zr metallic fuel

Chromium (Cr) has been recognized as a promising diffusion barrier candidate to mitigate the Fuel Cladding Chemical Interaction (FCCI) failure in metallic fuels for sodium-cooled fast reactor. This paper, for the first time, conducted an in-depth post-irradiation examination of the microstructure and composition evolution, and micromechanics of the Cr diffusion barrier in U-10Zr fuel/HT9 cladding irradiated in the Advanced Test Reactor (ATR) to 8.7% burnup at an averaged Peak Inner Cladding Temperature of 540–550 °C. Transmission Electron Microscope (TEM) characterization confirmed the preferential intergranular diffusion of Zr and U in the Cr diffusion barrier, suggesting that grain boundaries served as fast path for the diffusion of Zr and U into the Cr diffusion barrier. The interaction zone is dominated by nano crystalline α-ZrCr2 Laves phase. Despite the interaction, there is no microcracks being observed in the preserved Cr diffusion barrier and HT9 cladding, serving as a good barrier to mitigate FCCI under the studied in-reactor irradiation conditions. High density cavities in uniform distribution are observed inside Cr grains, nano particles contains Cr, Mn, and O are confirmed by Electron Energy Loss Spectroscopy (EELS) analysis. However, it is unclear whether the cavities will become an issue to the barrier integrity at higher burnup. In-situ Scanning Electron Microscopy (SEM) micro-tensile testing uncovered mechanical softening in the HT9 cladding nearing the Cr diffusion barrier, possibly due to the coarsening of lath structure and carbides precipitates.

Electron backscattering coefficients for Cr, Co, and Pd solids: A Monte Carlo simulation study

We have calculated electron backscattering coefficients, η(Ep), at primary electron energies Ep of 0.1–100 keV for three elemental and intermediate atomic number solids, Cr, Co and Pd, with an up-to-date Monte Carlo simulation model. A relativistic dielectric functional approach is adopted for the calculation of the electron inelastic cross section, where several different datasets of optical energy loss function (ELF) are adopted. The calculated backscattering coefficient is found to be substantially affected by the ELF, where the influence can be seen to follow the f- and ps-sum rules and the resultant energy dependence of electron inelastic mean free path. To understand the uncertainties involved in a comparison with experimental data both the theoretical uncertainty due to the elastic cross-section model and the experimental systematic error for the contaminated surfaces are investigated. A total of 192 different scattering potentials are employed for the calculation of Mott's electron elastic cross section and this theoretical uncertainty is confirmed to be small. On the other hand, the simulation of contaminated Co and Pd surfaces with several carbonaceous atomic layers can well explain the experimental data. The present results indicate that accurate backscattering coefficient data should be either measured from fully cleaned surfaces or obtained from modern Monte Carlo theoretical calculations involving reliable optical constants data. With the recent progress in the accurate measurement of optical constants by reflection electron energy loss spectroscopy technique, constructing a reliable theoretical database of electron backscattering coefficients for clean surfaces of elemental solids is highly hopeful.

Fabrication of monolayer h-BN/LaB6 heterostructure thin film with low work function and high chemical stability

To expand the applications of low work function materials, high chemical stability is necessary to prevent the surface from unfavorable reactions. We developed a 20-nm-thick lanthanum hexaboride (LaB6) thin film covered by a monolayer hexagonal boron nitride (h-BN), which exhibits not only low work function but also high chemical stability. Results demonstrated that the h-BN/LaB6 heterostructure can be formed by vacuum annealing a nitrogen-doped LaB6 thin film. The formation process was investigated using Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (HREELS), and X-ray absorption near edge structure (XANES) spectroscopy. We have elucidated that the doped nitrogen atoms and boron atoms in the film thermally diffuse into the surface during annealing, thereby forming the monolayer h-BN on the surface. Work function was measured using scanning tunneling microscopy (STM). From a practical perspective, chemical stability was evaluated with a heating temperature necessary for restoring the low work function state after air exposure. The work function was comparable to that of the clean LaB6(100) surface. Moreover, it recovered at a much lower temperature than the cleaning temperature of the LaB6(100) surface. We anticipate that this material development will facilitate implementation of the low work function material.

Differences in coupling between nuclear and electronic energy losses in UO2 with irradiation temperature: An in situ TEM study

To investigate the coupling between nuclear and electronic energy losses in UO2, we irradiated thin foils with 0.39 MeV Xe and/or 6 MeV Si ions at 93 K using single or simultaneous dual beam ion irradiations. The evolution of perfect dislocation loops was characterized by in situ transmission electron microscopy (TEM). Additional ex situ TEM characterizations at room temperature revealed for the first time in UO2 the presence of faulted Frank loops too small to be measured during in situ experiments and conventional bright field kinematical imaging conditions.For the single Xe irradiation, which favor dominant ballistic energy losses, we observed a continuous nucleation of small perfect dislocation loops, which increase in size for our last fluences by growing through mainly coalescence effect. Both the single Si and dual Xe & Si irradiations showed a coupling between nuclear and electronic energy losses, resulting in a significant loop density increase and a tangled line network formation, respectively. These phenomena occur at lower dpa levels, compared to the single Xe irradiation, likely resulting from the thermal spike effect of Si ions. The present results were compared to our previous work at 293 K to investigate the role of irradiation temperature on the energy losses coupling. For the Xe irradiation, the density increases and the loops are smaller at 93 K compared to 293 K, resulting from the uranium interstitials mobility being prevented or allowed. For the Si irradiation, the dislocation evolution kinetics are similar at both temperatures. The electronic excitations effect seems greater than the irradiation temperature effect in this temperature range. For the Xe & Si irradiation, the loop kinetics change resulting in a tangled line network formation is faster and thus the loop transformation into lines occurs at lower dpa levels at 93 K compared to 293 K. It appears that the irradiation temperature affecting the mobility of some small point defects reduces the electronic excitation effect in this case.

Engineering a Hierarchy of Disorder: A New Route to Synthesize High-Performance 3D Nanoporous All-Carbon Materials*.

A new nanoporous amorphous carbon (NAC) structure that achieves both ultrahigh strength and high electrical conductivity, which are usually incompatible in porous materials is reported. By using modified spark plasma sintering, three amorphous carbon phases with different atomic bonding configurations are created. The composite consisted of an amorphous sp2-carbon matrix mixed with amorphous sp3-carbon and amorphous graphitic motif. NAC structure has an isotropic electrical conductivity of up to 12000Sm-1, Young's modulus of up to ≈5GPa, and Vickers hardness of over 900MPa. These properties are superior to those of existing conductive nanoporous materials. Direct investigation of the multiscale structure of this material through transmission electron microscopy, electron energy loss spectroscopy, and machine learning-based electron tomography revealed that the origin of the remarkable material properties is the well-organized sp2/sp3 amorphous carbon phases with a core-shell-like architecture, where the sp3-rich carbon forms a resilient core surrounded by a conductive sp2-rich layer. This research not only introduces novel materials with exceptional properties but also opens new opportunities for exploring amorphous structures and designing high-performance materials.

Single atoms and metal nanoclusters anchored to graphene vacancies

Fabricating dispersed single atoms and size-controlled metal nanoclusters remains a difficult challenge due to sintering. Here, we demonstrate that atoms and clusters can be immobilized using atomically clean defect-engineered graphene as the matrix. The graphene is first cleaned of surface contamination with laser heating, after which low-energy Ar irradiation is used to create spatially well-separated vacancies into it. Metal atoms are then evaporated either via thermal or ebeam evaporation onto graphene, where they diffuse until being trapped into a vacancy. The density of embedded structures can be controlled through irradiation dose, and the size of the structures through evaporation time. The resulting structures are confirmed through atomic-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. We demonstrate here incorporation of Al, Ti, Fe, Ag and Au single atoms or nanoclusters, but the method should work equally well for other elements.