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The concept of electronic orbitals has enabled the understanding of a wide range of physical and chemical properties of solids through the definition of, for example, chemical bonding between atoms. In the transmission electron microscope, which is one of the most used and powerful analytical tools for high‐spatial‐resolution analysis of solids, the accessible quantity is the local distribution of electronic states. However, the interpretation of electronic state maps at atomic resolution in terms of electronic orbitals is far from obvious, not always possible, and often remains a major hurdle preventing a better understanding of the properties of the system of interest. In this review, the current state of the art of the experimental aspects for electronic state mapping and its interpretation as electronic orbitals is presented, considering approaches that rely on elastic and inelastic scattering, in real and reciprocal spaces. This work goes beyond resolving spectral variations between adjacent atomic columns, as it aims at providing deeper information about, for example, the spatial or momentum distributions of the states involved. The advantages and disadvantages of existing experimental approaches are discussed, while the challenges to overcome and future perspectives are explored in an effort to establish the current state of knowledge in this field. The aims of this review are also to foster the interest of the scientific community and to trigger a global effort to further enhance the current analytical capabilities of transmission electron microscopy for chemical bonding and electronic structure analysis. [ABSTRACT FROM AUTHOR]

In situ Electron Energy Loss Spectroscopy (EELS) combined with Transmission Electron Microscopy (TEM) has traditionally been pivotal for understanding how material processing choices affect local structure and composition. However, the ability to monitor and respond to ultrafast transient changes, now achievable with EELS and TEM, necessitates innovative analytical frameworks. Here, we introduce a machine learning (ML) framework tailored for the real-time assessment and characterization of in operando EELS Spectrum Images (EELS-SI). We focus on 2D MXenes as the sample material system, specifically targeting the understanding and control of their atomic-scale structural transformations that critically influence their electronic and optical properties. This approach requires fewer labeled training data points than typical deep learning classification methods. By integrating computationally generated structures of MXenes and experimental datasets into a unified latent space using Variational Autoencoders (VAE) in a unique training method, our framework accurately predicts structural evolutions at latencies pertinent to closed-loop processing within the TEM. This study presents a critical advancement in enabling automated, on-the-fly synthesis and characterization, significantly enhancing capabilities for materials discovery and the precision engineering of functional materials at the atomic scale. [ABSTRACT FROM AUTHOR]

Abstract In situ Electron Energy Loss Spectroscopy (EELS) combined with Transmission Electron Microscopy (TEM) has traditionally been pivotal for understanding how material processing choices affect local structure and composition. However, the ability to monitor and respond to ultrafast transient changes, now achievable with EELS and TEM, necessitates innovative analytical frameworks. Here, we introduce a machine learning (ML) framework tailored for the real-time assessment and characterization of in operando EELS Spectrum Images (EELS-SI). We focus on 2D MXenes as the sample material system, specifically targeting the understanding and control of their atomic-scale structural transformations that critically influence their electronic and optical properties. This approach requires fewer labeled training data points than typical deep learning classification methods. By integrating computationally generated structures of MXenes and experimental datasets into a unified latent space using Variational Autoencoders (VAE) in a unique training method, our framework accurately predicts structural evolutions at latencies pertinent to closed-loop processing within the TEM. This study presents a critical advancement in enabling automated, on-the-fly synthesis and characterization, significantly enhancing capabilities for materials discovery and the precision engineering of functional materials at the atomic scale.

The precise mechanism governing the reversible semiconductor‐to‐metal transition (SMT) in V2O5 remains elusive, yet its investigation is of paramount importance due to the remarkable potential of V2O5 as a versatile "smart" material in advancing optoelectronics, plasmonics, and photonics. In this study, distinctive experimental insights into the SMT occurring in amorphous V2O5 through the application of highly sensitive, temperature‐dependent, in situ analyses on a V2O5 thin film deposited on soda‐lime glass are presented. The ellipsometry measurements reveal that the complete SMT occurs at ≈340 °C. Remarkably, the refractive index and extinction coefficients exhibit reversible characteristics across visible and near‐infrared wavelengths, underscoring the switch‐like behavior inherent to V2O5. The findings obtained from ellipsometry are substantiated by calorimetry and in situ secondary ion mass spectrometry analyses. In situ electron microscopy observations unveil a separation of oxidation states within V2O5 at 320 °C, despite the thin film retaining its amorphous state. The comprehensive experimental investigations effectively demonstrate that alterations in electronic state can trigger the SMT in amorphous V2O5. It is revealed for the first time that the SMT in V2O5 is solely contingent upon electronic state changes, independent of structural transitions, and importantly, it is a reversible transformation within the amorphous state itself. [ABSTRACT FROM AUTHOR]

This study estimated the amount of oxygen deficiency in SrTiO 3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L 23 -edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO 3−δ , which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO 3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO 3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO 3 , which is similar to the results in thermally sintered SrTiO 3 polycrystals. [ABSTRACT FROM AUTHOR]

All-solid-state batteries (ASSBs) with solid electrolytes are expected to be promising energy storage devices. However, the large charge-transfer resistance at the electrode/electrode homo-interface and/or electrode/solid-electrolyte hetero-interface needs to be solved for practical applications. To overcome this problem, it is necessary to understand how the ions are transferred during battery operation. Here, we used operando electron energy-loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM) to directly visualize the Li-ion movement in the cathode materials in bulk-type ASSBs. We show that the ion movement is strongly related to the crystal orientations of the cathode particles, and that Li-ions move even in the open-circuit conditions of the batteries. [ABSTRACT FROM AUTHOR]

Using electron energy-loss spectroscopy in the scanning transmission electron microscope (STEM-EELS), the decomposition of a sulfide solid electrolyte (SSE) around a LiNbO3-coated Li(Ni0.8Co0.1Mn0.1)O2 cathode active material (CAM) in the charge/discharge cycle was clarified. In the initial cycle stage, Li3PS4 was directly assigned from an analysis of the S/P ratio by energy dispersive X-ray spectroscopy (EDX) and the EEL spectra of the P L-edge and S L-edge. In the cycled sample, an inhomogeneous decomposition was observed by the detection of POx species in the SSE around the CAM in the range of over approximately 100 nm. The Li K-edges observed in the initial cell and degraded cell showed that spectral changes had occurred, corresponding to the variation of the P L-edges.

LiNi1/3Mn1/3Co1/3O2 (NMC‐111) is one of the most popular cathode materials in Li‐ion batteries. However, chemical and structural instabilities of the cathode/electrolyte interface at high charge cut‐off voltages cause capacity fading. Surface modifications using metal oxides are promising candidates to suppress capacity fading. Here a systematic study on the degradation mechanism of an uncoated NMC‐111 powder electrode is presented. Moreover, the effect of an Al‐doped ZnO (Al:ZnO) coating layer on the structural and chemical stabilities of NMC‐111 electrode cycled at high charge cut‐off voltages is analyzed using X‐ray photoelectron spectroscopy, scanning electron microscopy and analytical transmission electron microscopy as well as electrochemical testing. The coating is applied to commercial NMC‐111 powder using a microwave‐assisted sol‐gel synthesis method. In the case of uncoated NMC‐111 electrodes, pitting corrosion due to hydrofluoric acid attacking the electrode surface, cation mixing, and an irreversible phase transformation from a trigonal layered to a rock‐salt phase occurs, causing capacity fading. While, in the case of Al:ZnO – coated NMC‐111 electrodes, pitting corrosion, cation mixing, and the irreversible phase transformation are mitigated. Therefore, the capacity retention and rate capability are improved as the coating layer protects the electrode surface from the direct electrolyte exposure. [ABSTRACT FROM AUTHOR]

This study presents an in‐depth investigation of the electronic properties and bandgap energy distribution in 1D molybdenum disulfide (1D‐MoS2) nanostructures. Through a combination of high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and electron energy‐loss spectroscopy (EELS), it reveals significant differences between 1D‐MoS2 nanostructures and their 2D counterparts, shedding light on their localized exciton behavior and their bandgap energy modulation within the nanostructures. Excitonic peaks at around 2 and 3 eV appear localized at the ends or along the sides of the 1D‐MoS2 nanostructures, while the plasmonic resonance at 8.3 eV retains its inner‐region localization. It demonstrates the spatial dependence of the bandgap energy, with the central region exhibiting a bandgap of approximately 1.2 eV, consistent with bulk MoS2, while regions characterized by curvature‐induced local strain fields exhibit instead a noticeable reduction. The findings provide valuable insights into the intricate relationship between excitonic behavior and bandgap sensitivity in 1D‐MoS2 nanostructures, streamlining the design and optimization of nanophotonic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract LiNi1/3Mn1/3Co1/3O2 (NMC‐111) is one of the most popular cathode materials in Li‐ion batteries. However, chemical and structural instabilities of the cathode/electrolyte interface at high charge cut‐off voltages cause capacity fading. Surface modifications using metal oxides are promising candidates to suppress capacity fading. Here a systematic study on the degradation mechanism of an uncoated NMC‐111 powder electrode is presented. Moreover, the effect of an Al‐doped ZnO (Al:ZnO) coating layer on the structural and chemical stabilities of NMC‐111 electrode cycled at high charge cut‐off voltages is analyzed using X‐ray photoelectron spectroscopy, scanning electron microscopy and analytical transmission electron microscopy as well as electrochemical testing. The coating is applied to commercial NMC‐111 powder using a microwave‐assisted sol‐gel synthesis method. In the case of uncoated NMC‐111 electrodes, pitting corrosion due to hydrofluoric acid attacking the electrode surface, cation mixing, and an irreversible phase transformation from a trigonal layered to a rock‐salt phase occurs, causing capacity fading. While, in the case of Al:ZnO – coated NMC‐111 electrodes, pitting corrosion, cation mixing, and the irreversible phase transformation are mitigated. Therefore, the capacity retention and rate capability are improved as the coating layer protects the electrode surface from the direct electrolyte exposure.

Dilute MgZnYalloy with a mille-feuille structure (MFS) exhibits a mechanical strength comparable to MgZnYalloy with long period stacking/ordered (LPSO) structure through kink deformation. In order to deepen understanding the thermal stability of the MFS-type Mg alloys, it is required to clarify the solute cluster structures composed of Zn and Y in solute enriched stacking faults (SESFs). In this study, electron energy-loss and energy dispersive X-ray spectroscopy based on scanning transmission electron microscopy (STEM-EELS/EDS) were conducted to investigate the electronic structure and composition of Zn and Y in the SESFs of the MFS-Mg alloy. Zn-L2,3 spectra indicated that the valence charges of Zn in the dilute Mg alloy were different from that of the LPSO-type MgZnYalloy. In addition, the intensity ratio of L3/L2 in Y-L2,3 spectrum of the dilute MFS-Mg alloy was larger than that of the LPSO-Mg alloy, reflecting the electron occupancies of 4d3/2 and 4d5/2 orbitals of Y atoms were different from those of the LPSO-Mg alloys. STEM-EELS analysis of the SESF composition in the dilute MFS-Mg alloy indicated that the Zn/Y ratio should be lower than that of the LPSO-Mg alloy, which was confirmed also by STEM-EDS measurements. These results indicate that the cluster structure in the SESFs of the dilute MFS-Mg alloy should be different from the ideal Zn6Y8 cluster in the LPSOtype MgZnY alloys. [ABSTRACT FROM AUTHOR]

Understanding the chemical and charge transport properties of grain boundaries (GBs) with high point defect concentrations (beyond the dilute solution limit) in polycrystalline materials is critical for developing ion-conducting solids for electrochemical energy conversion and storage. Elucidation and optimization of GBs are hindered by large variations in atomic structure, composition, and chemistry within nanometers or Ångstroms of the GB interface, which limits a fundamental understanding of electrical transport across and along GBs. Here we employ a novel correlated approach that is generally applicable to polycrystalline materials whose properties are affected by GB composition or chemistry. We demonstrate the connection between the nanoscopic chemical and transport properties of individual boundaries and the macroscopic ionic conductivity in oxygen-conducting Pr0.04Gd0.11Ce0.85O2-δ. The key finding is that GBs with higher solute concentration have lower activation energy for cross-GB ion conduction through a polycrystalline conductor. The resultant semiempirical framework presented here provides a tool for understanding, designing and optimizing polycrystalline ionic conductors.

Morphological control at the nanoscale paves the way to fabricate nanostructures with desired plasmonic properties. In this study, we discuss the nanoengineering of plasmon resonances in 1D hollow nanostructures of two different AuAg nanotubes, including completely hollow nanotubes and hybrid nanotubes with solid Ag and hollow AuAg segments. Spatially resolved plasmon mapping by electron energy loss spectroscopy (EELS) revealed the presence of high order resonator-like modes and localized surface plasmon resonance (LSPR) modes in both nanotubes. The experimental findings accurately correlated with the boundary element method (BEM) simulations. Both experiments and simulations revealed that the plasmon resonances are intensely present inside the nanotubes due to plasmon hybridization. Based on the experimental and simulated results, we show that the novel hybrid AuAg nanotubes possess two significant coexisting features: (i) LSPRs are distinctively generated from the hollow and solid parts of the hybrid AuAg nanotube, which creates a way to control a broad range of plasmon resonances with one single nanostructure, and (ii) the periodicity of the high-order modes are disrupted due to the plasmon hybridization by the interaction of solid and hollow parts, resulting in an asymmetrical plasmon distribution in 1D nanostructures. The asymmetry could be modulated/engineered to control the coded plasmonic nanotubes. [ABSTRACT FROM AUTHOR]

CeO2 and CeO2‐based materials are widely used as catalysts and catalyst supports for a variety of chemical reactions. The ability to form oxygen vacancies plays an important role in the catalytic activities in these materials. Therefore, revealing the reduction mechanism for CeO2 is crucial to understanding the catalytic activities. In this study, shape‐controlled CeO2 nanoparticles are fabricated and the distribution of surface oxygen vacancies on the (100) and (111) surfaces is systematically studied using scanning transmission electron microscopy and electron energy‐loss spectroscopy and the response to H2 reduction treatment. It is successfully demonstrated that both catalytic activities and the ability to form oxygen vacancies are strongly dependent on the type of lattice planes. Moreover, the present results provide important insights into the reduction mechanism for CeO2, in which bulk oxygen instead of the widely believed surface capping oxygen makes no small contribution to the initial reduction step. [ABSTRACT FROM AUTHOR]

Abstract CeO2 and CeO2‐based materials are widely used as catalysts and catalyst supports for a variety of chemical reactions. The ability to form oxygen vacancies plays an important role in the catalytic activities in these materials. Therefore, revealing the reduction mechanism for CeO2 is crucial to understanding the catalytic activities. In this study, shape‐controlled CeO2 nanoparticles are fabricated and the distribution of surface oxygen vacancies on the (100) and (111) surfaces is systematically studied using scanning transmission electron microscopy and electron energy‐loss spectroscopy and the response to H2 reduction treatment. It is successfully demonstrated that both catalytic activities and the ability to form oxygen vacancies are strongly dependent on the type of lattice planes. Moreover, the present results provide important insights into the reduction mechanism for CeO2, in which bulk oxygen instead of the widely believed surface capping oxygen makes no small contribution to the initial reduction step.

Optical polaritons appear when a material excitation strongly couples to an optical mode. Such strong coupling between molecular transitions and optical cavities results in far‐reaching opportunities in modifying fundamental properties of chemical matter. More recently an exciting prospect of self‐coupled polaritons has emerged by matter sustaining the optical mode with its geometry. Here, it is shown how strong coupling of the interband transition and surface plasmons can be engineered in nickel at the nanoscale to realize self‐coupled plasmon–interband polaritons inside metals. Using electron energy‐loss spectroscopy, it is demonstrated that in nickel thin films and nanoantennas the propagation and radiation losses result in a broadening of the plasmon linewidth and a transition from strong to weak coupling. Further, higher‐order plasmon resonances couple to the interband transition, and the multipolar‐coupled states acquire the field profile of the plasmon. The results provide a fundamental understanding of plasmon–interband coupling in metals and establish the base for the design of photocatalytic and magneto‐optical nanosystems. [ABSTRACT FROM AUTHOR]

We map the temperature distribution of suspended carbon nanotubes down to the 5-nm level inside a transmission electron microscope, by using electron energy-loss plasmon spectroscopy. The nanotubes are Joule heated in-situ, by individually contacting them using a biasing holder. The nanotubes can withstand current densities of over 5 × 107 A/cm2 and temperatures of over 2000 K without breaking. The temperature reaches its maximum around the nanoprobe contact, due to the comparatively large electrical resistance and small thermally-conductive area. The temperature remains high along the entire length of the CNTs, due to the excellent in-plane thermal conductivity (up to 2800 W/m/K) of the graphitic lattice. These results verify the expected robustness of these structures and confirm them as ideal candidates for applications as interconnects under extremely high current densities and temperatures. [Display omitted] • Temperature of suspended Joule-heated CNTs is mapped with 5-nm resolution in a TEM. • CNTs can withstand over 2000 K, more than 1000 K higher than previously measured. • Hot-spot near smaller electrical contact due to high resistance and low heat transfer. • High temperature along the entire CNT length because of high thermal conductivity. [ABSTRACT FROM AUTHOR]

In this work, we report the fabrication and spectroscopic characterization of subwavelength aluminum nanocavitiesâ€"consisting of hexamer or tetramer clusters of sub 10 nm width Al nanorodsâ€"with tunable localized surface plasmon resonance (LSPR) energies on suspended SiN x membranes. Here the volume plasmon (VP) and LSPR modes of lithographically-fabricated Al nanocavities are revealed by low-loss electron energy-loss spectroscopy (EELS) in an aberration corrected scanning transmission electron microscope (STEM). We show that the existence of grain boundaries (GBs) in these nanocavities results in shifts in the VP energy and a reduction in the VP lifetime. We map the VP energy and lifetime across GBs and we observe a decrease in VP energy and lifetime at GBs that is consistent with a reduction in free carrier density and increased plasmon scattering at these locations. Dipolar LSPR modes resonant in the UV and blue regions of the electromagnetic spectrum as well as higher-energy optically dark quadrupolar and hexapolar LSPR modes are also observed and mapped by STEM and EELS. All LSPR modes are confirmed via electromagnetic simulations based on the boundary element method. Both tetramer and hexamer structures support the excitation of dipolar bright and dipolar dark modes. Finally, we find that asymmetries in fabricated nanorod hexamer and tetramer nanocavities result in a mode mixing leading to a shift in dipolar dark LSPR modes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Local valence analysis was performed by electron energy-loss spectroscopy. • Solidification cellular microstructures were visualized due to solute segregation. • No obvious changes were observed in the energy-loss near-edge structures of Cr and Fe. • Segregation is unlikely to affect the corrosion resistance of LPBF 316L. Ultra-rapid cooling of laser powder bed fusion (LPBF) generates a cellular solidification microstructure with submicron-sized periodicity accompanied by non-negligible segregation. In 316L austenitic stainless steel, an important corrosion-resistant alloy, the effect of segregation, particularly variations in Cr concentration, on the corrosion resistance of the LPBF product is unknown. Local valence analysis of the LPBF-produced 316L by electron energy-loss spectroscopy revealed no obvious changes in the energy-loss near-edge structures of Cr and Fe measured within the solidification cellular microstructure, at the cell boundary, or at the melt-pool boundary. This result indicates that solidification segregation in the LPBF-produced 316L is unlikely to affect the corrosion resistance of the material. [ABSTRACT FROM AUTHOR]

A thorough investigation of the helium (He) bubble growth mechanism in metals is of crucial importance in proposing alloy design criteria to improve the radiation resistance of nuclear structure materials and the He-retaining ability of tritium storage alloys. In this study, He-containing alloy thin films of ZrCo, as well as TiZrHfMo 2 and TiZrHfNb 2 multi-principal element alloys (MPEAs) were prepared by magnetron sputtering under a working gas mixture of He and Ar. The He-retaining ability of Zr-based alloys with different composition complexities was investigated by the advanced techniques of electron-energy loss spectrum (EELS) and in-situ heating in a transmission electron microscopy (TEM). The effects of composition complexity, He/Ar flow ratio and in-situ heating temperature on the He bubble size, He volume density and average pressure were systematically analysed. The results show that the increase of the composition complexity inhibits the He atom diffusivity and induces a decrease in the average size of the He bubbles in the alloy, which is beneficial to enhancing the He-retaining ability of the alloy. The potentially higher mechanical strength of MPEAs might also contribute to a stronger strain force resisting He bubble growth in the severely distorted lattice and accommodating the He bubble with higher bubble pressure. Increase of the composition complexity would inhibit the He atom diffusivity and induce the decrease of the average size of the He bubbles in the alloy, which is beneficial to enhancing the He retaining ability of the alloy. [Display omitted] • The method to rapid evaluation He retaining ability of He containing film is improved. • A strategy for Tritium storage candidate material in MEPs is summarized. • The He retention properties/mechanism on MEPs were studied by EELS. • The He bubbles size in ZrCo/MPEAs at different He flow rates and temperature was compared. • Increase the composition complexity of alloy can improve the alloy's He retention ability. [ABSTRACT FROM AUTHOR]

A central mystery in high-temperature superconductivity is the origin of the so-called strange metal (i.e., the anomalous conductor from which superconductivity emerges at low temperature). Measuring the dynamic charge response of the copper oxides, [Formula: see text], would directly reveal the collective properties of the strange metal, but it has never been possible to measure this quantity with millielectronvolt resolution. Here, we present a measurement of [Formula: see text] for a cuprate, optimally doped Bi2.1Sr1.9CaCu2O8+x (Tc = 91 K), using momentum-resolved inelastic electron scattering. In the medium energy range 0.1-2 eV relevant to the strange metal, the spectra are dominated by a featureless, temperature- and momentum-independent continuum persisting to the electronvolt energy scale. This continuum displays a simple power-law form, exhibiting q2 behavior at low energy and q2/ω2 behavior at high energy. Measurements of an overdoped crystal (Tc = 50 K) showed the emergence of a gap-like feature at low temperature, indicating deviation from power law form outside the strange-metal regime. Our study suggests the strange metal exhibits a new type of charge dynamics in which excitations are local to such a degree that space and time axes are decoupled.

Controlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. Access to the ultraviolet requires materials with a high refractive index and wide band gap energy. Here, the authors systematically search for such materials by computing the frequency‐dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their scattering properties using Mie theory. This analysis reveals several interesting candidate materials among which boron phosphide (BP) appears most promising. Then BP nanoparticles are prepared and it is demonstrated that they support Mie resonances at visible and ultraviolet wavelengths using both far‐field optical measurements and near‐field electron energy‐loss spectroscopy. A laser reshaping method is also presented to realize spherical Mie‐resonant BP nanoparticles. With a refractive index over three and low absorption losses in a broad spectral range spanning from the infrared to the near ultraviolet, BP is an appealing material for a broad range of applications in dielectric nanophotonics. [ABSTRACT FROM AUTHOR]

Electron energy‐loss spectroscopy (EELS) is widely applied combining with transmission electron microscopes with high spatial resolution, but its interpretation is a challenging task. One of the reasons is that the factors affecting EELS are very complicated. In this paper, we focus on the several factors involved in density functional theory (DFT) calculations. The sensitivity of calculated energy‐loss near‐edge structure (ELNES) to spin order, pressure and on‐site Coulomb energy U has been discussed. Since EELS technique detects the local environment of atoms, the influence of spin order cannot be ignored. The chemical shifts and peak intensity of ELNES are also closely related to corresponding pressure. The correlation effects are very important for transition metal compounds and play a key role in EELS simulations. An overview of the effects of these factors on the ELNES is presented with the help of Wien2k code. The antiferromagnetic order results in the decreasing of intensities of related peaks and the moving of the peaks to high energy loss. The decreasing of lattice parameters causes the ELNES peaks to shift to high energy loss, and the peak shifts at the higher energy loss are more significant. The increase of correlation effect leads to the ELNES peaks to shift to high energy loss accompanied by the increase of the relative intensity of the peaks which locate at higher energy loss. Our work helps to understand how these factors affect EELS and to explain and predict the experimental EELS spectra. Through the discussion of these factors, we propose that some factors could not be ignored in EELS simulations. Lay description: Transmission electron microscope (TEM) is a powerful scientific instrument, which can be used for small size imaging. In recent decades, it has helped scientists to make important discoveries such as carbon nanotube and quasicrystal and has been widely used in materials science, condensed matter physics, structural biology and other fields. The principle of transmission electron microscope is similar to that of optical microscope, but its resolution is far superior to that of optical microscope. Compared with the resolution of optical microscope about 300 nm, the resolution of transmission electron microscope can reach 0.039 nm at present. In addition to excellent spatial resolution, transmission electron microscope has many functions such as structural analysis, elemental composition analysis and electronic structure analysis. TEM can be also used to carry out in situ observation and time resolution observation. Because of its several advantages mentioned above, transmission electron microscopy attracts much attention since its birth in the early 1930s. The early TEM was considered to be used only to magnify the observed object, but the electron energy‐loss spectroscopy (EELS) gives it the ability to determine the composition of the sample and analyse the electronic structure. EELS is widely applied combining with transmission electron microscopes with high spatial resolution, but its interpretation is a challenging task. One of the reasons is that the factors affecting EELS are very complicated. In this paper, we focus on several factors involved in density functional theory calculations. The sensitivity of calculated energy‐loss near‐edge structure to spin order, lattice compression and expansion, and on‐site Coulomb energy is discussed. Since EELS technique detects the local environment of atoms, the influence of spin order cannot be ignored. The chemical shift and peak intensity of EELS are also closely related to corresponding lattice parameters. The correlation effects are very important for transition metal compounds and play a key role in EELS simulations. Our work helps to understand how these factors affect EELS and to explain and predict the experimental EELS spectra. Through the discussion on these factors, we provide a useful guidance for more precise EELS simulations. [ABSTRACT FROM AUTHOR]

As advances in computing technology increase demand for efficient data storage solutions, spintronic magnetic tunnel junction (MTJ)-based magnetic random-access memory (MRAM) devices emerge as promising alternatives to traditional charge-based memory devices. Successful applications of such spintronic devices necessitate understanding not only their ideal working principles but also their breakdown mechanisms. Employing an in situ electrical biasing system, atomic-resolution scanning transmission electron microscopy (STEM) reveals two distinct breakdown mechanisms. Soft breakdown occurs at relatively low electric currents due to electromigration, wherein restructuring of MTJ core layers forms ultrathin regions in the dielectric MgO layer and edge conducting paths, reducing device resistance. Complete breakdown occurs at relatively high electric currents due to a combination of joule heating and electromigration, melting MTJ component layers at temperatures below their bulk melting points. Time-resolved, atomic-scale STEM studies of functional devices provide insight into the evolution of structure and composition during device operation, serving as an innovative experimental approach for a wide variety of electronic devices.

Tunable high-refractive-index nanostructures are highly desired for realizing photonic devices with a compact footprint. By harnessing the large thermo-optic effect in silicon, we show reversible and wide thermal tuning of both the far- and near-fields of Mie resonances in isolated silicon nanospheres in the visible range. We perform in situ heating in a transmission electron microscope and electron energy-loss spectroscopy to show that the Mie resonances exhibit large spectral shifts upon heating. We leverage the spectral shifts to demonstrate near-field tuning between different Mie resonances. By combining electron energy-loss spectroscopy with energy-dispersive X-ray analysis, we show a reversible and stable operation of single silicon nanospheres up to a temperature of 1073 K. Our results demonstrate that thermal actuation offers dynamic near-field tuning of Mie resonances, which may open up applications in tunable nonlinear optics, Raman scattering, and light emission.

Atom location by channeling‐enhanced microanalysis (ALCHEMI) is a technique to obtain atom‐site‐specific information on constituent elements in a crystalline sample by acquiring a set of core electron transition spectra while tilting the incident beam. This methodology has been extended to a more quantitative technique called high‐angular‐resolution electron‐channeled X‐ray/electron spectroscopy (HARECXS/HARECES). There is a growing demand for analyzing smaller areas, such as small particles and multilayers. However, the minimum size of a region of interest probed by the present hardware‐assisted automated HARECXS/HARECES scheme is limited to no smaller than 1 µm, not only by the size of the electron probe and its convergence angle but also by the movement of the probe position associated with the beam tilt due to aberrations of the hardware system. Herein, QED (quantitative electron diffraction), a commercial plug‐in working on an integrated software platform, Gatan Microscopy Suite, was modified to enable the calibration and control of the probe to resolve the aforementioned limitation. In addition, a more sophisticated scheme for QED was developed to realize the ALCHEMI method for energy‐dispersive X‐ray spectroscopy, electron energy‐loss spectroscopy or both concurrently. This allows access to ALCHEMI and its derivative methods, automatically executed with any type of current PC‐controlled commercial microscope on an area as small as 30 nm, without modifying the hardware system. [ABSTRACT FROM AUTHOR]

We studied the structural transformations and atomic rearrangements in strontium titanate (SrTiO3) via nanosecond pulsed laser irradiation-induced melting and ultrafast quenching. Using scanning transmission electron microscopy, we determine that the laser-irradiated surface in single-crystalline SrTiO3 transforms into an amorphous phase with an interposing disordered crystalline region between amorphous and ordered phases. The formation of disordered phase is attributed to the rapid recrystallization of SrTiO3 from the melt phase constrained by an epitaxial relation with the pristine region, which eases up on the surface, leading to amorphous phase formation. With electron energy-loss spectroscopic analysis, we confirm the transformation of Ti+4 to Ti+3 due to oxygen vacancy formation as a result of laser irradiation. In the disordered region, the maximum transformation of Ti+4 is observed to be 16.2 ± 0.2%, whereas it is observed to be 20.2 ± 0.2% in the amorphous region. Finally, we deduce that the degree of the disorder increases from atomically disordered to amorphous transition in SrTiO3 under laser-irradiation. The signatures of short-range ordering remain similar, leading to a comparable fingerprint of electronic structure. With these results, this study addresses the gap in understanding the atomic and electronic structure modified by pulsed laser irradiation and functionalizing pristine SrTiO3 for electronic, magnetic, and optical applications. [ABSTRACT FROM AUTHOR]

Zn-doped W-type Sr hexaferrite (SrZn x Fe 18 − x O 27 ; SrZn x -WHF) is an anticipated rare-earth-free hard magnetic material with strong magnetocrystalline anisotropy and saturation magnetization. To examine the origin of its high magnetic performance, the site distribution of Zn over seven crystallographically inequivalent Fe sites and the site-dependent valence states of Fe were investigated using site-selective elemental/chemical analysis techniques. The dominant occupation of Zn2+ at the 4e tet(S) and 4f tet(S) tetrahedral sites was determined quantitatively using high-angular-resolution electron-channeling X-ray spectroscopy and statistical data analysis. The combined application of high-angular-resolution electron channeling electron spectroscopy and atomic-column resolution scanning transmission electron microscopy–electron energy-loss spectroscopy helped unambiguously clarify that most of the Fe2+ ions existed at the 6g oct(S-S) octahedral site. Density functional theory calculations have shown that Zn doping leads to a redistribution of the charges toward Fe ions at this site. This redistribution preserves the local charge balance and amplifies the total number of parallel spins. Hence, the enhanced magnetocrystalline anisotropy and saturation magnetization in SrZn x -WHF can be inferred to originate from the charge redistribution at the 6g oct(S-S) site, which is influenced by the presence of nonmagnetic Zn. [Display omitted] • Zn-doped W-type Sr hexaferrites were investigated by TEM and DFT calculations. • Site-dependent dopant occupancies and Fe valence states were examined. • Preferential occupation sites of doped Zn²⁺ and existing Fe²⁺ were different. • Charge redistribution among Fe sites compensates for local charge imbalance. • Zn site distribution and charge redistribution improved the magnetic performance. [ABSTRACT FROM AUTHOR]

Electron microscopy (EM) remains the primary method for imaging cellular and tissue ultrastructure, although simultaneous localization of multiple specific molecules continues to be a challenge for EM. We present a method for obtaining multicolor EM views of multiple subcellular components. The method uses sequential, localized deposition of different lanthanides by photosensitizers, small-molecule probes, or peroxidases. Detailed view of biological structures is created by overlaying conventional electron micrographs with pseudocolor lanthanide elemental maps derived from distinctive electron energy-loss spectra of each lanthanide deposit via energy-filtered transmission electron microscopy. This results in multicolor EM images analogous to multicolor fluorescence but with the benefit of the full spatial resolution of EM. We illustrate the power of this methodology by visualizing hippocampal astrocytes to show that processes from two astrocytes can share a single synapse. We also show that polyarginine-based cell-penetrating peptides enter the cell via endocytosis, and that newly synthesized PKMζ in cultured neurons preferentially localize to the postsynaptic membrane.

Ln 2 Co 3 Ge 5 (Ln = lanthanide) intermetallics possess intriguing electronic and magnetic properties. The compound Sm 2 Co 3 Ge 5 exhibits antiferromagnetic ordering coupled with a magnetic moment that exceeds the theoretical moment of trivalent Sm suggesting a magnetic contribution from Co. Twinning is observed in Sn flux-grown monoclinic Sm 2 Co 3 Ge 5 along (100) planes. While the influence of twin boundaries on superconducting oxides and 2D-materials is well-studied, its effects on bulk lanthanide-based intermetallics are rarely explored. Using monochromated electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (TEM), we investigate the impact of twin domains on the local strain and electronic structure of Sm 2 Co 3 Ge 5. The boundaries between twinned domains primarily exhibit shear strain and have a constant oxidation state, but fine structure emerges in the Co L 2 , 3 edges at twin boundaries, indicative of 3 d -electron hybridization and occupation of states not present in bulk grain spectra. These findings provide insights into tuning the bulk properties of lanthanide-transition metal systems with complex magnetism. [Display omitted] [ABSTRACT FROM AUTHOR]

Morphological control at the nanoscale paves the way to fabricate nanostructures with desired plasmonic properties. In this study, we discuss the nanoengineering of plasmon resonances in 1D hollow nanostructures of two different AuAg nanotubes, including completely hollow nanotubes and hybrid nanotubes with solid Ag and hollow AuAg segments. Spatially resolved plasmon mapping by electron energy loss spectroscopy (EELS) revealed the presence of high order resonator-like modes and localized surface plasmon resonance (LSPR) modes in both nanotubes. The experimental findings accurately correlated with the boundary element method (BEM) simulations. Both experiments and simulations revealed that the plasmon resonances are intensely present inside the nanotubes due to plasmon hybridization. Based on the experimental and simulated results, we show that the novel hybrid AuAg nanotubes possess two significant coexisting features: (i) LSPRs are distinctively generated from the hollow and solid parts of the hybrid AuAg nanotube, which creates a way to control a broad range of plasmon resonances with one single nanostructure, and (ii) the periodicity of the high-order modes are disrupted due to the plasmon hybridization by the interaction of solid and hollow parts, resulting in an asymmetrical plasmon distribution in 1D nanostructures. The asymmetry could be modulated/engineered to control the coded plasmonic nanotubes.

Nanoscale variations of optical properties in transition metal dichalcogenide (TMD) monolayers can be explored with cathodoluminescence (CL) and electron energy loss spectroscopy (EELS) using electron microscopes. To increase the CL emission intensity from TMD monolayers, the MoSe 2 flakes are encapsulated in hexagonal boron nitride (hBN), creating van der Waals (VdW) heterostructures. Until now, the studies have been exclusively focused on scanning transmission electron microscopy (STEM-CL) or scanning electron microscopy (SEM-CL), separately. Here, we present results, using both techniques on the same sample, thereby exploring a large acceleration voltage range. We correlate the CL measurements with STEM-EELS measurements acquired with different energy dispersions, to access both the low-loss region at ultra-high spectral resolution, and the core-loss region. This provides information about the weight of the various absorption phenomena including the direct TMD absorption, the hBN interband transitions, the hBN bulk plasmon, and the core losses of the atoms present in the heterostructure. The S(T)EM-CL measurements from the TMD monolayer only show emission from the A exciton. Combining the STEM-EELS and S(T)EM-CL measurements, we can reconstruct different decay pathways leading to the A exciton CL emission. The comparison with SEM-CL shows that this is also a good technique for TMD heterostructure characterization, where the reduced demands on sample preparation are appealing. To demonstrate the capabilities of SEM-CL imaging, we also measured on a SiO 2 /Si substrate, quintessential in the sample preparation of two-dimensional materials, which is electron-opaque and can only be measured in SEM-CL. The CL-emitting defects of SiO 2 make this substrate challenging to use, but we demonstrate that this background can be suppressed by using lower electron energy., (© 2024 IOP Publishing Ltd.)

Free electrons are excellent tools to probe and manipulate nanoscale optical fields with emerging applications in ultrafast spectromicroscopy and quantum metrology. However, advances in this field are hindered by the small probability associated with the excitation of single optical modes by individual free electrons. Here, we theoretically investigate the scaling properties of the electron-driven excitation probability for a wide variety of optical modes including plasmons in metallic nanostructures and Mie resonances in dielectric cavities, spanning a broad spectral range that extends from the ultraviolet to the infrared region. The highest probabilities for the direct generation of three-dimensionally confined modes are observed at low electron and mode energies in small structures, with order-unity (∼100%) coupling demanding the use of <100 eV electrons interacting with eV polaritons confined down to tens of nanometers in space. Electronic transitions in artificial atoms also emerge as practical systems to realize strong coupling to few-eV free electrons. In contrast, conventional dielectric cavities reach a maximum probability in the few-percent range. In addition, we show that waveguide modes can be generated with higher-than-unity efficiency by phase-matched interaction with grazing electrons, suggesting a practical method to create multiple excitations of a localized optical mode by an individual electron through funneling the so-generated propagating photons into a confining cavity─an alternative approach to direct electron-cavity interaction. Our work provides a roadmap to optimize electron-photon coupling with potential applications in electron spectromicroscopy as well as nonlinear and quantum optics at the nanoscale.

Recent advances in the development of electron and X-ray detectors have opened up the possibility to detect single events from which its time of arrival can be determined with nanosecond resolution. This allows observing time correlations between electrons and X-rays in the transmission electron microscope. In this work, a novel setup is described which measures individual events using a silicon drift detector and digital pulse processor for the X-rays and a Timepix3 detector for the electrons. This setup enables recording time correlation between both event streams while at the same time preserving the complete conventional electron energy loss (EELS) and energy dispersive X-ray (EDX) signal. We show that the added coincidence information improves the sensitivity for detecting trace elements in a matrix as compared to conventional EELS and EDX. Furthermore, the method allows the determination of the collection efficiencies without the use of a reference sample and can subtract the background signal for EELS and EDX without any prior knowledge of the background shape and without pre-edge fitting region. We discuss limitations in time resolution arising due to specificities of the silicon drift detector and discuss ways to further improve this aspect. [ABSTRACT FROM AUTHOR]

Direct electron detection is currently revolutionizing many fields of electron microscopy due to its lower noise, its reduced point-spread function, and its increased quantum efficiency. More specifically to this work, Timepix3 is a hybrid-pixel direct electron detector capable of outputting temporal information of individual hits in its pixel array. Its architecture results in a data-driven detector, also called event-based, in which individual hits trigger the data off the chip for readout as fast as possible. The presence of a pixel threshold value results in an almost readout-noise-free detector while also defining the hit time of arrival and the time the signal stays over the pixel threshold. In this work, we have performed various experiments to calibrate and correct the Timepix3 temporal information, specifically in the context of electron microscopy. These include the energy calibration, and the time-walk and pixel delay corrections, reaching an average temporal resolution throughout the entire pixel matrix of 1. 37 ± 0. 04 ns. Additionally, we have also studied cosmic rays tracks to characterize the charge dynamics along the volume of the sensor layer, allowing us to estimate the limits of the detector's temporal response depending on different bias voltages, sensor thickness, and the electron beam ionization volume. We have estimated the uncertainty due to the ionization volume ranging from about 0.8 ns for 60 keV electrons to 8.8 ns for 300 keV electrons. • Timepix3 time calibration achieves 1.37 ns temporal resolution. • Energy and time-walk can be calibrated using uniform illumination datasets. • Electron–photon temporal correlation can be used to calibrate the pixel delay. • Cosmic rays tracks provides further insights about the sensor layer. [ABSTRACT FROM AUTHOR]

A new material characterization technique is emerging for the transmission electron microscope (TEM). Using electron energy-loss spectroscopy, real space mappings of the underlying electronic transitions in the sample, so called orbital maps, can be produced. Thus, unprecedented insight into the electronic orbitals responsible for most of the electrical, magnetic and optical properties of bulk materials can be gained. However, the incredibly demanding requirements on spatial as well as spectral resolution paired with the low signal-to-noise ratio severely limits the day-to-day use of this new technique. With the use of simulations, we strive to alleviate these challenges as much as possible by identifying optimal experimental parameters. In this manner, we investigate representative examples of a transition metal oxide, a material consisting entirely of light elements, and an interface between two different materials to find and compare acceptable ranges for sample thickness, acceleration voltage and electron dose for a scanning probe as well as for parallel illumination. • Characterization of electronic states using electron energy-loss spectroscopy. • Optimization of experimental parameters using an image difference metric. • Comparison between scanning and parallel beam transmission electron microscopy. [ABSTRACT FROM AUTHOR]

We studied the structural transformations and atomic rearrangements in strontium titanate (SrTiO3) via nanosecond pulsed laser irradiation-induced melting and ultrafast quenching. Using scanning transmission electron microscopy, we determine that the laser-irradiated surface in single-crystalline SrTiO3 transforms into an amorphous phase with an interposing disordered crystalline region between amorphous and ordered phases. The formation of disordered phase is attributed to the rapid recrystallization of SrTiO3 from the melt phase constrained by an epitaxial relation with the pristine region, which eases up on the surface, leading to amorphous phase formation. With electron energy-loss spectroscopic analysis, we confirm the transformation of Ti+4 to Ti+3 due to oxygen vacancy formation as a result of laser irradiation. In the disordered region, the maximum transformation of Ti+4 is observed to be 16.2 ± 0.2%, whereas it is observed to be 20.2 ± 0.2% in the amorphous region. Finally, we deduce that the degree of the disorder increases from atomically disordered to amorphous transition in SrTiO3 under laser-irradiation. The signatures of short-range ordering remain similar, leading to a comparable fingerprint of electronic structure. With these results, this study addresses the gap in understanding the atomic and electronic structure modified by pulsed laser irradiation and functionalizing pristine SrTiO3 for electronic, magnetic, and optical applications.

Control over the optical properties of atomically thin two-dimensional (2D) layers, including those of transition metal dichalcogenides (TMDs), is needed for future optoelectronic applications. Here, the near-field coupling between TMDs and graphene/graphite is used to engineer the exciton line shape and charge state. Fano-like asymmetric spectral features are produced in WS 2 , MoSe 2 , and WSe 2 van der Waals heterostructures combined with graphene, graphite, or jointly with hexagonal boron nitride ( h -BN) as supporting or encapsulating layers. Furthermore, trion emission is suppressed in h -BN encapsulated WSe 2 /graphene with a neutral exciton red shift (44 meV) and binding energy reduction (30 meV). The response of these systems to electron beam and light probes is well-described in terms of 2D optical conductivities of the involved materials. Beyond fundamental insights into the interaction of TMD excitons with structured environments, this study opens an unexplored avenue toward shaping the spectral profile of narrow optical modes for application in nanophotonic devices.

The interaction between a metal and a support, which is known as the metal-support interaction, often plays a determining role in the catalytic properties of supported metal catalysts. Herein, we have developed model Pt/CeO 2 catalysts, which enabled us to investigate the interface atomic and electronic structures between Pt and the {001}, {011}, and {111} planes of CeO 2 using scanning transmission electron microscopy and electron energy-loss spectroscopy. We found that the number of Ce 3+ ions around the Pt nanoparticles followed the order {001} > {011} > {111}, which was the opposite order of the generally accepted stability of low index surfaces of CeO 2 . Systematic first-principles calculations revealed that the presence of Pt nanoparticles facilitated the formation of oxygen vacancies and that the appearance of the Pt δ+ state was preferred when Pt nanoparticles were in contact with CeO 2 {001} planes due to direct charge transfer from Pt to CeO 2 . These results provide important insights into the nature of the metal-support interaction for a comprehensive understanding of the properties of supported metal catalysts.

Perovskite oxides, ABO3, are potential catalysts for the oxygen evolution reaction, which is important in the production of hydrogen as a sustainable energy resource. Optimizing the chemical composition of such oxides by substitution or doping with additional elements is an effective approach to improving the activity of such catalysts. Here, we characterized the crystal and electronic structures of fluorine-doped La0.5Sr0.5CoO3-δ particles using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM imaging demonstrated the formation of a disordered surface phase caused by fluorine doping. In addition, spatially resolved EELS data showed that fluorine anions were introduced into the interiors of the particles and that Co ions near the surfaces were slightly reduced by fluorine doping in conjunction with the loss of oxygen ions. Peak fitting of energy-loss near-edge structure data demonstrated an unexpected nanostructure in the vicinity of the surface. An EELS characterization comprising elemental mapping together with an energy-loss near-edge structure analysis indicated that this nanostructure could not be assigned to Co-based materials but rather to the solid electrolyte BaF2. Complementary structural and electronic characterizations using STEM and EELS as demonstrated herein evidently have the potential to play an increasingly important role in elucidating the nanostructures of functional materials., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Photonic integrated circuits (PICs) are revolutionizing the realm of information technology, promising unprecedented speeds and efficiency in data processing and optical communication. However, the nanoscale precision required to fabricate these circuits at scale presents significant challenges, due to the need to maintain consistency across wavelength-selective components, which necessitates individualized adjustments after fabrication. Harnessing spectral alignment by automated silicon ion implantation, in this work scalable and non-volatile photonic computational memories are demonstrated in high-quality resonant devices. Precise spectral trimming of large-scale photonic ensembles from a few picometers to several nanometres is achieved with long-term stability and marginal loss penalty. Based on this approach, spectrally aligned photonic memory and computing systems for general matrix multiplication are demonstrated, enabling wavelength multiplexed integrated architectures at large scales., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Conical metallic tapers represent an intriguing subclass of metallic nanostructures, as their plasmonic properties show interesting characteristics in strong correlation to their geometrical properties. This is important for possible applications such as in the field of scanning optical microscopy, as favourable plasmonic resonance behaviour can be tailored by optimizing structural parameters like surface roughness or opening angle. Here, we review our recent studies, where single-crystalline gold tapers were investigated experimentally by means of electron energy-loss and cathodoluminescence spectroscopy techniques inside electron microscopes, supported by theoretical finite-difference time-domain calculations. Through the study of tapers with various opening angles, the underlying resonance mechanisms are discussed. This article is part of a discussion meeting issue 'Dynamic in situ microscopy relating structure and function'. [ABSTRACT FROM AUTHOR]

Thin oxide films are of vast opportunities for modern electronics and can facilitate emergent phenomena by factors absent in the bulk counterparts, such as the ubiquitous epitaxial strain and interfacial charge doping. Here, we demonstrate the twisting of intended bulk-metallic phases in 10-unit-cell LaNiO _3 , PrNiO _3 , and NdNiO _3 films on (001)-oriented SrTiO _3 into distinct charge-lattice entangled states by epitaxial strains. Using atomically-resolved electron microscopy and spectroscopy, the interfacial electron doping into SrTiO _3 in the conventional context of band alignments are discounted. Instead, spontaneously doped holes that are localized and at the order of 10 ^13 cm ^−2 are atomically unraveled across all three heterointerfaces and associated with strain mitigations by the accompanied atomic intermixing with various ionic radii. The epitaxial strains also lead to condensations of monoclinic- C 2/ c lattice instabilities, which are hidden to the bulk phase diagram. The group-theoretical analysis of characteristic transition pathways unveils the strain resurrection of the hidden C 2/ c symmetry. While this strain-induced monoclinic phase in LaNiO _3 remains metallic at room temperature, those in PrNiO _3 and NdNiO _3 turn out to be insulating. Such strain-induced monoclinic lattice instabilities and parasitic localized holes go beyond the classical elastic deformations of films upon epitaxial strains and hint on plausible hidden orders in versatile oxide heterostructures with unexpected properties, of which the exploration is only at the infancy and full of potentials.

Summary: Electron Compton scattering is a technique that gives information on the electron momentum density of states and is used to characterize the ground state electronic structure in solids. Extracting the momentum density of states requires us to assume the so‐called 'impulse approximation', which is valid for large energy losses. Here, the robustness of the impulse approximation in the low energy transfer regime is tested and confirmed on amorphous carbon films. Compared to traditional Compton measurements, this provides additional benefits of more efficient data collection and a simplified way to probe valence electrons, which govern solid state bonding. However, a potential complication is the increased background from the plasmon signal. To overcome this, a novel plasmon background subtraction routine is proposed for samples that are resistant to beam damage. Lay Description: Properties of solids depend on their electronic structure which can be studied using electron Compton scattering technique. Here, an electron beam is used to penetrate a very thin sample. During the interaction between the electrons in the beam and electrons in the sample, the former transfer a part of their energy to the latter, resulting in a measurable energy loss of the transmitted beam. The amount of the energy transfer depends on the angle of incidence between the beam and the sample. Typically, the experiments are carried out using high tilt angles and high energy transfer; however, in this work, we show that even smaller angles of incidence are suitable, which improve the signal quality and ease data processing procedures. [ABSTRACT FROM AUTHOR]

The combination of scanning transmission electron microscopy (STEM) with analytical instruments has become one of the most indispensable analytical tools in materials science. A set of microscopic image/spectral intensities collected from many sampling points in a region of interest, in which multiple physical/chemical components may be spatially and spectrally entangled, could be expected to be a rich source of information about a material. To unfold such an entangled image comprising information and spectral features into its individual pure components would necessitate the use of statistical treatment based on informatics and statistics. These computer-aided schemes or techniques are referred to as multivariate curve resolution, blind source separation or hyperspectral image analysis, depending on their application fields, and are classified as a subset of machine learning. In this review, we introduce non-negative matrix factorization, one of these unfolding techniques, to solve a wide variety of problems associated with the analysis of materials, particularly those related to STEM, electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy. This review, which commences with the description of the basic concept, the advantages and drawbacks of the technique, presents several additional strategies to overcome existing problems and their extensions to more general tensor decomposition schemes for further flexible applications are described. [ABSTRACT FROM AUTHOR]

In this paper, a monochromator (MC) with double cylindrical lenses (CLs) is evaluated. The MC achieved an energy resolution of 37 meV with high repeatability and stability. The double CLs realized the coincidence of the beam positions at the exit. The beam profiles were evaluated in a relative manner. Comparing two conditions with or without the MC, the beam kept equivalent sizes and showed sufficiently fine profiles. This is because the first-order aberration was a dominant factor under the experimental condition, where the second-order aberration was canceled by the middle plane symmetry of the MC optics and the beam was limited in small angles by the incident aperture. The experimental results mean that the MC with double CLs functioned properly as designed. The MC has the additional advantage of a simple structure. The results confirm that this MC has a high possibility for application to electron microscopy. [ABSTRACT FROM AUTHOR]