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Transmission electron microscopy (TEM) offers unprecedent atomic resolution imaging and diverse characterizations capabilities, which has been proved to be effective in correlating the atomic structures and compositions with the physical/chemical properties of semiconductor nanomaterials. This review aims to provide an overview of the latest advancements regarding the atomic structure/property relationship in semiconductor nanomaterials. First, by employing off‐axis electron holography, a comprehensive overview of the quantitative investigations into the atomic‐electronic structure relationship of semiconductors is presented. Second, by integrating in situ TEM technique with micro/nanoelectromechanical systems (M/NEMS), this review summarizes the recent advancements achieved in elucidating the intricate relationship between structure and properties of nanomaterials subjected to diverse stimuli such as stress, thermal, and electric fields. Moreover, the impact of electron beam irradiation on the microstructure of semiconductor nanomaterials is discussed. Lastly, current challenges and future research opportunities are proposed along with their potential applications. [ABSTRACT FROM AUTHOR]

Off-axis electron holography was used to reveal remote doping in GaAs nanowires occurring during in situ annealing in a transmission electron microscope. Dynamic changes to the electrostatic potential caused by carbon dopant diffusion upon annealing were measured across GaAs nanowires with radial p-p+ coreâ€"shell junctions. Electrostatic potential profiles were extracted from holographic phase maps and built-in potentials (Vbi) and depletion layer widths (DLWs) were estimated as function of temperature over 300â€"873 K. Simulations in absence of remote doping predict a significant increase of Vbi and DLWs with temperature. In contrast, we measured experimentally a nearly constant Vbi and a weak increase of DLWs. Moreover, we observed the appearance of a depression in the potential profile of the core upon annealing. We attribute these deviations from the predicted behavior to carbon diffusion from the shell to the core through the nanowire sidewalls, i.e. to remote doping, becoming significant at 673 K. The DLW in the p and p+ regions are in the 10â€"30 nm range. [ABSTRACT FROM AUTHOR]

We have demonstrated and experimentally verified a nanovehicle which exhibits magnetoelectric phenomenon and provides a swift cell targeting technique. The magnetoelectric nanovehicle (MENV) is an inorganic core-shell nanostructure where the core and shell interact with each other in magnetic field excitation to exhibit magnetoelectric effect. Under oscillating magnetic field excitation, these MENV generates oscillating surface electric charge i.e., magnetoelectricity and attain directional propelling motion in fluidic medium due to the Lorentz forces. Further under magnetic field excitation, the MENV can dynamically sense the electric field of a single biological cell and gain propulsion speed in bio-cellular environment due to torque experience by electrostatic repulsion from the electrical field of the cells encountered on its propelling trajectory. The maximum speed attained by these MENV driven by ac magnetic field (40 Oe, 30 Hz) in Human Epithelial cell (HEP2) environment reaches to 258.159 μm/s as observed in the in-vitro experiments performed in microvascular structured microfluidic chamber. The MENVs can be transported and immobilized to a targeted cell at desired location with micron scale precision irrespective of the cellular density hindrance experienced on the propelling pathway. Interestingly the MENV excel the propelling speed with the increase in cellular density on its propulsion path. MENV does not need tertiary guidance system for the regulated directional movement while cell targeting.

Severe lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe(12‐x)CoxO19@Fe3O4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe(12‐x)CoxO19 serves as the core and soft magnetic Fe3O4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RLmin) of typical BaFe11.6Co0.4O19@Fe3O4 microcomposite reaches −48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss < −10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers. [ABSTRACT FROM AUTHOR]

Topologically protected spin textures, such as magnetic skyrmions, have attracted considerable attention owing to their emergent electromagnetic phenomena and potential applications in spintronics. The antiskyrmion, a new member of the skyrmion family in the nanoscale dimension, consists of alternating Néel‐ and Bloch‐type boundary walls; it has already been discovered in non‐centrosymmetric magnets with D2d/S4 symmetry. However, its complex spin textures and unique magnetic‐charge‐induced emergent field have not been explicitly visualized thus far. Here, state‐of‐the‐art off‐axis electron holography is employed to directly resolve the antiskyrmions in a non‐centrosymmetric Heusler magnet Mn1.4PtSn with D2d symmetry. The magnetic flux distribution inside and outside the antiskyrmion is clearly imaged, indicating the emergent magnetic field induced by the broken cylindrical symmetry. More importantly, the closed emergent flux between adjacent antiskyrmions is revealed, indicating the antiskyrmion‐antiskyrmion interactions (a different mechanism compared to that of conventional skyrmions). These findings provide a clear and deep insight into the intrinsic magnetic flux configuration in the antiskyrmion‐hosted magnets, thus paving the way for the manipulation of antiskyrmions in the future. [ABSTRACT FROM AUTHOR]

The magnetic properties of nanowires (NWs) and square nanorings, which were deposited by focused electron beam induced deposition (FEBID) of a Co carbonyl precursor, are studied using off-axis electron holography (EH), Lorentz transmission electron microscopy (L-TEM) and magnetic force microscopy (MFM). EH shows that NWs deposited using beam energies of 5 and 15 keV have the characteristics of magnetic dipoles, with larger magnetic moments observed for NWs deposited at lower energy. L-TEM is used to image magnetic domain walls in NWs and nanorings and their motion as a function of applied magnetic field. The NWs are found to have almost square hysteresis loops, with coercivities of ca. 10 mT. The nanorings show two different magnetization states: for low values of the applied in-plane field (0.02 T) a horseshoe state is observed using L-TEM, while for higher values of the applied in-plane field (0.3 T) an onion state is observed at remanence using L-TEM and MFM. Our results confirm the suitability of FEBID for nanofabrication of magnetic structures and demonstrate the versatility of TEM techniques for the study and manipulation of magnetic domain walls in nanostructures.

Summary: The growth of cobalt nanopatterns (NPs) using focused electron‐beam induced deposition (FEBID) for localised magnetic studies is presented. The initial FEBID products are shown to be polycrystalline and form hetero‐structured core‐shell NPs through surface oxidation. Off‐axis electron holography is performed to reconstruct their morphology, thickness profile and image their individual magnetic vortex domain states. In situ annealing to 400°C promoted migration of the Co‐overspray to grow the Co NPs and improved their crystallinity through coarsening, as well as induced diffusion of embedded carbon out of their surface. It is found that the change in their morphology and chemical instability under heating restricts their suitability for examining thermally induced magnetic variations. Lay Description: In this paper, electron microscopy is used to deposit magnetic cobalt nanopatterns and characterise the effect of in‐situ heating on their chemistry, structure and magnetic properties. The electron beam of the secondary electron microscope is used to dissociate an injected precursor gas near the SiN membrane substrate of in‐situ transmission electron microscopy (TEM) chips and locally deposit the elemental Co in circular patterns ∼ 90 nm in diameter. TEM reveals formation of a Co‐oxide shell and embedding of carbon from the precursor gas during growth. The technique of electron holography is used to image the magnetism of the core‐shell Co / Co‐oxide nanopatterns, which are shown to exhibit magnetic vortex states. In‐situ annealing results in migration of the Co overspray to increase their height and carbon diffusion from their surface, as well as change in their original magnetic state through change of orientation. It is found that the change in the morphology and chemistry of Co nanopatterns under heating limits their use for studying the effect of temperature on their magnetism in isolation. [ABSTRACT FROM AUTHOR]

Unique palladium‐gold hollow nanochains (PdAu HCs) with 1D architecture and an ultrathin Pd‐rich skin exhibit fantastic oxygen reduction reaction (ORR) enhancements due to their high conductivity, structural stability, and maximized atomic utilization. More importantly, such PdAu HCs possess periodic concave structures that boost ORR performance. These structures readily form high‐density high‐index facets, and fewer arc edges. Concave structures can deliver strong strain effects and surface charge accumulation is revealed by off‐axis electron holography. In addition, periodic concave structures can provide strong localized surface–plasmon coupling, which means that PdAu HCs have great potential as efficient surface‐enhanced Raman scattering (SERS) substrates. This study offers a novel and general approach for the design of complex noble metal‐based nanostructures as efficient ORR catalysts and SERS substrates. [ABSTRACT FROM AUTHOR]

Stray electric fields in free space generated by two biased gold needles have been quantified in comprehensive finite-element (FE) simulations, accompanied by first moment (FM) scanning TEM (STEM) and electron holography (EH) experiments. The projected electrostatic potential and electric field have been derived numerically under geometrical variations of the needle setup. In contrast to the FE simulation, application of an analytical model based on line charges yields a qualitative understanding. By experimentally probing the electric field employing FM STEM and EH under alike conditions, a discrepancy of about 60% became apparent initially. However, the EH setup suggests the reconstructed phase to be significantly affected by the perturbed reference wave effect, opposite to STEM where the field-free reference was recorded subsequently with unbiased needles in which possibly remaining electrostatic influences are regarded as being minor. In that respect, the observed discrepancy between FM imaging and EH is resolved after including the long-range potential landscape from FE simulations into the phase of the reference wave in EH. • Electric field of biased needles mapped by first-moment STEM and electron holography • Quantitative understanding of both signals obtained by finite element (FE) simulations • Referencing to field-free cases is fundamentally different for both methods • Perturbed reference wave in electron holography reproducible by extensive FE simulations • Electrode stray fields in electrically biased specimens contribute significantly to signal [ABSTRACT FROM AUTHOR]

Target skyrmion, characterized by a central skyrmion surrounded by a series of concentric cylinder domains known as kπ- skyrmions ( k ≥ 2), holds promise as a novel storage state in next-generation memories. However, target skyrmions comprising one or more concentric cylindrical domains have not been observed in chiral magnets, particularly at room temperature. In this study, we experimentally achieved kπ- skyrmions ( k = 2, 3, and 4) with diameters of ∼220, 320, and 410 nm, respectively, and room-temperature stability under zero magnetic field by tightly confining these topological spin textures in β-Mn-type Co 8 Zn 10 Mn 2 nanodisks. The magnetic configurations and their field-driven evolutions were simultaneously investigated by using in situ off-axis electron holography. In combination with numerical simulations, we further investigated the dependence of k max on the nanodisk diameter. These findings highlight the potential of k π-skyrmions as information carriers and offer insights into manipulation of k π-skyrmions in the future.

Highlights • Off-axis electron holography enables quantification of electrostatic fields. • Outline of theoretical basis and experimental aspects for electron holography. • Applications to many different types of materials problems briefly reviewed. • Challenges and opportunities for off-axis electron holography. Abstract Off-axis electron holography has evolved into a powerful electron-microscopy-based technique for characterizing electromagnetic fields with nanometer-scale resolution. In this paper, we present a review of the application of off-axis electron holography to the quantitative measurement of electrostatic potentials and charge density distributions. We begin with a short overview of the theoretical and experimental basis of the technique. Practical aspects of phase imaging, sample preparation and microscope operation are outlined briefly. Applications of off-axis electron holography to a wide range of materials are then described in more detail. Finally, challenges and future opportunities for electron holography investigations of electrostatic fields and charge density distributions are presented. [ABSTRACT FROM AUTHOR]

Highlights • Strong external magnetic stray field observed via off-axis electron holography. • Visualizing micro magnetic incorporations to illustrate magnetic loss behaviors. • Outstanding microwave absorption with reflection loss up to –53dB for the flakes. Abstract High permeability and high saturation magnetization are two key attributes to strong microwave absorption for magnetic loss composites, which depend on the chemical composition, particle size, surface profile, fabrication method, etc. However, it is still a challenge to understand the influences of these properties on micro magnetic behaviors to manipulate microwave absorption performances. In this study, magnetic absorbers with spherical and flaky shapes were adapted to investigate the influences of morphology on magnetic properties via off-axis electron holography. Stray magnetic flux lines were visualized to validate the difference in the forms of magnetic incorporation among spherical and flaked-shaped metallic particles, which then results in reflection loss (RL) up to −53 dB for the flakes and absorption (>99%) bandwidth up to 3 GHz for the spherical types. The micro-field detection using the powerful technique of off-axis electron holography sheds new light on the understanding about intrinsic magnetic micro behaviors for metallic composites. [ABSTRACT FROM AUTHOR]

Highlights • Mean-inner-potential of single crystal α-Al 2 O 3 sapphire measured at 16.90 ± 0.36 V using off-axis electron holography. • Measurement method, based on mechanically polished wedge sample, is discussed. • Density-Functional-Theory calculations of the mean-inner-potential based on VASP. • The plasmon mean free path for inelastic scattering of sapphire is measured. Abstract The mean inner potential (MIP) of a single crystal α-Al 2 O 3 sapphire was measured using off-axis electron holography. To measure the MIP, we use mechanically polished wedge specimens for transmission electron microscopy (TEM). This approach also enabled us to measure the plasmon mean free path for inelastic scattering (IMFP). The wedge specimen, chosen here at an angle of approximately 45°, allows to determine the MIP by measuring the gradient of phase variations of the reconstructed electron wave over extended regions across the sample. The angle of the wedge was measured to an accuracy of better than 1° by two methods: first, perpendicular sectioning in a focused ion beam for direct measurement by TEM and second, by a non-destructive approach of confocal optical microscopy. The validity of this methodology was examined on a single crystal Si(001) sample showing that the mechanically polished wedge approach can be applied to a wide range of materials. Our measurements concluded that the MIP of sapphire is V 0 = 16.90 ± 0.36 V. Furthermore, the IMFP of sapphire was measured at 136 ± 2 nm for 197 keV electrons with a collection angle of 18mrad. The measured MIP of sapphire reflects its degree of ionicity, which lies between theoretical calculations based on electron scattering factors of charged and neutral isolated atoms obtained by Dirac–Fock calculations. Our MIP measurements tend to the expected value for this predominantly ionic material. To account for chemical bonding and the role of the crystallographic plane at the surface of the sample, we compared the experimental measurements to density-functional-theory calculations of the MIP. Calculations of α-Al 2 O 3 slabs cut along (0001) and (1–100) planes obtained MIP values of 15.7 V and 16.7 V, respectively. [ABSTRACT FROM AUTHOR]

The technique of double exposure electron holography, which is based on the superposition of two off-axis electron holograms, was originally introduced before the availability of digital image processing to allow differences between electron-optical phases encoded in two electron holograms to be visualised directly without the need for holographic reconstruction. Here, we review the original method and show how it can now be extended to permit quantitative studies of phase shifts that oscillate in time. We begin with a description of the theory of off-axis electron hologram formation for a time-dependent electron wave that results from the excitation of a specimen using an external stimulus with a square, sinusoidal, triangular or other temporal dependence. We refer to the more general method as continuous exposure electron holography, present preliminary experimental measurements and discuss how the technique can be used to image electrostatic potentials and magnetic fields during high frequency switching experiments. [ABSTRACT FROM AUTHOR]

The phase and amplitude of the electron wavefunction that has passed through ultra-thin flakes of WSe 2 is measured from high-resolution off-axis electron holograms. Both the experimental measurements and corresponding computer simulations are used to show that, as a result of dynamical diffraction, the spatially averaged phase does not increase linearly with specimen thickness close to an [001] zone axis orientation even when the specimen has a thickness of only a few layers. It is then not possible to infer the local specimen thickness of the WSe 2 from either the phase or the amplitude alone. Instead, we show that the combined analysis of phase and amplitude from experimental measurements and simulations allows an accurate determination of the local specimen thickness. The relationship between phase and projected potential is shown to be approximately linear for extremely thin specimens that are tilted by several degrees in certain directions from the [001] zone axis. A knowledge of the specimen thickness then allows the electrostatic potential to be determined from the measured phase. By using this combined approach, we determine a value for the mean inner potential of WSe 2 of 18.9±0.8 V, which is 12% lower than the value calculated from neutral atom scattering factors. [ABSTRACT FROM AUTHOR]

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS. A finite-element three-dimensional (3D) calculation of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, we used off-axis electron holography (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estimated across the junction, though as opposed to the thermal equilibrium calculations significant accumulation of positive charge at the CdS side of the interface is detected. We conclude that the NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the experimental measurements. Thus, we show that OAEH can be used as a complementary methodology to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries. [ABSTRACT FROM AUTHOR]

The phase shift of the electron wave is a useful measure for the projected magnetic flux density of magnetic objects at the nanometer scale. More important for materials science, however, is the knowledge about the magnetization in a magnetic nano-structure. As demonstrated here, a dominating presence of stray fields prohibits a direct interpretation of the phase in terms of magnetization modulus and direction. We therefore present a model-based approach for retrieving the magnetization by considering the projected shape of the nano-structure and assuming a homogeneous magnetization therein. We apply this method to FePt nano-islands epitaxially grown on a SrTiO 3 substrate, which indicates an inclination of their magnetization direction relative to the structural easy magnetic [001] axis. By means of this real-world example, we discuss prospects and limits of this approach. [ABSTRACT FROM AUTHOR]

The physical properties of nanometer scale semiconductors are known to be sensitively influenced by their aspect ratios, but the intrinsic mechanisms still remain unclear. Shape-controlled anisotropic PbSe nanorods were obtained by means of the addition of MnCl 2 , and the aspect ratio of the nanorods can be continuously tuned from 1 to 10 by simply modulating the amount of chloride ions. It was demonstrated that an optimized concentration of Cl − anions is about 0.04 mmol, which controls the competition between thermodynamics and kinetics mechanisms. The emission peaks of the infrared absorbance and photoluminescence spectra were significantly tuned from 1664 nm to 1840 nm and from 1459 nm to 1938 nm only by the aspect ratios, respectively. A strong electric dipole phenomenon localized onside the surface of PbSe nanorods terminated by Pb 2+ charge was found by using high-spatial-resolution off-axis electron holography, which was furthermore evidenced by the quantitative analysis of the mean inner potential and the surfaces charge. The charge intensity depended on the aspect ratio of PbSe nanorods. The results provide clear evidence that the energy gap interval reduces as a result of the increasing of conduction charge amounts. A novel strategy to facilely shift the peak position of absorbance and photoluminescence emission was therefore proposed. [ABSTRACT FROM AUTHOR]

Effect of strain on space charge (SC) layer in nanowires (NWs) has been examined by in situ off-axis electron holography, where GaN NWs attach to an Au electrode inside a transmission electron microscope (TEM). Based on the phase image reconstructed from the complex hologram, the width of SC layer in a strained GaN NW is significantly reduced to about 60 nm, comparing to the 85 nm of the unstrained NW. About 29% reduction of the SC layer in the strained GaN NW resulted from significant decrease of electrons flowed from the GaN into Au. First principle calculations show that the strain reduced bandgap of GaN, narrowing the difference between GaN NW and Au electrode in Fermi level. [ABSTRACT FROM AUTHOR]

We use in situ Lorentz microscopy and off-axis electron holography to investigate the formation and characteristics of skyrmion lattice defects and their relationship to the underlying crystallographic structure of a B20 FeGe thin film. We obtain experimental measurements of spin configurations at grain boundaries, which reveal inversions of crystallographic and magnetic chirality across adjacent grains, resulting in the formation of interface spin stripes at the grain boundaries. In the absence of material defects, we observe that skyrmions lattices possess dislocations and domain boundaries, in analogy to atomic crystals. Moreover, the distorted skyrmions can flexibly change their size and shape to accommodate local geometry, especially at sites of dislocations in the skyrmion lattice. Our findings provide a detailed understanding of the elasticity of topologically protected skyrmions and their correlation with underlying material defects. [ABSTRACT FROM AUTHOR]

We measure the mean inner potential (MIP) of hematite, α-Fe2O3, using electron holography and transmission electron microscopy. Since the MIP is sensitive to valence electrons, we propose its use as a chemical bonding parameter for solids. Hematite can test the sensitivity of the MIP as a bonding parameter because of the Morin magnetic phase transition. Across this transition temperature, no change in the corundum crystal structure can be distinguished, while a change in hybridized Fe-3d and O-2p states was reported, affecting ionic bonding. For a given crystallographic phase, the change in the MIP with temperature is expected to be minor due to thermal expansion. Indeed, we measure the temperature dependence in corundum α-Al2O3(112¯0) between 95 and 295 K showing a constant MIP value of ∼16.8 V within the measurement accuracy of 0.45 V. Thus, our objectives are as follows: measure the MIP of hematite as a function of temperature and examine the sensitivity of the MIP as a bonding parameter for crystals. Measured MIPs of α-Fe2O3(112¯0) above the Morin transition are equal, 17.85 ± 0.50 V, 17.93 ± 0.50 V, at 295 K, 230 K, respectively. Below the Morin transition, at 95 K, a significant reduction of ∼1.3 V is measured to 16.56 ± 0.46 V. We show that this reduction follows charge redistribution resulting in increased ionic bonding., Competing Interests: Conflict of Interest The authors declare that they have no competing interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Microscopy Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Although assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self-aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi-ion synergistic regulation strategy to design assembled hollow-shaped cobalt spinel oxide microspheres. Dominated by the coordination-etching effects of F - and the hydrolysis-complex contributions of NH 4 + , the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe 2 bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe 4 bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe 2 O 4 composites exhibit excellent microwave absorption performances with minimal reflection losses (RL min ) as high as -51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi-ion and even multi-ion synergistic engineering mechanisms., (© 2023 Wiley-VCH GmbH.)

Electrostatic charging of specimens during electron, photon or ion irradiation is a complicated and poorly understood phenomenon, which can affect the acquisition and interpretation of experimental data and alter the functional properties of the constituent materials. It is usually linked to secondary electron emission, but also depends on the geometry and electrical properties of the specimen. Here, we use off-axis electron holography in the transmission electron microscope to study electron-beam-induced charging of an insulating Al 2 O 3 nanotip on a conducting support. The measurements are performed under parallel electron illumination conditions as a function of specimen temperature, electron dose, primary electron energy and surface cleanliness. We observe a lack of reproducibility of charge density measurements after cycling the specimen temperature. Surprisingly, we find both positively and negatively charged regions in closely adjacent parts of the specimen. • Study electrostatic charging of specimens in the TEM by off-axis electron holography. • Varying parameters, including specimen temperature, electron dose, primary electron energy and surface cleanliness. • Understanding charging requires improved control and knowledge of the specimen geometry, surface state, electrical contact and surrounding environment. [ABSTRACT FROM AUTHOR]

Electrostatic potential maps of GaAs nanowire, p-n junctions have been measured via off-axis electron holography and compared to results from in situ electrical probing, and secondary electron emission microscopy using scanning electron microscopy. The built-in potential and depletion length of an axial junction was found to be 1.5 ± 0.1 V and 74 ± 9 nm, respectively, to be compared with 1.53 V and 64 nm of an abrupt junction of the same end point carrier concentrations. Associated with the switch from Te to Zn dopant precursor was a reduction in GaAs nanowire diameter 3 ± 1 nm that occurred prior to the junction center (n = p) and was followed by a rapid increase in Zn doping. The delay in Zn incorporation is attributed to the time required for Zn to equilibrate within the Au catalyst. [ABSTRACT FROM AUTHOR]

Electron holography is a powerful technique for characterizing electrostatic potentials, charge distributions, electric and magnetic fields, strain distributions and semiconductor dopant distributions with sub-nm spatial resolution. Mapping internal electrostatic and magnetic fields within nanoparticles and other low-dimensional materials by TEM requires both high spatial resolution and high phase sensitivity. Carrying out such an analysis fully quantitatively is even more challenging, since artefacts such as dynamical electron scattering may strongly affect the measurement. In-line electron holography, one of the variants of electron holography, features high phase sensitivity at high spatial frequencies, but suffers from inefficient phase recovery at low spatial frequencies. Off-axis electron holography, in contrast, can recover low spatial frequency phase information much more reliably, but is less effective in retrieving phase information at high spatial frequencies when compared to in-line holography. We investigate gold nanoparticles using hybrid electron holography at both atomic-resolution and intermediate magnification. Hybrid electron holography is a novel technique that synergistically combines off-axis and in-line electron holography, allowing the measurement of the complex wave function describing the scattered electrons with excellent signal-to-noise properties at both high and low spatial frequencies. The effect of dynamical electron scattering is minimized by beam tilt averaging. [ABSTRACT FROM AUTHOR]

As proposed recently, a tilted reference wave in off-axis electron holography is expected to be useful for aberration measurement and correction. Furthermore, in dark-field electron holography, it is considered to replace the reference wave, which is conventionally diffracted in an unstrained object area, by a well-defined object-independent reference wave. Here, we first realize a tilted reference wave by employing a biprism placed in the condenser system above three condenser lenses producing a relative tilt magnitude up to 20/nm at the object plane (300 kV). Paraxial ray-tracing predicts condenser settings for a parallel illumination at the object plane, where only one half of the round illumination disc is tilted relative to the optical axis without displacement. Holographic measurements verify the kink-like phase modulation of the incident beam and return the interference fringe contrast as a function of the relative tilt between both parts of the illumination. Contrast transfer theory including condenser aberrations and biprism instabilities was applied to explain the fringe contrast measurement. A first dark-field hologram with a tilted – object-free – reference wave was acquired and reconstructed. A new application for bright/dark-field imaging is presented. [ABSTRACT FROM AUTHOR]

Off-axis electron holography has been used to quantitatively determine the mean inner potential of ZnO. [0 0 0 1] grown ZnO nanowires with hexagonal cross-sections were chosen as our samples because the angle between the adjacent surfaces is 120°, as confirmed by electron tomography, so the entire geometry of the nanowire could be precisely determined. The acceleration voltage of the transmission electron microscope was accurately calibrated by convergent beam electron diffraction (CBED)–higher-order Laue-zone (HOLZ) analyses. ZnO nanowires were tilted away from zone-axis to avoid strong dynamical diffraction effect, and the tilting angles were determined by CBED patterns. Our experimental data found a mean inner potential of ZnO as 14.30 ± 0.28 V. [ABSTRACT FROM AUTHOR]

The preparation of lightweight, as well as high-performance microwave absorption materials, has attracted much attention in recent years, but people are still suffering from the high cost and low yielding of the products. Here a HNTs@CNTs (HCS) microsphere was prepared by spray drying, and then surface assembly of CoFe 2 O 4 via the hydrothermal method to form HCS/CoFe 2 O 4 composite, followed by thermal reduction into HCS/FeCo under H 2 /Ar atmosphere. The HCS/FeCo show significant performance in both permittivity and permeability due to the combination of the large magnetic moment of the FeCo alloy and the high conductivity of carbon nanotubes, leading to a remarkable enhancement in microwave absorption properties. Thanks to the unique morphology and the synergistic effect of multiple loss mechanisms, the maximum reflection loss of HCS /FeCo reached − 57.77 dB at 12.10 GHz with a matching thickness of only 1.63 mm, and the absorption bandwidth with reflection loss exceeding − 10 dB reached 6.24 GHz (11.76–18.00 GHz), which can completely cover the Ku band. In this strategy, the lightweight halloysite nanotubes are used to match the impedance parameters of the composite, and the spray drying method will facilitate the industrialization of the material. Here a HNTs@CNTs (HCS) microsphere was prepared by spray drying, and then surface assembly of CoFe 2 O 4 via the hydrothermal method to form HCS/CoFe 2 O 4 composite, followed by thermal reduction into HCS/FeCo under H 2 /Ar atmosphere. Thanks to the unique morphology and the synergistic effect of multiple loss mechanisms, the maximum reflection loss of HCS/FeCo reached − 57.77 dB at 12.10 GHz with a matching thickness of only 1.63 mm, and the absorption bandwidth with reflection loss exceeding − 10 dB reached 6.24 GHz, which can completely cover the Ku band. In this strategy, a cost-effective lightweight natural clay mineral (halloysite) was introduced to match the impedance parameters of the composite, and the spray drying method will facilitate the industrialization of the material. [Display omitted] • HNTs@CNTs/FeCo triple phase microspheres can be fabricated via a pyrolysis route; • The introduction of hollow tubular halloysite lead to reflection and scattering of electromagnetic waves. • The synergistic effect of magnetic nanoparticles and carbon nanotubes lead to excellent absorbing properties. • The off-axis electronic holography clearly showed the magnetic loss mechanism. [ABSTRACT FROM AUTHOR]

Multilayers of Co 90 Fe 10 /Pd with different bilayer thicknesses, have been deposited by dc-magnetron sputtering on thermally oxidized Si wafers. Transmission electron microscopy showed that the highly textured crystalline films had columnar structure, while scanning transmission electron microscopy and atomic force microscopy respectively indicated some layer waviness and surface roughness. The magnetic domain structure and perpendicular magnetic anisotropy (PMA) of the Co 90 Fe 10 /Pd multilayers were investigated by off-axis electron holography and magnetic force microscopy. The Co 90 Fe 10 layer thickness was the primary factor determining the magnetic domain size and the perpendicular magnetization: both decreased as the thickness increased. The strongest PMA was observed in the sample with the thinnest magnetic layer of 0.45 nm. [ABSTRACT FROM AUTHOR]

Pronounced improvements in the understanding of semiconductor device performance are expected if electrostatic potential distributions can be measured quantitatively and reliably under working conditions with sufficient sensitivity and spatial resolution. Here, we employ off-axis electron holography to characterize an electrically-biased Si p – n junction by measuring its electrostatic potential, electric field and charge density distributions under working conditions. A comparison between experimental electron holographic phase images and images obtained using three-dimensional electrostatic potential simulations highlights several remaining challenges to quantitative analysis. Our results illustrate how the determination of reliable potential distributions from phase images of electrically biased devices requires electrostatic fringing fields, surface charges, specimen preparation damage and the effects of limited spatial resolution to be taken into account. [ABSTRACT FROM AUTHOR]

The recently derived general transfer theory for off-axis electron holography provides a new approach for reconstructing the electron wave beyond the conventional sideband information limit. Limited ensemble coherence of the electron beam between object and reference area leads to an attenuation of spatial frequencies of the object exit wave in the presence of aberrations of the objective lens. Concerted tilts of the reference wave under the condition of an invariant object exit wave are proposed to diminish the aberration impact on spatial frequencies even beyond the sideband information limit allowing its transfer with maximum possible contrast. In addition to the theoretical considerations outlined in detail, an experimental proof-of-principle is presented. A fully controlled tilt of the reference wave, however, remains as a promising task for the future. The use of a hologram series with varying reference wave tilt is considered for linearly synthesizing an effective aperture for the transfer into the sideband with broader bandwidth compared to conventional off-axis electron holography allowing us to correct the incoherent aberrations in transmission electron microscopy. Furthermore, tilting a reference wave with respect to a plane wave is expected to be an alternative way for measuring the coherent and incoherent aberrations of a transmission electron microscope. The capability of tilting the reference wave is expected to be beneficial for improving the signal-to-noise ratio in dark-field off-axis electron holography as well. [ABSTRACT FROM AUTHOR]

The proliferation of mobile devices in society accessing data via the 'cloud' is imposing a dramatic increase in the amount of information to be stored on hard disk drives (HDD) used in servers. Forecasts are that areal densities will need to increase by as much as 35% compound per annum and by 2,020 cloud storage capacity will be around 7 zettabytes corresponding to areal densities of 2 Tb/in. This requires increased performance from the magnetic pole of the electromagnetic writer in the read/write head in the HDD. Current state-of-art writing is undertaken by morphologically complex magnetic pole of sub 100 nm dimensions, in an environment of engineered magnetic shields and it needs to deliver strong directional magnetic field to areas on the recording media around 50 nm × 13 nm. This points to the need for a method to perform direct quantitative measurements of the magnetic field generated by the write pole at the nanometer scale. Here we report on the complete in situ quantitative mapping of the magnetic field generated by a functioning write pole in operation using electron holography. The results point the way towards a new nanoscale magnetic field source to further develop in situ transmission electron microscopy. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The reduced density matrix completely describes the quantum state of an electron scattered by an object in transmission electron microscopy. However, the detection process restricts access to the diagonal elements only. The off-diagonal elements, determining the coherence of the scattered electron, may be obtained from electron holography. In order to extract the influence of the object from the off-diagonals, however, a rigorous consideration of the electron microscope influences like aberrations of the objective lens and the Möllenstedt biprism in the presence of partial coherence is required. Here, we derive a holographic transfer theory based on the generalization of the transmission cross-coefficient including all known holographic phenomena. We furthermore apply a particular simplification of the theory to the experimental analysis of aloof beam electrons scattered by plane silicon surfaces. [ABSTRACT FROM AUTHOR]

Highlights: [•] Averaging scheme for series of holograms. [•] Compensation of instrumental drifts between exposures. [•] Reconstructed wave function with 75pm resolution. [Copyright &y& Elsevier]

Abstract: Off-axis electron holography is a method for the transmission electron microscope (TEM) that measures the electric and magnetic properties of a specimen. The electrostatic and magnetic potentials modulate the electron wavefront phase. The error in measurement of the phase therefore determines the smallest observable changes in electric and magnetic properties. Here we explore the summation of a hologram series to reduce the phase error and thereby improve the sensitivity of electron holography. Summation of hologram series requires independent registration and correction of image drift and phase wavefront drift, the consequences of which are discussed. Optimization of the electro-optical configuration of the TEM for the double biprism configuration is examined. An analytical model of image and phase drift, composed of a combination of linear drift and Brownian random-walk, is derived and experimentally verified. The accuracy of image registration via cross-correlation and phase registration is characterized by simulated hologram series. The model of series summation errors allows the optimization of phase error as a function of exposure time and fringe carrier frequency for a target spatial resolution. An experimental example of hologram series summation is provided on WS2 fullerenes. A metric is provided to measure the object phase error from experimental results and compared to analytical predictions. The ultimate experimental object root-mean-square phase error is 0.006rad (2π/1050) at a spatial resolution less than 0.615nm and a total exposure time of 900s. The ultimate phase error in vacuum adjacent to the specimen is 0.0037rad (2π/1700). The analytical prediction of phase error differs with the experimental metrics by +7% inside the object and −5% in the vacuum, indicating that the model can provide reliable quantitative predictions. [Copyright &y& Elsevier]