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Polar discontinuities occur in oxide heterostructures due to varying net charges in the sub-unit cell layers. These polar discontinuities lead to structural reconstruction and often create diverse functionalities. This work constructs polar discontinuous in La0.67Sr0.33MnO3/SrCuO2 (LSMO/SCO) heterostructures on a (001)-orientated SrTiO3 (STO) substrate under different configurations. By changing the growth order of LSMO and SCO, we found two different compensating mechanisms for polar discontinuity. When LSMO is grown on SCO, interfacial polarity discontinuities result in the generation of a large number of oxygen vacancies within the LSMO film. Thus, the LSMO magnetism deteriorates. For the SCO/LSMO/SCO trilayer, the SCO capping layer can recover the LSMO magnetism. The scanning transmission electron microscope results show an atomic reconstruction at the SCO-on-LSMO interface and several oxygen vacancies at the SrO sublayer. The interface reconfiguration releases the polar energy, thereby inhibiting the generation of oxygen vacancies and improving the ferromagnetism of the LSMO film. Our work studies the impact of polar discontinuity at the interface, providing insights into the effects of interface polar discontinuities on functional materials. [ABSTRACT FROM AUTHOR]

Strain engineering is an alternative to chemical modification in manipulating functionalities of materials. Here, we report the lattice strain could relax the abrupt phase transition of (Ni1−xFex)1−δS and lead to an excellent negative thermal expansion (NTE) effect. The high-resolution scanning transmission electron microscope and extended x-ray absorption fine structure unambiguously demonstrate that parallel Ni3S4-type nanosheets could be introduced into the matrix lattice by increasing the δ value. By forming the Ni(Fe)-S-Ni(Fe) bonds, the (1–11) plane of nanosheets epitaxially grows on the (002) plane of the hexagonal matrix. Those bonds are strong enough to bear the large lattice mismatch along the interface as the phase transition occurs. As the concentration of nanosheets increases, the weak and inhomogeneous strain in matrix lattice becomes strong and uniform, expanding the NTE window in different ways. This result opens an unconventional avenue for designing NTE materials and extends the research scope of lattice strain as well. [ABSTRACT FROM AUTHOR]

Lead-free antiferroelectric AgNbO3 ceramics have garnered extensive attention due to their rapid charge/discharge capabilities and environmentally friendly nature, holding immense potential for energy storage applications. However, the practical utilization of AgNbO3 has been hindered by its low energy storage density. This study employed an A/B-site co-doping strategy, which yielded positive effects on the energy performance of AgNbO3 ceramics. By modifying the A/B-sites with equivalent amounts of Bi3+ and Y3+ ions, enhanced maximum polarization, improved breakdown field, and slimmer hysteresis loops were simultaneously achieved, as the combined effects of refined grain size, wider optical bandgap, and randomly distributed antiferroelectric nanodomains, which were verified through the scanning electron microscope, transmission electron microscope, and ultraviolet–visible spectrum. As a consequence, a high energy storage density of 5.40 J/cm3 accompanied by an energy storage efficiency of 56.5% was achieved in the Ag0.97Bi0.01Nb0.994Y0.01O3 ceramic under a relatively low electric field of 190 kV/cm. This study underscores the effectiveness of A/B-site aliovalent co-doping as a viable strategy for developing high-performance ceramic capacitors for energy storage applications. [ABSTRACT FROM AUTHOR]

Ca9Zn4.5Sb9 Zintl compound is one of the promising thermoelectric materials with excellent performance, which can be further improved by Eu alloying. In this work, a series of Ca9−yEuyZn4.5+δSb9 compounds is investigated by using the advanced Cs-corrected high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) imaging technique at an atomic level. The HAADF-STEM images show that alloying Eu will lead to preferential substitution of Eu atoms at Ca(1) and Ca(5) sites. The further structural analysis and first-principles density functional theory calculation elucidate the origin that the Eu atoms are prone to replace Ca(1) and Ca(5) sites in Ca9−yEuyZn4.5+δSb9. The preferential substitutions may provide a new insight into revealing the structural transformation commonly found in Zintl phase thermoelectric materials. [ABSTRACT FROM AUTHOR]

Ca9Zn4.5Sb9 Zintl compound is one of the promising thermoelectric materials with excellent performance, which can be further improved by Eu alloying. In this work, a series of Ca9−yEuyZn4.5+δSb9 compounds is investigated by using the advanced Cs-corrected high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) imaging technique at an atomic level. The HAADF-STEM images show that alloying Eu will lead to preferential substitution of Eu atoms at Ca(1) and Ca(5) sites. The further structural analysis and first-principles density functional theory calculation elucidate the origin that the Eu atoms are prone to replace Ca(1) and Ca(5) sites in Ca9−yEuyZn4.5+δSb9. The preferential substitutions may provide a new insight into revealing the structural transformation commonly found in Zintl phase thermoelectric materials. [ABSTRACT FROM AUTHOR]

Images and spectra obtained from aberration corrected scanning transmission electron microscopes (STEM) are now used routinely to quantify the morphology, structure, composition, chemistry, bonding, and optical/electronic properties of nanostructures, interfaces, and defects in many materials/biological systems. However, obtaining quantitative and reproducible atomic resolution observations from some experiments is actually harder with these ground-breaking instrumental capabilities, as the increase in beam current from using the correctors brings with it the potential for electron beam modification of the specimen during image acquisition. This beam effect is even more acute for in situ STEM observations, where the desired outcome being investigated is a result of a series of complicated transients, all of which can be modified in unknown ways by the electron beam. The aim in developing and applying new methods in STEM is, therefore, to focus on more efficient use of the dose that is supplied to the sample and to extract the most information from each image (or set of images). For STEM (and for that matter, all electron/ion/photon scanning systems), one way to achieve this is by sub-sampling the image and using Inpainting algorithms to reconstruct it. By separating final image quality from overall dose in this way and manipulating the dose distribution to be best for the stability of the sample, images can be acquired both faster and with less beam effects. In this paper, the methodology behind sub-sampling and Inpainting is described, and the potential for Inpainting to be applied to novel real time dynamic experiments will be discussed. [ABSTRACT FROM AUTHOR]

High-quality flexible membranes have promoted a myriad of applications in soft electronics or spintronic devices. Nevertheless, magnetic membranes that can withstand strong folding and rolling distortions have rarely been reported. Here, we found that the few to tens of nanometer thick LaMnO3 membranes with single-crystalline qualities exhibit superflexibility, demonstrated by self-folding and rolling into few-micron and sub-micron features. The combined scanning transmission electron microscope and selected area electron diffraction experiments simultaneously confirm the 180° folded single crystalline structure and the associated bending curvature and strain as large as 2 μm−1 and 4%. Furthermore, the scanning electron microscope revealed that as the membrane thickness decreases from 40 to 20 nm and 8 nm, the 180° folding is replaced by self-rolling into few-micron size tubes. Magnetization measurements revealed a large saturation (remnant) magnetization enhancement of 21% (34%) achieved in a macroscopically forced bending state under a similar bending strain of 4.9%. This work demonstrates the superflexibility of manganite oxide membranes which promise superior potential in flexible magnetic device applications. [ABSTRACT FROM AUTHOR]

AlN/GaN/AlN quantum disks (Q-disks) embedded in self-assembled hexagonally shaped GaN nanowires have been grown on the Si (111) substrate by plasma-assisted molecular beam epitaxy. To correlate the structural and optical properties of individual Q-disks inside the nanowire, highly spatially resolved cathodoluminescence (CL) spectroscopy in a scanning transmission electron microscope has been performed at 18 K. CL spectrum linescans along a single nanowire clearly identify the emission from the GaN base around 354 nm as well as two recombination channels at 347 nm and 330 nm directly correlated with the AlN/GaN/AlN Q-disk. A detailed characterization of these individual quantum objects is presented. [ABSTRACT FROM AUTHOR]

In this study, a femtosecond laser etching method is proposed to pattern an aluminum nitride (AlN) film, grown by metal-organic chemical vapor deposition on sapphire. Via control of typical pulse energies, the designed pattern was precisely written in the AlN film. The morphology of the patterned structures was characterized using a three-dimensional laser scanning confocal microscope and a scanning electron microscope; crystalline quality and film strain were analyzed using a Raman spectrometer and a transmission electron microscope. The results indicate that consistent morphologies were achieved with only slight changes to the crystalline quality. The tensile stress of the AlN film was released, and the film surface was slightly compressed after laser patterning. Thus, femtosecond etching has the potential to be an in situ patterning method during film growth. [ABSTRACT FROM AUTHOR]

A perpendicularly magnetized film is essentially important for spintronics applications, such as spin-transfer-torque type magnetoresistive random access memories, STT-MRAMs, and large perpendicular anisotropy energy, K u , with small saturation magnetization, M s , is required for reducing the critical current for the STT induced magnetization switching phenomenon. In this study, an equiatomic intermetallic compound, MnGaGe, was investigated in epitaxially grown film samples. Perpendicularly magnetized films with an M s value of about 260 emu/cm3 at 300 K were fabricated onto MgO (100) single crystal substrates. The maximum value of K u was 8.1 × 106 erg/cm3 at room temperature. Microstructure analysis using a scanning transmission electron microscope atomically revealed the Cu2Sb type crystal structure in the film sample. First principles calculations were also carried out to discuss the electronic structure. Using the analysis of the projected density of states for 3d-orbitals, the hybridization of the 3d-orbitals was suggested as a possible factor for promoting magnetocrystalline anisotropy. The MnGaGe film with the large K u and relatively small M s would be potentially used for spintronics applications. [ABSTRACT FROM AUTHOR]

Mapping individual radiative recombination channels at the nanoscale in direct correlation with the underlying crystal structure and composition of III–V semiconductor nanostructures requires unprecedented highly spatially resolved spectroscopy methods. Here, we report on a direct one-by-one correlation between the complex radial structure and the distinct carrier recombination channels of single GaAs-AlGaAs core-multishell nanowire heterostructures using low temperature cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope. Based on an optimized focused ion beam fabrication of the optically active specimen, we directly visualize the radial luminescence evolution and identify four distinct emission lines, i.e., the near band edge and defect luminescence of the GaAs core (819 nm, 837 nm), the emission of the single embedded GaAs quantum well (QW, 785 nm), and the AlGaAs shell luminescence correlated with alloy fluctuations (650–674 nm). The detailed radial luminescence profiles are anticorrelated between QW luminescence and core emission, illustrating the radial carrier transport of the core-shell system. We inspected in detail the low-temperature capture of excess carriers in the quantum well and barriers. [ABSTRACT FROM AUTHOR]

This study investigates the effect of high-temperature (350–500 °C) annealing on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) directly formed on a flexible polyimide substrate, which has superior thermal tolerance. As the annealing temperature increases, the tunnel magnetoresistance (TMR) ratio enhances and reaches up to ∼200% at an annealing temperature of 450 °C. The annealing temperature dependence is similar to that of MTJs fabricated in the same way on a thermally oxidized silicon substrate. Images taken by a scanning transmission electron microscope confirm the improvement of the crystallization of the CoFeB and MgO layers, which can be an important factor in enhancing the TMR ratio. Furthermore, the endurance of the flexible MTJ against repeated stretching of its substrate is investigated. The TMR ratio shows no change during and after a 1000-cycle application of a tensile strain larger than 1%. The high TMR ratio and strain endurance demonstrated in this study suggest that the flexible MTJ structure is a promising candidate for a future strain-sensing device. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides such as molybdenum disulfide (MoS2) may see service in the heart of next-generation nanoelectronic devices, where highly localized power dissipation can produce nontrivial temperature gradients over nanometer-scale distances. Here, we demonstrate that MoS2 is a promising target for plasmon energy expansion thermometry (PEET), a high-spatial resolution temperature mapping technique employed in a scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS). We first use a calibrated, commercial MEMS-style TEM sample heater chip to measure the temperature dependence of the MoS2 bulk plasmon. We corroborate the chip's temperature calibration with Raman thermometry and determine the bulk thermal expansion coefficient (TEC) of MoS2 in the temperature range of 300–1100 K. Applying this TEC value to PEET measurements on a suspended MoS2 flake, we map 70–90 K/μm temperature gradients with a submicrometer spatial resolution. [ABSTRACT FROM AUTHOR]

We report electronic transport mapping in a single dielectric layer of a polycrystalline BaTiO3 multilayer ceramic capacitor (MLCC) by electron beam induced current (EBIC) measurements using a scanning transmission electron microscope. Ga+ focused ion beam-lift out techniques with organometallic Pt-deposition are used to extract and electrically connect to these devices while maintaining high (>gigaohm) resistance between electrodes. Different modes of EBIC are observed depending on device resistivity. We demonstrate the use of EBIC resulting from secondary electron emission as a method for performing resistance contrast imaging (RCI), with resistive grain boundaries appearing as steps in EBIC contrast. These RCI maps are also used to calculate the potential and electric field of the device under an arbitrary bias. A mix of high- and low-resistance ohmic as well as rectifying grain boundaries is observed. These results help to better establish the distribution of resistivities critical to the prevention of performance-limiting current leakage in MLCCs. [ABSTRACT FROM AUTHOR]

Subsampled image acquisition followed by image inpainting in a scanning transmission electron microscope is a novel approach to control dose and increase the image frame rate during experiments, thereby allowing independent control of the spatial and temporal dose envelope during image acquisition. Here, subsampled imaging is shown to permit precise in situ observations of the fundamental kinetic processes behind nucleation and growth of silver (Ag) nanoparticles from an aqueous solution. At high sampling-levels, nanoparticles can be observed with morphologies that are consistent with strong interface interactions, i.e., rafts and pillars, whereas at low sampling-levels, the particles exhibit regular spherical morphologies. The relative numbers of rafts/pillars and regular nanoparticles, their sizes, and their incubation times can be attributed to local changes in the molar concentration of the Ag ions in the aqueous solution; higher sampling-levels significantly increase the reactants in the vicinity of the window, leading to rapid supersaturation and the precipitation on the window surface. These precisely controlled kinetics highlight subsampled imaging as a method by which the driving force for nucleation and growth (i.e., the electron beam) can be disentangled from the spatial/temporal resolution of the observation in all in situ experiments, providing a pathway to identify and quantify the importance of individual kinetic factors behind nucleation and growth in a wide variety of complex materials systems and architectures. [ABSTRACT FROM AUTHOR]

We report on surface plasmons in the visible range in hexagonal close-packed (HCP) gold nanoparticles, synthesized by metastable solidification of Au-Ge eutectic liquid catalyst droplets at the tips of germanium nanowires at the cessation of vapor-liquid-solid nanowire growth. Using 300 kV electrons in a transmission electron microscope in scanning transmission mode with deep subnanometer spatial resolution, we characterize plasmons and interband transitions. Compared to conventional face-centered cubic (FCC) gold nanoparticles, plasmons and interband transitions are observed at different energies in HCP gold nanoparticles. We confirm lattice parameters unique to HCP gold by convergent beam electron diffraction and x-ray diffraction. Energy dispersive spectroscopy measured in a scanning transmission electron microscope verifies minimal impurity concentration in the HCP gold nanoparticles. These experimental results confirm that HCP gold is structurally distinct from FCC plasmonic materials, and also exhibits different electronic and optical properties. [ABSTRACT FROM AUTHOR]

A facile manganese ion Mn(II)-assisted assembly has been designed to fabricate microbowls by using graphene oxide nanosheets as basic building blocks, which were exfoliated ultrasonically from the oxidized soot powders in deionized water. From the morphology evolution observations of transmission electron microscope and scanning electron microscope, a coordinating-tilingcollapsing manner is proposed to interpret the assembly mechanism based on attractive Van der Waals forces, π-π stacking, and capillary action. It is interesting to note that the as-prepared microbowls present a room temperature superparamagnetic behavior. [ABSTRACT FROM AUTHOR]

A method for quantitative wettability study at nanoscale is presented. It is based on measuring transmitted electrons through nanodroplets using wet scanning transmission electron microscope (wet-STEM) detector in environmental scanning electron microscope. The quantitative information of the nanodroplet shape and contact angle is obtained by fitting Monte Carlo simulation results for transmitted electrons through spherical cap geometry with the experimental wet-STEM results. The characterization is demonstrated for particles and for initial stages of water droplet condensation over a nonhomogeneous holey carbon grid. The method is suggested for application in thin polymer and biological films. [ABSTRACT FROM AUTHOR]

Homogeneous shuttlelike nanoparticles of CuO are synthesized using pulsed-laser induced liquid-solid interface reaction. The shape-induced ultraviolet absorption (258 nm) is observed in the ultraviolet absorption spectrum of CuO shuttlelike nanoparticles. Theoretical calculations on the basis of discrete dipole approximation are employed to pursue the physical origin of the anomalous UV absorption peak. Both experiments and theories show that the shape of nanoparticles has a great influence on the optical properties. [ABSTRACT FROM AUTHOR]

Modification of silicon nitride nanopores under electron beam (e-beam) irradiation was investigated using a scanning electron microscope (SEM). Under e-beam irradiation, all pores with diameters ranging from 40 to 200 nm undergo shrinkage, and the shrinkage rate increases with the rate of energy deposition. By using the selected-area scanning tool in the SEM, the silicon nitride nanopores can be selectively reshaped based on localized e-beam irradiation, with a characteristic dimension smaller than 10 nm. A selected-area shaping technique was proposed to controllably shrink and shape the nanopores to a special structure. [ABSTRACT FROM AUTHOR]

Single-phase Er2SiO5 nanocrystal aggregates were produced on a large scale using Si nanowire (Si-NW) arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si (111) substrate. Afterwards, ErCl3·6H2O dissolved ethanol solution was spin coated and annealed first at 900 °C for 4 min in a flowing N2/O2 environment and then at 1200 °C in a flowing Ar environment for 3 min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er2SiO5 oxyorthosilicate nanocrystals. The crystalline nature of Er2SiO5 film and the loose nature of the aggregate result in an atomlike Er3+ spectrum with a very narrow luminescence linewidth at 1.53 μm, which together with a complete lack of temperature quenching of Er3+ luminescence and a high Er concentration indicate a viability of this method to fabricate efficient, high-gain Si-based optical material for Si photonics. [ABSTRACT FROM AUTHOR]

Tungsten oxide nanostructures were deposited on silicon substrates by a thermal oxidation approach. The major factors influencing their phase structure and growth morphology were found to be the substrate temperature and the chamber pressure. By investigating the growth process of these nanostructures, a phase growth diagram was constructed, with which one can realize the phase selection and morphology control of the tungsten oxide nanostructures by this thermal oxidation approach. The present study could be of great significance in fabricating tungsten oxide nanostructures for device applications. [ABSTRACT FROM AUTHOR]

We report on the direct fabrication of single-crystalline wurtzite-type hexagonal GaN nanotubes via a newly designed, controllable, and reproducible chemical thermal-evaporation process. The nanotubes are single crystalline, have one end closed, an average outer diameter of ∼300 nm, an inner diameter of ∼100 nm, and a wall thickness of ∼100 nm. The structure and morphology of the tubes are characterized using a scanning electron microscope and a transmission electron microscope. The cathodoluminescence of individual nanotubes is also investigated. The growth mechanism, formation kinetics, and crystallography of GaN nanotubes are finally discussed. [ABSTRACT FROM AUTHOR]

High-purity nanocables of iron-containing amorphous-silica-sheathed silicon carbide were synthesized by a thermal reaction method using silicon wafer as the silicon source and growth substrate, and ferrocene as the carbon and iron catalyst precursor. The nanocables were tens of μm in length and 40–60 nm in diameter. Iron oxide nanoparticles with a mean diameter of 5 nm were dispersed evenly in the amorphous silica layer. The nanocables were found to be ferromagnetic at both 10 K and room temperature, which indicates that they may have important potential applications in electromagnetic nanodevices. [ABSTRACT FROM AUTHOR]