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The presence of toxic organic pollutants in aquatic environments poses significant threats to human health and global ecosystems. Photocatalysis that enables in situ production and activation of H2O2 presents a promising approach for pollutant removal; however, the processes of H2O2 production and activation potentially compete for active sites and charge carriers on the photocatalyst surface, leading to limited catalytic performance. Herein, a hierarchical 2D/2D heterojunction nanosphere composed of ultrathin BiOBr and BiOI nanosheets (BiOBr/BiOI) is developed by a one‐pot microwave‐assisted synthesis to achieve in situ H2O2 production and activation for efficient photocatalytic wastewater treatment. Various experimental and characterization results reveal that the BiOBr/BiOI heterojunction facilitates efficient electron transfer from BiOBr to BiOI, enabling the one‐step two‐electron O2 reduction for H2O2 production. Moreover, the ultrathin BiOI provides abundant active sites for H2O2 adsorption, promoting in situ H2O2 activation for •O2− generation. As a result, the BiOBr/BiOI hybrid exhibits excellent activity for pollutant degradation with an apparent rate constant of 0.141 min−1, which is 3.8 and 47.3 times that of pristine BiOBr and BiOI, respectively. This work expands the range of the materials suitable for in situ H2O2 production and activation, paving the way toward sustainable environmental remediation using solar energy. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) imaging of thin, extended specimens at nanometer resolution is critical for applications in biology, materials science, advanced synthesis, and manufacturing. One route to 3D imaging is tomography, which requires a tilt series of a local region. However, capturing images at higher tilt angles is infeasible for such thin, extended specimens. Here, we explore a suitable alternative to reconstruct the 3D volume using a single, energy-filtered, bright-field coherent image. We show that when our specimen is homogeneous and amorphous, simultaneously inferring local depth and thickness for 3D imaging is possible in the near-field limit. We demonstrated this technique with a transmission electron microscope to fill a glaring gap for rapid, accessible 3D nanometrology. This technique is applicable, in general, to any coherent bright field imaging with electrons, photons, or any other wavelike particles. The authors experimentally demonstrate with a transmission electron microscope that single-shot 3D imaging is possible in the near-field limit, by simultaneously inferring local depth and thickness. The proposed reconstruction method uses priors from the homogenously amorphous specimen, and it can be extended for imaging multi-layered samples. [ABSTRACT FROM AUTHOR]

We present an overview of the atomic structure of extended defects in wurtzite III-nitrides, focusing on GaN heterostructures applicable to light-emitting optoelectronic devices (LEDs and lasers) and radio frequency (RF) power electronics. We provide experimental routines to visualize and recognize these defects with aberration-corrected scanning transmission electron microscopy (STEM). Line, planar, and volume defects are imaged, with examples taken from InGaN multi quantum well heterostructures, epitaxially grown on Si. We demonstrate how the different line and planar defects can be identified by visualizing either the extra or sheared planes that are characteristic to each defect or by differentiating their unique atomic column projections through depth-sectioning. Volume defects in the form of locally phase-separated InN and metallic indium precipitates were also identified via spatially resolved electron energy-loss spectroscopy. The classification of defects established in this work and the methods to visualize them will be a reference to researchers in this field and will provide a foundation for the targeted engineering of future III-nitrides. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered to be promising building blocks for the next generation electronic and optoelectronic devices. Various doping schemes and work function engineering techniques have been explored to overcome the intrinsic performance limits of 2D TMDs. However, a reliable and long-time air stable doping scheme is still lacking in this field. In this work, we utilize keV ion beams of H2+ to irradiate layered WSe2 crystals and obtain efficient n-type doping effect for all irradiated crystals within a fluence of 1 × 1014 protons·cm−2 (1e14). Moreover, the irradiated WSe2 remains an n-type semiconductor even after it is exposed to ambient conditions for a year. Localized ion irradiation with a focused beam can directly pattern on the sample to make high performance homogenous p-n junction diodes. Raman and photoluminescence (PL) spectra demonstrate that the WSe2 crystal lattice stays intact after irradiation within 1e14. We attribute the reliable electron-doping to the significant increase in Se vacancies after the proton irradiation, which is confirmed by our scanning transmission electron microscope (STEM) results. Our work demonstrates a reliable and long-term air stable n-type doping scheme to realize high-performance electronic TMD devices, which is also suitable for further integration with other 2D devices. [ABSTRACT FROM AUTHOR]

Defect engineering of atomically thin semiconducting crystals is an attractive route to developing single‐photon sources and valleytronic devices. For these applications, defects with well‐defined optical characteristics need to be generated in a precisely controlled manner. However, defect‐induced optical features are often complicated by the presence of multiple defect species, hindering the identification of their structural origin. Here, we report systematic generation of optically active atomic defects in monolayer MoS2, WS2, MoSe2, and WSe2 via proton‐beam irradiation. Defect‐induced emissions are found to occur ≈100 to 200 meV below the neutral exciton peak, showing typical characteristics of localized excitons such as saturation at high‐excitation rates and long lifetime. Using scanning transmission electron microscopy, it is shown that freshly created chalcogen vacancies are responsible for the localized exciton emission. Density functional theory and ab initio GW plus Bethe‐Salpeter‐equation calculations reveal that the observed emission can be attributed to transitions involving defect levels of chalcogen vacancy and the valence band edge state. [ABSTRACT FROM AUTHOR]

2D magnetic materials have been attracting enormous interest for both fundamental research and potential spintronic applications. Here, this work demonstrates the van der Waals epitaxial growth of air‐stable 2D magnetic CrS2 on mica substrate by chemical vapor deposition (CVD). The layered nature, high crystallinity, stoichiometry, and high‐purity 1T phase of the individual CrS2 crystallites are verified by a series of complementary characterization techniques including atomic force microscope, scanning transmission electron microscope and energy dispersive X‐ray spectroscopy. The single‐crystalline 1T‐phase CrS2 crystallites exhibit a metallic nature with a moderate conductivity of 1.78 × 102 S m−1 and a room‐temperature ferromagnetism with a coercive field of 28.7 Oe. The CVD growth of the air‐stable CrS2 crystallites with 1T phase and high crystallinity offer a new platform for the further physics research and spintronic device applications. [ABSTRACT FROM AUTHOR]

Thermoelectrics enable direct heat-to-electricity transformation, but their performance has so far been restricted by the closely coupled carrier and phonon transport. Here, we demonstrate that the quantum gaps, a class of planar defects characterized by nano-sized potential wells, can decouple carrier and phonon transport by selectively scattering phonons while allowing carriers to pass effectively. We choose the van der Waals gap in GeTe-based materials as a representative example of the quantum gap to illustrate the decoupling mechanism. The nano-sized potential well of the quantum gap in GeTe-based materials is directly visualized by in situ electron holography. Moreover, a more diffused distribution of quantum gaps results in further reduction of lattice thermal conductivity, which leads to a peak ZT of 2.6 at 673 K and an average ZT of 1.6 (323–723 K) in a GeTe system. The quantum gap can also be engineered into other thermoelectrics, which provides a general method for boosting their thermoelectric performance. Defects are believed to always scatter carriers. Here, the authors find that the quantum gaps in GeTe-based materials do not scatter carriers, which decouple the carriers and phonons transport leading to high thermoelectric performance. [ABSTRACT FROM AUTHOR]

Controlled incorporation of single atoms in a suitable host matrix can result in a radical transformation in catalytic properties. However, finding a straightforward synthetic strategy that offers a compelling combination of solution processing, atomic doping and a matching host is still a grand challenge. Here, a spontaneous heteroatom formation of atomic Zn sites in well‐defined wurtzite CoO nanorods, delivering high photoreduction rates, reaching 86.7 µmol g−1 h−1 for CO and 31.4 µmol g−1 h−1 for CH4 production is reported. Based on the validation of atomic Zn sites structures, catalytic process tracking via in situ/ex situ spectroscopic probes, and related structural simulations, a good description of the catalytic reaction kinetics for Zn/CoO as a function of applied potential is established, revealing how the single doping sites influence the CO2 photoreduction. [ABSTRACT FROM AUTHOR]

Chalcogenide phase change materials (PCMs) have been extensively applied in data storage, and they are now being proposed for high resolution displays, holographic displays, reprogrammable photonics, and all-optical neural networks. These wide-ranging applications all exploit the radical property contrast between the PCMs' different structural phases, extremely fast switching speed, long-term stability, and low energy consumption. Designing PCM photonic devices requires an accurate model to predict the response of the device during phase transitions. Here, we describe an approach that accurately predicts the microstructure and optical response of phase change materials during laser induced heating. The framework couples the Gillespie Cellular Automata approach for modelling phase transitions with effective medium theory and Fresnel equations. The accuracy of the approach is verified by comparing the PCM's optical response and microstructure evolution with the results of nanosecond laser switching experiments. We anticipate that this approach to simulating the switching response of PCMs will become an important component for designing and simulating programmable photonics devices. The method is particularly important for predicting the multi-level optical response of PCMs, which is important for all-optical neural networks and PCM-programmable perceptrons. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been rapidly established as promising building blocks for versatile atomic scale circuits and multifunctional devices. However, the high contact resistance in TMDs based transistors seriously hinders their applications in complementary electronics. In this work, we show that an Ohmic homojunction n-type tungsten diselenide (WSe2) transistor is realized through spatially controlling cesium (Cs) doping region near the contacts. We find that the remarkable electron doping effect of Cs stimulates a semiconductor to metal (2H to 1T') phase transition in WSe2, and hence the formation of 2H-1T' hetero-phase contact. Our method significantly optimizes the WSe2 transport behavior with a perfect low subthreshold swing of ∼ 61 mV/dec and ultrahigh current on/off ratio exceeding ∼ 109. Meanwhile, the electron mobility is enhanced by nearly 50 times. We elucidate that the ideal n-type behavior originates from the negligible Schottky barrier height of ∼ 19 meV and low contact resistance of ∼ 0.9 kΩ·µm in the 2H-1T' homojunction device. Moreover, based on the Ohmic hetero-phase configuration, a WSe2 inverter is achieved with a high gain of ∼ 270 and low power consumption of ∼ 28 pW. Our findings envision Cs functionalization as an effective method to realize ideal Ohmic contact in 2D WSe2 transistors towards high performance complementary electronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are a new class of electronic materials offering tremendous opportunities for advanced technologies and fundamental studies. Similar to conventional semiconductors, substitutional doping is key to tailoring their electronic properties and enabling their device applications. Here, we review recent progress in doping methods and understanding of doping effects in group 6 TMDs (MX2, M = Mo, W; X = S, Se, Te), which are the most widely studied model 2D semiconductor system. Experimental and theoretical studies have shown that a number of different elements can substitute either M or X atoms in these materials and act as n- or p-type dopants. This review will survey the impact of substitutional doping on the electrical and optical properties of these materials, discuss open questions, and provide an outlook for further studies. [ABSTRACT FROM AUTHOR]

The exploration of n‐type PbTe as thermoelectric materials always falls behind its p‐type counterpart, mainly due to their quite different electronic band structure. In this work, elemental Sb and Cu2Te are introduced into an n‐type base material (PbTe)81‐Sb2Te3. The introduction of extra Sb can effectively tune the concentration of electrons; meanwhile, Sb precipitates can also scatter low‐energy electrons (negatively contribute to the Seebeck coefficient) thus enhance the overall Seebeck coefficient. The added Cu2Te is found to always co‐precipitate with Sb, forming an interesting Sb/CuTe core/shell structure; moreover, the interface between core/shell precipitates and PbTe matrix simultaneously shows coherent lattice and strong strain contrast, beneficial for electron transport but adverse to phonon transport. Eventually, a peak figure of merit ZTmax ≈ 1.6 @ 823K and simultaneously an average ZT ≈ 1.0 (323–823 K) are realized in the (PbTe)81Sb2Te3‐0.6Sb‐2Cu2Te sample, representing the state of the art for n‐type PbTe‐based thermoelectric materials. Moreover, for the first time the three existing forms of Cu atoms in Cu2Te alloyed PbTe are unambiguously clarified with aberration‐corrected scanning transmission electron microscopy (Cs‐STEM). [ABSTRACT FROM AUTHOR]

Particle simulation has been widely used in studying plasmas. The technique follows the motion of a large assembly of charged particles in their self-consistent electric and magnetic fields. Plasmons, collective oscillations of the free electrons in conducting media such as metals, are connected to plasmas by very similar physics, in particular, the notion of collective charge oscillations. In many cases of interest, plasmons are theoretically characterized by solving the classical Maxwell's equations, where the electromagnetic responses can be described by bulk permittivity. That approach pays more attention to fields rather than motion of electrons. In this work, however, we apply the particle simulation method to model the kinetics of plasmons, by updating both particle position and momentum (Newton–Lorentz equation) and electromagnetic fields (Ampere and Faraday laws) that are connected by current. Particle simulation of plasmons can offer insights and information that supplement those gained by traditional experimental and theoretical approaches. Specifically, we present two case studies to show its capabilities of modeling single-electron excitation of plasmons, tracing instantaneous movements of electrons to elucidate the physical dynamics of plasmons, and revealing electron spill-out effects of ultrasmall nanoparticles approaching the quantum limit. These preliminary demonstrations open the door to realistic particle simulations of plasmons. [ABSTRACT FROM AUTHOR]

The crystal phase-based heterostructures of noble metal nanomaterials are of great research interest for various applications, such as plasmonics and catalysis. However, the synthesis of unusual crystal phases of noble metals still remains a great challenge, making the construction of heterophase noble metal nanostructures difficult. Here, we report a one-pot wet-chemical synthesis of well-defined heterophase fcc-2H-fcc gold nanorods (fcc: face-centred cubic; 2H: hexagonal close-packed with stacking sequence of "AB") at mild conditions. Single particle-level experiments and theoretical investigations reveal that the heterophase gold nanorods demonstrate a distinct optical property compared to that of the conventional fcc gold nanorods. Moreover, the heterophase gold nanorods possess superior electrocatalytic activity for the carbon dioxide reduction reaction over their fcc counterparts under ambient conditions. First-principles calculations suggest that the boosted catalytic performance stems from the energetically favourable adsorption of reaction intermediates, endowed by the unique heterophase characteristic of gold nanorods. The crystal phase-based heterostructures of noble metal nanomaterials are of interest for various applications. Here, the authors report the wet-chemical synthesis of gold nanorods with a well-defined fcc-2H-fcc heterophase, which possess unique optical and catalytic properties. [ABSTRACT FROM AUTHOR]

Abstract: Higher memory density and faster computational performance of resistive switching cells require reliable array‐accessible architecture. However, selecting a designated cell within a crossbar array without interference from sneak path currents through neighboring cells is a general problem. Here, a highly doped n++ Si as the bottom electrode with Ni‐electrode/HfOx/SiO2 asymmetric self‐rectifying resistive switching device is fabricated. The interfacial defects in the HfOx/SiO2 junction and n++ Si substrate result in the reproducible rectifying behavior. In situ transmission electron microscopy is used to quantitatively study the properties of the morphology, chemistry, and dynamic nucleation–dissolution evolution of the chains of defects at the atomic scale. The spatial and temporal correlation between the concentration of oxygen vacancies and Ni‐rich conductive filament modifies the resistive switching effect. This study has important implications at the array‐level performance of high density resistive switching memories. [ABSTRACT FROM AUTHOR]

Galvanic replacement (GR) is a simple and widely used approach to synthesize hollow nanostructures for applications in catalysis, plasmonics, and biomedical research. The reaction is driven by the difference in electrochemical potential between two metals in a solution. However, transient stages of this reaction are not fully understood. Here, we show using liquid cell transmission electron microscopy that silver (Ag) nanocubes become hollow via the nucleation, growth, and coalescence of voids inside the nanocubes, as they undergo GR with gold (Au) ions at different temperatures. These direct in situ observations indicate that void formation due to the nanoscale Kirkendall effect occurs in conjunction with GR. Although this mechanism has been suggested before, it has not been verified experimentally until now. These experiments can inform future strategies for deriving such nanostructures by providing insights into the structural transformations as a function of Au ion concentration, oxidation state of Au, and temperature. [ABSTRACT FROM AUTHOR]

The lower contrast and Ni signal intensity of the region under the smaller MNF (i.e., MNF2) indicates less Ni atoms migration in the smaller MNF compared to the larger one (i.e., MNF1). gl A useful feature of high-angle, annular dark field STEM images is that their contrast is proportional to the local atomic number; they are therefore also known as Z-contrast images. Keywords: in situ transmission electron microscopy; metal nanofilaments; resistive random access memory; energy dispersive X-ray spectrometry EN in situ transmission electron microscopy metal nanofilaments resistive random access memory energy dispersive X-ray spectrometry 1 6 6 10/06/21 20151101 NES 151101 B The evolution of metal nanofilaments formed in dielectric layers of Ni/HfO SB 2 sb /SiO I SB x sb i /n SP + sp Si stacks b and the role of Ni atoms during SET (low resistance) and RESET (high resistance) are quantitatively studied. Our study on Ni/HfO SB 2 sb /SiO I SB x sb i /n SP + sp Si-based (i.e., MIS) RRAM is crucial because this material system is the most obvious potential candidate for commercial RRAM devices, as it is based on the established silicon device CMOS platform. The EDX Ni map in Figure e (where brighter red represents higher concentrations of Ni atoms/ions) shows the extent over which the Ni has been redistributed. [Extracted from the article]

Harnessing the optical properties of noble metals down to the nanometre scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy-loss spectroscopy with a nanometre-sized electron probe. We prepare the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides. [ABSTRACT FROM AUTHOR]

Lithography provides the precision to pattern large arrays of metallic nanostructures with varying geometries, enabling systematic studies and discoveries of new phenomena in plasmonics. However, surface plasmon resonances experience more damping in lithographically–defined structures than in chemically–synthesized nanoparticles of comparable geometries. Grain boundaries, surface roughness, substrate effects, and adhesion layers have been reported as causes of plasmon damping, but it is difficult to isolate these effects. Using monochromated electron energy–loss spectroscopy (EELS) and numerical analysis, we demonstrate an experimental technique that allows the study of these effects individually, to significantly reduce the plasmon damping in lithographically–defined structures. We introduce a method of encapsulated annealing that preserves the shape of polycrystalline gold nanostructures, while their grain-boundary density is reduced. We demonstrate enhanced Q–factors in lithographically–defined nanostructures, with intrinsic damping that matches the theoretical Drude damping limit. [ABSTRACT FROM AUTHOR]

Grain boundaries in the polycrystalline microstructure of post-annealed high-j (HK) dielectrics are a major limitation in the reliability of HK dielectrics used for advanced CMOS technologies. Another challenge in the field of HK dielectrics is to ensure higher drain drive current in CMOS, while maintaining low leakage current. In this work, the authors demonstrate enhanced performance of HfO2 and CeO2 dielectrics by incorporating lanthanum. The resulting stacks show promising dielectric characteristics with reduced leakage current and uniform (amorphous) crystal structure. The improved HK characteristics were shown to occur even over nanometer-length scales using scanning probe microscopy and transmission electron microscopy, in agreement with previous studies based on micron-scale device-level measurement. [ABSTRACT FROM AUTHOR]

Dipole nano-antennas have predominantly been investigated in their lateral orientation with their long axes in plane with a supporting substrate. However, the response of coupled dipole antennas oriented vertically to a supporting substrate has so far been out of experimental reach. Here, we present a self-aligned electron-beam lithography technique for fabricating such antennas consisting of metal nanostructures on both sides of a suspended silicon nitride membrane. This 30 nm thick membrane provides an ultra-smooth metal/dielectric interface and uniformly defines the antenna feed-gap size in an array of antennas. It is also a suitable substrate for probing the nano-antenna response with monochromated electron energy-loss spectroscopy (EELS) in a transmission electron microscope. We provide details of this double-sided patterning process, and show the excitation of hybridized plasmon modes in EELS with electrons directed along, and at an angle to, the antenna axis. [ABSTRACT FROM AUTHOR]

The origin behind crystalline silicon surface passivation by Al2O3 films is studied in detail by means of spatially-resolved electron energy loss spectroscopy. The bonding configurations of Al and O are studied in as-deposited and annealed Al2O3 films grown on c-Si substrates by plasma-assisted and thermal atomic layer deposition. The results confirm the presence of an interfacial SiO2-like film and demonstrate changes in the ratio between tetrahedrally and octahedrally coordinated Al in the films after annealing. These observations reveal the underlying origin of c-Si surface passivation by Al2O3. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Here we report on the “scrolling” of planar graphene induced by water as a result of the interplay between water capillarity and graphene elasticity. This scrolling leads to the formation of stable nanochannels that encapsulate water and nanoscale objects. We demonstrate that these graphene nanochannels can be used as nanofluidic platforms for dynamic imaging of nanoscale processes in liquids with Transmission Electron Microscopes (TEMs). These water-impermeable graphene nanochannels have practical application in the design of nanofluidic devices used in biosensors and many analytical separation devices. [ABSTRACT FROM AUTHOR]