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We study the degradation process of closely spaced silver and gold nanocubes under high-energy electron beam irradiation using transmission electron microscopy (TEM). The high aspect ratio gaps between silver and gold nanocubes degraded in many cases as a result of protrusion and filament formation during electron beam irradiation. We demonstrate that the molecular coating of the nanoparticles can act as a protective barrier to minimize electron-beam-induced damage on passivated gold and silver nanoparticles. [ABSTRACT FROM AUTHOR]

Resistive random access memory (RRAM) devices with a nickel top electrode form controllable metal nanofilaments and have robust resistive switching performance. We investigate the Ni/HfO 2 /SiO x /n + Si RRAM structure, which forms a Ni-rich defect in the silicon underneath the Ni nanofilament in the dielectric layers after a SET process. The formation of these defects may affect the retention of the devices, so we applied a detailed Finite Element Method and Kinetic Monte Carlo approach to simulate the Ni-rich defect evolution under different compliance current settings. We confirm that the chemical composition of the defects is metallic NiSi 2 , and that their size is determined by the compliance current. These simulation results are supported by in-situ STM-like experiments inside a transmission electron microscope (TEM). NiSi 2 defects are shaped as truncated square pyramids, and we show that this is due to the low activation energy of Ni migration along the (111) crystal plane of Si. Our results demonstrate that electromigration is the main driving force for Ni migration initially, after which thermal migration and especially stress migration become the dominant mechanism. This work gives a fascinating example of an as-grown metal–insulator–semiconductor (MIS) system that can be controllably converted to a metal–insulator–metal (MIM) configuration for down-scaled RRAM operation. [ABSTRACT FROM AUTHOR]

Searching for new plasmonic building blocks which offer tunability and design flexibility beyond noble metals is crucial for advancing the field of plasmonics. Herein, we report that solution-synthesized hexagonal Bi2Te3 nanoplates, in the absence of grating configurations, can exhibit multiple plasmon modes covering the entire visible range, as observed by transmission electron microscopy (TEM)-based electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. Moreover, different plasmon modes are observed in the center and edge of the single Bi2Te3 nanoplate and a breathing mode is discovered for the first time in a non-noble metal. Theoretical calculations show that the plasmons observed in the visible range are mainly due to strong spin-orbit coupling induced metallic surface states of Bi2Te3. The versatility of shape- and size-engineered Bi2Te3 nanocrystals suggests exciting possibilities in plasmonics-enabled technology. [ABSTRACT FROM AUTHOR]

The question of whether resistance switching in conducting bridge random access memory (CBRAM) devices occurs through a single filament which repeatedly undergoes nucleation and rupture or through different filaments for different cycles is difficult to ascertain using conventional electrical tests on metal–insulator–metal (MIM) capacitor structures. In order to profile the spatial location of the conductive filament during multiple switching cycles, we make use of the Ni–HfO 2 –Si based metal–insulator–semiconductor (MIS) stack with a transistor test structure so that the lateral location of the filament along the source to drain can be probed electrically by considering the weighted ratio of source and drain currents measured. Our analysis reveals that filaments can evolve in spatially uncorrelated locations and switching is not always caused by the same filament over and over again. A simple statistical model is also provided to justify the inferences of the electrical study. The probability of a new filament nucleating elsewhere in the dielectric is a strong function of the oxide barrier thickness as well as the curvature radii of the previously ruptured metal filament edges. [ABSTRACT FROM AUTHOR]

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]

Conducting bridge random access memory (CBRAM) devices operate on the basis of repeated nucleation and rupture of the metallic filament during the SET and RESET transitions. One of the critical reliability metrics for any non-volatile memory (NVM) technology is read disturb immunity , which refers to the ability of the device to keep the filament stable and unperturbed during the reading phase. While read disturb has been analyzed in detail for OxRAM which works based on the principle of oxygen vacancy generation and oxygen ion drift/diffusion, the susceptibility of CBRAM to read disturb events has not been analyzed in-depth. We make use of electrical test data, first order thermal model and fundamental thermodynamics to assess the stability of the CBRAM filament in both the high resistance state (HRS) as well as low resistance state (LRS). Our analysis reveals that the HRS retention is very good, while LRS retention can be quite poor for the Nickel-based CBRAM stack. [ABSTRACT FROM AUTHOR]

Forming is one of the key phenomenon that governs the subsequent switchability in high-κ based resistive random access memory (RRAM) devices. The variability of subsequent switching events (voltage and resistance state), shape and size of filament, reliability of the non-volatile memory device in terms of endurance and retention as well as ultra-low power operation of the memory array all depend on the forming process in one way or the other. As a result, controllability of forming and reduction of the forming voltage is an important design activity in the RRAM technology development process. In this study, we analyze the various factors that affect the forming voltage distribution from a simulation perspective using a Kinetic Monte Carlo (KMC) based formulation of the vacancy defect evolution process in the dielectric. The impact of high-κ microstructure (grain boundaries), metal–oxide interface roughness, deposition process induced defect distribution as well as role of multi-layer dielectric films on the forming time and spread is investigated in detail. The results of the study provide guidelines for further reliability design initiatives in tightening the forming distribution. [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]

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]

Abstract: We study atomic-resolution annular electron energy-loss spectroscopy (AEELS) in scanning transmission electron microscopy (STEM) imaging with experiments and numerical simulations. In this technique the central part of the bright field disk is blocked by a beam stop, forming an annular entry aperture to the spectrometer. The EELS signal thus arises only from electrons scattered inelastically to angles defined by the aperture. It will be shown that this method is more robust than conventional EELS imaging to variations in specimen thickness and can also provide higher spatial resolution. This raises the possibility of lattice resolution imaging of lighter elements or ionization edges previously considered unsuitable for EELS imaging. [Copyright &y& Elsevier]

Abstract: A method for spectral acquisition, called binned gain averaging, will be described and tested. Systematic or correlated noise is efficiently suppressed with this method by averaging the gain over a series of CCD pixels. As a result, improved signal-to-noise ratios are obtained that allow the detection of very weak signals. At the same time, the spectral energy resolution is not degraded—even for long acquisition periods. It will be demonstrated that with this method, it is possible to significantly enhance the acquisition speed and quality of electron energy-loss (EEL) spectra and EELS maps. Examples will be given of double ionic scattering (i.e. the detection of the second boron K-edge) and the mapping of gold surface plasmons in the near-infrared and visible energy range. [Copyright &y& Elsevier]

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]

• Stabilization of P 3-major and O3-minor biphasic layered oxide. • Significant improvement of rate performance and capacity retention upon Ni doping. • Improving storage performance by avoiding complete phase transformation from P 3 to an unknown Z phase at high voltages. • Reduced internal resistance and enhanced hole conductivity upon complete desodiation due to Ni2+. We report synthesis and sodium storage performances of two biphasic P 3/O3 materials, Na 0.9 Fe 0.5 Mn 0.5 O 2 (P 3/O3 NFM) and Na 0.9 Fe 0.5 Mn 0.45 Ni 0.05 O 2 (P 3/O3 NFNM). The choice of composition and Ni doping context have been justified. On replacing 5 % Mn by Ni, we found improvements in (de)sodiation capacity and rate performance. The delivered storage capacities of P 3/O3 NFM and P 3/O3 NFNM in the first cycle between 4.4 and 2.0 V are 118 mAh g−1 and 148 mAh g−1 at C/10 (0.015Ag−1) rate, respectively. The subsequent cycles have a narrow voltage window of 4.2 to 1.9 V for optimized cycling performance. In this voltage window, P 3/O3 NFNM demonstrates more than twice the discharge capacity of P 3/O3 NFM at 3C rate (0.45Ag−1); further it retains 74 % of its capacity after 200 cycles at 1C rate (0.15Ag−1) as compared to 57 % in P 3/O3 NFM. X-ray diffraction studies confirm that Ni doping helps in retaining the P 3 phase throughout the charge cycle in P 3/O3 NFNM which helps in achieving a higher discharge capacity and better cycling. A greater reduction in the internal resistance, specifically the charge transfer resistance along with enhanced hole conductivity is observed from impedance studies of fully desodiated P 3/O3 NFNM due to the maintenance of the P 3 phase. XANES studies reveal that the charge compensation mechanism of Fe and Mn changes upon Ni doping which is attributed to the structural stability of P 3/O3 NFNM at higher voltages. [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]

Retention is one of the key reliability metrics for non-volatile memory devices. In oxygen ion transport based resistive switching memory (OxRAM), the retention phenomenon has been well studied from an electrical perspective and physical mechanisms explaining the origin of retention loss have also been speculated to support the observed data. However, the stochastic aspects of retention loss and its variability deserve to be investigated so that the time-dependent shift in the resistance distribution and the retention failure time statistics can be better quantified and estimated for a given set of operating conditions. We propose here a phenomenological Markovian multi-state model combined with the percolation framework and ion diffusion theory to analyze the distributions of retention failure in the low resistance state for OxRAM devices. [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]

Resistive switching materials are promising candidates for nonvolatile data storage and reconfiguration of electronic applications. Intensive studies have been carried out on sandwiched metal-insulator-metal structures to achieve high density on-chip circuitry and non-volatile memory storage. Here, we provide insight into the mechanisms that govern highly reproducible controlled resistive switching via a nanofilament by using an asymmetric metal-insulator-semiconductor structure. In-situ transmission electron microscopy is used to study in real-time the physical structure and analyze the chemical composition of the nanofilament dynamically during resistive switching. Electrical stressing using an external voltage was applied by a tungsten tip to the nanosized devices having hafnium oxide (HfO2) as the insulator layer. The formation and rupture of the nanofilaments result in up to three orders of magnitude change in the current flowing through the dielectric during the switching event. Oxygen vacancies and metal atoms from the anode constitute the chemistry of the nanofilament. [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]

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]

• Conventional GD method for scan-positional correction leads to errors when processing atom-resolved 4D-STEM datasets. • A new integrated constrained gradient descent (iCGD) protocol can recover different types of scan-positional errors. • The iCGD protocol contains subroutines derived from the nature of the raster scanning commonly used in 4D-STEM. • Electron ptychography with high accuracy and precision with the help of the iCGD is experimentally demonstrated. Correcting scan-positional errors is critical in achieving electron ptychography with both high resolution and high precision. This is a demanding and challenging task due to the sheer number of parameters that need to be optimized. For atomic-resolution ptychographic reconstructions, we found classical refining methods for scan positions not satisfactory due to the inherent entanglement between the object and scan positions, which can produce systematic errors in the results. Here, we propose a new protocol consisting of a series of constrained gradient descent (CGD) methods to achieve better recovery of scan positions. The central idea of these CGD methods is to utilize a priori knowledge about the nature of STEM experiments and add necessary constraints to isolate different types of scan positional errors during the iterative reconstruction process. Each constraint will be introduced with the help of simulated 4D-STEM datasets with known positional errors. Then the integrated constrained gradient decent (iCGD) protocol will be demonstrated using an experimental 4D-STEM dataset of the 1H-MoS 2 monolayer. We will show that the iCGD protocol can effectively address the errors of scan positions across the spectrum and help to achieve electron ptychography with high accuracy and precision. [ABSTRACT FROM AUTHOR]

We study the overgrowth process of silver-on-gold nanocubes in dilute, aqueous silver nitrate solution in the presence of a reducing agent, ascorbic acid, using in situ liquid-cell electron microscopy. Au-Ag core-shell nanostructures were formed via two mechanistic pathways: (1) nuclei coalescence, where the Ag nanoparticles absorbed onto the Au nanocubes, and (2) monomer attachment, where the Ag atoms epitaxially deposited onto the Au nanocubes. Both pathways lead to the same Au-Ag core-shell nanostructures. Analysis of the Ag deposition rate reveals the growth modes of this process and shows that this reaction is chemically mediated by the reducing agent. [ABSTRACT FROM AUTHOR]

Crystallization of sputter-deposited amorphous (FeSi2)1-xAlx on SiO2/Si substrate was studied for different fractions (x) of Al content varying from 0.033 to 0.081. The activation energy of crystallization for beta-phase iron-disilicide (β-FeSi2) was extracted by using the Kissinger’s method. It was found to be 2.93-4.01 eV for (β-FeSi2)1-xAlx thin film, increasing with x. The fraction of Al that can be incorporated into β-FeSi2 without any phase transformation is ∼0.066. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the formation of alpha-phase iron-disilicide (α-FeSi2) together with β-FeSi2 at temperatures as low as 600 °C for x ≥ 0.075. Micro-Raman spectroscopy and electron energy-loss spectroscopy (EELS) showed the presence of crystalline Si precipitates in β-FeSi2 for x ≥ 0.075. [ABSTRACT FROM AUTHOR]

Quantum tunneling between two plasmonic resonators links nonlinear quantum optics with terahertz nanoelectronics. We describe the direct observation of and control over quantum plasmon resonances at length scales in the range 0.4 to 1.3 nanometers across molecular tunnel junctions made of two plasmonic resonators bridged by self-assembled monolayers (SAMs). The tunnel barrier width and height are controlled by the properties of the molecules. Using electron energy-loss spectroscopy, we directly observe a plasmon mode, the tunneling charge transfer plasmon, whose frequency (ranging from 140 to 245 terahertz) is dependent on the molecules bridging the gaps. [ABSTRACT FROM AUTHOR]

Highlights: [•] The real-time observation of faster degradation at GB sites of HfO2 dielectric. [•] C-AFM results show enhanced defect generation rate at the GB sites. [•] Preferential breakdown of SiO x IL occurs below the degraded GB region. [•] A breakdown sequence in polycrystalline HfO2/SiO x dielectric stacks was proposed. [Copyright &y& Elsevier]

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]

Abstract: In this invited paper, we demonstrate how physical analysis techniques that are commonly used in integrated circuits failure analysis can be applied to detect the failure defects associated with ultrathin gate dielectric wear-out and breakdown in high-κ materials and investigate the associated failure mechanism(s) based on the defect chemistry. The key contributions of this work are perhaps focused on two areas: (1) how to correlate the failure mechanisms in high-κ/metal gate technology during wear-out and breakdown to device processing and materials and (2) how the understanding of these new failure mechanisms can be used in proposing “design for reliability” (DFR) initiatives for complex and expensive future CMOS nanoelectronic technology nodes of 22nm and 15nm. Hf-based high-κ materials in conjunction with various gate electrode technologies will be used as main examples while other potential high-κ gate materials such as cerium oxide (CeO2) will also be demonstrated to further illustrate the concept of DFR. [Copyright &y& Elsevier]

Abstract: We present electrical evidence on asymmetric metal–insulator–semiconductor (MIS) based test structures in support of the presence of two different independent switching mechanisms in a resistive random access memory (RRAM) device. The valid mechanism for switching depends on the compliance capping (Igl ) for forming/SET transition. Our results convincingly show that low compliance based switching only involves reversible oxygen ion drift to and from oxygen gettering gate electrodes, while high compliance switching involves formation and rupture of conductive metallic nanofilaments, as verified further by our physical analysis investigations. We have observed this unique dual mode switching mechanism only in NiSi-based gate electrodes, which have a moderate oxygen solubility as well as relatively low melting point. [Copyright &y& Elsevier]

Nanodisk heterostructures consisting of monoclinic Cu1.94S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu1.94S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu1.94S into CdS, yielding Cu1.94S-CdS nanoheterostructures. The original morphology of the Cu194S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu1.94S-ZnxCd1-xS nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells. [ABSTRACT FROM AUTHOR]

Localized progressive wear-out and degradation of ultra-thin dielectrics around the oxygen vacancy percolation path formed during accelerated time dependent dielectric breakdown tests is a well-known phenomenon documented for silicon oxynitride (SiON) based gate stacks in metal oxide semiconductor field effect transistors. This progressive or post breakdown stage involves an initial phase characterized by 'digital' random telegraph noise fluctuations followed by the wear-out of the percolation path, which results in an 'analog' increase in the leakage current, culminating in a thermal runaway and hard breakdown. The relative contribution of the digital and analog phases of degradation at very low voltage stress in ultra-thin SiON (16 Å) is yet to be fully investigated, which represents the core of this study. We investigate the wear-out process by combining electrical and physical analysis evidences with modeling and simulation results using Kinetic Monte Carlo defect generation and multi-phonon trap assisted tunneling (PTAT) models. We show that the transition from the digital to the analog regime is governed by a critical voltage (VCRIT), which determines the reliability margin in the post breakdown phase. Our results have a significant impact on the post-breakdown operational reliability of SiON and advanced high-κ-SiOx interfacial layer gate stacks, wherein the SiOx layer seems to be the weakest link for percolation event. [ABSTRACT FROM AUTHOR]

Resistive switching in transition metal oxides could form the basis for next-generation non-volatile memory (NVM). It has been reported that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only individually, limiting our understanding of the possibility of multiple conductive filaments nucleation and rupture and the correlation kinetics of their evolution. In this study, direct visualization of uncorrelated multiple conductive filaments in ultra-thin HfO2-based high-κ dielectric resistive random access memory (RRAM) device has been achieved by high-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS), for nanoscale chemical analysis. The locations of these multiple filaments are found to be spatially uncorrelated. The evolution of these microstructural changes and chemical properties of these filaments will provide a fundamental understanding of the switching mechanism for RRAM in thin oxide films and pave way for the investigation into improving the stability and scalability of switching memory devices. [ABSTRACT FROM AUTHOR]

Induction, tuning, or amplification of chirality in various classes of materials and probing their chiral response are subjects of growing research. Herein, a large chiral signal that is rapidly imprinted in achiral amorphous Ge2Sb2Te5 (GST) thin films measured using synchrotron circular dichroism spectroscopy is reported. The chirality is induced by illuminating the films with pulsed circularly polarized (chiral) laser light for less than 2 μs in total. The effects of laser fluence and film thickness on the chiral response are described. The correlation of the optical results with structural studies by electron diffraction and model simulations suggests that alignment of reamorphized fragments in the crystallized film along the electric field vector of the light forms the centers that are responsible for the observed chirality. These results suggest opportunities for practical applications of this phenomenon and provide avenues for further studies of chirality induction in materials with impact in a wide range of disciplines. [ABSTRACT FROM AUTHOR]