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The noise characteristics of gas cascade amplified electron signals in low vacuum scanning electron microscopy (LVSEM) are described and analyzed. We derive expressions for each component contributing to the total noise culminating in a predictive, quantitative model that can be used for optimization of LVSEM operating parameters. Signal and noise behavior is characterized experimentally and used to validate the model. Under most operating conditions, the noise is dominated by the excess noise generated in the gas amplification cascade. At high gains, the excess noise increases proportionally with gain such that the signal-to-noise ratio is constant. The effects of several instrument operating parameters, including working distance, gas pressure, beam current, and detector bias, are condensed and presented in the form of a master curve. [ABSTRACT FROM AUTHOR]

Water management by gas diffusion electrodes is a fundamental aspect of the performance of electrochemical cells. Herein, we introduce the characteristic constrictions size as a descriptor for microporous layers (MPL). This parameter is calculated by volumetric analysis of focused ion beam nanotomography and compared to mercury intrusion porosimetry measurements. [ABSTRACT FROM AUTHOR]

In situ scanning transmission electron microscopy enables observation of the domain dynamics in ferroelectric materials as a function of externally applied bias and temperature. The resultant data sets contain a wealth of information on polarization switching and phase transition mechanisms. However, identification of these mechanisms from observational data sets has remained a problem due to a large variety of possible configurations, many of which are degenerate. Here, an approach based on a combination of deep learning‐based semantic segmentation, rotationally invariant variational autoencoder (VAE), and non‐negative matrix factorization to enable learning of a latent space representation of the data with multiple real‐space rotationally equivalent variants mapped to the same latent space descriptors is introduced. By varying the size of training sub‐images in the VAE, the degree of complexity in the structural descriptors is tuned from simple domain wall detection to the identification of switching pathways. This yields a powerful tool for the exploration of the dynamic data in mesoscopic electron, scanning probe, optical, and chemical imaging. Moreover, this work adds to the growing body of knowledge of incorporating physical constraints into the machine and deep‐learning methods to improve learned descriptors of physical phenomena. [ABSTRACT FROM AUTHOR]

The activity and selectivity of the electrochemical CO2 reduction reaction (CO2RR) are often hindered by the limited access of CO2 to the catalyst surface and overtaken by the competing hydrogen evolution reaction. Herein, it is revealed that polymers used as catalyst binders can effectively modulate the accessibility of CO2 relative to H2O at the vicinity of the catalyst and thus the performance of CO2RR. Three polymers with different hydrophilicities (i.e., polyacrylic acid (PAA), Nafion, and fluorinated ethylene propylene (FEP)) are selected as binders for Cu catalysts. At a thickness of only ≈1.2 nm, these binders strongly affect the activity and selectivity toward multi‐carbon (C2+) products. The FEP coated catalyst exhibits a C2+ partial current density of over 600 mA cm−2 with ≈77% faradaic efficiency at −0.76 V versus RHE. This high performance is attributed to the hydrophobic (aerophilic) properties of FEP, which reduces the local concentration of H2O and enhances that of the reactant (i.e., CO2) and the reaction intermediates (i.e., CO). These findings suggest that tuning the hydrophobicity of electrocatalysts with polymer binders can be a promising way to regulate the performance of electrochemical reactions involving gas–solid–liquid interfaces. [ABSTRACT FROM AUTHOR]

Highlights: [•] CoFe2O4 films show epitaxial growth despite a large variation in lattice matching with substrates. [•] The relaxed films only show strain under the critical thickness close to the interface when presence. [•] Films are relaxed by epitaxial islands formation and growth defects with increasing thickness. [•] Epitaxial CoFe2O4 shows different growth mechanisms and large variation of magnetic properties. [ABSTRACT FROM AUTHOR]

Abstract: High aspect ratio silicon wire arrays with excellent pattern fidelity over wafer-scale area were grown by chemical vapor deposition at moderate temperature, using a gas mixture of silane and hydrogen chloride. An innovative two-step process was developed for in situ doping of silicon wires by diborane. This process led to high p-type doping levels, up to 1018–1019 cm−3, without degradation of the silicon wire array pattern fidelity. [Copyright &y& Elsevier]

Ferroelectric materials, upon electric field biasing, display polarization discontinuities known as Barkhausen jumps, a subclass of a more general phenomenon known as crackling noise. Herein, we follow and visualize in real time the motion of single 90° needle domains induced by an electric field applied in the polarization direction of the prototypical ferroelectric BaTiO3, inside a transmission electron microscope. The nature of motion and periodicity of the Barkhausen pulses leads to distinctive interactions between domains forming a herringbone pattern. Remarkably, the tips of the domains do not come into contact with the body of the perpendicular domain, suggesting the presence of strong electromechanical fields around the tips of the needle domains. Additionally, interactions of the domains with the lattice result in relatively free movement of the domain walls through the dielectric medium, indicating that their motion-related activation energy depends only on weak Peierls-like potentials. Control over the kinetics of ferroelastic domain wall motion can lead to novel nanoelectronic devices pertinent to computing and data storage applications. [ABSTRACT FROM AUTHOR]

Size, morphology, and surface sites of electrocatalysts have a major impact on their performance. Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable, active, and selective catalysts. Herein, we study the reconstruction of a Cu‐based nanocatalysts during the startup phase of the electrochemical CO2 reduction reaction by combining results from electrochemical in situ transmission electron microscopy with operando X‐ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the size increase and morphology change of the electrocatalyst. Furthermore, we point out the key role played by the formation of copper oxides in the process. Understanding of the underlying processes opens a pathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods. [ABSTRACT FROM AUTHOR]

Size, morphology, and surface sites of electrocatalysts have a major impact on their performance. Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable, active, and selective catalysts. Herein, we study the reconstruction of a Cu‐based nanocatalysts during the startup phase of the electrochemical CO2 reduction reaction by combining results from electrochemical in situ transmission electron microscopy with operando X‐ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the size increase and morphology change of the electrocatalyst. Furthermore, we point out the key role played by the formation of copper oxides in the process. Understanding of the underlying processes opens a pathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods. [ABSTRACT FROM AUTHOR]

Environmental scanning electron microscopy (ESEM) was used to perform electron beam induced deposition (EBID) using a WF6 precursor. The deposits consist of WO3 nanocrystals embedded in an amorphous matrix. Oxide formation is attributed to residual oxidizers present in the ESEM chamber during EBID. Under conditions of fixed low electron flux, the WO3 grain size and the degree of deposit crystallinity increase with time. These changes correlate with the degree of electron energy deposition into the material during growth, indicating that electron beam induced modification of as-grown material is significant in controlling the nanostructure and functionality of materials fabricated by EBID. [ABSTRACT FROM AUTHOR]

• Multi-modal and multi-scale (M3S) non-local means (NLM) method is proposed to extract atomically resolved spectroscopic maps from a low signal-to-noise dataset recorded inside a transmission electron microscope. A multi-modal and multi-scale non-local means (M3S-NLM) method is proposed to extract atomically resolved spectroscopic maps from low signal-to-noise (SNR) datasets recorded with a transmission electron microscope. This method improves upon previously tested denoising techniques as it takes into account the correlation between the dark-field signal recorded simultaneously with the spectroscopic dataset without compromising on the spatial resolution. The M3S-NLM method was applied to electron energy dispersive X-ray and electron-energy-loss spectroscopy (EELS) datasets. We illustrate the retrieval of the atomic scale diffusion process in an Al 1-x In x N alloy grown on GaN and the surface oxidation state of perovskite nanocatalysts. The improved SNR of the EELS dataset also allows the retrieval of atomically resolved oxidation maps considering the fine structure absorption edge of LaMnO 3 nanoparticles. [ABSTRACT FROM AUTHOR]

A primary method for the production of 2D nanosheets is liquid-phase delamination from their 3D layered bulk analogues. Most strategies currently achieve this objective by significant mechanical energy input or chemical modification but these processes are detrimental to the structure and properties of the resulting 2D nanomaterials. Bulk poly(triazine imide) (PTI)-based carbon nitrides are layered materials with a high degree of crystalline order. Here, we demonstrate that these semiconductors are spontaneously soluble in select polar aprotic solvents, that is, without any chemical or physical intervention. In contrast to more aggressive exfoliation strategies, this thermodynamically driven dissolution process perfectly maintains the crystallographic form of the starting material, yielding solutions of defect-free, hexagonal 2D nanosheets with a well-defined size distribution. This pristine nanosheet structure results in narrow, excitation-wavelength-independent photoluminescence emission spectra. Furthermore, by controlling the aggregation state of the nanosheets, we demonstrate that the emission wavelengths can be tuned from narrow UV to broad-band white. This has potential applicability to a range of optoelectronic devices. [ABSTRACT FROM AUTHOR]

A long-standing problem in the application of solid-state nanopores is the lack of the precise control over the geometry of artificially formed pores compared to the well-defined geometry in their biological counterpart, that is, protein nanopores. To date, experimentally investigated solid-state nanopores have been shown to adopt an approximately circular shape. In this Letter, we investigate the geometrical effect of the nanopore shape on ionic blockage induced by DNA translocation using triangular h-BN nanopores and approximately circular molybdenum disulfide (MoS2) nanopores. We observe a striking geometry-dependent ion scattering effect, which is further corroborated by a modified ionic blockage model. The well-acknowledged ionic blockage model is derived from uniform ion permeability through the 2D nanopore plane and hemisphere like access region in the nanopore vicinity. On the basis of our experimental results, we propose a modified ionic blockage model, which is highly related to the ionic profile caused by geometrical variations. Our findings shed light on the rational design of 2D nanopores and should be applicable to arbitrary nanopore shapes. [ABSTRACT FROM AUTHOR]

Keywords: CO 2 reduction; copper catalysts; electrocatalysis; hydrophobicity; polymer binders EN CO 2 reduction copper catalysts electrocatalysis hydrophobicity polymer binders 1 1 1 03/06/22 20220303 NES 220303 B Polymer Binders b In article number 2103663, Wen Luo and co-workers develop powder catalysts coated with a polymer binder for enhanced electrochemical CO SB 2 sb reduction to multi-carbon products, inspired by water-repulsive surfaces in nature. Enhanced Electrocatalytic CO2 Reduction to C2+ Products by Adjusting the Local Reaction Environment with Polymer Binders (Adv. CO 2 reduction, copper catalysts, electrocatalysis, hydrophobicity, polymer binders. [Extracted from the article]

Abstract: Doped SrTiO3 thin films, 55nm thick, were epitaxially grown by Pulsed Laser Deposition with niobium contents ranging from 2 to 5mol% on SrTiO3 and LaAlO3 substrates. The different templates result in different growth defects, film growth mechanism and therefore a different volume fraction of uniformly strained film under the critical thickness. The investigation of the conductivity reveals a significant difference between the two substrate choices, but only at elevated temperatures with conductivity values up to 30% larger for films on SrTiO3 substrates compared with LaAlO3. Whereas in bulk ceramics the niobium level dictates the total conductivity, here it was found that the substrate choice had a greater influence for thin films, in particular at temperatures over 400°C. This finding provides important information on conductive layers in complex heterostructures where strain and defects could work cooperatively. [Copyright &y& Elsevier]

Abstract: We study the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with aluminum as catalyst. We show that for a growth temperature of 600°C, the silicon precursor partial pressure (SiH4 in this study) is a key parameter for controlling the structural quality of the resulting SiNWs. We find by transmission electron microscopy that at high SiH4 partial pressure, the SiNWs are composed of a monocrystalline core with a high density of surface defects, mainly twins, sheathed by a rough amorphous silicon layer. By contrast, at low SiH4 partial pressure, the SiNWs are monocrystalline with a lower density of surface crystalline defects and a smooth surface. For the low SiH4 partial pressure SiNWs, Al atoms have been detected at the SiNW surface by Auger spectroscopy at level around 3at% and in the SiNW core by energy dispersive X-ray spectroscopy (EDS) at levels around 1at%. Interestingly, higher Al concentrations are measured inside the nano-twin domains by EDS (around ten times increase). Two possible explanations are proposed; stacking faults are induced by Al atoms that lower their energy formation, or Al atoms can be trapped inside these stacking faults due to segregation effect during growth. These findings will be important for growing high quality SiNWs using Al as metal catalyst in reduced-pressure CVD tool. [Copyright &y& Elsevier]