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Materials characterization is fundamental to our understanding of lithium ion battery electrodes and their performance limitations. Advances in laboratory-based characterization techniques have yielded powerful insights into the structure–function relationship of electrodes, yet there is still far to go. Further improvements rely, in part, on gaining a deeper understanding of complex physical heterogeneities in the materials. However, practical limitations in characterization techniques inhibit our ability to combine data directly. For example, some characterization techniques are destructive, thus preventing additional analyses on the same region. Fortunately, artificial intelligence (AI) has shown great potential for achieving representative, 3D, multi-modal datasets by leveraging data collected from a range of techniques. In this Perspective, we give an overview of recent advances in lab-based characterization techniques for Li-ion electrodes. We then discuss how AI methods can combine and enhance these techniques, leading to substantial acceleration in our understanding of electrodes.

Nanoscale, localized corrosion underpins billions of dollars in damage and material costs each year; however, the processes responsible have remained elusive due to the complexity of studying degradative material behavior at nanoscale liquid-solid interfaces. Recent improvements to liquid cell scanning/transmission electron microscopy and associated techniques enable this first look at the nanogalvanic corrosion processes underlying this widespread damage. Nanogalvanic corrosion is observed to initiate at the near-surface ferrite/cementite phase interfaces that typify carbon steel. In minutes, the corrosion front delves deeper into the material, claiming a thin layer of ferrite around all exposed phase boundaries before progressing laterally, converting the ferrite to corrosion product normal to each buried cementite grain. Over the following few minutes, the corrosion product that lines each cementite grain undergoes a volumetric expansion, creating a lateral wedging force that mechanically ejects the cementite grains from their grooves and leaves behind percolation channels into the steel substructure.

Chemomechanical weakening of layered phyllosilicate muscovite mica was studied as a function of chemical environment via in situ liquid-nanoindentation under four conditions (dry, deionized water, and two NaCl solutions of different pH). While traditional indentation analyses of layered materials with extreme mechanical anisotropy have been limited due to displacement bursts (pop-ins), here the bursts were used as proxies for delamination, fracture, and spalling events. Since displacement bursts during an indent represent a stochastic process, 120 indents were conducted for each condition to generate statistically significant amounts of data. In total, over 9000 bursts were assessed using a load–displacement threshold criterion, classifying this as a high-throughput nanoscale fracture technique. For each burst, initiation load, initiation displacement, plastic zone volume at initiation, and energy dissipation were analyzed. A power-law relationship between the burst load and burst energy was noted which separated the bursts into two continuous distributions: (1) bursts due only to the mechanics of the indent and (2) bursts due to both the mechanics of the indent and the environment. By using a cumulative probability distribution, it was found that the NaCl solutions decreased the minimum plastic zone volume necessary to initiate a displacement burst by an order of magnitude relative to the dry condition. Finally, the underlying mechanisms explaining the trends in initiation volume as a function of environment were discussed, with a focus on the chemomechanical degradation processes via chemical attack and cation exchange.

As the demand for higher-performance batteries has increased, so has the body of research on theoretical high-capacity anode materials. However, the research has been hindered because the high-capacity anode material properties and interactions are not well understood, largely due to the difficulty of observing cycling in situ. Using electrochemical scanning transmission electron microscopy (ec-STEM), we report the real-time observation and electrochemical analysis of pristine tin (Sn) and titanium dioxide-coated Sn (TiO2@Sn) electrodes during lithiation/delithiation. As expected, we observed a volume expansion of the pristine Sn electrodes during lithiation, but we further observed that the expansion was followed by Sn detachment from the current collector. Remarkably, although the TiO2@Sn electrodes also exhibited similar volume expansion during lithiation, they showed no evidence of Sn detachment. We found that the TiO2 surface layer acted as an electrochemically activated artificial solid-electrolyte interphase that serves to conduct Li ions. As a physical coating, it mechanically prevented Sn detachment following volume changes during cycling, providing significant degradation resistance and 80% Coulombic efficiency for a complete lithiation/delithiation cycle. Interestingly, upon delithiation, TiO2@Sn electrode displayed a self-healing mechanism of small pore formation in the Sn particle followed by agglomeration into several larger pores as delithiation continued.

Multivalent rechargeable metal batteries offer a safer, more sustainable, and higher energy density alternative to lithium-ion batteries, though several challenges remain. Recent demonstrations of room-temperature reversible electrodeposition and dissolution of Ca metal indicate that it is possible to stabilize metallic Ca anodes with spontaneously formed solid electrolyte interphases (SEIs). However, further progress toward the goal of an energy-efficient, long cycle-life Ca anode requires correlating interphase identity with electrode performance. In this work, we demonstrate that the SEI formed from calcium borohydride solvated in tetrahydrofuran, an electrolyte that supports reversible Ca deposition, is a compositionally and structurally heterogeneous oxide, sufficiently thin to support Ca2+ cation transmission while stabilizing Ca from corrosive loss during long-term electrolyte contact. The significant advance demonstrated here is that ionically nonconductive materials, like calcium oxide, can form cation-transmissive interphases in which conductivity can be tailored through control of heterogeneity, providing an approach for stabilizing reactive metal electrodes.

Abstract Multimodal in-situ experiments are the wave of the future, as this approach will permit multispectral data collection and analysis during real-time nanoscale observation. In contrast, the evolution of technique development in the electron microscopy field has generally trended toward specialization and subsequent bifurcation into more and more niche instruments, creating a challenge for reintegration and backward compatibility for in-situ experiments on state-of-the-art microscopes. We do not believe this to be a requirement in the field; therefore, we propose an adaptive instrument that is designed to allow nearly simultaneous collection of data from aberration-corrected transmission electron microscopy (TEM), probe-corrected scanning transmission electron microscopy, ultrafast TEM, and dynamic TEM with a flexible in-situ testing chamber, where the entire instrument can be modified as future technologies are developed. The value would be to obtain a holistic understanding of the underlying physics and chemistry of the process-structure–property relationships in materials exposed to controlled extreme environments. Such a tool would permit the ability to explore, in-situ, the active reaction mechanisms in a controlled manner emulating those of real-world applications with nanometer and nanosecond resolution. If such a powerful tool is developed, it has the potential to revolutionize our materials understanding of nanoscale mechanisms and transients. Graphical Abstract

Vacuum micro/nano-electronics can greatly benefit from the improved emission current density and temporal stability of the electron beam due to the morphological control and direct contact of cold field-emitters on a conducting substrate. In this work, high-performance vertically aligned carbon nanotube (VACNT) pillar-based field-emitter arrays (VACNT-P-FEAs) were synthesized directly on stainless-steel (SS) via plasma-enhanced chemical vapor deposition. Nanosphere lithography was employed to limit the growth sites of VACNTs and form VACNT-P-FEAs of different sizes on the SS substrate. The field emission (FE) properties of the VACNT-P-FEAs were dependent on the size of the pillar emitters. Remarkable FE properties, such as low turn-on electric field (ETo = 1.57 V/μm), low threshold electric field (ETh = 2.94 V/μm), high field enhancement factor (β = 4977), and high emission current density (∼33 mA/cm2 at a field of 4 V/μm) were observed from the VACNT-P-FEAs grown using polystyrene microspheres (450 nm diameter) for lithography. The excellent FE performance can be ascribed to the inherent properties of the sample, such as the high conductivity of the SS substrate, low contact resistance between the SS substrate and VACNTs, the suitable number of active VACNT pillar field-emitters, and the reduced screening effect between the VACNT pillars.

Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity experiments that revealed the binding of anionic surfactant to the negatively charged surface via adsorbed cations. At low loading, cylindrical micelles formed on the surface, with sulfate head groups bound to the surface by water molecules or adsorbed cations. Cation bridging was observed in the presence of weakly hydrating monovalent cations, while sulfate groups interacted with strongly hydrating divalent cations through water bridges. The adsorbed micelle structure was confirmed experimentally with cryogenic electronic microscopy, which revealed micelles approximately 2 nm in diameter at the basal surface. At higher AOT loading, the simulations reveal adsorbed bilayers with similar surface binding mechanisms. Adsorbed micelles were slightly thicker (2.2–3.0 nm) than the corresponding bilayers (2.0–2.4 nm). Upon heating the low loading systems from 300 K to 350 K, the adsorbed micelles transformed to a more planar configuration resembling bilayers. The driving force for this transition is an increase in the number of sulfate head groups interacting directly with adsorbed cations.

A micro-electromechanical system (MEMS) based technique is demonstrated for in situ transmission electron microscopy (TEM) measurements of stress relaxation with simultaneous observation of the underlying plastic deformation processes. True activation volumes are determined from repeated stress relaxation transients and thus provide a signature parameter of the governing mechanisms of plastic deformation. The technique is demonstrated with 100 nm-thick ultrafine-grained gold microspecimens under uniaxial tension. True activation volumes of approximately 3-5b3 (where b is the Burgers vector length) are obtained for tensile stresses ranging from 200-450 MPa. Grain boundary-dislocation interactions are observed via in situ TEM during stress relaxation measurements. The miniaturization of stress relaxation tests inside the TEM provides unique opportunities to characterize the plastic kinetics and underlying mechanisms in ultrafine-grained and nanocrystalline materials.

New cryogenic characterization techniques for exploring the nanoscale structure and chemistry of intact solid–liquid interfaces have recently been developed. These techniques provide high-resolution information about buried interfaces from large samples or devices that cannot be obtained by other means. These advancements were enabled by the development of instrumentation for cryogenic focused ion beam liftout, which allows intact solid–liquid interfaces to be extracted from large samples and thinned to electron-transparent thicknesses for characterization by cryogenic scanning transmission electron microscopy or atom probe tomography. Future implementation of these techniques will complement current strides in imaging of materials in fluid environments by in situ liquid-phase electron microscopy, providing a more complete understanding of the morphology, surface chemistry, and dynamic processes that occur at solid–liquid interfaces.

Vertically aligned carbon nanotube (VACNT) emitters were synthesized directly on stainless steel substrate using DC plasma-enhanced chemical vapor deposition. Remarkable field emission (FE) properties, such as low turn-on electric field (ETO = 1.40 V/μm) and low threshold electric field (ETH = 2.31 V/μm), were observed from VACNT arrays with long length and moderate density. The FE performance was significantly enhanced by a uniquely bundled structure of VACNTs formed through a simple water treatment process. The FE properties of VACNTs were further improved by coating the exterior of CNTs with a uniform layer of crystalline SnO2 nanoparticles; the ETO and ETH were reduced to 1.18 and 2.01 V/μm, respectively. The enhancement of FE properties by SnO2 coating can be attributed to the morphological change of VACNTs caused by the solution phase coating process. The coated samples also exhibited an improved FE stability which is attributed to the enhancement of the mechanical strength and chemical stability of the VACNTs after the SnO2 coating. The VACNT emitters with characteristic features such as a conductive substrate, low contact resistance between the VACNTs and the substrate, uniform coating, and bundled morphology can be ideal candidates for FE devices.

In the use of solution-based 3D nanoarchitectures for optics, drug delivery, and cancer treatment, the precise nanoparticle architecture morphologies, architecture sizes, interparticle distances, and the assembly stability are all critical to their functionality. 3D nanoparticle architectures in solution are difficult to characterize, as few techniques can provide individualized information on interparticle spacing (defined by linkage molecule), nanoparticle assembly size, morphology, and identification of false aggregation. Bulk characterization techniques, including small angle x-ray scattering, can provide architecture sizes, though they are unable to precisely measure differences within interparticle spacings for individual architectures and can falsely measure assemblies caused by non-linkage grouped nanoparticles. Two solution-based characterization techniques were used to determine which assembly type and linkage length would produce the fastest assembly rate for large DNA-directed gold nanoparticle assemblies. In-situ liquid-cell scanning transmission electron microscopy (LC-STEM), measured interparticle spacings between DNA-functionalized nanoparticles, and fluorescence correlation spectroscopy provided the bulk volume fraction of large and small assemblies for nanoparticle architectures that were assembled using two different types: (1) the hybrid assemblies join two complementary single-stranded DNA linkages, and (2) the bridged assemblies are comprised of single-stranded DNA (bridging component) that is double the length of two different complementary single-stranded DNA-functionalized gold nanoparticles. Assembly times were tested at 24-hrs intervals over 3 days. Statistics derived from the in-situ LC-STEM images provided data for interparticle distance measurements, which identified the fraction of nanoparticles within the images acquired that were at the expected double-stranded DNA-binding distance of the linkages (varied in three distances for each of the two different architectures). In general, longer linkage lengths assembled in the shortest amount of time. The bridged assemblies formed fewer large architectures at 24-hrs but ultimately assembled a greater fraction of nanoparticles, which was due to the longer functionalized DNA lengths for individual nanoparticles. Fluorescence correlation spectroscopy provided a bulk average of the gold nanoparticle assembly sizes over time, which supported the conclusions drawn from the in-situ LC-STEM data. The microscopy provided sub-2 nm precision in the interparticle distances between gold nanoparticles in a solution environment. This coupled microscopy and spectroscopy characterization approach can provide more detailed information than bulk characterization methods.

Lithium-metal anodes can theoretically enable 10× higher gravimetric capacity than conventional graphite anodes. However, Li-metal anode cycling has proven difficult due to porous and dendritic morphologies, extensive parasitic solid electrolyte interphase reactions, and formation of dead Li. We systematically investigate the effects of applied interfacial pressure on Li-metal anode cycling performance and morphology in the recently developed and highly efficient 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane electrolyte. We present cycling, morphology, and impedance data at a current density of 0.5 mA/cm2 and a capacity of 2 mAh/cm2 at applied interfacial pressures of 0, 0.01, 0.1, 1, and 10 MPa. Cryo-focused ion beam milling and cryo-scanning electron microscopy imaging in cross section reveal that increasing the applied pressure during Li deposition from 0 to 10 MPa leads to greater than a fivefold reduction in thickness (and therefore volume) of the deposited Li. This suggests that pressure during cycling can have a profound impact on the practical volumetric energy density for Li-metal anodes. A "goldilocks zone" of cell performance is observed at intermediate pressures of 0.1-1 MPa. Increasing pressure from 0 to 1 MPa generally improves cell-to-cell reproducibility, cycling stability, and Coulombic efficiency. However, the highest pressure (10 MPa) results in high cell overpotential and evidence of soft short circuits, which likely result from transport limitations associated with increased pressure causing local pore closure in the separator. All cells exhibit at least some signs of cycling instability after 50 cycles when cycled to 2 mAh/cm2 with thin 50 μm Li counter electrodes, though instability decreases with increasing pressure. In contrast, cells cycled to only 1 mAh/cm2 perform well for 50 cycles, indicating that capacity plays an important role in cycling stability.

Author(s): Jungjohann, KL; Gannon, RN; Goriparti, S; Randolph, SJ; Merrill, LC; Johnson, DC; Zavadil, KR; Harris, SJ; Harrison, KL | Abstract: The dramatic 50% improvement in energy density that Li-metal anodes offer in comparison to graphite anodes in conventional lithium (Li)-ion batteries cannot be realized with current cell designs because of cell failure after a few cycles. Often, failure is caused by Li dendrites that grow through the separator, leading to short circuits. Here, we used a new characterization technique, cryogenic femtosecond laser cross sectioning and subsequent scanning electron microscopy, to observe the electroplated Li-metal morphology and the accompanying solid electrolyte interphase (SEI) into and through the intact coin cell battery's separator, gradually opening pathways for soft-short circuits that cause failure. We found that separator penetration by the SEI guided the growth of Li dendrites through the cell. A short-circuit mechanism via SEI growth at high current density within the separator is provided. These results will inform future efforts for separator and electrolyte design for Li-metal anodes.

Correction for ‘In situ TEM measurement of activation volume in ultrafine grained gold’ by Saurabh Gupta et al., Nanoscale, 2020, 12, 7146–7158, DOI: 10.1039/D0NR01874K.

Li metal anodes are enticing for batteries due to their high theoretical storage capacity, but commercialization is plagued by dendritic Li growth and short circuits when cycled at high currents. Applied pressure has been suggested to improve morphology, and therefore performance. We hypothesized that increasing pressure would suppress dendritic growth at high currents. To test this hypothesis, here we extensively use cryogenic scanning electron microscopy to show that varying the applied pressure from 0.01-1 MPa has little impact on Li morphology after one deposition. We show that pressure improves Li density and preserves Li inventory after 50 cycles. However, contrary to our hypothesis, pressure exacerbates dendritic growth through the separator, promoting short circuits. Therefore, we suspect Li inventory is better preserved in cells cycled at high pressure only because the shorts carry a larger portion of the current, with less being carried by electrochemical reactions that slowly consume Li inventory.

Insights into the dynamics of electrochemical processes are critically needed to improve our fundamental understanding of electron, charge, and mass transfer mechanisms and reaction kinetics that influence a broad range of applications, from the functionality of electrical energy-storage and conversion devices (e.g., batteries, fuel cells, and supercapacitors), to materials degradation issues (e.g., corrosion and oxidation), and materials synthesis (e.g., electrodeposition). To unravel these processes, in situ electrochemical scanning/transmission electron microscopy (ec-S/TEM) was developed to permit detailed site-specific characterization of evolving electrochemical processes that occur at electrode–electrolyte interfaces in their native electrolyte environment, in real time and at high-spatial resolution. This approach utilizes “closed-form” microfabricated electrochemical cells that couple the capability for quantitative electrochemical measurements with high spatial and temporal resolution imaging, spectroscopy, and diffraction. In this article, we review the state-of-the-art instrumentation for in situ ec-S/TEM and how this approach has resulted in new observations of electrochemical processes.

Author(s): Zhang, X; Wang, QJ; Harrison, KL; Jungjohann, K; Boyce, BL; Roberts, SA; Attia, PM; Harris, SJ | Abstract: We offer an explanation for how dendrite growth can be inhibited when Li metal pouch cells are subjected to external loads, even for cells using soft, thin separators. We develop a contact mechanics model for tracking Li surface and sub-surface stresses where electrodes have realistically (micron-scale) rough surfaces. Existing models examine a single, micron-scale Li metal protrusion under a fixed local current density that presses more or less conformally against a separator or stiff electrolyte. At the larger, sub-mm scales studied here, contact between the Li metal and the separator is heterogeneous and far from conformal for surfaces with realistic roughness: the load is carried at just the tallest asperities, where stresses reach tens of MPa, while most of the Li surface feels no force at all. Yet, dendrite growth is suppressed over the entire Li surface. To explain this dendrite suppression, our electrochemical/mechanics model suggests that Li avoids plating at the tips of growing Li dendrites if there is sufficient local stress; that local contact stresses there may be high enough to close separator pores so that incremental Li+ ions plate elsewhere; and that creep ensures that Li protrusions are gradually flattened. These mechanisms cannot be captured by single-dendrite-scale analyses.

Applications such as energy storage and field emission devices demand direct growth of vertically aligned carbon nanotube (VACNT) arrays on conducting metal substrates, which has remained a challenge for a long time. Here, we report a controlled growth of VACNT arrays on a stainless steel (SS) substrate via dc plasma enhanced chemical vapor deposition without the addition of a metal catalyst layer. TEM and AFM examinations revealed the occurrence of nano-hills formed on the SS surface during heating process in an NH3 environment. This is a key step for uniform growth of VACNTs. The VACNTs have uniform length and diameter, good alignment, and uniform coverage over the substrate surface, superior to reported results. The particle on the tip of most of the VACNTs was found to be single crystalline Fe metal, although a few other VACNTs were found to have an alloy of Fe, Ni, Mn, and Cr at the tips. This highlights the dominating catalytic behavior of Fe over Ni, Cr, and Mn, which are the elemental composition of the nano-hills. The high quality VACNTs may find unique applications such as electron field emitters and dense nanoscale anode materials for lithium ion batteries.

Calcite (CaCO3) is one of the most abundant minerals in the Earth’s crust, and it is susceptible to subcritical chemically-driven fracturing. Understanding chemical processes at individual fracture tips, and how they control the development of fractures and fracture networks in the subsurface, is critical for carbon and nuclear waste storage, resource extraction, and predicting earthquakes. Chemical processes controlling subcritical fracture in calcite are poorly understood. We demonstrate a novel approach to quantify the coupled chemical-mechanical effects on subcritical fracture. The calcite surface was indented using a Vickers-geometry indenter tip, which resulted in repeatable micron-scale fractures propagating from the indent. Individual indented samples were submerged in an array of aqueous fluids and an optical microscope was used to track the fracture growth in situ. The fracture propagation rate varied from 1.6 × 10−8 m s−1 to 2.4 × 10−10 m s−1. The rate depended on the type of aqueous ligand present, and did not correlate with the measured dissolution rate of calcite or trends in zeta-potential. We postulate that chemical complexation at the fracture tip in calcite controls the growth of subcritical fracture. Previous studies indirectly pointed to the zeta-potential being the most critical factor, while our work indicates that variation in the zeta-potential has a secondary effect.

β-SnSb is known to be a highly stable anode for sodium ion batteries during cycling, but its sodiation–desodiation alloying reactions are poorly understood. Combining in situ TEM with electroanalytical methods, we demonstrate that β-SnSb forms Na3Sb and Na15Sn4 in sequence upon sodiation and re-forms as β-SnSb upon desodiation. The negative enthalpy of mixing for Sn and Sb is sufficient to cause sequentially deposited bilayers of Sn/Sb to transform into β-SnSb, resulting in comparable cycling stability. The good cycling stability of β-SnSb results from the complex two-phase amorphous–nanocrystalline microstructure in the partially charged–discharged states, as well as the intrinsic mechanical toughness of the β phase. Per the in situ TEM results, the sequential phase transformation shows minimal fracturing of the β-SnSb, indicating facile buffering of stresses. Extensively cycled specimens eventually show crystalline Sn phase segregation, which may be the source of the ultimate capacity fade in the alloy and bilayers.

The rising demand for food and energy crops has triggered interest in the use of nanoparticles for agronomy. Specifically, iron oxide-based engineered nanoparticles are promising candidates for next-generation iron-deficiency fertilizers. We used iron oxide and hybrid Pt-decorated iron oxide nanoparticles, at low and high concentrations, and at varied pHs, to model seed pre-soaking solutions for investigation of their effect on embryonic root growth in legumes. This is an environmentally friendly approach, as it uses less fertilizer, therefore less nanoparticles in contact with the soil. Analysis from varied material characterization techniques combined with a statistical analysis method found that iron oxide nanoparticles could enhance root growth by 88–366% at low concentrations (5.54 × 10−3 mg L−1 Fe). Hybrid Pt-decorated iron oxide nanoparticles and a higher concentration of iron oxide nanoparticles (27.7 mg L−1 Fe) showed reduced root growth. The combined materials characterization and statistical analysis used here can be applied to address many environmental factors to finely tune the development of vital nanofertilizers for high efficiency food production.

To understand the mechanism that controls low-aspect-ratio lithium deposition morphologies for Li-metal anodes in batteries, we conducted direct visualization of Li-metal deposition and stripping behavior through nanoscale in situ electrochemical scanning transmission electron microscopy (EC-STEM) and macroscale-cell electrochemistry experiments in a recently developed and promising solvate electrolyte, 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane. In contrast to published coin cell studies in the same electrolyte, our experiments revealed low Coulombic efficiencies and inhomogeneous Li morphology during in situ observation. We conclude that this discrepancy in Coulombic efficiency and morphology of the Li deposits was dependent on the presence of a compressed lithium separator interface, as we have confirmed through macroscale (not in the transmission electron microscope) electrochemical experiments. Our data suggests that cell compression changed how the solid-electrolyte interphase formed, which is likely responsible for improved morphology and Coulombic efficiency with compression. Furthermore, during the in situ EC-STEM experiments, we observed direct evidence of nanoscale self-discharge in the solvate electrolyte (in the state of electrical isolation). This self-discharge was duplicated in the macroscale, but it was less severe with electrode compression, likely due to a more passivating and corrosion-resistant solid-electrolyte interphase formed in the presence of compression. By combining the solvate electrolyte with a protective LiAl

We report a new hybrid integration scheme that offers for the first time a nanowire-on-lead approach, which enables independent electrical addressability, is scalable, and has superior spatial resolution in vertical nanowire arrays. The fabrication of these nanowire arrays is demonstrated to be scalable down to submicrometer site-to-site spacing and can be combined with standard integrated circuit fabrication technologies. We utilize these arrays to perform electrophysiological recordings from mouse and rat primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons, which revealed high signal-to-noise ratios and sensitivity to subthreshold postsynaptic potentials (PSPs). We measured electrical activity from rodent neurons from 8 days in vitro (DIV) to 14 DIV and from hiPSC-derived neurons at 6 weeks in vitro post culture with signal amplitudes up to 99 mV. Overall, our platform paves the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.

Alloyed and compound contacts between metal and semiconductor transistor channels enable self-aligned gate processes which play a significant role in transistor scaling. At nanoscale dimensions and for nanowire channels, prior experiments focused on reactions along the channel length, but the early stage of reaction in their cross sections remains unknown. Here, we report on the dynamics of the solid-state reaction between metal (Ni) and semiconductor (In0.53Ga0.47As), along the cross-section of nanowires that are 15 nm in width. Unlike planar structures where crystalline nickelide readily forms at conventional, low alloying temperatures, nanowires exhibit a solid-state amorphization step that can undergo a crystal regrowth step at elevated temperatures. In this study, we capture the layer-by-layer reaction mechanism and growth rate anisotropy using in situ transmission electron microscopy (TEM). Our kinetic model depicts this new, in-plane contact formation which could pave the way for engineered nanosca...

We present results from a systematic investigation of environmental effects on the frictional behavior of Au–Ni multilayer films of varying interlayer spacing. The current results, sliding against ruby spheres in a dry N2 atmosphere, are compared to prior work on the tribological behavior of these materials under ultra-high vacuum (UHV) (Cihan et al. in Sci Rep 9:1–10, 2019). Under both conditions, there is a regime of high friction when the interlayer spacing is large and a regime of low friction when the spacing is small. The low friction regime is associated with a critical grain size below which grain boundary sliding is expected to be the dominant mechanism of deformation. A shear-induced alloy formation (60–65 at.% Ni in Au) and a concomitant low friction coefficient was observed with multilayer spacings of 20 nm and lower under UHV. A distinct microstructure was found in dry N2, and is attributed to different interfacial characteristics due to adsorbed species; rather than mixing between Au and Ni layers, only the uppermost Au layers were affected by shearing. These observations are coupled with the friction and wear behavior of multilayer samples sliding under different environments.

Mitigating corrosion remains a daunting challenge due to localized, nanoscale corrosion events that are poorly understood but are known to cause unpredictable variations in material longevity. Here, the most recent advances in liquid-cell transmission electron microscopy were employed to capture the advent of localized aqueous corrosion in carbon steel at the nanoscale and in real time. Localized corrosion initiated at a triple junction formed by a solitary cementite grain and two ferrite grains and then continued at the electrochemically-active boundary between these two phases. With this analysis, we identified facetted pitting at the phase boundary, uniform corrosion rates from the steel surface, and data that suggest that a re-initiating galvanic corrosion mechanism is possible in this environment. These observations represent an important step toward atomically defining nanoscale corrosion mechanisms, enabling the informed development of next-generation inhibition technologies and the improvement of corrosion predictive models.

The plasma enhanced atomic layer deposition (PEALD) process for MnO2 was demonstrated, exhibiting self-limiting growth as well as stable composition and stable growth rate over a temperature window of 205–265 °C. The PEALD process for MnO2 was combined with the thermal ALD process for LiOH to synthesize Li1+xMn2−xO4 thin film cathodes, where the stoichiometry was effectively controlled to allow for crystallization in the electrochemically active spinel phase. A 3D nanostructure consisting of an Li1+xMn2−xO4 cathode layer, ALD LixAlySizO solid electrolyte, and SiGe nanowire anode was fabricated and characterized via TEM. The Li1+xMn2−xO4 thin films maintained 66% of the areal capacity upon a 100× increase in the rate (4–360 μA cm−2) as well as 97% capacity retention over 100 cycles at ∼5C. The ALD Li1+xMn2−xO4 thin films exhibited a volumetric capacity of 52 μAh cm−2 μm−1 at a C-rate of ∼0.5C and, coupled with the high operating voltage (4.0 V), offer some of best areal energy densities for ALD thin film cathodes, making it a viable material for integration with 3D lithium-ion microbatteries.

Li primary batteries have been used in commercial and military applications for decades due to their unrivaled energy density and long shelf-life. For years, the impressive shelf-life of these batteries has been primarily attributed to a stable solid electrolyte interphase (SEI), which hinders parasitic reactions at the anode/electrolyte interface. However, few published studies have probed electrode/electrolyte composition in commercial cells, and no previous studies have isolated contributions of the cathode and the electrolyte to SEI stability. To fill this knowledge gap, the present study attempts to de-convolute contributions from each entity by determining component compositions and unveiling the effect each constituent has on SEI stability. In this study, we investigate SEI compositions of three common Li primary chemistries - Li/MnO2, Li/FeS2 and Li/CFx, all of which display exceptional shelf-life. Additionally, due to the dynamic nature of the SEI, cells exposed to varying extents of ageing have been investigated to understand how the SEIs physical and chemical characteristics vary with time. Techniques such as X-ray Photoelectron Spectroscopy (XPS) and Energy-Dispersive Spectroscopy (EDS) are used to conduct chemical analysis of the SEI, while Scanning Electron Microscopy (SEM) is used to elucidate morphological changes in anode and SEI behavior as a function of extent of ageing and cathode/electrolyte chemistry. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Lithium-ion batteries have been the premiere power source in the mobile electronics industry due to their superior energy density and cycle life as compared to other battery chemistries. In the Era of the Internet of Things (IoT) there is an increasing need to find a viable power source to support millimeter-size and smaller scale devices in the fields of environmental sensing, biomedical devices, and wearable electronics. Three-dimensional battery architectures mitigate the limitations of traditional thin film batteries through improvement of ion transport properties allowing for higher areal loading of active materials. Atomic layer deposition not only offers the ability to synthesize a wide range of functional materials, but crucially is a non-line-of-sight deposition technique that allows for conformal deposition necessary for fabrication of 3D lithium-ion batteries. In this work, two ALD processes were developed to synthesize conformal thin films applicable to 3D battery fabrication—LiAlSiO4, a solid-state electrolyte, and LiMn2O4, a high-rate thin film cathode. LiAlSiO4 is a solid-electrolyte of interest, in which its quartz-like framework produces unique 1D channels for Li-ion transport along the c-axis, exhibiting ionic conductivities as high as 4.7x10-5 S/cm at room temperature,1, 2 where the ionic conductivity in its thin film form has shown to increase upon decreasing thicknesses, 3 In this work, ALD of LixAlySizO was demonstrated with careful tuning of the stoichiometry to allow for crystallization into the ionically conductive β-Eucryptite LiAlSiO4 phase. The rapid thermal annealed ALD film developed a well-defined epitaxial relationship to the silicon substrate: β-LiAlSiO4 (12 ̅10) || Si (100) and β-LiAlSiO4 (101 ̅0) || Si(001). The extrapolated room temperature ionic conductivity was found to be 1.2 x 10-7 S/cm in the [12 ̅10] direction with an activation energy of 0.63 eV, as compared to amorphous ALD LASO films with ionic conductivities on the order of 10-9 S/cm. Beyond the electrolyte layer, an equally crucial material is a thin film cathode with optimal interfacial properties to ensure homogeneous active material utilization, adequate cycle-life, and high rate performance. To realize this goal, LiMn2O4 was demonstrated utilizing O2 plasma and Tris(2,2,6,6Tetramethyl-3,5-heptanedione) Mn(III), where lithium incorporation was performed through a thermal ALD LiOtBu/H2O process. Thin films with stoichiometries of Li1+xMn2-xO4, where x>0 were observed (as-characterized via XPS) with LiOH ALD sub-cycle percentages lower than 1% of the total ALD supercycle. LiMn2O4 thin films exhibited great rate capability (66% capacity retention after increasing the rate from C/2 to 50C) as well as capacity retention (97% capacity retention after 100 cycles at 5C).Lastly, a proof-of-concept nanobattery consisting of a SiGe nanowire (anode) coated with LixAlySizO (electrolyte) and LiMn2O4 (cathode) was fabricated. Both materials show great promise for direct integration with three-dimensional lithium-ion microbatteries. 1. V. Thangadurai and W. Weppner, Ionics 8 (3), 281-292 (2002). 2. P. G. Bruce, Solid State Electrochemistry. (Cambridge University, Press, 1995). 3. S.-i. Furusawa, H. Tabuchi and T. Tsurui, Solid State Ionics 178 (15), 1033-1038 (2007).

Lithium-ion batteries are an important component in mobile electronics; however, their modest energy density makes them less than ideal for use in all-electric vehicles or localized grid residential/commercial energy storage. Multivalent-ion batteries (MIBs), including Mg2+, are promising high-energy density technologies that are cheaper and more abundant than lithium. Realizing the high theoretical energy density of MIBs requires the native multivalent-ion metal to be used as the anodic electrode, where densely controlled metal plating and stripping has yet to be achieved. The mechanisms governing plating/stripping of MIBs and the resulting microstructural impact on the battery performance must be understood before MIBs can be employed commercially. Understanding the role that the solid electrolyte interface has on multivalent-ion metal plating/stripping may lead to solutions for controlling reversible anodic cycling. Recent advances in cryogenic electron microscopy(cryo-EM) preparation have allowed for scanning transmission electron microscopy (STEM) investigation of intact solid/liquid interfaces and electron-beam-sensitive materials. Here we present results of our chemical and microstructural investigation of plated and stripped Mg2+ anodes, collected with cryo-FIB preparation, cryo-transfer, and cryo-STEM. Details will be presented on the anode porosity, grain orientation maps, chemical maps from the electrode/electrolyte interfaces, and high-resolution structural imaging of the electrode interfaces. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.

Calcium-based rechargeable batteries have received considerable interest due to high theoretical energy densities, low reduction potential of the Ca2+ cation, and high crustal abundance of calcium. The reversible plating and stripping of calcium metal has recently been demonstrated using several anion/solvent combinations, including (BF4)-/ethylene carbonate:propylene carbonate [1,2], (BH4)-/THF [3], (Bhfip)-/THF-glymes [4-6], and (BF4)-/1-ethyl-3-methylimidazolium trifluoromethanesulfonate [7]. These studies are significant advancements towards implementation of Ca-ion batteries, but the coulombic efficiencies (CE) have not yet reached high enough values for practical use. Secondary phases, including CaH2 and CaF2, likely contribute to CE suppression, but other factors, such as impurities and microstructure, have not yet been studied in detail. In this contribution, we describe the critical role that sodium plays in governing the electrochemical performance and morphology of electrodeposited calcium. Trace metal analysis reveals that sodium impurity levels vary across different sources of calcium salts; such variations are correlated with highly variable CE’s and deposition morphologies. By adding controlled levels of sodium (at the hundreds of ppm level) to calcium-based electrolytes, the CE of calcium cycling exceeds 98%, indicating significantly suppressed parasitic reactions. Additionally, sodium addition causes the dominant morphology to transition from loosely packed, ~50 nm calcium platelets to densely packed columnar structures. Detailed studies of electrolyte speciation (dielectric relaxation spectroscopy, Raman spectroscopy), electrochemical response (cyclic voltammetry, chronopotentiometry), deposit microstructure, and interphase composition (SEM, TEM, TOF-SIMS, XRD) are conducted to determine the specific role that sodium plays in directing interphase formation and microstructure evolution. Our results highlight the sensitivity of calcium electrodeposition to small changes in the electrolyte and underscore the broader need for consideration of impurity impact on redox processes in multivalent electrolyte systems. This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. References: Ponrouch, C. Frontera, F. Bardé, and M. R. Palacin. “Towards a calcium-based rechargeable battery,” Nat. Mater. 15, 169 (2016). Biria, S. Pathreeker, H. Li, and I. Hosein, “Plating and stripping of calcium in an alkyl carbonate electrolyte at room temperature,” ACS Appl. En. Mat. 2, 7738 (2019). Wang, X. Gao, Y. Chen, L. Jin, C. Kuss, and P. G. Bruce, "Plating and stripping calcium in an organic electrolyte," Nat. Mater. 17, 16 (2018). Shyamsunder, L. E. Blanc, A. Assoud, and L. F. Nazar, "Reversible calcium plating and stripping at room temperature using a borate salt," ACS Energy Letters 4, 2271 (2019). Li, O. Fuhr, M. Fichtner, and Z. Zhao-Karger, “Towards stable and efficient electrolytes for room-temperature rechargeable calcium batteries,” Energy Env. Sci. 12, 3496 (2018). Nielson, J. Luo, and T. L. Liu, “Optimizing calcium electrolytes by solvent manipulation for calcium batteries,” Batteries & Supercaps 3 (2020). DOI: 10.1002/batt.202000005 Biria, S. Pathreeker, F. Genier, H. Li, and I. Hosein. “Plating and stripping calcium at room temperature in an ionic-liquid electrolyte,” ACS Appl. En. Mat. 3, 2310 (2020).

A major challenge in gallium nitride (GaN) vertical power devices and other large bandgap materials is the high defect density that compromises the performance, reliability, and yield. Defects are typically nucleated at the heterointerface where there are both lattice and thermal mismatches. Here, we report the selective area growth (SAG) of thick GaN on Si and on the newly available Qromis Substrate Technology™ (QST) substrates that lead to a significant reduction of the defect densities to a level that is nearly comparable to that on native substrates by defect annihilation. We performed a parametric study of the electrical properties of the SAG GaN layers by fabricating and characterizing Schottky barrier diodes for SAG GaN layer thicknesses of 5, 10, 15, and 20 μm for GaN-on-Si, GaN-on-QST, and GaN-on-GaN diodes. While thicker layers led to a significant reduction in defect densities and improvement in the diode forward current characteristics, the GaN-on-QST diodes exhibited nearly similar characteristics to the GaN-on-GaN diodes. Further improvement in the device structure and/or SAG growth for GaN-on-Si is needed to achieve a comparable performance as the defect densities in the GaN-on-Si are comparable to that of GaN-on-QST substrates.

Lithium-ion batteries are an important component in mobile electronics; however, their modest energy density makes them less than ideal for use in all-electric vehicles or localized grid residential/commercial energy storage. Multivalent-ion batteries (MIBs), including Mg2+, are promising high-energy density technologies that are cheaper and more abundant than lithium. Realizing the high theoretical energy density of MIBs requires the native multivalent-ion metal to be used as the anodic electrode, where densely controlled metal plating and stripping has yet to be achieved. The mechanisms governing plating/stripping of MIBs and the resulting microstructural impact on the battery performance must be understood before MIBs can be employed commercially. Understanding the role that the solid electrolyte interface has on multivalent-ion metal plating/stripping may lead to solutions for controlling reversible anodic cycling. Recent advances in cryogenic electron microscopy(cryo-EM) preparation have allowed for scanning transmission electron microscopy (STEM) investigation of intact solid/liquid interfaces and electron-beam-sensitive materials. Here we present results of our chemical and microstructural investigation of plated and stripped Mg2+ anodes, collected with cryo-FIB preparation, cryo-transfer, and cryo-STEM. Details will be presented on the anode porosity, grain orientation maps, chemical maps from the electrode/electrolyte interfaces, and high-resolution structural imaging of the electrode interfaces. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.

Lithium-ion batteries are important for applications including portable electronics, electric vehicles, and grid storage. Lithium metal anodes can significantly increase energy density beyond lithium-ion batteries because their theoretical storage capacity is 10x larger than that for state-of-the-art graphite anodes. Development of functional lithium metal anodes is critically important for implementation of next-generation battery concepts like Li-S, Li-O2, and Li-metal batteries paired with traditional insertion cathodes. Unfortunately, lithium metal anodes suffer from parasitic reactions with electrolytes, high aspect ratio morphological evolution, and poor cycling behavior. Many strategies have been proposed to improve lithium metal anode cycling including the development of electrolytes that enable more favorable lithium morphology and minimize side reactions. One of the very promising electrolytes that have been developed is 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane (4 M LiFSI/DME).1 To better understand lithium metal plating and stripping processes in 4 M LiFSI/DME, we plated and stripped lithium metal using in-situ electrochemical scanning transmission electron microscopy (EC-STEM).2 We performed EC-STEM experiments using a customizable, sealed liquid cell STEM chip designed and built at Sandia National Laboratories. The Coulombic efficiency and morphology observed in the in-situ EC-STEM experiments2 differed from that in published coin cell results.1 Through macroscale (not TEM) experiments, we determined that the discrepancy could be explained by the absence of a separator and interfacial pressure at the lithium-electrolyte interface for the in-situ EC-STEM experiments. Thus, we concluded that lithium metal plating and stripping performance depends significantly on interfacial compression. Our data also suggests that compression changes how the solid electrolyte interphase forms, which could in turn affect how lithium metal deposits. Motivated by our observations that lithium plating and stripping behavior depends on interfacial compression, we systematically studied the role of interfacial compression on lithium plating and stripping. We performed electrochemical testing in pouch cells under varied loading and disassembled the cells for subsequent characterization. The electrode stacks were studied by cross sectioning the electrodes with cryo focused ion beam milling. These samples were then imaged using cryo scanning electron microscopy experiments to understand the impact of interfacial compression on morphological evolution. We confirm through these experiments that interfacial compression plays an important role in lithium plating and stripping behavior. This work was supported by the Joint Center for Energy Storage Research and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. 1. Qian, J., Henderson, W.A., Xu, W., Bhattacharya, P., Engelhard, M., Borodin, O. and Zhang, J.G., 2015. High rate and stable cycling of lithium metal anode. Nature communications, 6, p. 6362. 2. Harrison, K.L., Zavadil, K.R., Hahn, N.T., Meng, X., Elam, J.W., Leenheer, A., Zhang, J.G. and Jungjohann, K.L., 2017. Lithium self-discharge and its prevention: direct visualization through in situ electrochemical scanning transmission electron microscopy. ACS nano, 11(11), pp.11194-11205.