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Nanoscale ruthenium (Ru)-based materials are promising replacements for existing multilayered Cu interconnects in integrated circuits. However, it is not easy to apply the results of previously reported studies directly to the electrochemical damascene process because the previous studies have mainly focused on thin films by dry deposition. Here, we report the electrical resistivity and microstructure of electrodeposited Ru nanowires. We estimate that the resistivity value of a 10 nm diameter Ru nanowire to be 71.6 μΩ cm after analyzing the resistivity values of individual nanowires with various diameters. Furthermore, we investigate the electrical properties of RuxCo1-x nanowires where x is 0.04–0.99 at.% as possible replacements of the current TaN barrier structures. Over the entire composition range, the resistivity values of alloys are much lower than that of the conventional TaN. Additionally, Ru and Ru-alloy nanowires surrounded by dielectric silica are thermally stable after 450 °C heat treatment. Therefore, the nanoscale Ru and Ru-Co alloys possessing low resistivity values can be candidates for the interconnect and barrier materials, respectively.

Grain boundaries typically dominate the electrical properties of polycrystalline ceramics. To understand the effect of grain boundaries on the electrical conductivity of SiC ceramics sintered with 2000 ppm Y2O3, the electrical resistivity of individual grains and multi-grains across boundaries at the micron scale was measured using a nano-probing system equipped with nano-manipulators. The results revealed that grain resistivity was bimodal because of the existence of a core/rim structure in grains, and the electrical resistivity of multigrain samples slowly increased with an increase in the number of grain boundaries crossed. Specifically, the electrical resistivity of a grain without a core, a grain with a core, a bicrystal with a single boundary, a sample crossing three boundaries, and a bulk polycrystalline sample were 2.36 × 10-1, 5.05 × 10-1, 4.80 × 10-1, 5.04 × 10-1, and 5.84 × 10-1 Ω cm, respectively. The results suggest that the electrical resistivity of polycrystalline SiC ceramics is primarily influenced by the presence of a grain boundary or core and secondarily by the number of boundaries.

After the WHO designated COVID‐19 a global pandemic, face masks have become a precious commodity worldwide. However, uncertainty remains around several details regarding face masks, including the potential for transmission of bioaerosols depending on the type of mask and secondary spread by face masks. Thus, understanding the interplay between face mask structure and harmful bioaerosols is essential for protecting public health. Here, we evaluated the microbial survival rate at each layer of commercial of filtering facepiece respirators (FFRs) and surgical masks (SMs) using bacterial bioaerosols. The penetration efficiency of bacterial particles for FFRs was lower than that for SMs; however, the microbial survival rate for all tested masks was >13%, regardless of filtration performance. Most bacterial particles survived in the filter layer (44%–77%) (e.g., the core filtering layer); the outer layer also exhibited significant survival rates (18%–29%). Most notably, survival rates were determined for the inner layers (

Twin boundary sliding (TBS) is a deformation mode that is typically observed in nanocrystalline metals and usually occurs at multiple locations in the twinned region, including twin boundaries, of a crystal in a situation in which additional deformation via twinning is limited. Unlike the well-established dislocation slip and necking deformation process that occurs in large crystals, recent theories that explain TBS are often controversial, and much remains unsettled. Herein, we develop a factor that enables the prediction of deformation pathways by quantitatively analyzing the relative tendency for the formation of partial dislocations based on the dislocation and fault energy theories. The developed factor considers the effects of static/extrinsic features, such as the stacking fault energy (SFE) as well as the crystal size and orientation, and dynamic structural states characterized by the various fault energies of a material. The factor is initially validated using a Cu crystal exhibiting low SFE for various orientations and sizes. To determine whether the proposed factor can be generically extended to crystals with high SFE, we perform micro-mechanical tensile tests and molecular dynamics simulations on Al nanowires. The developed factor produces self-consistent results even for metals exhibiting different SFE values. The observations can be used as a guideline to design nanoscale structures for load-carrying applications.

Two-dimensional ReSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re1–xMoxS...

The bottom-up synthesis process often allows the growth of metastable phase nanowires instead of the thermodynamically stable phase. Herein, we synthesized Cd3As2 nanowires with a controlled three-...

Two-dimensional MoSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), although its catalytic activity needs to be further improved. Herein, we report Se-rich MoSe2 nanosheets synthesized using a hydrothermal reaction, displaying much enhanced HER performance at the Se/Mo ratio of 2.3. The transition from the 2H to the 1T' phase occurred as Se/Mo exceeded 2. Structural analysis revealed the presence of Se adatoms as well as the formation of Se-Se bonding. Based on first-principles calculations, we propose two equally stable Se-rich structures. In the first one, excess Se atoms bridge two MoSe2 layers via the interlayer Se-Se bonds. In the second one, the Se atoms substitute for the Mo atoms, and extra Se atoms are added closest to the Mo-substituted Se. Calculation of Gibbs free energy along the reaction path indicates that the Se adatoms of the second model are the most active sites for HER.

To obtain high catalytic properties, finely modulating the electronic structure and active sites of catalysts is important. Herein, we report the design and economical synthesis of Pd@Pt core-shell nanoparticles for high productivity in the direct synthesis of hydrogen peroxide. Pd@Pt core-shell nanoparticles with a partially covered Pt shell on a Pd cube were synthesized using a simple direct seed-mediated growth method. The synthesized Pd@Pt core-shell nanoparticles were composed of high index faceted Pt on the corners and edges, while the Pd-Pt alloy was located on the terrace area of the Pd cubes. Because of the high-indexed Pt and Pd-Pt alloy sites, the synthesized concave Pd@Pt7 nanoparticles exhibited both high H2 conversion and H2O2 selectivity compared with Pd cubes.

Two-dimensional transition metal dichalcogenides have recently attracted much attention as excellent electrocatalysts for the hydrogen evolution reaction (HER). Herein, Re1−xMoxS2 alloy nanosheets in the entire composition range were synthesized using a hydrothermal reaction. High-resolution scanning transmission electron microscopy revealed anisotropic atomic distribution of the alloy phase, in which the Re and Mo atoms tend to segregate along a crystallographic axis. The phase transition occurs from the triclinic phase (1T′′) ReS2 to the monoclinic phase (1T′) MoS2 at 50% Mo. Re0.5Mo0.5S2 exhibited the highest electrocatalytic HER activity, which was characterized by a current density of 10 mA cm−2 at an overpotential of 98 mV (vs. RHE) and a Tafel slope of 54 mV dec−1 in 0.5 M H2SO4. Extensive calculations using spin-polarized density functional theory showed that the most energetically stable configuration consists of separated MoS2 and ReS2 domains along the b axis, and the 1T′′ → 1T′ phase transition at 50% Mo, which agrees with the experimental results. The Gibbs free energy along the HER pathway indicates that the best performance at Mo 50% is due to the formation of S–H or Mo–H (at S vacancies) on the MoS2 domain.

The fabrication of battery anodes simultaneously exhibiting large capacity, fast charging capability, and high cyclic stability is challenging because these properties are mutually contrasting in nature. Here, we report a rational strategy to design anodes outperforming the current anodes by simultaneous provision of the above characteristics without utilizing nanomaterials and surface modifications. This is achieved by promoting spontaneous structural evolution of coarse Sn particles to 3D-networked nanostructures during battery cycling in an appropriate electrolyte. The anode steadily exhibits large capacity (∼480 mAhg-1) and energy retention capability (99.9%) during >1500 cycles even at an ultrafast charging rate of 12 690 mAg-1 (15C). The structural and chemical origins of the measured properties are explained using multiscale simulations combining molecular dynamics and density functional theory calculations. The developed method is simple, scalable, and expandable to other systems and provides an alternative robust route to obtain nanostructured anode materials in large quantities.

Guaiacol, a primary chemical derived from lignin, is still an attractive candidate as a cyclical carbon source in the petroleum industry. This work newly introduced Co/ZrP and Ni/ZrP catalysts and examined their activity for guaiacol hydrodeoxygenation (HDO) in a batch reactor at 573 K and under 70 bar of H2. Their catalytic, surface and textural properties were investigated by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD, NH3-TPD, HAADF-STEM and H2-chemisorption. In addition, the overall reaction pathways of guaiacol to cyclohexane on Co/ZrP and Ni/ZrP were proposed. Guaiacol was converted to cyclohexane through two different pathways via two major intermediates: phenol (demethoxylation, PHE route) and 2-methoxycyclohexanol (hydrogenation, 2-M route). Co/ZrP preferred the PHE-route, while Ni/ZrP dominantly favored the 2-M-route, which resulted in a high cyclohexane yield when using Co/ZrP (76%). In this study, an ‘intrinsic H2 supply’ was determined to be the main factor for selecting the reaction pathway. Co/ZrP, with a low intrinsic H2 supply capacity, promoted a less H2-consuming pathway (PHE route), and Ni/ZrP, with a high intrinsic H2 supply, favored the more H2-consuming 2-M route. Likewise, lowering the H2 pressure (from 70 to 40 bar) could promote the PHE route and increase cyclohexane production (80%). However, the opposite trend was observed when the reaction temperature was reduced from 573 K to 523 K. For both Co/ZrP and Ni/ZrP catalysts, the production of PHE significantly decreased, while the same yield of 2-M was almost maintained. Thus, the pathway preference of Co/ZrP was reversed to the 2-M-route. Guaiacol HDO pathway preference over Co/ZrP and Ni/ZrP catalysts was characterized and the reaction conditions were investigated in this study, which could provide a guideline for effective ways to produce desired chemicals from guaiacol using Co/ZrP and Ni/ZrP.

The anisotropic volume expansion of anode materials produces locally inhomogeneous residual stresses, which frequently induce fracture of the anode materials and reduce battery capacity and cycle life. Much of our understanding of the anisotropic swelling behavior of anode materials is based on electron microscopy and macroscopic structural analysis techniques, which are insufficient to elucidate the atomistic origin of the anisotropic swelling behavior. In this study, we perform in situ sodiation experiments with single-crystalline Sb anodes followed by atomic simulations to determine the diffusion kinetics governing the sodiation of Sb and its associated swelling behavior. In situ sodiation experiments demonstrate that the rate of diffusion of Na into single-crystalline Sb anodes differs by more than a factor of 2 depending on the orientation of the Sb crystal, causing the crystal to swell anisotropically. This observed anisotropic diffusion is explained here by determining the orientation-dependent dif...

We propose a new method for preparing atom probe tomography specimens from nanoparticles using a fusible bismuth–indium–tin alloy as an embedding medium. Iron nanoparticles synthesized by the sodium borohydride reduction method were chosen as a model system. The as-synthesized iron nanoparticles were embedded within the fusible alloy using focused ion beam milling and ion-milled to needle-shaped atom probe specimens under cryogenic conditions. An atom probe analysis revealed boron atoms in a detected iron nanoparticle, indicating that boron from the sodium borohydride reductant was incorporated into the nanoparticle during its synthesis.

One-dimensional semiconductor nanowires often contain polytypic structures, owing to the co-existence of different crystal phases. Therefore, understanding the properties of polytypic structures is of paramount importance for many promising applications in high-performance nanodevices. Herein, we synthesized nanowires of typical III–V semiconductors, namely, gallium phosphide and gallium arsenide by using the chemical vapor transport method. The growth directions ([111] and [211]) could be switched by changing the experimental conditions, such as H2 gas flow; thus, various polytypic structures were produced simultaneously in a controlled manner. The nanobeam electron diffraction technique was employed to obtain strain mapping of the nanowires by visualizing the polytypic structures along the [111] direction. Micro-Raman spectra for individual nanowires were collected, confirming the presence of wurtzite phase in the polytypic nanowires. Further, we fabricated the photodetectors using the single nanowires, and the polytypic structures are shown to decrease the photosensitivity. Our systematic analysis provides important insight into the polytypic structures of nanowires.

Alloyed semiconductor nanowires (NWs) are of great interest for next-generation integrated optoelectronic nanodevices owing to their tunable band gap and emission wavelength. In this study, we synthesized the GaAsSe ternary alloy nanowires (NWs) with various compositions between GaAs and Ga2Se3 using chemical vapor transport method. The band gap was continuously tuned in the range of 1.5–2.1 eV because of the completely miscible solid solution at all compositions. The alloy NWs (including Ga2Se3) consisted of a cubic phase with the [011] growth direction, in contrast with the GaAs NWs grown along the [111] direction. In particular, the GaAs1–xSex (x = 0.3) alloy NWs were grown from Ga-rich Au nanoparticles such as cubic-phase AuGa2 and had a defect-free single-crystalline nature. X-ray photoelectron spectroscopy analysis reveals much less surface oxide layers for x = 0.3, suggesting that Se incorporation at this composition effectively diminishes the surface defects. We fabricated photodetectors using the...

Two-dimensional layered MoS2 has recently been considered as an excellent catalyst for the water-splitting hydrogen evolution reaction (HER). Herein, we synthesize 1T′ phase MoS2 that was intercalated with a series of alkylated p-phenylenediamines (PDs). The substituted N atoms produced S vacancies, leading to a composition of MoS2−2xNx (x = 0.1). The more abundant methyl groups induce a larger charge transfer, resulting in excellent HER performance: for tetramethyl PD, the overpotential is 0.15 V at 10 mA cm−2 with a Tafel slope of 35 mV dec−1. The catalytic activity of the complexes depends on the concentration of the intercalated molecules, showing an optimum at a concentration of 8 mol%. First-principles calculations showed that the intercalated complexes (1T′ phase) having N atom–S vacancy (N–VS) pairs are stabilized by a large charge transfer from the PD molecules that is enhanced by the methyl groups (i.e., 0.40e–0.84e per molecule at 6.25 mol% intercalation). The charge transfer increases the density of states at and just above the Fermi level, thereby increasing the electron concentration at low cathodic bias. The active sites for the Volmer reaction are found to be N atoms in the proximal N–VS pairs. The activation barrier for the Heyrovsky reaction becomes higher at higher concentrations of the intercalants, suggesting that the experimental HER performance is also kinetically controlled.

Since the emergence of hydrogen generation by water-splitting as a core renewable-energy technology, the development of related catalysts with high efficiency, long-term stability, and low cost has been vigorously pursued. We report the temperature-controlled synthesis of two nickel phosphide polymorphs, Ni2P and Ni5P4, by phosphorization of Ni foil or foam using phosphine gas. The hexagonal phase Ni2P nanowires and Ni5P4 nanosheets were grown on Ni substrates with vertical alignment, and uniformly exposed active (001) planes. The Ni5P4 nanosheets possess significant stacking faults along the [0001] direction. Both Ni2P and Ni5P4 exhibit excellent electrocatalytic activity toward the hydrogen evolution reaction (HER). Their overpotential for 10 mA cm−2 was 0.126 and 0.114 V, and the Tafel slope was 42 and 34 mV dec−1 in 0.5 M H2SO4 electrolyte, respectively. A decrease in HER performance was observed for Ni5P4, but the change was negligible for Ni2P. Strain mapping using a precession-assisted nanobeam electron diffraction technique showed that only Ni5P4 underwent degradation of basal (001) planes during HER, which explains the lower stability of catalytic activity. Furthermore, the Ni2P nanowires demonstrated excellent catalytic activity toward overall water splitting, which could be attributed to the stable surface as well as the highly conductive crystal structures.

Recently there have been extensive efforts to develop novel two-dimensional (2D) layered structures, owing to their fascinating thickness-dependent optical/electrical properties. Herein, we synthesized thin GeP nanosheets that had a band gap (Eg) of 2.3 eV, which is a dramatic increase from the value in the bulk (0.9 eV) upon exfoliation. This Eg value is close to that of the GeP monolayer predicted by first-principles calculations (HSE06 functional). The calculations also indicate a strong dependence of Eg on the number of layers (2.306, 1.660, 1.470, and 1.397 eV for mono-, bi-, tri-, and tetralayers, respectively), and that the band edge positions are suitable for water splitting reactions. Field-effect transistor devices were fabricated using the p-type GeP nanosheets of various thicknesses, and the devices demonstrated a significant decrease in the hole mobility but an increased on–off ratio as the layer number decreased. The larger on–off ratio (104) for the thinner ones is promising for use in novel 2D (photo)electronic nanodevices. Further, liquid-exfoliated GeP nanosheets (thickness = 1–2 nm) deposited on Si nanowire arrays can function as a promising photoanode for solar-driven water-splitting photoelectrochemical (PEC) cells. Based on the calculated band offset with respect to the Fermi levels for the two half-reactions in the water splitting reaction, the performance of the PEC cell can be explained by the formation of an effective p-GeP/n-Si heterojunction.

Two-dimensional (2D) MoS2 nanostructures have been extensively investigated in recent years because of their fascinating electrocatalytic properties. Herein, we report 2D hybrid nanostructures consisting of 1T′ phase MoS2 and Fe-phthalocyanine (FePc) molecules that exhibit excellent catalytic activity toward both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). X-ray absorption spectra revealed an increased Fe–N distance (2.04 A) in the hybrid complex relative to the isolated FePc. Spin-polarized density functional theory calculations predicted that the Fe center moves toward the MoS2 layer and induces a non-planar structure with an increased Fe–N distance of 2.05 A, which supports the experimental results. The experiments and calculations consistently show a significant charge transfer from FePc to stabilize the hybrid complex. The excellent HER catalytic performance of FePc-MoS2 is characterized by a low Tafel slope of 32 mV dec−1 at a current density of 10 mA cm−2 and an overpotential of 0.123 V. The ORR catalytic activity is superior to that of the commercial Pt/C catalyst in pH 13 electrolyte, with a more positive half-wave potential (0.89 vs. 0.84 V), a smaller Tafel slope (35 vs. 87 mV·dec−1), and a much better durability (9.3% vs. 40% degradation after 20 h). Such remarkable catalytic activity is ascribed to the HER-active 1T′ phase MoS2 and the ORR-active nonplanar Fe–N4 site of FePc.

We synthesized cobaltocene (7–20%)-intercalated WS2 nanosheets using a solvothermal process. The intercalation of cobaltocene between the expanded 1T′ phase WS2 layers was confirmed by scanning transmission electron microscopy and electron energy loss spectroscopy. The intercalated complexes exhibited excellent performance for the catalytic hydrogen evolution reaction, with a Tafel slope of 40 mV dec−1 and a current density of 10 mA cm−2 at 0.17 V (vs. RHE). Spin-polarized density functional theory calculations showed that cobaltocene is intercalated with a fivefold symmetry parallel to the WS2 plane, driven by substantial charge transfer. Reaction pathway calculations suggest that the basal S atoms just above the Co atom are the active sites, and the activation barrier of the Heyrovsky reaction determines the catalytic activity.

Two-dimensional (2D) MoS2 nanostructures have attracted much attention in recent years because of their excellent electrocatalytic activity toward the hydrogen evolution reaction (HER). Herein, we report unique 2D hybrid nanostructures of MoS2 and melamine synthesized via a one-step solvothermal process. Remarkably, few-layer metallic 1T′ phase MoS2 nanoflakes and orthorhombic phase melamine aggregate to form nanoplates. At a controlled concentration, the melamine molecules intercalated into the 1T′ phase MoS2 by forming charge-transfer complexes. The hybrid complexes with 7% intercalated melamine exhibited excellent performance for the catalytic HER, with a current of 10 mA cm−2 at 0.136 V (vs. RHE) and a Tafel slope of 37 mV dec−1. First-principles calculations showed that the intercalation of hydrogen-bonded melamine clusters could stabilize the 1T′ phase MoS2via substantial charge transfer. The activation barrier was calculated for the Volmer–Heyrovsky reactions, by identifying the active sites of the Volmer reaction as the basal S atoms above the hydrogen-bonded amine group of melamine. This rationalizes the dependence of the catalytic activity on the concentration of intercalated melamine. The present study highlights the opportunities for producing unique 2D hybrid complexes to enhance the HER catalytic activity by controlling the intercalating organic molecules.

Lithiation kinetics of a Si-C composite anode for high-capacity lithium-ion batteries were investigated through in-situ lithiation with electrochemical C-V measurements using a focused ion beam. Here, we found in the lithiation procedure that Li migrates sequentially into carbon (C), nanopores, and silicon (Si) in the Si-C composite. In the first lithiation step, Li was intercalated inside C particles while spreading over the surface of the C particles. The second lithiation process occurred through the filling of nanopores existing between electrode particles that consisted of the Si-C composite. The nanopores acted as a Li reservoir during the pore-filling process. Finally, the Si particles were litheated with a volume expansion of 173%, corresponding to a 400% volume expansion of 25wt.% Si particles included in the composite anode. The nanopores did not accommodate a large volume expansion of ~400% in Si particles, because pore-filling lithiation occurred before the Si lithiation in the charging process.

Multi-metallic Pd@FePt core&ndash, shell nanoparticles were synthesized using a direct seed-mediated growth method, consisting of facile and mild procedures, to increase yield. The Fe/Pt ratio in the shell was easily controlled by adjusting the amount of Fe and Pt precursors. Furthermore, compared with commercial Pt/C catalysts, Pd@FePt nanoparticles exhibited excellent activity and stability toward the methanol oxidation reaction (MOR), making them efficient in direct methanol fuel cells (DMFC).

Metastable phases—kinetically favored structures—are ubiquitous in nature. Rather than forming thermodynamically stable ground-state structures, crystals grown from high-energy precursors often initially adopt metastable structures depending on the initial conditions such as temperature, pressure, or crystal size. As the crystals grow further, they typically undergo a series of transformations from metastable to lower-energy phases and ultimately energetically stable phases, as described by Wilhelm Ostwald. Metastable phases, however, sometimes provide superior chemical and physical properties, and hence, discovering and synthesizing novel metastable phases are promising avenues for achieving innovations in materials science. The most common strategy for synthesizing a metastable material involves manipulating thermodynamic conditions such as temperature and pressure during the course of synthesis. However, the search for metastable materials has mainly been heuristic, on the basis of experiences, intuitions, or even speculative predictions. This limitation necessitates the advent of a new paradigm to discover novel metastable phases, i.e., by “rational design and synthesis” instead of a “rule of thumb,” and based on ab initio methods, i.e., the calculation of thermodynamic and kinetic properties of materials with various compositions, crystal structures, and crystal sizes. The design rule is embodied in the discovery of a metastable hexagonal close-packed (HCP) palladium hydride (PdHx), synthesized in a liquid cell environment using a transmission electron microscope (TEM). The metastable HCP structure is stabilized through a unique interplay among the precursor concentrations in the solution: a sufficient supply of hydrogen (H) favors the HCP structure on the sub-nanometer scale, and an insufficient supply of Pd inhibits further growth and subsequent transition toward the thermodynamically stable face-centered cubic (FCC) structure. The crystal structure was modulated (HCP or FCC) by adjusting the H concentration inside the TEM liquid cell, providing strong evidence for the crucial role of the H concentration. Monte Carlo simulations reveal that an unexpected inhomogeneous distribution of interstitial H atoms, distinct from the predominant occupation at the octahedral interstitial sites, is key to stabilizing nanoscale HCP PdHx. Furthermore, insufficient Pd brings a multi-step nucleation and growth pathway, deduced from in situ liquid cell TEM combined with atomic electron tomography, which maintains the metastable phase intact. These findings provide new thermodynamic insights into metastability-engineering strategy to be deployed in discovering new metastable phases.

Memristive electrochemical metallization (ECM) devices based on cation migration and electrochemical metallization in solid electrolytes are considered promising for neuromorphic computing systems. Two-dimensional (2D) layered materials are emerging as potential candidates for electrolytes in reliable ECM devices due to their two-dimensionally confined material properties. However, electrochemical metallization within a single-crystalline 2D layered material has not yet been verified. Here, we use transmission electron microscopy and energy-dispersive X-ray spectroscopy to investigate the resistive switching mechanism of an ECM device containing a single-crystalline 2D layered CrPS4 electrolyte. We observe the various conductive filament (CF) configurations induced by an applied voltage in an Ag/CrPS4/Au device in the initial/low-resistance/high-resistance/breakdown states. These observations provide concrete experimental evidence that CFs consisting of Ag metal can be formed inside single-crystalline 2D layered CrPS4 and that their configuration can be changed by an applied voltage. Density functional theory calculations confirm that the sulfur vacancies in single-crystalline CrPS4 can facilitate Ag ion migration from the active electrode layer. The electrically induced changes in Ag CFs inside single-crystalline 2D layered CrPS4 raise the possibility of a reliable ECM device that exploits the properties of two-dimensionally confined materials. A 2D layered material has provided critical insights toward improving the stability of devices that can emulate biological synapses. Researchers in Seoul, South Korea, led by Jae-Pyoung Ahn at the Korea Institute of Science and Technology and Bae Ho Park from Konkuk University have used high-resolution microscopy to investigate electrochemical metallization cells, a new type of non-volatile computer memory. These cells, made by infusing insulators with tiny metallic filaments, can mimic the low and high conductivity states of synapses. When the team looked at the structure of a chromium thiophosphate insulator composed of numerous 2D crystal layers, they found that the pathways the filaments follow are guided by specific crystal defects. These findings may help manufacturers produce more reliable electrochemical metallization cells by reducing the likelihood of random, non-uniform filament formation. We report on the formation and rupture of CFs through Ag ion migration inside a single-crystalline 2D van der Waals (vdW) solid electrolyte material within an ECM device structure. This study provides clear experimental evidence that CFs consisting of Ag can be formed inside single-crystalline 2D layered chromium thiophosphate (CrPS4) and their configuration can be changed by an applied voltage. Density functional theory calculations confirm that the Ag ion migration is an energetically favorable process. The electrically induced changes in Ag CFs inside single-crystalline CrPS4 raise the possibility of a reliable ECM device that exploits the properties of two-dimensionally confined materials.

Metastable phases-kinetically favoured structures-are ubiquitous in nature

Deformation twinning (DT), one of the major deformation modes in a crystalline material, has typically been analyzed using generalized planar fault energy (GPFE) curves. Despite the significance of these curves in understanding the twin nucleation and its effect on the mechanical properties of crystals, their validity has never been evaluated experimentally. In this comparative study based on the first-principles calculation, molecular dynamics (MD) simulation, and quantitative in-situ tensile testing of Al nanowires (NWs) inside a transmission electron microscopy (TEM) system, we present both a theoretical and an experimental approach that enable the measurement of a part of the twin formation energy of the perfect Al crystal. The proposed experimental method is also regarded as an indirect but quantitative means for validating the GPFE theory.

Two-dimensional ReSe

The diffusion of carrier ions in alloying anodes often develops compressive stresses in front of the propagating interface, suppressing the carrier-ion diffusion and limiting their full penetration into alloying anodes during battery cycles. This phenomenon, termed "self-limiting diffusion (SLD)", reduces the rate performance of batteries and hinders the full usage of anode materials. However, SLD is mitigated in some systems where tensile residual stresses develop at the interface, causing them to manifest significantly improved rate performance and energy capacity. Here, a comparative study of LiSi and NaSn systems to elucidate how the differing diffusion kinetics displayed by the two systems can influence SLD behaviors and the rate performance of batteries is performed. Experiments show that the Na diffusion into soft Sn crystals induces tensile stresses near the interface, promoting the nucleation of high-density dislocations. Thus-formed dislocations facilitate Na diffusion at ultrafast rates by providing pathways for dislocation pipe diffusion and alleviate SLD, making crystalline Sn suitable for fast-charging anode material. The outcomes of this study, while filling the knowledge gaps on the reasons for SLD, offer some guidelines for the appropriate choice of potential anode materials with superior rate performance and energy capacity suitable for future applications.