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Understanding the nature of hot carrier pathways following surface plasmon excitation of heterometallic nanostructures and their mechanistic prevalence during photoelectrochemical oxidation of complex hydrocarbons, such as ethanol, remains challenging. This work studies the fate of carriers from Au nanorods before and after the presence of reductively photodeposited Pd at the single-particle level using scattering and emission spectroscopy, along with ensemble photoelectrochemical methods. A sub-2 nm epitaxial Pd

The ability to harness the catalytic oxidation of hydrocarbons is critical for both clean energy production and air pollutant elimination, which requires a detailed understanding of the dynamic role of the nanophase structure and surface reactivity under the reaction conditions. We report here findings of an in situ/operando study of such details of a ternary nanoalloy under the propane oxidation condition using high-energy synchrotron X-ray diffraction coupled to atomic pair distribution function (HE-XRD/PDF) analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalysts are derived by alloying Pt with different combinations of second (Pd) and third (Ni) transition metals, showing a strong dependence of the catalytic activity on the Ni content. The evolution of the phase structure of the nanoalloy is characterized by HE-XRD/PDF probing of the lattice strain, whereas the surface activity is monitored by DRIFTS detection of the surface intermediate formation during the oxidation of propane by oxygen. The results reveal the dominance of the surface intermediate species featuring a lower degree of oxygenation upon the first C-C bond cleavage on the lower-Ni-content nanoalloy and a higher degree of oxygenation upon the second C-C bond cleavage on the higher-Ni-content nanoalloy. The face-centered-cubic-type phase structures of the nanoalloys under the oxidation condition are shown to exhibit Ni-content-dependent changes of lattice strains, featuring the strongest strain with little variation for the higher-Ni-content nanoalloy, in contrast to the weaker strains with oscillatory variation for the lower-Ni-content nanoalloys. This process is also accompanied by oxygenation of the metal components in the nanoalloy, showing a higher degree of oxygenation for the higher-Ni-content nanoalloy. These subtle differences in phase structure and surface activity changes correlate with the Ni-composition-dependent catalytic activity of the nanoalloys, which sheds a fresh light on the correlation between the dynamic change of atomic strains and the surface reactivity and has significant implications for the design of oxidation catalysts with enhanced activities.

Colloidal synthesis of alloyed multimetallic nanocrystals with precise composition control remains a challenge and a critical missing link in theory-driven rational design of functional nanomateria...

Dynamic reconfigurability of material properties is essential to enabling innovative neuromorphic- and quantum-computing paradigms. The unique structure of van der Waals layers can facilitate a robust mechanism for this desired reconfigurability. Here, we present a highly versatile and effective approach, based on electrochemical intercalation of organometallics, to control the electron and phonon behavior in hafnium disulfide. Computational and experimental exploration of the physical properties in the intercalated material indicates a significant and measured change. Furthermore, the weak chemical interactions between the organometallics and hafnium disulfide enable an electric-field mediated intercalant drift and charge–discharge process. The control of organometallic concentration in this way provides a dynamic 400-fold control of cross-plane electrical conductivity (1.8 μS/cm–741 μS/cm) and a corresponding 4-fold control of cross-plane thermal conductivity in hafnium disulfide (0.35 Wm−1 K−1–1.45 Wm−1 K−1). Our findings unveil a broad approach to dynamically design layered-material properties for high-performance electronic and phononic applications.

This Article demonstrates the synthesis and catalysis of a functional material with one core and dual shells containing an alloyed FeCoNi core covered with a thin layer of spinel oxides and encapsu...

Aluminum alloys in the 5xxx series are susceptible to sensitization due to the formation of β (Al3Mg2) at grain boundaries at moderate to low temperatures. Little is known about the mechanism of β phase formation, which is thought to be preceded by the metastable phases β’’ and β’. Using high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy (EDS), and precession electron diffraction (PED), we determine a parameter space for β phase precipitates at various sensitization temperatures and investigate their growth habits and local matrix strain states along grain boundaries. Our findings reveal that metastable β-related phases are present at low aging temperatures, while the equilibrium β phase is present at temperatures well above the previously described solvus of similar alloys. Furthermore, the phases were found to prefer particular grain boundary planes and contribute to the local grain boundary strain state differently. Overall, these findings present a unified view of β phase evolution and its contribution to lattice strain environments in aluminum magnesium alloys, which serves as a foundation for use in a range of temperatures and environments.

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. This report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum-iron (PtFe) alloy catalyst (denoted as PtFe TNWs) with controllable bimetallic compositions. PtFe TNWs with an optimal initial composition of ∼24% Pt are shown to exhibit the highest mass activity (3.4 A/mg

Colloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

We report on the growth and characterization of wavelength-thick indium tin oxide (ITO) films deposited using high power impulse magnetron sputtering (HiPIMS) with post deposition processing to achieve an epsilon near zero (ENZ) property at 1550 nm telecom wavelengths. The goal is to fabricate 1550 nm ENZ films for use as claddings for waveguides, resonators, or high-contrast metastructures in photonic devices operated at telecom wavelengths. We developed a HiPIMS growth and post-annealing process to improve on existing ENZ ITO quality and uniformity. By consecutively annealing the ITO film, the plasma frequency gradually shifts, enabling fine tuning of the ENZ wavelength regime from 1800 to 1500 nm. The films were characterized using spectroscopic ellipsometry, transmission electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Our micro-analyses shows that the change in the microstructure resulted in the change in the optical properties of the ITO. These findings allow us to control the ENZ property at the desired wavelength and reduce the absorption loss, which is beneficial for device application.

High-fluence gallium $({\mathrm{Ga}}^{+})$ implantation at medium energies is proven to be an effective tool in forming superconducting (SC) thin films in germanium (Ge). By changing the post-implantation annealing conditions nanocrystalline to single-crystalline Ge matrices have been produced. Irrespective of crystallinity, such processes have mostly led to supersaturated Ge:Ga films where superconductivity is controlled by the extent of coherent coupling between Ga precipitates. Here we use ${\mathrm{Ga}}^{+}$ implantation energy as a means to tailor the spatial distribution and the coupling energy of the Ga precipitates. By systematic structural and magneto-transport studies, we unravel the complex connection between the internal structure of Ge:Ga films and their global SC parameters. At the shallowest implantation depth, we observe the strongest coupling leading to a robust superconductivity that sustains parallel magnetic fields as high as 9.95 T, above the conventional Pauli paramagnetic limit and consistent with a quasi-2D geometry. Further measurements at mK temperatures revealed an anomalous upturn in perpendicular critical field ${\mathrm{B}}_{\ensuremath{\perp}}$ vs temperature whose curvature and thus origin may be tuned between weakly coupled SC arrays and vortex glass states with quenched disorder. This warrants future investigations into Ge:Ga films for applications where tunable disorder is favorable, including test-beds for quantum phase transitions and superinductors in quantum circuits.

This study reports the use of numerical topology optimization schemes to design heat sinks for steady-state and transient operation. Using COMSOL 5.6, a circular heat sink design space is considered to model temperature as a function of design fill factor. An initial parameterization of Helmholtz filter (minimum feature size) from 125 to 2000µm and penalization factor from 2 to 7, shows that smaller feature size improves performance. Using a moderate selective laser melting tolerance of 250µm, we perform solid-isotropic-material-with-penalization (SIMP) simulations to show the impact of heat transfer coefficient (from 5 to 100 Wm-2K-1) on fill factor. Intuitively, higher heat transfer coefficient requires less aluminum fin material for a given design point. The transient results are less intuitive and represent a unique progression from a preference for larger quantities of material near the heat source with sparse or nonexistent fins to designs that converge to steady state solutions at large times. It is found that the transient approach is preferred over steady state, particularly for low time steps, where significant weight savings can be realized. These results demonstrate the benefits of transient topology optimization approaches using COMSOL 5.6 and set the stage for future numerical transient mitigation approaches.

We report our development of Indium tin oxide (ITO) films with thicknesses greater than the typical optical telecommunication wavelength bands (~1550 nm) having epsilon-near-zero (ENZ) property at 1550 nm wavelength for the purpose of providing a new ENZ material platform for building high-contrast metastructure and metasurface devices. The films were grown using a high-power impulse magnetron sputtering (HiPIMS) tool, which allows for more control over film growth. A post-growth thermal annealing allowed the ITO film to reach the ENZ condition at the desirable wavelength. Our goal is to understand how deposition parameters and post deposition annealing conditions affect the film’s optical properties, therefore obtaining a controllable fabrication process for a desired optical property. Using spectroscopic ellipsometry to characterize the films, we show that the thick ITO films grown with HiPIMS exhibit ENZ behavior after post deposition annealing. The regime in which the material exhibits ENZ behavior is shown to be tunable within the wavelength range of 1500-1650 nm by varying the anneal temperature, anneal time, and oxygen exposure during anneal. In comparison with other thick ITO films grown with conventional pulsed DC magnetron sputtering, the optical constants of HiPIMS ITO films are shown to be much more constant with less variation throughout the bulk of the film. This result shows that these ITO films can be used to design a new family of opto-electronic devices that use ENZ ITO as the low-index base for high-contrast metasurface devices and as cladding for waveguides or optical cavities.

We report our in-house R&D efforts of designing and developing key integrated photonic devices and technologies for a chip-scale optical oscillator and/or clock. This would provide precision sources to RF-photonic systems. It could also be the basic building block for a photonic technology to provide positioning, navigation, and timing as well as 5G networks. Recently, optical frequency comb (OFC)-based timing systems have been demonstrated for ultra-precision time transfer. Our goal is to develop a semiconductor-based, integrated photonic chip to reduce the size, weight, and power consumption, and cost of these systems. Our approach is to use a self-referenced interferometric locking circuit to provide short-term stabilization to a micro-resonator-based OFC. For long-term stabilization, we use an epsilon-near-zero (ENZ) metamaterial to design an environment-insensitive cavity/resonator, thereby enabling a chip-scale optical long-holdover clock.

Colloidal synthesis of alloyed multimetallic nanocrystals with precise composition control remains a challenge and a critical missing link in theory-driven rational design of functional nanomaterials. Liquid-phase transmission electron microscopy (LP-TEM) enables direct visualization of nanocrystal formation mechanisms that can inform discovery of design rules for nanocrystal synthesis, but it remains unclear whether the salient flask synthesis chemistry is preserved under electron beam irradiation during LP-TEM. Here, we demonstrate controlled

Colloidal synthesis of alloyed multimetallic nanocrystals with precise composition control remains a challenge and a critical missing link in theory-driven rational design of functional nanomaterials. Liquid phase transmission electron microscopy (LP-TEM) enables directly visualizing nanocrystal formation mechanisms that can inform discovery of design rules for colloidal multimetallic nanocrystal synthesis, but it remains unclear whether the salient chemistry of the flask synthesis is preserved in the extreme electron beam radiation environment during LPTEM. Here we demonstrate controlled in situ LP-TEM synthesis of alloyed AuCu nanoparticles while maintaining the molecular structure of electron beam sensitive metal thiolate precursor complexes. Ex situ flask synthesis experiments showed that nearly equimolar AuCu alloys formed from heteronuclear metal thiolate complexes, while gold-rich alloys formed in their absence. Systematic dose rate-controlled in situ LP-TEM synthesis experiments established a range of electron beam synthesis conditions that formed alloyed AuCu nanoparticles with similar alloy composition, random alloy structure, and particle size distribution shape as those from ex situ flask synthesis, indicating metal thiolate complexes were preserved under these conditions. Reaction kinetic simulations of radical-ligand reactions revealed that polymer capping ligands acted as effective hydroxyl radical scavengers during LP-TEM synthesis and prevented metal thiolate oxidation at low dose rates. In situ synthesis experiments and ex situ atomic scale imaging revealed that a key role of metal thiolate complexes was to prevent copper atom oxidation and facilitate formation of prenucleation cluster intermediates. This work demonstrates that complex ion precursor chemistry can be maintained during LP-TEM imaging, enabling probing nanocrystal formation mechanisms with LP-TEM under reaction conditions representative of ex situ flask synthesis.

This study reports the use of Additively Manufactured nitinol as a high-performance metallic solid-solid phase change material. Compared to standard phase change materials, which offer point solutions, it’s shown here that latent heat, thermal conductivity, and transformation temperature can be tuned in additively manufactured nitinol by adjusting the chemistry, processing parameters, and heat treatment. Leveraging these results, a 28% reduction in peak temperature during a simulated transient electronic application is demonstrated. It’s anticipated that these perennial results, combined with future optimization efforts, will encourage new phase change material development and architecture designs.

Helium bubbles are known to form in nuclear reactor structural components when displacement damage occurs in conjunction with helium exposure and/or transmutation. If left unchecked, bubble production can cause swelling, blistering, and embrittlement, all of which substantially degrade materials and—moreover—diminish mechanical properties. On the mission to produce more robust materials, nanocrystalline (NC) metals show great potential and are postulated to exhibit superior radiation resistance due to their high defect and particle sink densities; however, much is still unknown about the mechanisms of defect evolution in these systems under extreme conditions. Here, the performances of NC nickel (Ni) and iron (Fe) are investigated under helium bombardment via transmission electron microscopy (TEM). Bubble density statistics are measured as a function of grain size in specimens implanted under similar conditions. While the overall trends revealed an increase in bubble density up to saturation in both samples, bubble density in Fe was over 300% greater than in Ni. To interrogate the kinetics of helium diffusion and trapping, a rate theory model is developed that substantiates that helium is more readily captured within grains in helium-vacancy complexes in NC Fe, whereas helium is more prone to traversing the grain matrices and migrating to GBs in NC Ni. Our results suggest that (1) grain boundaries can affect bubble swelling in grain matrices significantly and can have a dominant effect over crystal structure, and (2) an NC-Ni-based material can yield superior resistance to irradiation-induced bubble growth compared to an NC-Fe-based material and exhibits high potential for use in extreme environments where swelling due to He bubble formation is of significant concern.

Titanium dioxide (TiO2) semiconductor photocatalysts were photosensitized to the visible spectrum with gold nanospheres (AuNSs) and gold nanorods (AuNRs) to study the ethanol photo-oxidation cycle, with an emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. The photocatalysts exhibited a localized surface plasmon resonance (SPR) that was harnessed to drive the complete photo-oxidation of formic acid (FA) and ethanol (EtOH) via augmented carrier generation/separation and photothermal conversion. Contributions of transverse and longitudinal localized SPR modes were decoupled by irradiating AuNSs–TiO2 and AuNRs–TiO2 with targeted wavelength ranges to probe their effects on plasmonically assisted photocatalytic oxidation of FA and EtOH. Photocatalytic performance was assessed by monitoring the yield of gaseous products during photo-oxidation experiments using a gas chromatography–mass spectrometry–multiple headspace extraction (GC–MS–MHE) analysis method. The complete oxidation of E...

Photocatalytic assembly of heterometallic nanoarchitectures via plasmonic hot electrons is demonstrated by liquid-phase, reductive photodeposition of platinum (Pt) onto gold nanorods (AuNR) under longitudinal surface plasmon (LSP) excitation. Nucleation of Pt0 from PtCl62– was initiated by plasmonic hot electrons at the Au surface. Sub-5 nm epitaxial overgrowth of Pt followed a core–shell morphology. Measured 6.5 longitudinal:transversal growth aspect ratio revealed longitudinal growth preferentiality that was consistent with the LSP dipole polarity. In situ spectroscopic monitoring of the photocatalytic growth process permitted real-time feedback into Au surface functionalization with PtCl62– according to 16 nm red-shift in its Cl–Pt ligand-to-metal charge-transfer (LπMCT) band involving ligand π orbitals. Subsequent Pt0 growth kinetics were tracked using the LπMCT band. Discrete dipole models elucidated evolving light-matter interactions of Pt-decorated AuNR that were consistent with experimental charac...

Iridium oxide (IrOx) forms a wide array of tailorable nanostructures, including plates, rods, and cones. Despite a strong body of literature on nanostructured IrOx, prior work did not explore the specific growth conditions and mechanisms for platelet formation. Here we report on how IrOx nanoplatelets take their form during DC reactive sputtering deposition, highlight the conditions and growth mechanisms that lead to unique nanostructures, and demonstrate changes in morphology and crystal orientation via x-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy and x-ray photoelectron spectroscopy. The XRD spectra indicate that IrOx undergoes a substantial transition with increasing oxygen flow rate during deposition, with the initial face-centered cubic (1 1 1), (2 0 0) and (2 2 0) peaks vanishing, while the rutile (1 0 1) and (1 1 0) peaks emerge, with several intermediate peaks indicating transition species. Ultimately (1 0 1) emerges as the preferred orientation of the IrOx nanostructures, as evidenced by the time-series XRD spectra. Corresponding stress analysis indicates that in the absence of oxygen flow, the IrOx films are highly compressive, and that the film stress becomes significantly less compressive with increasing oxygen flow. This unlocks the use of IrOx as a highly tailorable nanostructured material, ranging from dense film to high aspect ratio platelets, by simply adjusting oxygen flow rate and/or sputtering time.

Recrystallization and subsequent twin formation in > 99.99% pure copper is investigated by in situ annealing in a scanning electron microscope. Distinct microstructural evolution mechanisms are observed for specimens deformed using 5% and 25% cold-rolled reductions. Upon annealing the former, growth and twinning of existing grains via strain-induced boundary migration is observed while the latter exhibits nucleation and growth. Serial sectioning indicates that recrystallization in the low strain condition is surface dominant while nucleation occurs through thickness in the high strain condition. Geometrically necessary dislocation densities are calculated and mapped to identify the localized driving pressures for each recrystallization mechanism.

Grain boundary engineering of Fe-based austenitic stainless steels and other materials has been successful in producing a large increase in twin and twin related grain boundaries from a wide range of thermomechanical treatments. However, the exact mechanisms and effective grain boundary network descriptors to create the heavily twinned microstructures are yet to be fully understood. In this study, we provide insight into the grain boundary engineering process by examining sequential progression of the same spatial location of a twin related microstructure through thermomechanical processing. The results show that clusters of twin related grain boundaries called twin related domains form during primary recrystallization. The size of the twin related domains increases as the level of strain falls toward the critical strain for recrystallization. Growth of twin related domains during recrystallization results in the formation of twin boundaries behind the migrating grain boundary front. Formation of higher order twin boundaries occurs when two separate grain boundary fronts of the same twin related domain impinge upon each other. We also present relevant microstructural descriptors with emphasis on twin related domain statistics to recrystallization phenomena in grain boundary engineering materials.

The vast majority of our understanding about the deformation mechanisms in nanocrystalline materials is limited to information gained from experimental and theoretical characterization of FCC materials. Related behavior in nanocrystalline BCC materials is not as frequently studied, and thus outstanding questions remain regarding deformation regimes and Hall-Petch trends. Using in situ TEM, we investigate the deformation mechanisms of nanocrystalline BCC iron films with an average grain size of 35 nm produced by physical vapor deposition. The tensile experiments showed that fracture resulted after strains of about 5%. Crack propagation occurred primarily by separation of grain boundaries at the crack tip, which was accompanied by localized intragranular ductile (often superplastic) fracture. Deformation at the crack tip was accommodated by dislocation motion, grain rotation, and grain growth. No evidence was observed of twinning in nanocrystalline BCC iron. The concurrent nature of the grain rotation and dislocation motion indicates that grain rotation occurs at fairly large grain sizes and there is no sharp transition from dislocation-mediated to grain boundary sliding mechanisms as grain size is decreased in BCC iron.

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Disclinations, defects that accommodate rotational incompatibilities in a crystal lattice, have been described in detail in the literature, but rarely observed in solid materials. Recently, a method has been described by which it is proposed that disclination densities can be estimated using spatially resolved orientation data generated from electron backscatter diffraction or precession electron diffraction. Herein, a rigorous evaluation of this approach is performed. In this work, a series of constructed and real data sets are used to evaluate the methodology for estimating disclination densities from spatially mapped orientation data and demonstrate the inherent error associated with this approach. It is shown that the outcome of this analysis is heavily dependent on the how numerical approximations are implemented. If a self-consistent method is used, then the disclination tensor will always be zero and if an inconsistent method is used then the error in the estimation of the disclination tensor is unbounded. Therefore, although the theory behind the disclination tensor is sound, the inputs needed to calculate it are not experimentally accessible through the application of numerical approximation methods to orientation maps and a different methodology is needed.

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. The cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of −5 °C is compared. The texture of the tube with the Af of −5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. These observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.

In many cases, electron counting with direct detection sensors offers improved resolution, lower noise, and higher pixel density compared to conventional, indirect detection sensors for electron microscopy applications. Direct detection technology has previously been utilized, with great success, for imaging and diffraction, but potential advantages for spectroscopy remain unexplored. Here we compare the performance of a direct detection sensor operated in counting mode and an indirect detection sensor (scintillator/fiber-optic/CCD) for electron energy-loss spectroscopy. Clear improvements in measured detective quantum efficiency and combined energy resolution/energy field-of-view are offered by counting mode direct detection, showing promise for efficient spectrum imaging, low-dose mapping of beam-sensitive specimens, trace element analysis, and time-resolved spectroscopy. Despite the limited counting rate imposed by the readout electronics, we show that both core-loss and low-loss spectral acquisition are practical. These developments will benefit biologists, chemists, physicists, and materials scientists alike.

Nanocrystalline materials are radiation-tolerant materials’ candidates due to their high defect sink density. Here, nanocrystalline iron films were irradiated with 10 keV helium ions in situ in a transmission electron microscope at elevated temperatures. Grain-size-dependent bubble density changes and denuded zone occurrence were observed at 700 K, but not at 573 K. This transition, attributed to increased helium–vacancy migration at elevated temperatures, suggests that nanocrystalline microstructures are more resistant to swelling at 700 K due to decreased bubble density. Finally, denuded zone formation had no correlation with grain size and misorientation angle under the conditions studied.

Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a 0 /2 [111] Burgers vector were directly observed as a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (

Adding thermal conductivity enhancements to increase thermal power in solid-liquid phase-change thermal energy storage modules compromises volumetric energy density and often times reduces the mass and volume of active phase change material (PCM) by well over half. In this study, a new concept of building thermal energy storage modules using high-conductivity, solid-solid, shape memory alloys is demonstrated to eliminate this trade-off and enable devices that have both high heat transfer rate and high thermal capacity. Nickel titanium, Ni50.28Ti49.36, was solution heat treated and characterized using differential scanning calorimetry and Xenon Flash to determine transformation temperature (78deg-C), latent heat (183 kJm-3), and thermal conductivity in the Austenite and Martensite phases (12.92/12.64 Wm-1K-1). Four parallel-plate thermal energy storage demonstrators were designed, fabricated, and tested in a thermofluidic test setup. These included a baseline sensible heating module (aluminum), a conventional solid-liquid PCM module (aluminum/1-octadecanol), an all-solid-solid PCM module (Ni50.28Ti49.36), and a composite solid-solid/solid-liquid PCM module (Ni50.28Ti49.36/1-octadecanol). By using high-conductivity solid-solid PCMs, and eliminating the need for encapsulants and conductivity enhancements, we are able to demonstrate a 1.73-3.38 times improvement in volumetric thermal capacity and a 2.03-3.21 times improvement in power density as compared to the conventional approaches. These experimental results are bolstered by analytical models to explain the observed heat transfer physics and reveal a 5.86 times improvement in thermal time constant. This work demonstrates the ability to build high-capacity and high-power thermal energy storage modules using multifunctional shape memory alloys and opens the door for leap ahead improvement in thermal energy storage performance., Comment: 35 pages, 9 figures, submitted pre-decisional

Thin indium tin oxide (ITO) films have been used as a medium to investigate epsilon-near-zero (ENZ) behavior for unconventional tailoring and manipulation of the light-matter interaction. However, the ENZ wavelength regime has not been studied carefully for ITO films with thicknesses larger than the wavelength. Thick ENZ ITO film would enable the development of a new family of ENZ-based opto-electronic devices that take full advantage of the ENZ behavior. Here, we demonstrated wavelength-thick ITO films reaching the ENZ regime around a wavelength of 1550 nm, which permit the design of such devices operating in the common optical telecommunications wavelength band. We discovered that the permittivity of the film was non-uniform with respect to the growth direction. In particular, after annealing at a sufficiently high temperature, the real part of the permittivity showed a step change from negative to positive value, crossing zero permittivity near the middle of the film. Subsequently, we conducted comprehensive microanalysis with X-ray diffraction, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) to investigate the correlation of the permittivity variation with variations in the ITO crystallite morphology and relative concentrations of different atom species. The result of this study will allow us to design a new family of opto-electronic devices where ITO can be used as the cladding that guides light within an air-core waveguide to provide a new platform to explore ENZ properties such as environment insensitivity, super-coupling, and surface avoidance. We have also provided a comprehensive method to determine the permittivity in a non-uniform ENZ material by using an advanced physical model to the fit experimental data.

We demonstrate robust superconducting proximity effect in InAs$_{0.5}$Sb$_{0.5}$ quantum wells grown with epitaxial Al contact, which has important implications for mesoscopic and topological superconductivity. Unlike more commonly studied InAs and InSb semiconductors, bulk InAs$_{0.5}$Sb$_{0.5}$ supports stronger spin-orbit coupling and larger $g$-factor. However, these potentially desirable properties have not been previously measured in epitaxial heterostructures with superconductors, which could serve as a platform for fault-tolerant topological quantum computing. Through structural and transport characterization we observe high-quality interfaces and strong spin-orbit coupling. We fabricate Josephson junctions based on InAs$_{0.5}$Sb$_{0.5}$ quantum wells and observe strong proximity effect. These junctions exhibit product of normal resistance and critical current, $I_{c}R_{N} = \SI{270}{\micro V}$, and excess current, $I_{ex}R_{N} = \SI{200}{\micro V}$ at contact separations of 500~nm. Both of these quantities demonstrate a robust and long-range proximity effect with highly-transparent contacts.

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot electrons upon SPR irradiation drive reductive deposition of Pd on colloidal AuNR in the presence of [PdCl4]2-. Plasmon-driven reduction of secondary metals potentiates covalent, sub-wavelength deposition at targeted locations coinciding with electric field "hot-spots" of the plasmonic substrate using an external field (e.g., laser). The process described herein details a solution-phase deposition of a catalytically-active noble metal (Pd) from a transition metal halide salt (H2PdCl4) onto aqueously-suspended, anisotropic plasmonic structures (AuNR). The solution-phase process is amenable to making other bimetallic architectures. Transmission UV-vis monitoring of the photochemical reaction, coupled with ex situ XPS and statistical TEM analysis, provide immediate experimental feedback to evaluate properties of the bimetallic structures as they evolve during the photocatalytic reaction. Resonant plasmon irradiation of AuNR in the presence of [PdCl4]2- creates a thin, covalently-bound Pd0 shell without any significant dampening effect on its plasmonic behavior in this representative experiment/batch. Overall, plasmonic photodeposition offers an alternative route for high-volume, economical synthesis of optoelectronic materials with sub-5 nm features (e.g., heterometallic photocatalysts or optoelectronic interconnects).

In this work, the thermal conductivity and volumetric heat capacity of 50–50 NiTi shape memory alloys (SMA) with varying grain size are investigated as a function of temperature. SMAs, and NiTi in particular, have a critical role to play in next-generation solid-state refrigeration systems and long-term thermal storage applications. However, their performance in these applications is predicated on their latent heat, thermal conductivity and heat capacity. Complicating the prediction of their performance is the wide variability in reported results for each of these properties within the scientific literature and a lack of information regarding their temperature-dependence, particularly as SMAs experience a martensitic-austenitic phase transition. We use Frequency-Domain Thermoreflectance (FDTR) to probe the thermal transport properties of NiTi as a function of average grain size and temperature and report our results here. Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM) are used to characterize the phase transitions and microstructure of the NiTi, respectively. Collectively, these measurements provide a better understanding of the impact of grain size and phase transition on thermal transport and storage within NiTi as it changes phase, permitting improved predictions of their behavior in a host of important applications.

Hydrogen embrittlement is the deterioration of mechanical properties in a metal exposed to hydrogen, often characterized by brittle, intergranular fracture at low applied stresses. While grain boundary engineering has been applied to mitigate this issue, ambiguity in the mechanisms behind hydrogen embrittlement leads to ambiguity in the mechanism by which grain boundary engineering helps to mitigate this problem. In this study, grain boundary engineering was applied to improve resistance to hydrogen embrittlement in Custom Age 625 PLUS®, an alloy frequently used in corrosive environments where hydrogen embrittlement is of particular concern. Iterative low strain cold rolling followed by annealing at intermediate temperature successfully produced a grain boundary engineered microstructure with large twin-related domains and a high fraction of interconnected coincident site lattice (CSL) boundaries. Rising step load testing demonstrated that grain boundary engineering increased the stress intensity at which failure from hydrogen embrittlement occurred and caused a shift from intergranular to transgranular crack propagation. Evidence of localized plasticity on fracture surfaces suggest that hydrogen-enhanced localized plasticity (HELP) is the dominant mechanism of hydrogen embrittlement.

TiN and ZrN nanoparticles (NPs) are an emerging class of plasmonic materials that can be used for harvesting energy of visible light in order to drive chemical reactions on the photocatalyst surface [1-3]. These refractory NPs effectively absorb light over l = 450-1200 nm, covering most of the solar spectrum. Both TiN and ZrN have the optical appearence of gold, but with the advantages of thermal stability, corrosion resistance and low cost. Previous theoretical and experimental research have shown that TiN does not exhibit as strong of a plasmonic resonance as gold (broader response, sample variability due to defect-dependent metallicity) [2, 4]. ZrN is expected to have a sharper blue-shifted local surface plasmon resonance (LSPR) response in comparison to TiN [4, 5]. Indeed, this theoretical prediction was verified by observation of a sharp plasmonic maximum for ZrN NPs decorated by a thin layer of SiN [4]. However, ZrN NPs appear to be less chemically inert owing to zirconium’s strong affinity for oxygen. A layer of dielectric ZrO2 forms on the surface of ZrN NPs even in the presence of trace oxygen. The oxide layer has a detrimental effect on the LSPR, leading to its broadening and red-shifting [5]. Herein both experimental and computational approaches are used in order to optimize the performance of TiO2-supported TiN and ZrN NPs towards photoelectrochemical methanol (CH3OH) oxidation under visible excitation. UV excitation is utilized in order to provide complementary information on the interaction between photogenerated carriers at the plasmonic NP/semiconductor interface. The effects of plasmonic catalyst loading and applied potential were examined. Reaction products were determined by gas chromatography-mass spectrometry analysis of ZrN/TiO2 and TiN/TiO2 aqueous suspensions. Optical spectra for both TiN and ZrN NPs were computed using COMSOL including calculations of these NPs in solution and embedded in a TiO2 matrix. To examine the effect of oxide layer, the NPs were decorated with the corresponding oxide layers. ZrN NPs were synthesized by ammonolysis of Zr(NMe2)4. Clean Zr(NMe2)4 was prepared following a protocol from the literature [6]. In-house made ZrN powder and commercial TiN NPs (PlasmaChem) were dispersed into a P25 TiO2 matrix via the sonochemically mediated mixing of the transition metal nitride and TiO2 NPs in 50:50 (v/v) H2O:ethanol mixture overnight. The resulting photocatalysts contained 0.5 - 5 wt. % loadings of TiN and ZrN on TiO2. The ZrN/TiO2, TiN/TiO2 and bare TiO2 films for photoelectrochemical experiments were prepared by drop-casting 60 mL of ink comprising 20 mg of the photocatalyst, 30 ml of 5 wt% Nafion solution (Ion Power), 2.96 ml H2O and 0.74 ml iso-propanol, on FTO slide (coated surface area of 0.385 cm2). Experiments were conducted in a three-electrode photoelectrochemical cell. The photocatalyst films deposited on FTO-coated glass substrates served as working electrodes, while Pt foil and Ag/AgCl in 3 M NaCl (BioLogic, Inc) were used as counter and reference electrodes, respectively. Nine single-color LED lights were employed for illumination. The intensities varied between 10-100 mW/cm2, and 300-480 mW/cm2 in the wavelength range of 490-670 and 730-960 nm, respectively. Our results indicate that optical properties and photocatalytic activity of ZrN/TiO2 are strongly affected by ZrN surface oxidation and agglomeration. We found that under visible illumination, both in-house synthesized 17 nm ZrN and commercial 30 nm TiN NPs promote TiO2 activity for CH3OH oxidation, while under visible + UV excitation, an inhibition effect is observed. The differences between the TiN/TiO2 and ZrN/TiO2 interfaces are discussed and the mechanisms of promotion/inhibition of TiO2 photocatalytic activity by ZrN and TiN NPs are proposed. References [1] A. Naldoni, U. Guler, Z.X. Wang, M. Marelli, F. Malara, X.G. Meng, L.V. Besteiro, A.O. Govorov, A.V. Kildishev, A. Boltasseva, V.M. Shalaev, Advanced Optical Materials, 5 (2017) [2] O.A. Baturina, A. Epshteyn, B. Simpkins, N. Bhattarai, T.H. Brintlinger, E.Y. Santiago, A.O. Govorov, J. Electrochem. Soc 166 (2019) H485 [3] B. S. Simpkins, A. Purdy, A. Epshteyn and O. Baturina, J. Phys. Chem. C, 123 (2019) 13863 [4] T. Liu, L.V. Besteiro, Z. Wang, A.O. Govorov, Faraday Discussions, 214 (2019) 199. [5] S. Exarhos, A. Alvarez-Barragan, E. Aytan, A. A. Balandin and L. Mangolini, ACS Energy Lett., 3, 2349 (2018). [6] D. C. Bradley, I.M. Thomas, Proceedings of the Chemical Society, August 1959, 225-226.

Nanocrystalline metals are postulated as radiation resistant materials due to their high defect and particle (e.g. Helium) sink density. Here, the performance of nanocrystalline iron films is investigated in-situ in a transmission electron microscope (TEM) using He irradiation at 700 K. Automated crystal orientation mapping is used in concert with in-situ TEM to explore the role of grain orientation and grain boundary character on bubble density trends. Bubble density as a function of three key grain size regimes is demonstrated. While the overall trend revealed an increase in bubble density up to a saturation value, grains with areas ranging from 3000 to 7500 nm 2 show a scattered distribution. An extrapolated swelling resistance based on bubble size and areal density indicated that grains with sizes less than 2000 nm 2 possess the greatest apparent resistance. Moreover, denuded zones are found to be independent of grain size, grain orientation, and grain boundary misorientation angle.

The high density of interfaces in nanostructured materials are hypothesized to improve radiation tolerance compared to coarse-grained materials. In order to investigate the roles of vacancies, self-interstitials, and helium, both room temperature in situ TEM He+ implantation and annealing, as well as high temperature He+ implantation was performed on nanocrystalline iron. Dislocation loops are formed by the accumulation of mobile point defects rather than by displacement cascades at intermediate temperatures. Around 600 °C, loops disappeared through gradual shrinking, which is hypothesized to correspond to the annihilation of self-interstitial atoms by mobile vacancies that also resulted in cavity formation. The room temperature implantation resulted in cavities evenly distributed throughout the grain after annealing, whereas cavities were predominately observed at grain boundaries for the elevated temperature implantation. This difference is associated with the formation of stable helium-vacancy complexes in the grains during room temperature implantation, which is not present during high temperature implantation.

Transmission electron microscopy was coupled with precession electron diffraction methods to determine the role of local defect distributions in the formation and growth behavior of twin nuclei. Three distinct cases were observed that are indicative of three separate formation mechanisms, two as the result of annealing and the third as a result of deformation. While all of the observed cases are consistent with the proposed mechanisms for twin formation found in literature, this study marks the first experimental evidence to support all three mechanisms occurring simultaneously in the same microstructure.

Grain boundaries (GBs) are considered sinks where mobile defects are attracted and annihilated thereby hampering irradiation damage accumulation. Nanocrystalline (NC) metals characteristically have greater densities of GBs relative to their coarse-grained counterparts hence they are postulated to provide enhanced resistance to irradiation damage. The use of alloying as a means to impart synergistic properties such as corrosion resistance, increased toughness, or improved conductivity is well studied, yet the cooperative effects of solute addition and grain size in the nano-regime is not well understood. In this study, a combination of in situ ion irradiation, transmission electron microscopy (TEM), and automated crystal orientation mapping (ACOM) on model Ni, NiCr, Fe, and FeCr NC thin-films are used to provide experimental evidence that grain size and irradiation induced defect morphology (defect density and size) are not directly correlated due to defect agglomeration, annihilation at sinks, and saturation, while the addition of solute impedes defect mobility, altering the final damage state.

TiN and ZrN refractory transition metal nitride nanoparticles (NPs) have recently emerged as an alternative to noble metals in plasmonic applications. However, plasmon-driven photocatalysis by ZrN NPs is largely unexplored. In this study, optical properties, morphology, crystal structure and surface composition of in-house synthesized and commercial ZrN nanoparticles (NPs) are vigorously characterized in order to select the best candidate material for evaluation of activity towards CH3OH photoelectrochemical oxidation. The photocatalytic activity of TiO2-supported ZrN NPs is compared to that of TiN/TiO2 as a function of NP loading and illumination wavelength. Our results indicate that optical properties and photocatalytic activity of ZrN/TiO2 are strongly affected by ZrN surface oxidation and agglomeration. We found that under visible illumination, both in-house synthesized 17 nm ZrN and commercial 30 nm TiN NPs promote TiO2 activity for CH3OH oxidation, while under visible + UV excitation, an inhibition effect is observed. The differences between the TiN/TiO2 and ZrN/TiO2 interfaces are discussed and the mechanisms of promotion/inhibition of TiO2 photocatalytic activity by ZrN and TiN NPs are proposed. Electromagnetic simulations are used to facilitate interpretation of experimental extinctions and photocatalytic activities.