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Single atom catalysts (SACs) have shown high activity and selectivity in a growing number of chemical reactions. Many efforts aimed at unveiling the structure-property relationships underpinning th ...

Nonaqueous Zn-ion batteries are a promising candidate for a high-energy storage system to replace Li-ion batteries. Here, we report on CoS2 as a cathode material for Zn-ion batteries using nonaqueo...

3D structured porous electrodes have been considered as a possible solution for accommodating the volume change of alloying lithium ion battery anode materials during cycling. However, lab-scale porous electrodes tend to be thin, and the loading of the activity materials is also small, the combination of which results in electrodes with impractically low areal and volumetric capacities. Here, we develop a high areal and volumetric capacity 3D-structured Sn/C anode by using a two steps electroplating process. An electrode with a 20%v/v Sn loading exhibits a high volumetric/areal capacity of ∼879 mA h/cm3/6.59 mA h/cm2 after 100 cycles at 0.5 C and a good rate performance of about 750 mA h/cm3 and 5.5 mA h/cm2 (delithiation) at 10 C in a half-cell configuration. The 3D Sn/C anode also shows good compatibility with a commercial LCO cathode in a full cell configuration.

All-solid-state Li-ion batteries afford possibilities to enhance battery safety while improving their energy and power densities. Current challenges for achieving high-performance all-solid-state batteries with long cycle life include shorting resulting predominantly from Li dendrite formation and infiltration through the solid electrolyte (SE) and increases in cell impedance induced by SE decomposition at the SE/electrode interface. In this work, we evaluate the electrochemical properties of two interlayer materials, Si and LixAl(2–x/3)O3 (LiAlO), at the Li7P3S11 (LPS)/Li interface. Compared to the Li/LPS/Li symmetric cells in absence of interlayers, the presence of Si and LiAlO both significantly enhance the cycle number and total charge passing through the interface before failures resulting from cell shorting. In both cases, the noted improvements were accompanied by cell impedances that had increased substantially. The data reveal that both interlayers prevent the direct exposure of LPS to the metall...

Oxide-supported noble metal catalysts have been extensively studied for decades for the water gas shift (WGS) reaction, a catalytic transformation central to a host of large volume processes that variously utilize or produce hydrogen. There remains considerable uncertainty as to how the specific features of the active metal-support interfacial bonding—perhaps most importantly the temporal dynamic changes occurring therein—serve to enable high activity and selectivity. Here we report the dynamic characteristics of a Pt/CeO2 system at the atomic level for the WGS reaction and specifically reveal the synergistic effects of metal-support bonding at the perimeter region. We find that the perimeter Pt0 − O vacancy−Ce3+ sites are formed in the active structure, transformed at working temperatures and their appearance regulates the adsorbate behaviors. We find that the dynamic nature of this site is a key mechanistic step for the WGS reaction., Revealing the structure and dynamics of active sites is essential to understand catalytic mechanisms. Here the authors demonstrate the dynamic nature of perimeter Pt0−O vacancy−Ce3+ sites in Pt/CeO2 and the key effects of their dynamics on the mechanism of the water gas shift reaction.

Commercial smart window technologies for dynamic light and heat management in building and automotive environments traditionally rely on electrochromic (EC) materials powered by an external source. This design complicates building-scale installation requirements and substantially increases costs for applications in retrofit construction. Self-powered photoelectrochromic (PEC) windows are an intuitive alternative wherein a photovoltaic (PV) material is used to power the electrochromic device, which modulates the transmission of the incident solar flux. The PV component in this application must be sufficiently transparent and produce enough power to efficiently modulate the EC device transmission. Here, we propose Si solar microcells (μ-cells) that are i) small enough to be visually transparent to the eye, and ii) thin enough to enable flexible PEC devices. Visual transparency is achieved when Si μ-cells are arranged in high pitch (i.e. low-integration density) form factors while maintaining the advantages of a single-crystalline PV material (i.e., long lifetime and high performance). Additionally, the thin dimensions of these Si μ-cells enable fabrication on flexible substrates to realize these flexible PEC devices. The current work demonstrates this concept using WO₃ as the EC material and V₂O₅ as the ion storage layer, where each component is fabricated via sol-gel methods that afford improved prospects for scalability and tunability in comparison to thermal evaporation methods. The EC devices display fast switching times, as low as 8 seconds, with a modulation in transmission as high as 33%. Integration with two Si μ-cells in series (affording a 1.12 V output) demonstrates an integrated PEC module design with switching times of less than 3 minutes, and a modulation in transmission of 32% with an unprecedented EC:PV areal ratio.

The development of methods to synthesize and physically manipulate extremely thin, single-crystalline inorganic semiconductor materials, so-called nanomembranes, has led to an almost explosive growth of research worldwide into uniquely enabled opportunities for their use in new "soft" and other unconventional form factors for high-performance electronics. The unique properties that nanomembranes afford, such as their flexibility and lightweight characteristics, allow them to be integrated into electronic and optoelectronic devices that, in turn, adopt these unique attributes. For example, nanomembrane devices are able to make conformal contact to curvilinear surfaces and manipulate strain to induce the self-assembly of various 3D nano/micro device architectures. Further, thin semiconductor materials (e.g., Si-nanomembranes, transition metal dichalcogenides, and phosphorene) are subject to the impacts of quantum and other size-dependent effects that in turn enable the manipulation of their bandgaps and the properties of electronic and optoelectronic devices fabricated from them. In this Perspective, nanomembrane synthesis techniques and exemplary applications of their use are examined. We specifically describe nanomembrane chemistry exploiting high-performance materials, along with precise/high-throughput techniques for their manipulation that exemplify their growing capacities to shape outcomes in technology. Prominent challenges in the chemistry of these materials are presented along with future directions that might guide the development of next generation nanomembrane-based devices.

We demonstrate that solid–liquid nanocomposites derived from porous organic cages are effective lithium ion electrolytes at room temperature. A solid–liquid electrolyte nanocomposite (SLEN) fabricated from a LiTFSI/DME electrolyte system and a porous organic cage exhibits ionic conductivity on the order of 1 × 10–3 S cm–1. With an experimentally measured activation barrier of 0.16 eV, this composite is characterized as a superionic conductor. Furthermore, the SLEN displays excellent oxidative stability up to 4.7 V vs Li/Li+. This simple three-component system enables the rational design of electrolytes from tunable discrete molecular architectures.

Dynamic electrochemical surface stress response during the oxygen reduction reaction (ORR) on Pt and Pd cantilever electrodes in HClO 4 and KOH was examined to elucidate surface binding configurations during O 2 reduction electrocatalysis. Upon reduction of O 2 , the surface of Pt exhibits a compressive surface stress response, ΔStress, in both acid and base electrolytes due to adsorption of the ORR reactant and intermediates (O 2 , O, and OH). The magnitude of compressive ΔStress on Pt is greater in acid relative to base. On the other hand, the surface of Pd exhibits a negligible ΔStress in acid and a slight compressive ΔStress in base. Thus, magnitudes of the compressive ΔStress (surface expansion) during the ORR follow the order of Pt (acid) > Pt (base) > Pd (base) > Pd (acid) ∼ 0. Density functional theory (DFT) calculations of adsorbate-induced excess surface stress on Pt(111) and Pd(111) surfaces imply a greater compressive surface stress induced on Pt(111) for nearly all adsorbate geometries examined. This trend, which agrees with the experimental observations, can be correlated to a greater tensile intrinsic surface stress of Pt(111) relative to Pd(111) resulting from difference in bond strength and bulk modulus of two metals. On stepped Pt(221) and Pd(221) surfaces, both the intrinsic tensile stress of the clean surface and the adsorbate-induced excess compressive stress are significantly reduced due to the presence of less coordinated, flexible step sites. Moreover, this difference between surface stress at terrace and step sites is more pronounced on Pt, which exhibits a greater intrinsic surface stress.

In this work we describe a multimodal exploration of the atomic structure and chemical state of silica-supported palladium nanocluster catalysts during the hydrogenation of ethylene in operando conditions that variously transform the metallic phases between hydride and carbide speciations. The work exploits a microreactor that allows combined multiprobe investigations by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption fine structure (XAFS), and microbeam IR (μ-IR) analyses on the catalyst under operando conditions. The work specifically explores the reaction processes that mediate the interconversion of hydride and carbide phases of the Pd clusters in consequence to changes made in the composition of the gas-phase reactant feeds, their stability against coarsening, the reversibility of structural/compositional transformations, and the role that oligomeric/waxy byproducts (here forming under hydrogen-limited reactant compositions) might play in modifying activity. The results pr...

Quasi-binary thiophosphate-based solid electrolytes (SEs) are attracting substantial interest for lithium batteries due to their outstanding room temperature ionic conductivities. This work describes reactions occurring at the solid electrolyte (SE)/Au interface during Li deposition and stripping for two exemplary SE materials: β-Li3PS4 (β-LPS) and Li10GeP2S12 (LGPS). We used in situ Raman spectroscopy, along with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to evaluate potential-dependent changes in the chemistry of these materials at active electrode interfaces. For β-LPS, a partially reversible conversion of PS43– to P2S64– was found along with the formation of Li2S during Li deposition and stripping. In contrast, LGPS exhibited only irreversible changes at potentials below 0.7 V vs Li+/Li. The different behaviors likely relate to differences in the structures of the two SE materials and the availability of easily bridged anion components in close proximity. The work sh...

Luminescent solar concentrator (LSC) tandem-on-silicon (Si) provides a route towards achieving higher than 30% overall efficiency which can overcome the theoretical efficiency limit of a single junction Si cell. Here, we present optical coupling and performance of high V oc passivated contact Si bottom cell for LSC tandem-on-Si where the top module consists of highly efficient luminophores and an array of micro InGaP cells embedded in a poly (lauryl methacrylate) waveguide. In this device configuration, InGaP cell area coverage is only ~0.5% of the total LSC area which significantly reduces the high cost III-V material usage. The performance of Si sub-cell is investigated under LSC spectrum and is compared against the measurement done under 1 μm thick InGaP filter which mimics the spectrum seen by Si bottom cell in a conventional III-V/Si tandem. V oc of greater than 700 mV has been observed for the passivated contact Si bottom cell in these tandem applications.

© 2018 IEEE. Luminescent solar concentrators (LSCs) harness light generated by luminophores embedded in a light-trapping waveguide to concentrate onto smaller cells. LSCs can absorb both direct and diffuse sunlight, and thus can operate as flat plate receivers at a fixed tilt and with a conventional module form factor. However, current LSCs experience significant power loss through parasitic luminophore absorption and incomplete light trapping by the optical waveguide. Here, we introduce a tandem LSC device architecture that overcomes both of these limitations, consisting of a poly(lauryl methacrylate) polymer layer with embedded cadmium selenide core, cadmium sulfide shell (CdSe/CdS) quantum dot (QD) luminophores and an InGaP microcell array, which serves as high bandgap absorbers on the top of a conventional Si photovoltaic. We investigate the design space for a tandem LSC, using experimentally measured performance parameters for key components, including the InGaP microcell array, CdSe/CdS QDs, and spectrally selective waveguide filters. Using a Monte Carlo ray-tracing model, we compute the power conversion efficiency for a tandem LSC module with these components to be 29.4% under partially diffuse illumination conditions. These results indicate that a tandem LSC-on-Si architecture could significantly improve upon the efficiency of a conventional Si photovoltaic cell.

Solar energy-powered water electrolysis is a cost-effective and scalable method to produce hydrogen, an environment-friendly and potentially sustainable energy carrier. To this end, we report a microchannel water electrolyzer with a planar design that can be integrated with a photovoltaic cell, where the electrolyzer utilizes the waste heat generated during the photoelectric process to enhance the production of hydrogen (and oxygen) via the electrochemical splitting of water. We performed a systematic parametric investigation to study the effect of the channel dimensions, electrolyte temperature and flow rate, and the mode of operation (pulsed vs. continuous) on the electrolyzer's performance. The balance between mass, heat and ion/charge transport limitations acts to determine an optimal geometry and specific operating conditions for the device. The highest hydrogen production rate was observed for pulsed operation (15 s pulses) at a temperature of 60 °C, and a potential of 2.0 V, for a 400-μm tall electrolyzer chamber. We also show that tuning of the geometry and operating conditions can yield an almost 7-fold increase in the hydrogen production rate. This study not only reports a new and improved approach over existing photovoltaic thermal systems but also presents design and operational considerations for microfluidic-based electrochemical energy devices.

Escape cone loss is one of the primary limiting factors for efficient photon collection in large-area luminescent solar concentrators (LSCs). The Stokes shift of the luminophore, however, opens up an opportunity to recycle the escaped luminescence at the LSC front surface by utilizing a photonic band-stop filter that reflects photons in the luminophore’s emission range while transmitting those in its absorption range. In this study, we examine the functional attributes of such photonic filter designs, ones realized here in the form of a distributed Bragg reflector (DBR) fabricated by spin-coating alternating layers of SiO2 and SnO2 nanoparticle suspensions onto a supportive glass substrate. The central wavelength and the width of the photonic stopband were programmatically tuned by changing the layer thickness and the refractive index contrast between the two dielectric materials. We explore the design sensitivities for a DBR with an optimized stopband frequency that can effectively act as a top angle-res...

In order to more deeply understand the mechanisms of catalytic reactions, improved methods are needed to monitor changes that occur in the electronic, structural, and chemical properties of catalytic systems under the conditions in which they work. We describe here a microreactor-based approach that integrates the capabilities of advanced X-ray, electron, optical, and gas-phase compositional analysis techniques under operando conditions. For several exemplary catalytic systems, we demonstrate how this approach enables the characterization of three of the major factors that contribute to structure–property correlations in heterogeneous catalysis. Specifically, we describe how this approach can be used to better understand the atomic structure and elemental composition of nanocatalysts, the physiochemical properties of the support and catalyst/support interfaces, and the gas- and surface-phase chemistry that occurs under operando conditions. We highlight the generality of the approach, as well as opportunities for future developments.

We describe in this work Mg electrodeposition and dissolution from a wide range of inorganic ethereal electrolytes consisting of MgCl2 and a second chloride salt. Systematic variations of the cosalt reveal two broad classes of electrolytes, namely, the group 13 electrolytes, which require electrolytic cycling to improve their performance, and electrolytes based on heavy p-block chlorides, which exhibit Mg intermetallic formation. Results from electrospray ionization mass spectrometry demonstrate that Mg deposition and stripping only occur in electrolytes containing Mg multimers. We also explore the role of solvent in determining the electrochemical performance of chloride-based electrolytes. Our analysis establishes thermodynamic parameters that dictate the ability of a solvent to support Mg electrochemistry in the MgCl2–AlCl3 system. In their totality, these results illustrate important electrolyte design guidelines for future Mg-ion batteries.

We describe the use of light in a lithographic form of grayscale patterning as a means to program the properties and folding mechanics of flat, thin-film-polymeric materials. In this process, a finely dispersed (phase-separated) mixture of photoresist (SU-8 50) in polydimethylsiloxane (PDMS) is irradiated with ultraviolet light through a photomask. The subsequent photoresist cross-linking in the exposed regions causes changes in the material’s chemo-mechanical properties (notably making it stiffer and more resistant to solvent-induced swelling in the area of exposure). Light scattering due to the dispersed, non-index-matched photoresist domains leads to an intrinsic grayscale profile of the pattern width through the depth of the exposure field, a feature bringing significant and previously unexplored consequences for strain-induced folding dynamics. Solvent induced swelling, where PDMS absorbs a nonpolar solvent, is used to actuate folding mechanics with complex temporal and spatial profiles that explicitly follow the design rules established by the gradient cross-link density, features that elicit a programmable swelling (and therefore, folding) of the two-dimensional sheets. During investigation and optimization of the system, we observed an interesting temporal and biomimetic folding phenomenon that distinguishes the current results from other forms of strain induced folding reported in the literature. Under specific fabrication parameters, an evolution through an intermediate metastable state is observed, one in which the material will fold in one direction, then flatten and fold in the opposite direction. Mechanics modeling and finite element simulations have led to a detailed understanding of the system and the dynamics that allow a temporal evolution of 3-D structure through a double mode of folding. Insights into these mechanisms provide an advanced understanding of strain-induced folding in the field of soft materials.

There exists an emerging opportunity, engendered by advances made in experimental methods of research, to address long-standing questions about the nature of the molecular mechanisms that are operative in important heterogeneous catalytic processes, as well as the nature of the complex atomic and electronic structural features that mediate them. Of particular interest in this regard is the understanding of the dynamical attributes of catalytic processes—an understanding that might allow design principles to be applied to optimize the atomic and electronic structure of heterogeneous catalysts to sustain their performance in essentially any operating process condition. The current work explores these ideas—highlighting capabilities of in operando methods of spectroscopic characterization as applied to an exemplary heterogeneous catalytic process, olefin hydrogenation. No heterogeneous catalytic process has been studied more intensively than olefin hydrogenation. The extensive literature available establishe...

We describe a voltammetric and spectroscopic study of Mg electrodeposition/dissolution (MgDep/Dis) in borohydride diglyme electrolyte solution containing Li(+) carried out on a Pt ultramicroelectrode (UME, r = 5 μm). The data reveal Li(+) cation facilitation that has not been previously recognized in studies made using macroelectrodes. While a single broad, asymmetric stripping peak is expected following MgDep on a Pt macroelectrode in 0.1 M Mg(BH4)2 + 1.5 M LiBH4 diglyme solution on a Pt UME, the stripping reveals three resolved oxidation peaks, suggesting that MgDep/Dis consists of not only a Mg/Mg(2+) redox reaction but also contributions from Mg-Li alloying/dissolution reaction processes. Detailed XPS, SIMS, ICP, and XRD studies were performed that confirm the importance of Mg-Li alloy formation processes, the nature of which is dependent on the reduction potential used during the MgDep step. Based on the electrochemical and surface analysis data, we propose an electrochemical mechanism for MgDep/Dis in a borohydride diglyme electrolyte solution that, in the presence of 1.5 M Li(+) ions, proceeds as follows: (1) Mg(2+) + 2e(-) ⇌ Mg; (2) (1 - x)Mg(2+) + xLi(+) + (2 - x)e(-) ⇌ Mg(1-x)Lix, 0x ≤ 0.02; and (3) (1 - y)Mg(2+) + yLi(+) + (2 - y)e(-) ⇌ Mg(1-y)Liy, 0.02y ≤ 0.09. Most significantly, we find that the potential-dependent MgDep/Dis kinetics are enhanced as the concentration of the LiBH4 in the diglyme electrolyte is increased, a result reflecting the facilitating influences of reduced uncompensated resistance and the enhanced electro-reduction kinetics of Mg(2+) due to Mg-Li alloy formation.

This work reveals and quantifies the inherent intracluster heterogeneity in the atomic structure and charge distribution present in supported metal catalysts. The results demonstrate that these distributions are pronounced and strongly coupled to both structural and dynamic perturbations. They also serve to clarify the nature of the dynamic bonding of nanoscale catalytic metal clusters with their supports, and the mediation of these properties due to the presence of adsorbates. These findings are supported by theoretical modeling and experimental data measured for an exemplary supported metal catalyst, Pt supported on silica, using in situ high energy resolution X-ray absorption and emission spectroscopies; in situ diffuse reflectance infrared Fourier transform spectroscopy; and ex situ scanning transmission electron microscopy.

We describe in this report the electrochemistry of Mg deposition and dissolution from the magnesium aluminum chloride complex (MACC). The results define the requirements for reversible Mg deposition and definitively establish that voltammetric cycling of the electrolyte significantly alters its composition and performance. Elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) results demonstrate that irreversible Mg and Al deposits form during early cycles. Electrospray ionization mass spectrometry (ESI-MS) data show that inhibitory oligomers develop in THF-based solutions. These oligomers form via the well-established mechanism of a cationic ring-opening polymerization of THF during the initial synthesis of the MACC and under resting conditions. In contrast, MACC solutions in 1,2-dimethoxyethane (DME), an acyclic solvent, do not evolve as dramatically at open circuit potential. From these results, we propose a mechanism describing how the conditioning proces...

Supported Pt nanocatalysts generally exhibit anomalous behavior, including negative thermal expansion and large structural disorder. Finite temperature DFT/MD simulations reproduce these properties, showing that they are largely explained by a combination of thermal vibrations and low-frequency disorder. We show here that a full interpretation is more complex and that the DFT/MD mean-square relative displacements (MSRD) can be further separated into vibrational disorder, “dynamic structural disorder” (DSD), and long-time equilibrium fluctuations of the structure dubbed “anomalous structural disorder” (ASD). We find that the vibrational and DSD components behave normally, increasing linearly with temperature while the ASD decreases, reflecting the evolution of mean nanoparticle geometry. As a consequence the usual procedure of fitting the MSRD to normal vibrations plus temperature-independent static disorder results in unphysical bond strengths and Gruneisen parameters.

Determination of the factors that affect the d-band center of catalysts is required to explain their catalytic properties. Resonant inelastic X-ray scattering (RIXS) enables direct imaging of electronic transitions in the d-band of Pt catalysts in real time and in realistic environmental conditions. Through a combination of in situ, temperature-resolved RIXS measurements and theoretical simulations we isolated and quantified the effects of bond-length disorder and adsorbate coverage (CO and H2) on the d-band center of 1.25 nm size Pt catalysts supported on carbon. We found that the decrease in adsorbate coverage at elevated temperatures is responsible for the d band shifts towards higher energies relative to the Fermi level, whereas the effect of the increase in bond-length disorder on the d-band center is negligible. Although these results were obtained for a specific case of non-interacting support and weak temperature dependence of the metal-metal bond length in a model catalyst, this work can be extended to a broad range of real catalysts.

We utilize CdSe/CdS seeded nanorods as a tunable lumophore for luminescent concentration. Transfer-printed, ultrathin crystalline Si solar cells are embedded directly into the luminescent concentrator, allowing the study of luminescent concentrators with an area over 5000 times the area of the solar cell. By increasing the size of the CdS rod with respect to the luminescent CdSe seed, the reabsorption of propagating photons is dramatically reduced. At long luminescence propagation distances, this reduced reabsorption can overcome the diminished quantum yield inherent to the larger semiconductor structures, which is studied with lifetime spectroscopy. A Monte Carlo ray tracing model is developed to explain the performance of the luminescent concentrator and is then used as a design tool to determine the effect of luminescence trapping on the concentration of light using both CdSe/CdS nanorods and a model organic dye. We design an efficient luminescence trapping structure that should allow the luminescent concentrator based on CdSe/CdS nanorods to operate in the high-concentration regime.

The electronic and atomic structural properties of nanoscale metal catalysts exhibit complex influences with origins related to particle size, metal–support, and metal–adsorbate interactions. The experimental investigations of these factors, as well as the elucidation of the impacts they have on mechanisms in catalysis, are hindered by their interdependency in working catalysts. We demonstrate in this work that the features underpinning bond strains and adsorbate-bonding effects in nanometer-scale Pt catalysts supported on both γ-alumina and carbon can be distinguished and analyzed using combined high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy methods, namely, HERFD XANES and HERFD EXAFS. The work extends insights into the fluxional structural dynamics obtained in these systems, a feature harboring significant consequences for understandings of both their properties and mechanisms of action.

An analytical model is developed to study the thermal properties of microscale, inorganic light-emitting diodes (μ-ILEDs) with ultra-thin geometries and layouts. The predicted surface and μ-ILED temperatures agree well with experiments and finite-element simulations. A simple scaling law is obtained for the normalized μ-ILED temperature versus the normalized μ-ILED size. This study provides a theory to guide the design of layouts that minimize adverse thermal effects on the performance of μ-ILEDs not only for solid-state lighting but also for applications integrating μ-ILED devices on complex/soft substrate as are currently of interest in optogenetics and other emerging areas in biology.

We describe the results of an X-ray absorption spectroscopy (XAS) study of adsorbate and temperature-dependent alterations of the atomic level structure of a prototypical, noble metal hydrogenation and reforming catalyst: ∼1.0 nm Pt clusters supported on gamma alumina (Pt/γ-Al(2)O(3)). This work demonstrates that the metal-metal (M-M) bonding in these small clusters is responsive to the presence of adsorbates, exhibiting pronounced coverage-dependent strains in the clusters' M-M bonding, with concomitant modifications of their electronic structures. Hydrogen and CO adsorbates demonstrate coverage-dependent bonding that leads to relaxation of the M-M bond strains within the clusters. These influences are partially compensated, and variably mediated, by the temperature-dependent electronic perturbations that arise from cluster-support and adsorbate-support interactions. Taken together, the data reveal a strikingly fluxional system with implications for understanding the energetics of catalysis. We estimate that a 9.1 ± 1.1 kJ/mol strain exists for these clusters under H(2) and that this strain increases to 12.8 ± 1.7 kJ/mol under CO. This change in the energy of the particle is in addition to the different heats of adsorption for each gas (64 ± 3 and 126 ± 2 kJ/mol for H(2) and CO, respectively).

An in situ electrochemical X-ray absorption spectroscopy (XAS) cell has been fabricated that enables high oxygen flux to the working electrode by utilizing a thin poly(dimethylsiloxane) (PDMS) window. This cell design enables in situ XAS investigations of the oxygen reduction reaction (ORR) at high operating current densities greater than 1 mA in an oxygen-purged environment. When the cell was used to study the ORR for a Pt on carbon electrocatalyst, the data revealed a progressive evolution of the electronic structure of the metal clusters that is both potential-dependent and strongly current-dependent. The trends establish a direct correlation to d-state occupancies that directly tracks the character of the Pt-O bonding present.

Properties that can now be achieved with advanced, blue indium gallium nitride light emitting diodes (LEDs) lead to their potential as replacements for existing infrastructure in general illumination, with important implications for efficient use of energy. Further advances in this technology will benefit from reexamination of the modes for incorporating this materials technology into lighting modules that manage light conversion, extraction, and distribution, in ways that minimize adverse thermal effects associated with operation, with packages that exploit the unique aspects of these light sources. We present here ideas in anisotropic etching, microscale device assembly/integration, and module configuration that address these challenges in unconventional ways. Various device demonstrations provide examples of the capabilities, including thin, flexible lighting “tapes” based on patterned phosphors and large collections of small light emitters on plastic substrates. Quantitative modeling and experimental evaluation of heat flow in such structures illustrates one particular, important aspect of their operation: small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation.

This study examines the crystallographic anisotropy of strain evolution in model, single-crystalline silicon anode microstructures on electrochemical intercalation of lithium atoms. The 3D hierarchically patterned single- crystalline silicon microstructures used as model anodes were prepared using combined methods of photolithography and anisotropic dry and wet chemical etching. Silicon anodes, which possesses theoretically ten times the energy density by weight compared to conventional carbon anodes, reveal highly anisotropic but more importantly, variably recoverable crystallographic strains during cycling. Model strain-limiting silicon anode architectures that mitigate these impacts are highlighted. By selecting a specific design for the silicon anode microstructure, and exploiting the crystallographic anisotropy of strain evolution upon lithium intercalation to control the direction of volumetric expansion, the volume available for expansion and thus the charging capacity of these structures can be broadly varied. We highlight exemplary design rules for this self-strain-limited charging in which an anode can be variably optimized between capacity and stability. Strain-limited capacities ranging from 677 mAhg-1 to 2833 mAhg-1 were achieved by constraining the area available for volumetric expansion via the design rules of the microstructures.

This study describes a prototypical, bimetallic heterogeneous catalyst: compositionally well-defined Ir-Pt nanoclusters with sizes in the range of 1-2 nm supported on γ-Al(2)O(3). Deposition of the molecular bimetallic cluster [Ir(3)Pt(3)(μ-CO)(3)(CO)(3)(η-C(5)Me(5))(3)] on γ-Al(2)O(3), and its subsequent reduction with hydrogen, provides highly dispersed supported bimetallic Ir-Pt nanoparticles. Using spherical aberration-corrected scanning transmission electron microscopy (C(s)-STEM) and theoretical modeling of synchrotron-based X-ray absorption spectroscopy (XAS) measurements, our studies provide unambiguous structural assignments for this model catalytic system. The atomic resolution C(s)-STEM images reveal strong and specific lattice-directed strains in the clusters that follow local bonding configurations of the γ-Al(2)O(3) support. Combined nanobeam diffraction (NBD) and high-resolution transmission electron microscopy (HRTEM) data suggest the polycrystalline γ-Al(2)O(3) support material predominantly exposes (001) and (011) surface planes (ones commensurate with the zone axis orientations frequently exhibited by the bimetallic clusters). The data reveal that the supported bimetallic clusters exhibit complex patterns of structural dynamics, ones evidencing perturbations of an underlying oblate/hemispherical cuboctahedral cluster-core geometry with cores that are enriched in Ir (a result consistent with models based on surface energetics, which favor an ambient cluster termination by Pt) due to the dynamical responses of the M-M bonding to the specifics of the adsorbate and metal-support interactions. Taken together, the data demonstrate that strong temperature-dependent charge-transfer effects occur that are likely mediated variably by the cluster-support, cluster-adsorbate, and intermetallic bonding interactions.

Analytical electron microscopy--empowered by advances in electron optics and detectors--is poised to radically transform our understanding of the complex phenomena arising from atomic and electronic structure in materials chemistry. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

Monolayer membranes of conjugated carbon represent a class of nanomaterial with demonstrated uses in various areas of electronics, ranging from transparent, flexible, and stretchable thin film conductors, to semiconducting materials in moderate and high-performance field-effect transistors. Although graphene represents the most prominent example, many other more structurally and chemically diverse systems are also of interest. This article provides a review of demonstrated synthetic and integration strategies, and speculates on future directions for the field.

This work provides plasmonic crystal platforms for quantitative imaging mode biosensing and multispectral immunoassays, establishing and validating both the optical and equilibrium bases for their operation. We investigated the distance-dependent refractive index sensitivity of full 3D plasmonic crystals to thin polymeric films formed using layer by layer (LbL) assembly of polyelectrolytes as a model system. LbL was also used to determine the preferred gold thickness and plasmonic crystal design rules (nanowell diameter and periodicity) for improved thin-film sensitivity, and full 3D finite-difference time-domain (FDTD) calculations were used to quantitatively model and confirm the experimentally observed thin film sensitivities. The integrated multispectral response of the crystals increases approximately linearly with film thickness for values70 nm, which enables the use of molecular rulers with known thicknesses (such as self-assembled monolayers of alkanethiols on gold) to calibrate these optics for quantitative detection and speciation of surface binding events in a multiplexed imaging format. The utility of these sensors and multispectral analysis for applications in quantitative biosensing was further demonstrated by measuring the equilibrium response curve of an antibody/antigen pair (rabbit antigoat IgG/goat IgG) at increasing antigen concentrations. Fitting the integrated response to a Langmuir isotherm yielded a calculated binding constant on the order of approximately 10(7) M(-1), which is in agreement with the affinity constants reported in the literature for anti-IgG/IgG binding pairs and provides intrinsic detection limits of approximately 400 pM for such unamplified assays.

The ability to pattern soft materials at the microscale is critical for several emerging technologies, including tissue-engineering scaffolds, photonic crystals, sensors, and self-healing materials. Hydrogels are an important class of soft materials that can be fabricated in the form of 3D microperiodic structures by colloidal templating or interference lithography. However, neither approach allows one to omnidirectionally vary the spacing between patterned features over length scales ranging from sub-micrometer to tens of micrometers. By contrast, direct-write assembly enables a wide array of materials to be patterned in nearly arbitrary shapes and dimensions. Here, we report the fabrication of 1D and 3D microperiodic hydrogel scaffolds by direct-write assembly of an acrylamide-based ink. For the first time, we combine direct ink writing with in situ photopolymerization to obtain hydrogel scaffolds with micrometer-sized features (see Fig. 1). By plating 3T3 murine fibroblasts onto one-, two-, and four-layer hydrogel scaffolds, we demonstrate their cytocompatibility and, hence, potential suitability for tissue-engineering applications. Direct ink writing (DIW) is a layer-by-layer assembly technique in which materials are patterned in both planar and 3D forms with lateral feature sizes that are at least an order of magnitude smaller than those achieved by ink-jet printing and other rapid prototyping approaches, and nearly comparable in size to those produced by two-photon polymerization and interference holography. Central to our approach is the creation of concentrated inks that can be extruded through fine deposition nozzles in filamentary form, and then undergo rapid solidification to maintain their shape even as they span gaps in the underlying layer(s). Unlike prior efforts on polyelectrolyte inks that required reservoir-induced coagulation to enable 3D printing, we report the creation of hydrogel inks that can be printed directly in air, where they undergo solidification via photopolymerization (see Fig. 1a and b). The ink is created by first mixing monomeric acrylamide, glycerol, and water. Upon ageing for several hours under ambient conditions, the monomeric species polymerizes to yield a gel composed of 30w/o polyacrylamide chains. H NMR reveals that peaks associated with acrylamide, which are initially present, disappear after polymerization, followed by the emergence of two new peaks that correspond to alkyl chains (data not shown). Concomitantly, as the solution ages, sharp rises in both the shear elastic, G0, and loss, G00, moduli are observed, suggesting that the resulting gel is composed of physically entangled polyacrylamide chains (see Fig. 2a). To determine their degree of polymerization, N, the intrinsic viscosity, [h]0, of diluted polymer solutions is measured by capillary viscometry, and found to be [h]0 270mL g 1 (see Fig. 2b). Using the Mark– Houwink relation, h 1⁄2 01⁄4 KM, their molecular weight is determined to be 8.9 10 gmol , where K is 9.3 10 3 and a is taken to be 0.75 for polyacrylamide dissolved in an aqueous solution (0.5M NaCl). Hence, this initial polymerization process yields polyacrylamide chains with an average degree of polymerization N1⁄4 1.3 10 that is well above the entanglement value of Ne1⁄4 128. To further optimize the ink for direct-write assembly, this polymerizedmixture is diluted by addingmonomeric acrylamide, a crosslinking agent, N, N methylene bisacrylamide, a photoinitiator, diethoxyacetophenone, and deionized water at weight ratios (w/w) of 0.480, 0.036, 0.004, and 0.480, respectively. Notably, the initial polymerization step could be eliminated simply by adding high-molecular-weight polyacrylamide chains

We study the refractive index sensitive transmission of a 3D plasmonic crystal that consists of a square array of subwavelength cylindrical nanowells in a polymer conformally coated with a gold film. Using extensive 3D finite-difference time-domain simulations, we investigate the effect of system parameters such as periodicity, well diameter and depth, and metal thickness on its refractive index sensitivity. These theoretical results are also confirmed experimentally in some cases. Our calculations predict an enhancement in sensitivity by an order of magnitude when the plasmonic crystal characteristics are optimized.

a device form factor that can enable powerfulnew forms of multispectral, spectroscopic, and multiplexedimaging-mode assays.For example, we recently demonstrated one-dimensionalplasmonic imaging with micrometer spatial resolution andmonolayer sensitivity using quasi-three-dimensional (quasi-3D) plasmonic crystals as sensing optic.

Surface atoms have fewer interatomic bonds than those in the bulk that they often relax and reconstruct on extended two-dimensional surfaces. Far less is known about the surface structures of nanocrystals. Here, we show that coherent diffraction patterns recorded from individual nanocrystals are very sensitive to the atomic structure of nanocrystal surfaces. Nanocrystals of Au of 3-5 nm in diameter were studied by examining diffraction intensity oscillations around the Bragg peaks. Both results obtained from modelling the experimental data and molecular dynamics simulations strongly suggest inhomogeneous relaxations, involving large out-of-plane bond length contractions for the edge atoms (approximately 0.2 A); a significant contraction (approximately 0.13 A) for {100} surface atoms; and a much smaller contraction (approximately 0.05 A) for atoms in the middle of the {111} facets. These results denote a coordination/facet dependence that markedly differentiates the structural dynamics of nanocrystals from bulk crystalline surfaces.

CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by transfer printing of p-type and n-type single crystalline ribbons of silicon. The gain and the sum of high and low noise margins of the inverters were as high as ~150 and 4.5 V at supply voltages of 5 V, respectively. The frequencies of the ring oscillators reached 2.6 MHz at supply voltages of 10 V. These results, as obtained with devices that have relatively large critical dimensions (i.e., channel lengths in the several micrometer range), taken together with good mechanical bendability, suggest promise for the use of this type of technology for flexible electronic systems.

We describe a plasmonic crystal device possessing utility for optically transducing chemical forces. The device couples complex plasmonic fields to chemical changes via a chemoresponsive, surface-bound hydrogel. We find that this architecture significantly enhances the spectroscopic responses seen at visible wavelengths while enabling capacities for sensitive signal transduction, even in cases that involve essentially no change in refractive index, thus allowing analytical detection via colorimetric assays in both imaging and spectroscopic modes.

A 3D mechanically stable scaffold is shown to accommodate the volume change of a high-specific-capacity nickel-tin nanocomposite during operation as a Li-ion battery anode. The nickel-tin anode is supported by an electrochemically inactive conductive scaffold with an engineered free volume and controlled characteristic dimensions, which engender the electrode with significantly improved cyclability.