Two-dimensional silk.

Despite the promise of silk-based devices, the inherent disorder of native silk limits performance. Here, we report highly ordered two-dimensional silk fibroin (SF) films grown epitaxially on van der Waals (vdW) substrates. Using atomic force microscopy, nano-Fourier transform infrared spectroscopy, and molecular dynamics, we show that the films consist of lamellae of SF molecules that exhibit the same secondary structure as the nanocrystallites of native silk.

Mechanochemically accelerated deconstruction of chemically recyclable plastics.

Plastics redesign for circularity has primarily focused on monomer chemistries enabling faster deconstruction rates concomitant with high monomer yields. Yet, during deconstruction, polymer chains interact with their reaction medium, which remains underexplored in polymer reactivity. Here, we show that, when plastics are deconstructed in reaction media that promote swelling, initial rates are accelerated by over sixfold beyond those in small-molecule analogs.

In vitro investigation of protein assembly by combined microscopy and infrared spectroscopy at the nanometer scale.

The nanoscale structure and dynamics of proteins on surfaces has been extensively studied using various imaging techniques, such as transmission electron microscopy and atomic force microscopy (AFM) in liquid environments. These powerful imaging techniques, however, can potentially damage or perturb delicate biological material and do not provide chemical information, which prevents a fundamental understanding of the dynamic processes underlying their evolution under physiological conditions. Here, we use a platform developed in our laboratory that enables acquisition of infrared (IR) spectroscopy and AFM images of biological material in physiological liquids with nanometer resolution in a cell closed by atomically thin graphene membranes transparent to IR photons.

Resonant Soft X-ray Scattering Studies of Chemical Environment and Interparticle Dynamics of Cu Nanocatalysts for CO Electroreduction.

Understanding the chemical environment and interparticle dynamics of nanoparticle electrocatalysts under operating conditions offers valuable insights into tuning their activity and selectivity. This is particularly important to the design of Cu nanocatalysts for CO electroreduction due to their dynamic nature under bias. Here, we have developed electrochemical resonant soft X-ray scattering (EC-RSoXS) to probe the chemical identity of active sites during the dynamic structural transformation of Cu nanoparticle (NP) ensembles through 1 μm thick electrolyte.

Interface Sensitivity in Electron/Ion Yield X-ray Absorption Spectroscopy: The TiO-HO Interface.

To understand corrosion, energy storage, (electro)catalysis, etc., obtaining chemical information on the solid-liquid interface is crucial but remains extremely challenging. Here, X-ray absorption spectroscopy (XAS) is used to study the solid-liquid interface between TiO and HO.

Ligand removal of Au nanoclusters by thermal and electrochemical treatments for selective CO electroreduction to CO.

Undercoordinated metal nanoclusters have shown great promise for various catalytic applications. However, their activity is often limited by the covalently bonded ligands, which could block the active surface sites. Here, we investigate the ligand removal process for Au nanoclusters using both thermal and electrochemical treatments, as well as its impact on the electroreduction of CO to CO.

High-Performance Pt-Co Nanoframes for Fuel-Cell Electrocatalysis.

Pt-based alloy catalysts are promising candidates for fuel-cell applications, especially for cathodic oxygen reduction reaction (ORR) and anodic methanol oxidation reaction (MOR). The rational design of composition and morphology is crucial to promoting catalytic performances. Here, we report the synthesis of Pt-Co nanoframes via chemical etching of Co from solid rhombic dodecahedra.

Molecular-Scale Structure of Electrode-Electrolyte Interfaces: The Case of Platinum in Aqueous Sulfuric Acid.

Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understanding elemental processes in heterogeneous reactions. Using X-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.

X-ray-Induced Fragmentation of Imidazolium-Based Ionic Liquids Studied by Soft X-ray Absorption Spectroscopy.

We investigated the X-ray absorption spectroscopy (XAS) fingerprint of EMImTFSI ionic liquid (IL) and its fragmentation products created by X-ray irradiation. To accomplish this, we used an open geometry where an IL droplet is directly exposed in the vacuum chamber and an enclosed geometry where the IL is confined in a cell covered by an X-ray transparent membrane. In the open geometry, the XAS signature was stable and consistent with experimental and theoretical spectra reported in the literature.

Environment-Dependent Radiation Damage in Atmospheric Pressure X-ray Spectroscopy.

Atmospheric pressure X-ray spectroscopy techniques based on soft X-ray excitation can provide powerful interface-sensitive chemical information about a solid surface immersed in a gas or liquid environment. However, X-ray illumination of such dense phases can lead to the generation of considerable quantities of radical species by radiolysis. Soft X-ray absorption measurements of Cu films in both air and aqueous alkali halide solutions reveal that this can cause significant evolution of the Cu oxidation state.

Structure of the Clean and Oxygen-Covered Cu(100) Surface at Room Temperature in the Presence of Methanol Vapor in the 10-200 mTorr Pressure Range.

Using ambient pressure X-ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscopy (HPSTM), we show that in equilibrium with 0.01-0.2 Torr of methanol vapor, at room temperature, the Cu(100) surface is covered with methoxy species forming a c(2 × 2) overlayer structure.

Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy.

Atmospheric pressure X-ray photoelectron spectroscopy (XPS) is demonstrated using single-layer graphene membranes as photoelectron-transparent barriers that sustain pressure differences in excess of 6 orders of magnitude. The graphene serves as a support for catalyst nanoparticles under atmospheric pressure reaction conditions (up to 1.5 bar), where XPS allows the oxidation state of Cu nanoparticles and gas phase species to be simultaneously probed.

Probing electrode/electrolyte interfaces in situ by X-ray spectroscopies: old methods, new tricks.

Electrode/electrolyte interfaces play a vital role in various electrochemical systems, but in situ characterization of such buried interfaces remains a major challenge. Several efforts to develop techniques or to modify existing techniques to study such interfaces are showing great promise to overcome this challenge. Successful examples include electrochemical scanning tunneling microscopy (EC-STM), surface-sensitive vibrational spectroscopies, environmental transmission electron microscopy (E-TEM), and surface X-ray scattering.

Visualizing nanoscale excitonic relaxation properties of disordered edges and grain boundaries in monolayer molybdenum disulfide.

Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building blocks for atomically thin, flexible optoelectronic and catalytic devices. Although challenging for two-dimensional systems, sub-diffraction optical microscopy provides a nanoscale material understanding that is vital for optimizing their optoelectronic properties. Here we use the 'Campanile' nano-optical probe to spectroscopically image exciton recombination within monolayer MoS2 with sub-wavelength resolution (60 nm), at the length scale relevant to many critical optoelectronic processes.

Plasmonic near-field probes: a comparison of the campanile geometry with other sharp tips.

Efficient conversion of photonic to plasmonic energy is important for nano-optical applications, particularly imaging and spectroscopy. Recently a new generation of photonic/plasmonic transducers, the 'campanile' probes, has been developed that overcomes many shortcomings of previous near-field probes by efficiently merging broadband field enhancement with bidirectional coupling of far- to near-field electromagnetic modes. In this work we compare the properties of the campanile structure with those of current NSOM tips using finite element simulations.

Shape changes of Pt nanoparticles induced by deposition on mesoporous silica.

Polyvinylpyrollidone (PVP)-capped platinum nanoparticles (NPs) are found to change shape from spherical to flat when deposited on mesoporous silica substrates (SBA-15). Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) analyses are used in these studies. The SAXS results indicate that, after deposition, the 2 nm NPs have an average gyration radius 22% larger than in solution, while the EXAFS measurements indicate a decrease in first neighbor co-ordination number from 9.

Hyperspectral nanoscale imaging on dielectric substrates with coaxial optical antenna scan probes.

We have demonstrated hyperspectral tip-enhanced Raman imaging on dielectric substrates using linearly polarized light and nanofabricated coaxial antenna tips. A full Raman spectrum was acquired at each pixel of a 256 by 256 pixel contact-mode atomic force microscope image of carbon nanotubes grown on a fused silica microscope coverslip, allowing D and G mode intensity and D-mode peak shifts to be measured with ∼20 nm spatial resolution. Tip enhancement was sufficient to acquire useful Raman spectra in 50-100 ms.