Search

Cryo-electron microscopy is an essential tool for high-resolution structural studies of biological systems. This method relies on the use of phase contrast imaging at high defocus to improve information transfer at low spatial frequencies at the expense of higher spatial frequencies. Here we demonstrate that electron ptychography can recover the phase of the specimen with continuous information transfer across a wide range of the spatial frequency spectrum, with improved transfer at lower spatial frequencies, and as such is more efficient for phase recovery than conventional phase contrast imaging. We further show that the method can be used to study frozen-hydrated specimens of rotavirus double-layered particles and HIV-1 virus-like particles under low-dose conditions (5.7 e/Å2) and heterogeneous objects in an Adenovirus-infected cell over large fields of view (1.14 × 1.14 μm), thus making it suitable for studies of many biologically important structures.

Defects in materials give rise to fluctuations in electrostatic fields that reflect the local charge density, but imaging this with single atom sensitivity is challenging. However, if possible, this provides information about the energetics of adatom binding, localized conduction channels, molecular functionality and their relationship to individual bonds. Here, ultrastable electron-optics are combined with a high-speed 2D electron detector to map electrostatic fields around individual atoms in 2D monolayers using 4D scanning transmission electron microscopy. Simultaneous imaging of the electric field, phase, annular dark field and the total charge in 2D MoS2 and WS2 is demonstrated for pristine areas and regions with 1D wires. The in-gap states in sulphur line vacancies cause 1D electron-rich channels that are mapped experimentally and confirmed using density functional theory calculations. We show how electrostatic fields are sensitive in defective areas to changes of atomic bonding and structural determination beyond conventional imaging.

Electron ptychography has recently attracted considerable interest for high resolution phase-sensitive imaging. However, to date studies have been mainly limited to radiation resistant samples as the electron dose required to record a ptychographic dataset is too high for use with beam-sensitive materials. Here we report defocused electron ptychography using a fast, direct-counting detector to reconstruct the transmission function, which is in turn related to the electrostatic potential of a two-dimensional material at atomic resolution under various low dose conditions.

This work reports the thermal and electron beam stabilities of a series of isostructural metal–organic frameworks (MOFs) of type MFM-300(M) (M = Al, Ga, In, Cr). MFM-300(Cr) was most stable under the electron beam, having an unusually high critical electron fluence of 1111 e− Å−2 while the Group 13 element MOFs were found to be less stable. Within Group 13, MFM-300(Al) had the highest critical electron fluence of 330 e− Å−2, compared to 189 e− Å−2 and 147 e− Å−2 for the Ga and In MOFs, respectively. For all four MOFs, electron beam-induced structural degradation was independent of crystal size and was highly anisotropic, although both the length and width of the channels decreased during electron beam irradiation. Notably, MFM-300(Cr) was found to retain crystallinity while shrinking up to 10%. Thermal stability was studied using in situ synchrotron X-ray diffraction at elevated temperature, which revealed critical temperatures for crystal degradation to be 605, 570, 490 and 480 °C for Al, Cr, Ga, and In, respectively. The pore channel diameters contracted by ≈0.5% on desorption of solvent species, but thermal degradation at higher temperatures was isotropic. The observed electron stabilities were found to scale with the relative inertness of the cations and correlate well to the measured lifetime of the materials when used as photocatalysts. [ABSTRACT FROM AUTHOR]

Here we demonstrate the preparation of enzyme‐metal biohybrids of NAD+ reductase with biocatalytically‐synthesised small gold nanoparticles (NPs, <10 nm) and core‐shell gold‐platinum NPs for tandem catalysis. Despite the variety of methods available for NP synthesis, there remains a need for more sustainable strategies which also give precise control over the shape and size of the metal NPs for applications in catalysis, biomedical devices, and electronics. We demonstrate facile biosynthesis of spherical, highly uniform, gold NPs under mild conditions using an isolated enzyme moiety, an NAD+ reductase, to reduce metal salts while oxidising a nicotinamide‐containing cofactor. By subsequently introducing platinum salts, we show that core‐shell Au@Pt NPs can then be formed. Catalytic function of these enzyme‐Au@Pt NP hybrids was demonstrated for H2‐driven NADH recycling to support enantioselective ketone reduction by an NADH‐dependent alcohol dehydrogenase. [ABSTRACT FROM AUTHOR]

Herein we evaluate the promotive effect of Au and Sn incorporation into supported Pd nanoparticles for the direct synthesis of H2O2 from molecular H2 and O2. The introduction of both secondary metal modifiers was found to result in a significant enhancement in catalytic performance, although, in the case of the PdSn system, it was identified that relatively large quantities of the secondary metal were required to rival the activity observed over optimal Au-containing formulations, with the 0.25%Pd–2.25%Sn/TiO2 catalyst offering comparable H2O2 synthesis rates to the optimised 0.25%Pd–0.25%Au/TiO2 formulation. The introduction of Sn was found to considerably improve Pd dispersion, correlating with an improvement in selective H2 utilisation. Notably, the optimal PdSn catalyst identified in this work achieves superior H2O2 selectivities compared to the PdAu analogue and is able to rival the performance of state-of-the-art materials. [ABSTRACT FROM AUTHOR]