Show Abstract ▼

Abstract: Suspended specimens of 2D crystals and their heterostructures are required for a range of studies including transmission electron microscopy (TEM), optical transmission experiments and nanomechanical testing. However, investigating the properties of laterally small 2D crystal specimens, including twisted bilayers and air sensitive materials, has been held back by the difficulty of fabricating the necessary clean suspended samples. Here we present a scalable solution which allows clean free-standing specimens to be realized with 100% yield by dry-stamping atomically thin 2D stacks onto a specially developed adhesion-enhanced support grid. Using this new capability, we demonstrate atomic resolution imaging of defect structures in atomically thin CrBr3, a novel magnetic material which degrades in ambient conditions.

Open Access

Show Abstract ▼

Abstract: We develop herein plasmonic–catalytic Au–IrO2 nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO2 shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO2 layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO2, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au–IrO2 nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO2 and to the activation of Ir–O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

Show Abstract ▼

Abstract: GaSe and InSe are important members of a class of 2D materials, the III-VI metal monochalcogenides, which are attracting considerable attention due to their promising electronic and optoelectronic properties. Here an investigation of point and extended atomic defects formed in mono-, bi-, and few-layer GaSe and InSe crystals is presented. Using state-of-the-art scanning transmission electron microscopy (STEM), it is observed that these materials can form both metal and selenium vacancies under the action of the electron beam. Selenium vacancies are observed to be healable; recovering the perfect lattice structure in the presence of selenium or enabling incorporation of dopant atoms in the presence of impurities. Under prolonged imaging, multiple point defects are observed to coalesce to form extended defect structures, with GaSe generally developing trigonal defects and InSe primarily forming line defects. These insights into atomic behavior could be harnessed to synthesize and tune the properties of 2D post transition metal monochalcogenide materials for optoelectronic applications.

Show Abstract ▼

Abstract: The promotional effect of H2 on the oxidation of CO is of topical interest and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS) we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of non-thermal effects in the hydrogen promoted of oxidation of carbon monoxide. We have identified that H2 promotes the Langmuir Hinshelwood mechanism and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H2. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect.

Open Access

Show Abstract ▼

Abstract: A critical radiation damage assessment of the materials that will be present in a Geological Disposal Facility (GDF) for radioactive waste is a priority for building a safety case. Detailed analysis of the effects of high-energy a -particle damage in phyllosilicates such as mica is a necessity, as these are model structures for both the clay-based backfill material and the highly sorbent components of a crystalline host rock. The a -radiation stability of biotite mica [general formula: K(Mg,Fe)3(Al,Si3O10)(F,OH)2 ] has been investigated using the 5 MV tandem pelletron at the University of Manchester’s Dalton Cumbrian Facility (DCF) and both the microfocus spectroscopy (I18) and core X -ray absorption spectroscopy (B18) beamlines at Diamond Light Source (U.K.). Microfocus X-ray diffraction mapping has demonstrated extensive structural aberrations in the mica resulting from controlled exposure to the focused 4He2+ ion (a-particle) beam. Delivered doses were comparable to a-particle fluences expected in the highly active, near-field of a GDF. At doses up to 6.77 displacements per atom (dpa) in the region of highest particle fluence, biotite mica displays a heterogeneous structural response to irradiation on a micrometer scale, with sequential dilation and contraction of regions of the structure perpendicular to the sheets, as well as a general overall contraction of the phyllosilicate layer spacing. At the peak of ion fluence, the structure collapses under a high point defect density and amorphous areas are pervasive among altered domains of the original lattice. Such structural alterations are likely to affect the material’s capacity to sorb and retain escaped radionuclides over long timescales; increased edge site availability may favor increased sorption while interlayer uptake will likely be reduced due to collapse. Radiation-induced reduction of structural iron at the region of highest structural damage across an a-particle’s track has been demonstrated by Fe K-edge X-ray absorption near edge spectroscopy (XANES) and local structural disorder has been confirmed by analysis of both potassium K-edge XANES and Fe K-edge extended X-ray absorption fine structure analysis. An infrared absorption study of deformations in the OH– stretching region, along with electron probe microanalysis complements the synchrotron data presented here