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Abstract: Pt-nanocrystal:MoS2 hybrid materials have promising catalytic properties for hydrogen evolution, and understanding their detailed structures at the atomic scale is crucial to further development. Here, we use an in situ heating holder in an aberration-corrected transmission electron microscope to study the formation of Pt nanocrystals directly on the surface of monolayer MoS2 from a precursor on heating to 800 °C. Isolated single Pt atoms and small nanoclusters are observed after in situ heating, with two types of preferential alignment between the Pt nanocrystals and the underlying monolayer MoS2. Strain effects and thickness variations of the ultrasmall Pt nanocrystal supported on MoS2 are studied, revealing that single atomic planes are formed from a nonlayered face-centered cubic bulk Pt configuration with a lattice expansion of 7–10% compared to that of bulk Pt. The Pt nanocrystals are surrounded by an amorphous carbon layer and in some cases have etched the local surrounding MoS2 material after heating. Electron beam irradiation also initiates Pt nanocrystal etching of the local MoS2, and we study this process in real time at atomic resolution. These results show that the presence of carbon around the Pt nanocrystals does not affect their epitaxial relationship with the MoS2 lattice. Single Pt atoms within the carbon layer are also immobilized at high temperature. These results provide important insights into the formation of Pt:MoS2 hybrid materials.

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Abstract: The geometric and chromatic aberration coefficients of the probe-forming system in an aberration corrected transmission electron microscope have been measured using a Ronchigram recorded from monolayer graphene. The geometric deformations within individual local angular sub-regions of the Ronchigram were analysed using an auto-correlation function and the aberration coefficients for the probe forming lens were calculated. This approach only requires the acquisition of a single Ronchigram allowing rapid measurement of the aberration coefficients. Moreover, the measurement precision for defocus and two-fold astigmatism is improved over that which can be achieved from analysis of Ronchigrams recorded from amorphous films. This technique can also be applied to aberration corrected STEM imaging of any hexagonal two-dimensional material.

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Abstract: Monolayer 2D MoS2 grown by chemical vapor deposition is nanopatterned into nanodots, nanorods, and hexagonal nanomesh using block copolymer (BCP) lithography. The detailed atomic structure and nanoscale geometry of the nanopatterned MoS2 show features down to 4 nm with nonfaceted etching profiles defined by the BCP mask. Atomic resolution annular dark field scanning transmission electron microscopy reveals the nanopatterned MoS2 has minimal large-scale crystalline defects and enables the edge density to be measured for each nanoscale pattern geometry. Photoluminescence spectroscopy of nanodots, nanorods, and nanomesh areas shows strain-dependent spectral shifts up to 15 nm, as well as reduction in the PL efficiency as the edge density increases. Raman spectroscopy shows mode stiffening, confirming the release of strain when it is nanopatterned by BCP lithography. These results show that small nanodots (≈19 nm) of MoS2 2D monolayers still exhibit strong direct band gap photoluminescence (PL), but have PL quenching compared to pristine material from the edge states. This information provides important insights into the structure–PL property correlations of sub-20 nm MoS2 structures that have potential in future applications of 2D electronics, optoelectronics, and photonics.

Open Access

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Abstract: High-resolution observation of a large field of view with a high quality detector is important for single particle analysis or in-situ experiments. Consequently, evaluation of aberrations that depend on position in the field of view, (off-axial aberrations) is required. We report the experimental measurement of off-axial aberrations including higher order components in several optical conditions together with the corresponding off-axial phase maps.

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Abstract: Palladium-catalysed cross-coupling reactions, central tools in fine-chemical synthesis, predominantly employ soluble metal complexes despite recognized challenges with product purification and catalyst reusability. Attempts to tether these homogeneous catalysts on insoluble carriers have been thwarted by suboptimal stability, which leads to a progressively worsening performance due to metal leaching or clustering4. The alternative application of supported Pd nanoparticles has faced limitations because of insufficient activity under the mild conditions required to avoid thermal degradation of the substrates or products. Single-atom heterogeneous catalysts lie at the frontier. Here, we show that the Pd atoms anchored on exfoliated graphitic carbon nitride (Pd-ECN) capture the advantages of both worlds, as they comprise a solid catalyst that matches the high chemoselectivity and broad functional group tolerance of state-of-the-art homogeneous catalysts for Suzuki couplings, and also demonstrate a robust stability in flow. The adaptive coordination environment within the macroheterocycles of ECN facilitates each catalytic step. The findings illustrate the exciting opportunities presented by nanostructuring single atoms in solid hosts for catalytic processes that remain difficult to heterogenize.