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Abstract: Catalytic allylic alcohol oxidation to aldehydes is an industrial process that necessitates chemoselectivity. Surface PdO (on Pd) enables this transformation but does not represent optimal metal utilisation. Here we report a facile synthesis route to produce isolated surface PdO catalytic sites on an earth-abundant metal (NiO) for cinnamyl alcohol oxidation.

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Abstract: Disorder in organic semiconductors (OSCs) plays a determining role in energy transport properties underpinning optoelectronic device performance [1]. Both energetic disorder native to perfect crystals as well as deviations from crystalline order control transport properties [2,3]. Alongside crystallographic defects like stacking faults and grain boundaries, dislocations that distort molecular packing can introduce exciton- or charge-carrier traps that significantly hamper intermolecular energy transport [4]. Electron microscopy has been a mainstay for probing these crystallographic defects in inorganic semiconductors. Recent progress in atomically resolved electron microscopy has enabled imaging of individual defects in hybrid perovskites [5]. But while hybrid perovskites show structural degradation on the order of <200 e–Å-2 before [6], small molecule OSCs may undergo comparable loss of structure under exposures <30 e–Å-2 [7,8]. Methods that enable the crystallographic analysis of dislocations in beam-sensitive OSCs are therefore a necessary first step to establish their performance effects. A dislocation is described crystallographically in terms of a displacement vector in the lattice, termed a Burgers vector b. Most attempts to characterize dislocations in organic molecular crystals have relied on techniques at low spatial resolution, including etch pit imaging [9] and scanning probe techniques [10]. These approaches are unable to directly record the crystallography of dislocations or access the nanometre spatial resolution required to isolate individual defects. In contrast, electron microscopy combines the necessary spatial resolution to image the dislocation line as well as the crystallographic detail from electron diffraction to retrieve the Burgers vector. Typically, such an analysis is carried out by many repeated electron beam exposures and sample rotations aimed at identifying the crystal planes associated with a diffraction vector g that are not distorted by the dislocation, a so-called ‘invisibility criterion’ at g.b = 0. Here, we advance this approach for OSCs to carry out unambiguous analysis of the dislocation Burgers vector and type (screw, edge, or mixed) using four-dimensional scanning transmission electron microscopy (4D-STEM) now in a single exposure at a fluence of ~10 e–Å-2. Thin films of p-terphenyl and anthracene were prepared by solution crystallization as a set of benchmark organic optoelectronic materials [11]. On transfer to a lacey carbon support film for electron microscopy, the draping of the OSC crystals on the support film introduces a small amount of sample bending. This bending defines a set of diffraction conditions that produce ribbons of bright intensity running across images of the film referred to as bend contours. These bend contours exhibit an abrupt shift or break on crossing dislocations unless they satisfy the invisibility criterion. Our 4D-STEM approach specifically supports simultaneous analysis of many lattice planes approximately parallel to the crystal direction perpendicular to the film, i.e. [001] for p-terphenyl and [101] for anthracene. Plotting and fitting the magnitude of breaks in the bend contours as a function of the corresponding diffraction vectors (g) for each plane determines the Burgers vector. For instance, this analysis establishes mixed-type b = [010] dislocations in p-terphenyl and anthracene. These generalizable methods make an analysis of the Burgers vectors of dislocations in beam-sensitive OSC films a routine process. The capability to measure the character and type of dislocations will provide experimental input for models of distortions at these structural defects and enables assessing methods for inhibiting dislocation formation during crystal growth and reducing or removing their deleterious contributions to device performance.

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Abstract: Due to the reducible nature of TiO2, the encapsulation of cobalt nanoparticles (CoNPs) by reduced TiO2-x is often reported to decrease their catalytic performance in reactions such as Fisher-Tropsch synthesis (FTS). Here, we show using HAADF-STEM imaging and electron energy loss spectroscopy (EELS) that a residual C12E4 surfactant used to prepare the CoNPs, remains on the surface of a TiO2 rutile support, preventing the formation of Ti3+/Ti2+ oxides and therefore TiO2-x migration. Furthermore, the presence of these surfactant residues prevents the coalescence and aggregation of CoNPs during catalyst preparation, maintaining the dispersion of CoNPs. As such, using C12E4 in the preparation of Co/TiO2 can be considered beneficial for producing a catalyst with a greater number of active Co species.

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Abstract: An understanding the organic matter (OM) in primitive interplanetary materials can provide us with important constraints on both the early solar system carbon cycle and incipient prebiotic synthesis before the origin of life. As a window to the past, primitive chondrites preserve the most pristine record of parent body, nebular and interstellar components and the occurrence of OM in them has been shown in both soluble (SOM) (1) and insoluble (IOM) (2) form. Total organic carbon (TOC) abundance reaches ~3-4 wt% in the most primitive carbonaceous chondrite (CCs) (3), such as Ivuna-type chondrites (CIs) – thus making them highly desirable for the OM studies, and relevant to the study of Asteroid 162173 Ryugu samples from the Hayabusa-2 mission. A combination of both SOM and IOM analysis of organic bulk meteorite separates together with in-situ analysis of OM have provided a comprehensive account of chondritic OM (4). In the case of in-situ analysis, the combination of both scanning (SEM) and transmission electron microscopy (TEM) together with soft X-Ray scanning transmission microscopy (STXM) have shown the presence of micron to submicron distinctive organic particles (OPs) (5). Carbon K-edge X-ray absorption near edge structure (XANES) has shown the aromatic-carbonyl-carboxyl chemical nature of these organic particles (5). In addition, aromatic-poorer and carboxylic-richer diffuse OM (6) within both amorphous and phyllosilicate occurs as well. As observation techniques are getting better, aberration corrected TEM coupled with electron energy loss spectroscopy (EELS) might provide the same results as carbon XANES, but with higher image magnification, rapid data acquisition and better accessibility. In this context, we present the results of a comparative carbon K-edge XANES and EELS study of CI meteorite Ivuna. An approximately 100 nm lamella of the Ivuna meteorite was prepared using focused ion beam (FIB)-SEM with the Helios 5 Hydra DualBeam (CEITEC, Masaryk University, Czechia) and analysed by TEM-EELS with the JEOL ARM200CF (ePSIC, Diamond Light Source, UK) and STXM-XANES at Beamline BL19A of the KEK Photon Factory, Japan. We observed that (I) XANES on samples that did not experience TEM-EELS are in agreement with the previous studies of aromatic-carbonyl-carboxylic macromolecular OPs and IOM, while (II) the TEM-EELS of OPs show aromatic-carbonyl functional chemistry but with amorphous carbon convoluting the carboxylic peak, and aromatic-poor spectra with a sharp carbonate peak in diffuse OM. The difference between XANES and EELS particularly in the diffuse OM can be interpreted by electron-beam damage. Thickness and e-beam damage leads to amorphous C formation in the OPs. In the case of more labile OM in the phyllosilicate, its change by heating and oxidation is expected.

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Abstract: Up to date, the influence of ambient air exposure on the energetics and stability of silver clusters has rarely been investigated and compared to clusters in vacuum. Silver clusters up to 3000 atoms in size, on an amorphous carbon film, have been exposed to ambient air and investigated by atomic-resolution imaging in the aberration-corrected Scanning Transmission Electron Microscope. Ordered structures comprise more than half the population, the rest are amorphous. Here, we show that the most common ordered isomer structures is the icosahedron. These results contrast with the published behaviour of silver clusters protected from atmospheric exposure, where the predominant ordered isomer is face-centred cubic. We propose that the formation of surface oxide or sulphide species resulting from air exposure can account for this deviation in stable isomer. This interpretation is consistent with density functional theory calculations based on silver nanoclusters, in the size range 147-201 atoms, on which methanethiol molecules are adsorbed. An understanding of the effects of ambient exposure on the atomic structure and therefore functional properties of nanoparticles is highly relevant to their real-world performance and applications.