We report the ability to control the atomic structure of nanoclusters by systematically varying the gas-phase formation parameters during the generation of size-selected Au923. From aberration-corrected, scanning transmission electron microscopy (HAADF-STEM) imaging, we are able to identify the proportions of icosahedral (Ih), decahedral (Dh), and face-centered cubic (fcc) isomers within a set of populations, with each population corresponding to a specific set of formation conditions. We demonstrate that, by tuning the formation conditions, we can eliminate completely all icosahedral nanoclusters, which are commonly found under other conditions. In future, this approach may lead to the preparation of arrays or ensembles of nanoclusters containing a dominant or single isomer, thus enabling the investigation of nanocluster (or nanoparticle) properties as a function of both size and atomic configuration.
Identifying the ripening modes of supported metal nanoparticles used in heterogeneous catalysis can provide important insights into the mechanisms that lead to sintering. We report the observation of a crossover from Smoluchowski to Ostwald ripening, under realistic reaction conditions, for monomodal populations of precisely defined gold particles in the nanometer size range, as a function of decreasing particle size. We study the effects of the CO oxidation reaction on the size distributions and atomic structures of mass-selected Au(561±13), Au(923±20) and Au(2057±45) clusters supported on amorphous carbon films. Under the same conditions, Au(561±13) and Au(923±20) clusters are found to exhibit Ostwald ripening, whereas Au(2057±45) ripens through cluster diffusion and coalescence only (Smoluchowski ripening). The Ostwald ripening is not activated by thermal annealing or heating in O2 alone.
The high precision and scalable technology offered by atom interferometry has the opportunity to profoundly affect gravity surveys, enabling the detection of features of either smaller size or greater depth. While such systems are already starting to enter into the commercial market, significant reductions are required in order to reach the size, weight and power of conventional devices. In this article, the potential for atom interferometry based gravimetry is assessed, suggesting that the key opportunity resides within the development of gravity gradiometry sensors to enable drastic improvements in measurement time. To push forward in realizing more compact systems, techniques have been pursued to realize a highly portable magneto-optical trap system, which represents the core package of an atom interferometry system. This can create clouds of 107 atoms within a system package of 20 l and 10 kg, consuming 80 W of power.This article is part of the themed issue ‘Quantum technology for the 21st century’.
The synthesis, isolation and characterization of a previously undiscovered bimetallic endohedral fullerene, PrSc@C80, are presented, and this may pave the way for a whole family of bimetallic endohedral fullerenes in useful quantities.
We report the size-dependent propagation of gold nanoclusters through few-layer graphene (FLG). We employ aberration-corrected scanning transmission electron microscopy (STEM) to track the fate of Au55 and Au923 clusters that have been deposited, independently and isoenergetically, onto suspended FLG films using cluster beam deposition. We demonstrate that Au55 clusters penetrate through the FLG, whereas the monodisperse Au923 clusters reside at the surface. Our approach offers a route to the controlled incorporation of dopant nanoparticles and the generation of nanoscale defects in graphene.
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