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Atomic clusters

Christian Pöpsel, Jonathan Becker, Nari Jeon, Markus Döblinger, Thomas Stettner, Yeanitza Trujillo Gottschalk, Bernhard Loitsch, Sonja Matich, Marcus Altzschner, Alexander W Holleitner, Jonathan Finley, Lincoln J Lauhon, Gregor Koblmueller
Core-shell semiconductor nanowires (NW) with internal quantum heterostructures are among the most complex nanostructured materials to be explored for assessing the ultimate capabilities of diverse ultrahigh-resolution imaging techniques. To probe the structure and composition of these materials in their native environment with minimal damage and sample preparation calls for high-resolution electron or ion microscopy methods, which have not yet been tested on such classes of ultra-small quantum nanostructures...
May 21, 2018: Nano Letters
J M C Plane, J D Carrillo-Sanchez, T P Mangan, M M J Crismani, N M Schneider, A Määttänen
Recent measurements by the Imaging Ultraviolet Spectrograph (IUVS) instrument on NASA's Mars Atmosphere and Volatile EvolutioN mission show that a persistent layer of Mg+ ions occurs around 90 km in the Martian atmosphere but that neutral Mg atoms are not detectable. These observations can be satisfactorily modeled with a global meteoric ablation rate of 0.06 t sol-1 , out of a cosmic dust input of 2.7 ± 1.6 t sol-1 . The absence of detectable Mg at 90 km requires that at least 50% of the ablating Mg atoms ionize through hyperthermal collisions with CO2 molecules...
March 2018: Journal of Geophysical Research. Planets
Predrag S Krstic, Longtao Han, Stephan Irle, Hiromi Nakai
We performed nanosecond timescale computer simulations of clusterization and agglomeration processes of boron nitride (BN) nanostructures in hot, high pressure gas, starting from eleven different atomic and molecular precursor systems containing boron, nitrogen and hydrogen at various temperatures from 1500 to 6000 K. The synthesized BN nanostructures self-assemble in the form of cages, flakes, and tubes as well as amorphous structures. The simulations facilitate the analysis of chemical dynamics and we are able to predict the optimal conditions concerning temperature and chemical precursor composition for controlling the synthesis process in a high temperature gas volume, at high pressure...
April 21, 2018: Chemical Science
Joanna Ewa Rode, Krzysztof Lyczko, Magdalena Jawiczuk, Robert Kawęcki, Wojciech Stańczyk, Agnieszka Jaglińska, Jan Cz Dobrowolski
The IR and VCD spectra of both enantiomers of Me, iPr, nBu, Ph and CH2Ph substituted isoindolinones in solution and KBr pellets were measured and interpreted with DFT calculations. The spectra in solution revealed no important differences in the C=O stretching vibration region while the interpretation of very distinct spectra taken in pellets required determining the crystal structures. The studied compounds crystallized in the P212121 (Me, iPr, CH2Ph), P31 (nBu), and P21 (Ph) space groups. We found that the quality of simulated spectra strongly depends on the substituent, the structure of the molecular cluster assumed, basis set, and use of the dispersion correction...
May 18, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Tran Dieu Hang, Minh Tho Nguyen
(Abstract) Interaction, dissociation and dehydrogenation reactions of water monomer and dimer with pure and mixed tetrameric silicon clusters Si3X with X = Si, Be, Mg, Ca were investigated using high accuracy quantum chemical calculations. While geometries were optimized using the DFT/B3LYP functional with the aug-cc-pVTZ basis set, reaction energy profiles were constructed making use of the coupled-cluster theory with extrapolation to complete basis set, CCSD(T)/CBS. Cleavage of the O-H bond in water dimer is found to be more favored than that of water monomer in the reaction with Si4...
May 18, 2018: Journal of Physical Chemistry. A
Xiaoyang Pan, Chao Li, Jing Zheng, Shijing Liang, Rong Huang, Zhiguo Yi
Noble metal nanoparticles have attracted considerable attention due to their useful capabilities as heterogeneous catalysts. However, they are usually prepared using various organic stabilizing agents that negatively affect their catalytic activities. Herein, we report a facile, clean, and effective method for synthesizing supported ultrafine noble metal nanoparticles by utilizing the reductive property of a new pyrochlore oxide: Sn1.06 Nb2 O5.59 F0.97 (SnNbOF). Ultrafine Au, Pd, and Pt nanoparticles or clusters are homogeneously distributed on the SnNbOF surface...
May 18, 2018: Inorganic Chemistry
Qiaofeng Yao, Victor Fung, Cheng Sun, Sida Huang, Tiankai Chen, De-En Jiang, Jim Yang Lee, Jianping Xie
Atom-by-atom engineering of nanomaterials requires atomic-level knowledge of the size evolution mechanism of nanoparticles, which remains one of the greatest mysteries in nanochemistry. Here we reveal atomic-level dynamics of size evolution reaction of molecular-like nanoparticles, i.e., nanoclusters (NCs) by delicate mass spectrometry (MS) analyses. The model size-conversion reaction is [Au23 (SR)16 ]- → [Au25 (SR)18 ]- (SR = thiolate ligand). We demonstrate that such isoelectronic (valence electron count is 8 in both NCs) size-conversion occurs by a surface-motif-exchange-induced symmetry-breaking core structure transformation mechanism, surfacing as a definitive reaction of [Au23 (SR)16 ]-  + 2 [Au2 (SR)3 ]- → [Au25 (SR)18 ]-  + 2 [Au(SR)2 ]- ...
May 17, 2018: Nature Communications
Pawel Konieczynski, Grzegorz Szreder, Ewelina Tamowska, Marek Wesolowski
Many people after 50 year of life suffer pains caused by osteoarthritis (OA), which make their life difficult and painful. There is a probable association of OA with the concentration of certain elements in body fluids. Therefore the aim of the study was to relate the level of essential elements in synovial fluids of patients with OA with the treatment using antiarthritic drugs. Thus, flame-atomic absorption spectrometry was used to determine the concentrations of Fe, Zn, Cu, Mn, Na, K, Ca and Mg in 74 samples of synovial fluids taken from 36 patients...
July 2018: Journal of Trace Elements in Medicine and Biology
Fabien Drault, Clément Comminges, Fabien Can, Laurence Pirault-Roy, Florence Epron, Anthony Le Valant
Chemisorption of hydrogen on metallic particles is often used to estimate the metal dispersion ( D ), the metal particle size ( d ), and the metallic specific surface area ( SM ), currently assuming a stoichiometry of one hydrogen atom H adsorbed per surface metal atom M . This assumption leads to a large error when estimating D , d , and SM , and a rigorous method is needed to tackle this problem. A model describing the statistics of the metal surface atom and site distribution on perfect cuboctahedron clusters, already developed for Pt, is applied to Pd, Ir, and Rh, using the density functional theory (DFT) calculation of the literature to determine the most favorable adsorption sites for each metal...
May 16, 2018: Materials
Narendra Nath Dutta, Konrad Patkowski
We investigate the effect of adding midbond basis functions on the performance of various conventional and explicitly correlated (F12) estimates of complete basis set limit coupled-cluster (CCSD(T)/CBS) noncovalent interaction energies. In particular, we search for an improved "silver standard" of interaction energy calculations for systems where the CCSD(T) computation is feasible in a double-zeta basis but not in a triple-zeta one. We follow a recent study (Sirianni et al., J. Chem. Theory Comput...
May 17, 2018: Journal of Chemical Theory and Computation
Zhen Lei, Jiao-Jiao Li, Xian-Kai Wan, Wen-Han Zhang, Quan-Ming Wang
otal structure determination of a ligand-protected gold nanocluster Au144 has been successfully carried out. The title nanocluster has the composition of Au144(C≡CAr)60 (1, Ar = 2-F-C6H4-). Cluster 1 exhibits a quasi-spherical Russian doll-like architecture, comprising a Au54 two-shelled Mackay icosahedron (Au12@Au42), which is further enclosed by a Au60 anti-Mackay icosahedral shell. The Au114 kernel is wrapped by thirty linear ArC≡C-Au-C≡CAr staple motifs. Absorption spectrum of 1 shows two bands at 560 and 620 nm, which is distinctly different from that of thiolated Au144, which was predicted to have an almost identical metal kernel and very similar ligands arrangement in 1...
May 17, 2018: Angewandte Chemie
R R Nayak, D Behera, N Pradhan, D K Mishra
Silver nanoparticles are produced by a novel biosynthesis technique using fungus Penicillium purpurogenum NPMF (MTCC 7356). The biomass when subjected to heat treatment up to 700 °C produces the nanoparticles of silver due to the presence of free carbon which acts as encapsulation for silver nanoparticles. Increase in temperature above 700 °C causes a reduction in concentration of free carbon so that the nanoparticles come close to each other and form clusters in the shape of tetrapods to polypods. The micro-Raman analysis supports the formation of mesoporous carbon with increase in the calcined temperature...
January 1, 2018: Journal of Nanoscience and Nanotechnology
Yongliang Shi, Boao Song, Reza Shahbazian-Yassar, Jin Zhao, Wissam A Saidi
In nanometer clusters (NCs) each atom counts. It is the specific arrangement of these atoms that determines the unique size-dependent functionalities of the NCs and hence their applications. Here we employ a self-consistent, combined theoretical and experimental approach to determine atom-by-atom the structures of supported Pt NCs on MoS2. The atomic structures are predicted using a genetic algorithm utilizing atomistic force fields and density functional theory, which are then validated using aberration-corrected scanning transmission electron microscopy...
May 16, 2018: Journal of Physical Chemistry Letters
Leah G Dodson, John D Savee, Samer Gozem, Linhan Shen, Anna I Krylov, Craig A Taatjes, David L Osborn, Mitchio Okumura
The absolute photoionization spectrum of the hydroxyl (OH) radical from 12.513 to 14.213 eV was measured by multiplexed photoionization mass spectrometry with time-resolved radical kinetics. Tunable vacuum ultraviolet (VUV) synchrotron radiation was generated at the Advanced Light Source. OH radicals were generated from the reaction of O(1 D) + H2 O in a flow reactor in He at 8 Torr. The initial O(1 D) concentration, where the atom was formed by pulsed laser photolysis of ozone, was determined from the measured depletion of a known concentration of ozone...
May 14, 2018: Journal of Chemical Physics
Shanshan Wang, Hidetaka Sawada, Xiaoyu Han, Si Zhou, Sha Li, Zheng Xiao Guo, Angus I Kirkland, Jamie H Warner
We show that Pt nanoclusters preferentially nucleate along the grain boundaries (GBs) in polycrystalline MoS2 monolayer films, with dislocations acting as the seed site. Atomic resolution studies by aberration-corrected annular dark-field scanning transmission electron microscopy reveal periodic spacing of Pt nanoclusters with dependence on GB tilt angles and random spacings for the antiphase boundaries ( i.e., 60°). Individual Pt atoms are imaged within the dislocation core sections of the GB region, with various positions observed, including both the substitutional sites of Mo and the hollow center of the octahedral ring...
May 15, 2018: ACS Nano
Priscilla S-W Yeung, Megumi Yamashita, Christopher E Ing, Régis Pomès, Douglas M Freymann, Murali Prakriya
Store-operated Orai1 channels are activated through a unique inside-out mechanism involving binding of the endoplasmic reticulum Ca2+ sensor STIM1 to cytoplasmic sites on Orai1. Although atomic-level details of Orai structure, including the pore and putative ligand binding domains, are resolved, how the gating signal is communicated to the pore and opens the gate is unknown. To address this issue, we used scanning mutagenesis to identify 15 residues in transmembrane domains (TMs) 1-4 whose perturbation activates Orai1 channels independently of STIM1...
May 14, 2018: Proceedings of the National Academy of Sciences of the United States of America
Shao Huang, Weiqiang Wang, Shengfeng He, Rynson W H Lau
We present an approach to localize generic actions in egocentric videos, called temporal action proposals (TAPs), for accelerating the action recognition step. An egocentric TAP refers to a sequence of frames that may contain a generic action performed by the wearer of a head-mounted camera, e.g., taking a knife, spreading jam, pouring milk, or cutting carrots. Inspired by object proposals, this paper aims at generating a small number of TAPs, thereby replacing the popular sliding window strategy, for localizing all action events in the input video...
February 2018: IEEE Transactions on Image Processing: a Publication of the IEEE Signal Processing Society
Shuai Chen, Wei-Hui Fang, Lei Zhang, Jian Zhang
For the first time, multimetallic clusters of noble metals have been successfully stabilized by Ti-oxo clusters. Two unprecedented Ag6@Ti16-oxo nanoclusters with precise atomic structures were prepared and characterized. The octahedral Ag6 core represents strong Ag-Ag bonds (-2.7 Å), which is further stabilized by direct Ag-O-Ti coordination interactions. Moreover, due to different acidic/redox conditions in synthesis, the Ag6 core can adopt diverse geometric configurations inside the Ti16-O shell. Correspondingly, such structural difference has greatly influenced their optical limiting effects...
May 14, 2018: Angewandte Chemie
Jianrui Feng, Pengwan Chen, Mo Li
Atomic packing is still a mystery for the topologically disordered amorphous solids owing primarily to the absence of Bragg diffraction in this class of materials. Among many hypotheses, a fractal packing is suggested based on a scaling relation with "2.5 power law" in multicomponent metallic glasses. Here we examine the atomic packing critically in a pure Tantalum metallic glass under hydrostatic pressure. Without any complications of chemical compositions as in the multicomponent systems, the genuine amorphous structure in the single component metallic glass exhibits cubic scaling exponent that indicates absence of the 2...
May 14, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Mathew T Hembury, Nataliia Beztsinna, Hamed Asadi, Joep van den Dikkenberg, Johannes D Meeldijk, Wim E Hennink, Tina Vermonden
Ultrasmall gold atom clusters (< 2 nm in diameter) or gold nanoclusters exhibit emergent photonic properties (near-infrared absorption and emission) compared to larger plasmonic gold particles, due to the significant quantization of their conduction band. While single gold nanoclusters properties and applications are being increasingly investigated, little is still known about their behaviour and properties when assembled into suprastructures and even less studies are investigating their use for biomedical applications...
May 11, 2018: Biomacromolecules
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