Size as a Parameter to Stabilize New Phases: Rock Salt Phases of Pb_<i>m</i>Sb_2<i>n</i>Se_{<i>m</i>+3<i>n</i>}

A series of Pb_<i>m</i>Sb_2<i>n</i>Se_{<i>m</i>+3<i>n</i>} nanocrystals (<i>m</i> = 2, 4, 6 and 8; <i>n</i> = 1) are demonstrated that exist only as a distinct phase on the nanoscale. The nanocrystals aggregates are new compounds adopting the cubic NaCl-type structure. These materials form aggregates comprised of nanocrystallites that are attached at a preferred orientation. Elemental compositions were studied using the complementary techniques of scanning transmission electron microscopy/energy dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectroscopy. The new ternary nanocrystal aggregates are moderately monodisperse and exhibit well-defined band gap energies in the mid-IR region. The Pb_<i>m</i>Sb_2<i>n</i>Se_{<i>m</i>+3<i>n</i>} nanomaterials behave as homogeneous solid solutions with lattice parameter trending as a function of Sb incorporation at room temperature and tend to phase separate into PbSe and Sb₂Se₃ at 400 °C

Atomic Resolution Study of Reversible Conversion Reaction in Metal Oxide Electrodes for Lithium-Ion Battery

Electrode materials based on conversion reactions with lithium ions have shown much higher energy density than those based on intercalation reactions. Here, nanocubes of a typical metal oxide (Co₃O₄) were grown on few-layer graphene, and their electrochemical lithiation and delithiation were investigated at atomic resolution by <i>in situ</i> transmission electron microscopy to reveal the mechanism of the reversible conversion reaction. During lithiation, a lithium-inserted Co₃O₄ phase and a phase consisting of nanosized Co–Li–O clusters are identified as the intermediate products prior to the subsequent formation of Li₂O crystals. In delithiation, the reduced metal nanoparticles form a network and breakdown into even smaller clusters that act as catalysts to prompt reduction of Li₂O, and CoO nanoparticles are identified as the product of the deconversion reaction. Such direct real-space, real-time atomic-scale observations shed light on the phenomena and mechanisms in reaction-based electrochemical energy conversion and provide impetus for further development in electrochemical charge storage devices

Using Scanning-Probe Block Copolymer Lithography and Electron Microscopy To Track Shape Evolution in Multimetallic Nanoclusters

Here we describe a general method for synthesizing multimetallic core–shell nanoclusters on surfaces. By patterning seeds at predesignated locations using scanning-probe block copolymer lithography, we can track shape evolution in nanoclusters and elucidate their growth pathways using electron microscopy. The growth of core–shell nanostructures on surface-bound seeds is a highly anisotropic process and often results in multimetallic anisotropic nanostructures. The shell grows at specific edge and corner sites of the patterned seeds and propagates predominately from the top hemisphere of the seeds

Growth Mechanism of Transition Metal Dichalcogenide Monolayers: The Role of Self-Seeding Fullerene Nuclei

Due to their unique optoelectronic properties and potential for next generation devices, monolayer transition metal dichalcogenides (TMDs) have attracted a great deal of interest since the first observation of monolayer MoS₂ a few years ago. While initially isolated in monolayer form by mechanical exfoliation, the field has evolved to more sophisticated methods capable of direct growth of large-area monolayer TMDs. Chemical vapor deposition (CVD) is the technique used most prominently throughout the literature and is based on the sulfurization of transition metal oxide precursors. CVD-grown monolayers exhibit excellent quality, and this process is widely used in studies ranging from the fundamental to the applied. However, little is known about the specifics of the nucleation and growth mechanisms occurring during the CVD process. In this study, we have investigated the nucleation centers or “seeds” from which monolayer TMDs typically grow. This was accomplished using aberration-corrected scanning transmission electron microscopy to analyze the structure and composition of the nuclei present in CVD-grown MoS₂–MoSe₂ alloys. We find that monolayer growth proceeds from nominally oxi-chalcogenide nanoparticles which act as heterogeneous nucleation sites for monolayer growth. The oxi-chalcogenide nanoparticles are typically encased in a fullerene-like shell made of the TMD. Using this information, we propose a step-by-step nucleation and growth mechanism for monolayer TMDs. Understanding this mechanism may pave the way for precise control over the synthesis of 2D materials, heterostructures, and related complexes

<i>A</i>. <i>baumannii</i> (Ab) isolates with imipenem and/or meropenem MICs ≥ 0.25 μg/ml from 2002 to 2009.

<p>^<i>a</i> Parentheses refer to the number of patients</p><p><i>A</i>. <i>baumannii</i> (Ab) isolates with imipenem and/or meropenem MICs ≥ 0.25 μg/ml from 2002 to 2009.</p

PFGE dendrogram of 10 representative isolates from the three dominant clones.

<p>Allelic profile: seven loci in the order <i>gltA</i>, <i>gyrB</i>, <i>gdhB</i>, <i>recA</i>, <i>cpn60</i>, <i>gpi</i>, and <i>rpoD</i>; MIC μg/ml; IPM, imipenem; MEM, meropenem.</p

Antibiotic resistance profiles of the three main carbapenemase gene-harboring <i>A</i>. <i>baumannii</i> clones (MIC μg/ml).

<p>IPM, imipenem; MEM, meropenem; CSL, cefoperazone-sulbactam; SAM, ampicillin-sulbactam; FEP, cefepime; TZP, piperacillin-tazobactam; CAZ, ceftazidime; CRO, ceftriaxone; AMK, amikacin; CIP, ciprofloxacin; LEV, levofloxacin; SXT, trimethoprim-sulfamethoxazole; POL, polymixin B; MNO, minocycline; TGC, tigecycline</p><p>R, resistant; S, susceptible</p><p>^<i>a</i> CLSI (2007) breakpoint for cefoperazone was used for cefoperazone-sulbactam in this study.</p><p>^<i>b</i> U.S. FDA criteria for tigecycline were used in this study (susceptibility is defined as ≤ 2μg/ml; resistance as ≥ 8 μg/ml).</p><p>Antibiotic resistance profiles of the three main carbapenemase gene-harboring <i>A</i>. <i>baumannii</i> clones (MIC μg/ml).</p

Transition of <i>bla</i>_OXA-58-like to <i>bla</i>_OXA-23-like in <i>Acinetobacter baumannii</i> Clinical Isolates in Southern China: An 8-Year Study

<div><p>Background</p><p>The prevalence of carbapenem-resistant <i>Acinetobacter baumannii</i> in hospitals has been increasing worldwide. This study aims to investigate the carbapenemase genes and the clonal relatedness among <i>A</i>. <i>baumannii</i> clinical isolates in a Chinese hospital.</p><p>Methods</p><p>Carbapenemase genes and the upstream locations of insertion sequences were detected by polymerase chain reaction (PCR), and the clonal relatedness of isolates was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing.</p><p>Results</p><p>A total of 231 nonduplicate carbapenemase gene-harboring <i>A</i>. <i>baumannii</i> clinical isolates recovered from Shenzhen People’s Hospital, were investigated between 2002 and 2009. <i>bla</i>_OXA-23-like, <i>bla</i>_OXA-58-like, <i>bla</i>_OXA-40-like, and IS<i>Aba1</i>-<i>bla</i>_OXA-51-like were identified in 119, 107, 1, and 4 isolates, respectively. IS<i>1008</i>-ΔIS<i>Aba3</i>, IS<i>Aba3</i>, and IS<i>Aba1</i> were detected upstream of the <i>bla</i>_OXA-58-like gene in 69, 35, and 3 isolates, respectively. All <i>bla</i>_OXA-23-like genes but one had an upstream insertion of IS<i>Aba1</i>. <i>bla</i>_OXA-58-like was the most common carbapenemase gene in <i>A</i>.<i>baumannii</i> before 2008, thereafter <i>bla</i>_OXA-23-like became rapidly prevalent and replaced <i>bla</i>_OXA-58-like in 2009. The majority of <i>bla</i>_OXA-58-like-carrying isolates showed lower level of resistance to imipenem and meropenem (minimum inhibitory concentrations (MICs), 1 μg/ml to 16 μg/ml), compared with the majority of <i>bla</i>_OXA-23-like-carrying isolates (MICs, 16 μg/ml to 64 μg/ml for both imipenem and meropenem). All 231 <i>bla</i>_OXA carbapenemase gene-harboring isolates belonged to 14 PFGE types (A–N), and three dominant clones A, J, and H accounted for 43.3%, 42.0%, and 8.2% of the tested isolates, respectively. Clone A (sequence type ST92/ST208) with <i>bla</i>_OXA-58-like was the most prevalent before 2008. Clone H (ST229) with <i>bla</i>_OXA-23-like became striking between 2007 and 2008. Clone J (ST381) with <i>bla</i>_OXA-23-like rapidly spread and replaced clones A and H in 2009.</p><p>Conclusion</p><p>This study is the first to reveal that the distinct <i>bla</i>_OXA-23-like-carrying <i>A</i>. <i>baumannii</i> ST381 displaced the previously prevalent <i>bla</i>_OXA-58-like-carrying <i>A</i>. <i>baumannii</i> ST92/ST208, resulting in the rapidly increasing resistance to carbapenems in <i>A</i>. <i>baumannii</i> in Shenzhen People’s Hospital in 2009.</p></div

MIC distributions of imipenem and meropenem against <i>A</i>. <i>baumannii</i> (Ab) isolates with various ISs upstream of the <i>bla</i>_OXA-58-like.

<p>MIC distributions of imipenem and meropenem against <i>A</i>. <i>baumannii</i> (Ab) isolates with various ISs upstream of the <i>bla</i>_OXA-58-like.</p

PFGE types of carbapenemase gene-carrying <i>A</i>. <i>baumannii</i> (Ab) from 2002 to 2009.

<p>PFGE types of carbapenemase gene-carrying <i>A</i>. <i>baumannii</i> (Ab) from 2002 to 2009.</p