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      Single Au Atom Doping of Silver Nanoclusters

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          Abstract

          Ag 29 nanoclusters capped with lipoic acid (LA) can be doped with Au. The doped clusters show enhanced stability and increased luminescence efficiency. We attribute the higher quantum yield to an increase in the rate of radiative decay. With mass spectrometry, the Au-doped clusters were found to consist predominantly of Au 1Ag 28(LA) 12 3–. The clusters were characterized using X-ray absorption spectroscopy at the Au L 3-edge. Both the extended absorption fine structure (EXAFS) and the near edge structure (XANES) in combination with electronic structure calculations confirm that the Au dopant is preferentially located in the center of the cluster. A useful XANES spectrum can be recorded for lower concentrations, or in shorter time, than the more commonly used EXAFS. This makes XANES a valuable tool for structural characterization.

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          Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities.

          Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1-3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the stability, metal-ligand interfacial bonding, ligand assembly on particle surfaces, aesthetic structural patterns, periodicities, and emergence of the metallic state) and to develop a range of potential applications such as in catalysis, biomedicine, sensing, imaging, optics, and energy conversion. Although most of the research activity currently focuses on thiolate-protected gold nanoclusters, important progress has also been achieved in other ligand-protected gold, silver, and bimetal (or alloy) nanoclusters. All of these types of unique nanoparticles will bring unprecedented opportunities, not only in understanding the fundamental questions of nanoparticles but also in opening up new horizons for scientific studies of nanoparticles.
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            Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles.

            Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible-near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters protected with proteins, with a large Stokes shift, has been used for various sensing applications, down to a few tens of molecules/ions, in air and water. Catalytic properties of clusters, especially oxidation of organic substrates, have been examined. Materials science of these systems presents numerous possibilities and is fast evolving. Computational insights have given reasons for their stability and unusual properties. The molecular nature of these materials is unequivocally manifested in a few recent studies such as intercluster reactions forming precise clusters. These systems manifest properties of the core, of the ligand shell, as well as that of the integrated system. They are better described as protected molecules or aspicules, where aspis means shield and cules refers to molecules, implying that they are "shielded molecules". In order to understand their diverse properties, a nomenclature has been introduced with which it is possible to draw their structures with positional labels on paper, with some training. Research in this area is captured here, based on the publications available up to December 2016.
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              On the ligand's role in the fluorescence of gold nanoclusters.

              The fluorescence of metal nanoparticles (such as gold and silver) has long been an intriguing topic and has drawn considerable research interest. However, the origin of fluorescence still remains unclear. In this work, on the basis of atomically monodisperse, 25-atom gold nanoclusters we present some interesting results on the fluorescence from [Au(25)(SR)(18)](q) (where q is the charge state of the particle), which has shed some light on this issue. Our work explicitly shows that the surface ligands (-SR) play a major role in enhancing the fluorescence of gold nanoparticles. Specifically, the surface ligands can influence the fluorescence in two different ways: (i) charge transfer from the ligands to the metal nanoparticle core (i.e., LMNCT) through the Au-S bonds, and (ii) direct donation of delocalized electrons of electron-rich atoms or groups of the ligands to the metal core. Following these two mechanisms, we have demonstrated strategies to enhance the fluorescence of thiolate ligand-protected gold nanoparticles. This work is hoped to stimulate more experimental and theoretical research on the atomic level design of luminescent metal nanoparticles for promising optoelectronic and other applications.
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                Author and article information

                Journal
                ACS Nano
                ACS Nano
                nn
                ancac3
                ACS Nano
                American Chemical Society
                1936-0851
                1936-086X
                20 November 2018
                26 December 2018
                : 12
                : 12
                : 12751-12760
                Affiliations
                []Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University , Universiteitslaan 99, 3584 CG Utrecht, The Netherlands
                []European Synchrotron Radiation Facility , 71 Avenue des Martyrs, CS 40220, 38043 Grenoble, France
                []Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University , Princetonplein 1, 3584 CC Utrecht, The Netherlands
                [§ ]Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University , Princetonplein 1, 3584 CC Utrecht, The Netherlands
                Author notes
                Article
                10.1021/acsnano.8b07807
                6328285
                30458110
                efb435bc-1847-4ad3-b052-c98e9ecfd5b8
                Copyright © 2018 American Chemical Society

                This is an open access article published under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution License, which permits copying and redistribution of the article, and creation of adaptations, all for non-commercial purposes.

                History
                : 12 October 2018
                : 20 November 2018
                Categories
                Article
                Custom metadata
                nn8b07807
                nn-2018-07807a

                Nanotechnology
                bimetallic nanocluster,doping,ag29,au1ag28,luminescence,x-ray spectroscopy,structure elucidation

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