{"71128":{"#nid":"71128","#data":{"type":"news","title":"Study Reveals Principles Behind Gold Nanocluster Stability","body":[{"value":"\u003Cp\u003EA report published in the July 8 issue of the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E (\u003Cem\u003EPNAS\u003C\/em\u003E) is the first to describe the principles behind the stability and electronic properties of tiny nanoclusters of metallic gold. The study, which confirms the \u0027divide and protect\u0027 bonding structure, resulted from the work of researchers at four universities on two continents.\u003C\/p\u003E\n\u003Cp\u003E\u0022While gold nanoparticles are being used by so many researchers - chemists, materials scientists and biomedical engineers - no one understood their molecular and electronic structures until now,\u0022 said Robert Whetten, a professor in the Georgia Institute of Technology\u0027s School of Physics and School of Chemistry and Biochemistry. \u0022This research opens a new window for nanoparticle chemistry.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EGold and sulfur atoms tend to aggregate in specific numbers and highly symmetrical geometries. Sometimes these clusters are called \u0027superatoms\u0027 because they can mimic the chemistry of single atoms of a completely different element.\n\u003C\/p\u003E\n\u003Cp\u003EResearchers commonly use gold nanoparticles because they are stable and exhibit distinct optical, electronic, electrochemical and bio-labeling properties. However, understanding the physicochemical properties of such clusters is a challenge, according to Whetten, because that requires knowledge of their atomic structures. \n\u003C\/p\u003E\n\u003Cp\u003EA significant advance came in late 2007 though, when Stanford University researchers reported the first-ever total structure determination of a 102-atom gold cluster. The X-ray structure study revealed that pairs of organic sulfur (\u0027thiolate\u0027) groups extracted gold atoms from the gold layer to form a linear thiolate-gold-thiolate bridge while interacting weakly with the metal surface below. These gold-thiolate complexes formed a sort of protective crust around the nanoparticles.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This discovery contradicted what most chemists believed was going on - which was that the sulfur atom merely sat atop the uppermost gold layer, bound to three adjacent metal atoms,\u0022 said Whetten.\n\u003C\/p\u003E\n\u003Cp\u003EWith the experimentally determined structural coordinates, an international team of researchers from Georgia Tech, Stanford University, the University of Jyvaskyla in Finland and Chalmers University of Technology in Sweden set out to determine the electronic principles underlying the 102-atom gold compound and others like it. The team conducted large-scale electronic structure calculations in supercomputing centers in Espoo, Finland; Stockholm, Sweden; and Juelich, Germany.\n\u003C\/p\u003E\n\u003Cp\u003EThe researchers found that the 102-atom gold cluster was a \u0027superatom\u0027 with a core of 79 gold atoms arranged into a truncated decahedron: two pyramids with pentagonal bases joined together into a faceted shape, but with the pyramids-tips chopped off. Around the core, 23 gold atoms formed an unusual pattern, joining the thiolates in shapes that resemble handles. \n\u003C\/p\u003E\n\u003Cp\u003EThe results confirmed the \u0027divide and protect\u0027 structure first predicted by team member Hannu Hakkinen, a professor at the University of Jyvaskyla and former senior research scientist at Georgia Tech in the laboratory of Uzi Landman. Hakkinen and Henrik Gronbeck of the Chalmers University of Technology previously proposed that a cluster of 38-atom gold contained a central metallic core of 14 gold atoms and a protective layer of 24 gold atoms bound to sulfur. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022In 2006, we predicted that gold atoms in this bonding motif were divided in two groups - those that made the metal core and those that helped to protected it,\u0022 explained Hakkinen. \u0022Now there was evidence that this was true.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EIn the study reported in \u003Cem\u003EPNAS\u003C\/em\u003E, the researchers found that the clusters were stable because the surface gold atoms in the core each had at least one surface-chemical bond and the gold core exhibited a strong electron shell closing.\n\u003C\/p\u003E\n\u003Cp\u003EWith the 102-atom gold cluster, each gold atom in the cluster donated one valence electron. Forty-four of those electrons were immobilized in bonds between gold atoms and thiolates, leaving 58 electrons to fill a shell around the \u0027superatom.\u0027 In this configuration, the cluster wouldn\u0027t benefit from adding or shedding electrons, which would destabilize its structure.  This process is similar to what happens in noble gases, which are chemically inert because they have just the right number of electrons to fill a shell around each atom\u0027s nucleus.\n\u003C\/p\u003E\n\u003Cp\u003EAssociated with the filled electron shell, the gold-thiolate compound also had a major energy gap to unoccupied states. The calculated energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital states for the 102-atom compound was significant - 0.5 electron volts. Metals typically have a gap of zero, so this gap indicates an atypical electronic stability of the compound, explained Whetten.\n\u003C\/p\u003E\n\u003Cp\u003EBesides the 102-atom compound, the researchers also determined the electronic structures for 11-, 13- and 39-atom gold cluster compounds. They found that the 11- and 13-gold atom clusters form closed electronic shells with 8 electrons and the 39-atom gold clusters with 34.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The theoretical concepts published in this paper provide a solid background for further understanding of the distinct electrical, optical and chemical properties of the stable mono-layer-protected gold nanoclusters,\u0022 said Whetten, whose funding for this research came from the National Science Foundation and the U.S. Department of Energy. Former Georgia Tech graduate student Ryan Price and current graduate student James Bradshaw also contributed to this work.\n\u003C\/p\u003E\n\u003Cp\u003EThe study also shows that experimentally well-characterized, structure-resolved, thermodynamically stable species of thiolate-, phosphine-halide-, and phosphine-thiolate-protected gold nanoparticles share common factors underlying their stability. \n\u003C\/p\u003E\n\u003Cp\u003EOnce this initial work was completed, the researchers started predicting the structures of other stable gold cluster compositions that are still awaiting a precise structure determination.\u003Cbr \/\u003E\nIn the March 26 issue of the \u003Cem\u003EJournal of the American Chemical Society\u003C\/em\u003E, the research team predicted the structure for a cluster containing 25 gold atoms. They determined that the structure was comprised of an icosahedron-like 13-atom gold core protected by six \u0027V-shaped\u0027 long units, creating a \u0027divide and protect\u0027 composition. The structural prediction was recently confirmed by another group\u0027s experimental work.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022We now have a unified model that provides a solid background for nanoengineering ligand-protected gold clusters for applications in catalysis, sensing, photonics, bio-labeling and molecular electronics,\u0022 said Hakkinen.\n\u003C\/p\u003E\n\u003Cp\u003EAdditional authors on the \u003Cem\u003EPNAS\u003C\/em\u003E paper included Michael Walter, Jaakko Akola and Olga Lopez-Acevedo of the University of Jyvaskyla; and Pablo Jadzinsky, Guillermo Calero and Christopher Ackerson of Stanford University.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\n\u003C\/strong\u003E\u003C\/p\u003E\n\u003Cp\u003EMedia Relations Contacts: Abby Vogel (404-385-3364); E-mail: (\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E) or John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter:\u003C\/strong\u003E Abby Vogel\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"International team confirms \u0027divide and protect\u0027 bonding structure"}],"field_summary":[{"value":"A report published in the July 8 issue of the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E (PNAS) is the first to describe the principles behind the stability and electronic properties of tiny nanoclusters of metallic gold.","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers from four universities report on nanoclusters"}],"uid":"27206","created_gmt":"2008-07-11 00:00:00","changed_gmt":"2016-10-08 03:03:19","author":"Abby Vogel Robinson","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-07-14T00:00:00-04:00","iso_date":"2008-07-14T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"71129":{"id":"71129","type":"image","title":"102-atom gold nanocluster","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"},"71130":{"id":"71130","type":"image","title":"25-atom gold nanocluster","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"},"71131":{"id":"71131","type":"image","title":"39- and 11-atom gold nanoclusters","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"}},"media_ids":["71129","71130","71131"],"related_links":[{"url":"http:\/\/www.physics.gatech.edu\/","title":"Georgia Tech School of Physics"},{"url":"http:\/\/www.chemistry.gatech.edu\/","title":"School of Chemistry and Biochemistry"},{"url":"http:\/\/www.chemistry.gatech.edu\/faculty\/Whetten\/","title":"Robert Whetten"},{"url":"http:\/\/dx.doi.org\/10.1073\/pnas.0801001105","title":"PNAS article"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"7288","name":"bio-labeling"},{"id":"2507","name":"catalysis"},{"id":"89","name":"chemistry"},{"id":"2529","name":"cluster"},{"id":"7283","name":"divide"},{"id":"7287","name":"electrochemical"},{"id":"6884","name":"electron"},{"id":"4186","name":"electronic"},{"id":"213","name":"energy"},{"id":"7291","name":"gap"},{"id":"2185","name":"gold"},{"id":"7082","name":"metal"},{"id":"3030","name":"molecular"},{"id":"2286","name":"nano"},{"id":"2528","name":"nanocluster"},{"id":"1143","name":"optical"},{"id":"7282","name":"orbital"},{"id":"2290","name":"photonics"},{"id":"7284","name":"protect"},{"id":"170866","name":"stability"},{"id":"169761","name":"structure"},{"id":"170840","name":"sulfur"},{"id":"170867","name":"superatom"},{"id":"167325","name":"supercomputer"},{"id":"7289","name":"thiol"},{"id":"7290","name":"valence"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EAbby Robinson\u003C\/strong\u003E\u003Cbr \/\u003EResearch News and Publications\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=avogel6\u0022\u003EContact Abby Robinson\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-385-3364\u003C\/strong\u003E","format":"limited_html"}],"email":["abby@innovate.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}