{"72346":{"#nid":"72346","#data":{"type":"news","title":"Scientists Find Why Conductance of Nanowires Vary","body":[{"value":"\u003Cp\u003EA Georgia Tech physics group has discovered how and why the electrical conductance of metal nanowires changes as their length varies.  In a collaborative investigation performed by an experimental team and a theoretical physics team, the group discovered that measured fluctuations in the smallest nanowires\u0027 conductance are caused by a pair of atoms, known as a dimer, shuttling back and forth between the bulk electrical leads. Determining the structural properties of nanowires is a big challenge facing the future construction of nanodevices and nanotechnology. The paper appears in the January 26th issue of Physical Review Letters.\u003C\/p\u003E\n\u003Cp\u003E\u0022By combining the data from the electrical conductance experiments with high-level first principles quantum mechanical calculations, we\u0027ve been able to draw an accurate picture of the physical mechanisms that govern these properties. It\u0027s like measuring current through an object you can\u0027t see to tell you what it looks like,\u0022 said Uzi Landman, director of the Center for Computational Materials Science, Regents\u0027 and Institute professor, and Callaway chair of physics at Georgia Tech.\n\u003C\/p\u003E\n\u003Cp\u003ELeading the experimental team, Alexei Marchenkov, assistant professor in the School of Physics, formed niobium nanowires using the mechanically controlled break junction technique - that is bending a thin nanofabricated strip of niobium until it breaks. In the final stage before the strip breaks completely, all that\u0027s left is a nanowire made of a short chain of niobium atoms that bridge the gap between the two sides of the strip. Working at low temperatures, Marchenkov was able to hold the nanowires at successive stretching stages for many hours, long enough to perform thorough conductance measurements, and much longer than the seconds typically characteristic of this technique.\n\u003C\/p\u003E\n\u003Cp\u003EConducting the experiment at 4.2 degrees Kelvin (far below niobium\u0027s superconductivity transition temperature of 9.2 Kelvin), as well as performing measurements  above the transition temperature, Marchenkov\u0027s team measured the electrical conductance of the atomic nanowire as it is stretched during the bending of the strip. As this bending occurs, the atoms separate from each other. The researchers were capable of controlling this separation with a precision better than 1 picometer (one thousandth of a nanometer), which is about 100 times smaller than the typical size of atoms.\n\u003C\/p\u003E\n\u003Cp\u003EAs the nanowire is slowly pulled, the conductance drops. The drop in conductance was gradual until a rapid decrease in the conductance was observed in a narrow region of just 0.1 angstrom . Upon further pulling of the wire, the conductance resumed its gradual decline.\u003C\/p\u003E\n\u003Cp\u003E\u0022Focusing on this narrow region, we found that this steep drop in conductance wasn\u0027t as smooth as it seemed at first,\u0022 said Marchenkov. \u0022We saw that the conductance actually jumps between two values.  Close to the onset of the rapid drop, the conductance was mostly rather high and then there would be random short periods were it drops to a significantly lower value. On the other side of the interval, the pattern reversed itself and  mostly the low conductance values were spotted with  the random occurrence of sharp  spikes of high conductance,\u0022 said Marchenkov.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022That\u0027s where the theoretical simulations come in,\u0022 said Landman. \u0022We needed to find out what physical phenomenon would account for these sharp drops and spikes in the conductance.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EAt first, the team thought a single atom must be randomly shuttling itself back and forth between two positions in the space separating the electrical leads, but the data didn\u0027t fit. So, they tried running the simulations with a connected pair of atoms, or dimer.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022When we performed electronic structure and electrical conductance calculations on a shuttling dimer, we found good agreement with the experimentally measured conductance and its variation with the wire length,\u0022 said Landman.\n\u003C\/p\u003E\n\u003Cp\u003EWhen the dimer is closer to one lead, the electrons that make up the electrical current have a longer way to hop from the dimer to the other lead, making current flow more difficult. When the dimer is in the center between the leads, the distance the electrons have to hop is shorter and more manageable, allowing the current to flow better. As the wire bends more and more, the dimer begins to spend more of its time closer to one electrical lead than in the center, accounting for the overall decrease in conductance.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Determining the structures of nanowires is a very big challenge in this field,\u0022 said Landman. \u0022This research shows that if you make detailed measurements and analyze them theoretically, you can determine the physical structures. In this way, measurements of electronic transport can serve not only as a probe of the electronic state of nanowires but also as a microscopy of the atomic arrangements,\u0022 said Landman.\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"A Georgia Tech physics group has discovered how and why the electrical conductance of metal nanowires changes as their length varies. Determining the structural properties of nanowires is a big challenge facing the future of nanotechnology.","format":"limited_html"}],"field_summary_sentence":[{"value":"Discovery has implications for nanotech development"}],"uid":"27310","created_gmt":"2007-02-02 01:00:00","changed_gmt":"2016-10-08 03:01:37","author":"David Terraso","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2007-02-05T00:00:00-05:00","iso_date":"2007-02-05T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"72347":{"id":"72347","type":"image","title":"Dimer illustration","body":null,"created":"1449177454","gmt_created":"2015-12-03 21:17:34","changed":"1475894656","gmt_changed":"2016-10-08 02:44:16"},"72348":{"id":"72348","type":"image","title":"Electrical leads","body":null,"created":"1449177454","gmt_created":"2015-12-03 21:17:34","changed":"1475894656","gmt_changed":"2016-10-08 02:44:16"}},"media_ids":["72347","72348"],"related_links":[{"url":"http:\/\/www.physics.gatech.edu\/people\/faculty\/amarchenkov.html","title":"Alexei Marchenkov"},{"url":"http:\/\/www.physics.gatech.edu\/people\/faculty\/ulandman.html","title":"Uzi Landman"}],"groups":[{"id":"1214","name":"News Room"}],"categories":[{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"2504","name":"conductance"},{"id":"2505","name":"conductivity"},{"id":"2503","name":"dimer"},{"id":"1631","name":"landman"},{"id":"2334","name":"marchenkov"},{"id":"2286","name":"nano"},{"id":"382","name":"nanoscience"},{"id":"107","name":"Nanotechnology"},{"id":"2502","name":"nanowire"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Cstrong\u003EGeorgia Tech Media Relations\u003C\/strong\u003E\u003Cbr \/\u003ELaura Diamond\u003Cbr \/\u003E\u003Ca href=\u0022mailto:laura.diamond@comm.gatech.edu\u0022\u003Elaura.diamond@comm.gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-894-6016\u003Cbr \/\u003EJason Maderer\u003Cbr \/\u003E\u003Ca href=\u0022mailto:maderer@gatech.edu\u0022\u003Emaderer@gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-660-2926\u003C\/p\u003E","format":"limited_html"}],"email":["david.terraso@comm.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}