{"54682":{"#nid":"54682","#data":{"type":"news","title":"Study Quantifies the Effects of Placing Metal Contacts on Graphene","body":[{"value":"\u003Cp\u003EUsing large-scale supercomputer calculations, researchers have analyzed how the placement of metallic contacts on graphene changes the electron transport properties of the material as a factor of junction length, width and orientation. The work is believed to be the first quantitative study of electron transport through metal-graphene junctions to examine earlier models in significant detail. \u003C\/p\u003E\u003Cp\u003EInformation on the ways in which attaching metal contacts affects electron transport in graphene will be important to scientists studying the material -- and to designers who may one day fabricate electronic devices from the carbon-lattice material. \u003C\/p\u003E\u003Cp\u003E\u0022Graphene devices will have to communicate with the external world, and that means we will have to fabricate contacts to transport current and data,\u0022 said Mei-Yin Chou, a professor and department chair in the School of Physics at the Georgia Institute of Technology. \u0022When they put metal contacts onto graphene to measure transport properties, researchers and device designers need to know that they may not be measuring the instrinsic properties of pristine graphene. Coupling between the contacts and the material must be taken into account.\u0022 \u003C\/p\u003E\u003Cp\u003EInformation on the effects of metal contacts on graphene was reported in the journal \u003Cem\u003EPhysical Review Letters\u003C\/em\u003E on February 19th. The research was supported by the U.S. Department of Energy, and involved interactions with researchers at the National Science Foundation (NSF)-supported Materials Research Science and Engineering Center (MRSEC) at Georgia Tech. \u003C\/p\u003E\u003Cp\u003EUsing large-scale, first-principles calculations done at two different NSF-supported supercomputer centers, the Georgia Tech research team -- which included postdoctoral fellows Salvador Barraza-Lopez and Mihajlo Vanevic, and assistant professor Markus Kindermann -- conducted detailed atomic-level calculations of aluminum contacts grown on graphene. \u003C\/p\u003E\u003Cp\u003EThe calculations studied two contacts up to 14 nanometers apart, with graphene suspended between them. In their calculations, the researchers allowed the aluminum to grow as it would in the real world, then studied how electron transfer was induced in the area surrounding the contacts. \u003C\/p\u003E\u003Cp\u003E\u0022People have been able to come up with phenomenological models that they use to find out what the effects are with metallic contacts,\u0022 Chou explained. \u0022Our calculations went a few steps farther because we built contacts atom-by-atom. We built atomistically-resolved contacts, and by doing that, we solved this problem at the atomic level and tried to do everything consistent with quantum mechanics.\u0022 \u003C\/p\u003E\u003Cp\u003EBecause metals typically have excess electrons, physically attaching the contacts to graphene causes a charge transfer from the metal. Charge begins to be transferred as soon as the contracts are constructed, but ultimately the two materials reach equilibrium, Chou said. \u003C\/p\u003E\u003Cp\u003EThe study showed that charge transfer at the leads and into the freestanding section of the material creates an electron-hole asymmetry in the conductance. For leads that are sufficiently long, the effect creates two conductance minima at the energies of the Dirac points for the suspended and clamped regions of the graphene, according to Barraza-Lopez. \u003C\/p\u003E\u003Cp\u003E\u0022These results could be important to the design of future graphene devices,\u0022 he said. \u0022Edge effects and the impact of nanoribbon width have been studied in significant detail, but the effects of charge transfer at the contacts may potentially be just as important.\u0022 \u003C\/p\u003E\u003Cp\u003EThe researchers modeled aluminum, but believe their results will apply to other metals such as copper and gold that do not form chemical bonds with graphene. However, other metals such as chromium and titanium do chemically alter the material, so the effects they have on electron transport may be different. \u003C\/p\u003E\u003Cp\u003EBeyond the new information provided by the calculations, the research further proposes quantitative models that can be used under certain circumstances to describe the impact of the contacts. \u003C\/p\u003E\u003Cp\u003E\u0022Earlier models had been based on physical insights, but nobody really knew how faithfully they described the material,\u0022 Kindermann said. \u0022This is the first calculation to show that these earlier models apply under certain circumstances for the systems that we studied.\u0022 \u003C\/p\u003E\u003Cp\u003EData from the study may one day help device designers engineer graphene circuits by helping them understand the effects they are seeing. \u003C\/p\u003E\u003Cp\u003E\u0022When we modify graphene, we need to understand what changes occur as a result of adding materials,\u0022 added Chou. \u0022This is really fundamental research to understand these effects and to have a numerical prediction for what is going on. We are helping to understand the basic physics of graphene.\u0022 \u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by Department of Energy grant DE-FG02-97ER45632. Comments and conclusions in this article are those of the researchers and do not necessarily reflect the views of the Department of Energy.\u003C\/em\u003E \u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003EGeorgia Institute of Technology\u003Cbr \/\u003E75 Fifth Street, N.W., Suite 314\u003Cbr \/\u003EAtlanta, Georgia 30308 USA\u003C\/strong\u003E \u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) or Abby Vogel (404-385-3364)(\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E). \u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon \u003C\/p\u003E\u003Cp\u003E\u0026nbsp;\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EUsing large-scale supercomputer calculations, researchers have analyzed how the placement of metallic contacts on graphene changes the electron transport properties of the material as a factor of junction length, width and orientation.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Placing contacts onto graphene changes the material\u0027s properties."}],"uid":"27303","created_gmt":"2010-02-25 01:00:00","changed_gmt":"2016-10-08 03:05:38","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2010-02-25T00:00:00-05:00","iso_date":"2010-02-25T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"54683":{"id":"54683","type":"image","title":"Research team and findings","body":null,"created":"1449175459","gmt_created":"2015-12-03 20:44:19","changed":"1475894481","gmt_changed":"2016-10-08 02:41:21","alt":"Research team and findings","file":{"fid":"172616","name":"tlq13442.jpg","image_path":"\/sites\/default\/files\/images\/tlq13442_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/tlq13442_0.jpg","mime":"image\/jpeg","size":702218,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tlq13442_0.jpg?itok=vUuBgEHz"}},"54684":{"id":"54684","type":"image","title":"Graphic showing metal contacts","body":null,"created":"1449175459","gmt_created":"2015-12-03 20:44:19","changed":"1475894481","gmt_changed":"2016-10-08 02:41:21","alt":"Graphic showing metal contacts","file":{"fid":"172617","name":"tjy13058.jpg","image_path":"\/sites\/default\/files\/images\/tjy13058_0.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/tjy13058_0.jpg","mime":"image\/jpeg","size":199182,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/tjy13058_0.jpg?itok=-Zf8NoJS"}}},"media_ids":["54683","54684"],"related_links":[{"url":"http:\/\/www.physics.gatech.edu\/","title":"Georgia Tech School of Physics"},{"url":"http:\/\/prl.aps.org\/abstract\/PRL\/v104\/i7\/e076807","title":"Physical Review Letters paper"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"8858","name":"contacts"},{"id":"429","name":"graphene"},{"id":"7435","name":"material"},{"id":"7415","name":"transport"}],"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\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}