{"334451":{"#nid":"334451","#data":{"type":"news","title":"Researchers develop world\u2019s thinnest electric generator","body":[{"value":"\u003Cp\u003EResearchers from Columbia Engineering and the Georgia Institute of Technology have reported the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS\u003Csub\u003E2\u003C\/sub\u003E), resulting in a unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable.\u003C\/p\u003E\u003Cp\u003EIn a paper published online October 15, 2014, in the journal \u003Cem\u003ENature\u003C\/em\u003E, research groups from the two institutions demonstrate the mechanical generation of electricity from the two-dimensional (2D) MoS\u003Csub\u003E2\u003C\/sub\u003E material. The piezoelectric effect in this material had previously been predicted theoretically.\u003C\/p\u003E\u003Cp\u003EPiezoelectricity is a well-known effect in which stretching or compressing a material causes it to generate an electrical voltage (or the reverse, in which an applied voltage causes it to expand or contract). But for materials of only a few atomic thicknesses, no experimental observation of piezoelectricity has been made, until now. The observation provides a new property for two-dimensional materials such as molybdenum disulfide, opening the potential for new types of mechanically controlled electronic devices.\u003C\/p\u003E\u003Cp\u003E\u201cThis material \u2013 just a single layer of atoms \u2013 could be made as a wearable device, perhaps integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge your cell phone in your pocket,\u201d said James Hone, professor of mechanical engineering at Columbia and co-leader of the research.\u003C\/p\u003E\u003Cp\u003E\u201cProof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials,\u201d said Zhong Lin Wang, Regents\u2019 Professor in Georgia Tech\u2019s School of Materials Science and Engineering and a co-leader of the research. \u201cThe materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.\u201d\u003C\/p\u003E\u003Cp\u003EHone and his research group demonstrated in 2008 that graphene, a 2D form of carbon, is the strongest material. He and Lei Wang, a postdoctoral fellow in Hone\u2019s group, have been actively exploring the novel properties of 2D materials like graphene and MoS\u003Csub\u003E2\u003C\/sub\u003E as they are stretched and compressed.\u003C\/p\u003E\u003Cp\u003EZhong Lin Wang and his research group pioneered the field of piezoelectric nanogenerators for converting mechanical energy into electricity. He and postdoctoral fellow Wenzhuo Wu are also developing piezotronic devices, which use piezoelectric charges to control the flow of current through the material just as gate voltages do in conventional three-terminal transistors.\u003C\/p\u003E\u003Cp\u003EThere are two keys to using molybdenum disulfide for generating current: using an odd number of layers and flexing it in the proper direction. The material is highly polar, but, Zhong Lin Wang notes, so an even number of layers cancels out the piezoelectric effect. The material\u2019s crystalline structure also is piezoelectric in only certain crystalline orientations.\u003C\/p\u003E\u003Cp\u003EFor the Nature study, Hone\u2019s team placed thin flakes of MoS\u003Csub\u003E2\u003C\/sub\u003E on flexible plastic substrates and determined how their crystal lattices were oriented using optical techniques. They then patterned metal electrodes onto the flakes. In research done at Georgia Tech, Wang\u2019s group installed measurement electrodes on samples provided by Hone\u2019s group, then measured current flows as the samples were mechanically deformed. They monitored the conversion of mechanical to electrical energy, and observed voltage and current outputs.\u003C\/p\u003E\u003Cp\u003EThe researchers also noted that the output voltage reversed sign when they changed the direction of applied strain, and that it disappeared in samples with an even number of atomic layers, confirming theoretical predictions published last year. The presence of piezotronic effect in odd layer MoS\u003Csub\u003E2\u003C\/sub\u003E was also observed for the first time.\u003C\/p\u003E\u003Cp\u003E\u201cWhat\u2019s really interesting is we\u2019ve now found that a material like MoS\u003Csub\u003E2\u003C\/sub\u003E, which is not piezoelectric in bulk form, can become piezoelectric when it is thinned down to a single atomic layer,\u201d said Lei Wang.\u003C\/p\u003E\u003Cp\u003ETo be piezoelectric, a material must break central symmetry. A single atomic layer of MoS\u003Csub\u003E2\u003C\/sub\u003E has such a structure, and should be piezoelectric. However, in bulk MoS\u003Csub\u003E2\u003C\/sub\u003E, successive layers are oriented in opposite directions, and generate positive and negative voltages that cancel each other out and give zero net piezoelectric effect.\u003C\/p\u003E\u003Cp\u003E\u201cThis adds another member to the family of piezoelectric materials for functional devices,\u201d said Wenzhuo Wu.\u003C\/p\u003E\u003Cp\u003EIn fact, MoS\u003Csub\u003E2\u003C\/sub\u003E is just one of a group of 2D semiconducting materials known as transition metal dichalcogenides, all of which are predicted to have similar piezoelectric properties.\u0026nbsp; These are part of an even larger family of 2D materials whose piezoelectric materials remain unexplored.\u0026nbsp; Importantly, as has been shown by Hone and his colleagues, 2D materials can be stretched much farther than conventional materials, particularly traditional ceramic piezoelectrics, which are quite brittle.\u003C\/p\u003E\u003Cp\u003EThe research could open the door to development of new applications for the material and its unique properties.\u003C\/p\u003E\u003Cp\u003E\u201cThis is the first experimental work in this area and is an elegant example of how the world becomes different when the size of material shrinks to the scale of a single atom,\u201d Hone added. \u201cWith what we\u2019re learning, we\u2019re eager to build useful devices for all kinds of applications.\u201d\u003C\/p\u003E\u003Cp\u003EUltimately, Zhong Lin Wang noted, the research could lead to complete atomic-thick nanosystems that are self-powered by harvesting mechanical energy from the environment. This study also reveals the piezotronic effect in two-dimensional materials for the first time, which greatly expands the application of layered materials for human-machine interfacing, robotics, MEMS, and active flexible electronics.\u003C\/p\u003E\u003Cp\u003EFor this study, the research team also worked with Tony Heinz, David M. Rickey Professor of Optical Communications at Columbia Engineering and professor of physics at Columbia\u2019s Graduate School of Arts and Sciences.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe study was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES) (No. DE-FG02-07ER46394) and U.S. National Science Foundation (DMR-1122594).\u003C\/em\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia 30332-0181 USA\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: Georgia Tech: John Toon (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) (404-894-6986) or Brett Israel (\u003Ca href=\u0022mailto:brett.israel@comm.gatech.edu\u0022\u003Ebrett.israel@comm.gatech.edu\u003C\/a\u003E) (404-385-1933) or Columbia Engineering: Holly Evarts (\u003Ca href=\u0022mailto:holly.evarts@columbia.edu\u0022\u003Eholly.evarts@columbia.edu\u003C\/a\u003E) (212-854-3206).\u003Cbr \/\u003E\u003Cbr \/\u003E\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EResearchers from Columbia Engineering and the Georgia Institute of Technology have reported they have made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2), resulting in a unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have made the first experimental observation of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide."}],"uid":"27303","created_gmt":"2014-10-15 13:26:53","changed_gmt":"2016-10-08 03:17:19","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2014-10-15T00:00:00-04:00","iso_date":"2014-10-15T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"334401":{"id":"334401","type":"image","title":"Molybdenum disulfide sample","body":null,"created":"1449245150","gmt_created":"2015-12-04 16:05:50","changed":"1475895046","gmt_changed":"2016-10-08 02:50:46","alt":"Molybdenum disulfide sample","file":{"fid":"200456","name":"molybdenum-disulfide-6.jpg","image_path":"\/sites\/default\/files\/images\/molybdenum-disulfide-6_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/molybdenum-disulfide-6_0.jpg","mime":"image\/jpeg","size":1997423,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/molybdenum-disulfide-6_0.jpg?itok=4aTAEDCI"}},"334411":{"id":"334411","type":"image","title":"Molybdenum disulfide sample2","body":null,"created":"1449245150","gmt_created":"2015-12-04 16:05:50","changed":"1475895046","gmt_changed":"2016-10-08 02:50:46","alt":"Molybdenum disulfide sample2","file":{"fid":"200457","name":"molybdenum-disulfide-7.jpg","image_path":"\/sites\/default\/files\/images\/molybdenum-disulfide-7_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/molybdenum-disulfide-7_0.jpg","mime":"image\/jpeg","size":1421595,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/molybdenum-disulfide-7_0.jpg?itok=6-YOc0Sh"}},"334421":{"id":"334421","type":"image","title":"molybdenum disulfide - Zhong Lin Wang","body":null,"created":"1449245150","gmt_created":"2015-12-04 16:05:50","changed":"1475895046","gmt_changed":"2016-10-08 02:50:46","alt":"molybdenum disulfide - Zhong Lin Wang","file":{"fid":"200458","name":"molybdenum-disulfide-9.jpg","image_path":"\/sites\/default\/files\/images\/molybdenum-disulfide-9_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/molybdenum-disulfide-9_0.jpg","mime":"image\/jpeg","size":1564247,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/molybdenum-disulfide-9_0.jpg?itok=tUTIxtRM"}},"334431":{"id":"334431","type":"image","title":"molybdenum disulfide - researchers","body":null,"created":"1449245150","gmt_created":"2015-12-04 16:05:50","changed":"1475895046","gmt_changed":"2016-10-08 02:50:46","alt":"molybdenum disulfide - researchers","file":{"fid":"200459","name":"molybdenum-disulfide-8.jpg","image_path":"\/sites\/default\/files\/images\/molybdenum-disulfide-8_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/molybdenum-disulfide-8_0.jpg","mime":"image\/jpeg","size":1761968,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/molybdenum-disulfide-8_0.jpg?itok=AgG98S6l"}}},"media_ids":["334401","334411","334421","334431"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[],"keywords":[{"id":"13689","name":"energy harvesting"},{"id":"6300","name":"generator"},{"id":"106571","name":"molybdenum disulfide"},{"id":"7699","name":"piezoelectric"},{"id":"13750","name":"piezotronics"},{"id":"13751","name":"Zhong Lin Wang"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39471","name":"Materials"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E404-894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}