{"452781":{"#nid":"452781","#data":{"type":"news","title":"First Optical Rectenna \u2013 Combined Rectifier and Antenna \u2013 Converts Light to DC Current","body":[{"value":"\u003Cp\u003EUsing nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.\u003C\/p\u003E\u003Cp\u003EBased on multiwall carbon nanotubes and tiny rectifiers fabricated onto them, the optical rectennas could provide a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity \u2013 and ultimately for a new way to efficiently capture solar energy.\u003C\/p\u003E\u003Cp\u003EIn the new devices, developed by engineers at the Georgia Institute of Technology, the carbon nanotubes act as antennas to capture light from the sun or other sources. As the waves of light hit the nanotube antennas, they create an oscillating charge that moves through rectifier devices attached to them. The rectifiers switch on and off at record high petahertz speeds, creating a small direct current.\u003C\/p\u003E\u003Cp\u003EBillions of rectennas in an array can produce significant current, though the efficiency of the devices demonstrated so far remains below one percent. The researchers hope to boost that output through optimization techniques, and believe that a rectenna with commercial potential may be available within a year.\u003C\/p\u003E\u003Cp\u003E\u201cWe could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way\u201d said \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/faculty\/cola\u0022\u003EBaratunde Cola\u003C\/a\u003E, an associate professor in the \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/\u0022\u003EGeorge W. Woodruff School of Mechanical Engineering\u003C\/a\u003E at Georgia Tech. \u201cAs a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture.\u201d\u003C\/p\u003E\u003Cp\u003EThe research, supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center and the Army Research Office (ARO), was reported September 28 in the journal \u003Cem\u003ENature Nanotechnology\u003C\/em\u003E.\u003C\/p\u003E\u003Cp\u003EDeveloped in the 1960s and 1970s, rectennas have operated at wavelengths as short as ten microns, but for more than 40 years researchers have been attempting to make devices at optical wavelengths. There were many challenges: making the antennas small enough to couple optical wavelengths, and fabricating a matching rectifier diode small enough and able to operate fast enough to capture the electromagnetic wave oscillations. But the potential of high efficiency and low cost kept scientists working on the technology.\u003C\/p\u003E\u003Cp\u003E\u201cThe physics and the scientific concepts have been out there,\u201d said Cola. \u201cNow was the perfect time to try some new things and make a device work, thanks to advances in fabrication technology.\u201d\u003C\/p\u003E\u003Cp\u003EUsing metallic multiwall carbon nanotubes and nanoscale fabrication techniques, Cola and collaborators Asha Sharma, Virendra Singh and Thomas Bougher constructed devices that utilize the wave nature of light rather than its particle nature. They also used a long series of tests \u2013 and more than a thousand devices \u2013 to verify measurements of both current and voltage to confirm the existence of rectenna functions that had been predicted theoretically. The devices operated at a range of temperatures from 5 to 77 degrees Celsius.\u003C\/p\u003E\u003Cp\u003EFabricating the rectennas begins with growing forests of vertically-aligned carbon nanotubes on a conductive substrate. Using atomic layer chemical vapor deposition, the nanotubes are coated with an aluminum oxide material to insulate them. Finally, physical vapor deposition is used to deposit optically-transparent thin layers of calcium then aluminum metals atop the nanotube forest. The difference of work functions between the nanotubes and the calcium provides a potential of about two electron volts, enough to drive electrons out of the carbon nanotube antennas when they are excited by light.\u003C\/p\u003E\u003Cp\u003EIn operation, oscillating waves of light pass through the transparent calcium-aluminum electrode and interact with the nanotubes. The metal-insulator-metal junctions at the nanotube tips serve as rectifiers switching on and off at femtosecond intervals, allowing electrons generated by the antenna to flow one way into the top electrode. Ultra-low capacitance, on the order of a few attofarads, enables the 10-nanometer diameter diode to operate at these exceptional frequencies.\u003C\/p\u003E\u003Cp\u003E\u201cA rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode,\u201d Cola explained. \u201cThe closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode \u2013 which is the structure we made.\u201d\u003C\/p\u003E\u003Cp\u003EThe rectennas fabricated by Cola\u2019s group are grown on rigid substrates, but the goal is to grow them on a foil or other material that would produce flexible solar cells or photodetectors.\u003C\/p\u003E\u003Cp\u003ECola sees the rectennas built so far as simple proof of principle. He has ideas for how to improve the efficiency by changing the materials, opening the carbon nanotubes to allow multiple conduction channels, and reducing resistance in the structures.\u003C\/p\u003E\u003Cp\u003E\u201cWe think we can reduce the resistance by several orders of magnitude just by improving the fabrication of our device structures,\u201d he said. \u201cBased on what others have done and what the theory is showing us, I believe that these devices could get to greater than 40 percent efficiency.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis work was supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center, Pacific under YFA grant N66001-09-1-2091, and by the Army Research Office (ARO), through the Young Investigator Program (YIP), under agreement W911NF-13-1-0491. The statements in this release are those of the authors and do not necessarily reflect the official views of DARPA, SPAWAR or ARO. Georgia Tech has filed international patent applications related to this work under PCT\/US2013\/065918 in the United States (U.S.S.N. 14\/434,118), Europe (No. 13847632.0), Japan (No. 2015-538110) and China (No. 201380060639.2)\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Asha Sharma, Virendra Singh, Thomas L. Bougher and Baratunde A. Cola, \u201cA carbon nanotube optical rectenna,\u201d (Nature Nanotechnology, 2015). \u003Ca href=\u0022http:\/\/dx.doi.org\/10.1038\/nnano.2015.220\u0022\u003Ehttp:\/\/dx.doi.org\/10.1038\/nnano.2015.220\u003C\/a\u003E\u003C\/p\u003E\u003Cp\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\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) (404-894-6986)\u003Cbr \/\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 nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.\u0026nbsp;\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have demonstrated the first optical rectenna, a device that converts light directly into DC current."}],"uid":"27303","created_gmt":"2015-09-28 10:40:23","changed_gmt":"2016-10-08 03:19:40","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2015-09-28T00:00:00-04:00","iso_date":"2015-09-28T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"452711":{"id":"452711","type":"image","title":"Optical rectenna schematic","body":null,"created":"1449256297","gmt_created":"2015-12-04 19:11:37","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Optical rectenna schematic","file":{"fid":"203384","name":"rectenna1_0.jpg","image_path":"\/sites\/default\/files\/images\/rectenna1_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/rectenna1_0.jpg","mime":"image\/jpeg","size":377954,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/rectenna1_0.jpg?itok=-ESG-ij_"}},"452731":{"id":"452731","type":"image","title":"Optical rectenna converts laser light","body":null,"created":"1449256297","gmt_created":"2015-12-04 19:11:37","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Optical rectenna converts laser light","file":{"fid":"203386","name":"rectenna2.jpg","image_path":"\/sites\/default\/files\/images\/rectenna2_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/rectenna2_0.jpg","mime":"image\/jpeg","size":2203971,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/rectenna2_0.jpg?itok=mdS-b85V"}},"452741":{"id":"452741","type":"image","title":"Measuring output from optical rectenna","body":null,"created":"1449256297","gmt_created":"2015-12-04 19:11:37","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Measuring output from optical rectenna","file":{"fid":"203387","name":"rectenna6.jpg","image_path":"\/sites\/default\/files\/images\/rectenna6_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/rectenna6_0.jpg","mime":"image\/jpeg","size":2806905,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/rectenna6_0.jpg?itok=RYtr5xPg"}},"452751":{"id":"452751","type":"image","title":"Optical rectenna research team","body":null,"created":"1449256297","gmt_created":"2015-12-04 19:11:37","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Optical rectenna research team","file":{"fid":"203388","name":"rectenna7.jpg","image_path":"\/sites\/default\/files\/images\/rectenna7_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/rectenna7_0.jpg","mime":"image\/jpeg","size":6256441,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/rectenna7_0.jpg?itok=QZI6g3N9"}}},"media_ids":["452711","452731","452741","452751"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"144","name":"Energy"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"2616","name":"antenna"},{"id":"8875","name":"Baratunde Cola"},{"id":"5209","name":"carbon nanotubes"},{"id":"14545","name":"George W. Woodruff School of Mechanical Engineering"},{"id":"431","name":"nanoscale"},{"id":"107","name":"Nanotechnology"},{"id":"142851","name":"optical rectenna"},{"id":"142901","name":"rectifier"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39531","name":"Energy and Sustainable Infrastructure"},{"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\u003E(404) 894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}