{"228141":{"#nid":"228141","#data":{"type":"news","title":"Device Captures Signatures with Tiny Piezo-Phototronic LEDs","body":[{"value":"\u003Cp\u003EResearchers at the Georgia Institute of Technology want to put your signature up in lights \u2013 tiny lights, that is. Using thousands of nanometer-scale wires, the researchers have developed a sensor device that converts mechanical pressure \u2013 from a signature or a fingerprint \u2013 directly into light signals that can be captured and processed optically.\u003C\/p\u003E\u003Cp\u003EThe sensor device could provide an artificial sense of touch, offering sensitivity comparable to that of the human skin. Beyond collecting signatures and fingerprints, the technique could also be used in biological imaging and micro-electromechanical (MEMS) systems. Ultimately, it could provide a new approach for human-machine interfaces.\u003C\/p\u003E\u003Cp\u003E\u201cYou can write with your pen and the sensor will optically detect what you write at high resolution and with a very fast response rate,\u201d said \u003Ca href=\u0022http:\/\/www.mse.gatech.edu\/faculty-staff\/faculty\/zhong-lin-wang\u0022\u003EZhong Lin Wang\u003C\/a\u003E, Regents\u2019 professor and Hightower Chair in the \u003Ca href=\u0022http:\/\/www.mse.gatech.edu\/\u0022\u003ESchool of Materials Science and Engineering\u003C\/a\u003E at Georgia Tech. \u201cThis is a new principle for imaging force that uses parallel detection and avoids many of the complications of existing pressure sensors.\u201d\u003C\/p\u003E\u003Cp\u003EIndividual zinc oxide (ZnO) nanowires that are part of the device operate as tiny light emitting diodes (LEDs) when placed under strain from the mechanical pressure, allowing the device to provide detailed information about the amount of pressure being applied. Known as piezo-phototronics, the technology \u2013 first described by Wang in 2009 \u2013 provides a new way to capture information about pressure applied at very high resolution: up to 6,300 dots per inch. \u0026nbsp;\u003C\/p\u003E\u003Cp\u003EThe research was reported August 11, 2013, in the journal \u003Cem\u003ENature Photonics\u003C\/em\u003E. It was sponsored by the U.S. Department of Energy\u2019s Office of Basic Energy Sciences, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.\u003C\/p\u003E\u003Cp\u003EPiezoelectric materials generate a charge polarization when they are placed under strain. The piezo-phototronic devices rely on that physical principle to tune and control the charge transport and recombination by the polarization charges present at the ends of individual nanowires. Grown atop a gallium nitride (GaN) film, the nanowires create pixeled light emitters whose output varies with the pressure, creating an electroluminescent signal that can be integrated with on-chip photonics for data transmission, processing and recording.\u003C\/p\u003E\u003Cp\u003E\u201cWhen you have a zinc oxide nanowire under strain, you create a piezoelectric charge at both ends which forms a piezoelectric potential,\u201d Wang explained. \u201cThe presence of the potential distorts the band structure in the wire, causing electrons to remain in the p-n junction longer and enhancing the efficiency of the LED.\u201d\u003C\/p\u003E\u003Cp\u003EThe efficiency increase in the LED is proportional to the strain created. Differences in the amount of strain applied translate to differences in light emitted from the root where the nanowires contact the gallium nitride film.\u003C\/p\u003E\u003Cp\u003ETo fabricate the devices, a low-temperature chemical growth technique is used to create a patterned array of zinc oxide nanowires on a gallium nitride thin film substrate with the c-axis pointing upward. The interfaces between the nanowires and the gallium nitride film form the bottom surfaces of the nanowires. After infiltrating the space between nanowires with a PMMA thermoplastic, oxygen plasma is used to etch away the PMMA enough to expose the tops of the zinc oxide nanowires.\u003C\/p\u003E\u003Cp\u003EA nickel-gold electrode is then used to form ohmic contact with the bottom gallium-nitride film, and a transparent indium-tin oxide (ITO) film is deposited on the top of the array to serve as a common electrode.\u003C\/p\u003E\u003Cp\u003EWhen pressure is applied to the device through handwriting or other source of pressure, nanowires are compressed along their axial directions, creating a negative piezo-potential, while uncompressed nanowires have no potential.\u003C\/p\u003E\u003Cp\u003EThe researchers have pressed letters into the top of the device, which produces a corresponding light output from the bottom of the device. This output \u2013 which can all be read at the same time \u2013 can be processed and transmitted.\u003C\/p\u003E\u003Cp\u003EThe ability to see all of the emitters simultaneously allows the device to provide a quick response. \u201cThe response time is fast, and you can read a million pixels in a microsecond,\u201d said Wang. \u201cWhen the light emission is created, it can be detected immediately with the optical fiber.\u201d\u003C\/p\u003E\u003Cp\u003EThe nanowires stop emitting light when the pressure is relieved. Switching from one mode to the other takes 90 milliseconds or less, Wang said.\u003C\/p\u003E\u003Cp\u003EThe researchers studied the stability and reproducibility of the sensor array by examining the light emitting intensity of the individual pixels under strain for 25 repetitive on-off cycles. They found that the output fluctuation was approximately five percent, much smaller than the overall level of the signal. The robustness of more than 20,000 pixels was studied.\u003C\/p\u003E\u003Cp\u003EA spatial resolution of 2.7 microns was recorded from the device samples tested so far. Wang believes the resolution could be improved by reducing the diameter of the nanowires \u2013 allowing more nanowires to be grown in a given space \u2013 and by using a high-temperature fabrication process.\u003C\/p\u003E\u003Cp\u003EIn addition to Wang, the research team also included Caofeng Pan, Lin Dong, Guang Zhu, Simiao Niu, Ruomeng Yo, Qing Yang and Ying Liu, all associated with Georgia Tech. In addition, Pan is associated with the Beijing Institute of Nanoenergy and Nanosystems in the Chinese Academy of Sciences.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-07ER46394; the National Science Foundation (NSF) under award CMMI-040367; and by the Knowledge Innovation program of the Chinese Academy of Sciences under KJCX2-YW-M13. The opinions and conclusions expressed are those of the authors and do not necessarily represent the official views of the DOE or NSF.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Caofeng Pan, et al., \u0022High resolution electroluminescent imaging of pressure distribution using a piezoelectric nanowire-LED array,\u0022 (Nature Photonics 2013). \u003Ca href=\u0022http:\/\/dx.doi.org\/10.1038\/nphoton.2013.191\u0022\u003Ehttp:\/\/dx.doi.org\/10.1038\/nphoton.2013.191\u003C\/a\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\u0026nbsp; 30332-0181\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\u003Cbr \/\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EGeorgia Tech researchers want to put your signature up in lights. Using thousands of nanometer-scale wires, the researchers have developed a sensor device that converts mechanical pressure \u2013 from a signature or a fingerprint \u2013 directly into light signals that can be captured and processed optically.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have developed a sensor device that converts mechanical pressure directly into light signals."}],"uid":"27303","created_gmt":"2013-08-10 13:07:04","changed_gmt":"2016-10-08 03:14:42","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-08-11T00:00:00-04:00","iso_date":"2013-08-11T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"228121":{"id":"228121","type":"image","title":"Piezo-phototronic LEDs2","body":null,"created":"1449243566","gmt_created":"2015-12-04 15:39:26","changed":"1475894899","gmt_changed":"2016-10-08 02:48:19","alt":"Piezo-phototronic LEDs2","file":{"fid":"197463","name":"piezo-phototronic137.jpg","image_path":"\/sites\/default\/files\/images\/piezo-phototronic137_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/piezo-phototronic137_0.jpg","mime":"image\/jpeg","size":1053938,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/piezo-phototronic137_0.jpg?itok=PiHW9wgi"}},"228111":{"id":"228111","type":"image","title":"Piezo-phototronic LEDs","body":null,"created":"1449243566","gmt_created":"2015-12-04 15:39:26","changed":"1475894899","gmt_changed":"2016-10-08 02:48:19","alt":"Piezo-phototronic LEDs","file":{"fid":"197462","name":"piezo-phototronic105.jpg","image_path":"\/sites\/default\/files\/images\/piezo-phototronic105_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/piezo-phototronic105_0.jpg","mime":"image\/jpeg","size":1305079,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/piezo-phototronic105_0.jpg?itok=nqtHxB6V"}},"228131":{"id":"228131","type":"image","title":"Piezo-phototronic LED schematic","body":null,"created":"1449243582","gmt_created":"2015-12-04 15:39:42","changed":"1475894774","gmt_changed":"2016-10-08 02:46:14","alt":"Piezo-phototronic LED schematic","file":{"fid":"197464","name":"piezo-phototronic_device.jpg","image_path":"\/sites\/default\/files\/images\/piezo-phototronic_device_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/piezo-phototronic_device_0.jpg","mime":"image\/jpeg","size":295059,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/piezo-phototronic_device_0.jpg?itok=p8EoCzZn"}}},"media_ids":["228121","228111","228131"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"14922","name":"LED"},{"id":"4497","name":"Materials Science and Engineering"},{"id":"2502","name":"nanowire"},{"id":"71221","name":"piezo-phototronics"},{"id":"365","name":"Research"},{"id":"13751","name":"Zhong Lin Wang"},{"id":"7649","name":"zinc oxide"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39471","name":"Materials"}],"news_room_topics":[],"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":""}}}