{"73835":{"#nid":"73835","#data":{"type":"news","title":"Nanohelix Structure Provides New Building Block","body":[{"value":"\u003Cp\u003EA previously-unknown zinc oxide nanostructure that resembles the helical configuration of DNA could provide engineers with a new building block for creating nanometer-scale sensors, transducers, resonators and other devices that rely on electromechanical coupling.\n\u003C\/p\u003E\n\u003Cp\u003EBased on a superlattice composed of alternating single-crystal \u0022stripes\u0022 just a few nanometers wide, the \u0022nanohelix\u0022 structure is part of a family of nanobelts - tiny ribbon-like structures with semiconducting and piezoelectric properties - that were first reported in 2001.\n\u003C\/p\u003E\n\u003Cp\u003EThe nanohelices, which get their shape from twisting forces created by a small mismatch between the stripes, are produced using a vapor-solid growth process at high temperature.  Information about the growth and analysis of the new structures was reported in the September 9 issue of the journal \u003Cem\u003EScience\u003C\/em\u003E.\n\u003C\/p\u003E\n\u003Cp\u003EThe research was sponsored by the National Science Foundation, NASA Vehicle Systems Program, U.S. Department of Defense Research and Engineering (DDR\u0026amp;E), the Defense Advanced Research Projects Agency (DARPA), and the Chinese Academy of Sciences.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This structure provides a new building block for nanodevices,\u0022 said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology.  \u0022From them we can make resonators, place molecules on their surfaces to create frequency shifts - and because they are piezoelectric, make electromechanical couplings.  This adds a new structure to the toolbox of nanomaterials.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EWith their superlattices composed of many near-parallel single-crystal stripes each about 3.5 nanometers wide and offset about five degrees, the nanohelices are very different from the nanosprings and nanorings of zinc oxide reported by the same research group in \u003Cem\u003EScience\u003C\/em\u003E in 2004.  Nanosprings are composed of a single crystal whose shape is governed by balancing the electrostatic forces created by opposite electrical charges on their edges with the elastic deformation energy of the entire structure.\n\u003C\/p\u003E\n\u003Cp\u003EThe nanohelices reach lengths of up to 100 microns, with diameters from 300 to 700 nanometers and widths from 100 to 500 nanometers.  The nanohelices exist in both right- and left-handed versions, with production split approximately 50-50 between the two directions.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This is a brand new structure which shows a new growth model for nanomaterials,\u0022 Wang said.  \u0022But from the properties point of view, these are like the earlier nanobelts in having semiconducting and piezoelectric properties which makes them good for electromechanical coupling.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EHowever, unlike the earlier single-crystal nanosprings which are elastic, the nanohelices are rigid and retain their shape even when cut apart.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022When we first saw these structures, we were amazed by their perfection,\u0022 said Wang, who is also director of Georgia Tech\u0027s Center for Nanoscience and Nanotechnology.  \u0022Once you form a nanohelix, it is perfectly uniform.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe nanohelices are formed using a simple process similar to the one used for fabricating other nanobelts.  However, changing the growth conditions leads to entirely different structures.\n\u003C\/p\u003E\n\u003Cp\u003EZinc oxide (ZnO) powder is positioned inside an alumina tube in a horizontal high-temperature tube furnace.  Under vacuum, the material is heated to approximately 1,000 degrees Celsius, at which point an argon carrier gas is introduced.  Heating continues until the furnace reaches approximately 1,400 degrees.  The nanohelix structures form on a polycrystalline aluminum oxide (Al2O3) substrate in the furnace.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The key difference between growing nanohelices and the earlier types of nanobelt is that we control raising the temperature and when we introduce the carrier gas,\u0022 explained Wang.  \u0022With the earlier structures, we introduced the carrier gas flow at the beginning.  With these nanohelices, we only introduce the carrier gas when the temperature reaches a certain level.  That allows formation to begin in a vacuum, which is the key to controlling the helix formation.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EHeating the zinc oxide powder in a vacuum leads to formation of structures with polar surfaces.  When the carrier gas is introduced, the growth changes to minimize the polar surfaces, creating the superlattice structure with mismatches at the crystalline interfaces.  The nanohelices begin and end with conventional single-crystal nanobelt structures.  \u0022By the time the carrier gas is introduced, the crystal orientation is fixed, but the structures must continue to grow,\u0022 Wang explained.  \u0022Introducing the carrier gas initiates a transition to the superlattice structure.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EFormation of a nanohelix is initiated from a single-crystal stiff nanoribbon that is dominated by polar surfaces.  An abrupt structural transformation of the single-crystal nanoribbon into stripes of the superlattice-structured nanobelt leads to the formation of a uniform nanohelix due to rigid structural alteration, Wang said.  The superlattice nanobelt is a periodic, coherent, epitaxial and parallel assembly of two alternating stripes of zinc oxide crystals oriented with their c-axes perpendicular to one another.  Growth of the nanohelix is terminated by transforming the partially polar-surface-dominated nanobelt into a non-polar-surface-dominated single-crystal nanobelt.  \n\u003C\/p\u003E\n\u003Cp\u003E\u0022The data suggest that reducing the polar surfaces could be the driving force behind the formation of the superlattice structure, and the rigid structural rotation and twist caused by the superlattice results in the initiation and formation of the nanohelix,\u0022 Wang explained.\n\u003C\/p\u003E\n\u003Cp\u003EThe first dozen batches of nanohelices produced a yield of only about 10 percent, but Wang believes that can be improved over time.  \n\u003C\/p\u003E\n\u003Cp\u003EThus far, Wang\u0027s research team has produced nearly 20 different zinc oxide nanostructures, including nanobelts, aligned nanowires, nanotubes, nanopropellor arrays, nanobows, nanosprings, nanorings, nanobowls and others.  And there may yet be other structures discovered.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022You never know what other structures might be out there that could be added to this toolbox,\u0022 he said.  \u0022From the richness of this configuration and the complete properties, this is a unique material that could become the new material for nanotechnology following carbon nanotubes.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EA wideband semiconductor, zinc oxide also has interesting piezoelectric and optical properties, can produce ultraviolet laser emissions and shows electroluminescence at room temperature.  Those properties make it potentially useful in many applications.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022You can use it for spintronics, biomedical applications and many things you can make with silicon technology,\u0022 Wang said.  \u0022Zinc oxide is much cheaper and easier to work with than gallium nitride.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EOther collaborators on this work included Pu Xian Gao, Yong Ding, Wenjie Mai, William Hughes, and Changshi Lao, all in Georgia Tech\u0027s School of Materials Science and Engineering.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:john.toon@edi.gatech.edu\u0022\u003Ejohn.toon@edi.gatech.edu\u003C\/a\u003E); Fax: (404-894-4545) or Jane Sanders (404-894-2214); E-mail: (\u003Ca href=\u0022mailto:jane.sanders@edi.gatech.edu\u0022\u003Ejane.sanders@edi.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contact\u003C\/strong\u003E: Zhong L. Wang (404-894-8008); E-mail: (\u003Ca href=\u0022mailto:zhong.wang@mse.gatech.edu\u0022\u003Ezhong.wang@mse.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"New superlattice nanobelts could become sensors, transducers or resonators"}],"field_summary":[{"value":"A previously-unknown zinc oxide nanostructure that resembles the helical configuration of DNA could provide engineers with a new building block for creating nanometer-scale sensors, transducers, resonators and other devices that rely on electromechanical coupling.","format":"limited_html"}],"field_summary_sentence":[{"value":"Nanohelix structure could be basis for new devices"}],"uid":"27303","created_gmt":"2005-09-09 00:00:00","changed_gmt":"2016-10-08 03:03:38","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2005-09-09T00:00:00-04:00","iso_date":"2005-09-09T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"73836":{"id":"73836","type":"image","title":"Professor Zhong Lin Wang","body":null,"created":"1449178020","gmt_created":"2015-12-03 21:27:00","changed":"1475894681","gmt_changed":"2016-10-08 02:44:41"},"73837":{"id":"73837","type":"image","title":"Microscope image of nanohelices","body":null,"created":"1449178020","gmt_created":"2015-12-03 21:27:00","changed":"1475894681","gmt_changed":"2016-10-08 02:44:41"},"73838":{"id":"73838","type":"image","title":"Wang research team","body":null,"created":"1449178020","gmt_created":"2015-12-03 21:27:00","changed":"1475894681","gmt_changed":"2016-10-08 02:44:41"}},"media_ids":["73836","73837","73838"],"related_links":[{"url":"http:\/\/www.mse.gatech.edu\/","title":"Georgia Tech School of Materials Science and Engineering"},{"url":"http:\/\/www.nanoscience.gatech.edu\/zlwang\/","title":"Team Web site"},{"url":"http:\/\/www.mse.gatech.edu\/FacultyStaff\/MSE_Faculty_researchbios\/Wang\/wang.html","title":"Zhong Lin Wang"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[],"keywords":[],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\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","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}