Home > Press > Growing Nanowires Horizontally Yields New Benefit:: 'Nano-LEDs'
 |
Transmission electron microscope image of “nano LEDs” emitting light.
Credit: NIST |
Abstract:
While refining their novel method for making nanoscale wires, chemists at the National Institute of Standards and Technology (NIST) discovered an unexpected bonus—a new way to create nanowires that produce light similar to that from light-emitting diodes (LEDs). These "nano-LEDs" may one day have their light-emission abilities put to work serving miniature devices such as nanogenerators or lab-on-a-chip systems.
Growing Nanowires Horizontally Yields New Benefit:: 'Nano-LEDs'
Gaithersburg, MD | Posted on September 29th, 2010
Nanowires typically are "grown" by the controlled deposition of molecules—zinc oxide, for example—from a gas onto a base material, a process called chemical vapor deposition (CVD). Most CVD techniques form nanowires that rise vertically from the surface like brush bristles. Because the wire only contacts the substrate at one end, it tends not to share characteristics with the substrate material—a less-than-preferred trait because the exact composition of the nanowire will then be hard to define. Vertical growth also produces a dense forest of nanowires, making it difficult to find and re-position individual wires of superior quality. To remedy these shortcomings, NIST chemists Babak Nikoobakht and Andrew Herzing developed a "surface-directed" method for growing nanowires horizontally across the substrate (see "NIST Demos Industrial-Grade Nanowire Device Fabrication" NIST Tech Beat, Oct. 25, 2007, at www.nist.gov/public_affairs/techbeat/tb2007_1025.htm#nanowire).
Like many vertical growth CVD methods, the NIST fabrication technique uses gold as a catalyst for crystal formation. The difference is that the gold deposited in the NIST method is heated to 900 degrees Celsius (1,652 degrees Fahrenheit), converting it to a nanoparticle that serves as growth site and medium for the crystallization of zinc oxide molecules. As the zinc oxide nanocrystal grows, it pushes the gold nanoparticle along the surface of the substrate (in this experiment, gallium nitride) to form a nanowire that grows horizontally across the substrate and so exhibits properties strongly influenced by its base material.
In recent work published in ACS Nano,* Nikoobakht and Herzing increased the thickness of the gold catalyst nanoparticle from less than 8 nanometers to approximately 20 nanometers. The change resulted in nanowires that grew a secondary structure, a shark-like "dorsal fin" (referred to as a "nanowall") where the zinc oxide portion is electron-rich and the gallium nitride portion is electron-poor. The interface between these two materials—known as a p-n heterojunction—allows electrons to flow across it when the nanowire-nanowall combination was charged with electricity. In turn, the movement of electrons produced light and led the researchers to dub it a "nano LED."
Unlike previous techniques for producing heterojunctions, the NIST "surface-directed" fabrication method makes it easy to locate individual heterojunctions on the surface. This feature is especially useful when a large number of heterojunctions must be grouped in an array so that they can be electrically charged as a light-emitting unit.
Transmission electron microscope (TEM) examination of the zinc oxide-gallium nitride nanowires and nanowalls revealed few structural defects in the nanowires and very distinct p-n heterojunctions in the nanowalls, both affirmations of the effectiveness of the NIST "surface directed" fabrication method.
Nikoobakht and Herzing hope to improve the nano LEDs in future experiments using better geometry and material designs, and then apply them in the development of light sources and detectors useful in photonic devices or lab-on-a-chip platforms.
* B. Nikkoobakht and A. Herzing. Formation of planar arrays of one-dimensional p-n heterojunctions using surface-directed growth of nanowires and nanowalls. ACS Nano. Published online Sept. 15, 2010.
####
About NIST
The National Institute of Standards and Technology (NIST) is an agency of the U.S. Commerce Department.
For more information, please click here
Contacts:
Michael E. Newman
301-975-3025
Copyright © NIST
If you have a comment, please
Contact us.
Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Bookmark:
News and information
Aspen Aerogels Announces $22.5 Million Private Placement May 18th, 2013
NanoInk, Inc. Assets To Be Sold May 18th, 2013
Beautiful "flowers" self-assemble in a beaker: Elaborate nanostructures blossom from a chemical reaction perfected at Harvard May 17th, 2013
Scientists capture first direct proof of Hofstadter butterfly effect May 17th, 2013
Display technology/LEDs/SS Lighting/OLEDs
Cambrios Taps Sriram Peruvemba to Oversee Worldwide Marketing May 8th, 2013
Microwave oven cooks up solar cell material: Nanocrystal semiconductor for photovoltaics, medical sensors, heat reuse May 6th, 2013
Cause of LED Efficiency Droop Finally Revealed: Researchers at UC Santa Barbara and École Polytechnique confirm that Auger recombination theory is responsible for LED droop phenomenon April 23rd, 2013
New research findings open door to zinc-oxide-based UV lasers, LED devices April 23rd, 2013
Govt.-Legislation/Regulation/Funding/Policy
Beautiful "flowers" self-assemble in a beaker: Elaborate nanostructures blossom from a chemical reaction perfected at Harvard May 17th, 2013
Artificial Forest for Solar Water-Splitting: Berkeley Lab Researchers Report First Fully Integrated Artificial Photosynthesis Nanosystem May 17th, 2013
Moth-Inspired Nanostructures Take the Color Out of Thin Films May 17th, 2013
NIA Public Briefing: Nanotechnology and the Council of Europe May 17th, 2013
Discoveries
Beautiful "flowers" self-assemble in a beaker: Elaborate nanostructures blossom from a chemical reaction perfected at Harvard May 17th, 2013
Artificial Forest for Solar Water-Splitting: Berkeley Lab Researchers Report First Fully Integrated Artificial Photosynthesis Nanosystem May 17th, 2013
Moth-Inspired Nanostructures Take the Color Out of Thin Films May 17th, 2013
Scientists capture first direct proof of Hofstadter butterfly effect May 17th, 2013
Announcements
Aspen Aerogels Announces $22.5 Million Private Placement May 18th, 2013
NanoInk, Inc. Assets To Be Sold May 18th, 2013
NIA Public Briefing: Nanotechnology and the Council of Europe May 17th, 2013
Scientists capture first direct proof of Hofstadter butterfly effect May 17th, 2013
Energy
Artificial Forest for Solar Water-Splitting: Berkeley Lab Researchers Report First Fully Integrated Artificial Photosynthesis Nanosystem May 17th, 2013
Moth-Inspired Nanostructures Take the Color Out of Thin Films May 17th, 2013
Solar panels as inexpensive as paint? It’s possible due to research at UB, elsewhere May 13th, 2013
Flawed Diamonds Promise Sensory Perfection: Berkeley Lab researchers and their colleagues extend electron spin in diamond for incredibly tiny magnetic detectors May 10th, 2013
Battery Technology/Capacitors/Generators/Piezoelectrics
Add boron for better batteries: Rice University theorists say graphene-boron mix shows promise for lithium-ion batteries May 17th, 2013
New Mechanism Converts Natural Gas to Energy Faster, Captures CO2 May 7th, 2013
Microwave oven cooks up solar cell material: Nanocrystal semiconductor for photovoltaics, medical sensors, heat reuse May 6th, 2013
Improving materials that convert heat to electricity and vice-versa May 5th, 2013