Nanotechnology Now







Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Reversible doping: Hydrogen flips switch on vanadium oxide: Rice University physicists find reversible way to alter VO2's unique electronic about-face

Gold electrodes rest on clumps of vanadium oxide (VO2) wires that are each about 1,000 times smaller than a human hair. When baked in the presence of hydrogen gas, the wires next to the electrodes (dark region) absorb hydrogen and exhibit altered electronic behavior.
CREDIT: Jiang Wei/Rice University
Gold electrodes rest on clumps of vanadium oxide (VO2) wires that are each about 1,000 times smaller than a human hair. When baked in the presence of hydrogen gas, the wires next to the electrodes (dark region) absorb hydrogen and exhibit altered electronic behavior.

CREDIT: Jiang Wei/Rice University

Abstract:
If you are not a condensed matter physicist, vanadium oxide (VO2) may be the coolest material you've never heard of. It's a metal. It's an insulator. It's a window coating and an optical switch. And thanks to a new study by physicists at Rice University, scientists have a new way to reversibly alter VO2's electronic properties by treating it with one of the simplest substances -- hydrogen.

Reversible doping: Hydrogen flips switch on vanadium oxide: Rice University physicists find reversible way to alter VO2's unique electronic about-face

Houston, TX | Posted on May 21st, 2012

So what is VO2? It's an oxidized form of the metal vanadium, an ingredient in hardened steel. When oxygen reacts with vanadium to form VO2, the atoms form crystals that look like long rectangular boxes. The vanadium atoms line up along the four edges of the box in regularly spaced rows. A single crystal of VO2 can have many of these boxes lined up side by side, and the crystals conduct electricity like wire as long as they are kept warm.

"The weird thing about this material is that if you cool it, when you get to 67 degrees Celsius, it goes through a phase transition that is both electronic and structural," said Rice's Douglas Natelson, lead co-author of the study in this week's Nature Nanotechnology. "Structurally, the vanadium atoms pair up and each pair is slightly canted, so you no longer have these long chains. When the phase changes, and these pairings take place, the material changes from being a electrical conductor to an electrical insulator."

While other materials exhibit a similar electronic about-face, VO2 is unique in that the change occurs at a relatively modest temperature -- around 153 degrees Fahrenheit -- and sometimes at incredible speed -- less than a trillionth of second. In recent years, scientists have put these quirky properties to work. In 2004, a group in London used VO2 to design a temperature-sensitive window coating that could absorb sunlight on cold days and turn reflective on hot days. And electronics researchers are also working to create optical switches from VO2.

"As an experimental physicist, VO2 is intriguing because the detailed physics of the material are still not well understood, and theoretical models alone cannot give us the answers," said Natelson, professor of physics and astronomy and of electrical and computer engineering at Rice. "Experiments are key to understanding this."

In 2010, Natelson and postdoctoral research associate Jiang Wei began to systematically study the phase changes in VO2. Wei and graduate student Heng Ji began by using a process called vapor deposition to grow VO2 wires that were about 1,000 times smaller than a human hair. One set of experiments on wires that had been baked in the presence of hydrogen gas returned particularly odd readings. Wei, Ji and Natelson determined that the hydrogen was apparently modifying the VO2 nanowires, but only those in contact with metal electrodes.

"The gold electrodes we were using to supply current to the experiment were acting as a catalyst that split the hydrogen gas molecules into atomic hydrogen, which could then diffuse into channels in the VO2," Natelson said. "It appears that the hydrogen is taken up into the VO2 crystals, and this changes their electronic properties. If a little hydrogen is added, the phase transition happens at a slightly lower temperature, and the insulating phase becomes more conductive. If enough hydrogen is added, the transition to the insulating phase disappears altogether."

To gain insight into just how the hydrogen is able to alter the transition, the experimenters consulted with theoretical physicist Andriy Nevidomskyy, assistant professor of physics and astronomy at Rice. Nevidomskyy's calculations showed that the hydrogen changes the amount of charge in the VO2 material and also forces the crystal to expand slightly. Both of these effects favor the metallic state.

This is not the first time physicists have lowered the transition temperature of VO2 by adding other materials -- a technique known as "doping." But Natelson said Rice's hydrogen doping is unique in that it is completely reversible: To remove the hydrogen, the material simply has to be baked in an oven at moderate temperature.

"On the applied side, there may be a number of applications for this, like ultrasensitive hydrogen sensors," Natelson said. "But the more immediate payoff will likely be in helping us to better understand the physics involved in the VO2 phase transition. If we can find out exactly how much hydrogen is required to shut down the transition, then we will have a knob that we can turn to systematically raise or lower the temperature in future experiments."

Research co-authors include Natelson, Wei, Ji, Nevidomskyy and Wenhua Guo, transmission electron microscope manager at Rice's Shared Equipment Authority. The research was funded by the Department of Energy's Office of Science and an Evans Atwell/Welch postdoctoral fellowship from the Robert A. Welch Foundation.

####

About Rice University
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its "unconventional wisdom." With 3,708 undergraduates and 2,374 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for "best value" among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to www.rice.edu/nationalmedia/Rice.pdf.

For more information, please click here

Contacts:
David Ruth
713-348-6327


Jade Boyd
713-348-6778

Copyright © Rice University

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:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

A copy of the Nature Nanomaterials paper is available at:

Related News Press

News and information

Crystal light: New light-converting materials point to cheaper, more efficient solar power: University of Toronto engineers study first single crystal perovskites for new solar cell and LED applications January 30th, 2015

Hiden Gas Analysers at PITTCON 2015 | Visit us on Booth No. 1127 January 29th, 2015

Discovery Channel taps Angstron Materials for segment featuring graphene advances January 29th, 2015

Asteroid Mining 101: A New Book by World-Renowned Expert Dr. John S. Lewis - Exclusive Sneak-Peek Opportunity for Book Reviewers and Media January 29th, 2015

Physics

New pathway to valleytronics January 27th, 2015

Visualizing interacting electrons in a molecule: Scientists at Aalto University and the University of Zurich have succeeded in directly imaging how electrons interact within a single molecule January 26th, 2015

Nano-beaker offers insight into the condensation of atoms January 21st, 2015

Atoms can be in 2 places at the same time: Researchers of the University of Bonn have shown that cesium atoms do not follow well-defined paths January 20th, 2015

Govt.-Legislation/Regulation/Funding/Policy

Nanoscale Mirrored Cavities Amplify, Connect Quantum Memories: Advance could lead to quantum computing and the secure transfer of information over long-distance fiber optic networks January 28th, 2015

Detecting chemical weapons with a color-changing film January 28th, 2015

'Bulletproof' battery: Kevlar membrane for safer, thinner lithium rechargeables January 28th, 2015

Researchers Make Magnetic Graphene: UC Riverside research could lead to new multi-functional electronic devices January 27th, 2015

Chip Technology

Creating new materials with quantum effects for electronics January 29th, 2015

Advantest to Exhibit at SEMICON Korea in Seoul, South Korea February 4-6 Showcasing Broad Portfolio of Semiconductor Products, Technologies and Solutions January 29th, 2015

Nanometrics to Present at the Stifel 2015 Technology, Internet and Media Conference January 27th, 2015

New pathway to valleytronics January 27th, 2015

Discoveries

Crystal light: New light-converting materials point to cheaper, more efficient solar power: University of Toronto engineers study first single crystal perovskites for new solar cell and LED applications January 30th, 2015

Creating new materials with quantum effects for electronics January 29th, 2015

Los Alamos Develops New Technique for Growing High-Efficiency Perovskite Solar Cells: Researchers’ crystal-production insights resolve manufacturing difficulty January 29th, 2015

Iranian Scientists Use MOFs to Eliminate Dye Pollutants January 29th, 2015

Materials/Metamaterials

Crystal light: New light-converting materials point to cheaper, more efficient solar power: University of Toronto engineers study first single crystal perovskites for new solar cell and LED applications January 30th, 2015

The Original Frameless Shower Doors Installs DFI's FuseCube™ to Offer Hydrophobic Protective Coating as a Standard Feature: First DFI FuseCube™ Installed on the East Coast to Enable Key Differentiator for the Original Frameless Shower Doors January 29th, 2015

Creating new materials with quantum effects for electronics January 29th, 2015

Spider electro-combs its sticky nano-filaments January 28th, 2015

Announcements

Crystal light: New light-converting materials point to cheaper, more efficient solar power: University of Toronto engineers study first single crystal perovskites for new solar cell and LED applications January 30th, 2015

Park Systems Announces Innovations in Bio Cell Analysis with the Launch of Park NX-Bio, the only 3-in-1 Imaging Nanoscale Tool Available for Life Science Researchers January 29th, 2015

2015 Nanonics Image Contest January 29th, 2015

Iranian Scientists Use MOFs to Eliminate Dye Pollutants January 29th, 2015

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More










ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2015 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE