Nanotechnology Now







Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Scientists solve mystery of colorful armchair nanotubes: Rice University researchers tag excitons in search for hues' clues

Armchair-enriched batches of nanotubes show their colors in an array of varying types. The vial at left is a mix of nanotubes straight from the furnace, suspended in liquid. The vials at right show nanotubes after separation through ultracentrifugation. Excitons absorb light in particular frequencies that depend on the diameter of the tube; the mix of colors not absorbed are what the eye sees. (Credit: Erik Hároz/Rice University)
Armchair-enriched batches of nanotubes show their colors in an array of varying types. The vial at left is a mix of nanotubes straight from the furnace, suspended in liquid. The vials at right show nanotubes after separation through ultracentrifugation. Excitons absorb light in particular frequencies that depend on the diameter of the tube; the mix of colors not absorbed are what the eye sees.

(Credit: Erik Hároz/Rice University)

Abstract:
Rice University researchers have figured out what gives armchair nanotubes their unique bright colors: hydrogren-like objects called excitons.

Scientists solve mystery of colorful armchair nanotubes: Rice University researchers tag excitons in search for hues' clues

Houston, TX | Posted on January 9th, 2012

Their findings appear in the online edition of the Journal of the American Chemical Society.

Armchair carbon nanotubes - so named for the "U"-shaped configuration of the atoms at their uncapped tips - are one-dimensional metals and have no band gap. This means electrons flow from one end to the other with little resistivity, the very property that may someday make armchair quantum wires possible.

The Rice researchers show armchair nanotubes absorb light like semiconductors. An electron is promoted from an immobile state to a conducting state by absorbing photons and leaving behind a positively charged "hole," said Rice physicist Junichiro Kono. The new electron-hole pair forms an exciton, which has a neutral charge.

"The excitons are created by the absorption of a particular wavelength of light," said graduate student and lead author Erik Hároz. "What your eye sees is the light that's left over; the nanotubes take a portion of the visible spectrum out." The diameter of the nanotube determines which parts of the visible spectrum are absorbed; this absorption accounts for the rainbow of colors seen among different batches of nanotubes.

Scientists have realized that gold and silver nanoparticles could be manipulated to reflect brilliant hues - a property that let artisans who had no notions of "nano" create stained glass windows for medieval cathedrals. Depending on their size, the particles absorbed and emitted light of particular colors due to a phenomenon known as plasma resonance.

In more recent times, researchers noticed semiconducting nanoparticles, also known as quantum dots, show colors determined by their size-dependent band gaps.

But plasma resonance happens at wavelengths outside the visible spectrum in metallic carbon nanotubes. And armchair nanotubes don't have band gaps.

Kono's lab ultimately determined that excitons are the source of color in batches of pure armchair nanotubes suspended in solution.

The results seem counterintuitive, Kono said, because excitons are characteristic of semiconductors, not metals. Kono is a professor of electrical and computer engineering and of physics and astronomy.

While armchair nanotubes don't have band gaps, they do have a unique electronic structure that favors particular wavelengths for light absorption, he said.

"In armchair nanotubes, the conduction and valence bands touch each other," Kono said. "The one-dimensionality, combined with its unique energy dispersion, makes it a metal. But the bands develop what's called a van Hove singularity," which appears as a peak in the density of states in a one-dimensional solid. "So there are lots of electronic states concentrated around this singularity."

Exciton resonance tends to occur around these singularities when hit with light, and the stronger the resonance, the more distinguished the color. "It's an unusual quality of these particular one-dimensional materials that these excitons can actually exist," Hároz said. "In most metals, that's not possible; there's not enough Coulomb interaction between the electron and the hole for an exciton to be stable."

The new paper follows on the heels of work by Kono and his team to create batches of pure single-walled carbon nanotubes through ultracentrifugation. In that process, nanotubes were spun in a mix of solutions with different densities up to 250,000 times the force of gravity. The tubes naturally gravitated toward separated solutions that matched their own densities to create a colorful "nano parfait."

As a byproduct of their current work, the researchers proved their ability to produce purified armchair nanotubes from a variety of synthesis techniques. They now hope to extend their investigation of the optical properties of armchairs beyond visible light. "Ultimately, we'd like to make one collective spectrum that includes frequency ranges all the way from ultraviolet to terahertz," Hároz said. "From that, we can know, optically, almost everything about these nanotubes."

Co-authors of the paper include Robert Hauge, a distinguished faculty fellow in chemistry at Rice; Rice alumnus Benjamin Lu; and professors Pavel Nikolaev and Sivaram Arepalli of Sungkyunkwan University, Suwon, Korea.

The research was supported by the Department of Energy, the Robert A. Welch Foundation, the Air Force Research Laboratory and the World Class University Program at Sungkyunkwan University.

####

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 less than 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


Mike Williams
713-348-6728

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

Read the abstract at:

Related News Press

News and information

MIG Takes a Roll-Up-Your-Sleeves Approach with Revamped MEMS/Sensors Technical Event -- MIG welcomes technologists to MEMS Technical Congress, emphasizes working groups and breakout sessions on emerging MEMS & sensors, tech transfer and integration March 6th, 2015

Phenom-World announces the Phenom XL, world’s fastest desktop SEM to handle large samples March 6th, 2015

Air Bearing Stage / Systems Introduced by PI at Photonics West March 6th, 2015

Consistent Scalable Functionalised Graphene Capacity March 5th, 2015

Imaging

Phenom-World announces the Phenom XL, world’s fastest desktop SEM to handle large samples March 6th, 2015

Govt.-Legislation/Regulation/Funding/Policy

New research could lead to more efficient electrical energy storage March 4th, 2015

Energy-generating cloth could replace batteries in wearable devices March 4th, 2015

The taming of magnetic vortices: Unified theory for skyrmion-materials March 3rd, 2015

Black phosphorus is new 'wonder material' for improving optical communication March 3rd, 2015

Nanotubes/Buckyballs

Researchers turn unzipped nanotubes into possible alternative for platinum: Aerogel catalyst shows promise for fuel cells March 2nd, 2015

Chromium-Centered Cycloparaphenylene Rings as New Tools for Making Functionalized Nanocarbons February 24th, 2015

Building tailor-made DNA nanotubes step by step: New, block-by-block assembly method could pave way for applications in opto-electronics, drug delivery February 23rd, 2015

Half spheres for molecular circuits: Corannulene shows promising electronic properties February 17th, 2015

Discoveries

Enhanced Graphene Components for Next Generation Racing Yacht March 5th, 2015

American Chemical Society Presidential Symposia: nanoscience, international chemistry March 5th, 2015

Strength in numbers: Researchers develop the first-ever quantum device that detects and corrects its own errors March 4th, 2015

New research could lead to more efficient electrical energy storage March 4th, 2015

Announcements

MIG Takes a Roll-Up-Your-Sleeves Approach with Revamped MEMS/Sensors Technical Event -- MIG welcomes technologists to MEMS Technical Congress, emphasizes working groups and breakout sessions on emerging MEMS & sensors, tech transfer and integration March 6th, 2015

Phenom-World announces the Phenom XL, world’s fastest desktop SEM to handle large samples March 6th, 2015

Air Bearing Stage / Systems Introduced by PI at Photonics West March 6th, 2015

Get ready for NanoDays! March 5th, 2015

Military

Black phosphorus is new 'wonder material' for improving optical communication March 3rd, 2015

Researchers turn unzipped nanotubes into possible alternative for platinum: Aerogel catalyst shows promise for fuel cells March 2nd, 2015

Simulating superconducting materials with ultracold atoms: Rice physicists build superconductor analog, observe antiferromagnetic order February 23rd, 2015

New nanogel for drug delivery: Self-healing gel can be injected into the body and act as a long-term drug depot February 19th, 2015

Quantum Dots/Rods

Optical nanoantennas set the stage for a NEMS lab-on-a-chip revolution February 24th, 2015

QD Vision Named Edison Award Finalist for Innovative Color IQ™ Quantum Dot Technology February 23rd, 2015

Ocean Optics Names Winner of 2015 Young Investigator Award: Cash prize and grant awarded during SPIE BiOS/Photonics West 2015 conference February 21st, 2015

Rediscovering spontaneous light emission: Berkeley researchers develop optical antenna for LEDs February 3rd, 2015

Research partnerships

French Institutes IRT Nanoelec and CMP Team up to Offer World’s First Service for Post-process 3D Technologies on Multi-Project-Wafer March 5th, 2015

New research could lead to more efficient electrical energy storage March 4th, 2015

Cambrios and Heraeus Jointly Create New, High-Conductivity Transparent Conductors: Two Companies' Combined Products Dramatically Extend Flexible Substrate Capabilities for Next-Generation Mass-Market Technology Products March 3rd, 2015

The taming of magnetic vortices: Unified theory for skyrmion-materials March 3rd, 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