Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Measuring Excitement for Carbon Nanotubes

Ball and stick model of two crossing (10, 10) carbon nanotubes on a graphite surface.

Credit: Tobias Hertel, Institute for Physical Chemistry, University of Wurzburg
Ball and stick model of two crossing (10, 10) carbon nanotubes on a graphite surface.

Credit: Tobias Hertel, Institute for Physical Chemistry, University of Wurzburg

Abstract:
Studying light pulses in nanoscale molecules brings scientists closer to understanding properties that may lead to a multitude of applications

Measuring Excitement for Carbon Nanotubes

Arlington, VA | Posted on February 10th, 2009

Carbon is the fourth most abundant element in the universe by weight, and without it, there would be no life on Earth. Depending on its crystal structure--how its atoms bond together--carbon can form several different substances, ranging from sooty coal to glittering diamonds to slippery-smooth graphite.

Slice a chunk of graphite into a flat, single-atom thick sheet, and you get another form of carbon: graphene. Take a sheet of graphene and roll it up like a newspaper, and you get a carbon nanotube (CNT).

CNTs are nanoscale molecules made up of large numbers of carbon atoms, each bonded to three other atoms in a hexagonal (six-sided) pattern, resembling a roll of chicken wire. The pattern can be aligned with the tube's central axis, or it can be twisted. Although a CNT may reach a few centimeters in length, the entire tube is only a few nanometers across, or about 100,000 times thinner than a human hair. At this size, it behaves as if it were one-dimensional.

Promising Properties

So much for the what. But why are CNTs making headlines in fields as diverse as aerospace, opto-electronics and bio-medicine? In a word, properties. Because of their superior structural, chemical, optical and electrical properties, carbon nanotubes are among the most promising candidates for use in tomorrow's ever-shrinking technology.

Mechanically, CNTs are five to 50 times stronger than steel, even though they are incredibly small and light. They also conduct heat extremely well. But it's their optical and electrical characteristics that have many scientists and engineers proposing applications ranging from flexible electronics and photovoltaics, to sensing and fluorescent markers in life sciences.

"CNTs have potential for complementing or replacing many current technologies," said Oscar O. Bernal, NSF program director for condensed matter physics. "For instance, they could one day become the main components in lighting devices and consumer electronics. They could represent savings in energy usage and would have the advantage of being very small, allowing miniaturization beyond current limits."

According to Bernal, understanding how particles move through CNTs is one of the necessary steps in the process of developing new applications.

Tobias Hertel, chair for physical chemistry at the University of Würzburg, is developing an experimental tool to study the unique light-emitting properties of CNTs. Hertel began the work while an associate professor at the department of physics and astronomy at the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE), and is supported by a continuing grant from NSF.

Hertel, along with other scientists from Italy and Germany, recently published an article in Nature Physics, entitled, "Size and mobility of excitons in (6, 5) carbon nanotubes," which looks at how photons travel through a semiconductor type of CNT.

"CNTs become semiconducting or metallic depending on their specific diameter and twist," said Hertel. "In this case, we chose a chiral type nanotube, with chains of atoms curled like a corkscrew."

Chiral CNTs can be visualized as twisting a piece of chicken wire so that one hexagon overlaps another on both a different row AND a different column of the pattern. The amount and direction of twist in a CNT can be coded as (n, m), where n is the number of rows and m is the number of columns from the initial atom to the overlapping atom.

Pumping Photons

In order to study a single type of CNT, the scientists first learned how to separate them. Then, using a process called optical pumping, they flashed extremely fast laser light pulses (just femto-seconds in length) through the CNTs.

"Using these ultra-short laser pulses, we can study how energy pumped into the material is redistributed--that is, we learn about how the energy moves through the tubes," Hertel said."

Specifically, the scientists measured optical transitions, or changes in energy. "Say you ride an elevator to the top of a skyscraper: This takes energy, so you have undergone a transition from a low energy state to a high energy state," Hertel explained. "In carbon nanotubes, the transitions we studied also cost energy, which we provided in the form of photons, or light

The photons pumped into the CNTs created something known as an exciton. "Excitons are a type of higher energy state inside a solid body, in which a negatively charged electron is bound to a positively charged particle in much the same way that an electron can be tied to an atom," Hertel explained.

"The size of the exciton determines how it behaves," said Hertel. "For example, if you had a huge ship in a canal, it could move either upstream or downstream. However if the ship was tiny, it could also go sideways across the canal. Just as the size of a ship plays a decisive role for how it can move about in the canal, the size of an exciton affects its motion along a CNT."

Measuring Excitons

The scientists measured the size of the excitons by studying how many would fit into a nanotube. "Say we had a one-gallon sized container filled with marbles," Hertel said. "If we wanted to know how big each marble is, we could simply count the number of marbles in the container." So, for example, if there were 128 marbles, each one would take about as much space as one fluid ounce, since there are 128 fluid ounces in a gallon.

"We found the excitons to be of similar size as the width of the nanotubes, which means that they can either travel forward or backwards in the tubes but not sideways, similar to the big ship in the canal," Hertel said. "Theory had predicted only slightly smaller exciton size than what we observed, but it was nevertheless surprising to find they were so large. We interpret this as a manifestation of the truly one-dimensional character of excitons in CNTs."

In addition to size, the scientists studied the mobility of the excitons. "Mobility is crucial because it allows us to better understand what can happen to an exciton over its lifetime," Hertel explained. "If excitons have a large mobility, they are likely to travel all the way to the ends of CNTs--where some 'bad' things (like non-radiative decay) may happen to them. But we found that the mobility is actually rather small and that excitons don't travel all that far during their lifetime."

Theoretical predictions of exciton behavior in such systems are still rather difficult and need to be corroborated by experiments, Hertel believes.

Questions remain for the scientists. "Exploring the effect of the environment on exciton size and mobility is the next step," said Hertel. "Can we tailor the environment to alter the exciton size and mobility in a desired way?"
-- Holly Martin, National Science Foundation

Investigators
Tobias Hertel

Related Institutions/Organizations
Vanderbilt University

Locations
Tennessee

Related Programs
Condensed Matter Physics

####

For more information, please click here

Copyright © National Science Foundation

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 News Press

News and information

Chemical trickery corrals 'hyperactive' metal-oxide cluster December 8th, 2016

Researchers peer into atom-sized tunnels in hunt for better battery: May improve lithium ion for larger devices, like cars December 8th, 2016

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D: Up-close, real-time, chemical-sensitive 3-D imaging offers clues for reducing cost/improving performance of catalysts for fuel-cell-powered vehicles and other applications December 8th, 2016

Exotic insulator may hold clue to key mystery of modern physics: Johns Hopkins-led research shows material living between classical and quantum worlds December 8th, 2016

Display technology/LEDs/SS Lighting/OLEDs

Trace metal recombination centers kill LED efficiency: UCSB researchers warn that trace amounts of transition metal impurities act as recombination centers in gallium nitride semiconductors November 3rd, 2016

Diamond nanothread: Versatile new material could prove priceless for manufacturing: Would you dress in diamond nanothreads? It's not as far-fetched as you might think November 3rd, 2016

Researchers surprised at the unexpected hardness of gallium nitride: A Lehigh University team discovers that the widely used semiconducting material is almost as wear-resistant as diamonds October 31st, 2016

Inspiration from the ocean: An interdisciplinary team of researchers at UC Santa Barbara has developed a non-toxic, high-quality surface treatment for organic field-effect transistors October 18th, 2016

Govt.-Legislation/Regulation/Funding/Policy

Chemical trickery corrals 'hyperactive' metal-oxide cluster December 8th, 2016

Researchers peer into atom-sized tunnels in hunt for better battery: May improve lithium ion for larger devices, like cars December 8th, 2016

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D: Up-close, real-time, chemical-sensitive 3-D imaging offers clues for reducing cost/improving performance of catalysts for fuel-cell-powered vehicles and other applications December 8th, 2016

Exotic insulator may hold clue to key mystery of modern physics: Johns Hopkins-led research shows material living between classical and quantum worlds December 8th, 2016

Chip Technology

Chemical trickery corrals 'hyperactive' metal-oxide cluster December 8th, 2016

Leti IEDM 2016 Paper Clarifies Correlation between Endurance, Window Margin and Retention in RRAM for First Time: Paper Presented at IEDM 2016 Offers Ways to Reconcile High-cycling Requirements and Instability at High Temperatures in Resistive RAM December 6th, 2016

Tokyo Institute of Technology research: 3D solutions to energy savings in silicon power transistors December 6th, 2016

Physicists decipher electronic properties of materials in work that may change transistors December 6th, 2016

Discoveries

Chemical trickery corrals 'hyperactive' metal-oxide cluster December 8th, 2016

Researchers peer into atom-sized tunnels in hunt for better battery: May improve lithium ion for larger devices, like cars December 8th, 2016

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D: Up-close, real-time, chemical-sensitive 3-D imaging offers clues for reducing cost/improving performance of catalysts for fuel-cell-powered vehicles and other applications December 8th, 2016

Exotic insulator may hold clue to key mystery of modern physics: Johns Hopkins-led research shows material living between classical and quantum worlds December 8th, 2016

Announcements

Chemical trickery corrals 'hyperactive' metal-oxide cluster December 8th, 2016

Researchers peer into atom-sized tunnels in hunt for better battery: May improve lithium ion for larger devices, like cars December 8th, 2016

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D: Up-close, real-time, chemical-sensitive 3-D imaging offers clues for reducing cost/improving performance of catalysts for fuel-cell-powered vehicles and other applications December 8th, 2016

Exotic insulator may hold clue to key mystery of modern physics: Johns Hopkins-led research shows material living between classical and quantum worlds December 8th, 2016

Photonics/Optics/Lasers

ANU invention to inspire new night-vision specs December 7th, 2016

Shape matters when light meets atom: Mapping the interaction of a single atom with a single photon may inform design of quantum devices December 4th, 2016

Controlled electron pulses November 30th, 2016

New method for analyzing crystal structure: Exotic materials called photonic crystals reveal their internal characteristics with new method November 30th, 2016

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