Nanotechnology Now







Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > “Waviness” Explains Why Carbon Nanotube Forests Have Low Stiffness

This montage includes images of carbon nanotube forests. New research explains why the CNT forests have less stiffness than expected.
Images courtesy of Justin Chow
This montage includes images of carbon nanotube forests. New research explains why the CNT forests have less stiffness than expected.

Images courtesy of Justin Chow

Abstract:
A new study has found that "waviness" in forests of vertically-aligned carbon nanotubes dramatically reduces their stiffness, answering a long-standing question surrounding the tiny structures. Instead of being a detriment, the waviness may make the nanotube arrays more compliant and therefore useful as thermal interface material for conducting heat away from future high-powered integrated circuits.

“Waviness” Explains Why Carbon Nanotube Forests Have Low Stiffness

Atlanta, GA | Posted on October 1st, 2013

Measurements of nanotube stiffness, which is influenced by a property known as modulus, had suggested that forests of vertically-aligned nanotubes should have a much higher stiffness than what scientists were actually measuring. The reduced effective modulus had been blamed on uneven growth density, and on buckling of the nanotubes under compression.

However, based on experiments, scanning electron microscope (SEM) imaging and mathematical modeling, the new study found that kinked sections of nanotubes may be the primary mechanism reducing the modulus.

"We believe that the mechanism making these nanotubes more compliant is a tiny kinkiness in their structure," said Suresh Sitaraman, a professor in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. "Although they appear to be perfectly straight, under high magnification we found waviness in the carbon nanotubes that we believe accounts for the difference in what is measured versus what would be expected."

The research, which was supported by the Defense Advanced Research Projects Agency (DARPA), was published online August 31, 2013, in the journal Carbon. It will appear later in the journal's print issue.

Carbon nanotubes provide many attractive properties, including high electrical and thermal conductivity, and high strength. Individual carbon nanotubes have a modulus ranging from 100 gigapascals to 1.5 terapascals. Arrays of vertically-aligned carbon nanotubes with a low density would be expected to a have an effective modulus of at least five to 150 gigapascals, Sitaraman said, but scientists have typically measured values that are four orders or magnitude less - between one and 10 megapascals.

To understand what might be causing this variation, Sitaraman and Ph.D. students Nicholas Ginga and Wei Chen studied forests of carbon nanotubes grown atop a silicon substrate, then covered the tips of the structures with another layer of silicon. They then used sensitive test apparatus - a nanoindenter - to compress samples of the nanotubes and measure their stiffness. Alternately, they also placed samples of the silicon-nanotube sandwiches under tensile stress - pulling them apart instead of compressing them.

What they found was that the effective modulus remained low - as much as 10,000 times less than expected - regardless of whether the nanotube sandwiches were compressed or pulled apart. That suggests growth issues, or buckling, could not fully account for the differences observed.

To look for potential explanations, the researchers examined the carbon nanotubes using scanning electron microscopes located in Georgia Tech's Institute for Electronics and Nanotechnology facilities. At magnification of 10,000 times, they saw the waviness in sections of the nanotubes.

"We found very tiny kinks in the carbon nanotubes," said Sitaraman. "Although they appeared to be perfectly straight, there was waviness in them. The more waviness we saw, the lower their stiffness was."

They also noted that under compression, the nanotubes contact one another, influencing nanotube behavior. These observations were modeled mathematically to help explain what was being seen across the different conditions studied.

"We took into account the contact between the carbon nanotubes," said Chen. "This allowed us to investigate the extreme conditions under which the deformation of nanotubes is constrained by the presence of neighboring nanotubes in the forest."

Though the loss of modulus might seem like a problem, it actually may be helpful in thermal management applications, Sitaraman said. The compliance of the nanotubes allows them to connect to a silicon integrated circuit on one side, and be bonded to a copper heat spreader on the other side. The flexibility of the nanotubes allows them to move as the top and bottom structures expand and contract at different rates due to temperature changes.

"The beauty of the carbon nanotubes is that they act like springs between the silicon chip and the copper heat spreader," said Sitaraman. "They can conduct lots of heat because of good thermal properties, and at the same time, they are supple and compliant."

Carbon nanotubes have extraordinarily high thermal conductivity, as much as ten times that of copper, making them ideal for drawing heat away from the chips.

"The demand for heat removal from chips is continuing to increase," said Ginga. "Industry has been looking for new materials and new techniques to add to their toolbox for heat transfer. Different approaches will be needed for different devices, and this provides the industry with a new way to address the challenge."

####

For more information, please click here

Contacts:
Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia 30332-0181 USA

John Toon

404-894-6986
or
Brett Israel

404-385-1933

Copyright © Georgia Institute of Technology

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

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

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

Arrowhead to Present at 2015 Barclays Global Healthcare Conference March 4th, 2015

Chip Technology

Experiment and theory unite at last in debate over microbial nanowires: New model and experiments settle debate over metallic-like conductivity of microbial nanowires in bacterium March 4th, 2015

Magnetic vortices in nanodisks reveal information: Researchers from Dresden and Jülich use microwaves to read out information from smallest storage devices 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

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

Nanoelectronics

New nanowire structure absorbs light efficiently: Dual-type nanowire arrays can be used in applications such as LEDs and solar cells February 25th, 2015

Ultra-thin nanowires can trap electron 'twisters' that disrupt superconductors February 24th, 2015

Improved fire detection with new ultra-sensitive, ultraviolet light sensor February 17th, 2015

Nanotechnology facility planned in Lund, Sweden: A production facility for start-ups in the field of nanotechnology may be built in the Science Village in Lund, a world-class research and innovation village that is also home to ESS, the European Spallation Source February 15th, 2015

Discoveries

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

Experiment and theory unite at last in debate over microbial nanowires: New model and experiments settle debate over metallic-like conductivity of microbial nanowires in bacterium March 4th, 2015

Magnetic vortices in nanodisks reveal information: Researchers from Dresden and Jülich use microwaves to read out information from smallest storage devices March 4th, 2015

CiQUS researchers obtain high-quality perovskites over large areas by a chemical method March 4th, 2015

Announcements

Experiment and theory unite at last in debate over microbial nanowires: New model and experiments settle debate over metallic-like conductivity of microbial nanowires in bacterium March 4th, 2015

Magnetic vortices in nanodisks reveal information: Researchers from Dresden and Jülich use microwaves to read out information from smallest storage devices March 4th, 2015

CiQUS researchers obtain high-quality perovskites over large areas by a chemical method March 4th, 2015

Arrowhead to Present at 2015 Barclays Global Healthcare Conference March 4th, 2015

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

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

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

Experiment and theory unite at last in debate over microbial nanowires: New model and experiments settle debate over metallic-like conductivity of microbial nanowires in bacterium March 4th, 2015

Magnetic vortices in nanodisks reveal information: Researchers from Dresden and Jülich use microwaves to read out information from smallest storage devices March 4th, 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