Scientists discover new method for creating high-yield single-walled carbon nanotubes

Oct 25, 2005

Cousins of the 1996 Nobel Prize-winning buckyball, carbon nanotubes have taken the nanotechnology industry by storm. Exhibiting extraordinary strength, flexibility and unique electrical, mechanical and optical properties, these hollow microscopic fibers are being integrated into numerous electronic and biological products—high-performance computer chips, combat jackets, bomb detectors and drug delivery devices for the treatment of diseases.

Pushing the field one step further, scientists at Stanford University have devised a novel method for growing vertical single-walled carbon nanotubes (SWNTs) on a large scale, a feat that has eluded researchers until now. By modifying the industry's standard approach to producing carbon-based materials—plasma-enhanced chemical vapor deposition (PECVD)—they achieved ultra-high-yield growth of SWNTs, thus increasing their application into commercial products. They report their research in the Oct. 26 issue of Proceedings of the National Academy of Sciences.

Carbon nanotubes are cylindrical molecules 2 nanometers in diameter—more than 10,000 times smaller than the width of a human hair. Since their discovery in 1991, multi-walled carbon nanotubes have been easily synthesized using several methods. Yet, large-scale production of smaller single-walled nanotubes into ordered films has remained intangible.

Given widespread commercial use of the PECVD method for economical, robust production of various materials by the semiconductor industry, scientists hoped to harness this same method for generating high-quality single-walled nanotubes. PECVD works by exposing substrates densely seeded with catalytic particles to a hydrocarbon gas such as methane, which should theoretically produce a plush carpet of carbon nanotubes. Previous attempts, however, have generated only sparse and inefficient synthesis of SWNTs.

Hongjie Dai, associate professor of chemistry, and his colleagues discovered the key component to attaining single-walled fibers—adding oxygen to the reaction.

"There is a dilemma here," Dai said. "What we found is that the carbon atoms are good and needed for nanotube growth, but the hydrogen atoms are bad. The carbon atoms try to form the nanotube's planar structure, while at the same time the hydrogen radicals are eating the carbon tube away. This was never realized before in nanotube synthesis."

Adding oxygen remedies the problem. By scavenging up the hydrogen radicals—creating a carbon-rich and hydrogen-deficient environment—growth is jumpstarted, spawning a vertical forest of nanotubes.

Using this method, Dai and his colleagues were able to create 4-inch wafers blanketed with SWNTs. In addition, they devised a method for lifting the nanotubes off their original growth substrate and transferring them onto a variety of more desirable mediums such as plastics and metals—materials incompatible with the high temperatures required for nanotube growth. These planted plastics and metals further expand the nanotubes' commercial utility.

Testing already has begun to determine the effectiveness of single-walled carbon nanotube wafers as a thermal interface material, conducting and dissipating heat away from computer chips. The researchers are pursuing additional applications as well.

Postdoctoral fellow Guangyu Zhang is lead author of the study. Other co-authors are chemistry graduate students David Mann, Li Zhang, Ali Javey, Yiming Li and Erhan Yenilmez, research associate Qian Wang and staff scientist James McVittie. James Gibbons, former dean of the School of Engineering, and Yoshio Nishi, director of the Stanford Nanofabrication Facility, both professors of electrical engineering, also contributed to the work.

The study was supported in part by the Global Climate and Energy Project at Stanford. The synthesized nanotubes may be used for hydrogen storage.

Source: Stanford University (by Anne Strehlow)

Explore further: A stretchy mesh heater for sore muscles

Related Stories

Graphene oxide biodegrades with help of human enzymes

Jun 02, 2015

Graphene Flagship researchers show how graphene oxide suspended in water biodegrades in a reaction catalysed by a human enzyme, with the effectiveness of the breakdown dependent on the colloidal stability ...

Carbon nanotubes grown in combustion flames

Jun 01, 2015

An international research team's theoretical simulation of the synthesis of single-walled carbon nanotubes has revealed important details of the mechanisms at play. This could lead to better ways to control ...

Manipulating cell membranes using nanotubes

Jun 01, 2015

Japanese researchers have developed a targeted method for opening up cell membranes in order to deliver drugs to, or manipulate the genes of, individual cells.

Recommended for you

A stretchy mesh heater for sore muscles

14 hours ago

If you suffer from chronic muscle pain a doctor will likely recommend for you to apply heat to the injury. But how do you effectively wrap that heat around a joint? Korean Scientists at the Center for Nanoparticle ...

Polymer mold makes perfect silicon nanostructures

17 hours ago

Using molds to shape things is as old as humanity. In the Bronze Age, the copper-tin alloy was melted and cast into weapons in ceramic molds. Today, injection and extrusion molding shape hot liquids into ...

Better memory with faster lasers

Jul 02, 2015

DVDs and Blu-ray disks contain so-called phase-change materials that morph from one atomic state to another after being struck with pulses of laser light, with data "recorded" in those two atomic states. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.