Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Theorists find mechanism behind nearly pure nanotubes from the unusual catalyst

27.07.2018

Growing a batch of carbon nanotubes that are all the same may not be as simple as researchers had hoped, according to Rice University scientists.

Rice materials theorist Boris Yakobson and his team bucked a theory that when growing nanotubes in a furnace, a catalyst with a specific atomic arrangement and symmetry would reliably make carbon nanotubes of like chirality, the angle of its carbon-atom lattice.


Rice University scientists have decoded the unusual growth characteristic of carbon nanotubes that start out as one chirality but switch to another, resulting in nearly homogenous batches of single-walled nanotubes. The nanotubes grow via chemical vapor deposition with a carbon-tungsten alloy catalyst.

Credit: Evgeni Penev/Rice University

Usage Restrictions: For news reporting purposes only.

Instead, they found the catalyst in question starts nanotubes with a variety of chiral angles but redirects almost all of them toward a fast-growing variant known as (12,6). The cause appears to be a Janus-like interface that is composed of armchair and zigzag segments - and ultimately changes how nanotubes grow.

Because chirality determines a nanotube's electrical properties, the ability to grow chiral-specific batches is a nanotechnology holy grail. It could lead to wires that, unlike copper or aluminum, transmit energy without loss. Nanotubes generally grow in random chiralities.

The Rice theoretical study detailed in the American Chemical Society journal Nano Letters could be a step toward catalysts that produce homogenous batches of nanotubes, Yakobson said.

Yakobson and colleagues Evgeni Penev and Ksenia Bets and graduate student Nitant Gupta tackled a conundrum presented by other experimentalists at a 2013 workshop who used an alloy of cobalt and tungsten to catalyze single-walled nanotubes. In that lab's batch, more than 90 percent of the nanotubes had a chirality of (12,6).

The numbers (12,6) are coordinates that refer to a nanotube's chiral vector. Carbon nanotubes are rolled-up sheets of two-dimensional graphene. Graphene is highly conductive, but when it is rolled into a tube, its conductivity depends on the angle -- or chirality -- of its hexagonal lattice.

Armchair nanotubes -- so called because of the armchair-like shape of their edges -- have identical chiral indices, like (9,9), and are highly desired for their perfect conductivity. They are unlike zigzag nanotubes, such as (16,0), which may be semiconductors. Turning a graphene sheet a mere 30 degrees will change the nanotube it forms from armchair to zigzag or vice versa.

Penev said the experimentalists explained their work "in a way which was puzzling from the very beginning. They said this catalyst has a specific symmetry that matches the (12,6) edge, so these nanotubes preferentially nucleate and grow. This was the emergence of the so-called symmetry matching idea of carbon nanotube selective growth.

"We read and digested that, but we still couldn't wrap our minds around it," he said.

Shortly after the 2013 conference, the Yakobson lab published its own theory of nanotube growth, which showed that the balance between two opposing forces -- the energy of the catalyst-nanotube contact and the speed at which atoms attach themselves to the growing tube at the interface -- are responsible for chirality.

Five years later, that turns out to be just as true in their new paper, though with a twist. The Rice calculations show that the alloy Co7W6 promotes the formation of the Janus-like interface that ensures the necessary kink at the edge and allows carbon atoms to attach themselves to the nanotube's foundation. But the catalyst also forces the nanotube to incorporate defects that alter its initial chirality midstream.

"We uncovered two things," Yakobson said. "One is that the carbon atom types at the base of the nanotube separate into armchair and zigzag segments. The second is the tendency for the formation of defects that drive the chirality, or helicity, change. That makes (12,6) a sort of transient attractor, at least during short experiments. If they were able to grow forever, (12,6) nanotubes would eventually switch to armchairs."

The unusual growth pattern might have been diagnosed much earlier if it weren't for an age-old typo that required some dogged detective work.

"The trouble was in a standard online database that gives the crystal structure of this cobalt-tungsten alloy," said Bets, co-lead author of the paper with Penev. "One entry was wrong. That messed up the structure so badly that we couldn't use it in our density functional theory calculations."

Once they found the error, Bets and co-author Gupta went back to the 1938 German paper that was first to correctly detail the structure of Co7W6. Even with that in hand, the team's calculations used every bit of computing power they could find to simulate the energetic connections between each atom in the catalyst and carbon feedstock.

"We figured out that if we had run the calculations in series instead of in parallel, they would have taken the equivalent of at least 2,000 years of computer time," Bets said.

"This paper is remarkable in many aspects: in the timing, the amount of detail and the surprises we found," Penev said. "We've never had a project like this. We don't yet know how this will be applicable to other materials, but we're working on it."

"There are four or five experimental papers, pretty recent ones, that also show a change of chirality during growth," Bets said. "In fact, because it's a probabilistic process, it's essentially unavoidable. But until now it's never been considered in the theoretical investigation of growth."

###

Yakobson is the Karl F. Hasselmann Professor of Materials Science and NanoEngineering and a professor of chemistry at Rice. Penev is an assistant research professor and Bets is a research administrator, both in the Department of Materials Science and NanoEngineering.

The National Science Foundation supported the research. Computing resources were provided by the National Energy Research Scientific Computing Center, supported by the Department of Energy Office of Science; the Department of Defense Supercomputing Resource Center; the NSF-supported XSEDE supercomputer; and the NSF-supported DAVinCI cluster at Rice, administered by the Center for Research Computing and procured in partnership with Rice's Ken Kennedy Institute for Information Technology.

Read the abstract at https://pubs.acs.org/doi/10.1021/acs.nanolett.8b02283

This news release can be found online at http://news.rice.edu/2018/07/26/two-faced-edge-makes-nanotubes-obey/

Follow Rice News and Media Relations via Twitter @RiceUNews

Related materials:

Scientists refine formula for nanotube types: http://news.rice.edu/2014/09/16/scientists-refine-formula-for-nanotube-types-2/

Yakobson Research Group: https://biygroup.blogs.rice.edu

Evgeni Penev bio: https://msne.rice.edu/content/evgeni-penev

Rice Department of Materials Science and NanoEngineering: https://engineering.rice.edu

George R. Brown School of Engineering: https://msne.rice.edu

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 home to the Baker Institute for Public Policy. With 3,970 undergraduates and 2,934 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for quality of life and for lots of race/class interaction and No. 2 for happiest students by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.com/RiceUniversityoverview.

Media Contact

David Ruth
david@rice.edu
713-348-6327

 @RiceUNews

http://news.rice.edu 

David Ruth | EurekAlert!
Further information:
http://dx.doi.org/10.1021/acs.nanolett.8b02283

Further reports about: Computing Materials Science NanoEngineering catalyst conductivity

More articles from Materials Sciences:

nachricht Molecular switch detects metals in the environment
15.08.2018 | Université de Genève

nachricht Breakthrough in nanoresearch - Quantum chains in graphene nanoribbons
09.08.2018 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

Unraveling the nature of 'whistlers' from space in the lab

15.08.2018 | Physics and Astronomy

Diving robots find Antarctic winter seas exhale surprising amounts of carbon dioxide

15.08.2018 | Earth Sciences

Early opaque universe linked to galaxy scarcity

15.08.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>