Featured Research

from universities, journals, and other organizations

Dreidel-like dislocations lead to remarkable properties

Date:
December 14, 2012
Source:
Rice University
Summary:
Dreidel-shaped dislocations put a new spin on two-dimensional materials for advanced electronics, hinting at sub-nanometer signal paths.

Illustrations show the precise arrangement of atoms in dislocations in two-dimensional molybdenum/sulfur. Dislocations happen when two growing blooms of material come together at different angles in chemical vapor deposition. At a specific angle, the lines along which these dislocations form can become conductive.
Credit: Xiaolong Zou/Yakobson Lab

A new material structure predicted at Rice University offers the tantalizing possibility of a signal path smaller than the nanowires for advanced electronics now under development at Rice and elsewhere.

Theoretical physicist Boris Yakobson and postdoctoral fellow Xiaolong Zou were investigating the atomic-scale properties of two-dimensional materials when they found to their surprise that a particular formation, a grain boundary in metal disulfides, creates a metallic -- and therefore conducting -- path only a fraction of a nanometer wide.

That's basically the width of a chain of atoms, Yakobson said.

The discovery reported this week in the American Chemical Society journal Nano Letters sprang from an investigation of how atoms energetically relate to each other and form topological defects in two-dimensional semiconductors. In recent work, Yakobson's group has analyzed defects in graphene, the single-atom sheet of carbon that is under intense scrutiny by labs around the world.

But flat graphene has no band gap; electrons flow straight through. "There is a lot of effort to open a gap in graphene, but this is not easy," said Yakobson, Rice's Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science and professor of chemistry. "People are trying different ways, but none of them are straightforward. This motivated the search for other two-dimensional materials."

Molybdenum/sulfur (or tungsten/sulfur) materials are becoming interesting to scientists because they have a useful natural band gap, about two electron volts in the case of molybdenum/sulfur. And while they are technically two-dimensional materials, the energies at play force their atoms into a staggered arrangement.

"It's more complex than graphene," Yakobson said. "There's a layer of metal in the middle, with sulfur atoms above and below, but they're fully connected by covalent bonds in a honeycomb lattice, so it's one compound."

Chemical vapor deposition is typically used to grow such material; under high temperatures the atoms (like carbon for graphene) fall into line and form sheets. But when two such blooms appear and they meet, they don't necessarily line up. Where they merge, they form what are called "grain boundaries," akin to grains in wood that join at awkward angles. (Think of a branch meeting a tree trunk.) Those grain boundaries affect the electrical properties of the merged material.

Zou calculated those properties based on the atomic energies of the elements. In looking at the elemental bonds, the researchers found the expected "dislocations" where the energies force atoms out of their regular patterns. "Where the sheets meet, they cannot have an ideal lattice structure, so they have these stitches, the dislocations. Each grain boundary is just a series of these dislocations," Yakobson said.

It was only coincidence that the dislocations took on dreidel-like shapes for a paper published during Hanukkah, he said.

"We found order in this complexity and chaos, the exact structures that are possible at the grain boundaries and the dislocations types," he said.

The growing molybdenum/sulfur sheets can meet at any angle, and though the sheets are semiconducting, the boundaries between them generally stop electrical signals in their tracks. But at one particular angle -- 60 degrees -- the periodic dislocations are close enough to pass signals on from one to the next along the length of the boundary. "Basically, they're metallic in this direction," Yakobson said.

"So in the middle of these domains of semiconducting material, you have this boundary line that carries current in one direction, like a wire. And it's only a few angstroms wide," he said.

"Metal disulfides may be promising for future electronic devices based on materials with reduced dimensions," Zou said. "It is important to understand the effects of topological defects on the electronic properties as we push toward post-silicon devices."

Yuanyue Liu, a graduate student in Yakobson's group, is a co-author of the paper.

A U.S. Army Research Office Multidisciplinary University Research Initiative grant and the National Science Foundation (NSF) supported the research. Computations were performed at the NSF-funded Data Analysis and Visualization Cyberinfrastructure at Rice.


Story Source:

The above story is based on materials provided by Rice University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Xiaolong Zou, Yuanyue Liu, Boris I. Yakobson. Predicting Dislocations and Grain Boundaries in Two-Dimensional Metal-Disulfides from the First Principles. Nano Letters, 2012; 121214084937009 DOI: 10.1021/nl3040042

Cite This Page:

Rice University. "Dreidel-like dislocations lead to remarkable properties." ScienceDaily. ScienceDaily, 14 December 2012. <www.sciencedaily.com/releases/2012/12/121214191245.htm>.
Rice University. (2012, December 14). Dreidel-like dislocations lead to remarkable properties. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2012/12/121214191245.htm
Rice University. "Dreidel-like dislocations lead to remarkable properties." ScienceDaily. www.sciencedaily.com/releases/2012/12/121214191245.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins