Navigation Links
Dreidel-like dislocations lead to remarkable properties
Date:12/14/2012

HOUSTON (Dec. 14, 2012) 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."


'/>"/>

Contact: David Ruth
david@rice.edu
713-348-6327
Rice University
Source:Eurekalert  

Related biology technology :

1. Waterfront Properties Proud To Have Prestigious Max Planck Society in its Back Yard
2. Unique properties of graphene lead to a new paradigm for low-power telecommunications
3. Discovery of material with amazing properties
4. Physical properties predict stem cell outcome
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Dreidel-like dislocations lead to remarkable properties
(Date:6/23/2016)...  The Prostate Cancer Foundation (PCF) is pleased to announce 24 ... for prostate cancer. Members of the Class of 2016 were selected from a ... Read More About the Class of 2016 PCF Young Investigators ... ... ...
(Date:6/23/2016)... , June 23, 2016   EpiBiome , a ... $1 million in debt financing from Silicon Valley Bank ... automation and to advance its drug development efforts, as ... facility. "SVB has been an incredible strategic ... services a traditional bank would provide," said Dr. ...
(Date:6/23/2016)... , ... June 23, 2016 , ... STACS DNA Inc., ... Leader at the Arkansas State Crime Laboratory, has joined STACS DNA as a Field ... DNA team,” said Jocelyn Tremblay, President and COO of STACS DNA. “In further expanding ...
(Date:6/23/2016)... , June 23, 2016 Apellis Pharmaceuticals, ... 1 clinical trials of its complement C3 inhibitor, ... and multiple ascending dose studies designed to assess ... of subcutaneous injection in healthy adult volunteers. ... either as a single dose (ranging from 45 ...
Breaking Biology Technology:
(Date:6/2/2016)... -- Perimeter Surveillance & Detection Systems, Biometrics ... Support & Other Service  The latest report ... analysis of the global Border Security market . ... $17.98 billion in 2016. Now: In November ... software and hardware technologies for advanced video surveillance. ...
(Date:5/12/2016)... WearablesResearch.com , a brand of Troubadour Research & ... Q1 wave of its quarterly wearables survey. A particular ... a program where they would receive discounts for sharing ... "We were surprised to see that so many ... CEO of Troubadour Research, "primarily because there are segments ...
(Date:4/26/2016)... and LONDON , ... Finacle, part of EdgeVerve Systems, a product subsidiary ... Onegini today announced a partnership to integrate the ...      (Logo: http://photos.prnewswire.com/prnh/20151104/283829LOGO ) ... provide their customers enhanced security to access and ...
Breaking Biology News(10 mins):