Navigation Links
Researchers tune the strain in graphene drumheads to create quantum dots

Tightening or relaxing the tension on a drumhead will change the way the drum sounds. The same goes for drumheads made from graphene, only instead of changing the sound, stretching graphene has a profound effect on the material's electrical properties. Researchers working at the National Institute of Standards and Technology (NIST) and the University of Maryland have shown that subjecting graphene to mechanical strain can mimic the effects of magnetic fields and create a quantum dot, an exotic type of semiconductor with a wide range of potential uses in electronic devices.

The results were reported in the June 22, 2012, issue of Science.*

Graphene is a single layer of carbon atoms arranged in a honeycomb lattice. Able to conduct electricity with little resistance at room temperature, graphene is a prime candidate for applications ranging from flexible displays to high speed transistors.

However, the same lack of electrical resistance that makes graphene attractive for some uses also makes it ill-suited for digital computing applications. Graphene conducts electricity so well because it doesn't have a band gapan energetic threshold beneath which the material won't conduct electricity. This means that graphene can't be turned "off," and computers need "on" and "off" signals to transmit and process information.

Because substrates slow the speed of electrons moving through graphene, Nikolai Klimov, a University of Maryland postdoctoral researcher working at NIST, suspended the graphene over shallow holes in a substrate of silicon dioxideessentially making a set of graphene drumheads. To measure the graphene's properties, the team used a unique scanning probe microscope designed and built at NIST.

When they began to probe the drumheads, they found that the graphene rose up to meet the tip of the microscope a result of the van der Waals force, a weak electrical force that creates attraction between objects that are very close to each other.

"While our instrument was telling us that the graphene was shaped like a bubble clamped at the edges, the simulations run by our colleagues at the University of Maryland showed that we were only detecting the graphene's highest point," says NIST scientist Nikolai Zhitenev. "Their calculations showed that the shape was actually more like the shape you would get if you poke into the surface of an inflated balloon, like a teepee or circus tent."

The researchers discovered that they could tune the strain in the drumhead using the conducting plate upon which the graphene and substrate were mounted to create a countervailing attraction and pull the drumhead down. In this way, they could pull the graphene into or out of the hole below it. And their measurements showed that changing the degree of strain changed the material's electrical properties.

For instance, the group observed that when they pulled the graphene membrane into the tent-like shape, the region at the apex acted just like a quantum dot, a type of semiconductor in which electrons are confined to a small region of space.

Creating semiconducting regions like quantum dots in graphene by modifying its shape might give scientists the best of both worlds: high speed and the band gap crucial to computing and other applications.

According to Zhitenev, the electrons flow through graphene by following the segments of the hexagons. Stretching the hexagons lowers the energy near the apex of the tent-like shape and causes the electrons to move in closed, clover-shaped orbitsmimicking nearly exactly how the electrons would move in a vertically varied magnetic field.

"This behavior is really quite remarkable," says Zhitenev. "There is a little bit of electron leakage, but we found that if we complemented the pseudomagnetic field with an actual magnetic field, there was no leakage whatsoever."

"Normally, to make a graphene quantum dot, you would have to cut out a nanosize piece of graphene," says NIST Fellow Joseph Stroscio. "Our work shows that you can achieve the same thing with strain-induced pseudomagnetic fields. It's a great result, and a significant step toward developing future graphene-based devices."

Contact: Mark Esser
National Institute of Standards and Technology (NIST)

Related biology technology :

1. WHEATON® Introduces a New Web Community for Scientists, Researchers, and Biopharmaceutical Packagers
2. Stevenage Bioscience Catalyst to Welcome Cambridge University Researchers
3. Syracuse University researchers use nanotechnology to harness power of fireflies
4. Researchers discover hereditary enzyme deficiency
5. JCVI Researchers, as Part of NIH Human Microbiome Project Consortium, Publish Papers Detailing the Variety and Abundance of Microbes Living on and in the Human Body
6. Produce Safety Researchers Awarded by ABC Research Laboratories
7. CNIO researchers describe a new target for developing anti-angiogenic and anti-tumoral therapies
8. U of S researchers create powerful new tool for research and drug development
9. Researchers love triangles
10. Sensing the infrared: Researchers improve IR detectors with single-walled carbon nanotubes
11. Generex Enhances Antigen Express Scientific Advisory Board for the AE37 Breast Cancer Vaccine with Renowned Breast Cancer Researchers
Post Your Comments:
(Date:11/25/2015)... November 25, 2015 2 nouvelles études ... les différences entre les souches bactériennes retrouvées dans ... des êtres humains . Ces recherches  ouvrent une ... la prise en charge efficace de l,un des ... les chats .    --> 2 nouvelles ...
(Date:11/25/2015)... Studies reveal the differences in species of bacteria ... for more effective treatment for one of the most commonly ... --> --> Gum disease is one ... relatively little was understood about the bacteria associated with it ... researchers from the WALTHAM Centre for Pet Nutrition together with ...
(Date:11/25/2015)... HOLLISTON, Mass. , Nov. 25, 2015 ... a biotechnology company developing bioengineered organ implants for life-threatening ... will present at the LD Micro "Main Event" investor ... PT. The presentation will be webcast live and posted ... also be available at the conference for one-on-one meetings ...
(Date:11/25/2015)... DIEGO , Nov. 25, 2015  Neurocrine Biosciences, ... Kevin Gorman , President and CEO of Neurocrine Biosciences, ... Healthcare Conference in New York . ... to visit the website approximately 5 minutes prior to ... A replay of the presentation will be available on ...
Breaking Biology Technology:
(Date:11/20/2015)... , November 20, 2015 NXTD ... focused on the growing mobile commerce market and creator ... Gino Pereira , was recently interviewed on The ... air on this weekend on Bloomberg Europe , ... . --> NXTD ) ("NXT-ID" or the ...
(Date:11/19/2015)... Calif. , Nov. 19, 2015  Based on ... Frost & Sullivan recognizes BIO-key with the 2015 Global ... Each year, Frost & Sullivan presents this award to ... line catering to the needs of the market it ... product line meets and expands on customer base demands, ...
(Date:11/19/2015)... Nov. 19, 2015  Although some 350 companies are ... by a few companies, according to Kalorama Information. These include ... of the market share of the 6.1 billion-dollar molecular ... World Market for Molecular Diagnostic s .    ... is still controlled by one company and only a ...
Breaking Biology News(10 mins):