MIT - Page 11

It's been known for a long time that Graphene generates current from light. Up until now everybody assumed it was due to the photovoltaic effect, but a new research by MIT researchers shows that this is not true. They found that light on graphene causes it to develop two regions with different electrical properties which creates a temperature difference.

This "hot-carrier response" is what generates the current - and it's very unusual - it's been observed before but only under very low temperature or when using intense high power laser. The reason for this unusual thermal response is that graphene is the strongest material known. In most materials, superheated electrons would transfer energy to the lattice around them. In the case of graphene, however, that’s exceedingly hard to do, since the material’s strength means it takes very high energy to vibrate its lattice of carbon nuclei — so very little of the electrons’ heat is transferred to that lattice.

MIT's new Center for Graphene Devices and Systems (MIT-CG) has an ambitious plan - to produce a one-kilometer square sheet of graphene. They are currently starting to develop the basic science and technology - which is based on the printing press. The idea is to grow graphene in a roll to roll process. MIT hopes that if they manage to develop this technology they'll enable a whole new graphene industry.

Currently they've been able to grow small sheets only using this technology (a "few centimeters" in size). The largest graphene sheet made to date was 30" square (produced by Japanese and Korean researches in June 2010) - which was also made in a roll-to-roll printing process. There were reports of a 40" graphene sheet produced by Samsung in January 2011 but these reports weren't confirmed.

MIT announced the creation of the MIT/MTL Center for Graphene Devices and Systems (MIT-CG). This is an interdepartmental center which is part of the Microsystems Technology Laboratories (MTL) with an aim to bring together MIT researchers and industrial partners to advance the science and engineering of graphene-based technologies.

The MIT-CG will research the basic physical properties of graphene and will also explore advanced technologies and strategies that will lead to graphene-based materials, devices and systems for a variety of applications (including graphene-enabled systems for energy generation, smart fabrics and materials, radio-frequency communications, and sensing).

Researchers from MIT are developing graphene based membranes for gas separation. They expect those membranes to have very high permeance which would lead into high energy efficiency. The membranes will also have a high degree of selectivity through size exclusion. The research will focus on separating methane from hydrogen at first - which is useful for natural gas processing.

This research was just granted some seed money and will last for 2 years.

Researchers from the University of Arizona, MIT and Japan's NMSI discovered that placing graphene on boron nitride (instead of the commonly used silicon dioxide) could significantly improve its electronic properties.

Boron nitride is structurally basically the same as Graphene, but it's different electronically - Graphene is a conductor and boron nitride is an insulator. Putting graphene on an insulator makes it possible to study the properties of Graphene alone.

Researchers from MIT developed a new way to use Graphene as an electrode for organic solar cells. The biggest problem with using Graphene in such a device was getting the material to adhere to the panel. Graphene repels water, so typical procedures for producing an electrode on the surface by depositing the material from a solution won’t work.

The team tried a variety of approaches to alter the surface properties of the cell or to use solutions other than water to deposit the carbon on the surface, and they found that doping the surface — that is, introducing a set of impurities into the surface — changed the way it behaved, and allowed the graphene to bond tightly. As a bonus, it turned out the doping also improved the material’s electrical conductivity.

Pablo Jarillo-Herrero has won the 2009 David and Lucile Packard fellowship. He was granted 875k$ (a five-year grant). Pablo will use this to study unique features of Graphene and also to study topological insulators.

Researchers at MIT have designed new hierarchical assemblies of graphene nanoribbons through hydrogen bonds, inspired by biological structures found in nature such as proteins and DNA macromolecules. Their work brings about a synergistic viewpoint that combines advances in materials development and insight gained from biological structures, and leads to new understanding of the mechanics and physics hydrogen bonds at the bio-nano interface.

Buehler, the Esther and Harold E. Edgerton Associate Professor at MIT's Department of Civil and Environmental Engineering, together with his postdoctoral associate Zhiping Xu, have investigated the mechanical and electronic properties of graphene nanoribbons through first principles calculations. They demonstrate that hierarchical graphene nanoribbons not only preserve the unique electronic properties of individual graphene nanoribbons in the bulk, but are also energetically and mechanically stable.