The wish list for qualities of the perfect electronic material is relatively short, among them: high electron mobility, high mechanical strength and high thermal conductivity. In the quest for smaller, faster, cheaper computers, mobile phones and other personal digital devices these traits are key.
Since graphene's discovery in 2004, researchers have found record-high values of all of these attributes in the new "wonder" material's freestanding form. However, for most practical applications, graphene needs to be supported on a substrate or embedded in a medium.
Now engineers and scientists at The University of Texas at Austin, Boston College and the France Commission for Atomic Energy report graphene withstood another major test along its path to proven perfection: it still possesses its coveted heat conducting capability even when supported on a substrate.
This characteristic is crucial as electronic devices become smaller and smaller, presenting engineers with a fundamental problem of keeping the devices cool enough to operate efficiently.
A very promising new material in electronics, graphene offers broad adaptability partly because of its simple make-up: a flat sheet of pure carbon rings in flawless order--just one atom thick. Because of the strong bonding between carbon atoms in the chicken wire-like structure, researchers have documented unprecedented strength, electron mobility and thermal conductivity in its suspended form, as well as compatibility with thin film silicon transistor devices, making it feasible for low-cost, mass production.
A major question has been whether contact with a substrate would compromise its superior properties, exactly because graphene is only one atom thick and thus its properties can be sensitive to interaction with the environment.
In the April 9 issue of Science, a multidisciplinary team led by Li Shi, mechanical engineering professor at The University of Texas at Austin, detail how graphene still greatly outperforms silicon and copper nanostructures in the latest computer chips for conducting heat even when it is supported on a substrate. This qualifies graphene as a prime candidate for solving the heat dissipation problems currently limiting development of nanoelectronics. The heat problem is no minor barrier--heat generated per unit area in computer chips are becoming as high as that of a nuclear reactor.
Other researchers have also found that supported graphene still greatly outperforms silicon and copper in terms of electron mobility, a measure of how smoothly an electron can move in a conductor without losing its momentum or energy. Combined with this earlier result, the Shi team's recent findings suggest that electronic devices made of graphene will potentially generate less heat and conduct heat away from hot spots much more efficiently than devices made of silicon and copper nanostructures. As such, the devices will consume less energy, be cooler and more reliable, and operate faster than current-generation devices.
Other researchers contributing to these findings included: Aerospace Engineering Associate Professor Rui Huang, Mechanical Engineering Professor Rodney Ruoff, Physics Associate Professor Zhen Yao, Postdoctoral Fellow Jae Hun Seol, Xuesong Li and students Insun Jo, Arden Moore, Zachary Aitken, Michael Pettes of The University of Texas at Austin; David Broido and Lucas Lindsay of Boston College; and Natalio Mingo of the France Commission for Atomic Energy.
The work was supported by the Thermal Transport Processes Program and the Mechanics of Materials Program of the National Science Foundation, the U.S. Office of Naval Research, the U.S. Department of Energy Office of Science and The University of Texas at Austin.