This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The objective of this research is to perform the first comprehensive experimental study of the thermal conductivity of graphene, the atomically-thin sheets of carbon that make up graphite. Excitement regarding thermal aspects of graphene are two-fold. From the fundamental perspective, graphene has a unique electron dispersion relation which enables study of "massless", pseudo-relativistic, quantum particles. From an applications perspective, graphene's superb electrical and thermal properties, and prospects for wafer-scale processing, make it a strong candidate to transform the era of post-silicon microelectronics. Graphene is expected to have very high thermal conductivity, approximately 4000- 5000 W/mK, but only very recently were the first data published to support such expectations, in a study using Raman spectroscopy. The objective of the present research is to experimentally quantify the following essential phenomena, none of which have been measured previously in graphene: the effects of temperature, sample size and thickness, surface conditions, electron vs. phonon contributions, ballistic vs. diffusive transport, and thermal contact resistance. Intellectual Merit. Three complementary experimental approaches will be taken: (1) a novel heat spreader method measures the heat transfer along a graphene sheet encased between dielectric layers, thereby mimicking microelectronics applications and also yielding the thermal contact resistance, (2) a self-heating method using suspended graphene is simple to fabricate and interpret, but is restricted to diffusive transport, and (3) a microfabricated sensors method is also based on suspended graphene, and works for both ballistic and diffusive transport. This research builds on the PIs' existing collaboration and preliminary results, and their respective strengths in thermal measurements of nanostructures (Dames) and graphene deposition and electrical measurements (Lau). By conducting experiments over a large parameter space, the results are expected to constitute the first comprehensive experimental study of graphene's thermal conductivity, thus resolving the many conflicting theoretical predictions which may disagree by up to an order of magnitude. To build confidence in the measurements, the methods can be cross-checked against one another, and this will also provide valuable comparison for the initial Raman measurements in the literature. The experiments will detail the relevant thermal properties, including thermal contact resistance, that are essential to evaluate graphene's performance in possible microelectronics applications. Thus, this new knowledge has the potential to transform the fundamental understanding of heat transfer in atomically-thin films, the ways in which these films are measured, and their applications in industry. Broader Impacts. Considering the tremendous importance of heat dissipation in modern microelectronics, a comprehensive study of graphene's thermal properties will be critical for its application in post-Si device technology, resulting in a broad positive impact to society. Additionally, an integrated education plan will exploit UC Riverside's position as the most diverse UC campus and a national leader in graduating underrepresented minorities. This interdisciplinary research brings together undergraduate and graduate students from Physics and Mechanical Engineering. The research results will be disseminated broadly, in journals, at conferences, and in courses. More uniquely, the results will be incorporated into UC Riverside's Summer Physics Academy, a workshop program for high school science teachers: Each teacher with be provided with a simple kit for their classroom, to build creative, human-scale analogues of the nanoworld. Each kit will include documentation and a million-scale representation of various nanomaterials including DNA, carbon nanotubes, and graphene, as well as scaled material samples to convey the tremendous heat-carrying capacity of graphene as compared to conventional materials like aluminum.
