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Heat Transfer in Graphene and Nanostructured Materials

Seminar: Solid State Technology and Devices | February 8 | 1-2 p.m. | 521 Cory Hall

Professor Chris Dames, Mechanical Engineering, UC Berkeley

Electrical Engineering and Computer Sciences (EECS)

The thermal conductivity of nanostructured materials can differ from that of
their bulk single-crystal counterparts by orders of magnitude, with major
impacts on diverse applications including transistors, lasers, and energy
conversion. Here I will describe two examples:

(1) Although suspended graphene has been reported to have very high in-plane
thermal conductivity, most applications would require graphene to be
supported or encased within dielectric layers. Our measurements of encased
graphene and ultrathin graphite show that the constraints of the encasing
layers reduce the in-plane thermal conductivity by at least a factor of 10
as compared to bulk graphite.

(2) Bulk nanocrystalline materials are appealing because they combine some
of the performance advantages of nanostructuring with scalable, low-cost
synthesis. To clearly quantify the effects of grain boundaries in reducing
the phonon thermal conductivity in such materials, we measured undoped
nanocrystalline silicon as a model system. The results show that the
effective boundary scattering length is somewhat smaller than the average
grain size, and reveal a previously unidentified frequency dependence which
we show is consistent with asymptotic analysis of atomistic simulations from
the literature., 510-642-2911