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[cancelled] First principles-based modeling of metal-thermoelectric materials contacts and incommensurate graphene on BN

Speaker: 
Catalin Spataru (Sandia National Laboratories, USA)
Date: 
Wed, 15/06/2016 - 11:00am to 12:00pm
Location: 
Physics Conference Room (S11-02-07)
Host: 
Quek Su Ying
Event Type: 
Seminars

Abstract

Metal contacts play an important role for thin-film thermoelectric (TE) devices, especially in high heat-flux applications (e.g. chip cooling) where reduced contact resistivity (ρC ) is critical to device performance. In the first part of the talk I will present our effort towards understanding the limits of low-ρC in realistic metal-contacts to TE materials. Using a combination of approaches ranging from ab initio calculations to higher-level continuum theories we investigate the structural, electronic and transport properties of electrical contacts to TE materials. The study benefits from experimental input that provides atomic scale structure validation of the interfaces considered computationally.

Various properties of supported graphene films depend strongly on the exact positions of carbon atoms with respect to the underlying substrate. While density functional theory (DFT) can predict atom position in many systems, it cannot be applied straightforwardly to systems that are incommensurate or have large unit cells, such as graphene on a BN surface. In the second part of the talk I will present our effort in addressing these limitations by developing a simple moiré model with parameters derived from DFT calculations for systems strained into commensurate structures. Our moiré model, which takes into account the flexural rigidity of graphene and includes the influence of the substrate, is able to reproduce the DFT-relaxed carbon positions with an accuracy of <0.01 Å.

About the speaker

Catalin Spataru is an expert in ab initio modeling of material properties. He has over 15 years of experience with studies of structural, electronic and optical properties of solids and novel materials of various kinds, ranging from bulk to low-dimensional systems, and from metals to insulators, in both equilibrium and out-of-equilibrium conditions. He has extensive experience on the use of ab initio Density Functional Theory and quantum many-particle methods such as the GW approximation for the electron self-energy and the Bethe-Salpeter method for excitonic effects.

Catalin obtained his PhD in Physics at the University of California at Berkley (USA) in 2004, following which he held postdoctoral positions at the Lawrence Berkeley National Laboratory and Columbia University. In 2008 he became a member of the technical staff at the Sandia National Laboratories.

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