Crystalline-Amorphous Interface: Molecular Dynamics Simulation of Thermal Conductivity
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Crystalline-Amorphous Interface: Molecular Dynamics Simulation of Thermal Conductivity
Sebastian von Alfthan, Antti Kuronen, Kimmo Kaski Helsinki University of Technology, Laboratory of Computational Engineering P.O.Box 9400, FIN-02015 HUT, FINLAND
ABSTRACT Effect of a crystalline-amorphous interface on heat conduction has been studied using atomistic simulations of a silicon system. System with amorphous silicon was created using the bond-switching Monte Carlo simulation method and heat conduction near room temperature was studied by molecular dynamics simulations of this system. INTRODUCTION As the sizes of electronic devices decrease an increasing amount of heat has to be dissipated by ever decreasing volume of the device material. The details of device structures, namely interfaces, surfaces and defects in them affect the heat conduction, which can give rise to behavior that differs drastically from behavior in bulk materials [1, 2]. In addition to the interest in improving the heat dissipation from electronic components, different nanostructures can be utilized to decrease heat conduction where it is not desired. One example of this are the new thermoelectric devices where thermal conduction is reduced by ultra-short-period superlattices [3]. When the dimensions of nanostructures become comparable to the phonon mean free path in the material the Fourier law describing thermal conduction in macroscopic systems becomes inapplicable. Heat conduction is influenced – among other things – by phonon scattering from interfaces, by phonon interference and the modification of the phonon dispersion relation due to small dimensions of the device. These events can be included in kinetic theories of heat conduction [4] in an approximate way. However, in order to get a reliable estimate how the atomic level structure of the device influences the heat conduction, atomic level studies are needed. In this work we study heat conduction through an interface between crystalline (c) and amorphous (a) material. We use molecular dynamics (MD) method to study the effect of the crystalline silicon and amorphous silicon (c-Si/a-Si) interface on the heat conduction near room temperature. We have chosen this particular system with only structural (not chemical) differences in order to study the basic effects of the interface. This study – which is interesting on own right – serves as a necessary but yet insufficiently explored precursor for investigating perhaps the most important interface in electronics; namely an interface between crystalline silicon and amorphous silicon dioxide.
V6.2.1
COMPUTATIONAL DETAILS Our simulation system consisted of a layer of a-Si between slabs of c-Si (see Fig. 3). In order to avoid complication with open surfaces periodic boundary conditions were applied in all three dimensions. However, this means that the system is effectively a superlattice. Three systems (denoted A, B, and C) with different sizes were studied (see Fig. 3): A: Lc
= 296
˚ La A,
= 100
˚ d = 32 A, ˚ 20736 atoms A,
B: Lc
= 187
˚
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