Influence of Core-Shell Architecture Parameters on Thermal Conductivity of Si-Ge Nanowires
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Influence of Core-Shell Architecture Parameters on Thermal Conductivity of Si-Ge Nanowires Sevil Sarikurt1,2, Cem Sevik3 , Alper Kinaci2,4, Justin B. Haskins5,6 and Tahir Cagin2,6 1
Department of Physics, Faculty of Science, Dokuz Eylul University, Izmir, 35390, TURKEY Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843-3003, USA 3 Department of Mechanical Engineering, Faculty of Engineering, Anadolu University, Eskisehir, 26555, TURKEY 4 Argonne National Laboratory, Argonne, IL 60439, USA 5 NASA Ames Research Center, Moffett Field, CA 94035, USA 6 Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122
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ABSTRACT In this work, we investigate the influence of the core-shell architecture on nanowire (1D) thermal conductivity targeting to evaluate its validity as a strategy to achieve a better thermoelectric performance. To obtain the thermal conductivity values, equilibrium molecular dynamic simulations is applied to Si and Ge systems that are chosen to form core-shell nanostructures. To explore the parameter space, we have calculated thermal conductivity values of the Si-core/Ge-shell and Ge-core/Si-shell nanowires at different temperatures for different cross-sectional sizes and different core contents. Our results indicate that (1) increasing the cross-sectional area of pristine Si and pristine Ge nanowire increases the thermal conductivity (2) increasing the Ge core size in the Si-core/Ge-shell structure results in a decrease in the thermal conductivity values at 300 K (3) thermal conductivity of the Si-core/Ge-shell nanowires demonstrates a minima at specific core size (4) no significant variation in the thermal conductivity observed in nanowires for temperature values larger than 300 K (5) the predicted thermal conductivity around 10 W m −1 K −1 for the Si and Ge core-shell architecture is still high to get desired ZT values for thermoelectric applications. On the other hand, significant decrease in thermal conductivity with respect to bulk thermal conductivity of materials and pristine nanowires proves that employing core–shell architectures for other possible thermoelectric material candidates would serve valuable opportunities to achieve a better thermoelectric performance. INTRODUCTION The thermoelectric figure of merit, which is defined by ZT = ( S 2σ / κ )T is of great importance for characterizing the performance of thermoelectric devices [1], where S , σ , κ , T are the Seebeck coefficient, electrical, thermal conductivities, and temperature, respectively. Hicks and Dresselhaus [2-3] theoretically showed that, thermoelectric properties of a material can be tuned by going to lower dimensional structures such as nanoscale thin films or superlattices (2D), nanowires (1D), and quantum dots (0D). This leads to substantial change in thermal and electronic transport properties due to the change in the electronic or phononic density of states. For efficient thermoelectric materials, lowering the thermal conductivity
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