Measurement of Thermal Properties at the Interface of Graphene and Bi2Te3 Substrate

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공과대학 기계항공공학부
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서울대학교 대학원
학위논문 (석사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2018. 8. 고승환.
Graphene, a two-dimensional hexagonal honey comb lattice, has been attracted tremendous attentions due its extremely high thermal and electrical, mechanical properties. Owing to these superior properties, there have been many attempts to exploit graphene to practical applications since it was discovered in 2004.Among many research area, thermoelectric field is known as one of the promising research field that graphene can be applied.

On the other hand, bismuth telluride (Bi2Te3) is one of the representative thermoelectric materials due to the high thermoelectric performance at the room temperature. For this reason, Bi2Te3has been already used in various research area and commercial devices, such as thermoelectric generator, peltier cooler.

Recently, a Graphene-Bi2Te3composite, synthesized in the thermoelectric field, has been experimentally proved to exhibit an enhanced thermoelectric performance. This is due to the reduced overall thermal conductivity at the composites. The additional phonon-scattering at the interface of graphene and Bi2Te3is thought to be a possible factor for this reduced thermal conductivity. However, the concrete mechanism why overall thermal conducivity of composites was ruduced is not fully understaned.

Generally, thermal properties at the interface of composite are believed to play an important role in the thermal transport in composite materials. Therefore, it is important to know thermal properties at the interface to understand thermal transport in the composite. In this paper, the thermal properties, particularly thermal contact conductance (Gc) and graphene thermal conductivity (kg),considered as important factors to the reduced thermal conductivity in the composite, were measured.

In many study pertaining to the supported graphene, they empolyed an optothermal Raman technique to measure thermal properties of supported graphene. One of the major difficulties of the optothermal Raman technique for supported graphene is how to obtain the absorptivity of graphene and the substrate. For many studies, the absorptivity of suspended graphene was equally used as the absorptivity of supported graphene. However, absorption value can be changed depending on the type of substrate like semi-conductor or conductor. This is because the electric field inside the material can be changed and influence on the absoprtion values of sample. Therefore, the absorption values should be estimated exactly for the supported graphene. We estimated absorptivities using the Fresnels equation from the refractive index of each matrial. This obtained absoprtion values were used in our experiment.

In short, measusring thermal contact conductance between graphene and Bi2Te3andthermal conductivity, we expected that these result values would be applied to further reasearch in designingoptimizinggraphene-Bi2Te3compositesand optimizing its performance.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Mechanical Aerospace Engineering (기계항공공학부)Theses (Master's Degree_기계항공공학부)
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