Thermoelectric (TE) materials are of increasing interest as environmental friendly and sustainable energy conversion, which are able to convert heat into electricity, and vice versa. Despite those materials have been studied as promising new energy source for recent decades, the energy conversion efficiency still remains as an obstacle to propel commercialization. To tackle this, various efforts have been conducted to enhance their energy conversion efficiency, ZT=$S^2\sigma$T/K (S: Seebeck coefficient, $\sigma$: electrical conductivity, T: operating temperature, and k: thermal conductivity). Over the past two decades, two different approaches have been developed to search for the next generation of thermoelectric materials: one is finding and using new families of bulk thermoelectric materials with complex crystal structures, and the other is synthesizing and using lowdimensional thermoelectric materials systems. There is also much interest in the accurate measurement of thermoelectric properties as the studies on nanostructured materials for the enhancement of ZT are advanced.
We studied on the measurement method using the platform and design of platform that matches the size of the structure for the reliable measurement of nanostructures. Homemade microfabricatied thermoelectric properties measurement platform [MTMP] for the nanowire, nanosheet, and nano patterned 3-D structure was fabricated. And devised a manipulation system that uses a tungsten tip and AAO template with van der waals force allows easy transfer sample to platform.
In order to reduce the loss of electrical transport by contact resistance, appropriate ohmic contact conditions are established and on the bridge type MTMP for thermal conductivity measurement. Thermal conductivity was measured about the heat passed by nanostructured material through the heat dissipation (Fourier heat transport) for the simple and reliable measurement.
This dissertation is organized in the following manner. Chapter 1, the introduction, discusses the motivation for current research. Chapter 2 introduces the synthesis of undoped and Si-doped InAs NWs to investigate the effect of carrier concentration and the lattice thermal conductivity on ZT. All TE parameters of S, σ, and k with temperature on the microfabricated TE measurement platforms (MTMPs) were measured and photoinduced thermoelectric properties of InAs NWs was evaluated in Chapter 3. Micromanipulation and thermoelectric characteristic of of 2-D black phosphorus nanosheets are presented in Chapter 4. Also enhancement of thermoelectric properties of black phosphorus nanosheets by gating effect was discussed. Finally, Chapter 5 summarizes the conclusions of this work and the insight gained from performing these experimental investigations and points out the future work that may contribute to the development of nanotechnology.
환경문제가 대두되면서 환경친화적인 열전 물질에 대한 관심이 증가하고있다. 지속 가능한 에너지로 열을 전기로 직접적으로 변환할 수 있는 열전 에너지는 유망한 새로운 에너지원으로서 많은 연구가 이루어지고 있다. 최근 수십 년간, 에너지 변환효율이 여전히 장애물로 남아 효율을 증대시켜 상용화하기위한 많은 노력이 이루어지고있다. 열전 효율 ZT는 높은 전기전도도, 제백계수, 그리고 낮은 열전도도를 갖을 때, 최적화 될 수있다. 열전 효율을 높이기 위해 수십 년간에 걸쳐 두가지 접근법이 개발되어 왔다. 첫번째로 벌크 열전 물질로 새로운 군을 찾는 방법과 나노구조를 같은 물질의 합성 및 제작을 통해 열전 효율을 높이고자 하였다. 이러한 나노구조 열전 재료에 대한 연구가 활발해짐에 따라 나노구조 재료의 신뢰성 있는 측정에 대한 관심도 높아져 가고 있다. 본연구에서는 나노구조의 신뢰성있는 측정 및 분석을 위해 열전 특성 플랫폼을 제작하여 나노와이어, 나노시트, 나노 패터닝3 차원 구조물등의 다양한 나노재료의 열전 특성을 평가하였다.
