雙雷射共沈積系統之開發:碲化鉍/奈米碳管熱電異質複合材料之製備

Abstract

近年來由於綠色能源工業的快速成長，加上現代奈米科技的進步，越來越多高熱 電優值係數(ZT)之奈米熱電材料被相繼發現，使得學界及業界再度凝聚研發能量於新 穎熱電材料之上。從目前各種重要理論及實驗研究結果可以發現，「異質奈米熱電材料 之複合化」是一個大幅提昇熱電優值係數之有效策略。而熱電複合材料之材料種類、 複合結構設計、以及製備方法，將直接影響其熱電相關特性。 為了製備高熱電優值係數之熱電異質複合材料，本研究計畫係基於本研究室現有 之技術經驗，設計開發一個新穎之「雙雷射共沈積」製程設備，此特殊設計可以在單 一製程步驟中，製備出各式高品質異質熱電複合材料。其優勢在於此製程方式屬於單 一步驟高真空物理薄膜沈積，除了可以避免多步驟製程中進出真空系統所造成之氧化 及受潮，並可避免使用化學製程中常見之介面活性劑，故能有效降低晶界及異質介面 之阻抗，提昇熱電特性。此外，此雙雷射系統由於可以分別調控雷射源之波長及能量， 故可以針對欲複合之材料，調控最佳之沈積參數，進而精確控制複合材料之各種結構 參數。 在異質熱電複合材料的選擇方面，本研究基於過去之基礎，鎖定常溫型之碲化鉍 (Bi2Te3)作為熱電複合材料之主體，並選擇奈米碳管(CNT)作為異質複合之材料，主要 係因奈米碳管具有極佳之熱電潛力，可以與所有類型之熱電材料作有效搭配，再加上 其易於調控成長為各式具高方向性之CNT 陣列，將有助於製備各式複合結構，探討最 佳化之異質複合設計。

Thermoelectric materials have recently reattracted much attention due to the rapid growth of various clean-energy industries and the great development of nanotechnologies, a series of novel thermoelectric materials with comparable high figure of merit (ZT) have been widely discovered. Acadamic and industrial research effort thus tends to refocus on development of novel thermoelectric materials. According to numbers of outstanding theoretical and experimental studies, it is found that the thermoelectric heterocomposites seems can be considered as an effective strategy to greatly enhance the ZT value for most thermoelectric materials. The thermoelectric performance will thus completely depend on the materails, design of the composite structure as well as the preparation method. Based on our present techniques and experiences, this project attempts to develop a novel double-laser co-deposition system for the preparation of thermoelectric heterocomposites with high ZT values. Due to the high-vacuum physical deposition, different thermoelectric materials can be co-deposited without exposing to atmosphere to avoid oxidation and contamination. In addition, the absence of surfactant and catalysts as frequently used in the chemical process can also decrease the resistance distributed from grain boundaries and interfaces and thus can enhance the overall thermoelectric properties. Additionally, the double-laser can be individually optimized to fit the deposition requirement of different thermoelectric materials and to control the structural parameters. This advantage is the main point of the present project. In this project, we aim at two thermoelectric materials for the heterocomposites, i.e. Bi2Te3 and carbon nanotube (CNT). Recently, many studies have demonstrated great potentials of various types of CNTs for thermoelectric applications. The deposition and control techniques of CNTs have been well known and it is easy to prepare highly oriented CNT arrays. Here we will use these preparation advantages to co-deposit various Bi2Te3/CNT composite structures for optimizing composite structures.