諸多的研究顯示，和塊材相比，低維度的材料其物理性質會有所不同，為了探究熱電材料在低維度下對其熱電性質所造成的效應，我們合成了BixSb2-xTe3-y奈米線並量測其熱電性質。本實驗藉由熱處理薄膜製備奈米線的方法合成單晶BixSb2-x Te3-y奈米線。我們先利用脈衝雷射沉積系統將BixSb2-x Te3鍍在矽基板上形成薄膜，再將薄膜以350 ℃至490 ℃熱處理5到21天，奈米線即為了平衡因薄膜與矽基板彼此熱膨脹係數不同所造成的應力而自薄膜上長出，其直徑為幾十奈米至幾百奈米不等，長度則為幾微米至幾十微米。為了瞭解奈米線之構成與量測其熱電性質，我們結合微影製程及操縱技術，將單根奈米線架空於附有電極、加熱元件及溫度感測元件之量測平台上，由於奈米線已被架空，我們便能透過選區繞射分析奈米線其結晶性，並使用能量散射分析儀得知奈米線之成分，利用四點量測可得知奈米線的電阻率ρ，以加熱元件在奈米線兩端產生溫差，並量測因西貝克效應 (Seebeck effect) 所造成之電壓差即能得到西貝克係數 S (Seebeck coefficient)，三倍頻技術要求所量測的樣品必須要架空於基板上，運用三倍頻技術 (3ω method) 可量測奈米線之熱導率κ及比熱。結合微影製程、操縱技術以及量測系統，我們成功得到單根奈米線的三個熱電係數ρ、S以及κ，並了解低維度對熱電性質所造成的影響。 / Compare with the bulk materials, many researches had revealed that physical properties were different in low dimensional materials. To study the low-dimensional effects on thermoelectric properties of thermoelectric materials, BixSb2-xTe3-y nanowires were synthesized and studied for their thermoelectric properties. Single-crystallized BixSb2-xTe3-y nanowires were synthesized by on-film formation of nanowires. First, BixSb2-xTe3 thin films were deposited on SiO2/Si substrates by using the pulsed laser deposition system. BixSb2-xTe3-y nanowires grew from the films by annealing the films at 350~490 ℃ for 5~21 days through the stress release of the thermal expansion mismatch between the film and the substrate. A series of BixSb2-xTe3-y nanowires were prepared with the diameter from few tens of nanometers to few hundreds of nanometers and the length from few micrometers to few tens of micrometers. In order to analyze the components and measure the thermoelectric properties of the nanowires, the technique of combining microfabrication and manipulation for suspending a single BixSb2-xTe3-y nanowire on a measurement platform with electrodes, heater and thermometers was developed. As long as the wire is suspended, the crystallization of the nanowire is able to be analyzed by the selected area electron diffraction (SAED). The composition of the nanowire can be analyzed by the STEM-EDX. Resistivity ρ is measured by the four-point probe method. In order to get the Seebeck coefficient S, temperature difference were generated by the heater and thermoelectric voltage generated by Seebeck effect were measured. The 3ω method which demands that the wire should be suspended was applied to measure the thermal conductivity κ and specific heat c. By using the developed technique and the measurement system, three thermoelectric parameter ρ, S, κ of a single nanowire were successfully measured and the low-dimensional effect on thermoelectric properties were examined.

找尋新穎的熱電材料是現在許多物理、化學以及材料學家的熱門研究，熱電材料的益處在於可將生活中所產生的廢熱轉化成電能再度利用，可應用在於熱機或是冷凍機之上。 首先，在第一個研究之中，透過布理奇曼法在1050 ℃之下維持10個小時用以製作Cu0.01Bi2Te2.7Se0.3塊材，以及透過水熱法製造出Cu0.01Bi2Te2.7Se0.3奈米粒子，並且將兩種不同尺寸的粒子做不同比例的混合：奈米粒子(粒徑：20~100奈米)重量百分比0、10、20、30和100；接著探討火花電漿燒結法及奈米聚合物對熱電性質之影響。在實驗中發現材料中混入百分之三十的奈米粒子可提升熱電優質係數約一倍，由0.35提升至0.74。若是可以將起初塊材的熱電優質係數提升至較良好的0.7以上，再透過奈米聚合和燒結，其熱電係數在400 K左右是可以超過1的。由這個研究顯示出：火花電漿燒結以及奈米聚合是可以有效的提升熱電優質係數，其主要原因來自於成功的降低熱傳導係數並同時維持住原本所擁有的電阻率以及席貝克係數的提升，而熱傳導降低因於樣品中的奈米結構所造成的粒子邊界增加、晶格的不匹配導致抑制聲子的傳熱所形成的結果。 第二個研究為一樣是透過布理奇曼法在750 ℃之下維持12個小時用以製作BixSb2-xTe3塊材，其中x分別為0.4、0.45、0.5以及0.6，本實驗主要為探討Bi的量對於BiSbTe所造成的影響。由結果中顯示x高於0.5和低於0.5所呈現的熱傳性質的趨勢有些許不同。在x為0.45的塊材中，得到本實驗中在室溫之下，最佳的熱電優質係數1.5，獲得此結果的主要原因來自於相對較低的電阻率，並可觀察到x為0.45的載子濃度高於0.4、0.5和0.6的結果，其將可以佐證x=0.45塊材的低電組率所造成的優質係數提升。 / Physicists, chemists and material scientists at many major universities and research institutions throughout the world are attempting to create novel materials with high thermoelectric (TE) efficiency. It will be beneficial to harvest waste heat into electrical energy. Specialty heating and cooling are other major applications for this class of new TE materials. In the first study, bulk and nanoparticles of Cu0.01Bi2Te2.7Se0.3 were prepared separately. The Cu0.01Bi2Te2.7Se0.3 bulk was fabricated by Bridgeman method at 1050 ℃ for 10 hrs and the nanoparticles were made through hydrothermal method. Two kinds of powders were mixed with the ratios of NPs 0, 10, 20, 30 and 100 wt% and sintered by the SPS technique to form the composite specimens. The ZT value can be enhanced over 100% from 0.35 to 0.74 for specimen with 30 wt% nanoparticles. The consequence indicates that the SPS process and mixing nanocomposite can effectively enhance ZT value. The enhancements were caused mainly by the presence of nanostructured regions existing within the samples which lowered the thermal conductivity. The phenomenon is due to the presence of significant number of grain boundaries, shorten phonon mean free path and lattice mismatch. For another investigation, the BixSb2-xTe3 ingots with x=0.4, 0.45, 0.5 and 0.6. were fabricated by Bridgeman method at 750 ℃ for 12 hrs. We studied the effects of amount of Bi in BixSb2-xTe3 and the SPS process on the ZT enhancement. The experiment showed that for x >0.5, the thermal property changed from a curve to a relatively linear line at the end. The best ZT is 1.5 ingot at 300 K for x=0.45 specimen. The significant ZT improvement arises from the much-reduced electric resistivity. The lowest resistivity for x=0.45 specimen is mainly due to the highest carrier concentration than those with x=0.4, 0.5 and 0.6 ingots.