雙脈衝雷射共沉積碲化鎵/碲化銻側向組裝奈米異質結構於熱電轉換之應用

Abstract

異質奈米結構化(Heterogeneous nanostructuring)已然成為開發具高熱電優值(Thermoelectric figure of merit; ZT)先進熱電材料的重要策略之一。其主要利用異質奈米材料之結合，來達到自由調控成份比例、組裝構造、乃至強化整體熱電特性之目的。本研究主要利用雙脈衝雷射共沉積(Dual-beam pulsed laser deposition, DBPLD)，獨立調控碲化鎵(Ga2Te3)與銻(Sb)雙靶材之雷射剝蝕速率，並改變後退火處理之參數，成功製造一系列新穎之碲化鎵/碲化銻(Sb2Te3)橫向有序奈米異質結構薄膜。結構中，碲化鎵之島狀奈米組裝體是為主相，外圍環覆碲化銻單晶薄層是為次相，主次相形成網絡狀之二維擬週期結構。結果發現，碲化銻單晶析出之量會隨著後退火溫度的提高而增加，且與導電度呈高度依存性。在275oC退火後，常溫導電率與功率因子分別為3335 Sm-1與60 Wm-1K-2，約是當前所發表碲化鎵最佳功率因子(奈米結構塊材)之266倍。

Heterogeneous nanostructuring, in the field of thermoelectrics, which couples various functional compounds with desired fractions and assembling architectures, and thus providing the greatest flexibility in tuning the overall thermoelectric properties has become one of the most important strategies for developing advance thermoelectric materials with enhanced thermoelectric figure of merit, ZT. In this work, a series of laterally- and periodically-assembled Ga2Te3/Sb2Te3 hetero-nanocomposite films were successfully fabricated by applying dual-beam pulsed laser deposition (DBPLD) with two isolated targets, Ga2Te3 and Sb, and the subsequent post-annealing processes. The island-like Ga2Te3 nanoassemblies are surrounded with the networking Sb2Te3 single-crystalline walls to form unique two-dimensional pseudo-periodic structures. It was found that, the fraction of the Sb2Te3 precipitate of increases with the increase of the annealing temperature and is strongly correlated with the overall electric conductivity. Eventually, the optimized Ga2Te3/Sb2Te3 hetero-nanocomposite films annealed at 275 oC reveal the highest electrical conductivity of 3335 Sm-1 and the corresponding power factor of 60.12 Wm-1K-2 which is about 266 times higher than that of the best value been reported up to date.