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  • 學位論文

(Bi,Sb)2Te3 奈米結構的熱電性質與金奈米棒的光熱性質之研究與應用

Thermoelectricity of (Bi,Sb)2Te3 nanomaterials and photothermal properties of Au nanorods

指導教授 : 林樹均 陳洋元

摘要


奈米材料的光、熱、電的傳輸與轉換近來受到極大的矚目,除了基礎科學的研究,其中熱電材料與癌症光熱治療佔有很重要的一部分。本論文第一部分,利用電化學沈積技術成長鍗化鉍(Bi2Te3)和鍗化銻 (Sb2Te3) 兩種熱電材料的薄膜與奈米線,以探討低維度對熱電性質的影響。以線寬120 nm的Bi2Te3奈米線為例,其熱電動勢雖比塊材小,但電導率卻優於塊材;將熱擴散與比熱數據帶入有效介質理論模型,估算出該奈米線的熱傳導係數,在室溫約0.75 W/m K。綜合這些參數,得到室溫奈米線的優質係數ZT為 0.45。預估當溫度超過 350 K,ZT可超過1,比塊材更大。至於Sb2Te3,於室溫下成長的薄膜及奈米線都是非結晶型,需經熱處理方能得到結晶相。隨著奈米線徑的縮小,其傳輸行為由半金屬性轉為半導體性。熱電動勢約+100 μV/K,與塊材相近。其熱傳導率也和Bi2Te3奈米線的結論一樣,都顯著的減小。 本論文第二部分,主要研究以雷射脈衝激發金奈米棒之表面電漿,所產生的光熱效應如何殺死癌細胞。我們以化學合成法準確地製備出長短軸比例為3.92 的無毒性奈米棒,使其最大吸收峰值落在800 nm,此波長對生物體有最深的穿透性,可達到雷射激發的最佳效果。此金奈米棒植入老鼠乳腺癌細胞(EMT-6)後,可清楚地看到細胞內,金奈米棒受雷射雙光子激發產生的螢光點,這非常有利即時性的雙光子顯微影像觀察。研究發現,細胞膜的破裂是因金奈米棒的光熱效應所引發局部高溫氣化膨脹所致。同時,癌細胞內金奈米棒的數量越多,殺死癌細胞所需的能量越小。以一個細胞攝入10-30個團簇(一個團簇約含30-100個金奈米棒)為例,在接受能量約93 mJ/cm2的脈衝雷射光(時間為505微秒),便可有效地殺死癌細胞。若細胞攝入數量達60-100的金奈米棒團簇,則18 mJ/cm2的能量即可殺死癌細胞,此值遠低於國際雷射治療的安全標準100 mJ/cm2。經由此一研究可了解奈米材料在癌細胞光熱解作用的機制與過程,並有助於光熱療法應用在臨床上。

關鍵字

熱電 光熱性質 鍗化鉍 鍗化銻 金奈米棒

並列摘要


Thermoelectric transport and photothermal conversion in nanomaterials have attracted considerable attention, not only due to their fundamental scientific interests, but also their potential applications in thermoelectricity and cancer therapies. In the first part of this thesis, we study low-dimensional effects on thermoelectric materials. In the study, films and nanowires of Bi2Te3 and Sb2Te3 were fabricated by potentiostatical electrodeposition. In the case of 120 nm- Bi2Te3 nanowires, a smaller thermopower is revealed, while observing a better electric conductivity compared to bulk material. By coupling thermal diffusivity and heat capacity data, and then applying a modified effective medium theory, a thermal conductivity of 0.75 W/m-K at 300 K was estimated. From this, the ZT of this nanowire was calculated to be 0.45 at 300 K, and is expected to exceed 1 at T > 350 K, which is larger than bulk value. For Sb2Te3, the as-prepared films and nanowires are amorphous. To obtain a crystalline phase, a further annealing treatment is required. As the diameter of wires reduce to nanoscale, the temperature dependence of resistance for nanowires reveals a phase transition from semimetal-like to semiconducting behavior. The Seebeck coefficients of the crystalline films and nanowire are +100 uV/K at 300 K, equal to the bulk value. The considerable reduction in estimated thermal conductivity of Sb2Te3 nanowires is similar to that of Bi2Te3 nanowires. In the second part, we present the study on cancer photothermolysis mediated by gold nanorods. The surface plasmons of nanorods were excited by laser pulses to investigate the destruction process of cells caused by photothermal effect. The nontoxic AuNRs with an aspect ratio of 3.92 were precisely controlled and synthesized by a chemical method. This yields a resonant peak of AuNRs at 800 nm, which has the maximum optical transmission through tissues. The AuNRs displayed excellent two-photon photoluminescence imaging; this makes them ideal probes for in situ real-time observations. The results revealed internal cavities in cells, created from thermal explosions triggered by AuNRs localized photothermal effect. The energy threshold for cell therapy depended significantly on the number of nanorods taken up per cell. For an ingested AuNR cluster quantity N~10-30 per cell, it is found that the energy fluences E of 93 mJ/cm2 from a pulse laser with a duration of 505 μs can lead to effective cell destruction in a crumbled form. With N~60-100 AuNR clusters, a non-instant, but progressive cell deterioration can be achieved with an energy as low as E=18 mJ/cm2; this result is much lower than the established safety standard for medical lasers (100 mJ/cm2).

參考文獻


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被引用紀錄


何思瑩(2015)。英語電子繪本提升國小低成就學生創造力之行動研究〔碩士論文,中原大學〕。華藝線上圖書館。https://doi.org/10.6840%2fcycu201500368

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