金奈米顆粒的二階段熱膨脹現象

Two-step thermal expansion of Au nanoparticles

林政延(Cheng-Yen Lin)

指導教授 ： 李文献

國立中央大學/理學院/物理學系/碩士(2011年)

摘要

本論文探討金奈米顆粒的二階段熱膨脹現象，並透過觀測實空間電荷分佈圖來進行分析。
　　由熱蒸鍍冷凝法製備的金奈米顆粒，其XRD譜圖經分析得粒徑為1.6 nm。由變溫XRD實驗對金奈米顆粒做各溫度的掃描，分析的結果發現以200 K為分界的二階段熱膨脹現象：80 K至200 K晶格常數隨溫度變動不大，200 K至300 K則為熱膨脹。
　　透過GSAS軟體將各溫度的XRD譜圖富立葉轉換成實空間的電荷分佈圖來觀測晶格單胞中電荷分佈隨溫度的變化。分析的結果發現80 K至200 K由於電子從正電荷範圍移出造成正電荷範圍的熱縮，抗衡了聲子熱膨脹效應，使晶格常數隨溫度變動不大。而200 K至300 K則由於電子移入正電荷範圍造成正電荷範圍的熱膨脹，與聲子熱脹效應共同對晶格常數造成熱膨脹。

關鍵字

熱收縮 ； d軌域 ； 電子轉移 ； 二階段熱膨脹 ； 奈米顆粒 ； 金 ； 實空間電荷分佈圖

並列摘要

The two-step thermal expansion phenomenon of 1.6 nm Au nanoparticles was observed in this study. Moreover, employing the direct observation technique of charge distribution reveals charge transference that affects thermal expansion.
The gold nanoparticles powder was fabricated by employing the thermal evaporation method. The mean diameter of the sample is merely 1.6 nm determined by analyzing the X-ray diffraction pattern.
Temperature-dependent X-ray diffraction patterns were measured to study the thermal evolution of lattice constant. The results reveal a two-step thermal expansion phenomenon demarcated at 200 K. The lattice constant wouldn’t vary obviously from 80 K to 200 K, and from 200 K to 300 K it’s thermal expansion.
The X-ray diffraction patterns were also transformed into charge distribution maps through the Fourier function of GSAS. The results reveal charge transference that corresponds to the two-step thermal expansion. The electron gradually leaves from the region of positive charge from 80 K to 200 K which reduces the positive region, and that contends the phonon contribution to the expansion of lattice constant. The electron come into the positive region from 200 K to 300 K which expands the positive region and together with the phonon effect that cause thermal expansion of lattice constant.

並列關鍵字

two-step thermal expansion ； d-orbital ； theraml contraction ； nanoparticles ； gold ； FOBS ； charge distribution map ； electron transference ； NTE

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