用各種多面體奈米金粒子製備有序排列的超級晶體並觀察其形成過程

Fabrication of Supercrystals from Various Polyhedral Gold Nanocrystals and the Examination of Their Formation Process

廖晴文(Ching-Wen Liao)

指導教授 ： 黃暄益

國立清華大學/理學院/化學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00207

摘要

在本篇實驗中，我們使用本實驗室以植晶法所開發出來的奈米金立方體、菱形十二面體、八面體及截角八面體來製備出超級晶體。在高濕度環境下，將含有奈米金溶液滴於基板上，以較慢的揮發速率讓粒子有足夠的時間進行高密度堆積，由此得到微米級且具有立方體、三角形、八面體及菱形十二面體等不同形貌的超級晶體。值得注意的是，這些巨型結構是均勻分散在液滴乾後的範圍內，而非文獻常探討會集中在邊緣處(咖啡環效應)，同時我們也對它們的排列模式加以研究探討，其中，由文獻記載及我們的分析，不同於奈米球的緊密堆疊，多面體會受形狀效應主導它們的大規模排列。它們形成的過程與機制始終令許多科學家們感興趣，我們利用同步輻射中心所提供的穿透式 X 光顯微鏡進行即時影像紀錄，其中有觀察到類似成核長晶聚集成超級晶體的影像，還有藉由光學顯微鏡下，觀察到在液滴邊緣處粒子會以較快地對流運動進而形成完美的超級晶體結構。所形成的超級晶體即使經由強力震盪仍會緊密地吸附在基板上，不過當經過氫氧化鈉鹼溶液處理矽基板後，由於鹼會腐蝕矽，使得超級晶體對於基板的親和力變弱而能將其完整地取出。另外，我們發現由八面體構築的超級晶體有著豐富的孔隙空間，注入鈀溶液填滿其孔洞內可使還原成奈米粒子，透過電子顯微鏡證實鈀奈米粒子的形成，也因此這種超級晶體可視為一新形的中孔洞奈米金材料。這些超級晶體因熱區多應可作為表面增強拉曼光譜的良好基材。

關鍵字

超級晶體 ； 自組裝 ； 奈米金

並列摘要

In this work, we have successfully used gold nanocubes, rhombic dodecahedra, octahedra, and corner-truncated octahedra as building blocks with different sizes for the fabrication of supercrystals under a controlled solvent evaporation process. The gold nanocrystals were synthesized using a seed-mediated growth approach developed in our laboratory. The nanocrystal droplets were placed on a substrate in a moist environment. Using a slow solvent evaporation rate, these nanocrystals can have sufficient time to contact each other and form many micron-sized supercrystals with cubic, triangular, octahedral, and rhombic dodecahedral shapes. Remarkably, the supercrystals were found to scatter everywhere within the evaporating droplet, rather than concentrate near the rim of the droplet. The packing arrangements in these supercrystals have been carefully examined and their packing models are presented. Unlike the typical packing by spherical nanoparticles, large-scale assembly by non-spherical polyhedral nanocrystals is strongly shape-guided. The formation process was also studied by using transmission X-ray microscopy, which records in-situ nanocrystal assembly process on the substrate with a nanocrystal droplet. Optical microscopic observation revealed swirling motion at the rim of the droplet that may facilitate the formation of perfect supercrystals. These supercrystals remain adherent to the substrate when subjected to sonication, suggesting their use as modified electrodes. Treatment with NaOH solution can remove the entire supercrystals from the substrate. The presence of ample void spaces, particularly for supercrystals constructed from octahedral particles, may endow the supercrystals with mesoporosity. Accessibility of the mesopores was demonstrated by infusion of palladium source into the supercrystals and the deposition of Pd nanoparticles within the pores. Thus, the supercrystals may be considered as mesoporous gold with ordered pore geometry and arrangement. The supercrystals may also find use as excellent substrates for surface-enhanced Raman spectroscopy (SERS).

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