製備銀反蛋白石結構並以穿透式Ｘ光顯微鏡做結構分析

Abstract

本研究透過半自動化垂直電泳沈積法沈積粒徑約450nm的聚苯乙烯(PS)次微米球，形成排列整齊並且大面積的最密堆積結構，接著再以電化學沈積法沈積金屬銀，最後移除聚苯乙烯(PS)次微米球後即成功製備出銀反蛋白石結構。 而透過穿透式Ｘ光顯微術(TXM)分析反蛋白石結構，我們可得到穿透投影圖(簡稱二維影像)以及三維立體重建影像。在二維影像中，可看到以往SEM所看不到的形貌，且由於此種投影圖是穿透整體結構所顯現之圖形，因此結構內部的資訊亦會完整被顯現，如：結構有序性、晶界與缺陷分布以及結晶度等等。而在三維立體重建影像中，可清楚觀察反蛋白石結構內不為人知的秘密，例如發現各晶粒之成長方向並非完全相同，我們推測在最開始電泳沈積時，PS次微米球堆積成長方向即並非相同。此外在模型圖中可清楚分辨層與層之間排列的相對位置，進而推論內部結構是面心立方最密堆積(fcc)或是六方最密堆積(hcp)結構。用TXM分析反蛋白石結構不管在台灣或是於世界上都是無人分析過之技術，透過此分析術將為TXM開拓全新分析領域，也為反蛋白石結構開展一目了然且更為精確的結構分析方式。

We employ an electrophoresis process to prepare colloidal crystals in a planar form (basing on polystyrene (PS) microspheres of 450±50 nm in diameter) with superb surface uniformity. Subsequently, the colloidal crystal is served as a template to allow for the electroplating of silver into the interstitial voids among the PS microspheres, followed by the removal of the PS microspheres to obtain a porous silver skeleton at controlled layers/thickness. Next, the structural characteristics of the sample are determined by a transmission X-ray microscopy (TXM). The TXM is a powerful tool to obtain two-dimensional and three-dimensional images, as well as the composition profiles at nanometer resolution by illuminating the sample with intense X-ray photons and record any variation in the resulting transmittance from two-dimensional incident angle of 150°. The three-dimensional image is reconstructed via a mathematic algorithm combining various two-dimensional image contrasts. We demonstrate that the TXM can be used to determine relevant crystallographic information including defects, grain size, grain boundary, grain orientation and stacking sequence of the assembled PS microspheres.