雷射捕陷誘發分子與膠體晶體動態成長機制之反射影像光譜解析

Abstract

本計畫的主要目標是用光譜去探究分子與膠體在液氣介面之雷射捕陷的動態過程。分子和膠體均 可藉由雷射捕陷作用在液體表面產生分子及膠體結晶化，我將利用空間解析反射影像光譜技術來探 討其成長過程。由於X 光分析需要高品質的分子晶體，而膠體晶體在光學裝置中的應用也越來越受 注目，因此根據現有的成果，本計畫未來會使用雷射精確地控制分子和膠體晶體的成長過程。 在2013 年，本人成功地使用雷射捕陷技術在液氣介面形成L-phenylalanine 晶體與晶體狀的奈米粒 子集合體，並在光學暗視野反射影像中觀察其晶體的成長過程。在影像中可清楚地觀察到因干涉所 形成的色彩變化，其色彩變化反映出單一晶體的厚度變化與內部奈米粒子的組合結構，所以必須要 進一步的以光譜分析結果來討論其成長機制。 在計畫第一年的工作中，將使用光學顯微系統去測量在雷射捕陷下單點的晶體反射光譜，藉此探 討L-phenylalanine 結晶化與其集合體的成形過程。預期將透過改變實驗操作參數，如:雷射功率、極化 率、濃度和溶劑，以及進一步的光譜分析，來觀察晶體垂直成長過程以及奈米粒子重排過程。研究 計劃所獲得的成果，將有助於未來相關工作中更精確而有效的控制晶體的成長。 第二年的計劃工作中，運用空間光學共焦顯微掃描技術，可將晶體反射光譜從單點測量拓展成 二維的動態測量，以此四維的測量技術(三維空間+時間)去測量晶體厚度與平面變化。本研究成果將 有助於雷射捕陷之動態過程與晶體成長機制的了解， 更可進一步藉此方法嘗試加速片狀 L-phenylalanine 晶體垂直方向的成長。運用空間光學共焦顯微掃描技術，可在此測量下觀測奈米粒子 集合體之粒子間距、晶體結構均勻性與規則排列厚度，所得到的資料圖譜將有助於光子膠體晶體製 備的相關進階研究。

The main objective of my project is to reveal spectroscopically laser trapping dynamics of molecules and colloids at an air/solution interface. The molecules and colloids evolve into molecular and colloidal crystals through surface laser trapping, respectively, and I intend to investigate their growth behavior using a spatial-resolved reflection spectroscopic technique based on optical interference. Needless to say, a high-quality molecular crystal is necessary for X-ray crystallographic analysis, and a colloidal crystal has received much attention toward the application of photonic devices. The results and knowledge obtained in this work will make it possible to precisely control crystal growth process of molecules and colloids by laser. In 2013, I succeeded in demonstrating formation of a plate-like L-phenylalanine crystal and a crystal-like nanoparticle assembly by surface laser trapping. Their growth processes were examined by monitoring their dark-field reflection images. In the imaging, we could clearly observe coloration due to interference of the incident white light, which gives information of crystal thickness and internal packing structure of nanoparticle assembly. As a next step, spectroscopic analysis of the reflected light during laser trapping is necessary and indispensable to discuss the laser trapping dynamics and mechanism quantitatively through crystallization and colloidal assembly. In the first year, we set up a new microscope system to measure a spatially-resolved reflection spectrum during laser trapping. Utilizing the developed system, we examine temporal change in reflection spectra of single L-phenylalanine crystal and single colloidal assembly formed by laser trapping. The quantitative analysis of the obtained spectra will reveal dynamics and mechanism of the crystal growth behavior perpendicular to solution surface and the nanoparticle rearrangement. Incidentally, the conventional transmission imaging never gives quantitative information to them. We change experimental parameters, such as laser power, polarization, concentration, and solvent, and investigate the parameter dependence of the trapping behaviors leading to the crystallization and the nanoparticle assembly. These results will give us critical insights to control the vertical crystal growth and the nanoparticle rearrangement by laser trapping. In the second year, we develop the spatially-resolved reflection spectroscopy from a single spot to the two-dimensional dynamic measurement using a scanning detection system. Simultaneous measurements of the time evolution of two-dimensional distribution of the crystal thickness and the temporal change in the crystal plane area are made possible by this system. Namely, the crystal growth behavior can be understood four-dimensionally (3D space + time). The understanding of trapping dynamics and mechanism under laser trapping will be elucidated quantitatively through the crystal growth behavior. Based on these findings, we also try to accelerate vertical growth of a plate-like L-phenylalanine crystal by this laser trapping technique toward real crystal engineering. In the nanoparticle assembly formation, inter-particle distance, homogeneity of the packing structure, and thickness of an ordered structure are mapped as functions of the spatial position and time, and the experimental condition dependence are investigated. These mapping are indeed considered to a new category of laser trapping studies on nanoparticle assembly, which will receive much attention from the viewpoints of fabrication of high-quality photonic colloidal crystals.