光化學法調控嵌段共聚物有序奈米結構薄膜及其模板之應用

Tailoring Nanostructures of Diblock Copolymers by Photochemistry and Its Applications in Spatial Control of Ag and Ag@Au Nanoparticles

劉峻佑(Jiun-You Liou)

指導教授 ： 孫亞賢

國立中央大學/工學院/化學工程與材料工程學系/博士(2015年)

摘要

本研究利用聚苯乙烯聚2乙烯吡啶(polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP)之甲苯溶液，用以製備一微胞薄膜於矽基板上，透過原子力顯微鏡(Atomic Force Microscopy, AFM)與低掠角小角度散射儀(Grazing Incidence Small Angle X-ray Scattering, GISAXS)進行表面形貌之定性與定量分析。隨著提高製備溶液之濃度，即增加了微胞的覆蓋率，進一步發現到薄膜上的微胞結構呈現三種階段性的特徵型態:堆疊鬆散的球狀微胞、帶狀奈米結構以及雙層微胞之堆疊。除了得到旋鍍濃度與微胞結構之間的關係外，藉由分析此微胞薄膜之結構，循序漸進地建構了一套完整的擬合模型之系統，能夠延伸應用於微胞結構範疇內之研究對象。
首先，於第三章節介紹將建構的擬合系統套用於在大氣環境下紫外光(Ultraviolet, UV)照射促使微胞模板產生光劣化反應之GISAXS動態量測實驗。從一系列的影像擬合程序中，便可取得定量化的微胞結構演化資訊，並進一步比較微胞在UV光照降解下，其側向與縱向尺度變化程度可歸納出三階段演變，依序為:異向性蝕刻、等向性蝕刻與蝕刻終點。除了結構探討外，針對光化學造成高分子之化學鍵結的斷鍵與新官能基的衍生，更利用X-射線光電子光譜(X-ray photoelectron spectroscopy, XPS)深入鑑定其衍生物的種類，並將碳譜與氮譜作一分峰之數據處理，能夠精確了解各組成的含量變化用以解釋光降解對微胞結構的影響。此外，調控不同氣氛的照光條件，如氮氣環境下，發現到能大幅度減緩光降解反應，以提高光交聯反應程度，這將有效改善微胞結構的熱性質，以提升熱裂解溫度。
除了上述的UV光處理外，在第四章節中，進一步採用了常見的表面處理方法:紫外光/臭氧(UV/ozone, UVO)處理，作用於聚苯乙烯聚4乙烯吡啶(PS-b-P4VP)微胞薄膜上，意圖利用氧原子的掺雜作用下，造成醚氧鍵與酯鍵於高分子鏈段之中，而具有網狀交聯的複雜結構。因此，可抵制外界溶劑氣氛的膨潤現象，維持於當下奈米結構之型態。除了UVO處理的交聯效果外，再添加由上至下(top-down)的製程概念，即用以光罩(masks)達成區域性的交聯反應進而展現UVO lithography的技術，可任意調控任一奈米結構型態之區域分布。此外，更進一步地整合四種要素:UVO lithography、溶劑浸潤(solvent immersion, SI)、溶劑退火(solvent vapor annealing, SVA)與逐層沉積(layer by layer deposition)，可實現具有相異奈米結構型態分布的雙層薄膜。
第五章節，在操縱銀粒子陣列的實驗中，為了製備高碳餘率的碳化模板，我們由上述研究奠定了模板結構與光化學關係之中，選擇一最適化的光交聯反應之實驗條件，將PS-b-P2VP微胞薄膜進行了氮氣環境下的光照處理，隨後於惰性氣體下(argon)在430 oC中進行碳化反應用以製備碳化模板。藉由物理氣相沉積(physical vapor disposition, PVD)方式蒸鍍一層銀粒子在碳化模板上，利用熱回火誘使銀粒子產生重組現象，透過碳化模板的表面差異，促使銀粒子朝向碳材區域產生遷移，達到誘導陣列的效果。銀粒子遷移過程中除了藉助FE-SEM觀察外，也利用GISAXS進行動態量測實驗。
最後，透過PVD製備的銀粒子可由賈凡尼置換反應(galvanic replacement reaction, GRR)合成出合金金屬的奈米粒子。此外，我們也仿照常見的微胞合成金屬粒子的方法，將銀氨錯離子裝填於PS-b-P2VP微胞內製備銀粒子陣列模板。兩種製備的銀粒子均作為待置換的金屬，利用含有四氯金酸的乙醇與水溶液，以及氫氧化鈉或碳酸鉀中和的四氯金酸溶液，進行置換反應用以合成金銀合金的奈米粒子。在四種四氯金酸溶液之中，由於碳酸鉀中和的氯金酸鹽溶液(K-gold)，其氫氧化金具有較高的還原電位，因此最能夠達到具有空殼結構的金銀合金奈米粒子。

關鍵字

雙團鏈共聚物 ； 紫外光 ； 銀 ； 低掠角小角度散射

並列摘要

In Chapter 2, the lateral order and self-organized morphology of diblock copolymer polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP, micelles on silicon substrates (SiOx/Si) is reported in the thesis. The surface morphology was investigated by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). Upon progressively increased surface coverage with increasing concentration, loosely packed spherical micelles, ribbon-like nanostructures, and a second layer of spherical micelles were obtained sequentially. Afterwards, model simulations were constructed to analyze the 2D GISAXS patterns. The quantitative data analysis of GISAXS provides more details about the shape, dimension, and size distribution of micelles at different surface coverage densities on SiOx/Si.
In Chapter 3, the structural evolution of the PS-b-P2VP micellar film was investigated during UV exposure (UVE) treatment in air by in-situ GISAXS characterization and model simulations. This result indicates that three stages of structural change were identified: anisotropic etching, isotropic etching and etching termination. Quantitative analysis of carbon- and nitrogen-containing functional groups was probed by X-ray photoelectron spectroscopy (XPS). The structural evolutions of micelles induced by photo-oxidation and photo-degradation at three different stages of UVE in air were detailed and interpreted on basis of the XPS analysis. On the other hand, UVE irradiation was also imposed on PS-b-P2VP micelles in nitrogen (N2) for comparison. In N2, the cross-linking reaction was dominant over chain scission so that the thermal property of micelles was significantly improved.
In Chapter 4, a study worked on the stabilization of nanodomains within the thin films comprised of PS-b-P4VP micelles with UV/ozone (UVO) exposure, by which the swelling and shrinking for the nanostructures during solvent vapor annealing (SVA) could be inhibited. Upon selective stabilization of nanodomains by UVE irradiation through a mask, the film can concurrently have different types of nanostructures packed with a pattern defined by the mask. Furthermore, four crucial factors involving UVO lithography, solvent immersion (SI), SVA and layer by layer (LbL) deposition were combined to develop a feasible method of fabricating three-dimensional nanostructures.
In Chapter 5, a study focuses on the arrays of Ag NPs tailored by the spatial arrangement of nanostructured carbons. First, thin films of monolayer of PS-b-P2VP micelles with a hexagonal array were prepared by spin coating on SiOx/Si. Then UVE in N2 was implemented to stabilize PS-b-P2VP micellar films. Nanostructured carbons with hexagonal order were obtained by pyrolysis of the UVE-exposed films at 430 oC in argon (Ar) for 1 h. The top of the carbon templates was capped with a uniform Ag layer by thermal vapor deposition and then the specimens were subjected to thermal annealing at high temperatures. According to the different compatibility of silver NPs on top of carbons and SiOx/Si, the Ag NPs preferentially migrate onto the carbons. As a result, the spatial order of the Ag NPs could be controlled by the carbon templates. Ex-situ FE-SEM and in-situ GISAXS characterizations were used to analyze the structural evolution of the Ag NPs during thermal annealing.
In the final chapter, the ordered arrays of Ag NPs can be further used as sacrificial metals to synthesize bimetallic Ag-Au NPs through the galvanic replacement reaction (GRR). In addition to the above mentioned Ag NPs, a method of using BCPs micelles was also demonstrated as an encapsulated container to fabricate the Ag NPs. Furthermore, a array of bimetallic Ag-Au NPs using GRR with four types of precursor solutions was synthesized from the sacrificial Ag NPs based on BCPs and carbon templates, involving HAuCl4 ethanol solution, acidic and neutralized HAuCl4 aqueous solution and the potassium-containing basic solution of gold salt (K-gold). Among them, the K-gold solution is an appropriate agent to deposit the second metal due to the high reduction potential of the gold hydroxide.

並列關鍵字

Block copolymer ； UV ； silver ； GISAXS

參考文獻

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