- 學位論文
Ag-SrTiO3 奈米核-殼結構粒子 之研究與製備
Study and fabrication of Ag-SrTiO3 core-shell nanoparticles
摘要
中文摘要 核-殼結構(Core-Shell structure)界面層之奈米尺度，由於界面原子異質鍵結使得界面結構產生過渡區之組合。因而使核-殼形式之奈米粒子具有許多特殊電、磁性質、光學性質、及觸媒催化等的應用，引起廣泛的注意與研究。多晶材料之晶粒與晶界關係可視為一種核-殼結構，製作多晶材料之晶界能障層電容，具有超高等效介電常數（K＞104），但其晶粒需是導體，晶界為絕緣體的機制，形成所謂的背對背蕭特基能障（back to back Schottky barrier）之結構。本研究即利用核-殼結構之概念，預做晶界能障層；製作核為導體，殼為絕緣體之獨立晶粒與晶界關係之核-殼結構粒子，對其製程及界面關係做研究探討。本研究分為以商用銀粒子（~0.1mm）製備Ag-SrTiO3之核-殼結構；其次為以合成之奈米銀製備Ag-SiO2-SrTiO3核-殼結構；第三部份為以商用銀粒子及合成之奈米銀粒子製備Ag-TiO2之核-殼結構。在第一部份，使用水熱法改質商用銀粉，有頸縮效應，造成凝聚現象，在低濃度（0.028M）及水熱溫度低（150℃）時，凝聚現象大幅降低。而利用酸洗活化銀粉表面時，必須避免OH基的披覆而阻礙了偶合劑-APS在銀顆粒表面的完全反應。水熱製程促使鈦酸鍶結晶生成的粒徑約20~50nm範圍，較溶膠-凝膠/水熱製程所生成之鈦酸鍶粒徑小；由於水熱法的溶解-析出反應機制，破壞有機偶合劑的結構，使披覆之鈦酸鍶分離形成鈦酸鍶粒子，以致生成部份的Ag-SrTiO3核-殼結構。在第二部分，還原奈米銀的水溶液為金黃色，當銀粒子外披覆SiO2殼層時，溶液呈現暗黃色。經過溶膠-凝膠法，藉由在活性較大的奈米銀表面結合之偶合劑-APS鍵結二氧化矽，以此二氧化矽為界面層，披覆鈦酸鍶的殼層；因此偶合劑的使用對核-殼結構的形成具有其重要性。於第三部份，將奈米銀接合偶合劑-APS，以sol-gel方法於115℃反應1天，披覆上二氧化鈦；經由600℃熱處理，可以使披覆層達到完全緻密的效果，製備出單一的核-殼結構。若未使用偶合劑，表面活性大的奈米銀易與檸檬酸鈉進行螯合反應，二氧化鈦將受螯合披覆在奈米銀表面，形成一Ag-TiO2的核-殼結構。
並列摘要
Abstract The inhomogeneous atomic bonding was generated in nano-transition zone between core and shell structure. Thus, several researchers have focused on special electro-magnetic properties, optical characteristics and catalytic properties of core-shell structure particles. The ultra-high equivalent dielectric constant （K>104） resulted from polycrystalline grain boundary barrier capacitors is based on the back to back Schottky barrier model. In this model, the requirement is for the grains conductive and the grain boundaries insulate. This study will prepare the core-shell structure of conductor-insulator based on the concept of Schottky model and will further study the interfaces of the core-shell structure. There are three parts herein including Ag-SrTiO3 core-shell structure preparation by commercially available silver particles (~0.1mm); Ag-SiO2-SrTiO3 core-shell structure preparation by synthesized nano-silver particles and only Ag-TiO2 core-shell structure preparation by commercially available silver particles. In the first part, the particles necking and then aggregate was observed on surface modified commercial silver particles. The aggregate behavior could be improved at lower silver concentration (0.028M) and lower hydrothermal treatment temperature (150℃). However, the OH group residue on acid activated silver surface should be avoided to prevent coupling agent-APS from uncompleted reaction on the silver surface. The particle size distribution of strontium titanate is in the range of 20~50nm by hydrothermal process, which is smaller than by sol gel/hydrothermal process. The obtained partial Ag-SrTiO3 core-shell particles and few discrete strontium titanate particles were believed that the coupling agent layer was broken-down due to dissolution/precipitation in the hydrothermal process. In the second part, we observed that the synthesized nano-silver solution after reduction exhibited color of light yellow, but the aqueous solution containing Ag-SiO2 core-shell particles exhibited color of dark yellow. The core-shell structure of Ag-SiO2-SrTiO3 was successfully synthesized by use of coupling agent-APS coupled with nano-Ag surface and bonded to SiO2, then the SrTiO3 surrounded SiO2 layer completely. Therefore, the coupling agent played an important role for the formation of core-shell structure. For the third part, the nano-silver and organic titanium were both coupled with APS to react in sol-gel process at 115°C for one day. The dense core-shell structure of Ag-TiO2 was obtained after 600°C heat treatment. Another core-shell structure of Ag-TiO2 was also observed by chelating sodium citrate on nano-silver without use of coupling agent.