電化學法成長金奈米結構在表面增強拉曼散射上之應用

Abstract

在本論文中，我們透過簡易的電化學法在基材上成長金的奈米片狀、奈米尖錐、奈米線等結構，這些金奈米結構是直接成長於基材上之晶種層並且以十分高的密度覆蓋著基材表面。整個合成反應的過程是經由一個簡單的二電極式的電化學沉積系統來完成。高密度的金奈米結構直接成長於基材上，在經過48個小時的成長之後，獲得的金奈米片狀結構的厚度約為150-200奈米厚；金奈米尖錐結構長約1-3微米，底部寬約300-500奈米，尖端處約為 20奈米；在金奈米線的部分，直徑約為50-80奈米，長度可達約20微米。整個過程中不需要使用任何的模板來幫助非等向性結構的成長。 我們關注於金奈米結構在表面電漿共振與表面增強拉曼散射之激發波長間的交互關係；透過使用表面電漿共振最大吸收峰之波長來當做表面增強拉曼散射之激發波長可達到最佳化的增益。我們對金奈米線之表面增強拉曼散射做進一步的探討，我們觀察到金奈米線的長度和密度對表面增強拉曼散射有顯著的影響，是歸因於在基材上金奈米線的交疊而造成局部電場的增強，這些增加的位置又稱為表面增強拉曼散射之熱點(hot spot)，我們可以觀察到這些由金奈米線交疊而形成的熱點之數量確實對表面增強拉曼散射有著很大的影響，並且我們可以金奈米線之基材感測到10-9 M 之低濃度R6G分子之表面增強拉曼散射的訊號。

We demonstrate a facile fabrication of gold nanostructures including Au nanoplates (NPs), Au nanothorns (NTs) and Au nanowires (NWs) on indium-tin-oxide (ITO) substrates via electrochemical growths. A simple two-electrode electrochemical deposition system was applied for the fabrication process. Dense Au nanostructures were grown directly on an Au seeding layer on the substrate. After 48 h, the Au NPs were 2 – 5 □m in width and 150 – 200 nm in thickness. The Au NTs were 1 – 3 □m in height, 300 – 500 nm in bottom side width, and 20 nm at the apex. The Au NWs were 30 – 80 nm in diameter and about 20 □m in length. The entire process was template-free and economical. We investigated the correlation between SPR and SERS effects of the Au nanostructures with different excitation wavelengths. By using the SPR absorption maxima of the nanostructures as the excitation wavelengths for SERS, the highest SERS enhancements were achieved. SERS effects of the Au NWs were investigated further. We discovered that the length and the density of the Au NWs affected the SERS performance significantly. The result is rationalized by the amount of “hot spot” generated at the crossing of the Au NWs. Using the Au NWs, Rhodamine 6G (R6G) can be detected at a concentration as low as 10-9 M.