本研究嘗試結合氧化鋅(ZnO)奈米柱與金屬奈米粒子，探討此種複合結構對表面增益拉曼散射(surface enhanced Raman scattering, SERS)的影響。ZnO有兩種結構，六方纖鋅礦結構和立方閃鋅礦結構。這兩種晶體結構具有對稱性，因此具有壓電效應的特性，在應用上可發展為表面聲波元件、氣體偵測器等等。為了製作出具有SERS-active的基板，我們使用水熱合成法，在低溫的環境下，在矽基板上合成大面積且分布均勻的ZnO奈米柱。為了引發侷域表面電漿效應，我們在奈米柱上蒸鍍金屬，並利用快速退火的方式，把金屬薄膜形變為金屬奈米顆粒。金屬奈米顆粒形成的侷域表面電漿共振效應，會讓金屬奈米顆粒之間出現「熱點」，也就是拉曼訊號被極度放大的區域，這個放大訊號的機制，可用來偵測表面分子的濃度。 我們嘗試不同厚度的金屬薄膜: 10、20、30、40、50 nm，探討金屬厚度對表面增益拉曼效應的影響。找到效果最佳的厚度後，我們再以不同退火溫度: 300、400、500 ℃，探討退火溫度對表面增益拉曼效應的影響。 為了評估奈米結構的靈敏度，也就是可偵測的最低濃度，我們調製不同濃度的R6G(rhodamine 6G)螢光分子，並量測相對應的拉曼強度。量測結果顯示，這種奈米結構的SERS基板可測到濃度低達10-9 M的R6G分子，而無ZnO奈米結構的SERS，只能測到濃度在10-3M以上的R6G。增益因數為1.5×104，此結果證實ZnO奈米柱和金屬奈米粒子的結合，能提升拉曼訊號的強度。 ;This study investigated the effect of ZnO nanorods decorated with metallic nanoparticles on surface enhanced Raman scattering(SERS). ZnO has two crystalline structures, i.e. the hexagonal wurtzite structure and the cubic sphalerite structure. These two structures are of symmetric lattices and thus exhibit piezoelectric characteristics, be useful in the applications on surface acoustic wave devices, gas detectors, etc. In order to produce a SERS-active substrate, we employ a low-temperature hydrothermal method to synthesize large-area and uniform ZnO nanorods on silicon substrates . To attain the localized surface plasma resonance (LSPR) effect, we deposit a thin metal film on the nanorods, and use an annealing process to produce metal nanoparticles. The LSPR effect leads to the "hot spots" between adjacent metal nanoparticles, rendering greatly amplified Raman scattering intensities. The amplified SERS intensities can be used to determine the concentrations of fluorescent molecules. Different metal thicknesses (10, 20, 30, 40, and 50nm) on the ZnO-nanorod SERS substrate were firstly investigated to maximized the Raman scattering intensity. And then the effect of annealing temperature was studied with the optimized metal thickness. In order to evaluate the lowest detectable molecule concentration, we prepared the R6G (rhodamine 6G) solutions with different concentrations. The lowest detectable concentration was found to be 10-9 M, whereas the flat substrate gave the lowest detectable concentration of 10-3 M. Enhancement factor is 1.5×104. The result confirms that the ZnO-nanorod SERS substrate is effective in enhancing the Raman scattering intensity of fluorescent molecules.
