本計畫欲以一年的時間，利用氮化物奈米結構，在單分子偵測上開發一條新的研究途徑。我們將以此種新式的奈米結構產生“表面強化拉曼散射(surface enhanced Raman scattering, SERS)”，並利用增益介質(gain medium)的機制，將SERS訊號放大至單分子偵測所需的強度。此種檢測平台以金屬/奈米量子井的複合結構產生所謂的“熱點(hot spots)”，也就是SERS訊號被極度放大的區域。奈米量子井的材料為InGaN，是以有機金屬化學氣相沉積法(MOCVD)磊晶而成。MOCVD的磊晶參數，可有效而均勻地控制奈米量子井的尺寸與分佈密度。與傳統的平面式金屬奈米顆粒團(metal nanoparticle aggregates on flat surface)相較，MOCVD產生的奈米結構，可藉由磊晶參數的調整，大幅提高hot spots的可控制度，使得單分子的訊號更容易被偵測到。由於量子井可視為SERS的增益介質，用來補償能量至金屬與奈米表面所形成的表面電漿結構，以增強SERS的放大程度，因此量子井的發光波長、發光效率以及表面粗糙程度等條件，將直接影響hot spots 的密度與訊號強度。在目前的研究文獻中，此種具備增益介質的SERS平台相當少見，我們希望本計畫提出的奈米量子井結構，能解決單分子偵測上常遭遇的兩大困境：訊號密度太低、訊號強度太弱。 ;This project is to map out a new route for single molecule detection. We propose a III-nitride nanostructure as the next-generation platform for surface enhanced Raman scattering (SERS), with which the SERS intensity will be greatly boosted via a gain medium. The platform employs a metal/nano-quantum-well composite as the surface structure to form the so-called“hot spots”, i.e. the regions with significantly enhanced SERS intensities. The nanostructured quantum wells are made of InGaN and grown by metal-organic chemical vapor deposition (MOCVD), whose operation parameters can uniformly control geometric dimension and distribution density of the hot spots. Compared with the commonly used nanoparticle aggregates on flat surface, hot spots created by the MOCVD method are of much higher controllability, and are expected to improve the detection sensitivity. The InGaN quantum wells (QWs) act as the gain medium, pumping energy to the surface plasmons created at the metal/semiconductor interface. Consequently, the QW properties (including emission wavelength, emission intensity, surface roughness, etc.) are closely related to the density and the intensity of the hot spots. GaN and its compounds are chemically inert, physically robust, and biocompatible, making the compound an ideal substrate for single molecule detection. The proposed SERS structure is not only expecting much enhanced detection sensitivity, but also shows promising potentials in industrial applications. We aim to provide keys to the conundrums faced by single-molecule-detection studies over the years.
