摘要
類分子金屬奈米團簇其特殊類分子特性有:強光致發光和吸收以及固有生物相容性等。而金屬奈米團簇的高光穩定性和與尺寸相關的自發發光特性，可將其擴展至化學傳感器，生物醫學，光電子以及環境等各面上的應用。然而，我們將探討受激雷射發射使其能得更進一步的應用。在本研究中，我們提供一項達成此出色特性的方法。雙曲線超材料（hyperbolic metamaterials）因多層的金屬與介電質交錯構成的獨特設計，使其在動量空間等頻率曲線( iso-frequency curve )有雙曲線分布的特徵。藉由雙曲線超材料與高發光特性的銀金屬奈米團簇，可於室溫下以374 nm脈衝雷射激發以達擁有約0.5 kW cm-2 低閾值的強受激發射(隨機雷射)。銀金屬奈米團簇結合雙曲線超材料與以矽為基板相比，可使光致發光增強約35倍。由雙曲線超材料激發的高k模態 ( high-k modes ) 提供形成隨機雷射所需的相干閉合反饋迴路的可能性，從而減少與光子傳播相關的能量損失。我們以時域有限差分法( finite-difference time-domain )進行模擬，而結果也與實驗相吻合。此研究中我們僅初步展示自金屬奈米團簇的受激雷射，相信其存在許多其他替代方案來探索該令人振奮的研究主題，以用於未來具有成本效益與生物相容性的光電元件之發展。
並列摘要
Atomically precise molecular-like metal nanoclusters exhibit unique properties, such as strong photoluminescence and absorption with inherent biocompatibility, which enable to extend its applications to chemical sensing, biomedical imaging, optoelectronics, and many other areas. However, to upgrade their more advanced functionalities, stimulated laser emission is greatly desirable. Here, we provide a plausible approach to achieve this outstanding characteristic out of metal nanoclusters. Quite interestingly, by integrating hyperbolic metamaterials (HMM) with highly luminescent silver metal nanoclusters (Ag-TSA MNCs), a strong stimulated emission (random lasing action) with a low threshold of ~0.5 kW cm-2 is discovered. The light emission is enhanced by ~35 times when the solid-state assembly of Ag-TSA MNCs is integrated with HMM in comparison to that with a silicon substrate. The high-k modes excited by the HMM offer the possibilities of forming coherent closed feedback loops necessary for random lasing actions, thereby decreasing the energy loss associated with photons' propagation in the matrix. The simulations derived from the finite-difference time-domain (FDTD) method support the experimental results. Our study shown here paves an initial step to demonstrate stimulated laser action from metal nanoclusters. It is believed that there exist many other alternatives to explore this emerging research topic for the future development of cost-effective and biocompatible optoelectronic devices.