Refractometric sensing of silicon layer coupled plasmonic–colloidal crystals
Introduction
It is essential to identify and quantitate hazardous chemical or biological agents remotely before they achieve dangerous levels [1], [2], [3]. Attractive approaches to chemical and biological sensing would use methods that require no sample preparation and only need simple spectrum determinations. Many efforts have been made by using the polarized surface electron oscillations [4], [5], [6] in the well designed plasmonic structures [7], [8], [9], [10], [11], [12], [13]. Currently, great attention on the sensing has been attracted for the plasmonic M–CCs [14], [15], [16] thanks to their simple and low-cost fabrication features. Nevertheless, due to the highly confined optical cavity-like mode existing in the CC, relatively low sensitivity is obtained [16], which inevitably leads to strong limitations for further applications.
Herein, we demonstrate a novel spectral behavior with dual enhanced transmission peaks of an optimized M–CC via using a silicon layer as the buffer layer, which acts as an efficient optical field coupler and could produce strong electric field extraction [17], [18], [19] and reconfiguration effects [20], [21]. Improved sensing performances together with unique distinct sensing behaviors for these dual-band resonances are achieved. Moreover, the structure is quite simply designed and could be fabricated in a straightforward manner over large areas by the colloidal self-assembly methods [22] together with the standard metal/dielectric deposition techniques [23].
Section snippets
Experimental details
Monolayer CC consisting of monodisperse polystyrene (PS) spheres with diameters of 1.0 μm is self-assembled on a quartz substrate [16] as shown in Fig. 1(a). Si layer with controllable thickness (t=130 nm) is then sputtered on top of this CC to form the Si–CC [16], [23]. Finally, a 40 nm metal film (Au) is deposited on top of the Si–CC (Fig. 1(b)) by argon ion beam sputtering (Model 682 PECS, Gatan Corp.) in a vacuum of 5×10−6 Torr (1 Torr=133 Pa) at a rate of 0.6 A s−1. Numerous simulations are
Results and discussion
Fig. 1(c) shows an optical microscopy photo of the fabricated M–Si–CC and confirms the highly ordered large-area hexagonal-close-packed crystal. Scanning electron microscopy images of the M–CC and M–Si–CC are shown in Fig. 1(d) and (e), respectively. As discussed in the previous reports [16], [20], [21], [26], optically guided resonances could be supported by the spherical CC. In the case of ellipsoidal CC, the reshaped structure could show different optical properties due to the competitive
Conclusions
We have demonstrated a novel M–Si–CC structure with high-performance dual-band refractometric sensing. The introduced Si layer shows strong optical field coupling with the top metal film and the bottom CC. Moreover, the reconfigurations of the electric field distribution of the resonances for the M–Si–CC by the Si layer provide significantly improved plasmonic sensing responses. Distinct sensing behaviors are obtained due to the different optical responses of the resonances. Our findings might
Acknowledgments
This work was supported by National Natural Science Foundation of China (Grants. 11464019, 11264017 and 11304159), Natural Science Foundation of Jiangxi Province (Grant 20142BAB212001), Young Scientist Development Program of Jiangxi Province (Grant 20142BCB23008), Technological Projects of Jiangxi Provincial Education Department (Grant GJJ14253), and Key Projects of Jiangxi Normal University (Grants 6047, 5460).
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