Abstract
Metamaterials are a new class of artificial electromagnetic materials in which the size of building elements is smaller than the wavelength of illuminating light. Based on the collective resonances in the internal structures, metamaterials enable optical and physical properties which have not been presented in naturally existing materials. Among them, the split-ring resonator (SRR) remains the most common artificial structure and its fundamental resonant behaviors are conventionally understood by the equivalent LC circuit model. Nevertheless, the nature of multiple resonances in SRR still cannot be elucidated well. Thus, at first we reported the model of standing-wave plasmonic resonances. Such expression explicitly provides the universal model for the multiple resonances in SRR and additionally allows us to estimate the wavelength of multiple resonances. Next, the dependence between the polarizations of incident wave and the resonant characteristics in SRR was experimentally investigated. The origin of these resonances can be elucidated by both quantitative spectroscopic measurements and the distribution of the simulated surface current density, indicating that the resonances of the SRR stem from the superposition of the horizontally and vertically electric excitations. In addition, we demonstrate scalable MSRRs which present the tailored electric and magnetic responses at desired frequencies, paving ways toward integrated nanophotonic applications. Finally, we introduce the coupling of plasmonic resonances in the SRR pairs, especially in the asymmetric one that supports an extraordinary electromagnetic response referred to as asymmetrically coupled resonance (ACR). By artificially mimicking the subradiant and superradiant modes in a plasmonic manner, we observe that the ACR response is excited in case of strong coupling between a narrow subradiant mode with a broad superradiant mode, and this ACR can be modulated by varying the spacing of two SRR constituents. The excitation of ACR is further associated with excellent sensitivity and narrow bandwidth, leading a remarkable optical sensing technique of freeing from label agents and optical couplers but possessing great values of FOM, to benefit practical applications of chemical and biological detection. In addition, the synthesis of single-crystalline, well-aligned and large-area SiNW arrays with the morphological control of their orientations, diameters and lengths is demonstrated. We utilized a statistic electroless metal deposition method (SEMD) to synthesize SiNWs from three oriented Si (100), (110) and (111) substrates. The preferential crystallographic orientation of fabricating SiNWs is the <100> direction, proved by both TEM diffraction patterns and the orthographic projections on three oriented Si substrates. The formation mechanism of anisotropic SiNWs can be successfully elucidated in accordance with both the lattice configuration of oriented Si surfaces and the passivation effect on the H-terminated planes. The diameter control of SiNWs is achieved by employing the Taguchi methods, promising the capability of controlling the diameter with narrow distribution and comprehension of the influences from all process factors. The length of SiNWs presents fast (up to 1 □m/min) and linear dependence with the immersion time. Finally, the thermal conductivity of SiNW arrays was measured, showing about 40% of reduced values in comparison with bulk Si wafer. The SEMD technique reported here provides advantages such as almost room-temperature operation and catalyst/dopant free, paving a way towards the implementation of SiNW-based devices in nanoelectronics, nanoscale optoelectronics, nano-electro-mechanical systems, and biological detection.