A triple-band perfect plasmonic metamaterial absorber based on a metal/insulator/metal (MIM) structure is designed. A new freedom through tuning the thicknesses of each ring structures is introduced to realize a quasi-three-dimensional perfect absorber at three extinction wavelengths by using the finite difference time domain method. The physical machine is explained by the time domain field analyses and the coupled mode theory. The characteristics of the absorber make our proposed strategy applicable for the design of more general multiband and broadband perfect absorbers. In addition, these perfect absorbing metamaterials are found to exhibit excellent performance in refractive index sensing.

With the development of advanced nanofabrication technologies over the past decade, plasmonic nanostructures have attracted wide attention for their potential in label-free biosensing applications. However, the sensing performance of nanostructured plasmonic sensors is primarily limited by the broad-line-width features with low peak-to-dip signal ratio in the extinction spectra that result from strong radiative damping. Here, we propose and systematically investigate the in-plane and out-of-plane dipolar interactions in an array of plasmonic nanoring resonators that are from the spatial combination of classic nanohole and nanodisk structures. Originating from the strong coupling of the dipolar modes from parent nanohole and nanodisk structures, the subradiant lattice plasmon resonance in the nanoring resonator array exhibits narrow-line width spectral features with high peak-to-dip signal ratio and strong near-field electromagnetic enhancement, making it an ideal platform for high-sensitivity chemical and biomedical sensing. We experimentally demonstrate that the plasmonic nanoring resonator array can be used for high-sensitivity refractive index sensing and real-time monitoring of biomolecular specific binding interactions at nanomolar concentration. Moreover, due to its simple normal incident illumination scheme and polarization independent optical response, we further transfer the plasmonic nanoring resonator array onto the optical fiber tip to demonstrate an integrated and miniaturized platform for label-free remote biosensing, which implies that the plasmonic nanoring resonator array may be a potential candidate for developing high performance and highly integrated photonic biosensing systems.

Graphene-semiconducting single-wall carbon nanotubes' (graphene-s-SWCNTs) thin-film photodetector based on a double-layer stacked heterostructure was fabricated. The carbon-based heterostructure exhibits excellent long-range van der Waals interactions. The as-fabricated device was demonstrated with an ultra-broadband photodetection characteristic with a high responsivity of 78 A/W at a visible wavelength and a fast response time of 80 μs. Moreover, the high photoconductive gain based on the photogating effect for the graphene-s-SWCNTs device was realized. In addition, the temperature-dependent photoresponse performance was also demonstrated. Benefiting from the high photoconductive gain, ultra-fast response time, and high stable quality of carbon materials, our devices exhibit great potential applications for high sensitivity detection to weak target signals in extreme environments.

Metamaterial based on a metal/insulator/metal (MIM) tri-layer structure provides an agile platform to realize high absorption efficiency for a variety of applications including semiconductor optoelectronic detectors. In this work, we use the finite time domain difference (FDTD) method and coupled mode theory (CMT) to numerically study metal/semiconductor/metal (MSM) structures and discuss their effective absorption for optoelectronic application. We compare MSM structures with a different top metal layer design and find that cross shaped absorber (CSA) and it's complementary cross shaped absorber (CCSA) exhibit different phase diagrams due to a distinctive dependence of radiation loss on geometrical parameters. Our results show that CSA (CCSA) structures are suitable for thinner (thicker) sandwiched semiconductor with a larger (smaller) imaginary part of its dielectric constant. The necessary condition to realize a maximum figure of merit (FOM) value for effective absorption is discussed in comparison with the perfect absorber condition. Our work may provide guidelines to design the general light-harvesting optoelectronic devices with high efficiencies based on metamaterial-semiconductor hybrid systems.