No abstract

The need for wideband metamaterial absorbers (WBMA) for applications other than sensing and filtering has demanded modifications to the conventional three-layer metal-insulator-metal (MIM) absorber configuration. This modification often results in complex geometries and an increased number of layers requiring complex lithographic processes for fabrication. Here, we show that a metamaterial absorber with rectangular geometry in the simple MIM configuration can provide wideband absorption covering the ultraviolet and near-infrared spectral range. Due to its asymmetric nature, the WBMA is sensitive to the polarization of the incident light and independent of the angle of incidence up to about 45° depending on the polarization of the incident light. The characteristics of the WBMA presented here may be useful for applications such as detectors for wide spectral band applications.

We propose and demonstrate a scalable technique to grow a thin polycrystalline graphitic film directly onto a fused silica substrate. The technique is based on the pyrolysis of a photoresist in the presence of a sacrificial 10 nm thick nickel catalyst layer. The synthesized graphitic film with a thickness of about 50 nm possesses almost constant 40% absorptance over visual and near infrared spectral regions. By using Raman characterization, third harmonic generation spectroscopy, and the Z-scan technique we perform a comparative study of the films pyrolyzed with and without a Ni catalyst. We show that the amorphous carbon dominates the linear and nonlinear optical properties of the resist film pyrolyzed without the Ni catalyst. In contrast, in presence of a Ni catalyst layer, the pyrolysis leads to a graphitic film that demonstrates a strong saturable absorption behavior at 1550 nm wavelength and has a nonlinear refractive index comparable with that of graphene. Thus, the developed, transfer-free synthesis technique provides an alternative route towards the controllable growth of wafer scale graphitic films on the dielectric substrates for photonics applications.

We demonstrate that predepositing on the dielectric surface a nanometrically thin nickel film is sufficient to transform amorphous pyrolyzed photoresist film (PPF) into a graphitic film (GRF) enriched with nickel particles. The GRF shows three orders of magnitude higher carrier mobility than that of amorphous PPF, while its electrical conductivity doubles after etching away the nickel remains. The pronounced 2D peak in the Raman spectrum, almost dispersionless absorbance in the spectral range of 750 -2000 nm, and saturable absorption coefficient indicate that GRF possesses graphene-like band structure. The proposed cost-efficient and scalable synthesis route opens avenues towards fabrication of micron size patterned graphitic structures of any shape directly on a dielectric substrate. Having graphene-like transport and electrical properties at the 20 times higher absorbance than the single layer graphene, GRF is attractive for fabrication of fast modulators of optical radiation, bolometers and other photonics and optoelectronic devices that require an enhanced optical absorption.