Kandammathe Valiyaveedu Sreekanth

Graphene-gold metasurface architectures for ultrasensitive plasmonic biosensing

Graphene-gold metasurface architectures that can provide significant gains in plasmonic detection sensitivity for trace-amount target analytes are reported. Benefiting from extreme phase singularities of reflected light induced by strong plasmon-mediated energy confinements, the metasurface demonstrates a much-improved sensitivity to molecular bindings nearby and achieves an ultralow detection limit of 1 × 10(-18) m for 7.3 kDa 24-mer single-stranded DNA.

Excitation of surface electromagnetic waves in a graphene-based Bragg grating

Here, we report the fabrication of a graphene-based Bragg grating (one-dimensional photonic crystal) and experimentally demonstrate the excitation of surface electromagnetic waves in the periodic structure using prism coupling technique. Surface electromagnetic waves are non-radiative electromagnetic modes that appear on the surface of semi-infinite 1D photonic crystal. In order to fabricate the graphene-based Bragg grating, alternating layers of high (graphene) and low (PMMA) refractive index materials have been used. The reflectivity plot shows a deepest, narrow dip after total internal reflection angle corresponds to the surface electromagnetic mode propagating at the Bragg grating/air boundary. The proposed graphene based Bragg grating can find a variety of potential surface electromagnetic wave applications such as sensors, fluorescence emission enhancement, modulators, etc.

Excitation of gap modes in a metal particle-surface system for sub-30 nm plasmonic lithography

In this Letter, a near-field optical excitation of gap modes in a metal particle-surface system for patterning periodic nanostructure is proposed and numerically demonstrated using the finite-difference time-domain method. It is observed that high-density sub-30 nm periodic structures were achievable by employing an aluminium nanosphere-silver surface system. A 2D resist profile cross section using the modified cellular automata model, which was obtained through this proposed configuration, is also presented.

Interferometric lithography for nanoscale feature patterning: a comparative analysis between laser interference, evanescent wave interference, and surface plasmon interference

In this paper, we experimentally demonstrate and compare single-exposure multiple-beam interference lithography based on conventional laser interference, evanescent wave interference, and surface plasmon interference. The proposed two-beam and four-beam interference approaches are carried out theoretically and verified experimentally, employing the proposed configurations so as to realize the patterning of one- and two-dimensional periodic features on photoresists. A custom-fabricated grating is employed in the configuration in order to achieve two- and four-beam interference.

A planar layer configuration for surface plasmon interference nanoscale lithography

A planar layer configuration for surface plasmon interference lithography to realize one-dimensional periodic nanostructure is proposed and numerically demonstrated in this letter. High electric field distribution compared to conventional prism based configuration is found to be achievable with this and hence facilitate high contrast and high resolution features with good exposure depth. Finite-difference time-domain simulation results indicate that the feature size approximately at sub-65-nm is achievable by using silver metal layer and a p-polarized 427 nm wavelength illumination. Simulated resist profiles, using cellular automata model, obtained through this proposed configuration is also presented.

Four beams surface plasmon interference nanoscale lithography for patterning of two-dimensional periodic features

The interference of multiple counterpropagating surface plasmon waves as a lithography technique to pattern periodic two-dimensional features is proposed and illustrated in this article. The surface plasmons are generated by prism coupling method, by employing a custom made prism layer configuration and with a single exposure. 175nm periodic two-dimensional dot array patterns, with feature size as small as 93nm, have been realized using an exposure radiation of 364nm wavelength.

Surface plasmon enhancement in gold nanoparticles in the presence of an optical gain medium: an analysis

The localized surface plasmon (LSP) enhancement in a gold nanoparticle is demonstrated in this paper. The enhancement of LSP is influenced by both size and the dielectric gain medium surrounding the nanoparticles. The nanoparticle is found to induce plasmonic enhancement of varying degrees depending on its size, and it is inferred that a gold nanoparticle of size 60 nm exhibits the maximum LSP for 532 nm excitation. Singularity due to cancellation of SP loss by an infinite gain medium and LSP enhancement are studied using a pump-probe Rayleigh scattering experiment. Gold nanoparticles of average size 60 nm exhibit the lowest threshold power to observe Rayleigh scattering. Furthermore, compared with the bare nanoparticles, a 12.5 fold enhancement of LSP is observed when the nanoparticle of average size 60 nm is kept in the gain medium.

Gap modes assisted enhanced broadband light absorption in plasmonic thin film solar cell

In this paper, gap modes assisted enhanced broadband light localization and possible absorption in a thin film silicon solar cell is presented. The existence of gap modes in metal particle-surface based thin film silicon solar cell is numerically investigated for improved light absorption. About 10.2% increment in light absorption compared to bare thin film silicon solar cell is obtained and enhanced light absorption at longer wavelength range is observed. The enhancement is due to the modification of localized surface plasmon modes around the nanoparticles via exciting the gap modes in the space between the nanoparticle and the surface.

Biosensing with the singular phase of an ultrathin metal-dielectric nanophotonic cavity

The concept of point of darkness has received much attention for biosensing based on phase-sensitive detection and perfect absorption of light. The maximum phase change is possible at the point of darkness where the reflection is almost zero. To date, this has been experimentally realized using different material systems through the concept of topological darkness. However, complex nanopatterning techniques are required to realize topological darkness. Here, we report an approach to realize perfect absorption and extreme phase singularity using a simple metal-dielectric multilayer thin-film stack. The multilayer stack works on the principle of an asymmetric Fabry–Perot cavity and shows an abrupt phase change at the reflectionless point due to the presence of a highly absorbing ultrathin film of germanium in the stack. In the proof-of-concept phase-sensitive biosensing experiments, we functionalize the film surface with an ultrathin layer of biotin-thiol to capture streptavidin at a low concentration of 1 pM.Optical sensors generally rely on abrupt phase changes to detect the presence of an analyte, but oftentimes they require complex nanostructures. Here, Sreekanth et al. use a simple asymmetric thin-film multilayer stack to demonstrate a point of darkness and phase singularity to develop a sensitive biosensor.

Single-exposure maskless plasmonic lithography for patterning of periodic nanoscale grating features

A lithography technique for patterning one-dimensional (1-D) nanoscale grating features based on surface plasmon (SP) interference is demonstrated both experimentally and numerically. We report a cost-effective, single-exposure maskless plasmonic lithography to generate 156-nm periodic grating lines at an exposure wavelength of 364 nm.