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Plasmonics and Metamaterials

Interactions between single metal nanoparticles:

The enhanced scattering cross sections due to Localized Surface Plasmon Resonance (LSPR) allow the imaging of single metal nanoparticles using a dark-field (DF) microscope. In Prof. Manoj Varma‘s lab, DF imaging is being used to study interactions between functionalized single nanoparticles and biomolecules.

3D plasmonic metamaterials

The focus of the research pursued by the group led by Dr. Ambarish Ghosh is to engineer plasmonic interactions in three dimensions to develop novel optical metamaterials. While 1D and 2D plasmonic systems are quite well understood, study of 3D plasmonic systems in three dimensions has been limited. While recent advances in nanotechnology pave the way for successful design and fabrication of 3D plasmonic metamaterials, challenges still exist at optical frequencies.

Ours is the first experimental group in the world to develop a wafer scale technology to fabricate porous 3D plasmonic metamaterial which can be used over a wide range of wavelengths, including the visible. Our technology allows a wide range of materials and geometries, and therefore highly versatile. We have used a technique called GLAD (Glancing Angle Deposition- a technique known for generating various porous 3D dielectric structures) and have integrated plasmonics to develop an arrangement of metal-dielectric layers in 3D. The system can serve as a powerful platform to investigate plasmonic (near and far field) interactions such as to design various photonic devices of technological importance, such as the development of perfect reflectors and absorbers.

Chiral metamaterials

At resonance, the plasmons of individual metallic NPs can be strongly coupled to each other via dipolar interactions. By arranging the metallic NPs in a chiral (e.g. helical) geometry, it is possible to induce collective excitations that oscillate along a plasmonic chiral structure of a certain handedness, which lead to differential optical response of the structure to right- and left circularly polarized light (e.g. Circular Dichroism – CD). Recent advances in this field include novel techniques of synthesizing metallic nanoparticles on helical scaffolds made from DNA, certain proteins etc. In our research, we have developed new ways of fabricating chiral complexes made of metallic NPs, which demonstrate a very strong chiro-optical response. These metamaterials are potential candidates for showing negative indices of refraction, and may work as very efficient broadband polarization devices as well.

Graphene-plasmonic hybrid photonic devices

We are interested in coupling plasmonic materials with atomically thin membranes, such as Graphene, MoS2 etc to make opto-electronic devices of with new and improved functionalities. Very recently, we have demonstrated a conceptually novel method to integrate plasmonic nanoparticles with graphene, such as to achieve unprecedented EM field enhancement and photodetection sensitivity (almost 100 times more than previous graphene-hybrid photodetectors). The scalability of the entire process flow allow the development of large area devices, while the fabrication technique is general enough to be easily applicable to plasmonic nanoparticles of other sizes and materials, arrays of other 2D geometries, as well as other atomically thin membranes.