Monolayers of the transition metal dichalcogenides (TMDCs) are optically active direct bandgap semiconductors. These TMDCs are promising candidates for various optoelectronic and photonic applications such as sensing, nanolasers, photodetection and even solar cells. A monolayer of the TMDCs is atomically thin and it is known that its optical response dramatically changes if we stretch it. We can produce strain in these TMDCs in several ways: in-plane via stretching of the underlying PDMS film or its thermal expansion and out of plane by transferring it over the nanostructured surfaces and or by poking it with AFM tips. Engineering strain in these semiconducting TMD materials serves as a direct tuning knob for its band structure and consequently, it opens up a new avenue to study tunable optoelectronics for both fundamental as well as applied physics of TMDs.
Custom-made multi-purpose free optical characterization setup: The setup is built by me in LOQM from scratch. We can perform micro-photoluminescence, micro-Raman, micro-reflectance, and transmittance spectroscopy. We integrated the 514 nm, 532 nm, 632 nm, and tunable superK laser wavelength from 400 nm to 800 nm. We are also perform the lifetime and g(2) measurements with the 514 nm pulsed laser integrated with the same setup. In our setup, we can perform PL spectra and photon counts together.
Raman and PL microscopy setup: The setup is the central facility in the SAIF-CRNTS IIT Bombay. I have been exploring this setup for the last five years, and we can perform the experiments with four different lasers 385 nm, 532 nm, 633 nm, and 830 nm. We also have integrated closed cycle He-cryostat, where we can go up to 10K. In this setup we can also attach a Linkam heating stage, which can go up to 1500C.
Growth of Monolayer WSe2 using chemical vapor deposition method ;(a) Schematic of the two zone furnace, (b,c) Optical microscopy images of the CVD grown WSe2, (d) Atomic force microscopy image to show monolayer thickness (e,f) Raman and PL spectroscopy confirming the monolayer property of the WSe2.
Nanocone fabrication using colloidal lithography (a) Process Flow diagram for the fabrication of PTFE cone array, (b) SEM image of large scale PTFE nanocone array after etching (inset showing zoomed view of the cone),
Integration of the monolayer with nanostructure by wet transfer method (a) Process flow diagram for the wet transfer method (b) SEM image of the WSe2 monolayer transferred over the cone array (inset showing the WSe2 over single cone)
PL enhancement at the nanocones for WSe2. (a) micro-PL spectra of the transferred WSe2 over PTFE and Au nanocone structures. PL intensity with the variation of the excitation energy (b) For the PTFE cones (c) Au cones and (d) ratio (R) between Au to the PTFE (inset shows the line plot for ratio R for a maximum of the PL peak intensity (Au/PTFE) with the excitation power). FDTD simulation for the calculation of Field enhancement (e) For PTFE cone (f) For the Au cone
Sensing application using hydrophobicity and plasmonic properties of the nanocone ;(a). Contact angle measurements to check the hydrophobic nature of the (a) SiO2 deposited nanocone (b) SiO2+Au deposited nanocone (c,d) Raman Spectra of the R6G at SiO2 nanocone and SiO2+Au nanocone