2D materials: fundamentals and applications
This is the newest research area we are involved with most diverse range of materials and opportunities. Starting with graphene and graphene oxide, over the recent years, we started synthesizing MoS2, WS2 flakes and quantum dots for their utilization in photodetectors and LEDs. Black phosphorous, MoSe2, PbS nanocrystals, graphene quantum dots are some of the current materials we are highly focused on. We explore their optoelectronic properties depending on nanocrystal size and nature of surface modifications. Recently, we have also ventured in the development of van-der-Waals' heterostructures of different 2D materials with the aim of non-linear photonics and optoelectronic devices. Collaboration within the group allows playing with these wide variety of 2D materials with other traditional semiconductors and plasmonic nanoparticles to study their optoelectronic properties and device performances. Light-matter interactions in the layered 2D materials (MoS2, WS2) via metal plasmonic integrations are also being studied along with many-body physics (excitonic complexes) in 2D semiconductors using miscellaneous optical spectroscopy tools, such as femtosecond pump-probe, near-field absorption and photoluminescence analysis.
Solvent-engineered performance improvement of GQD for solar cells
Unlike traditional dye-sensitized solar cells, N-GQDs replace toxic and readily degradable organic dyes as an active material, due to enhanced stability, cost-efficient fabrication, and environment-friendly processing. The report discussed compositional, optical, and electronic properties of N-GQDs synthesized in different solvents, and their role in the photoconversion efficiency of quantum dots sensitized solar cells.
-Dey, T et al., "Solvent-engineered performance improvement of graphene quantum dot sensitized solar cells with nitrogen functionalized GQD photosensitizers", Solar Energy (2022) DOI: 10.1016/j.solener.2022.02.048
Plasmonic enhancement of broadband photodetection metal-2D hybrid
The superior broadband photodetection characteristics of few-layer phosphorene known as black phosphorus (BP) nanosheets integrated with silver nanoparticles (Ag NPs) using vertical heterojunctions on a Si platform. The hybrid sample exhibits broadband light absorption with a strong plasmonic peak around ∼425 nm due to the localized surface plasmon resonance (LSPR) of Ag NPs of average size ∼6.0 nm. Spectroscopic analysis of the Ag-BP hybrid ascertains strong light–matter interactions around the LSPR band of Ag NPs. The size-dependent optical response of BP nanostructure/Si state-of-the-art broadband (300–1600 nm) photodiodes has been studied extensively.
-Jana, S et al., "Plasmonic Silver Nanoparticle-Mediated Enhanced Broadband Photoresponse of Few-Layer Phosphorene/Si Vertical Heterojunctions", ACSami (2021) DOI: 10.1021/acsami.1c19309
Substrate-dependent synergistic many-body effects in 2D materials
A systematic investigation of many-body effects is reported on ML WS2, while considering the modulated dielectric screening of three different substrates, viz., silicon dioxide, sapphire, and gold. Substrate doping effects on ML WS2 are discussed using the Raman fingerprints and photoluminescence spectral weight, which are further corroborated using theoretical density functional theory calculations. The variation of the Mott point, as well as the excitonic Bohr radius, is explained via the substrate-induced dielectric screening effect for both dielectric substrates, which is, however, absent in ML WS2 on Au.
-Das, S et al., "Substrate-dependent synergistic many-body effects in atomically thin two-dimensional WS2", PRM (2021) DOI: 10.1103/PhysRevMaterials.5.124001
Plasmonic enhancement of light-matter interaction in Au-MoS2 coupled System
In this work, the enhanced light–matter interactions by integrating plasmonic Au nanostructures as a light harvester on two-dimensional (2D) MoS2 carrier sink layers are reported, leading to broadband optical absorption and significantly enhanced Raman scattering. Theoretical modelling and experimental evidences suggest metal induced doping in MoS2 and the enhancement of electromagnetic field through localized surface plasmon resonance at the Au/MoS2 interface by forming a number of hot spots, corroborating the spectroscopic results. The ultrafast time-domain results reveal a 200-fold enhancement in the carriers’ lifetime for plasmonic nanohybrid.
-Mukherjee, S et al., "Plasmon Triggered, Enhanced Light–Matter Interactions in Au–MoS2 Coupled System with Superior Photosensitivity", JPCC (2021) DOI: 10.1021/acs.jpcc.1c00652
Solution processed 2D material-plasmonic nano-hybrid
MoSe2–Cu2–xS nanocomposites were synthesized using a colloidal route, where defect sites present on solution-processed MoSe2 nanosheets act as nucleation centers for the vertical growth of Cu2–xS islands with plasmonic characteristics. The djurleite phase (Cu1.97S) of Cu2–xS along with Cu2S nanoparticles which exhibit the localized surface plasmon resonance (LSPR) in the near-infrared (NIR) wavelength have applications in broadband photodetectors.
-Sarkar, S. S et al., "MoSe2–Cu2–xS/GaAs Heterostructure-Based Self-Biased Two Color-Band Photodetectors with High Detectivity", JPCC (2021) DOI: 10.1021/acs.jpcc.1c02038
Chemically synthesized highly-crystalline MoS2 & MoSe2 flakes
Bottom-up growth of 2D materials are required for large-scale applications. A redox-mediated green route growth of ultrathin, highly-crystalline MoSe2 nanosheets and nanocrystals is reported here. At solvothermal condition, molybdenum acetate [(CH3COO–)2Mo2+]2 at (+II) oxidation state is employed as the molybdenum source for the first time to grow 2D MoSe2 of 2H phase. The bottom-up solution-processed method differs distinctly from other available synthesis methods in terms of the 2D MoSe2 nanosheet growth of the semiconducting phase (2H) without using any template or any external reducing agent.
-Ghorai, A et al., "MoSe2 Nanosheets with Tuneable Optical Properties for Broadband Visible Light Photodetection", ACSanm (2021) DOI: 10.1021/acsanm.1c00129
In another report, a novel hydrothermal chemical approach used to synthesize micron sized few layer 2H-MoS2 on a large scale for broadband photodetectors and photocatalytic applications. Sodium molybdate and ammonium thiocyanate have been used as precursors to obtain template-free 2H-MoS2 in solution.
-Midya, A et al., "Hydrothermal growth of few layer 2H-MoS2 for heterojunction photodetector and visible light induced photocatalytic applications", JMCA (2016) DOI: 10.1039/C5TA09003B
Double Fano resonances in discrete excitons and single plasmon-continuum
Here, we present an experimental observation on time-domain response of the double Fano asymmetries in a metal–two-dimensional semiconductor hybrid prototype at room temperature. The ultrafast interactions in two discrete spin-resolved excitons of MoS2 and a single metal plasmon-continuum allow us to observe the generation and evolution of the double Fano line profiles in real time.
-Chowdhury, R. K et al., "Ultrafast real-time observation of double Fano resonances in discrete excitons and single plasmon-continuum", PRB (2020) DOI: 10.1103/PhysRevB.101.245442
Investigation of ultrafast light-matter interactions
Ultrafast real‐time observation of individual bright exciton–plasmon polaritons in Au nanostructures–layered WS2 hybrids is reported through helicity‐controlled pump‐probe spectroscopy technique at room temperature. Introducing metal nanostructures with specific dimensions, discrete anticrossing is attributed to strong coupling of individual bright excitons and plasmons in time domain. Both the polaritons show high Rabi‐splitting energies with similar stable plexciton formation times.
-Chowdhury, R. K et al., "Ultrafast Investigation of Individual Bright Exciton–Plasmon Polaritons in Size‐Tunable Metal–WS2 Hybrid Nanostructures", Adv. Opt. Mat. (2020) DOI: 10.1002/adom.201901645
2D material nanocrystals for optoelectronics
Nanocrystals of various 2D materials viz. graphene, MoS2, WS2, MoSe2, and BP show exceptional optoelectronic properties. The increase of confinement effects in the nanoscale results in exceptional properties like direct band gap photoluminescence. Solution-processed 2D nanocrystals have been applied to Si-CMOS compatible large scale optoelectronic devices. We have successfully demonstrated light emitting diodes [Ghorai, A et al. 1, Mukherjee, et al. 2], broadband photodetectors [Maity, R et al. 3, Mukherjee, S et al. 2 4, Chowdhury, R. K et al. 5, Sarkar, S, S et al. 6, Dey, T et al. 7, Jana, S et al. 8]. Follow the publications section for more.
