My research interests have been the development and study of novel low dimensional materials (2D van der Waal heterostructures) through building atomically-thin-Lego from graphene, molybdenum disulfide (MoS2) and other similar van der Waals materials for highly sensitive photodetection and quantum sensing applications e.g. number resolved single photon detection etc.
Our experimental investigations have confirmed that the electrical property of one van der Waals material (graphene, bilayer-graphene) can be combined with the optical property of the other van der Waals material (molybdenum disulphide (MoS2)) by physically stacking these together and forming heterostructures (Nature Nanotechnology 8, 826-830 (2013)). Irrespective of the nanoscale thickness (< 10 nm), such combination allows achieving extremely large photoresponsivity which is not observed in conventional photo-sensitive materials/devices. Our recent results with bilayer-graphene-MoS2 heterostructures show that such devices can be operated as number-resolved single photon detectors (Advanced Materials, In press (October-2017)).
In collaboration with Paria et al., we have also demonstrated that nanostructure of dimers can be used to enhance light matter interaction in a monolayer graphene leading high photoresponsivity (Advanced Materials 27, 1751-1758 (2015)).
I am currently looking into the electrical transport properties as well as the optical response of ultra-thin semiconducting Tellurium (Te) nanowires (NWs). The preliminary transport results show that the transport in Te NWs is thermally activated in high temperature (>170K) and in the low temperature (<170K), Mott Variable Range Hopping (VRH) takes place. On the other hand, Te NW serves as an excellent candidate for near-infra red detector, as it is a narrow band-gap semiconductor (~0.6 eV). This allows us to investigate this interesting and highly popular field full of new novel physics of light-matter interaction as well as basic applications.
High-mobility graphene heterostructures provide the unique opportunity to probe the intrinsic properties of graphene, as well as promise to broaden the application potential of graphene. My research focuses on exploring the transport and scattering mechanisms of Dirac carriers in high mobility graphene devices, especially at the graphene metal interface. We also study low-frequency noise in such heterostructures with the dual aim of fundamentally probing the noise mechanisms, and to understand the origin of noise to eventually minimize device noise for potential applications
Thermo-electric transport in Van der Waal junctions.
When two planar atomic membranes are placed within the van der Waals distance, the charge and heat transport across the interface are coupled by the rules of momentum conservation and structural commensurability, lead to outstanding thermoelectric properties. My research focuses on exploring the electric and thermoelectric transport across the van der Waals gap formed in twisted bilayer graphene (tBLG). The Tunability of cross-plane Seebeck effect in van der Waals junctions may be valuable in creating a new genre of versatile thermoelectric systems with layered solids.
Publications: “Seebeck coefficient of a single van der Waals junction in twisted bilayer graphene”, P. S. Mahapatra, K. Sarkar, H. R. Krishnamurthy, S. Mukerjee and A. Ghosh(accepted Nano Letters DOI:10.1021/acs.nanolett.7b03097)
Electronic and Structural properties of Interface engineered atomically thin 2-D crystals:
Transition Metal Di-Chalcogenides (TMDCs) have gained enormous attention due to their rich electronic and structural properties i.e. direct Eg in 1L, thickness dependent Eg, spin valley coupling etc. Although TMDCs are normally semiconductors, It has been theoretically predicted that they can have a variety of crystalline phases which are normally unstable. A novel technique to stabilize one such ferroelectric phase in MoS2 has been discovered. Our spectroscopic and electronic evidences confirm that 1L MoS2 can be converted into a ferroelectric. The ferroelectric negative capacitance is being subsequently used to break the theoretical lower limit of subthreshold slope in FET.
Electronic, optoelectronic and low frequency noise measurements in transition metal dichalcogenide (TMDC) field effect transistors. Fabrication and characterization of TMDC based heterostructures aimed at optical and ferroelectric applications.
My research focuses on probing magnetism along grain boundaries in 2D materials. Grain boundaries have long been considered a bane in the large scale fabrication of 2D materials such as graphene and transition metal dichalcogenides (TMDCs) by chemical vapour deposition (CVD) leading to polycrystallinity and poor structural and electrical performance. However, recent theoretical studies have predicted the manifestation of magnetism along such grain boundaries due to the nature of defects that constitute them. It will be interesting to probe and quantify the magnetic field strength arising out of these structural defects and suggest potential applications for their use in spintronics, spin filters or even in the hunt for the elusiveMajorana fermions.