OUR RESEARCH

Membranes from Exfoliation and Vaccum Filtration

To exploit the fascinating properties of two-dimensional materials, we exfoliate and re-assemble them to construct membranes of desired properties. With liquid-phase exfoliation and mechanical exfoliation methods, we fabricate centimeter and micrometer-sized membranes to study the transport of electrons, ions, protons, and gas molecules through them. We also fabricate nanotubes via hydrothermal methods. The electronic structure, surface charge, and the nature of the surface, whether hydrophobic or hydrophilic, is expected to influence the transport properties. An understanding of electrostatic, steric, hydrophobic interactions at the smallest scale help us to build new-generation membranes.

Membranes from Chemical vapor deposition (CVD) 

We use a chemical vapor deposition technique to grow mono- to a few layers of two-dimensional materials. Gas or solid precursors are typically used in this process. The grown thin materials are utilized in making membranes in the form of pores and heterostructures. We also use CVD to grow new materials and explore its electrical and magnetic properties with potential applications in magnetic sensing, quantum computing, etc. Currently, we are exploring the possibility of growing MXenes in our setup. 

We also work on liquid-based CVD processes. An atomizer is used to produce liquid droplets, which are exposed to a temperature sufficient to vaporize the droplets. A carrier gas is used to transport the species that are in the vapor form. We use ANSYS CFD simulations to understand the atomization process of droplets in the liquid-based CVD process and also to model the turbulent process.

The hunt for renewable energy sources has brought attention to the vast potential of a hydrogen-based economy. Hydrogen and its isotopes find a variety of applications in areas like fuel cells, nuclear fusion and spectroscopy etc. Proton exchange membranes (PEM) are an essential part of the fuel cells as they prevent the crossover of undesired species and increase the efficiency of the fuel cells. Finding a high-temperature-stable alternative to commercially used PEMs is a  critical problem in this area. We investigate various 2D materials for the fabrication of thermally stable, large-area membranes for potential usage in fuel cells.

Hydrogen isotope separation is another problem of our interest due to the energy and cost-intensive nature of traditional cryogenic techniques. The ever-growing library of 2D materials makes it possible to tailor the channel size of the membranes according to the application. In this regard, we design membranes with few angstrom channel sizes to see the isotope effects at room temperature by making use of phenomena like quantum tunnelling and quantum sieving.

The significant salt concentration difference at the seawater and river water interface is an enormous source of osmotic/blue energy. Tapping this green energy source is crucial in solving our future energy demands. In this context, membrane-based reverse electrodialysis (RED) technology that relies on the transport of salt ions is actively pursued. Several membranes were demonstrated to provide good power densities, however, meeting the industry standard of 5 W/m^2 is still a difficult task. 

We design membranes to harvest energy from the flow of ions and water through nanometer-sized channels. The water flows through narrow capillaries driven by evaporation and interacts with functional groups that are present on the capillaries to generate electricity. Natural evaporation can convert the thermal energy of water into electric power. 

We fabricate cost and energy-effective 2D membranes that can generate blue energy and hydro-voltaic energy with sufficiently large power densities that meet industry requirements.

We use finite element simulations to understand the transport of dilute species through angstrom-scale capillaries. At this scale, the size of the species becomes very important and many interesting effects such as dehydration and steric effects start to appear in the simulations. We use simulations to understand and visualize the distribution of electric potential inside a nanochannel and estimate the transport parameters of ionic species and water molecules, such as mobility, through confined nanochannels under various experimental conditions. The driving forces behind the transport could be a concentration gradient, potential gradient, or pressure gradient. We solve Navier-Stokes and Poisson-Nernst-Planck equations to estimate flux and ion selectivity, under both steady-state and transient conditions.

We also use ANSYS CFD simulations to understand the atomization process of droplets, their vaporization upon heat exchange, and the transport of vapors, in the liquid-based CVD process.

Manipulating the fluidic properties at the smallest scale is crucial to advance nanofluidics. We use an electric field to control the transport of ions through tiny capillaries that are present in membranes. The membrane is typically transferred onto a SiN or any platform that is mechanically strong, for measurement. Using lithography and etching process, we pre-fabricated apertures less than 10 um in size on the SiN membrane (having a thickness of 300 nm) and transferred 2D material on top of the aperture for transport measurements. Fabrication of the SiN template helps us to investigate the transport of ions, protons, and molecules across the thickness direction. 

2D materials are ideal for investigating the electric field effects of the transport properties. We explore both solid and liquid-gated devices to observe exotic properties such field induced metal-insulator transition, insulator-superconductor transition, magnetoresistance, modulation of proton currents, non-linear Hall effect, etc. These studies help us to understand the fundamentals that are responsible for these transitions as well as to design novel bolometers, fuel cells, magnetic sensors, etc. The device fabrication involves lithography, etching, and making contact with the thermal evaporator. 

We investigate electrical and magnetic transport properties of two-dimensional materials and their heterostructures, in the temperature range of 400 K - 1.5 K and magnetic fields up to 9 T. Our aim is to understand the artificial hexagonal structures, look for potential candidates exhibiting topological properties, new Dirac systems in 2D and 3D form, non-linear transport properties, anisotropic properties. For example, the observation of superconductivity, ferroelectricity, etc. at a magic angle between two hexagons, excited researchers to look for exotic properties that are arising from the twist of the Hexagons. The emergence of new symmetry or breaking of symmetry is realizable with different combinations of hexagons. The emerging field of twistronics is very promising and there is so much to explore, given the large family of hexagons.