Research
Dr. Das is focused on designing modular cutting edge research projects suitable for undergraduate students.
I. Search for New Types of Memory Devices
The discovery of resistance switching memristors marks a paradigm shift in the search for alternative non-volatile memory components in the semiconductor industry. Normally a dielectric in these bistable memory cells changes its resistance with an applied electric field or current, albeit retaining the resistive state based on the history of the applied field. Despite showing immense potential, sustainable growth of this new memory technology is bogged down by several factors including cost, intricacies of design, lack of efficient tunability, and issues with scalability and eco-friendliness.
We have found an easy and environment friendly solution of this bottleneck. This work is featured as one of the top 100 Scientific Reports physics papers in 2018.
To learn more about our research on light activated memristors please checkout this link:
II. Frugal Science:
Plasma in a Kitchen Microwave
Plasma is ubiquitous in nature and readily observed as lightning on a stormy night, or as a static electric spark the moment before touching a door knob on a dry winter day. It is also found naturally occurring in stars , solar winds, upper atmospheric lighting and the awe generating lightning glow known as St. Elmo’s fire that sailors wondered about for centuries. Practical applications of plasma span a vast domain including, but not limited to, fusion energy generation, plasma TV displays, plasma enhanced chemical vapor deposition (PECVD), sputtering, semiconductor device fabrication, substrate cleaning and sterilization. Plasma is also referred to as the fourth state of matter.
Plasmas have never been easy to create or exploit. But now we can make them in our own kitchen. Our work on plasma has been featured by the MIT Technology Review.
This is a collaborative research project with Dr. Arturo Dominguez of the Princeton Plasma Physics Laboratory (PPPL).
For more details on the microwave plasma generation process please checkout this link:
III. Frugal Science: Benchtop Photolithography and Low Reynolds Number Microfluidic Mixing
ABSTRACT
When fluids flow through straight channels sustained turbulence occurs only at high Reynolds numbers [typically Re∼𝑂(1000)]. It is difficult to mix multiple fluids flowing through a straight channel in the low Reynolds number laminar regime [Re<𝑂(100)] because in the absence of turbulence, mixing between the component fluids occurs primarily via the slow molecular diffusion process. This Letter reports a simple way to significantly enhance the low Reynolds number (in our case Re≤10) passive microfluidic flow mixing in a straight microchannel by introducing asymmetric wetting boundary conditions on the floor of the channel. We show experimentally and numerically that by creating carefully chosen two-dimensional hydrophobic slip patterns on the floor of the channels, we can introduce stretching, folding, and/or recirculation in the flowing fluid volume, the essential elements to achieve mixing in the absence of turbulence. We also show that there are two distinctive pathways to produce homogeneous mixing in microchannels induced by the inhomogeneity of the boundary conditions. It can be achieved either by (1) introducing stretching, folding and twisting of fluid volumes, i.e., via a horse-shoe type transformation map, or (2) by creating chaotic advection, achieved through manipulation of the hydrophobic boundary patterns on the floor of the channels.
This paper has been published in Physics of Fluids (Letters): https://doi.org/10.1063/5.0088014
IV. Micro and Nano-scale Heat and Mass Transfer
In collaboration with Dr. Hadi Ghasemi of University of Houston we have developed a new models to understand the physics of evaporation in submicron and nano-scale. Surface tension and interface curvature play critical roles in generating evaporative mass flux in this scale and can boost the heat transfer by orders of magnitude.
This research was featured as a cover article in the ACS Applied Nano Materials:
https://pubs.acs.org/doi/abs/10.1021/acsanm.0c01304
Other related works on heat and mass transfer:
1. https://www.sciencedirect.com/science/article/pii/S0017931006002742
2. http://www2.mie.utoronto.ca/labs/tkl/publications/DasWardSurfTherm.pdf
V. Laser Scribed Graphene Supercapacitors
In past decades, the application of fractals to electrode design for enhanced signaling and electrochemical performance was a popular subject and enabled the growth of consumer micro-electronics. Supercapacitors, which are energy storage devices with many promising characteristics, have largely grown alongside of such developments in electronics, but little work has been done to use fractal electrodes in supercapacitors. In this project we investigate, plane-filling and fractal patterns in laser scribed graphene supercapacitor electrodes, allowing the scaling laws of capacitance with respect to fractal order and complexity to be examined for the first time. An interesting exponential relationship between capacitance and fractal order for the more open structured fractals was observed, the exponent of which was proportional to the Hausdorff dimension. Additional non-linear relationships between capacitance and order were observed for other structures which was correlated with inter-plate repulsion and differences in path length. These findings provide the first step in maximizing the efficiency of fractal-based electrolytic devices by exploring the non-intuitive trends in capacitance with respect to fractal order and complexity. To learn more about this work please see https://arxiv.org/abs/1810.00221
VI. Organic solar cells with bio and nano materials:
Photosynthesis is the most efficient solar energy conversion process through which solar photos can be captured and converted into other forms of usable energy.
Chlorophyll, a natural green pigment naturally found in leaves, absorbs photons and excites electrons from an occupied orbital to be promoted to a higher energy empty orbital. The excited state chlorophyll molecule has extra energy that it can transfer to other molecules and provide the energy necessary for a chemical reaction.
Similar to chlorophyll, anthocyanin is a common pigment commonly found in dark colored fruits and flowers. Highly efficient in absorbing light in the visible range (green to yellow), monolayers of anthocyanin pigments absorbed in an optically transparent thin layer of semiconductors such as Titanium Dioxide can generate free electrons when a photon is absorbed by the pigment, giving rise to electron injection in the conduction band of the semiconductor (Fig. 1). On the other hand natural perovskite (organo-halide) materials show similar behavior of photo excitation.
Our research group has been successful to harvest solar energy by mimicking nature and its solar energy harvesting process in photosynthesis.
We have extracted anthocyanin from different dark colored fruits, vegetables and flowers and/or used charge-transfer inorganic dyes and perovskite materials in conjunction with nano-particle like carbon nano-particles, nano-tubes, graphene and its composites to harvest solar energy in a paint based solar cell. The advantage of using bio and organic materials in photovoltaics are manifold, ranging from bio-degradability to material flexibility, while reducing significant carbon footprint in the manufacturing process.
For more details please checkout this link:
For more details please see: https://arxiv.org/abs/1810.00221
VII. Making nano-inductors Using Graphene
There is great interest in so-called nano-electronic devices due to the furious rate of device miniaturization. Fabrication of micro and nano scale resistors and capacitors have already been achieved steadily, but so far, there has been little development in the way of nano-scale coil inductors. This is because of the physical limitations in miniaturization of the design of a solenoid with wires coiled around a metallic core. So, while transistors get steadily smaller, basic inductors in electronics remained relatively bulky. Few methods exist for creating conductive polymer coils and graphene-based kinetic nano-inductors, but their large-scale fabrication process is complex and mostly beyond the current commercial technology available. So, a simpler, scalable, and robust fabrication technique is needed to overcome this bottleneck. In this work we demonstrate a new technique consisting of the laser lithography using a laser engraver of a (poly)vinyl alcohol (PVA)/graphene oxide film composite which results in a large inductive effect. We attribute this behavior to the formation of high curvature twisted screw dislocation type conductive pathways composed of polyacetylene chains linked by pi-pi interactions to reduced graphene oxide flakes resulting in inductive effect.
More details on this work can be found here.
VIII. Clay Composites as Separation Membranes
In collaboration with Dr. Aaron Persad of MIT we are investigating rotation of various shapes of solid objects to analyze their rotational modes and understand their dynamics in zero-g conditions.
Photos and videos of Zero-g Project
In the parabolic flight.
In the parabolic flight.
The ZeroG team.
UMES payload.
Payload for solid body rotation study in zero-g.
Payload for solid body rotation study in zero-g.
Payload for solid body rotation study in zero-g.
www.bigyan.org.in
The team.
3D printed asteroid 243 Ida
Sensor room inside the asteroid 243 Ida.
PCB designed and coded by UMES undergraduates.