“…as we go down in size, there are a number of interesting problems that arise. All things do not simply scale down in proportion. There is the problem that materials stick together by the molecular van der Waals attractions. It would be like this: After you have made a part and you unscrew the nut from a bolt, it isn’t going to fall down because the gravity isn’t appreciable; it would even be hard to get it off the bolt. It would be like those old movies of a man with his hands full of molasses, trying to get rid of a glass of water. There will be several problems of this nature that we will have to be ready to design for.” Feynman 29 Dec 1959
I am as curious as any other Homo sapiens. The only difference is I feed my curiosity as much time as it needs. Hence, I practice a life of a scientists. It enables me to seek answers to any interesting scientific questions, irrespective of any field. Some of my current research interests are enlisted here.
Trapping single molecule in liquid solution is challenging due to their fast diffusion (for eg. Rhodamine 6G, an organic dye molecule's diffusion coefficient is ~280 µm^2/s). We have built a modified version of anti-Brownian electro kinetic trap and tried to trap single molecules. Despite various efforts, trapping of a single molecule cannot be achieved for prolonged duration [Kumbhakar et al. 2014]. We decided to bring some extra muscles in the fluidic system, which will not allow the single molecule to go out of detection volume. Suppressing the diffusion in two dimensions and keeping one dimension free for mobile single molecules were required for this. Developing such fluidic system was not straightforward because the fluidic channels should have a diameter much less than the focal diameter i.e. the detection region (minimum of 400 nm). I have developed a nanofabrication method which is capable of producing multiple nanofluidic channels simultaneously with a diameter ranging from 30 nm to 100 nm. I have successfully performed single molecule experiment inside these nanochannels [Ghosh et al. 2020]
Single photon sources can be identified not only by photon antibunching but also by defocused imaging. Previously, we found using defocused imaging that carbon nanodots and ZnO nanorods show single-photon emission behaviour using defocused imaging. Defocused imaging is also useful to identify the orientation of the dipole or in other words orientation of nanomaterials. Information on the orientation of nanomaterials is not only useful to the electrodynamic interaction at the surface but also useful in manipulating the sensing or detection efficiency (from the biomolecular sensing perspective).
Molecular quantum mechanics of light-matter interactions
We used time-dependent density functional tight-binding calculation (TD-DFTB) to identify the structure of the atomic structure of the carbon nanodots with single-photon emission behaviour. We named a particular kind of carbon nanodots as graphene quantum dots (GQD). The photophysical behaviour of GQD shows a significant dependence on its structure (edge termination, shape, and number of atoms).
Shadow angle e-beam deposition
We have developed a high-throughput nanofabrication process for creating multiple nanofluidic channels [Ghosh et al. 2020]. These nanofluidic channels are useful in studying single-molecule level experiment as mentioned above.
Single-photon multilayer lithography
We have developed a single-photon multilayer lithography techniques, which is capable of producing high-aspect-ratio nanostructures. The highest aspect ratio obtained by us was 200:1. These nanostructures are intended to create for nanomechanical sensing.
We created a novel ZnO nanorods which show ultra-high piezoelectric as well as ferroelectric behaviour (ZnO is intrinsically a non-ferroelectric material with density functional piezoelectric response). While studying their electromechanical behaviour of individual single ZnO nanorods, Dr Ghosh's nanorods repeatedly showed a significant discrepancy from earlier reports. With this motivation, we have recently shown that atomic defects play a significant role in the mechanics of nanostructures [Ghosh et al. 2016]. Our finding is based on atomic force microscopy, hight resolution transmission electron microscopy, and large-scale atomistic simulation. Until our study, the role of defects was neglected while studying single-crystalline nanomaterials.
We have developed an AFM correlated electron microscopy-based method to study the nanotribology of articular cartilage, which contains a fragile complex network collagen fibres [Ghosh et al. 2012]. The aim of the study was to avoid measuring measurement induced artefacts on the soft and complex surface of cartilage. We developed a three-dimensional image reconstruction technique which contains high-resolution information from electron microscopy. The nanoscale information provided by the method have a potential impact on the arthritis research.
PortOscope: Portable optical microscopy
For public awareness, forensic application, and to excavate the history of astro-optics, we are developing a portable microscope which I call Protoscope. The project involves serious research and scrutiny of various optical elements and mechanical designing where I intend to use structural optimisation.
My active research works are related to:
# Long-range interaction between exciton-polariton condensates,
# Non-dissipative single-molecule-detection,
# Dynamic heterogeneity of protein,
# Opto-mechano-electronics of 2D materials,
# Single-molecule nanofluidics,
# Persistent-current in resistive nanomaterials.
Open Academic Research
An idealistic academic environment that is open to everyone. We create intellectual outputs towards a sustainable society and develop opportunities to seek answers to open questions. Creative thinking and curiosity-driven minds are the two core principles of the group. If we need to build a textile technology, we can not leave a weaver. Similarly, if we need to understand poverty, we bring economists. We avoid looking into academic achievements, instead seek talents and nurture them for the use of a sustainable society. We do not want to predict the future of our creative thinkers and fellows. We firmly believe in 'bright minds for a bright future'.