Soumen Das

Bio: Soumen Das is an academic researcher from Indian Institute of Technology Kharagpur. The author has contributed to research in topics: Surface micromachining & Electrode. The author has an hindex of 25, co-authored 145 publications receiving 1937 citations. Previous affiliations of Soumen Das include Indian Institutes of Technology & Purdue University.

Novel Colloidal MoS2 Quantum Dot Heterojunctions on Silicon Platforms for Multifunctional Optoelectronic Devices.

Abstract: Silicon compatible wafer scale MoS2 heterojunctions are reported for the first time using colloidal quantum dots. Size dependent direct band gap emission of MoS2 dots are presented at room temperature. The temporal stability and decay dynamics of excited charge carriers in MoS2 quantum dots have been studied using time correlated single photon counting spectroscopy technique. Fabricated n-MoS2/p-Si 0D/3D heterojunctions exhibiting excellent rectification behavior have been studied for light emission in the forward bias and photodetection in the reverse bias. The electroluminescences with white light emission spectra in the range of 450–800 nm are found to be stable in the temperature range of 10–350 K. Size dependent spectral responsivity and detectivity of the heterojunction devices have been studied. The peak responsivity and detectivity of the fabricated heterojunction detector are estimated to be ~0.85 A/W and ~8 × 1011 Jones, respectively at an applied bias of −2 V for MoS2 QDs of 2 nm mean diameter. The above values are found to be superior to the reported results on large area photodetector devices fabricated using two dimensional materials.

Coronavirus disease 2019 (COVID-19) outbreak: some serious consequences with urban and rural water cycle

Abstract: The COVID-19 outbreak due to SARS-CoV-2 has raised several concerns for its high transmission rate and unavailability of any treatment to date Although major routes of its transmission involve respiratory droplets and direct contact, the infection through faecal matter is also possible Conventional sewage treatment methods with disinfection are expected to eradicate SARS-CoV-2 However, for densely populated countries like India with lower sewage treatment facilities, chances of contamination are extremely high; as SARS-CoVs can survive up to several days in untreated sewage; even for a much longer period in low-temperature regions With around 18 billion people worldwide using faecal-contaminated source as drinking water, the risk of transmission of COVID-19 is expected to increase by several folds, if proper precautions are not being taken Therefore, preventing water pollution at the collection/distribution/consumption point along with proper implementation of WHO recommendations for plumbing/ventilation systems in household is crucial for resisting COVID-19 eruption

Tunable Direct Bandgap Optical Transitions in MoS2 Nanocrystals for Photonic Devices

Abstract: Highly luminescent MoS2 nanocrystals (NCs) with controlled size distribution have been achieved using a simple yet inexpensive and impurity free sono-chemical exfoliation method followed by gradient centrifugation. The size of nanocrystals could be varied within the diameter range of ∼4 to 70 nm. Typical MoS2 nanocrystal has exhibited high crystalline quality with 0.25 nm lattice fringe spacing for (002) planes for 2-H phase of MoS2. Raman spectra has revealed that both out-of-plane and in-plane vibrational modes are stiffen due to the edge effect of MoS2 NCs. The size tunable optical properties of MoS2 NCs have been investigated by optical absorption and photoluminescence spectroscopy. The coexistence of direct band gap emission from 2D MoS2 nanosheets and quantum confined nanocrystals has been achieved. A strong and tunable photoluminescence (560–518 nm) emission due to the quantum size effect of tiny NCs below a critical dimension is reported for the first time. The photocurrent measurement of the Au/M...

Study of hydrophilicity and stability of chemically modified PDMS surface using piranha and KOH solution

Abstract: Successful realization of various BioMEMS devices demands effective surface modification techniques of PDMS elastomer. This paper presents a detailed report on a simple and cost effective approach for surface modification of PDMS films involving wet chemical treatment in two-step processes: primarily involving piranha solution followed by KOH dip to improve hydrophilicity and stability of PDMS surface. Chemical composition of the solution and surface treatment condition have been varied and optimized to significantly increase the surface energy. The effect of surface modification of the elastomer after wet chemical treatment is analyzed using contact angle measurement and FTIR-ATR study. PDMS surface treated in piranha solution with H2O2 and H2SO4 in the ratio of 2:3 followed by a dip in KOH solution for 15 min duration each, demonstrated a maximum reduction of contact angle to ∼27° as compared to untreated sample having a contact angle of ∼110°. The removal of hydrophobic methyl group from elastomer surface and subsequent hydrophilization of surface by wet chemical process was confirmed from FTIR-ATR spectra. This result is also supported by improved adhesion and electrical continuity of deposited aluminum metal film over the modified PDMS surface. Copyright © 2011 John Wiley & Sons, Ltd.

Design of Phase-Differentiated Reconfigurable Array Antennas With Minimum Dynamic Range Ratio

Abstract: In this letter, we propose a real-coded genetic algorithm (GA) for optimal design of reconfigurable dual-beam linear array antennas with phase only control. The problem is to find a common amplitude distribution with minimum dynamic range ratio (DRR) that will generate a pencil beam with zero phases and a flat-top beam with continuously controllable phases of an analog phase shifter. Results are also shown for the same design without minimizing dynamic range ratio (amax /amin) of excitation amplitude

Principles Of Fluorescence Spectroscopy

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Soft matter with hard skin : From skin wrinkles to templating and material characterization

Abstract: The English-language dictionary defines wrinkles as "small furrows, ridges, or creases on a normally smooth surface, caused by crumpling, folding, or shrinking". In this paper we review the scientific aspects of wrinkling and the related phenomenon of buckling. Specifically, we discuss how and why wrinkles/buckles form in various materials. We also describe several examples from everyday life, which demonstrate that wrinkling or buckling is indeed a commonplace phenomenon that spans a multitude of length scales. We will emphasize that wrinkling is not always a frustrating feature (e.g., wrinkles in human skin), as it can help to assemble new structures, understand important physical phenomena, and even assist in characterizing chief material properties.

Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem : a review

Abstract: Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.