SARTHAK DAS - Academia.edu (original) (raw)

Papers by SARTHAK DAS

IEEE Transactions on Radiation and Plasma Medical Sciences

The rise in multidrug-resistant (MDR) ESKAPE bacteria have become a major therapeutic challenge g... more The rise in multidrug-resistant (MDR) ESKAPE bacteria have become a major therapeutic challenge globally. Recently, novel cold atmospheric pressure plasma (CAP) as an antimicrobial is becoming popular. In this study, an indigenously developed AC cold atmospheric pressure plasma jet (CAPJ) fed with argon gas was used to evaluate its antimicrobial efficacy on these bacteria isolated from clinical specimens such as urine, blood, and sputum in a tertiary care hospital in India. The difference in CAP's antimicrobial activity on Gram-negative bacilli (MDR E. coli) and Grampositive cocci (MDR S. aureus) was observed with various input parameters, such as microbial concentration, CAP exposure time, and exposure distance. It was observed that oxidative stress induced by reactive oxygen and nitrogen species (O2-, NO + , OH. , H2O2, ONOO-, NO. , NO2. , HO2. , O3-, etc.) and electrostatic stress by ions (Ar + , O + , O2-, OH-, NO + , OH + , NO3-, NO2-, O3-, etc.) might play a crucial role in microbial inactivation. In addition to this, a decrease in adenosine triphosphate concentration post-CAP exposure in a liquid media suggested an efficient microbial inactivation effect. The outcome of this research would be extremely beneficial to multidisciplinary researchers in this field. Index terms: Antimicrobial, cold atmospheric pressure plasma jet, multidrug-resistant ESKAPE bacteria, clinical isolates Abbreviations: CAP: Cold atmospheric pressure plasma; CAPJ: Cold atmospheric pressure plasma jet; RONS: Reactive oxygen and nitrogen species; MDR: Multidrug-resistant; MHA: Mueller-Hinton Agar; AST: Antimicrobial susceptibility testing; ATP: Adenosine-triphosphate; RLU: Relative This work did not involve human subjects or animals in its research. All authors declare that they have no known conflicts of interests in terms of competing financial interests or personal relationships that could have an influence or are relevant to the work reported in this paper.

ACS Photonics, 2020

In 1H monolayer transition metal dichalcogenide, the inversion symmetry is broken, while the refl... more In 1H monolayer transition metal dichalcogenide, the inversion symmetry is broken, while the reflection symmetry is maintained. On the contrary, in the bilayer, the inversion symmetry is restored, but the reflection symmetry is broken. As a consequence of these contrasting symmetries, here we show that bilayer WS 2 exhibits a quantum confined Stark effect (QCSE) that is linear with the applied out-of-plane electric field, in contrary to a quadratic one for a monolayer. The interplay between the unique layer degree of freedom in the bilayer and the field driven partial 1 arXiv:2011.06790v1 [cond-mat.mes-hall] 13 Nov 2020 inter-conversion between intra-layer and inter-layer excitons generates a giant tunability of the exciton oscillator strength. This makes bilayer WS 2 a promising candidate for an atomically thin, tunable electro-absorption modulator at the exciton resonance, particularly when stacked on top of a graphene layer that provides an ultra-fast non-radiative relaxation channel. By tweaking the biasing configuration, we further show that the excitonic response can be largely tuned through electrostatic doping, by efficiently transferring the oscillator strength from neutral to charged exciton. The findings are prospective towards highly tunable, atomically thin, compact and light, on chip, reconfigurable components for next generation optoelectronics.

ACS Applied Materials & Interfaces, 2020

Interface of transition metal dichalcogenide (TMDC) and high-k dielectric transition metal oxides... more Interface of transition metal dichalcogenide (TMDC) and high-k dielectric transition metal oxides (TMO) had triggerred umpteen discourses due to the indubitable impact of TMO in reducing the contact resistances and restraining the Fermi-level pinning for the metal-TMDC contacts. In the present work, we focus on the unresolved tumults of large-area TMDC/TMO interfaces, grown by adopting different techniques. Here, on a pulsed laser deposited (PLD) MoS 2 thin film, a layer of TiO 2 is grown by using both atomic layer deposition (ALD) and PLD. These two different techniques emanate TiO 2 layers with different crystalline properties, thicknesses and interfacial morphologies, subsequently influencing the electronic and optical properties of the interfaces. In contrast to the earlier reports of n-type doping for exfoliated MoS 2 /TiO 2 interfaces, large-area MoS 2 /Anatase-TiO 2 films had demonstrated a ptype doping of the underneath MoS 2 , irrespective of the adopted deposition technique. In addition, they manifest a boost in the extent of p-type doping with increasing thickness of TiO 2 , as emerged after analyzing the core-level shifts of the X-ray photoelectron spectra (XPS). Density functional analysis of the MoS 2 /Anatase-TiO 2 interfaces, for pristine and in presence of a wide range of interfacial defects, could explain the interdependence of doping and the terminating atomic-surface of TiO 2 on MoS 2. The theoretical results resemble well with the realistic scenario of large-area growths after incorporating minimization of surfacestrain via mutual rotation of the constituent layers. The optical properties of the interface, encompassing the photoluminescence (PL), transient absorption and z-scan two-photon absorption indicate the presence of defect-induced localized mid-gap levels in MoS 2 /TiO 2 (PLD), resulting quenched exciton signals. On the contrary, the relatively defect-free interface in MoS 2 /TiO 2 (ALD) demonstrates a clear presence of both A and B excitons of MoS 2. This outcome corroborates with the first-principles observation of the presence of localized traps at the interfacial band-structure in presence of the point defects. From the investigation of optical properties, we indicate that MoS 2 /TiO 2 (PLD) interface may act as a promising saturable absorber, having a significant non-linear response for the sub-bandgap excitations. Moreover, MoS 2 /TiO 2 (PLD) interface had resulted a better photo-transport. A potential application of MoS 2 /TiO 2 (PLD) is demonstrated by the fabrication of a p-type photo-transistor with the ionic-gel top gate. This endeavor to analyse and understand the MoS 2 /TiO 2 interface establishes the prospectives of large-area interfaces in the field of optics and optoelectronics.

IEEE Transactions on Radiation and Plasma Medical Sciences

The rise in multidrug-resistant (MDR) ESKAPE bacteria have become a major therapeutic challenge g... more The rise in multidrug-resistant (MDR) ESKAPE bacteria have become a major therapeutic challenge globally. Recently, novel cold atmospheric pressure plasma (CAP) as an antimicrobial is becoming popular. In this study, an indigenously developed AC cold atmospheric pressure plasma jet (CAPJ) fed with argon gas was used to evaluate its antimicrobial efficacy on these bacteria isolated from clinical specimens such as urine, blood, and sputum in a tertiary care hospital in India. The difference in CAP's antimicrobial activity on Gram-negative bacilli (MDR E. coli) and Grampositive cocci (MDR S. aureus) was observed with various input parameters, such as microbial concentration, CAP exposure time, and exposure distance. It was observed that oxidative stress induced by reactive oxygen and nitrogen species (O2-, NO + , OH. , H2O2, ONOO-, NO. , NO2. , HO2. , O3-, etc.) and electrostatic stress by ions (Ar + , O + , O2-, OH-, NO + , OH + , NO3-, NO2-, O3-, etc.) might play a crucial role in microbial inactivation. In addition to this, a decrease in adenosine triphosphate concentration post-CAP exposure in a liquid media suggested an efficient microbial inactivation effect. The outcome of this research would be extremely beneficial to multidisciplinary researchers in this field. Index terms: Antimicrobial, cold atmospheric pressure plasma jet, multidrug-resistant ESKAPE bacteria, clinical isolates Abbreviations: CAP: Cold atmospheric pressure plasma; CAPJ: Cold atmospheric pressure plasma jet; RONS: Reactive oxygen and nitrogen species; MDR: Multidrug-resistant; MHA: Mueller-Hinton Agar; AST: Antimicrobial susceptibility testing; ATP: Adenosine-triphosphate; RLU: Relative This work did not involve human subjects or animals in its research. All authors declare that they have no known conflicts of interests in terms of competing financial interests or personal relationships that could have an influence or are relevant to the work reported in this paper.

ACS Photonics, 2020

In 1H monolayer transition metal dichalcogenide, the inversion symmetry is broken, while the refl... more In 1H monolayer transition metal dichalcogenide, the inversion symmetry is broken, while the reflection symmetry is maintained. On the contrary, in the bilayer, the inversion symmetry is restored, but the reflection symmetry is broken. As a consequence of these contrasting symmetries, here we show that bilayer WS 2 exhibits a quantum confined Stark effect (QCSE) that is linear with the applied out-of-plane electric field, in contrary to a quadratic one for a monolayer. The interplay between the unique layer degree of freedom in the bilayer and the field driven partial 1 arXiv:2011.06790v1 [cond-mat.mes-hall] 13 Nov 2020 inter-conversion between intra-layer and inter-layer excitons generates a giant tunability of the exciton oscillator strength. This makes bilayer WS 2 a promising candidate for an atomically thin, tunable electro-absorption modulator at the exciton resonance, particularly when stacked on top of a graphene layer that provides an ultra-fast non-radiative relaxation channel. By tweaking the biasing configuration, we further show that the excitonic response can be largely tuned through electrostatic doping, by efficiently transferring the oscillator strength from neutral to charged exciton. The findings are prospective towards highly tunable, atomically thin, compact and light, on chip, reconfigurable components for next generation optoelectronics.

ACS Applied Materials & Interfaces, 2020

Interface of transition metal dichalcogenide (TMDC) and high-k dielectric transition metal oxides... more Interface of transition metal dichalcogenide (TMDC) and high-k dielectric transition metal oxides (TMO) had triggerred umpteen discourses due to the indubitable impact of TMO in reducing the contact resistances and restraining the Fermi-level pinning for the metal-TMDC contacts. In the present work, we focus on the unresolved tumults of large-area TMDC/TMO interfaces, grown by adopting different techniques. Here, on a pulsed laser deposited (PLD) MoS 2 thin film, a layer of TiO 2 is grown by using both atomic layer deposition (ALD) and PLD. These two different techniques emanate TiO 2 layers with different crystalline properties, thicknesses and interfacial morphologies, subsequently influencing the electronic and optical properties of the interfaces. In contrast to the earlier reports of n-type doping for exfoliated MoS 2 /TiO 2 interfaces, large-area MoS 2 /Anatase-TiO 2 films had demonstrated a ptype doping of the underneath MoS 2 , irrespective of the adopted deposition technique. In addition, they manifest a boost in the extent of p-type doping with increasing thickness of TiO 2 , as emerged after analyzing the core-level shifts of the X-ray photoelectron spectra (XPS). Density functional analysis of the MoS 2 /Anatase-TiO 2 interfaces, for pristine and in presence of a wide range of interfacial defects, could explain the interdependence of doping and the terminating atomic-surface of TiO 2 on MoS 2. The theoretical results resemble well with the realistic scenario of large-area growths after incorporating minimization of surfacestrain via mutual rotation of the constituent layers. The optical properties of the interface, encompassing the photoluminescence (PL), transient absorption and z-scan two-photon absorption indicate the presence of defect-induced localized mid-gap levels in MoS 2 /TiO 2 (PLD), resulting quenched exciton signals. On the contrary, the relatively defect-free interface in MoS 2 /TiO 2 (ALD) demonstrates a clear presence of both A and B excitons of MoS 2. This outcome corroborates with the first-principles observation of the presence of localized traps at the interfacial band-structure in presence of the point defects. From the investigation of optical properties, we indicate that MoS 2 /TiO 2 (PLD) interface may act as a promising saturable absorber, having a significant non-linear response for the sub-bandgap excitations. Moreover, MoS 2 /TiO 2 (PLD) interface had resulted a better photo-transport. A potential application of MoS 2 /TiO 2 (PLD) is demonstrated by the fabrication of a p-type photo-transistor with the ionic-gel top gate. This endeavor to analyse and understand the MoS 2 /TiO 2 interface establishes the prospectives of large-area interfaces in the field of optics and optoelectronics.