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Papers by Asoka Kumar Das

Research paper thumbnail of Bactericidal efficiency of nanostructured Al–O/Ti–O composite thin films prepared by dual magnetron reactive co-sputtering technique

Ceramics International, 2014

Mixed oxide Al-O/Ti-O composite nanostructured thin films were prepared at Ar:O 2 gas ratio of 70... more Mixed oxide Al-O/Ti-O composite nanostructured thin films were prepared at Ar:O 2 gas ratio of 70:30 (7:3 in sccm) by reactive magnetron co-sputtering method. The effect of Al in the films on the antibacterial efficiency has been studied. In situ optical emission spectra (OES) were recorded in order to study the plasma chemistry as well as nucleation and growth process during deposition. The films were characterised by Xray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), field emission scanning electron microscope (FESEM), optical contact angle (OCA) and UV-visible transmission spectra (UV-vis). The qualitative and quantitative bactericidal efficiency was studied through SEM image of the treated E. coli cells (Escherichia coli NCIM 2809) and optical density (OD) measurement using UV-vis spectrometer, respectively. The better bactericidal efficiency was observed in the film with more Al content. The crystallinity, surface chemical composition, band gap in context of Al present in the films were discussed and correlated to bactericidal efficiency in the light of in situ investigation of plasma from OES.

Research paper thumbnail of Synthesis of AlN∕Al Polycrystals along with Al Nanoparticles Using Thermal Plasma Route

This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride cry... more This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride crystals during synthesis of aluminum nanoparticles in dc transferred arc thermal plasma reactor by gas phase condensation in nitrogen plasma. The structural and morphological study of as synthesized AlN crystal and aluminium nanoparticles was done by using the x-ray diffraction method, scanning electron microscopy and

Research paper thumbnail of Numerical investigation of nanoparticle synthesis in supersonic thermal plasma expansion

Research paper thumbnail of Bias-independent growth of carbon nanowalls by microwave electron-cyclotron resonance plasma CVD

Journal of Experimental Nanoscience, 2012

The investigations reported here describe the synthesis of carbon nanowalls (CNWs) by microwave e... more The investigations reported here describe the synthesis of carbon nanowalls (CNWs) by microwave electron-cyclotron resonance (ECR) plasma-assisted chemical vapour deposition (PACVD) process without an application of external bias to the substrate during growth. CNWs were grown on silicon (Si) substrates using hydrogen (H2)/methane (CH4) plasma at 650°C substrate temperature. Nickel (Ni) was used as a catalyst for the synthesis of

Research paper thumbnail of Free-flowing, transparent γ-alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

Current Applied Physics, 2012

Research paper thumbnail of Variation of axial and radial temperature in an expanded thermal plasma jet

Journal of Plasma Physics, 2010

ABSTRACT

Research paper thumbnail of Ion extraction from a flowing plasma using electrostatic field: Simulation and experiment

ABSTRACT The mechanism of ion extraction from flowing plasma using an external electrostatic fiel... more ABSTRACT The mechanism of ion extraction from flowing plasma using an external electrostatic field is investigated experimentally and computationally. The plasma is generated by electron impact ionization of a copper atomic beam. The plasma, along with the atomic beam vapor, flows upward and ions from the plasma are extracted using an external electrostatic field set up by a pair of parallel-plate electrodes. The extraction mechanism is studied using in-house developed hybrid 2D Particle-In-Cell (2D-PIC) code. The experimental results are found to be in good agreement with the computationally obtained values.

Research paper thumbnail of Attenuation of electron gun generated surges in an electron beam evaporation system using ferrite beads

Vacuum, 2012

ABSTRACT Vacuum breakdown is a very common problem during the operation of any electron gun, more... more ABSTRACT Vacuum breakdown is a very common problem during the operation of any electron gun, more so for e-guns used for vacuum evaporation. This not only spoils the coating or welding job but also causes damage to the electronics of the power system. This paper discusses an approach to attenuate the breakdown current near the gun itself, so that the surge does not propagate to cause any detrimental effect on the power source and thereby on the job. In this paper, ferrite beads on both the feed lines have been used to suppress the high frequency content and reduce the amplitude of the breakdown signal. An induction coil sensor has been designed to monitor the breakdown signal. The high frequency surge in the MHz range could be attenuated to a lower range of KHz by use of ferrite bead. A detailed quantitative analysis of the breakdown signal has been presented in this paper.

Research paper thumbnail of A possible explanation of the anomalous emissive probe behavior in a reactive RF plasma

Plasma Sources Science and Technology, 2012

Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of ... more Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of argon (Ar)-methane (CH 4) and ArCH 4-hexa methyl disiloxane (HMDSO). These plasmas are used for the deposition of diamond-like carbon (DLC) and SiO x-containing DLC films, respectively. While performing the experiments it was found that the probe characteristics had two saturation regions instead of one. The same measurements when repeated in Ar and Ar-N 2 plasmas showed a single saturation as expected. The first experiments when repeated again showed the same anomaly. The experimental findings question the validity of emissive probe diagnostics in reactive plasmas. A possible model of dust formation inside the reactive plasma is predicted and the first saturation is linked to dust. The second saturation is credited as the actual plasma potential. The concept of dust was invoked after being sure that no effects of RF and reference electrode contamination are responsible for this behavior. The results indicate that we should remain cautious when using emissive probes in reactive plasmas as they may occasionally lead to erroneous results.

Research paper thumbnail of Optical Emission Spectroscopic Study During the Evaporation of Aluminium in the Thermal Plasma Reactor

Plasma Science and Technology, 2010

The oxidation of aluminium was studied using optical emission spectroscopy (OES) during the evapo... more The oxidation of aluminium was studied using optical emission spectroscopy (OES) during the evaporation of aluminium in traces of oxygen in a thermal plasma reactor. The ratio of the measured line intensities of Al-O with that of Al follows the exact trend as of that obtained from the corresponding line intensities in X-ray diffraction spectra of the synthesized samples. In

Research paper thumbnail of Synthesis of AlN/Al Polycrystals along with Al Nanoparticles Using Thermal Plasma Route

This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride cry... more This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride crystals during synthesis of aluminum nanoparticles in dc transferred arc thermal plasma reactor by gas phase condensation in nitrogen plasma. The structural and morphological study of as synthesized AlN crystal and aluminium nanoparticles was done by using the x-ray diffraction method, scanning electron microscopy and transmission electron microscopy.

Research paper thumbnail of A simpler and elegant algorithm for computing fractal dimension in higher dimensional state space

Pramana, 2000

Chaotic systems are now frequently encountered in almost all branches of sciences. Dimension of s... more Chaotic systems are now frequently encountered in almost all branches of sciences. Dimension of such systems provides an important measure for easy characterization of dynamics of the systems. Conventional algorithms for computing dimension of such systems in higher dimensional state space face an unavoidable problem of enormous storage requirement. Here we present an algorithm, which uses a simple but very powerful technique and faces no problem in computing dimension in higher dimensional state space. The unique indexing technique of hypercubes, used in this algorithm, provides a clever means to drastically reduce the requirement of storage. It is shown that theoretically this algorithm faces no problem in computing capacity dimension in any dimension of the embedding state space as far as the actual dimension of the attractor is finite. Unlike the existing algorithms, memory requirement offered by this algorithm depends only on the actual dimension of the attractor and has no explicit dependence on the number of data points considered.

Research paper thumbnail of Promoting a Climate for University Research: OURIIP, the Odisha University Research and Innovation Incentivization Plan

Dialogue - Science, Scientists, and Society

Research paper thumbnail of Assessing the purity of CNT from its composite with polymer - A new approach

ABSTRACT This study focuses on calculating the electrical properties of composites of CNTs with p... more ABSTRACT This study focuses on calculating the electrical properties of composites of CNTs with polystyrene within the framework of percolation theory. Nano-composites, with multiwall carbon nanotubes (MWCNTs) as a filler; especially synthesized in a dc arc plasma system in presence of focusing electric field, have been shown to exhibit metallic behavior. The purity of the MWCNTs prepared under the optimized focusing voltage of 400 V is then seen to be much higher as compared to the one synthesized at zero focusing voltage.

Research paper thumbnail of Fluctuations in Atmospheric Pressure Arc Plasma Devices : A Theoretical Investigation Supported with Experiments

Research paper thumbnail of Pulsed power sources based on MHD generators (a state-of-art review)

Research paper thumbnail of Thermal Plasma Synthesized NiFe2O4 Nanoparticles for Adsorption of Bovine Serum Albumin

Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesised by the DC Thermal Plasma Arc met... more Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesised by the DC Thermal Plasma Arc method. The adsorption of protein (BSA) on the nickel ferrite surfaces was studied. The synthesized nickel ferrite nanoparticles were characterized by XRD, TEM and FTIR techniques. The measurements for adsorption of Bovine Serum Albumin on nanocrystalline Nickel Ferrites were carried out at body temeprature(37oC) and pH 7.2. FTIR spectroscopy confirmed the adsorption of bovine serum albumin (BSA) and also found that there is no significant chemical interaction between NiFe2O4 and BSA.

Research paper thumbnail of Magic frequency based multifunctional atomic device: an atomic magnetometer and an atomic clock (appeared in LabTalk : J Phys B, 8th June 2015)

Research paper thumbnail of A non-scanning atomic magnetometer based on coherent population trapping

The method of operation of an atomic magnetometer based on coherent population trapping (CPT) wit... more The method of operation of an atomic magnetometer based on coherent population trapping (CPT) without any requirement of radio frequency scanning is demonstrated. Using a hybrid approach comprising of polarization rotation and tailored transmission due to CPT states, the simultaneous operation of the device as atomic frequency standard as well as atomic magnetometer is investigated. The magnetometer sensitivity can be further improved by utilizing the inherent option of magnetic field assisted synchronized radio frequency scanning.

Research paper thumbnail of REV.SCI.INS.2013 Jana

Research paper thumbnail of Bactericidal efficiency of nanostructured Al–O/Ti–O composite thin films prepared by dual magnetron reactive co-sputtering technique

Ceramics International, 2014

Mixed oxide Al-O/Ti-O composite nanostructured thin films were prepared at Ar:O 2 gas ratio of 70... more Mixed oxide Al-O/Ti-O composite nanostructured thin films were prepared at Ar:O 2 gas ratio of 70:30 (7:3 in sccm) by reactive magnetron co-sputtering method. The effect of Al in the films on the antibacterial efficiency has been studied. In situ optical emission spectra (OES) were recorded in order to study the plasma chemistry as well as nucleation and growth process during deposition. The films were characterised by Xray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), field emission scanning electron microscope (FESEM), optical contact angle (OCA) and UV-visible transmission spectra (UV-vis). The qualitative and quantitative bactericidal efficiency was studied through SEM image of the treated E. coli cells (Escherichia coli NCIM 2809) and optical density (OD) measurement using UV-vis spectrometer, respectively. The better bactericidal efficiency was observed in the film with more Al content. The crystallinity, surface chemical composition, band gap in context of Al present in the films were discussed and correlated to bactericidal efficiency in the light of in situ investigation of plasma from OES.

Research paper thumbnail of Synthesis of AlN∕Al Polycrystals along with Al Nanoparticles Using Thermal Plasma Route

This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride cry... more This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride crystals during synthesis of aluminum nanoparticles in dc transferred arc thermal plasma reactor by gas phase condensation in nitrogen plasma. The structural and morphological study of as synthesized AlN crystal and aluminium nanoparticles was done by using the x-ray diffraction method, scanning electron microscopy and

Research paper thumbnail of Numerical investigation of nanoparticle synthesis in supersonic thermal plasma expansion

Research paper thumbnail of Bias-independent growth of carbon nanowalls by microwave electron-cyclotron resonance plasma CVD

Journal of Experimental Nanoscience, 2012

The investigations reported here describe the synthesis of carbon nanowalls (CNWs) by microwave e... more The investigations reported here describe the synthesis of carbon nanowalls (CNWs) by microwave electron-cyclotron resonance (ECR) plasma-assisted chemical vapour deposition (PACVD) process without an application of external bias to the substrate during growth. CNWs were grown on silicon (Si) substrates using hydrogen (H2)/methane (CH4) plasma at 650°C substrate temperature. Nickel (Ni) was used as a catalyst for the synthesis of

Research paper thumbnail of Free-flowing, transparent γ-alumina nanoparticles synthesized by a supersonic thermal plasma expansion process

Current Applied Physics, 2012

Research paper thumbnail of Variation of axial and radial temperature in an expanded thermal plasma jet

Journal of Plasma Physics, 2010

ABSTRACT

Research paper thumbnail of Ion extraction from a flowing plasma using electrostatic field: Simulation and experiment

ABSTRACT The mechanism of ion extraction from flowing plasma using an external electrostatic fiel... more ABSTRACT The mechanism of ion extraction from flowing plasma using an external electrostatic field is investigated experimentally and computationally. The plasma is generated by electron impact ionization of a copper atomic beam. The plasma, along with the atomic beam vapor, flows upward and ions from the plasma are extracted using an external electrostatic field set up by a pair of parallel-plate electrodes. The extraction mechanism is studied using in-house developed hybrid 2D Particle-In-Cell (2D-PIC) code. The experimental results are found to be in good agreement with the computationally obtained values.

Research paper thumbnail of Attenuation of electron gun generated surges in an electron beam evaporation system using ferrite beads

Vacuum, 2012

ABSTRACT Vacuum breakdown is a very common problem during the operation of any electron gun, more... more ABSTRACT Vacuum breakdown is a very common problem during the operation of any electron gun, more so for e-guns used for vacuum evaporation. This not only spoils the coating or welding job but also causes damage to the electronics of the power system. This paper discusses an approach to attenuate the breakdown current near the gun itself, so that the surge does not propagate to cause any detrimental effect on the power source and thereby on the job. In this paper, ferrite beads on both the feed lines have been used to suppress the high frequency content and reduce the amplitude of the breakdown signal. An induction coil sensor has been designed to monitor the breakdown signal. The high frequency surge in the MHz range could be attenuated to a lower range of KHz by use of ferrite bead. A detailed quantitative analysis of the breakdown signal has been presented in this paper.

Research paper thumbnail of A possible explanation of the anomalous emissive probe behavior in a reactive RF plasma

Plasma Sources Science and Technology, 2012

Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of ... more Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of argon (Ar)-methane (CH 4) and ArCH 4-hexa methyl disiloxane (HMDSO). These plasmas are used for the deposition of diamond-like carbon (DLC) and SiO x-containing DLC films, respectively. While performing the experiments it was found that the probe characteristics had two saturation regions instead of one. The same measurements when repeated in Ar and Ar-N 2 plasmas showed a single saturation as expected. The first experiments when repeated again showed the same anomaly. The experimental findings question the validity of emissive probe diagnostics in reactive plasmas. A possible model of dust formation inside the reactive plasma is predicted and the first saturation is linked to dust. The second saturation is credited as the actual plasma potential. The concept of dust was invoked after being sure that no effects of RF and reference electrode contamination are responsible for this behavior. The results indicate that we should remain cautious when using emissive probes in reactive plasmas as they may occasionally lead to erroneous results.

Research paper thumbnail of Optical Emission Spectroscopic Study During the Evaporation of Aluminium in the Thermal Plasma Reactor

Plasma Science and Technology, 2010

The oxidation of aluminium was studied using optical emission spectroscopy (OES) during the evapo... more The oxidation of aluminium was studied using optical emission spectroscopy (OES) during the evaporation of aluminium in traces of oxygen in a thermal plasma reactor. The ratio of the measured line intensities of Al-O with that of Al follows the exact trend as of that obtained from the corresponding line intensities in X-ray diffraction spectra of the synthesized samples. In

Research paper thumbnail of Synthesis of AlN/Al Polycrystals along with Al Nanoparticles Using Thermal Plasma Route

This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride cry... more This paper for the first time reports the (200) oriented growth of hexagonal Aluminum nitride crystals during synthesis of aluminum nanoparticles in dc transferred arc thermal plasma reactor by gas phase condensation in nitrogen plasma. The structural and morphological study of as synthesized AlN crystal and aluminium nanoparticles was done by using the x-ray diffraction method, scanning electron microscopy and transmission electron microscopy.

Research paper thumbnail of A simpler and elegant algorithm for computing fractal dimension in higher dimensional state space

Pramana, 2000

Chaotic systems are now frequently encountered in almost all branches of sciences. Dimension of s... more Chaotic systems are now frequently encountered in almost all branches of sciences. Dimension of such systems provides an important measure for easy characterization of dynamics of the systems. Conventional algorithms for computing dimension of such systems in higher dimensional state space face an unavoidable problem of enormous storage requirement. Here we present an algorithm, which uses a simple but very powerful technique and faces no problem in computing dimension in higher dimensional state space. The unique indexing technique of hypercubes, used in this algorithm, provides a clever means to drastically reduce the requirement of storage. It is shown that theoretically this algorithm faces no problem in computing capacity dimension in any dimension of the embedding state space as far as the actual dimension of the attractor is finite. Unlike the existing algorithms, memory requirement offered by this algorithm depends only on the actual dimension of the attractor and has no explicit dependence on the number of data points considered.

Research paper thumbnail of Promoting a Climate for University Research: OURIIP, the Odisha University Research and Innovation Incentivization Plan

Dialogue - Science, Scientists, and Society

Research paper thumbnail of Assessing the purity of CNT from its composite with polymer - A new approach

ABSTRACT This study focuses on calculating the electrical properties of composites of CNTs with p... more ABSTRACT This study focuses on calculating the electrical properties of composites of CNTs with polystyrene within the framework of percolation theory. Nano-composites, with multiwall carbon nanotubes (MWCNTs) as a filler; especially synthesized in a dc arc plasma system in presence of focusing electric field, have been shown to exhibit metallic behavior. The purity of the MWCNTs prepared under the optimized focusing voltage of 400 V is then seen to be much higher as compared to the one synthesized at zero focusing voltage.

Research paper thumbnail of Fluctuations in Atmospheric Pressure Arc Plasma Devices : A Theoretical Investigation Supported with Experiments

Research paper thumbnail of Pulsed power sources based on MHD generators (a state-of-art review)

Research paper thumbnail of Thermal Plasma Synthesized NiFe2O4 Nanoparticles for Adsorption of Bovine Serum Albumin

Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesised by the DC Thermal Plasma Arc met... more Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesised by the DC Thermal Plasma Arc method. The adsorption of protein (BSA) on the nickel ferrite surfaces was studied. The synthesized nickel ferrite nanoparticles were characterized by XRD, TEM and FTIR techniques. The measurements for adsorption of Bovine Serum Albumin on nanocrystalline Nickel Ferrites were carried out at body temeprature(37oC) and pH 7.2. FTIR spectroscopy confirmed the adsorption of bovine serum albumin (BSA) and also found that there is no significant chemical interaction between NiFe2O4 and BSA.

Research paper thumbnail of Magic frequency based multifunctional atomic device: an atomic magnetometer and an atomic clock (appeared in LabTalk : J Phys B, 8th June 2015)

Research paper thumbnail of A non-scanning atomic magnetometer based on coherent population trapping

The method of operation of an atomic magnetometer based on coherent population trapping (CPT) wit... more The method of operation of an atomic magnetometer based on coherent population trapping (CPT) without any requirement of radio frequency scanning is demonstrated. Using a hybrid approach comprising of polarization rotation and tailored transmission due to CPT states, the simultaneous operation of the device as atomic frequency standard as well as atomic magnetometer is investigated. The magnetometer sensitivity can be further improved by utilizing the inherent option of magnetic field assisted synchronized radio frequency scanning.

Research paper thumbnail of REV.SCI.INS.2013 Jana