We have performed experimental studies of the effect of static axial magnetic fields on the plasm... more We have performed experimental studies of the effect of static axial magnetic fields on the plasma dynamics of laser produced carbon and titanium plasmas. The laser plasmas are produced in vacuum, with a Nd:YAG laser, 3.5 ns, 340 mJ at 1.06 4 µm, operating at 10 Hz, and propagate in static magnetic fields of maximum value ∼0.2 T. Laser plasma features are characterized using 50 ns time resolved plasma imaging, time and space resolved visible spectroscopy and Faraday cup measurements. The presence of the magnetic field is found to affect plasma dynamics, plasma emission and plasma ions energy spectrum. Based on these measurements, a detailed analysis of the confinement effects of the magnetic field on the laser plasma will be presented.
Submitted for the DPP16 Meeting of The American Physical Society Study of a dual frequency capaci... more Submitted for the DPP16 Meeting of The American Physical Society Study of a dual frequency capacitively coupled rf discharge in the background of multi-component plasma and its validation by a simple analytical sheath model 1 HEMAN BHUYAN, PARTHA SAIKIA, MARIO FAVRE, EDMUNDO WYNDHAM, FELIPE VELOSO, Faculty of Physics, Pontificia Universidad Catlica de Chile-The behavior of a phase-locked dual frequency capacitively coupled rf discharges (2f-CCRF) in the background of multi-component plasma is experimentally studied by rf current-voltage measurements and optical emission spectroscopy (OES). The multi-component plasma is produced by adding hydrogen to the argon CCRF discharge. Variation of experimental parameters, like working pressure, low frequency (LF) and high frequency (HF) rf power indicate significant changes in the electron density and temperature as well as the DC self-bias developed on the power electrode. It is observed that the electron density decreases as the percentage of hydrogen increases in the argon plasma while the electron temperature follows opposite trend. An analytical sheath model for the 2f-CCRF discharge in the background of multi-component plasma is developed and its prediction on the observed variation of DC self-bias is well agreed with the experimental observations.
2018 IEEE International Conference on Plasma Science (ICOPS), 2018
A ring shape plasma can be produced by focusing a laser beam over a solid target, using a combina... more A ring shape plasma can be produced by focusing a laser beam over a solid target, using a combination of ax icon prism and convergent lens1. We present preliminary experimental studies of the dynamics of an annular plasma in background gases. The initial plasma is produced by focusing a Nd:YAG laser beam (1064 nm, 3.5 ns FWHM, $-2\cdot 10^{9}$ W / cm2) onto a flat target employing a combination of a 10 mrad axicon prism and a converging lens, which results in an initial ringlike shape plasma of 1 mm radius and $\sim 150\mu\mathrm{n}$ thickness. Observations of the optical self-emission of Titanium plasmas at 80 mTorr Argon background indicate that the plasma propagates inwards in a time scale ~90 ns, which is then followed by on axis stagnation and formation of a jet-like column. The resulting plasma jet propagates axially forming a planar shock, with characteristic initial velocity $\sim 2\cdot 10^{6}$ cm/s. This planar shock transits to a bow-shock in characteristic timescales of ~600 ns. Further investigations employing two parallel coaxial NdFeB magnets, which produce a static magnetic field of ~0.1 T, suggest that confinement effects due to the magnetic field increases the transition time from planar to bow-shock to ~ 700 ns. Additional experiments have been conducted with Graphite and Titanium target in high pressure Argon and air backgrounds. By using schlieren laser imaging (532 nm, 3.5 ns FWHM) from Carbon and Titanium annular plasmas it is found that the characteristic on-axis stagnation times increase up to ~300 ns at 760 Torr. In a first approximation, both, the radial expansion of the annular plasma and the axial propagation of the resulting plasma jet can be described adequately by the drag model2. Based on these observations, a comprehensive description of the dynamics of laser produced annular plasmas, over a wide set of parameters, will be presented.
A capacitively coupled radio frequency discharge driven by two harmonics substantially different ... more A capacitively coupled radio frequency discharge driven by two harmonics substantially different from each other allows some degrees of independent control of the ion energy and ion flux. The low frequency (ωLF) source controls the ion energy, while the ion flux is controlled by the high frequency (ωHF) source. The choices of the driving frequencies can influence the properties of the dual frequency capacitively coupled plasmas (2f CCP). Here, we study the effect of the driving frequencies on the properties of the 2f CCPs, i.e., on the generation of a DC self-bias, the excitation of the non-linear Plasma Series Resonance (PSR) effect as well as the independent control over the mean ion energy and the flux in three different 2f CCP experiments: namely (2.26 + 13.56) MHz, (2.26 + 27.12) MHz, and (13.56 + 27.12) MHz. We also use a non-liner global model that consists of a description of the plasma bulk based on a fluid dynamic approach coupled to a separate model of the sheath. We use ...
We present preliminary experimental observations of the collision processes between two orthogona... more We present preliminary experimental observations of the collision processes between two orthogonal laser produced plasmas in a low pressure neutral gas background. A Nd:YAG laser, 340 mJ, 3.5 ns, at 1.06 µm, operating at 10 Hz, is used in the experiments. The main laser beam is divided in two beams by a 50% beam splitter, and then focused over two rotating graphite targets, with characteristic fluence 3.5 J/cm 2. Experiments are conducted in a range from a base pressure of 0.3 mTorr, up to 50 mTorr argon. The dynamics of the laser plasmas is characterized by time resolved and time integrated optical emission spectroscopy (OES), with 20 ns and 10 ms time resolution, and 50 ns time resolved plasma imaging of visible plasma emission. Clear effects of the neutral gas background on the postcollision plasma dynamics are identified. The overall dynamics of the post-collision plasma is found to be consistent with high collisionality of the carbon plasma plumes, which results in full stagnation on collisioning.
The properties and performance of thin films deposited by plasma assisted processes are closely r... more The properties and performance of thin films deposited by plasma assisted processes are closely related to their manufacturing techniques and processes. The objective of the current study is to investigate the modification of plasma parameters occurring during hydrogen addition in N 2 + Ar magnetron plasma used for titanium nitride thin film deposition, and to correlate the measured properties of the deposited thin film with the bulk plasma parameters of the magnetron discharge. From the Langmuir probe measurements, it was observed that the addition of hydrogen led to a decrease of electron density from 8.6 to 6.2 × (10 14 m −3) and a corresponding increase of electron temperature from 6.30 to 6.74 eV. The optical emission spectroscopy study reveals that with addition of hydrogen, the density of argon ions decreases. The various positive ion species involving hydrogen are found to increase with increase of hydrogen partial pressure in the chamber. The thin films deposited were characterized using standard surface diagnostic tools such as xray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), xray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM) and energy dispersive xray spectroscopy (EDS). Although it was possible to deposit thin films of titanium nitride with hydrogen addition in nitrogen added argon magnetron plasma, the quality of the thin films deteriorates with higher hydrogen partial pressures.
We report the effect of single and dual radio frequency (RF) plasma discharge on the composition ... more We report the effect of single and dual radio frequency (RF) plasma discharge on the composition and dynamics of a titanium plasma plume produced in a plasma-enhanced pulsed laser deposition (PE-PLD) system. The study was carried out in a nitrogen environment at different pressures. Time-resolved images, optical emission spectroscopy, and interferometry were employed to analyze the plasma. We were able to fit time-resolved images using different expansion models, obtained an expansion velocity between 6 and 30 x 10 3 m/s. Emission lines from N II, Ti II, were observed by changing the pressure and RF conditions. An increase in emission line intensity from N II was observed by increasing the pressure and RF power. We used Ti II lines to estimate the plasma temperature by using the Boltzmann equation, and we obtained the density from the Ti II line (454.9 nm) through Stark broadening. In addition, a Mach-Zehnder interferometer was employed to make a twodimensional map of the electron density at early times. The estimated temperatures and densities are between 0.8-2.0 eV and 10 17-10 18 cm-3 , respectively. The results suggest that increasing RF power enhanced the TiN atoms interaction, which is crucial in titanium nitride film applications.
Classical dual-frequency capacitively coupled plasmas (2f CCPs) operating at low pressures and si... more Classical dual-frequency capacitively coupled plasmas (2f CCPs) operating at low pressures and significantly different frequencies are often used for a variety of applications in semiconductor manufacturing in order to control the mean ion energy at the electrodes separately from the ion flux. However, recent computational studies have indicated that this separate control is limited by the frequency coupling effects and by the contribution of secondary electrons to the ionization dynamics [Donk o et al., Appl. Phys. Lett. 97, 081501 (2010); Schulze et al., Plasma Sources Sci. Technol. 20, 045007 (2011)]. Here, we verify these simulation results experimentally by measuring the ion flux to an electrode as a function of the low frequency (LF) and high frequency power at different neutral gas pressures in a 2f CCP operated at 2.26 MHz and 13.56 MHz in argon. In agreement with previous computational predictions, we find the ion flux to decrease as a function of the LF power at a low pressure of 1 mTorr due to the frequency coupling and to increase as a function of the LF power at a higher pressure of 60 mTorr due to the presence of secondary electrons. These experimental findings show that separate control of ion properties in classical 2f CCPs is generally not possible, but potentially limited to specific discharge conditions.
International Journal of Applied Physics and Mathematics
Low temperature radio frequency plasma is widely used in low temperature plasma processing medium... more Low temperature radio frequency plasma is widely used in low temperature plasma processing medium for material processing in many fields including microelectronics, aerospace, and the biology. For proper utilization of the process, it is very much important to know the plasma parameters. In this paper a technique is reported to determine the plasma parameters from the electrical discharge characteristic of a capacitivly couple radio frequency argon plasma. The homogeneous discharge model is modified to make it applicable in low pressure by incorporating the plasma series resonance effect. The effect on the plasma resistance by the change in drift velocity of the electron with rf electric filed is also considered. The electron density and temperature is found to be well agreed with the Langmuir probe diagnostic result, which is in the range of 0.5x10 10 to 4.5x10 10 cm-3 and 1.4 to 1.6 ev for wide range of rf power. Index Terms-Capacitive couple radio frequency plasma, discharge characteristic, homogeneous discharge model, plasma parameters, power balance.
Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerf... more Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerful tools for enabling long and reliable biological studies. Such markers should not only have a long half-life under several assay conditions showing no photo bleaching or blinking but also, they must allow for their conjugation or functionalization as a crucial step for numerous applications such as cellular tracking, biomarker detection and drug delivery. We report the functionalization of stable fluorescent markers based on nanodiamonds (NDs) with a bifunctional peptide. This peptide is made of a cell penetrating peptide and a six amino acids long β-sheet breaker peptide that is able to recognize amyloid β (Aβ) aggregates, a biomarker for the Alzheimer disease. Our results indicate that functionalized NDs (fNDs) are not cytotoxic and can be internalized by the cells. The fNDs allow ultrasensitive detection (at picomolar concentrations of NDs) of in vitro amyloid fibrils and amyloid ag...
ABSTRACT We report on the production of different types of sub-micron characteristic size carbon ... more ABSTRACT We report on the production of different types of sub-micron characteristic size carbon composite coatings, using high energy carbon ion beam irradiation of solid targets. The carbon ion beams of characteristic charge state C+ 4 and C+ 5 and energy in the 50 to 600 keV range, are produced in a 1.8 kJ, 160 kA plasma focus (PF) device operating in CH4, with a hollow anode. The interaction of the high energy carbon ion beams with different substrates, including silicon (100) and titanium, result in the formation of surface coatings, with different characteristic morphologies and compositions. In the case of a silicon substrate, a step bunched surface layer of hexagonal SiC or an amorphous carbon layer is formed, depending on the PF anode material, whereas, in the case of titanium, gradient layers of TiC with embedded carbon nanostructures are observed. Detailed characterizations of the different surface coatings have been conducted, using SEM, EDX, XRD, AFM, AES and Raman spectroscopy. The natural angular anisotropy of PF ion beams allows the effect of ion beam characteristic energy and flux on the resulting coatings to be investigated. On the base of the different morphologies and compositions of the resulting coatings an empirical model of PF induced deposition is discussed, which attributes the process to a combination of ion beam implantation and transient physical vapour deposition due to a plasma bubble ejected from the anode, as a result of high energy electron beam bombardment.
We have investigated the plasma properties of a Hollow Cathode Discharge (HCD) using different di... more We have investigated the plasma properties of a Hollow Cathode Discharge (HCD) using different dimensions of hollow cathode aperture (1 to 8 mm) in argon operating medium. The diagnostic used to investigate the plasma properties is a tiny Langmuir probe. The diameter and length of the Langmuir probe was chosen such that it draws a measurable current from the plasma causing a minimal perturbation to the surrounding plasma and remains rigid within the plasma as well as the cylindrical probe theories are applicable while calculating the electron temperature and plasma density. The probe was placed perpendicular to the axis of the hollow cathode at a distance of 20 mm from the hollow cathode side. The HCD was operated in the voltage range of 600 to 1000 V and pressures range of 70 to 100 mtorr. We observed that electron temperature and density varies with the operational condition. The estimated electron temperature is less than 10 eV and the temperature is maximum in the range of 3 to 5 mm diameter of the hollow cathode and a pressure range of 75 to 85 mTorr. The calculated maximum density is of the order of 10 10 cm-3 .
We have investigated the ion flux, ion energy and anisotropy of carbon ion emission, at different... more We have investigated the ion flux, ion energy and anisotropy of carbon ion emission, at different angular positions, from a low energy Plasma Focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angles with respect to the PF axis (0°, 10°,
We have performed experimental studies of the effect of static axial magnetic fields on the plasm... more We have performed experimental studies of the effect of static axial magnetic fields on the plasma dynamics of laser produced carbon and titanium plasmas. The laser plasmas are produced in vacuum, with a Nd:YAG laser, 3.5 ns, 340 mJ at 1.06 4 µm, operating at 10 Hz, and propagate in static magnetic fields of maximum value ∼0.2 T. Laser plasma features are characterized using 50 ns time resolved plasma imaging, time and space resolved visible spectroscopy and Faraday cup measurements. The presence of the magnetic field is found to affect plasma dynamics, plasma emission and plasma ions energy spectrum. Based on these measurements, a detailed analysis of the confinement effects of the magnetic field on the laser plasma will be presented.
Submitted for the DPP16 Meeting of The American Physical Society Study of a dual frequency capaci... more Submitted for the DPP16 Meeting of The American Physical Society Study of a dual frequency capacitively coupled rf discharge in the background of multi-component plasma and its validation by a simple analytical sheath model 1 HEMAN BHUYAN, PARTHA SAIKIA, MARIO FAVRE, EDMUNDO WYNDHAM, FELIPE VELOSO, Faculty of Physics, Pontificia Universidad Catlica de Chile-The behavior of a phase-locked dual frequency capacitively coupled rf discharges (2f-CCRF) in the background of multi-component plasma is experimentally studied by rf current-voltage measurements and optical emission spectroscopy (OES). The multi-component plasma is produced by adding hydrogen to the argon CCRF discharge. Variation of experimental parameters, like working pressure, low frequency (LF) and high frequency (HF) rf power indicate significant changes in the electron density and temperature as well as the DC self-bias developed on the power electrode. It is observed that the electron density decreases as the percentage of hydrogen increases in the argon plasma while the electron temperature follows opposite trend. An analytical sheath model for the 2f-CCRF discharge in the background of multi-component plasma is developed and its prediction on the observed variation of DC self-bias is well agreed with the experimental observations.
2018 IEEE International Conference on Plasma Science (ICOPS), 2018
A ring shape plasma can be produced by focusing a laser beam over a solid target, using a combina... more A ring shape plasma can be produced by focusing a laser beam over a solid target, using a combination of ax icon prism and convergent lens1. We present preliminary experimental studies of the dynamics of an annular plasma in background gases. The initial plasma is produced by focusing a Nd:YAG laser beam (1064 nm, 3.5 ns FWHM, $-2\cdot 10^{9}$ W / cm2) onto a flat target employing a combination of a 10 mrad axicon prism and a converging lens, which results in an initial ringlike shape plasma of 1 mm radius and $\sim 150\mu\mathrm{n}$ thickness. Observations of the optical self-emission of Titanium plasmas at 80 mTorr Argon background indicate that the plasma propagates inwards in a time scale ~90 ns, which is then followed by on axis stagnation and formation of a jet-like column. The resulting plasma jet propagates axially forming a planar shock, with characteristic initial velocity $\sim 2\cdot 10^{6}$ cm/s. This planar shock transits to a bow-shock in characteristic timescales of ~600 ns. Further investigations employing two parallel coaxial NdFeB magnets, which produce a static magnetic field of ~0.1 T, suggest that confinement effects due to the magnetic field increases the transition time from planar to bow-shock to ~ 700 ns. Additional experiments have been conducted with Graphite and Titanium target in high pressure Argon and air backgrounds. By using schlieren laser imaging (532 nm, 3.5 ns FWHM) from Carbon and Titanium annular plasmas it is found that the characteristic on-axis stagnation times increase up to ~300 ns at 760 Torr. In a first approximation, both, the radial expansion of the annular plasma and the axial propagation of the resulting plasma jet can be described adequately by the drag model2. Based on these observations, a comprehensive description of the dynamics of laser produced annular plasmas, over a wide set of parameters, will be presented.
A capacitively coupled radio frequency discharge driven by two harmonics substantially different ... more A capacitively coupled radio frequency discharge driven by two harmonics substantially different from each other allows some degrees of independent control of the ion energy and ion flux. The low frequency (ωLF) source controls the ion energy, while the ion flux is controlled by the high frequency (ωHF) source. The choices of the driving frequencies can influence the properties of the dual frequency capacitively coupled plasmas (2f CCP). Here, we study the effect of the driving frequencies on the properties of the 2f CCPs, i.e., on the generation of a DC self-bias, the excitation of the non-linear Plasma Series Resonance (PSR) effect as well as the independent control over the mean ion energy and the flux in three different 2f CCP experiments: namely (2.26 + 13.56) MHz, (2.26 + 27.12) MHz, and (13.56 + 27.12) MHz. We also use a non-liner global model that consists of a description of the plasma bulk based on a fluid dynamic approach coupled to a separate model of the sheath. We use ...
We present preliminary experimental observations of the collision processes between two orthogona... more We present preliminary experimental observations of the collision processes between two orthogonal laser produced plasmas in a low pressure neutral gas background. A Nd:YAG laser, 340 mJ, 3.5 ns, at 1.06 µm, operating at 10 Hz, is used in the experiments. The main laser beam is divided in two beams by a 50% beam splitter, and then focused over two rotating graphite targets, with characteristic fluence 3.5 J/cm 2. Experiments are conducted in a range from a base pressure of 0.3 mTorr, up to 50 mTorr argon. The dynamics of the laser plasmas is characterized by time resolved and time integrated optical emission spectroscopy (OES), with 20 ns and 10 ms time resolution, and 50 ns time resolved plasma imaging of visible plasma emission. Clear effects of the neutral gas background on the postcollision plasma dynamics are identified. The overall dynamics of the post-collision plasma is found to be consistent with high collisionality of the carbon plasma plumes, which results in full stagnation on collisioning.
The properties and performance of thin films deposited by plasma assisted processes are closely r... more The properties and performance of thin films deposited by plasma assisted processes are closely related to their manufacturing techniques and processes. The objective of the current study is to investigate the modification of plasma parameters occurring during hydrogen addition in N 2 + Ar magnetron plasma used for titanium nitride thin film deposition, and to correlate the measured properties of the deposited thin film with the bulk plasma parameters of the magnetron discharge. From the Langmuir probe measurements, it was observed that the addition of hydrogen led to a decrease of electron density from 8.6 to 6.2 × (10 14 m −3) and a corresponding increase of electron temperature from 6.30 to 6.74 eV. The optical emission spectroscopy study reveals that with addition of hydrogen, the density of argon ions decreases. The various positive ion species involving hydrogen are found to increase with increase of hydrogen partial pressure in the chamber. The thin films deposited were characterized using standard surface diagnostic tools such as xray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), xray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM) and energy dispersive xray spectroscopy (EDS). Although it was possible to deposit thin films of titanium nitride with hydrogen addition in nitrogen added argon magnetron plasma, the quality of the thin films deteriorates with higher hydrogen partial pressures.
We report the effect of single and dual radio frequency (RF) plasma discharge on the composition ... more We report the effect of single and dual radio frequency (RF) plasma discharge on the composition and dynamics of a titanium plasma plume produced in a plasma-enhanced pulsed laser deposition (PE-PLD) system. The study was carried out in a nitrogen environment at different pressures. Time-resolved images, optical emission spectroscopy, and interferometry were employed to analyze the plasma. We were able to fit time-resolved images using different expansion models, obtained an expansion velocity between 6 and 30 x 10 3 m/s. Emission lines from N II, Ti II, were observed by changing the pressure and RF conditions. An increase in emission line intensity from N II was observed by increasing the pressure and RF power. We used Ti II lines to estimate the plasma temperature by using the Boltzmann equation, and we obtained the density from the Ti II line (454.9 nm) through Stark broadening. In addition, a Mach-Zehnder interferometer was employed to make a twodimensional map of the electron density at early times. The estimated temperatures and densities are between 0.8-2.0 eV and 10 17-10 18 cm-3 , respectively. The results suggest that increasing RF power enhanced the TiN atoms interaction, which is crucial in titanium nitride film applications.
Classical dual-frequency capacitively coupled plasmas (2f CCPs) operating at low pressures and si... more Classical dual-frequency capacitively coupled plasmas (2f CCPs) operating at low pressures and significantly different frequencies are often used for a variety of applications in semiconductor manufacturing in order to control the mean ion energy at the electrodes separately from the ion flux. However, recent computational studies have indicated that this separate control is limited by the frequency coupling effects and by the contribution of secondary electrons to the ionization dynamics [Donk o et al., Appl. Phys. Lett. 97, 081501 (2010); Schulze et al., Plasma Sources Sci. Technol. 20, 045007 (2011)]. Here, we verify these simulation results experimentally by measuring the ion flux to an electrode as a function of the low frequency (LF) and high frequency power at different neutral gas pressures in a 2f CCP operated at 2.26 MHz and 13.56 MHz in argon. In agreement with previous computational predictions, we find the ion flux to decrease as a function of the LF power at a low pressure of 1 mTorr due to the frequency coupling and to increase as a function of the LF power at a higher pressure of 60 mTorr due to the presence of secondary electrons. These experimental findings show that separate control of ion properties in classical 2f CCPs is generally not possible, but potentially limited to specific discharge conditions.
International Journal of Applied Physics and Mathematics
Low temperature radio frequency plasma is widely used in low temperature plasma processing medium... more Low temperature radio frequency plasma is widely used in low temperature plasma processing medium for material processing in many fields including microelectronics, aerospace, and the biology. For proper utilization of the process, it is very much important to know the plasma parameters. In this paper a technique is reported to determine the plasma parameters from the electrical discharge characteristic of a capacitivly couple radio frequency argon plasma. The homogeneous discharge model is modified to make it applicable in low pressure by incorporating the plasma series resonance effect. The effect on the plasma resistance by the change in drift velocity of the electron with rf electric filed is also considered. The electron density and temperature is found to be well agreed with the Langmuir probe diagnostic result, which is in the range of 0.5x10 10 to 4.5x10 10 cm-3 and 1.4 to 1.6 ev for wide range of rf power. Index Terms-Capacitive couple radio frequency plasma, discharge characteristic, homogeneous discharge model, plasma parameters, power balance.
Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerf... more Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerful tools for enabling long and reliable biological studies. Such markers should not only have a long half-life under several assay conditions showing no photo bleaching or blinking but also, they must allow for their conjugation or functionalization as a crucial step for numerous applications such as cellular tracking, biomarker detection and drug delivery. We report the functionalization of stable fluorescent markers based on nanodiamonds (NDs) with a bifunctional peptide. This peptide is made of a cell penetrating peptide and a six amino acids long β-sheet breaker peptide that is able to recognize amyloid β (Aβ) aggregates, a biomarker for the Alzheimer disease. Our results indicate that functionalized NDs (fNDs) are not cytotoxic and can be internalized by the cells. The fNDs allow ultrasensitive detection (at picomolar concentrations of NDs) of in vitro amyloid fibrils and amyloid ag...
ABSTRACT We report on the production of different types of sub-micron characteristic size carbon ... more ABSTRACT We report on the production of different types of sub-micron characteristic size carbon composite coatings, using high energy carbon ion beam irradiation of solid targets. The carbon ion beams of characteristic charge state C+ 4 and C+ 5 and energy in the 50 to 600 keV range, are produced in a 1.8 kJ, 160 kA plasma focus (PF) device operating in CH4, with a hollow anode. The interaction of the high energy carbon ion beams with different substrates, including silicon (100) and titanium, result in the formation of surface coatings, with different characteristic morphologies and compositions. In the case of a silicon substrate, a step bunched surface layer of hexagonal SiC or an amorphous carbon layer is formed, depending on the PF anode material, whereas, in the case of titanium, gradient layers of TiC with embedded carbon nanostructures are observed. Detailed characterizations of the different surface coatings have been conducted, using SEM, EDX, XRD, AFM, AES and Raman spectroscopy. The natural angular anisotropy of PF ion beams allows the effect of ion beam characteristic energy and flux on the resulting coatings to be investigated. On the base of the different morphologies and compositions of the resulting coatings an empirical model of PF induced deposition is discussed, which attributes the process to a combination of ion beam implantation and transient physical vapour deposition due to a plasma bubble ejected from the anode, as a result of high energy electron beam bombardment.
We have investigated the plasma properties of a Hollow Cathode Discharge (HCD) using different di... more We have investigated the plasma properties of a Hollow Cathode Discharge (HCD) using different dimensions of hollow cathode aperture (1 to 8 mm) in argon operating medium. The diagnostic used to investigate the plasma properties is a tiny Langmuir probe. The diameter and length of the Langmuir probe was chosen such that it draws a measurable current from the plasma causing a minimal perturbation to the surrounding plasma and remains rigid within the plasma as well as the cylindrical probe theories are applicable while calculating the electron temperature and plasma density. The probe was placed perpendicular to the axis of the hollow cathode at a distance of 20 mm from the hollow cathode side. The HCD was operated in the voltage range of 600 to 1000 V and pressures range of 70 to 100 mtorr. We observed that electron temperature and density varies with the operational condition. The estimated electron temperature is less than 10 eV and the temperature is maximum in the range of 3 to 5 mm diameter of the hollow cathode and a pressure range of 75 to 85 mTorr. The calculated maximum density is of the order of 10 10 cm-3 .
We have investigated the ion flux, ion energy and anisotropy of carbon ion emission, at different... more We have investigated the ion flux, ion energy and anisotropy of carbon ion emission, at different angular positions, from a low energy Plasma Focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angles with respect to the PF axis (0°, 10°,
Uploads
Papers by HEMAN BHUYAN