Neli Bundaleska - Academia.edu (original) (raw)

Papers by Neli Bundaleska

Journal of Physics: Conference Series, 2014

A microwave plasma torch operating at 2.45 GHz and atmospheric pressure has been used as a medium... more A microwave plasma torch operating at 2.45 GHz and atmospheric pressure has been used as a medium and a tool for decomposition of alcohol in order to produce molecular hydrogen. Plasma in a gas mixture of argon and ethanol/methanol, with or without water, has been created using a waveguide surfatron launcher and a microwave generator delivering a power in the range 0.2−2.0 kW. Mass, Fourier Transform Infrared, and optical emission spectrometry have been applied as diagnostic tools. The decomposition yield of methanol was nearly 100 % with H 2 , CO, CO 2 , H 2 O, and solid carbon as the main reaction products. The influence of the fraction of Ar flow through the liquid ethanol/methanol on H 2 , CO, and CO 2 partial pressures has been investigated, as well as the dependence of the produced H 2 flow on the total flow and power. The optical emission spectrum in the range 250−700 nm has also been detected. There is a decrease of the OH(A-X) band intensity with the increase of methanol in the mixture. The emission of carbon atoms in the near UV range (240−300 nm) exhibits a significant increase as the amount of alcohol in the mixture grows. The obtained results clearly show that this microwave plasma torch at atmospheric pressure provides an efficient plasma environment for hydrogen production.

Materials Research Express

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricate... more In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow – the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300 K down to 10 K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperatur...

Physical Chemistry Chemical Physics, 2020

Scheme of ethanol/ammonia plasma driven decomposition pathways considering injection of the nitro... more Scheme of ethanol/ammonia plasma driven decomposition pathways considering injection of the nitrogen precursor in “hot” and “mild” plasma zone.

Plasma Processes and Polymers, 2016

The thermal decomposition of biomass particles in a microwave plasma operating at atmospheric pre... more The thermal decomposition of biomass particles in a microwave plasma operating at atmospheric pressure conditions has been theoretically investigated. The set of equations, including thermal balance equations for the gas and biomass particles and kinetic rate balance equations for stable and intermediate components of biomass decomposition was solved for two different assumptions: thermal equilibrium and non-equilibrium. The thermal equilibrium assumption is acceptable given the high temperature and high reaction rates achievable in the microwave plasma environment, and although it hides the evolution of the pyrolysis process, it allows the description of the detailed chemical composition of the stable pyrolysis by-products (H2, CO, C2H2, and C [solid]).

Plasma Sources Science and Technology, 2014

It is well recognized at present that the unique, high energy density plasma environment provides... more It is well recognized at present that the unique, high energy density plasma environment provides suitable conditions to dissociate/atomize molecules in remediation systems, to convert waste and biomass into sustainable energy sources, to purify water, to assemble nanostructures, etc. The remarkable plasma potential is based on its ability to supply simultaneously high fluxes of charged particles, chemically active molecules, radicals (e.g. O, H, OH), heat, highly energetic photons (UV and extreme UV radiation), and strong electric fields in intrinsic sheath domains. Due to this complexity, low-temperature plasma science and engineering is a huge, highly interdisciplinary field that spans many research disciplines and applications across many areas of our daily life and industrial activities. For this reason, this review deals only with some selected aspects of low-temperature plasma applications for a clean and sustainable environment. It is not intended to be a comprehensive survey, but just to highlight some important works and achievements in specific areas. The selected issues demonstrate the diversity of plasma-based applications associated with clean and sustainable ambiance and also show the unity of the underlying science. Fundamental plasma phenomena/processes/features are the common fibers that pass across all these areas and unify all these applications. Browsing through different topics, we try to emphasize these phenomena/processes/features and their uniqueness in an attempt to build a general overview. The presented survey of recently published works demonstrates that plasma processes show a significant potential as a solution for waste/biomass-to-energy recovery problems. The reforming technologies based on non-thermal plasma treatment of hydrocarbons show promising prospects for the production of hydrogen as a future clean energy carrier. It is also shown that plasmas can provide numerous agents that influence biological activity. The simultaneous generation in water discharges of intense UV radiation, shock waves and active radicals (OH, O, H 2 O 2 , etc), which are all effective agents against many biological pathogens and harmful chemicals, make these discharges suitable for decontamination, sterilization and purification processes. Moreover, plasmas appear as invaluable tools for the synthesis and engineering of new nanomaterials and in particular 2D materials. A brief overview on plasma-synthesized carbon nanostructures shows the high potential of such materials for energy conversion and storage applications.

Plasma Sources Science and Technology, 2013

ABSTRACT In this work, an experimental investigation of microwave plasma-assisted reforming of di... more ABSTRACT In this work, an experimental investigation of microwave plasma-assisted reforming of different alcohols is presented. A microwave (2.45 GHz) 'tornado'-type plasma with a high-speed tangential gas injection (swirl) at atmospheric pressure is applied to decompose alcohol molecules, namely methanol, ethanol and propanol, and to produce hydrogen-rich gas. The reforming efficiency is investigated both in Ar and Ar+ water vapor plasma environments. The hydrogen yield dependence on the partial alcohol flux is analyzed. Mass spectrometry and Fourier transform infrared spectroscopy are used to detect the outlet gas products from the decomposition process. Hydrogen, carbon monoxide, carbon dioxide and solid carbon are the main decomposition by-products. A significant increase in the hydrogen production rate is observed with the addition of a small amount of water. Furthermore, optical emission spectroscopy is applied to detect the radiation emitted by the plasma and to estimate the gas temperature and electron density. (Some figures may appear in colour only in the online journal)

Journal of Physics D: Applied Physics, 2013

The production of cellulosic ethanol from sugarcane biomass is an attractive alternative to the u... more The production of cellulosic ethanol from sugarcane biomass is an attractive alternative to the use of fossil fuels. Pretreatment is needed to separate the cellulosic material, which is packed with hemicellulose and lignin in cell wall of sugarcane biomass. A microwave 'tornado'-type air–water plasma source operating at 2.45 GHz and atmospheric pressure has been applied for this purpose. Samples of dry and wet biomass (~2 g) have been exposed to the late afterglow plasma stream. The experiments demonstrate that the air–water highly reactive plasma environment provides a number of long-lived active species able to destroy the cellulosic wrapping. Scanning electron microscopy has been applied to analyse the morphological changes occurring due to plasma treatment. The effluent gas streams have been analysed by Fourier-transform infrared spectroscopy (FT-IR). Optical emission spectroscopy and FT-IR have been applied to determine the gas temperature in the discharge and late afterglow plasma zones, respectively. The optimal range of the operational parameters is discussed along with the main active species involved in the treatment process. Synergistic effects can result from the action of singlet O2(a 1Δg) oxygen, NO2, nitrous acid HNO2 and OH hydroxyl radical.

International Journal of Hydrogen Energy, 2014

Microwave plasma steam reforming of ethanol under vortex gas flow and atmospheric pressure condit... more Microwave plasma steam reforming of ethanol under vortex gas flow and atmospheric pressure conditions has been investigated. The main gas products of the steam reforming are H 2 and CO as detected by mass spectrometry and Fourier transform infrared spectroscopy. A "black" carbon deposit on the wall has been observed. A previously developed theoretical model for ethanol decomposition accounting for the gas thermal balance and the chemical kinetics has been further extended to account for the addition of steam to the argon/ethanol feeding background gas. The mechanisms of ethanol and water decomposition depend on the ethanol/steam ratio, and several hydrogen production regimes have been identified and discussed. An integral reaction scheme for ethanol/water decomposition is suggested.

International Journal of Hydrogen Energy, 2013

Ethanol reforming in microwave argon plasma, operating at 2.45 GHz under atmospheric pressure and... more Ethanol reforming in microwave argon plasma, operating at 2.45 GHz under atmospheric pressure and vortex gas flow has been investigated. Hydrogen, carbon monoxide and solid carbon are the main outlet products. H 2 and CO have been detected by mass spectrometry (MS) and Fourier transform infrared spectroscopy (FT-IR) whereas "black" carbon deposited at the wall has also been observed. The hydrogen yield has an average value of 98.4%, for ethanol fluxes in the range 4e15 sccm. An increase of about 32% in the energetic hydrogen mass yield has been observed as compared to laminar flow conditions. A theoretical model based on a set of non-linearly coupled differential equations accounting for the gas thermal balance and the chemical kinetics has been developed. An integral reaction scheme considering ethanol decomposition via two parallel channels was proposed and experimentally validated. Taking into account the diffusion of carbon into colder zones, the formation of solid carbon has also been analyzed. Some part of the solid carbon is deposited on the tube wall while another part is carried away with the outlet gas flow. The theoretical predictions for the H 2 and CO relative densities agree well with experimental data.

International Journal of Hydrogen Energy, 2011

A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen prod... more A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen production from the decomposition of alcohols (methanol and ethanol). The hydrogen yield dependence on the gas fluxes and the microwave input power has been investigated both in Ar and Ar þ water plasma environments. Mass and FTIR spectroscopy have been used to detect the molecular hydrogen produced and the H 2 O, CO 2 and CO molecules in the exhaust gas stream. Nearly 100% decomposition of methanol molecules was achieved in the Ar plasma torch. It was further found that the H 2 yield increases significantly when water is added into the Ar/methanol/ethanol mixtures. Moreover, optical emission spectroscopy has been applied to determine the gas temperature, the electron density and the radiative species present in the plasma torch. The results clearly show that this device provides an efficient plasma environment for hydrogen production.

2020 IEEE International Conference on Plasma Science (ICOPS), 2020

One of the grand challenges in the carbon-based nanomaterials research lies in the complexity and... more One of the grand challenges in the carbon-based nanomaterials research lies in the complexity and sensitivity of the synthesis processes. Plasmas are an alternative and sustainable strategy to synthesize disruptive nanostructures since they allow the effective control over the nucleation and assembling mechanisms at atomic scale level.

Contributions to Plasma Physics, 2015

The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom,... more The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom, namely self-alignment → non-alignment and alignment ↔ orientation is studied by monitoring the voltage across the discharge in a range of hollow cathode discharge (HCD) lamps. The application of a magnetic field to the discharge disorders the self-alignment. Alignment and orientation are optically induced and their effect on the discharge conductance is compared by measuring the optogalvanic signals. The degenerate states investigated are found to contribute to the gas discharge conductance in a manner which depends on their degree of coherence. Various hollow cathode discharge media are studied including Ne/As, Ne/Cu, Ne/Ni, Ne/Cd, Ne/Li and Ne/Ca in the corresponding trademarked HCD spectral lamps.

Opto-Electronics Review

ABSTRACT

The opto-galvanic signals from oriented and aligned ensemble of atoms are detected and compared. ... more The opto-galvanic signals from oriented and aligned ensemble of atoms are detected and compared. A Ne/Ca hollow cathode discharge (HCD) lamp is used as a plasma medium illuminated with He-NE laser. The measurements are performed at low gas pressure 4 Torr in range 0,3 ÷ 8 mA discharge current. The established differences in signals are ascribed to proper coherent conductivity

The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with... more The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an optogalvanic (OG) experimental ar- rangement. The work function dependence on the applied sub-breakdown voltage was investigated. The PE component in a real OG measurement was found to manifest itself as an instrumental effect together with nonresonant ionization which we call here space ionization (SP). The convolution of these components was determined experimentally as an instrumental function. A deconvolution procedure to determine the actual OG signal was developed.

Vacuum, 2004

The atomization and coherent-conductivity properties of a hollow cathode discharge (HCD) plasma a... more The atomization and coherent-conductivity properties of a hollow cathode discharge (HCD) plasma are analyzed. Under operating conditions of an Ar gas pressure of 38 Pa and discharge current of 8 mA the real sputtering coefficient of the process Ar þ ! Cd is obtained with a fair approach to accuracy to be S k ¼ 1:15 Â 10 À 1 atoms per ion. The back diffusion of sputtered atoms due to the gas ambient has been calculated and taken into account for this S k Àvalue. A different self-conductivity of the same ensemble of atoms (oriented and aligned) is measured by using the optogalvanic technique. This fact suggests that the ionization cross-section depends also on the coherence of the initial state.

Optics Communications, 2002

The radial behavior of hollow cathode discharge (HCD) proper emission function has been studied b... more The radial behavior of hollow cathode discharge (HCD) proper emission function has been studied by using a double Fabri–Perot interferogram, i.e., simultaneous recording of spectral line shapes, emitted from two different regions. Radial inhomogeneity and shift of the line shape center are established at buffer gas pressure lower than 0.3 Torr. At these pressures electric field in cathode dark space is concluded/found to penetrate into the negative glow and keeping the fast electron radial vector. It is a precondition for self-alignment of the atoms in HCD. The optical manifestation of this coherence is observed.

Journal of Physics D: Applied Physics, 2005

ABSTRACT

Journal of Physics: Conference Series, 2014

A microwave plasma torch operating at 2.45 GHz and atmospheric pressure has been used as a medium... more A microwave plasma torch operating at 2.45 GHz and atmospheric pressure has been used as a medium and a tool for decomposition of alcohol in order to produce molecular hydrogen. Plasma in a gas mixture of argon and ethanol/methanol, with or without water, has been created using a waveguide surfatron launcher and a microwave generator delivering a power in the range 0.2−2.0 kW. Mass, Fourier Transform Infrared, and optical emission spectrometry have been applied as diagnostic tools. The decomposition yield of methanol was nearly 100 % with H 2 , CO, CO 2 , H 2 O, and solid carbon as the main reaction products. The influence of the fraction of Ar flow through the liquid ethanol/methanol on H 2 , CO, and CO 2 partial pressures has been investigated, as well as the dependence of the produced H 2 flow on the total flow and power. The optical emission spectrum in the range 250−700 nm has also been detected. There is a decrease of the OH(A-X) band intensity with the increase of methanol in the mixture. The emission of carbon atoms in the near UV range (240−300 nm) exhibits a significant increase as the amount of alcohol in the mixture grows. The obtained results clearly show that this microwave plasma torch at atmospheric pressure provides an efficient plasma environment for hydrogen production.

Materials Research Express

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricate... more In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow – the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300 K down to 10 K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperatur...

Physical Chemistry Chemical Physics, 2020

Scheme of ethanol/ammonia plasma driven decomposition pathways considering injection of the nitro... more Scheme of ethanol/ammonia plasma driven decomposition pathways considering injection of the nitrogen precursor in “hot” and “mild” plasma zone.

Plasma Processes and Polymers, 2016

The thermal decomposition of biomass particles in a microwave plasma operating at atmospheric pre... more The thermal decomposition of biomass particles in a microwave plasma operating at atmospheric pressure conditions has been theoretically investigated. The set of equations, including thermal balance equations for the gas and biomass particles and kinetic rate balance equations for stable and intermediate components of biomass decomposition was solved for two different assumptions: thermal equilibrium and non-equilibrium. The thermal equilibrium assumption is acceptable given the high temperature and high reaction rates achievable in the microwave plasma environment, and although it hides the evolution of the pyrolysis process, it allows the description of the detailed chemical composition of the stable pyrolysis by-products (H2, CO, C2H2, and C [solid]).

Plasma Sources Science and Technology, 2014

It is well recognized at present that the unique, high energy density plasma environment provides... more It is well recognized at present that the unique, high energy density plasma environment provides suitable conditions to dissociate/atomize molecules in remediation systems, to convert waste and biomass into sustainable energy sources, to purify water, to assemble nanostructures, etc. The remarkable plasma potential is based on its ability to supply simultaneously high fluxes of charged particles, chemically active molecules, radicals (e.g. O, H, OH), heat, highly energetic photons (UV and extreme UV radiation), and strong electric fields in intrinsic sheath domains. Due to this complexity, low-temperature plasma science and engineering is a huge, highly interdisciplinary field that spans many research disciplines and applications across many areas of our daily life and industrial activities. For this reason, this review deals only with some selected aspects of low-temperature plasma applications for a clean and sustainable environment. It is not intended to be a comprehensive survey, but just to highlight some important works and achievements in specific areas. The selected issues demonstrate the diversity of plasma-based applications associated with clean and sustainable ambiance and also show the unity of the underlying science. Fundamental plasma phenomena/processes/features are the common fibers that pass across all these areas and unify all these applications. Browsing through different topics, we try to emphasize these phenomena/processes/features and their uniqueness in an attempt to build a general overview. The presented survey of recently published works demonstrates that plasma processes show a significant potential as a solution for waste/biomass-to-energy recovery problems. The reforming technologies based on non-thermal plasma treatment of hydrocarbons show promising prospects for the production of hydrogen as a future clean energy carrier. It is also shown that plasmas can provide numerous agents that influence biological activity. The simultaneous generation in water discharges of intense UV radiation, shock waves and active radicals (OH, O, H 2 O 2 , etc), which are all effective agents against many biological pathogens and harmful chemicals, make these discharges suitable for decontamination, sterilization and purification processes. Moreover, plasmas appear as invaluable tools for the synthesis and engineering of new nanomaterials and in particular 2D materials. A brief overview on plasma-synthesized carbon nanostructures shows the high potential of such materials for energy conversion and storage applications.

Plasma Sources Science and Technology, 2013

ABSTRACT In this work, an experimental investigation of microwave plasma-assisted reforming of di... more ABSTRACT In this work, an experimental investigation of microwave plasma-assisted reforming of different alcohols is presented. A microwave (2.45 GHz) 'tornado'-type plasma with a high-speed tangential gas injection (swirl) at atmospheric pressure is applied to decompose alcohol molecules, namely methanol, ethanol and propanol, and to produce hydrogen-rich gas. The reforming efficiency is investigated both in Ar and Ar+ water vapor plasma environments. The hydrogen yield dependence on the partial alcohol flux is analyzed. Mass spectrometry and Fourier transform infrared spectroscopy are used to detect the outlet gas products from the decomposition process. Hydrogen, carbon monoxide, carbon dioxide and solid carbon are the main decomposition by-products. A significant increase in the hydrogen production rate is observed with the addition of a small amount of water. Furthermore, optical emission spectroscopy is applied to detect the radiation emitted by the plasma and to estimate the gas temperature and electron density. (Some figures may appear in colour only in the online journal)

Journal of Physics D: Applied Physics, 2013

The production of cellulosic ethanol from sugarcane biomass is an attractive alternative to the u... more The production of cellulosic ethanol from sugarcane biomass is an attractive alternative to the use of fossil fuels. Pretreatment is needed to separate the cellulosic material, which is packed with hemicellulose and lignin in cell wall of sugarcane biomass. A microwave 'tornado'-type air–water plasma source operating at 2.45 GHz and atmospheric pressure has been applied for this purpose. Samples of dry and wet biomass (~2 g) have been exposed to the late afterglow plasma stream. The experiments demonstrate that the air–water highly reactive plasma environment provides a number of long-lived active species able to destroy the cellulosic wrapping. Scanning electron microscopy has been applied to analyse the morphological changes occurring due to plasma treatment. The effluent gas streams have been analysed by Fourier-transform infrared spectroscopy (FT-IR). Optical emission spectroscopy and FT-IR have been applied to determine the gas temperature in the discharge and late afterglow plasma zones, respectively. The optimal range of the operational parameters is discussed along with the main active species involved in the treatment process. Synergistic effects can result from the action of singlet O2(a 1Δg) oxygen, NO2, nitrous acid HNO2 and OH hydroxyl radical.

International Journal of Hydrogen Energy, 2014

Microwave plasma steam reforming of ethanol under vortex gas flow and atmospheric pressure condit... more Microwave plasma steam reforming of ethanol under vortex gas flow and atmospheric pressure conditions has been investigated. The main gas products of the steam reforming are H 2 and CO as detected by mass spectrometry and Fourier transform infrared spectroscopy. A "black" carbon deposit on the wall has been observed. A previously developed theoretical model for ethanol decomposition accounting for the gas thermal balance and the chemical kinetics has been further extended to account for the addition of steam to the argon/ethanol feeding background gas. The mechanisms of ethanol and water decomposition depend on the ethanol/steam ratio, and several hydrogen production regimes have been identified and discussed. An integral reaction scheme for ethanol/water decomposition is suggested.

International Journal of Hydrogen Energy, 2013

Ethanol reforming in microwave argon plasma, operating at 2.45 GHz under atmospheric pressure and... more Ethanol reforming in microwave argon plasma, operating at 2.45 GHz under atmospheric pressure and vortex gas flow has been investigated. Hydrogen, carbon monoxide and solid carbon are the main outlet products. H 2 and CO have been detected by mass spectrometry (MS) and Fourier transform infrared spectroscopy (FT-IR) whereas "black" carbon deposited at the wall has also been observed. The hydrogen yield has an average value of 98.4%, for ethanol fluxes in the range 4e15 sccm. An increase of about 32% in the energetic hydrogen mass yield has been observed as compared to laminar flow conditions. A theoretical model based on a set of non-linearly coupled differential equations accounting for the gas thermal balance and the chemical kinetics has been developed. An integral reaction scheme considering ethanol decomposition via two parallel channels was proposed and experimentally validated. Taking into account the diffusion of carbon into colder zones, the formation of solid carbon has also been analyzed. Some part of the solid carbon is deposited on the tube wall while another part is carried away with the outlet gas flow. The theoretical predictions for the H 2 and CO relative densities agree well with experimental data.

International Journal of Hydrogen Energy, 2011

A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen prod... more A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen production from the decomposition of alcohols (methanol and ethanol). The hydrogen yield dependence on the gas fluxes and the microwave input power has been investigated both in Ar and Ar þ water plasma environments. Mass and FTIR spectroscopy have been used to detect the molecular hydrogen produced and the H 2 O, CO 2 and CO molecules in the exhaust gas stream. Nearly 100% decomposition of methanol molecules was achieved in the Ar plasma torch. It was further found that the H 2 yield increases significantly when water is added into the Ar/methanol/ethanol mixtures. Moreover, optical emission spectroscopy has been applied to determine the gas temperature, the electron density and the radiative species present in the plasma torch. The results clearly show that this device provides an efficient plasma environment for hydrogen production.

2020 IEEE International Conference on Plasma Science (ICOPS), 2020

One of the grand challenges in the carbon-based nanomaterials research lies in the complexity and... more One of the grand challenges in the carbon-based nanomaterials research lies in the complexity and sensitivity of the synthesis processes. Plasmas are an alternative and sustainable strategy to synthesize disruptive nanostructures since they allow the effective control over the nucleation and assembling mechanisms at atomic scale level.

Contributions to Plasma Physics, 2015

The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom,... more The galvanic manifestation of two transformations of degenerate magnetic states of the neon atom, namely self-alignment → non-alignment and alignment ↔ orientation is studied by monitoring the voltage across the discharge in a range of hollow cathode discharge (HCD) lamps. The application of a magnetic field to the discharge disorders the self-alignment. Alignment and orientation are optically induced and their effect on the discharge conductance is compared by measuring the optogalvanic signals. The degenerate states investigated are found to contribute to the gas discharge conductance in a manner which depends on their degree of coherence. Various hollow cathode discharge media are studied including Ne/As, Ne/Cu, Ne/Ni, Ne/Cd, Ne/Li and Ne/Ca in the corresponding trademarked HCD spectral lamps.

Opto-Electronics Review

ABSTRACT

The opto-galvanic signals from oriented and aligned ensemble of atoms are detected and compared. ... more The opto-galvanic signals from oriented and aligned ensemble of atoms are detected and compared. A Ne/Ca hollow cathode discharge (HCD) lamp is used as a plasma medium illuminated with He-NE laser. The measurements are performed at low gas pressure 4 Torr in range 0,3 ÷ 8 mA discharge current. The established differences in signals are ascribed to proper coherent conductivity

The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with... more The photoelectron emission (PE) from the cathode surface of a hollow cathode discharge (HCD) with a sub-breakdown bias applied, and hence no discharge present, was measured within the framework of an optogalvanic (OG) experimental ar- rangement. The work function dependence on the applied sub-breakdown voltage was investigated. The PE component in a real OG measurement was found to manifest itself as an instrumental effect together with nonresonant ionization which we call here space ionization (SP). The convolution of these components was determined experimentally as an instrumental function. A deconvolution procedure to determine the actual OG signal was developed.

Vacuum, 2004

The atomization and coherent-conductivity properties of a hollow cathode discharge (HCD) plasma a... more The atomization and coherent-conductivity properties of a hollow cathode discharge (HCD) plasma are analyzed. Under operating conditions of an Ar gas pressure of 38 Pa and discharge current of 8 mA the real sputtering coefficient of the process Ar þ ! Cd is obtained with a fair approach to accuracy to be S k ¼ 1:15 Â 10 À 1 atoms per ion. The back diffusion of sputtered atoms due to the gas ambient has been calculated and taken into account for this S k Àvalue. A different self-conductivity of the same ensemble of atoms (oriented and aligned) is measured by using the optogalvanic technique. This fact suggests that the ionization cross-section depends also on the coherence of the initial state.

Optics Communications, 2002

The radial behavior of hollow cathode discharge (HCD) proper emission function has been studied b... more The radial behavior of hollow cathode discharge (HCD) proper emission function has been studied by using a double Fabri–Perot interferogram, i.e., simultaneous recording of spectral line shapes, emitted from two different regions. Radial inhomogeneity and shift of the line shape center are established at buffer gas pressure lower than 0.3 Torr. At these pressures electric field in cathode dark space is concluded/found to penetrate into the negative glow and keeping the fast electron radial vector. It is a precondition for self-alignment of the atoms in HCD. The optical manifestation of this coherence is observed.

Journal of Physics D: Applied Physics, 2005

ABSTRACT