Rf Gas Discharge Research Articles

Applicability of Electron-Beam and Hybrid Plasmas for Polyethylene Terephthalate Processing to Obtain Hydrophilic and Biocompatible Surfaces.

The applicability of beam-plasma chemical reactors generating cold hybrid plasma for the production of noncytotoxic polymeric surfaces with high hydrophilicity and good biocompatibility with human fibroblast culture and human red blood cells was studied. Oxygen hybrid plasma was excited by the joint action of a continuous scanning electron beam and a capacity-coupled RF-gas discharge. Experiments showed that hybrid plasma treatment caused polar oxygen-containing functional group formation in the surface layer of poly (ethylene terephthalate) films. No thermal or radiative damage in tested polymer samples was found. The plasma-modified polymers turned out to be noncytotoxic and revealed good biocompatibility with human fibroblasts BJ-5ta as well as lower hemolytic activity than untreated poly (ethylene terephthalate). Experiments also demonstrated that no phenomena caused by the electrostatic charging of polymers occur in hybrid plasma because the electron beam component of hybrid plasma eliminates the item charge when it is treated. The electron beam can effectively control the reaction volume geometry as well as the fluxes of active plasma particles falling on the item surface. This provides new approaches to the production of abruptly structured patterns or smooth gradients of functionalities on a plane and 3D polymeric items of complicated geometry.

Temperature-related effects in the polarization of atoms in a magnetized plasma as a promising feature towards high He3 nuclear polarization

We report on further investigation of nuclear hyperpolarization of $^{3}\mathrm{He}$ in magnetized plasma at a magnetic field of 3.66 T and at different experimental conditions in a dual cell of relatively large volume, compared to those reported in the original polarization of atoms in a magnetized plasma (PAMP) paper by Maul et al. [Phys. Rev. A 98, 063405 (2018)]. It was found that steady-state nuclear polarizations obtained by this method strongly increase with temperature and rf gas discharge power. We managed to reach almost 8% at the highest possible temperature in our setup which is to date the highest polarization obtained by this method at 10 mbar. It was also shown that atomic oxygen in plasma, considered as an impurity, could be a good probe of plasma parameters relevant for the PAMP process, either in the temperature or the metastable $^{3}\mathrm{He}$ density. The polarization buildup rates with the cell temperature stabilized near room temperature are found to be of the order of 1 ${\mathrm{s}}^{\ensuremath{-}1}$, which is by two orders of magnitude faster than was reported in the original PAMP paper for the same filling pressure. These observations promise a further optimization of experimental conditions towards strong and fast hyperpolarization by this method.

Hybrid plasma chemical reactors for bio-polymers processing

Design of a hybrid plasma-chemical reactor in which strongly non-equilibrium low-temperature plasma is generated by joint action of a continuous electron beam and RF-gas discharge on gaseous media at moderate pressures (0.1–10 Torr) is described. Several versions of the reactor in a co-axial configuration were tested on the special experimental setup. Main characteristics of the reaction zone were studied as functions of electron beam and gas discharge parameters, plasma-generating media properties and peculiarities of the working process features. Temperature regimes of the materials processing were reliably controlled by the electron beam parameters. The reactor was applied to thin films and dispersed powders of natural polysaccharides (chitosan) and biomaterials (wood) processing to produce valuable low-molecular and bioactive compounds. In hybrid plasma of oxygen, the active particles responsible for the materials modification effects are atomic oxygen, ozone and singlet oxygen. Special software simulating the reactor operation and material treatment processes in plasmas of oxygen was developed and experimentally verified.

Nuclear hyperpolarization of He3 by magnetized plasmas

We describe a method to hyperpolarize 3He nuclear spins at high magnetic fields (4.7 Tesla) solely by a magnetized plasma. The conditions for such a magnetized plasma are fulfilled when the mean free path of the free electrons is much larger than their gyration radius in the rf gas discharge. Investigations are carried out in the 1-15 mbar pressure range with rf excitation at ~100 MHz. Quantitative NMR measurements show that for different cell sizes and 3He densities nuclear polarizations in the range 1% to 9% are observed. We explain this phenomenon by an alignment-to-orientation conversion mechanism in the excited 2 3P state of 3He which is most efficient when the Zeeman and the spin-orbit energies are comparable. The method appears as a very attractive alternative to established laser polarization techniques (spin exchange or metastability exchange optical pumping). Application to 3He nuclear magnetometry with a relative precision of 10-12 is demonstrated.

Optical anisotropy and dielectric parameters of (Ba0.5Sr0.5)Nb2O6 films on a Pt(111)/Si(001) substrate

(Ba0.5Sr0.5)Nb2O6 films were synthesized on a Pt(111)/Si(001) substrate by RF gas-discharge sputtering in pure oxygen atmosphere. It was found that the films have a dominant crystallographic orientation in the [001] direction and natural unipolarity, which was revealed through analysis of dielectric and piezoelectric parameters. It was demonstrated that the optical parameters of film material in the Ba0.5Sr0.5, Nb2O6/Pt(111)/Si(001) heterostructure match those typical for a (Ba0.5Sr0.5)Nb2O6 single crystal.

Self-organisation of regular dusty structures in plasma trap

The formation of ordered dusty structures in the special RF-gas discharge (plasma trap) capable of capturing and confining nano- and micro-particles in electromagnetic field was studied experimentally. Two ways of the dust-plasma structure formation were investigated: (1) The condensation of preliminary evaporated organic or inorganic substances. The plasma trap could confine the vapour clusters during their growth up to the several micrometres in size. (2) The mechanical injection of mono- or poly-dispersed powders into the RF-discharge. To realise the first way a small-size target of acetylsalicylic acid, polyethylene, polypropylene or amorphous carbon was evaporated by a short pulse of the powerful electron beam (EB). Powders of proteins, polysaccharides, amorphous carbon and oxides of various metals were used for mechanical injection. Air, oxygen, noble gases and some hydrocarbons were used for gas-discharge plasma generation. The topology of the ordered dusty structures was proved to be controlled by the EB injection.

An oscillator circuit to produce a radio-frequency discharge and application to metastable helium saturated absorption spectroscopy

We present a rf gas discharge apparatus which provides an atomic frequency reference for laser manipulation of metastable helium. We discuss the biasing and operation of a Colpitts oscillator in which the discharge coil is part of the oscillator circuit. Radiofrequency radiation is reduced by placing the entire oscillator in a metal enclosure.

Complex Plasmas With Rodlike Particles

Ordered structures of rodlike (cylindrical) particles in dc and rf gas discharge plasmas were investigated. It was shown theoretically and observed experimentally that only two orientations (parallel and perpendicular to the external electric field) of cylindrical particles are possible and that changing the discharge parameters can result in the change of the particle orientation.

Transport of microparticles in weakly ionized gas-discharge plasmas under microgravity

Effective structural (pair correlation function) and transport (diffusion constant) characteristics of the system of microparticles (dusty plasma) have been measured in a set of experiments in dc- and rf gasdischarge plasmas in ground-based and microgravity conditions on the board of Russian “Mir” Space Station and International Space Station. The comparison between these measurements and numerical simulations were used for dusty plasma diagnostics. Specifically, the effective coupling parameter, which mainly governs structural and dynamical properties of the system, was determined for different experimental conditions. The application of these measurements to estimate the particle charge and the plasma screening length is discussed.

Overview of Ordered Dust Structures in Dusty Plasmas

Dust particle ordering is discussed in various types of low-temperature plasma, such as DC glow discharges, UV- and radioactivity induced plasmas. Both theoretical and experimental study of strongly coupled plasma over a wide range of plasma pressures and temperatures were carried out. The plasma was investigated under conditions of low pressure DC and RF gas discharges. The plasma was also formed from charged dust grains in the presence of a flux of ultraviolet (UV) photons and nuclear-induced radiation. The dust concentration, the pair correlation function, the dust temperatures and diffusion coefficients have been measured. The coupling parameter, characteristic dust frequency and particle charges have been obtained.

The role of negative ions in experiments with complex plasma

The influence of negative ions on the state of an rf gas-discharge dusty (complex) plasma containing electronegative gaseous impurities was investigated. A simple one-dimensional argon-discharge model allowing for the impurity-induced plasmachemical reactions was taken as an example to show that the addition of even a minor amount of molecular oxygen changes appreciably the plasma composition and plasma transport properties, as well as the microparticle charges. In turn, these changes have a strong effect on the microparticle force balance and on the formation of various dusty structures in the discharge.

Transport of microparticles in weakly ionized gas-discharge plasmas under microgravity conditions.

Measurements of effective structural (pair correlation function) and transport (diffusion constant) characteristics of the system of microparticles in dc and rf gas-discharge plasmas under microgravity conditions are reported. The comparison between these measurements and numerical simulations is used for complex plasma diagnostics.

Liquid and crystal dust structures in low temperature plasmas

A study of the strongly coupled dusty plasma was carried out over a wide range of plasma pressures and temperatures. The plasma was investigated under conditions of low pressure dc current and inductively-coupled rf gas discharges and under nuclear induced plasma conditions. The plasma was also formed from positively charged dust grains in the presence of a flux of ultraviolet photons. The results of experimental observations of ordered dust structures are reported, and the characteristic features of the dust structures and the conditions for their appearance are discussed.

Two-dimensional mesoscopic dusty plasma clusters: Structure and phase transitions

A two-dimensional mesoscopic cluster of “dusty plasma” particles, which can be interpreted as a system of microparticles in an rf gas discharge, is investigated. The ground-state configurations and corresponding eigenfrequencies and eigenvectors are found for clusters of N=22–40 particles in a harmonic confining potential. It is shown that a change in the Debye screening length R of the particle charge in the plasma can cause structural transformations of the ground state of the system, manifested as first-order or second-order phase transitions with respect to the parameter R. The disorder (“melting”) of the clusters is analyzed in detail by Monte Carlo simulation and molecular dynamics. By varying the characteristic range of particle interaction in a cluster, it is possible to modulate its thermodynamic properties and the character of the phase transitions, thereby causing a controlled transition of the system into the fully ordered, orientationally disordered, or fully disordered state. The possibility of dusty plasma clusters coexisting in different states is discussed.

Production of atomic hydrogen in an rf gas discharge and mass spectrometer diagnostics of the process

84 investigated in the present study as part of the preparation for a series of experiments on the influence of variations in the electron environment on the lifetime of the b-active tritium nucleus. In the first experiment of the series it is proposed to investigate the chemical shift of the half-life for an atomicmolecular tritium pair. Since the energy of dissociation of molecular tritium is close to that of molecular protium, and since atomic tritium, because of its higher mass and lower mobility, recombines more slowly than atomic protium, the procedure used to obtain atomic tritium can be worked out in experiments with protium ~called hydrogen from now on!. Atomic hydrogen is produced by thermal dissociation in a tungsten furnace, by low-frequency and radio-frequency gas discharges, or by means of a plasma arc. In the present study we have used the rf gas discharge method to obtain atomic hydrogen. The high efficiency of this method helps to minimize the heating of the discharge cell and can be implemented without the intrusion of electrodes in the discharge volume, thereby ensuring high purity of the atomic hydrogen product. The problems associated with the stabilization and detection of atomic hydrogen stem from its high chemical activity, by virtue of which atoms rapidly recombine at the walls of the discharge volume and in mutual collisions. For this reason, most diagnostic techniques applied to atomic hydrogen are based on measurements of secondary effects attributable to the presence of atomic hydrogen. For example, a chemical target of molybdenum oxide has been used as the atomic hydrogen detector in some studies. When hydrogen atoms are incident on such a target, the oxide undergoes reduction, and the target changes color. However, the small range of measurement of the flux density (10–10 atoms/s •cm) and low accuracy (630% error! limit the possibilities of this method. Bass and Broida have measured the optical spectra of hydrogen atoms in the condensed and gaseous phases, but did not establish any relationship between the concentration of hydrogen atoms and the line intensities of the optical spectra. One approach that looks promising is the determination of hydrogen atoms by electron spin resonance ~ESR!. This method utilizes the presence of an unpaired electron due to the paramagnetism of the hydrogen atom, a property that can be exploited for detection by ESR. Only papers in which ESR has been used to measure atomic hydrogen in the condensed phase are known in the literature. Here we report mass spectrometer measurements of atomic hydrogen produced in an rf gas discharge. The experimental apparatus ~Fig. 1! consists of an rf oscillator 1 ~1 MHz, 300 W!, a discharge tube 2, an MI 1201 mass spec-

Direct measurement of the electrical impedance of narrow gap radio frequency gas discharges in the 100 MHz region

A discharge cell is described in which direct measurements of the inter-electrode voltage, current density and phase angle of narrow gap RF gas discharges are possible, with good accuracy in the 50 to 200 MHz region. Examples are given of the use of the arrangement to determine the electrical impedance of discharges in slab waveguide carbon dioxide lasers.

Pressure and frequency dependence of ion bombardment energy distributions from rf discharges

Experimental measurements of the energy distribution and flux of ions bombarding an electrode of a parallel-plate rf reactor were performed in argon, neon, and a 95% helium-5% argon mixture using a hemispherical retarding grid energy analyzer. Quadrupole mass analysis was performed to identify the ions which were bombarding the electrode. Frequencies from 2.5 to 20 MHz and pressures from 0.025 to 1.6 Torr were studied. For a given amplitude of the applied rf potential, the ratio of the frequency of the applied rf potential to the reactor gas pressure was found to be the critical parameter in determining the shape of the measured ion bombardment energy distributions. The total ion flux to the electrode surface was found to be proportional to the square of the frequency and insensitive to the reactor gas pressure, for a fixed amplitude of the applied rf potential. These results are discussed with reference to the physics of rf gas discharges.

Determination of sheath potentials in rf plasmas

High resolution energy spectra of ions, accelerated across the sheath at the powered electrode of an rf gas discharge, are presented. The measured profiles are explained by a simple model. Ion energy, ion mass, total ion flux and time averaged sheath thickness are thus obtained. In the presence of a magnetic field fast electrons modify the sheath, resulting in an increased ion flux and a decreased sheath thickness.

Parameters affecting the performance of a rf excited CO2 waveguide laser

This paper summarizes the results of a series of rf gas discharge experiments which were performed to assess the factors which influence the efficient operation of a transversely excited CO2 waveguide laser. Using multiple resonating inductors for impedance matching, the longitudinal voltage variations are shown to be affected by the rf operation frequency and the discharge geometry. The effect of the gas mixture and the rf input power density upon the discharge field to pressure ratio is also investigated.

The incorporation of phosphorus in amorphous silicon

Amorphous films of SiP alloys were prepared by plasma deposition in an rf gas discharge of mixtures of SiH 4 and PH 3. The relative gas phase content of PH 3 was varied between 5·10 −5 and unity. The phosphorus incorporation ratio was determined by neutron activation analysis and atomic absorption spectroscopy; it decreases from about 6 at low concentrations to unity at high concentrations. The films were characterized by measurements of the dark conductivity and its activation energy. - To explain our results we propose that, in the range of P contents investigated, most of the P atoms are 3-fold coordinated; a small fraction is 4-fold coordinated and accounts for the doping.