Dc Discharge Plasma Research Articles

Nonlinear Dynamics of a Grain in a Discharge Plasma Sheath

Recently the dynamics of dust grains trapped in the sheath region of radio-frequency (rf) or dc plasma discharges under low pressure conditions has attracted the attention of the dusty plasma community. Several experiments have been performed in order to explore the dynamics of dust grains levitating above the negatively biased electrode. Under very low pressures, several experimental groups have observed the generation of self excited large amplitude vertical oscillations which arise by lowering either the background pressure or the plasma number density. In other experiments, the vertical oscillations have been driven by an external sinusoidal voltage applied to a wire in the sheath region. A theoretical model is presented that successfully describes the phenomenology in these various experiments including the observed self excited oscillations and nonlinear resonance oscillations.

Self-excited motion of dust particles in a inhomogeneous plasma

Abstract Two novel types of instabilities in inhomogeneous dusty plasma are considered. It is shown that spatial dust charge variation provides an effective mechanism to excite the motion of particles. The results of experimental observation of various self-excited motions of dust particles in a dc-discharge plasma are presented. Conditions suitable for growing the considered instabilities in the dc-glow discharge are discussed.

Fine-particle clouds controlled in a DC discharge plasma

The spatial shape of fine-particle clouds in a strongly coupled state is controlled by varying a radial potential profile provided by radially segmented electrode for particle levitation and confinement under a completely DC configuration. Fine-particle clouds change their shapes from a usual two-dimensional disk to a three-dimensional cone, and finally concave cone with an increase in the radial potential slope. These profiles are closely related to an axial variation of the radial potential profile in the ion sheath above the segmented electrode. When we apply to the segmented electrode a potential profile with peaks between the radial center and edge, fine particles are rearranged to form azimuthal rings on the horizontal plane. The radial width of the rings is controlled by changing the peak width of the radial potential profile.

Non-Maxwellian shape of electron distribution function in ion acoustic turbulence

In a DC discharge plasma system, in which two meshes are installed, the current-driven ion acoustic instability is excited when a de potential V/sub m/ is applied to one of them. When the instability fully grows, the system reaches a very turbulence state, the so-called ion acoustic turbulence. The experimental measurement of energy distribution function of electrons in ion acoustic turbulence measured by the Langmuir probe shows a non-Maxwellian nature along with electron heating.

Detection of CN radicals in DC nitrogen plasma used for deposition of CN x layers

Emission spectra from a DC plasma discharge of nitrogen with a graphite cathode used for deposition of CN x layers were investigated in the visible range 350–900 nm. The spectra recorded at low and high resolution from both the negative glow and the positive column of the discharge were studied separately. All spectra are dominated by neutral and ionised N 2 emission. In the positive column the violet band of the cyanogen (CN) radical was identified and analysed for vibrational structure. From a computer simulation of the rotationally resolved violet band, vibrational temperatures were derived and found to be in the intensity distribution for the v=0, 1 and 2 levels from thermal equilibrium. In the negative glow the strong N 2 + features completely mask the spectral region of the violet band of CN. Conclusions were drawn concerning the CN formation by chemical sputtering, and the role of CN radicals in the formation of polymeric CN x layers of 1:1=C:N stoichiometry.

Electron cyclotron resonance negative ion source

Production and control of electron cyclotron resonance (ECR) plasmas for negative ion sources have been studied. A new production method using permanent magnets is proposed as one possibility for a large diameter high density uniform microwave plasma. The microwave power is launched by an annular slot antenna into the circumference of a chamber with a line-cusp or a ring-cusp type permanent magnets, where magnetic field can be applied in a local region and plasmas can be efficiently produced if the ECR condition is satisfied. In this article, we report the structure of the ECR negative ion source, the characteristics of the ECR plasmas, and comparison of the ECR plasmas with dc discharge plasmas from the viewpoint of a negative ion source for neutral beam injector. H− volume production is confirmed in ECR plasmas although the effect of the magnetic filter for controlling plasma parameters is different from that in dc discharge plasmas.

109 高周波プラズマによるDLC膜の合成及びその機械的特性の評価(OS 材料の超精密加工とマイクロ加工)

Diamond-like carbon (DLC) films were prepared on SiO_2 substrates by the rf-magnetoron sputtering using a sintered diamond target. It was found that the optical transmittance of the DLC film grown from sintered diamond target with an Ar ion laser beam was about fourfold lager than that grown from graphite target. DLC films were also grown on SUS630 steel substrates by DC-discharge plasma CVD. The nano-indentation hardness test and the ball-on-disk wear test were performed on the DLC coated SUS630 substrates, and the results of these tests revealed that not only the hardness but also the wear resistance of SUS 630 substrates were significantly improved by the DLC coating.

Negative Ion Volume Production in Electron Cyclotron Resonance Hydrogen Plasmas

Production and control of electron cyclotron resonance (ECR) plasmas for negative ion sources have been studied. A new production method using permanent magnets is proposed as one possibility for generating a large-diameter high-density uniform microwave plasma. The microwave power is launched by an annular slot antenna into the circumference of a chamber with a ring-cusp or a line-cusp permanent magnet, where a magnetic field can be applied in a local region and plasmas can be efficiently generated if the ECR condition is satisfied. In this paper, we report the structure of the ECR negative ion source, the characteristics of the ECR plasmas, and the comparison of the ECR plasmas with DC discharge plasmas from the viewpoint of a negative ion source.

Influence of the substrate bias on epitaxial growth of Si films by dc-discharge plasma chemical vapour deposition

We report on the investigation of the influence of the substrate bias on the structure of epitaxial Si films grown on Si (100) by low-energy dc-discharge plasma enhanced chemical vapour deposition in the temperature range between and . The effect of the substrate bias was studied by reflection high-energy electron diffraction, cross-sectional transmission electron microscopy (XTEM) and scanning tunnelling microscopy (STM). The XTEM investigations showed that the Si films grown at a negative substrate bias below 10 V are of good quality and defect free. In the films grown at a higher negative substrate bias a critical thickness was observed up to which the films remain free of extended defects. This critical thickness was found to be related to the ion bombardment of the surface during growth and to be substrate temperature dependent. The STM studies showed that the nucleation of stacking faults at this critical thickness is connected to an evolution of the surface roughness and a change of the growth mode from two- to three-dimensional at ion energies above 10 eV.

Dynamic potential formation of a rf sheath near the substrate in a dc discharge plasma

The dynamic potential formation of a radio-frequency (rf) sheath near the substrate was experimentally studied over a wide range of the frequency under a fixed plasma density produced by an Ar dc discharge plasma. Potential structures of the rf sheath obtained by detecting spatial profiles of the crest and trough potentials in the rf oscillation provided a strong frequency dependence. The sheath thickness of the trough potential expanded in the high-frequency region unlike the rf electrode in the conventional capacitively coupled rf discharge plasma. The potential well with a depth of an electron temperature formed in front of the substrate on the crest profile in the low-frequency region. Similar experiments in a dc discharge plasma producing negative ions were also performed. The virtual anode formed in the crest profile and its potential height grew with increasing applied frequency.

Generation of a large area thermal induction plasma by applying a 50 kHz magnetic field

Inductively coupled radio frequency plasmas are gradually becoming an important source of high-temperature and high-reactivity plasmas for processing new functional materials or for removal of unwanted substances. Spatially wider plasmas are required for higher rate, more uniform processing in the future. Although low MHz frequencies have been usually used for induction plasmas, an attempt to expand the high temperature plasma fields was made by superimposing lower frequency 50-kHz magnetic fields on the DC plasma discharge to obtain a small source plasma. Because the penetration depth in such a low frequency field is as long as a few hundred mm, a larger radius plasma can be expected. As a first step, we have investigated the operating conditions under which a stable low frequency plasma is generated, based on theoretical calculations that include the time dependent rate equations for heat transfer and fluid flow in conjunction with the Maxwell electro-magnetic equations. Results showed that the minimum necessary power for expanding a small DC plasma to a wider plasma 100 mm in diameter by applying a 50-kHz magnetic field, is about 130 kW at 0. 1-MPa pressure. This power level is recognized to be within the available range in existing high-power oscillator systems. Measurements were carried out of the time variation of the spectral emission from the plasma immediately after superimposing the 50-kHz magnetic field upon a small area plasma generated with DC power of 1.5 kW at a pressure of 0.01 MPa in Ar gas. At a low power level of about 60 kW, the small plasma starts to expand in the radial direction, and finally, converges to a new wider plasma with 100 mm diameter. FFT analysis of the oscillograph showed that during the transient state, a period fluctuation in light emission occurs at a few tens of Hz reflecting the thermal time constant of a few tens of ms, besides the power frequency of 41.7 kHz. The plasma temperature was estimated by using the spectroscopic line intensities from neutral Ar atoms, as between 8,000 and 11,000 K. A uniformly distributed temperature field was successfully produced by applying the 50-kHz magnetic field, as expected. © 1998 Scripta Technica, Electr Eng Jpn, 123 (4): 48–57, 1998

Surface Modifaction of Ultra High Molecular Weight Polyethylene by Low Energy DC Plasma Discharge

AbstractSurface effects produced by plasma processing Ultra High Molecular Weight polyethylene (UHMW) were examined. The goal was to enhance adhesion of UHMW to a variety of polar polymers. This research focussed on enhancing adhesion to polyurethane. UHMW samples were immersed in a DC discharge and subjected to various processing conditions. The background gases experimented with were oxygen, nitrogen, and argon, and the pressure was varied between 6-67 Pa. The processing time, discharge current and discharge potential were also varied. A polar polymer (polyurethane) was subsequently applied to the processed UHMW samples and the tensile strength of the bonds was measured. Standard dogbone specimens were fabricated, and the polymer interfaces placed in the middle of the gage section and oriented normal to the tensile axis. The specimens were tested to failure in displacement control at an approximate strain rate of 0.2% per sec. In general, significant enhancement in yield strength was observed over unprocessed samples, where essentially no bonding occurred. Samples subjected to plasma processing in oxygen showed the strongest adhesion, while those in argon were almost as good, followed by nitrogen.The contact angle of water on the processed UHMW samples ranged from about 45° to less than 2°, while unprocessed samples had a contact angle of about 70°. These data correlated with the yield tests. XPS was used to examine the composition of the UHMW surfaces before and after plasma processing with oxygen. It is believed that the plasma etched off surface layers, creating unsaturated carbon bonds that can chemically react with polar polymer groups. Precast, processed UItMW surfaces were found to be reactive for periods of up to one week. Optimum conditions of plasma processing were identified, and will be discussed in light of the chemistry occurring at the interface.

Influence of Heavy Particle Collision on Optical Emission in Cathode Fall of DC Argon/Silane Glow Discharge

Spatially resolved optical emission profiles were investigated in dc silane-argon discharge plasmas under the high E/N condition, where E is electric field strength and N is gas density. The optical line emission intensities of Ar, H, and SiH in both the cathode fall and negative glow regions were well explained by a simple collisional excitation model, in which heavy particle collisions in the cathode fall and electron collisions in the negative glow are taken into account, respectively. As a result, it was confirmed that radical production by heavy particle collision is indispensable in such chemical vapor deposition (CVD) plasmas for operation under the high E/N condition.

An all-carbon cathode for dc plasma chemical vapor deposition of diamond films

The fabrication and behavior of an all-carbon cathode for the growth of diamond films by dc discharge plasma chemical vapor deposition is presented. A graphite rod with a diameter of 2.5 mm was passivated in a methane dc plasma. During this process, the graphite was coated with pyrolytic carbon. Simultaneously, a thorn shaped protuberance (hereafter referred to simply as the thorn) of the same material grew from the end face of the rod towards the anode. The pyrolytic carbon prevented excessive sputtering of the cathode during diamond film synthesis in the hydrogen–methane plasma and the thorn presented a pointlike electron emitter providing a stable discharge. Using such cathodes, polycrystalline diamond films with well faceted crystallites have been grown at rates of approximately 5 μm/h. Nucleation and growth of individual, well faceted diamond crystallites even occurred on the cathode. When producing diamond films at methane concentrations above 1 vol %, a tubular form grows on the end of the cathode thorn.

Synthesis of Diamond Films on Stainless Steel Substrates

The continuous diamond films have been deposited on the stainless steel substrate using the hot cathode dc discharge plasma chemical vapor deposition method. The characteristics of diamond film are reported and the pretreatment of stainless steel substrate before deposition is also described.

Surface modification of polyethylene by remote dc discharge plasma treatment

AbstractThe surface modification of polyethylene in a remote nitrogen, oxygen, and hydrogen dc discharge plasma was investigated. In the case of the nitrogen plasma a strong correlation exists between the concentration of active nitrogen species, as detected by Langmuir probe measurements and plasma emission spectroscopy, and the time dependence of the polymer surface modification, as detected by contact‐angle measurements. The obtained contact‐angle data were interpreted in terms of the acid–base model for the interaction of the test liquid with the polymer surface. There was a great similarity in the functionalization of the polyethylene surfaces treated with nitrogen as well as with oxygen plasma, except in the intial stage, where in the former, mainly functional groups acting as electron acceptors were formed, whereas in the latter a sharp increase in the content of both electron donor as well as electron acceptor groups was detected. Thus, a determining influence of oxygen residues in the remote nitrogen plasma was indicated. The absence of such an effect in the case of the hydrogen plasma could result from direct quenching of reactive oxygen species and / or the chemical reduction of formed oxygen containing functionalities by hydrogen species. © 1993 John Wiley & Sons, Inc.

Electron-temperature control by movable pins installed in a hollow cathode for discharge plasmas

In order to control electron energy distributions in discharge plasmas, we have developed a new hollow cathode with pins inside. With an increase in the pin length, the electron temperature is observed to decrease continuously by an order of magnitude, being accompanied by a change of local plasma structure, in weakly magnetized low-pressure Ar dc discharge plasmas.

Effect of low pressure dc plasma discharge on laser ablated ferroelectric Pb(Zr,Ti)O3 thin films

Ferroelectric thin films of PZT [Pb(Zr,Ti)O3] were deposited on platinum coated silicon and bare silicon by excimer laser (248 nm) ablation and were in situ crystallized, with and without an oxygen discharge. Films deposited at various oxygen discharge voltages exhibited variations in polarization switching, dielectric constant, and loss, and current-voltage (I-V) characteristics. Crystalline perovskite PZT films deposited with a discharge voltage of +300 V offered stoichiometric and crystalline films, with a dielectric constant of 850, a remnant polarization of 22 μC/cm2, and a coercive field of 40 kV/cm, a resistivity of about 1012 Ω cm and a charge storage density of as high as 100 fC/μm2 at 5 V. Besides the property enhancement, the presence of O2+ discharge plasma appeared to have reduced the deposition temperature to relatively lower values (500 °C).

Improved Intensity Formulae for the Determination of Rotational Temperature from the Perturbed Band Structure

Improved formulae for the intensity profile of the rotational lines have been derived for the [ ndσΣ+, ndπII, ndδΔ] (Hund's case d)- n'pπII (case b) electronic bands of diatomic molecules with respect to the l-uncoupling interaction among the upper states. As an application of the formulae, the rotational temperature in the dc discharge plasma was determined from the analysis of the band structure of the He2[3 dσf3Σ+ u, 3 dπf3II u, 3 dδf3Δ u] ← 2 pπb3II g (0-0) absorption bands. The formulae were also applied to the H2 [3 dσg3Σ+ u, 3 dπi3II u, 3 dδj3Δ u] → 2 pπc3II g (0-0) emission bands.

EVALUATING THE INFLUENCE OF GROWTH PARAMETERS ON CVD DIAMOND DEPOSITION USING FACTORIAL ANALYSIS

The deposition of diamond films by low pressure CVD methods has been demonstrated using a number of thermal and plasma assisted CVD techniques. Addition of oxygen to the methane-hydrogen feedstock has been reported to improve the quality of diamond deposited and decrease the temperature at which diamond deposition is feasible. Oxygen also effects the growth rate and possibly the uniformity of the film. In this paper an experimental design methodology, factorial analysis, is presented which is, in principle, applicable to any CVD process. The factorial analysis identifies the most influential growth parameters and any interactions between independently variable parameters. fie analysis has been applied to diamond growth using CH4 -02 -Hz mixtures in a microwave assisted CVD process.The effect of oxygen addition on growth rate and film quality is discusst;d. The chemical vapour deposition of diamond films has been demonstrated by a wide range of methods including thermal filament, DC discharge, rf and microwave plasma assisted CVD, oxyacetylene and plasma torch 111. Growth conditions for the deposition of diamond requires substrate temperatures to be monitored between 700 and 1000T using a gas feedstock of 0.3- 5% methane diluted in hydrogen. Other parameters such as the excitation source (plasma or filament temperature), its distance from the substrate, flow rates and pressure also influence the growth rate and the quality of the deposited film. Some general conclusions may be drawn from the extensive range of studies that have been made in an attempt to 'optimise' the diamond growth process. Firstly, the amount of amorphous-graphitic carbon that is co-deposited with the diamond increases with methane concentration. The amorphous-graphitic carbon content can be reduced and hence the quality of the diamond film increased at higher substrate temperatures up to some threshold value of approximately l000T. A compromise between growth rate and film quality occurs as the growth rate decreases with decreasing methane partial-pressure. It has been proposed that the addition of oxygen to the methane-hydrogen feedstock has the effect of reducing the temperature at which good quality diamond films can be grown ie.below 70095 /2/. This is advantageous in the coating of temperature sensitive substrates, with the possibility of opening up new application areas such as hard coatings on polymeric materials. It has also been postulated that oxygen additions permit the deposition of high quality films using extended methane concentrations which would overcome the sacrifice in deposition rate. Hirose and Terasawa I31 have observed qualitative improvements in film quality and growth