L. Soukup

Barrier-torch discharge plasma source for surface treatment technology at atmospheric pressure

The description and investigation of a new atmospheric plasma source for the treatment and coatings of surfaces are presented in this paper. This new system is a modification of a well-known atmospheric torch discharge stabilized by a flowing channel of the working gas through an RF powered nozzle. The new version of this source prevents the transition to the regime with hot electrodes. This modification is suitable for surface and coatings applications of such substrates sensitive to overheating causing undesirable phase transition or melting. The new source called in our paper as an RF barrier-torch atmospheric discharge employs dielectrically coated nozzles instead of bare metallic ones. In that case, the plasma jet has quite different properties, as it is clear from presented experiments. The new version allowed excitation of the atmospheric plasma channel interacting with the substrate independently on the conductivity of the substrate. Simultaneously it is possible to hold the substrate temperature under atmospheric jet interaction below the limit point of aluminium melting or below an even lower limit of 80°C in a pulse-modulated mode. Extension to the multi-nozzle barrier-torch system was attained with the application of nine quartz nozzles. This multi-plasma jet excitation and its interaction was demonstrated with the substrate made of either quartz or aluminium plate, both possibly with non-flat shape. Emission spectroscopy and RF voltage and current amplitude measurements were employed in order to characterize the RF barrier-torch discharge.

Germanium nitride layers prepared by supersonic r.f. plasma jet

Abstract Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) have been used to characterize GexNy films grown on Si substrates. The films were deposited in a plasma chemical reactor by a radio frequency (r.f.)-generated supersonic plasma jet. The Ge nozzle of the r.f. electrode was reactively sputtered in the plasma jet generated in the nitrogen and the germanium nitride films were created in the reactor. The RBS method showed that the ratio Ge:N in the layer was close to the expected stoichiometric ratio 3:4 (for example, 0.73, which is within experimental error) when traces of oxygen were suppressed. The chemical bonding state of GeN, as found by XPS analysis, showed that, close to the thin film surface, the Ge:N ratio was also near 3:4. The impurities present, although in small amount, were preferentially bonded into the film.

Deposition of InxOy and SnOx thin films on polymer substrate by means of atmospheric barrier-torch discharge

Abstract Barrier torch discharge was used for low temperature deposition of In x O y and SnO x thin films at atmospheric pressure on polymer substrates. Vapors of Sn- and In-acetylacetonat were used as growth precursors for the deposition process of SnO x and In x O y thin films. Transparent films of conductivity σ SnO ≈10 S/cm for SnO x and σ InO ≈10 2 S/cm for In x O y were deposited on polymer substrates under conditions when the atmospheric plasma jet directly interacted with the polymer substrate. Plasma jet excitation had to be pulse modulated in order to avoid thermal damages of the polymer substrate. SnO x and In x O y were also deposited in a different discharge mode, in which interaction of the light emitting plasma jet with the substrate did not directly occur. In this case, the films had pure adhesion and had electrical conductivity lower than σ −3 S/cm. The analysis by an electron microprobe system has shown that the films had chemical composition close to SnO 2 and In 2 O 3 , respectively. XRD diffraction did not confirm any crystalline phase in all the deposited samples.

Low-pressure RF multi-plasma-jet system for deposition of alloy and composite thin films

A plasma-chemical reactor with a multi-plasma-jet RF hollow-cathode system has been developed for the deposition of alloy and composite thin films. Two primary plasma-jet channels and one secondary plasma channel were created in the volume of the reactor. High-density plasma flowing in these plasma-jet channels is generated inside the nozzles. These work simultaneously as RF hollow cathodes. An RF hollow cathode discharge is generated in these nozzles and is subsequently blown out of the reactor, creating flowing plasma jets. These jets were used for the deposition of SiGe and ZrCN thin films as an example of the deposition of alloy and composite thin films with this system. Co-sputtering or reactive co-sputtering of the nozzle material using high-density RF hollow-cathode plasma was applied for the deposition process. Control of the composition of the thin films was accomplished by setting the relative distance between the nozzle outlets without changing the plasma density inside the RF hollow cathodes. The composition of films was investigated with an electron microprobe system equipped with an X-ray microanalyser. This apparatus allowed quantitative analysis of the films. The stoichiometric homogeneity of the films was studied with this technique. Optical emission spectroscopy was used to investigate the secondary plasma-jet channel.

CNx coatings deposited by pulsed RF supersonic plasma jet: hardness, nitrogenation and optical properties

Abstract A low pressure pulsed RF supersonic plasma jet system (RPJ) has been used for deposition of CN x thin films. The aim of the CN x thin films deposition was an application for tribological coatings. Chemical composition, mechanical and optical properties of deposited CN x films have been measured. The obtained parameters were found to be similar to those of CN x films prepared by DC magnetron sputtering. The deposition rate for the CN x films prepared in RPJ reactor was of approximately 2 μm/h. During the deposition process, the substrate temperature did not exceed 250°C, as required for certain kinds of machine tribological coatings. A strong correlation between DC bias magnitude, nitrogen concentration and mechanical properties was found. The value of the substrate bias V DC =−100 V was found to be optimal for deposition of hard CN x films with maximum microhardness H =22 GPa. The films with the highest microhardness had the lowest atomic concentration of nitrogen. Analogous correlation has been found in ‘Diamond Relat. Mater. 7 (1998) 417’, although the deposition method and conditions were quite different. The chemically active plasma has been investigated in the RF supersonic plasma jet channel during the deposition process by means of ‘in situ’ emission spectroscopy. The mechanism of CN x formation has been studied as well.

Investigation of the atmospheric RF torch-barrier plasma jet for deposition of CeOx thin films

Abstract An atmospheric pressure RF torch-barrier discharge system with flowing plasma jet channel was studied as a tool for coatings of aluminum substrates by CeO x thin films. Cerium precursors were supplied to the plasma jet in the form of aerosol of the water solution of cerium salts. CeO x thin films were obtained on the Al substrate at certain deposition conditions. Properties of deposited CeO x films were studied by electron microprobe system. Surface of the films was analyzed by XPS method. ‘In situ’ emission spectroscopy of active plasma jet channel was performed in order to obtain more parameters about atmospheric plasma jet channel.

Probe diagnostics of the RF barrier-torch discharge at atmospheric pressure

Abstract Accurate control of plasma microparameters at the position of the substrate is crucial factor in applications of the barrier-torch plasma source for technological purposes. We present measurements of the electron temperature T e in the RF barrier-torch discharge by means of the planar RF-compensated Langmuir probe. The probe was mounted at the substrate position. The error caused by collisions of charged particles with neutrals in the space-charge sheath around the probe (collision probe working regime) at atmospheric pressure is discussed. In order to minimize this error the single probe technique was used to acquire the probe data, which were then recalculated to get the double probe characteristic. From this the electron temperature T e has been obtained in usual manner. The T e was measured at the position of the substrate in the single- and multi-torch barrier atmospheric plasma-jet systems. Using He as a working gas T e was found to be in the interval T e =2.7–6 eV depending on the applied RF power and system configuration. The neutral gas temperature has been measured by optical diagnostics and found to be 400–800 K. The plasma of the RF barrier-torch discharge is therefore strongly non-isothermal even at such high operation pressure.

The Radio Frequency Hollow Cathode Discharge Induced by the RF Discharge in the Plasma‐Jet Chemical Reactor

In the recent decade an RF driven, low-pressure plasma reactor with supersonic plasma jet was developed (RPJ). This reactor was successfully used for deposition of thin films of various materials. The deposition of thin films indicates that the properties of the deposited films are dependent on the sputtering or reactive sputtering processes appearing inside the nozzle (hollow cathode). The nozzle (hollow cathode) fabricated of different kinds of materials and alloys works both as a cathode of the radio frequency (RF) hollow cathode discharge and as a nozzle for plasma jet channel generation as well. The RF hollow cathode discharge is a secondary discharge, which is induced by the primary RF plasma generated in the reactor chamber. The present paper deals with the experimental study of this RF hollow cathode discharge. The stress is laid on the investigation of the axial distribution of discharge parameters and sputtering processes inside the nozzle. On the base of experiments, the simple model of the axial distribution of the investigated RF hollow cathode discharge has been developed.

Radio-frequency low pressure supersonic jet plasma chemical system

This paper presents a refined model for the generation of a supersonic plasma jet by a hollow cathode discharge inside the nozzle of a low pressure r.f. plasma chemical reactor. Through the nozzle which is placed in the r.f. electrode the working gas flows to the reactor chamber. If at the outlet of the nozzle the gas flow is supersonic, a well-defined plasma jet is created inside the reactor chamber. The application of this system for the deposition of germanium nitride thin films is shown.