Reactive Plasma Processing Research Articles

Radical Controlled Plasma and Its Application

The reactive plasma processing has played important roles in etching, deposition and surface modification and sustained the basis of all science and technological fields. However, the plasma processing has been developed by using external parameters of apparatus such as power, pressure and gas flow rate and so on in the industrial fields since the species, in particular, radicals in the plasma have not been able to be measured. For past 15 years, however, many diagnostics tools to measure radicals in reactive plasmas have been developed. Particularly, the measurement of radicals enabled to make a new approach for developing of plasma processing, where the plasma is precisely controlled on the basis of measured results of radicals. In this article, the radical controlled plasma and its application, where the high performances are obtained based on insights into behaviors of radicals in the reactive plasma, is described.

Synthesis of functional TiO2-based nanoparticles in radio frequency induction thermal plasma

Abstract A method of synthesizing functional nanostructured powders by using reactive thermal plasma processing has been developed. Nanosized TiO2 powders have been synthesized by the plasma oxidation of solid and liquid precursors. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, are used to affect the quench rate and hence the particle size of the resultant powders. The experimental results are well supported by numerical analysis of the effects of the quench gas on flow pattern and temperature field of the thermal plasma as well as trajectory and temperature histories of the particles. The plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by conventional wet processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step by reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated. Applications of highly functional nanoparticles are thought to require nanoparticles structured in the forms of (1) dispersoids, (2) fillers, and (3) patterns. For these purposes, plasma-synthesized nanocrystallites seem to be suitable.

熱プラズマプロセスによる高機能ナノ粒子の合成

A method of synthesizing functional nanostructured powders through thermal plasma processing has been developed. Nano-submicron-size metal and carbide particles were synthesized through evaporation and subsequent condensation of powders in thermal plasma. The synthesis of nano-size titanium oxide powders was performed by the oxidation of solid and liquid precursors. The plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by the conventional wetchemical processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via the reactive thermal plasma processing.

Synthesis of ceramic nanoparticles with non-equilibrium crystal structures and chemical compositions by controlled thermal plasma processing

The synthesis of functional nanostructured powders has been developed through reactive thermal plasma processing. Nanosized particles of titanium oxide powder with high crystallinity and non-equilibrium chemical composition were synthesised by one-step processing based on the oxidation of solid and liquid precursors. Spherical carbon powders were treated in a reactive thermal plasma. Crystallinity, chemical composition, and surface morphology were changed in plasma-treated carbon powders. Plasma-treated carbon powders were used as the anode of a lithium-ion rechargeable battery, and improvements in discharge capacity and efficiency were recognized. The generation of pulse-modulated RF inductively coupled plasmas (PM-ICPs) was developed for the first time. The non-equilibrium states were recognized at the instances of pulse-on and pulse-off, and the concentration of chemically active radical species was increased. This offers a unique physico-chemical condition for materials processing.

Insights into sticking of radicals on surfaces for smart plasma nano-processing

In reactive plasma processing, species produced in the plasma reach the surface of a substrate and cause etching, deposition and surface modification through surface reactions. These reactions are characterized by the densities and energies of species incident on the surfaces. In order to realize nano-scale plasma processing, important species for plasma processing have been identified and characterized, and their behavior, not only in the gas phase, but also on the surface, have been clarified and controlled. One of the most critical parameters for insights into surface reaction kinetics of radicals is sticking and surface loss probability. On the basis of radical densities measured by various methods, the sticking and surface reaction loss probabilities have been compiled, and they enable the quantitative understanding of the kinetics of radicals on the surface in the plasma. In this article, the sticking and surface reaction loss probabilities measured thus far are reviewed focusing on fluorocarbon gas, silane gas and methane gas based plasma processes. The establishment of a smart plasma process and the development of an autonomous production device with control of radicals on the basis of insights into the surface reactions for nano-scale plasma processing are presented.

プラズマプロセスを利用したナノ構造粉末材料の高機能化

Synthesis of functional nano-structured powders has been developed through the reactive thermal plasma processing. Spherical carbon powders, such as phenolic resin, glassy carbon and graphite powders, were treated in reactive thermal plasma. Crystallinity, chemical composition, and surface morphology were changed in plasma-treated carbon powders depending on the plasma conditions. Plasma-treated powders were applied to the anode of lithium-ion rechargeable battery, and improvement of the discharge capacity and the discharge efficiency was recognized. Also, the synthesis of nano-size titanium oxide powders has been performed by the oxidation of solid and liquid precursors. Plasma-synthesized TiO2 nano-particles showed the different phase preference from those synthesized by conventional wet processes. The nano-size particles of high crystallinity and non-equilibrium chemical composition were formed by one-step processing.

Study on Reactive Non-thermal Plasma Process combined with Metal Oxide Catalyst for Removal of Dilute Trichloroethylene

In order to improve energy efficiency in the dilute trichloroethylene removal using the nonthermal plasma process, the barrier discharge treatment combined with manganese dioxide was experimentally studied. Reaction kinetics in this process was studied on the basis of final byproducts distribution. Decomposition efficiency was improved to about <TEX>$99\;\%$</TEX> at the specific energy of 40 J/L with passing through manganese dioxide. C=C <TEX>${\pi}$</TEX> bond cleavage of TCE substances gave DCAC, which has the single bond of C-C through oxidation reaction during the barrier discharge plasma treatment. Those DCAC were broken easily in the subsequent catalytic reaction due to the weak bonding energy about <TEX>$3{\sim}4\;eV$</TEX> compared with the double bonding energy in TCE molecules. Oxidation byproducts of DCAC and TCAA from TCE decomposition are generated from the barrier discharge plasma treatment and catalytic surface chemical reaction, respectively. Complete oxidation of TCE into COx is required to about 400 J/L, but <TEX>$CO_2$</TEX> selectivity remains about <TEX>$60\;\%$</TEX>.

Reactive glow discharges: comparison of steady-state versus pulsed operation

In this work we compare glow discharges using traditional, inert gases and alternative reactive gases. More specifically, argon is systematically replaced by nitrogen (or oxygen) at increasing levels, culminating in a plasma completely sustained by nitrogen (or oxygen). To decouple the reactive plasma processes from potentially reactive surface reactions, we employed gold as a non-reactive cathode material. A common trend with nitrogen and oxygen addition is the significant loss of the Ar and ArH ion signals. As the argon ion signal decreases, the molecular oxygen ion increases; however the molecular nitrogen ion does not exhibit the same trend. Our studies include monitoring ions produced in the glow discharge, comparing direct current and pulsed discharges, and evaluating sputter rates.

Temporal development of the composition of Zr and Cr cathodic arc plasma streams in a N2 environment

We describe the temporal development of the plasma composition in a pulsed plasma stream generated by cathodic arc. Cathodes of Zr and Cr were operated at various nitrogen pressures. The time-resolved plasma composition for the cathode materials was analyzed with time-of-flight charge-to-mass spectrometry, and was found to be a strong function of the nitrogen pressure. Large plasma composition gradients were detected within the first 60 μs of the pulse, the nitrogen ion concentration increasing with increasing pressure. The results are explained by the formation and erosion of a compound layer formed at the cathode surface in the presence of a reactive gas. The average charge state was also found to be affected by the reactive gas pressure as well as by the time after ignition. The charge states were highest in the beginning of the pulse at low nitrogen pressure, decreasing to a steady-state value at higher pressure. These results are of importance for reactive plasma processing and for controlling the evolution of thin film composition and microstructure.

NOVEL REACTIVE PLASMA PROCESSING FOR TRANSFORMING SURFACES OF METALS AND INTERMETALLICS TO CERAMICS

The surface of Ti, Zr, and TiAl was directly transformed to ceramics with a graded composition by carburizing, nitriding, and oxidizing using novel reactive plasma processing that has been developed by the present authors. Thick modified layers which consist of TiC, TiN, ZrC, ZrN (Zr2N), ZrO2, and Ti2AlN were successfully synthesized by this plasma process. The ceramic layers exhibited higher hardness and elastic modulus than the substrates. The formation behavior of these ceramic layers was analyzed with ab initio molecular orbital simulation and thermodynamic calculation. The chemical interaction of the interstitial atoms with the lattice of substrate materials was found to govern the diffusion and ordering processes to form the ceramic layers.

Measurement techniques of radicals, their gas phase and surface reactions in reactive plasma processing

In order to realize the high performance of material process, various measurement methods for radical densities in the reactive plasmas have been developed and the behaviors of important radicals in the gas phase, which have been impossible to measure in the past, have recently been clarified. With these measurement techniques, it is requested strongly that the quantitatively understanding of kinetics of the surface reaction of radicals and hereby clarifying the precursors for etching and thin film deposition for controlling the process with a high accuracy. In this article, the findings of measurement techniques of radical densities, the behaviors of radicals in the gas phase and on the surface have been described.

609 Carburization of TiAl alloys by reactive plasma process at elevated temperatures

609 Carburization of TiAl alloys by reactive plasma process at elevated temperatures

Ceramic layers formed on metals by reactive plasma processing

Abstract Thick layers of ceramics mainly composed of TaC, ZrO 2 and Ti 2 AlN were successfully synthesized on the surfaces of Ta, Zr and TiAl by means of novel plasma dry processing with or without 20 MeV-electron beam irradiation as the pretreatment. The thickness of these ceramic layers reached 10–100 μm under appropriate process conditions. Vickers hardness of the layers including TaC, ZrO 2 and Ti 2 AlN were estimated to be approximately 3000, 1300 and 3500 Hv[kg/mm 2 ], respectively. The cross-sectional profiles of constituent elements graded gradually in the modified surface regions, suggesting that these ceramics must have some properties of functionally graded materials.

Surface Modification of EPDM Rubber by Reactive Argon-Oxygen Plasma Process

The ethylene-propylene diene monomer (EPDM) rubber is an important material for rocket engine technology due to its thermal and mechanical characteristics. The improvement of the adhesion character...

Surface Modification of EPDM Rubber by Reactive Argon-Oxygen Plasma Process

The ethylene-propylene diene monomer (EPDM) rubber is an important material for rocket engine technology due to its thermal and mechanical characteristics. The improvement of the adhesion characteristics of EPDM on other kinds of polymers, using plasma technology, has been the major subject of many research works carried out during the last years. In this work, the EPDM surface activation process was carried out in a reactive ion etching reactor (RIE) operated at 13,54 MHz using pure oxygen and a gas mixture of argon and oxygen. These essays were performed varying the process pressure from 70 mTorr to 1000 mTorr, process time from 1 min to 10 min and RF power input from 50 W to 200: W. The surfaces of the treated samples were analyzed by Fourier transform infrared attenuated total reflection spectroscopy (FTIR- ATR). The evolution of the C-OH, and C=O and R-O chemical groups were observed as a function of the plasma process parameters. The analysis of the IR spectra showed that there are experimental condition of the process in which the production of new radical groups on this rubber surface is maximized.

Direct Surface Modification of Zirconium by Reactive Plasma Processing at Elevated Temperatures

This paper investigates a surface modification process for Zr to improve its durability, in order to make use of Zr in a blanket module as an effective neutron multiplier with (n, 2n) reaction. Modified ceramic layers were successfully synthesized on Zr substrates by carburizing, nitriding and oxidizing using reactive plasma processes. The microstruc- tural evolution during the plasma process is governed both by the kinetics of the diffusion and by the kinetics of the ordering to form the reaction products. In the case of carburizing, the growth rate of the carbide layer is restrained by the diffusion of C, which was clarified to exhibit high covalency with the neighboring Zr atoms by a first principles molecular orbital simulation, through the layer. By contrast, the diffusion of O which exhibits high ionicity rather than covalency with the Zr lattice is much faster than the rate of ordering to form the monoclinic ZrO2 phase. A 20 MeV electron beam pre-irradiation process was also conducted at ambient temperatures as a pre-treatment before the plasma process. The electron beam irradiation can influence the reaction behavior during the plasma process, depending on the process conditions.

Transformation of titanium surface to TiC- or TiN-ceramics by reactive plasma processing

The sub-surfaces of pure Ti-plates were transformed to the cermets TiC and TiN by plasma processing. The thickness and hardness of the modified layers increased with the processing temperature, distinguishably, over 1000°C. The maximum values of Vicker's hardness and thickness of the modified layers of TiC and TiN processed for 5 and 2 h at processing temperatures of 1400 and 1300°C, respectively, were approximately 5000 kg·mm −2/40 μm and 5400 kg·mm −2/55 μm. A distribution profile of carbon at the interface region of TiC characterized by electron probe micro-analysis (EPMA) suggested that the modified layer of ceramics was regarded as a kind of functionally graded material.

Chemical Reaction of TiAl Intermetallics with a Nitrogen Plasma

Direct surface nitridation of TiAl alloy was successfully performed using a reactive plasma process. The modified layer, composed of a double-layer structure, was fabricated using this plasma process. The top surface layer mainly consisted of a ternary nitride, Ti2AlN. The reaction mechanism in this plasma process is divided into three stages: surface reaction, diffusion of atomic nitrogen, and rearrangement of atomic configuration. The driving force to form the ternary nitride from TiAl was considered by a quantum chemical simulation. As a result of the simulation, the strong Coulomb attractive interaction between Ti and interstitial N atoms in the TiAl alloy is inferred to be predominate in the rearrangement of the atomic configuration, rather than the covalency between Al and N atoms. The surface modified layer significantly exhibits a higher hardness than the TiAl alloy. The subsurface layer retains sufficient ductility, although solution hardening was slightly achieved.

Direct Surface Modification of Zirconium by Reactive Plasma Processing at Elevated Temperatures.

Direct Surface Modification of Zirconium by Reactive Plasma Processing at Elevated Temperatures.

Studies on reactive sputtering process of TiN films using small mass analyzers

Investigation on the reactive sputtering plasma process for the TiN films has been carried out, using small mass analyzers located in a discharge vessel without differential pumping units. A reaction mechanism is studied on time-dependent data of the transition of a Ti-target surface from nitride to the metallic state. The flux of ionic species from the plasma has been measured as well, and is discussed in association with the electric potential formation.