Plasma-induced Reactions Research Articles

Electron Spin Resonance (ESR) Observation of Radicals on Biological Organism Interacted with Plasmas

ABSTRACTWe report the kinetic analysis of radicals on fungal spores of Penicillium digitatum interacted with charged-neutral oxygen species (O*) generated plasma discharge using real time in situ electron spin resonance (ESR) measurements. The ESR signal from the spores was observed at a g-value of around 2.004 with a line width of approximately 5G. We have successfully obtained information regarding the reaction mechanism with free radicals and realtime in situ ESR has proven to be a useful method to elucidate plasma-induced surface reactions on biological specimens

Use of Proteomics to Investigate Plasma-Cell Interactions

The understanding of basic mechanisms of plasma effects on living cells is one of the main preconditions to develop systematically innovative therapy options in the new and emerging field of plasma medicine. In this study, proteomics have been used for the first time to analyze the influences of physical plasma on vital constituents of mammalian cells. Treatment of human keratinocytes (HaCaT cells) by an atmospheric pressure argon plasma jet resulted in changes of charges of several cell proteins, but not in mass changes. These first re - sults indicate plasma-induced reactions of functional groups or ligands, but no fragmentation, degradation, or complexation of cell proteins. Hereby, the importance to examine internal cel- lular changes caused by plasma treatment to elucidate the influence of plasma on the metabo - lism of human cells next to morphological changes, cell performance, and cell viability could be demonstrated. Starting from now, proteomics will become a useful tool for basic research in the field of plasma medicine.

Observation of Plasma Chemical Vapor Deposition Process of Amorphous Carbon Film

Understanding and controlling of plasma-induced surface reactions are quite important for developing the future plasma processing including thin film deposition. We used “in-situ”, “real-time” infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS), to elucidate the mechanism of plasma-induced surface reactions during plasma enhanced chemical vapor deposition of amorphous carbon film. We examined the influence of substrate temperature on the surface reaction process, by analyzing infrared absorption spectra of Si surfaces during deposition of amorphous carbon film. We found that the deposition rate and the growth mode drastically change with varying the substrate temperature. We suggest that at low substrate temperature the film growth depends predominantly on the gas phase reaction, while at high temperature the film growth mode depends on the surface reaction as well as the gas phase reactions.

Analysis of the Roles of Nitrogen and Oxygen in the Synthesis of an Alcohol Polymer during Plasma-Induced Reactions

This paper investigates the roles of nitrogen and oxygen in forming a 1-butanol polymer. The analyses show that nitrogen is the key species for forming a stable 1-butanol polymer, and the viscosity of the polymer is increased as the ratio of nitrogen in the polymer is increased. In contrast, oxygen does not contribute to forming the polymer but rather prevents formation of the polymer instead. This article also analyzes the origin of C=O bonding in the 1-butanol polymer. IR analysis demonstrates that oxygen in the atmosphere is fixed in the polymer as C=O bonds, instead oxidizing the O-H group in 1-butanol.

From Chemical Kinetics to Streamer Corona Reactor and Voltage Pulse Generator

This paper discusses the global chemical kinetics of corona plasma-induced chemical reactions for pollution control. If there are no significant radical termination reactions, the pollution removal linearly depends on the corona energy density and/or the energy yield is a constant. If linear radical termination reactions play a dominant role, the removal rate shows experimental functions in terms of the corona energy density. If the radical concentration is significantly affected by nonlinear termination reactions, the removal rate depends on the square root of the corona energy density. These characteristics are also discussed with examples of VOCs and NOx removal and multiple processing. Moreover, this paper also discusses how to match a corona plasma reactor with a voltage pulse generator in order to increase the total energy efficiency. For a given corona reactor, a minimum peak voltage is found for matching a voltage pulse generator. Optimized relationship between the voltage rise time, the output impedance of a voltage pulse generator, and the stray capacitance of a corona reactor is presented. As an example, the paper discusses a 5.0-kW hybrid corona nonthermal plasma system for NOx removal from exhaust gases.

RF frequency effects on molecular fragmentation

The chlorine contents of 40 kHz and 13.56 MHz RF silicontetrachloride and dichlorosilane plasmas were investigated using actinometric evaluation in a parallel-plate (stainless-steel disk electrodes, stainless-steel reactor) electrode and in an electrodeless (external electrodes and glass reactor) discharges, in the 50-500 W RF power and 100-500 mTorr pressure ranges. It was found that the frequency has a significant effect on the molecular fragmentation of dichlorosilane and a less important effect on the fragmentation of silicontetrachloride. This behaviour was related to the molecular structures of the two starting components. The plasma-induced surface chemistries and morphology changes were also investigated and related to the different chemistries driven under 40 kHz and 13.56 MHz frequency environments. Plasma-induced and frequency-controlled molecular fragmentation reactions can be envisaged based on these findings.

Emission Spectroscopic Studies of Plasma-Induced NO Decomposition and Water Splitting

Plasma methods have been extensively used in materials processing and the abatement of air pollutants such as halogenated hydrocarbons, NO{sub x}, and SO{sub x}. Other plasma research areas include ozone formation, ammonia synthesis, and activation of CH{sub 4}, H{sub 2}O, and CO{sub 2}. NO decomposition and water splitting with ac (alternating current) power plasmas at atmospheric pressure have been studied using both quartz and metal reactors. Optical emission spectroscopic (OES) studies have been carried out by employing a CCD (charge-coupled device) detector to monitor the change of plasma species neat and in the presence of reactants and metal surfaces to provide mechanistic information. Selective features of energy transfer from excited helium species to reactant molecules have been observed. Energy transfer in nitrogen plasmas is nonselective, whereas in argon plasmas it is slightly selective. Energy efficiency of plasma-induced reactions is largely determined by the efficiency of energy transfer and catalytic effects of metal surfaces. A mechanism has been proposed on the basis of OES and activity data that comprise energy transfer from excited carrier gas species to reactant molecules and heterogeneous catalysis of metal electrodes involving adsorption and combination of intermediates (oxygen radicals) on metal surfaces.

Modelling plasma-induced reactions on polymer surfaces using aliphatic self-assembling and LB layers

Oxygen functional groups can be formed at the surface of aliphatic monolayers, oligomers and polymers by short-time oxygen low-pressure glow discharge plasma treatment without degradation of chains and building blocks. The molecular orientation is nearly preserved if not more than ~25% of all carbon atoms are functionalized. Longer exposure to oxygen plasma results in further increases in functionalization accompanied by cross-linking, degradation and disorientation of molecular chains. Polymer-specific degradation was exemplified by the cracking and splitting up of aromatic rings as seen in the NEXAFS spectra and by random cracking or depolymerization of macromolecular chains evidenced by an occurrence of new fragment peaks and by shifts in the molecular weight distribution as detected by MALDI mass spectrometry.

Crystallization of nanosized silicon powder prepared by plasma-induced clustering reactions

Nanosized silicon powders were prepared by gas-phase cluster agglomeration reactions in a low-pressure silane plasma. The formation and agglomeration of clusters leading to the growth of primary pa ...

Cluster-induced crystallization of nano-silicon particles

The possibility of producing from 20 nm to 100 nm sized silicon powders by plasma-induced reactions of silane including the formation of high-mass hydrogenated silicon anion clusters has been recently demonstrated. Careful HREM imaging showed circular contrast features, 1.5 to 2.5 nm in size, embedded in the amorphous particles which was attributed to the presence of medium range order in these regions. This non-homogeneous atomic distribution with partially ordered regions of a couple of nanometer dimension became more pronounced upon annealing upto the onset of crystallization. This observation and the formation of fivefold crystallites thereafter indicate that the clusters serve as seeds in the amorphous-to-crystalline transition.

Spectrochemistry of Plasma-Induced Free Radicals in Cellulose Derivatives.

We report here the specific features of plasma-induced free radicals of cellulose derivatives such as ethylcellulose (EC) and hydroxyethylcellulose (HEC) on its comparison with those of cellulose. The electron spin resonance (ESR) spectra of Ar plasma-irradiated EC and HEC consist of three kinds of discrete spectral components, two isotropic spectra [doublets (I) and triplets (II), both being assigned to hydroxylalkyl radicals] and one anisotropic spectrum [doublet of doublets (IV) assigned to an acylalkyl radical], and a single broad line spectrum (III). The special feature here is the fact that the spectrum (III) is a major component, contrary to cellulose, which was assigned to an immobilized dangling-bond site (DBS) at the cross-linked region. The results suggest that plasma-induced cross-linking reactions are very predominant in EC and HEC relative to that of cellulose, due to the presence of alkyl substituents in EC and HEC.

Plasma reactions of methane in nitrogen and nitrogen/oxygen carriers by matrix isolation FTIR spectroscopy

The plasma-induced reactions of traces of methane in nitrogen and nitrogen/oxygen carriers have been investigated by freezing the products onto a 10 K CsI substrate and performing FTIR analysis on the product mixture. Isotopic substitution studies have been used to assist in identification of reaction intermediates and final products. A combination of low (10 mTorr) and high (2 Torr) pressure discharges has also been used to help in the identification of these products. Oxygen concentration was increased in a stepwise fashion to determine its effect on the reaction product distribution. In the present work, methyl radical was the principal product in low-pressure N2/CH4 plasmas, and small amounts of HCN and NH3 were also produced. In the higher-pressure plasmas, HCN and NH3 were the principal products. As O2 was added to the plasmas, CO, H2O, CO2, N2O, NO, O3, HONO, and HNO3 were produced in approximately the order shown, i.e., CO was formed in good yield at low oxygen partial pressures, but HNO3 was produced only in slight yield even at the highest oxygen pressures used in this work. These results are discussed in terms of the development of a plasma device having potential application for destruction of environmentally hazardous materials and how trace organic pollutants might react in such a system.