Plasma Chemistry and Plasma Processing (v.31, #3)

This work reports a new laser molecular beam time-of-flight mass spectrometry (LMB-TOFMS) instrument built at Plasma Spectroscopy Lab in Dalian University of Technology (DUT). The preliminary investigation of the intermediate species distribution of acetylene plasma in an atmospheric-pressure fast-flow nanosecond-pulsed dc-discharge has been carried out. The CxH2 species (x = 4,6,8), believed to be the dominant source of negative ions in C2H2 plasma, have been detected with relatively intense peak signals and some complex radical species like C7H7, C9H5, C10H5 are also observed. The addition of Ar gas significantly influenced the detection of the intermediate species. This is might be due to the metastable Ar* with energies of 11.5 and 11.7 eV and a long lifetime. The potentialities of LMB-TOFMS for hydrocarbon plasmas diagnosis have been discussed.
Keywords: LMB-TOFMS; Acetylene plasma; Intermediate species; Reactive plasma

Time-Resolved Fourier Transform Emission Spectroscopy of CF3Br and CF3CFHCF3 in a Pulsed Electrical Discharge by Martin Ferus; Svatopluk Civiš; Petr Kubelík; Václav Nevrlý; Petr Bitala; Eva Grigorová; Michal Střižík; Pavel Kubát; Zdeněk Zelinger (417-426).
The environmentally important decomposition of halogenated species CF3Br and CF3CHFCF3 in helium discharge plasma was investigated by time-resolved high-resolution Fourier transform infrared emission spectroscopy. Contrary to classical pyrolysis, a deeper fragmentation of precursors up to atoms and lower molecular species was observed. Excited molecular products CF, CF2 and CF4 achieved the maximal concentration in the afterglow. The high concentration of all these species is in agreement with a kinetic model based on radical chemistry. The non-detectable concentration of CF3 can be connected to its high reactivity and the formation of more stable products, CF4 and CF2, by addition or release of a fluorine atom, respectively. Other products included HF, HBr, CO and cyano compounds that were produced by secondary reactions with traces of water vapor, atmospheric oxygen and nitrogen present in original industrial samples as impurities.
Keywords: Helium discharge plasma; CF3Br; CF3CHFCF3 ; Fluorocarbon radicals; Time-resolved FTIR

We have studied the production of synthesis gas and other hydrocarbons in a dielectric barrier discharge using mixtures of helium, methane and carbon dioxide. It was found that helium has a significant influence on the discharge, decreasing the breakdown voltage and increasing the rate of conversion of CH4 and CO2. However it also decreases the selectivities and the range of stable operating conditions for the discharge. The main products obtained were H2, CO, C2H6 and C3H8 but traces of other hydrocarbon, carbon deposition and the formation of condensable products were also detected. The rate of conversion and conversion abilities were obtained by fitting the conversion results to a model.
Keywords: Methane conversion; Synthesis gas; Carbon dioxide; Dielectric barrier discharge

Effects of Plasma and Acid Treatment on the Dispersion of Carbon Nanotubes in Liquids by Yin Jiang; Yue-Feng Zhu; Feng-Ying Wang; Wen-Jia Chen (441-448).
Carbon nanotubes (CNTs) with different diameters were treated by plasma and acid. The CNTs were dispersed in water and the light transmittance of the CNTs dispersoid (the mixture of CNTs and water) was measured to characterize the dispersibility of CNTs. With the light transmittance of water as the baseline, relative transmittance (RT) of CNTs dispersoid was calculated and the curves of RT varying with time were fitted with a function. The effects of CNTs diameter, acid treatment and plasma treatment on the dispersion of CNTs in water were studied according to the fitting results. It could be concluded that the dispersibility of the CNTs with bigger diameters was better. Plasma treatment could improve the dispersibility of CNTs and if the CNTs were acid-treated, plasma treatment could improve their dispersibility further.
Keywords: Carbon nanotube; Plasma; Transmittance; Dispersion

Sulfur dioxide Plasma Treatment of the Clay (LAPONITE®) Particles by Kateryna Fatyeyeva; Fabienne Poncin-Epaillard (449-464).
Low temperature plasma treatment of the inorganic clay (LAPONITE®) using sulfur dioxide (SO2) as a process gas was carried out in order to graft the functional groups containing sulfur and oxygen (sulfonic acid groups) onto the inert clay surface. Conditions for SO2 plasma modification were optimized by the measurement of the sulfur content as a function of the plasma power, gas flow rate and treatment time. It was found that the sulfur content increased with the increasing of the plasma power as well as the treatment time. Optical emission spectroscopy was presented in order to control the plasma phase and to characterize the different excitation processes of atomic species in SO2 plasma under different discharge conditions. X-ray diffraction spectrometry, X-ray photoelectron spectroscopy, FTIR and thermal analysis measurements of grafted LAPONITE® powder completed the characterization.
Keywords: LAPONITE®; Plasma treatment; Optical emission spectroscopy; Sulfonation; Surface modification

Microstructural Characterization and Mechanical Property of Iridium Coating Produced by Double Glow Plasma by Wangping Wu; Xin Lin; Zhaofeng Chen; Zhou Chen; Xiangna Cong; Tengzhou Xu; Jinlian Qiu (465-475).
Ir is the most interesting as an effective oxygen diffusion barrier for super high-temperature structural materials. In this study, an Ir coating, approximately 7 μm thick, was deposited onto Mo substrate by double glow plasma at substrate temperature of about 1,120 K in an argon atmosphere. The crystal orientation, morphology and mechanical property of the Ir coating were investigated by XRD, SEM, AFM, TEM, nanoindentation and scratch test. The results indicated that the (220)-oriented Ir coating was composed of the columnar grains. The surface roughness of the Ir coating was higher than that of the substrate. The hardness and the elastic modulus of the Ir coating were about 9.5 and 340 GPa, respectively. The coating had a high hardness due to the sub-micrometer size grains. The coating had good scratch resistance due to the strong adhesion of the coating to the substrate.
Keywords: Coating; Morphology; Hardness; Plasma discharge

Structure–Property Relationship of Thin Plasma Deposited Poly(allyl alcohol) Films by A. Fahmy; R. Mix; A. Schönhals; J. F. Friedrich (477-498).
Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements.
Keywords: Allyl alcohol; Dielectric properties; Plasma polymerization; Surface and bulk characterization; Thermal stability

Amorphization of various solid materials has attracted increasing attentions. We report here an amorphization of metal–organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) using dielectric-barrier discharge (DBD) treatment at ambient pressure and low gas temperature (around 120°C). The irreversible amorphization was confirmed by x-ray diffraction (XRD) characterization. The result of N2 adsorption–desorption measurements revealed a collapse of pores, which further supported the XRD results. The destroying of part of carboxylate groups might be the main reason resulting in the amorphization of MOF-5.
Keywords: Amorphization; Metal–organic framework; Dielectric-barrier discharge

Plasma Characteristics of Internal Inductively Coupled Plasma Source with Ferrite Module by Jong Hyeuk Lim; Kyong Nam Kim; Min Hwan Jeon; Jong Tae Lim; Geun Young Yeom (507-515).
Electrical and plasma properties of a U-shaped internal inductively coupled plasma (ICP) source with/without a Ni-Zn ferrite module installed above the ICP antenna were investigated. By installing the ferrite module on the antenna, the increase of plasma density and the decrease of plasma potential could be observed. The increase of plasma density was related to the efficient inductive coupling to the plasma by concentrating the induced magnetic field between the antenna and the substrate. At 800 W of ICP power and 20mTorr Ar, a high density plasma on the order of 4.5′1011/cm3 could be obtained.
Keywords: Ferrite ICP; Inductive coupling