Volume 80, Issue 9

The 18th International Symposium on Plasma Chemistry (ISPC-18) was held at Kyoto University in Kyoto, Japan from 26 to 31 August 2007 under the sponsorship of the International Union of Pure and Applied Chemistry (IUPAC) and the International Plasma Chemistry Society (IPCS). This is the second time that ISPC was held in Japan since ISPC-8 (Tokyo, 1987), and it was cosponsored by the 153rd Committee on Plasma Materials Science of Japan Society for Promotion of Science (JSPS), the Japan Society of Applied Physics (JSAP), the Graduate School of Engineering at Kyoto University, the Kyoto Nanotechnology Cluster (Kyo-NANO), and the Research Institute for Applied Science (RIAS). Prior to the symposium the IUPAC Summer School on Plasma Chemistry was held from 23 to 25 August, and the Industrial Workshop on Plasma Chemistry followed the symposium on the afternoon of the last day. ISPC is a biennial international conference with topics encompassing the whole area of plasma chemistry and plasma processing science from fundamentals to applications. There were 671 participants from 40 countries including 189 students. The topics covered the frontiers of nanotechnologies and biomedical and environmental applications as well as the traditional areas of plasma sources, diagnostics, modeling, and material syntheses. The symposium contained four plenary lectures, 21 topical invited talks, 179 oral presentations, and 547 poster presentations in the 14 categorized scientific topics. The industrial workshop consisted of 6 presentations and a panel discussion intended to focus on recycling technology for environmental issues. The large number of high-quality contributed papers reflects the continuously growing interest of researchers in the areas of plasma chemistry. This issue of Pure and Applied Chemistry contains 13 papers based on the plenary lectures and topical invited talks presented at ISPC-18. I sincerely hope that this issue provides readers an overview of current and future scientific and industrial developments in plasma chemistry. Kunihide Tachibana Conference Chair

When the electric field in the dark gas phase reaches the threshold value, an electron avalanche (breakdown) occurs, which causes dissociation of organic molecules, excitation of chemically reactive molecular gas, and/or ionization of atomic gas, depending on the type of gas involved. The principles that govern these electron-impact reactions are collectively described by the term "electron dynamics". The electron-impact dissociation of organic molecules is the key factor for the deposition plasma. The implications of the interfacial avalanche of the primary electrons on the deposition plasma and also other plasma processes are discussed. The system dependency of low-pressure plasma deposition processes is an extremely important factor that should be reckoned, because the electron dynamic reactions are highly dependent on every aspect of the reaction system. The secondary electron emission from the cathode is a misinterpretation of the interfacial electron avalanche of the primary electrons described in this paper.

Plasma polymerization covers a broad range of plasma deposits from soft to hard coatings. Nanoscale coatings are formed within a dry and eco-friendly process on different substrate materials and structures. To gain a deeper insight into plasma polymerization, a macroscopic approach using the concept of chemical quasi-equilibria might be useful. Following this macroscopic approach, the reaction parameter power input per gas flow W / F , which represents the specific energy invested per particle within the active plasma zone, solely determines the mass deposition rate. Hence, plasma polymerization can be described by measuring the deposited mass and examining the power input and gas flow which contributes to it. Thus, the control, investigation, and up-scaling of plasma polymerization processes are enabled. Different examples are given to make use of the macroscopic approach.

The unique ability of nonthermal plasmas to form high-quality nanocrystals (NCs) of covalently bonded semiconductors, including the group IV elements silicon (Si) and germanium (Ge), has been extensively demonstrated over the past few years. Recently, plasma processing was also extended to the surface functionalization of NCs, imparting further functionalities to plasma-produced NCs such as solution-processability or the passivation of electronic surface states. This paper focuses on the synthesis and surface functionalization of Si- and Ge-NCs, and on their application in luminescent and photovoltaic devices.

The paper presents an investigation of self-organizational and -assembly processes of nanostructure growth on surfaces exposed to low-temperature plasmas. We have considered three main growth stages-initial, or sub-monolayer growth stage, separate nanostructure growth stage, and array growth stages with the characteristic sizes of several nm, several tens of nm, and several hundreds of nm, respectively, and have demonstrated, by the experimental data and hybrid multiscale numerical simulations, that the plasma parameters can strongly influence the surface processes and hence the kinetics of self-organization and -assembly. Our results show that plasma-controlled self-organization is a promising way to assemble large regular arrays of nanostructures.

We report on the operation and characteristics of radio frequency (RF) plasma beam sources based on the expansion of the discharge outside of limited spaces with small interelectrode gaps. The appropriate electrode configuration, combined with high mass flow values and appropriate power levels, leads to small- or large-size plasma jets, working stably at low, intermediate, and atmospheric pressures. The sources are promising tools for a wide range of applications in thin film deposition, surface modification, and cleaning, including the case of temperature-sensitive substrates.

Generation and features of the radio frequency (RF) hollow cathode discharge (HCD) are compared for the atmospheric and moderate pressures. The atmospheric-pressure plasma systems, fused hollow cathode (FHC) and hybrid hollow electrode-activated discharge (H-HEAD), are described. Examples of applications where both FHC and H-HEAD have already been employed are given, and potentials for new processes are discussed.

Nonequilibrium low-pressure plasma discharges are extensively studied for their applications in the field of decontamination and sterilization of medical devices. The aim of this contribution is to discuss and demonstrate feasibility of oxygen low-pressure inductively coupled plasma (ICP) discharges for removal of various kinds of biological contamination. We demonstrate the ability of ICP discharges for the sterilization of bacterial spores and the removal of biological contamination from proteins and pyrogens.

Gas discharge plasma inactivation of microorganisms at low (close to ambient) temperature is a promising area of investigation that is attracting widespread interest. This paper describes atmospheric-pressure, nonthermal plasma (NTP) methods for cold sterilization of liquids and thermal sensitive surfaces. These methods are based on the use of direct current (DC) gas discharge plasma sources fed with steady-state high voltage. Parameters characterizing the plasma sources used (plasma-forming gas, gas flow rate, electric power consumed, etc.) are given. The results for plasma sterilization of different microorganisms (vegetative cells, spores, fungi, biofilms) are presented. An empirical mathematical approach is developed for describing NTP inactivation of microorganisms. This approach takes into account not only the destruction of different components of the cells, but their reparation as well.

A method of synthesizing functional nanostructured powders by using reactive thermal plasma processing has been developed. Nanosized TiO 2 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 TiO 2 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.

The recently developed plasma spray processes using liquid precursors make it possible to produce finely structured coatings with a broad range of microstructures and, thus, properties. However, coating reproducibility and control of the deposition efficiency are critical to industrial acceptance of these processes. Both depend on time-dependent interactions between the plasma jet and liquid material. Transient and realistic modeling of the liquid spray process may help to increase the understanding of the process. A comprehensive model should involve the formation of the plasma jet inside the torch and the transient specific treatment (break-up, droplet collision, coalescence, evaporation, chemistry) of the liquid material in the plasma jet. If much progress has been recently made on the modeling of the interaction of arc and transverse flow in the plasma torch, further theoretical and experimental research is needed, especially in respect of liquid injection and fragmentation under plasma spray conditions.

A thermal plasma treatment experiment was conducted on stormwater detention pond sludge. The original sludge compositions were analyzed by neutron activation multi-element analysis. Thirty-two elements were detected in the sludge samples, and nine of them were below detection limit. The assessment of Zn, As, Mn, and Fe concentrations against the Ontario Ministry of Environment's Sediment Quality Guidelines indicated a marginal-to-significant pollution, and the concentration of Cr presented a gross pollution. After thermal plasma treatment, the mean weight percentage removal at 0 and 2 L/min of air flow rates was 2.78 ± 0.51 and 3.85 ± 1.35 %, respectively. The maximum weight removal of 5.87 % was achieved with 2 L/min air flow rate and 2 h of treatment time. Reduction of total organic carbon (TOC) increased with increasing treatment time and air flow rate. Eight gas compounds, CO, CO 2 , NO, NO 2 , NO x , SO 2 , H 2 S, and C x H y were measured and observed during the treatment process.

Liquid-phase plasma is not well known, although it has been used sparingly in water treatments and electrical discharge machining. We have named the liquid-phase plasma "solution plasma" and developed solution plasma processing (SPP). This paper reports the applications of SPP to syntheses of nanoparticles, surface modification of metals, and sterilization of water.

A microplasma thruster has been developed of electrothermal type using azimuthally symmetric microwave-excited microplasmas. The microplasma source was ~2 mm in diameter and ~10 mm long, being operated at around atmospheric pressures; the micronozzle was a converging-diverging type, having a throat ~0.2 mm in diameter and ~1 mm long. Numerical and experimental results with Ar as a working gas demonstrated that this miniature electrothermal thruster gives a thrust of >1 mN, a specific impulse of ~100 s, and a thrust efficiency of ~10 % at a microwave power of <10 W, making it applicable to attitude-control and station-keeping maneuver for a microspacecraft of <10 kg.

Isothermal titration calorimetry (ITC) is widely used to determine the thermodynamics of biological interactions including protein-protein, small molecule-protein, protein-DNA, small molecule-DNA, and antigen-antibody interactions. An ITC measurement consists of monitoring the transfer of heat between an analyte solution in a sample vessel and a reference solution in a reference vessel upon injection of a small aliquot of titrant solution into the sample vessel at a fixed ITC operating temperature. A binding isotherm is generated from the heat-transferred-per-injection data and values for the binding constants, the apparent binding enthalpies, and the apparent ratio of the amount of titrant to analyte for the binding reaction are then determined from fits of a binding model, whether it is a single site, identical multi-site, or an interacting multi-site binding model, to the binding isotherm. Prior to the fitting procedure, corrections should be made for contributions from extraneous heat of mixing determined separately from injections of the titrant into just the dialysate/buffer solution. Ultra-high binding constants, which cannot be directly determined from an ITC measurement, can be determined by a displacement ITC method where injections of the tight-binding titrant into a solution of a weaker-binding titrant-analyte complex displaces the weaker-binding titrant from the complex. The Michaelis and catalytic constants can be determined for an enzyme reaction from injections of a substrate or enzyme titrant into an enzyme or substrate analyte solution. Several binding reactions are suggested to check the operating performance of the ITC. The reporting of ITC results must be specific with regard to the composition of the titrant and the analyte solutions, the temperature, and the model used in the analysis.

Expanded definitions of rotaxanes and pseudorotaxanes, their components, and other terms concerning rotaxanes are given. The uniform classification and nomenclature principles for naming different types of rotaxanes and pseudorotaxanes are described and illustrated with examples. Recommendations are provided for unambiguous description of rotaxane isomerism with special descriptors that include information about position of rotaxane components.