Electrical,Thermal and Optical Diagnostics of an Atmospheric Plasma Jet System

Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures between 319 and 347 K.     

Atmospheric Pressure Plasma Discharge for Polysiloxane Thin Films Deposition and Comparison with Low Pressure Process

An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltage-current measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process.     

Optical and Electrical Properties of Polymerizing Plasmas and Their Correlation with DLC Film Properties

Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixtures, at different excitation powers, P. The effects of this parameter on the plasma potential, electron density, electron temperature, and plasma activity were investigated using a Langmuir probe. The mean electron temperature increased from about 0.5 to about 7.0 eV while the mean electron density decreased from about 1.2 × 10⁹ to about 0.2 × 10⁹ cm^–3 as P was increased from 25 to 150 W. Both the plasma potential and the plasma activity were found to increase with increasing P. Through actinometric optical emission spectrometry, the relative concentrations of CH, [CH], and H, [H], in the discharge were mapped as a function of the applied power. A rise in [H] and a fall in [CH] with increasing P were observed and are discussed in relation to the plasma characteristics and the subimplantation model. The optical properties of the films were calculated from ultraviolet-visible spectroscopic data; the surface resistivity was measured by the two-point probe method. The optical gap, E _G, and the surface resistivity, _s, fall with increasing P. E _G and _s are in the ranges of about 2.0–1.3 eV and 10¹⁴–10¹⁶ /, respectively. The plasma power also influences the film self-bias, V _b, via a linear dependence, and the effect of V _b on ion bombardment during growth is addressed together with variation in the relative densities of sp² and sp³ bonds in the films as determined by Raman spectroscopy.     

Atmospheric Pressure Dielectric Barrier Discharges for the Deposition of Organic Plasma Polymer Coatings for Biomedical Application

Plasma Chemistry and Plasma Processing - Atmospheric pressure dielectric barrier discharges (DBDs) are proving to have great potential in the bioengineering and medical field for functionalisation...     

Effect of Plasma Deposition Using Low-Power/Non-thermal Atmospheric Pressure Plasma on Promoting Adhesion of Composite Resin to Enamel

This study investigated the effect of monomer deposition through a low-power, non-thermal atmospheric pressure plasma (NT-APP) on adhesion of resin composite to enamel and its durability. The adhesion of resin composite to enamel and its durability were compared using micro-shear bond strength (MSBS) tests, with or without monomer deposition and before or after thermocycling (TC). The bond strength data were interpreted using Weibull analysis. Hydrophilicities of treated ceramic surfaces were compared with contact angle measurements. Surface characterization was performed with a Fourier transform infra-red spectrophotometer and X-ray photoelectron spectroscopy. The fracture mode at the interface was evaluated using a stereomicroscope and a scanning electron microscope. The plasma polymer deposition of benzene and 1,3-butadiene using the low-power NT-APP improved the MSBS of resin composite to enamel (p < 0.05). Surface characterization suggested improved wettability and changes in the chemical composition of the plasma-deposited enamel surface. However, the mean values of the MSBS of the plasma polymer-deposited groups decreased after TC (p < 0.05). After TC, the Weibull modulus (m) values increased in all the groups, especially in the plasma polymer-deposited groups. Plasma polymer deposition improved enamel adhesion but failed to improve durability in terms of mean bond strength. However, the plasma polymer deposition increased the Weibull modulus m after TC, which indicated that the scatter of the bond strength was narrowed with respect to durability.     

Influence of Cold Atmospheric Pressure Plasma on Pea Seeds: DNA Damage of Seedlings and Optical Diagnostics of Plasma

Plasma Chemistry and Plasma Processing - Cold atmospheric pressure plasma treatment is currently being explored as an alternative way to improve the germination and growing parameters of plant...     

Deposition of Polyacrylic Acid Films by Means of an Atmospheric Pressure Dielectric Barrier Discharge

The present work describes the plasma polymerisation of acrylic acid at atmospheric pressure. The influence of two operating parameters (monomer concentration and discharge power) on the properties of the deposited films is investigated. Results show that at a monomer concentration of 2.5 ppm and a discharge power of 9.5 W, the monomer is only slightly fragmented leading to a high amount of carboxylic acid groups on the deposited films. In contrast, when monomer concentration is decreased or discharge power increased, the incidence of monomer fragmentation processes is higher, leading to a lower amount of carboxylic acid groups on the films. This behaviour can be explained by a higher energy amount available per monomer molecule at low monomer concentrations and high discharge powers and a higher flux of positive ions attacking the surface at high discharge powers. Taking into account these results, it can be concluded that the deposition parameters should be carefully selected in order to preserve the stability of the monomer and thus obtain coatings with high carboxylic acid densities.     

Excitation of Species in an Expanded Argon Microwave Plasma at Atmospheric Pressure

The excitation capability of an argon microwave plasma flame expanded at atmospheric pressure has been studied. For this purpose, argon with different proportions of nitrogen was introduced at the end of the expanded flame, where the population densities of the atomic argon levels were still high enough. Optical emission spectra allowed the identification of different excited species in the plasma. When argon containing nitrogen was added at the end of the plasma flame, all argon lines emitted in this region were highly quenched, emission due to species containing nitrogen (NH, CN) was enhanced and a noticeable increase in the emission of N₂ (C ³Π_u ? B ³Π_g) was observed. On the contrary, the weak emission of $ {\text{N}}_{2}^{ + } \left( {B^{ 2} \sum_{u}^{ + } - X^{ 2} \sum_{g}^{ + } } \right) $ was scarcely affected. According to these results it is possible to conclude that metastable argon atoms from the expanded flame are the main energy carriers when generating N₂ reactive species in this plasma zone.     

Overview of Atmospheric Pressure Discharges Producing Nonthermal Plasma

Recently, much attention has been paid to gas discharges producing nonthermal plasma because of many potential benefits in industrial applications. Historically, past work focused on Dielectric Barrier (silent) Discharges (DBD) and pulse-periodical corona discharges. Recently, a number of new different discharge techniques succeeded in producing stable gas discharge at atmospheric pressure. Among these are repetitively pulsed glow discharge; continuous glow discharge in a gas flow; hollow-cathode atmospheric pressure discharge; RF and microwave (MW) discharges. Several new variants of the DBD have been demonstrated over a rather wide range of frequencies. All these forms of gas discharge are characterized by a strong nonequilibrium plasma state. We attempt to classify these discharges with respect to their properties, and an overview of possible applications is made. Conditions for the existence of homogenous and filamentary forms of each of the discharge types are discussed.     

PMMA Surface Functionalization Using Atmospheric Pressure Plasma for Development of Plasmonically Active Polymer Optical Fiber Probes

In this paper, we demonstrate the development of plasmonically active PMMA optical fiber probes by the attachment of gold nanoparticles to the probe surface functionalized by means of flowing post-discharges from dielectric barrier discharge (DBD) plasmas for the first time. Polymer optical fiber (POF) probes (U shape to improve absorbance sensitivity) were subjected to reactive gas atmospheres in the post-discharge region of a coaxial DBD plasma reactor run at atmospheric pressure in different gases (Ar, Ar + 10 % O₂, O₂, N₂, N₂ + 0.5 % H₂). Plasma treatments in Ar or N₂ gave rise to water-stable electrophilic functional groups on PMMA surface, whereas the amine groups generated by N₂-containing plasmas were not stable. Subsequently, PMMA surfaces were treated with hexamethylene diamine (HMDA) to obtain stable amine groups through the reaction of electrophilic groups. Gold nanoflowers (AuNF, 37 nm, peak 570 nm) binding to the amine functionalized fiber probes was monitored in real-time by recording the optical absorbance changes at 570 nm with the help of a UV–vis spectrometer. Absorbance response from Ar or N₂ plasma treated probes are 100 and 60 times, respectively, that of untreated control probes. A 25 fold improvement in absorbance response was obtained for Ar plasma treated POF in comparison with only HMDA treated POF. The shelf life of the hence fabricated plasmonically active probes was found to be at least 3 months. In addition, plasmonic activity of U-bent fiber probes treated in Ar plasma is better than the conventional wet-chemical activation by environmentally hazardous acid pre-treatment approaches.     

Oxidation of Dilute Benzene in an Alumina Hybrid Plasma Reactor at Atmospheric Pressure

The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO₃pellets and porous Al₂O₃pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al₂O₃pellets. Furthermore, there was a higher selectivity to CO₂in the products from the hybrid than from a plasma reactor packed with BaTiO₃pellets alone. The presence of the Al₂O₃pellets suppressed the formation of N₂O.     

Correlation of Plasma Sprayed Coating Deposition Efficiency with Volume Flux Measurements by Phase Doppler Anemometry (PDA)

The use of phase-Doppler anemometry (PDA) to characterize the detail in-flight plasma sprayed particle behavior has been demonstrated previously [Ma et al. Plasma Chem Plasma Process 24(1):85; 25(1):56] The present articles shows further that a direct relationship may exist between the PDA measured particle volume flux and the coating microstructure and deposition efficiency (DE). In the situation when the precise particle temperature information is not available, the PDA measured particle volume flux may provide an alternative to predict quantitatively the variation of the coating microstructure and the DE. By monitoring the in-flight particle volume flux variations, instead of the particle velocity, size and temperature individually and simultaneously, the optimal settings of the plasma spraying parameters may also be determined conveniently. However, it is noted that the effective applications of such approach depend largely on the particle surface morphology and the pre-determination of the particle size range.     

Measurement of Reactive Hydroxyl Radical Species Inside the Biosolutions During Non-thermal Atmospheric Pressure Plasma Jet Bombardment onto the Solution

Non-thermal atmospheric pressure plasma jet could generate various kinds of radicals on biosolution surfaces as well as inside the biosolutions. The electron temperature and ion density for this non-thermal plasma jet have been measured to be about 0.8~1.0 eV and 1 × 10¹³ cm^?3 in this experiment, respectively, by atmospheric pressure collisional radiative model and ion collector current. In this context, the hydroxyl OH radical density inside the biosolutions has been also investigated experimentally by ultraviolet absorption spectroscopy when the Ar non-thermal plasma jet has been bombarded onto them. It is found that the emission and absorption profiles for the other reactive oxygen species such as NO (226 nm) and O₂*^? (245 nm) are shown to be very small inside the biosolution in comparison with those for the OH radical species. It is found that the densities of OH radical species inside the biosolutions are higher than those on the surface in this experiment. The densities of the OH radical species inside the deionized water, Dulbecco’s modified eagle medium, and phosphate buffered saline are measured to be about 2.1 × 10¹⁶, 1.1 × 10¹⁶, and 1.0 × 10¹⁶ cm^?3, respectively, at 2 mm downstream from the surface under optimized Ar gas flow of 200 sccm. It is also found that the critical hydroxyl OH radical density for the lung cancer H460 cells to experience an apoptosis is observed to be around 0.3 × 10¹⁶ cm^?3 under 1 min plasma exposure in this experiment.     

Decomposition of Acetaldehyde in Atmospheric Pressure Filamentary Nitrogen Plasma

The removal of 500?ppm acetaldehyde in nitrogen at 1?bar is characterized in a pulse dielectric barrier discharge generating a spatial random distribution of plasma filaments. The identification and the quantification of numerous by-products are performed. At 20?°C, CH₃CHO is efficiently dissociated, probably owing to quenching of N₂ metastable states. The most abundant by-products are CO, H₂, and CH₄, in consistency with the three important exit channels for the quenching of the N₂(A³?? _u ⁺ ) state by CH₃CHO proposed by Faider et al. (2011). In order of importance, other products are HCN, C₂H₆, CH₃CN, HNCO, CO₂, CH₃COCH₃, C₂H₄, C₂H₅CN, NH₃, C₂H₂, and a group of nitriles and of ketones. An increase of the temperature from 20?°C up to 300?°C induces a strong decrease of the removal characteristic energy, but the by-products types remain unchanged. Probably the reaction of H with CH₃CHO plays a role in the removal of the molecule at 300?°C.     

On the Correlation Between Deposition Rate and Process Parameters in Remote Plasma-Enhanced Chemical Vapor Deposition

Plasma-enhanced chemical vapor deposition has become one of the most important thin film deposition technologies. To avoid direct plasma exposure the substrates may be placed in the remote region. A carrier gas conveys the plasma energy to the deposition area where the reactions with the monomer molecules take place. For the engineering of such a process the modeling of the achievable deposition rate is of great interest. Among different possibilities semiempirical models provide a fast and easily utilizable tool without intensive computer simulations or the necessity of detailed knowledge about the chemistry involved. From deposition experiments with oxygen and an organosilicon monomer (hexamethyldisiloxane, HMDSO) the remote composite parameter is suggested. It combines microwave power, monomer and carrier gas flow rate, and the distance of the substrate from the plasma source. This parameter was derived from the ratio between atomic oxygen and monomer flow rate. In the parameter range considered the deposition rate is described as well ordered and the energy- and monomer-deficient regions are clearly separated.     

吖啶酮类衍生物的光电性质研究

测定了8个吖啶酮类衍生物的紫外吸收光谱、荧光光谱和荧光量子产率,以研究它们的结构与光学性质之间的关系,用循环伏安法测出它们各自的电子势．发现吖啶酮类衍生物都具有较高的电子亲和势,表现出比常用的电子传输材料2-(4-联苯基)-5-(叔丁苯基1—1,3,4-二唑(PBD)更容易被还原的优良电化学性能。     

电化学沉积金纳米线结构及其电学特性

用电化学沉积方法,在有机介孔模板上制备出直径为90nm的金纳米线.透射电子显微镜(TEM)分析结果表明,纳米线表面光滑并呈单晶结构.去除有机模板的金纳米线阵列用扫描电子显微镜(SEM)测试,纳米线顶端呈平台状,直径分布均一.我们利用原子力显微镜(AFM)测量了金纳米线阵列的微观结构,得到与SEM相一致的结果.在大气和室温条件下,用导电AFM针尖在接触模式下测量了单根纳米线的轴向I-V特性曲线,其结果为金属性.     

Degradation of Organic Pollutants Using Atmospheric Pressure Glow Discharge Plasma

A method of plasma treatment in which a glow discharge was generated in the small gas gap between an electrode and a water surface was designed and employed in this study. By using this method, many active species were generated on the wastewater surface to degrade organic pollutants. The electric field distribution of the designed electrode model was simulated using the MAXWELL 3D^® simulation software, and the discharge parameters were measured to investigate the impact of design optimization. In addition, we designed an equipotential multi-electrode configuration to treat a methyl orange solution and an azobenzene solution. The experimental and simulation results indicate that the designed electrodes can realize glow discharge with a relatively low voltage and that the generated plasma covers a large area and is in a stable state. Accordingly, the method helped reduce the cost of the reactor and improved the effectiveness of wastewater treatment.     

Characteristics of Argon Laminar DC Plasma Jet at Atmospheric Pressure

Argon DC plasma jets in stable laminar flow were generated at atmospheric pressure with a specially designed torch under carefully balanced generating conditions. Compared with turbulent jets of short length with expanded radial appearance and high working noise, the laminar jet could be 550 mm in length with almost unchanged diameter along the whole length and very low noise. At gas feeding rate of 120 cm³/s, the jet length increases with increasing arc current in the range of 70–200 A, and thermal efficiency decreases slightly at first and then leveled off. With increasing gas flow rate, thermal efficiency of the laminar jets increases and could reach about 40%, when the arc current is kept at 200 A. Gauge pressure distributions of the jets impinging on a flat plate were measured. The maximum gauge pressure value of a laminar jet at low gas feeding rate is much lower than that of a turbulent jet. The low pressure acting on the material surface is favorable for surface cladding of metals, whereas the high pressure associated with turbulent jets will break down the melt pool.