Effect of dielectric barrier discharge on semiconductor Si electrode surface

Electrode materials and shapes affected the discharge modes. Meanwhile, the discharge has influence upon electrode surface. In order to study the effect of discharge on semiconductor electrode, the experiments were carried out using single crystal Si wafer as high voltage electrode of atmospheric pressure dielectric barrier discharge in air. The effects of dielectric barrier discharge on Si electrode surface are analyzed by means of field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). The results show that surface roughness and oxidation increase with discharge time, while surface nitridation is not observed on Si electrode surface. It is different from Cu electrode. The difference is due to different chemical reactions between electrode surface and air plasma but could also be ascribed to the different analysis techniques used.     

The effect of air plasma on barrier dielectric surface in dielectric barrier discharge

Barrier dielectric is an important part of atmospheric pressure dielectric barrier discharge (AP-DBD), which partly affects discharge characteristics. Conversely, discharge plasma also has influence on dielectric surface properties. To investigate this influence, some experiments were carried out on a home-built AP-DBD system with glass plate as barrier dielectric. Surface wettability was evaluated by water contact angles on a drop shape analysis system. The morphologies and chemical compositions of the glass sample surfaces were observed by field-emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS) attached to FESEM. The results show that water contact angles decrease as discharge energy increases, micro-discharge etching zones are formed into glass surface and different from the control glass in surface micro-structure and chemical compositions.     

Effect of atmospheric pressure dielectric barrier discharge air plasma on electrode surface

In order to study the influence of plasma on electrode, atmospheric pressure dielectric barrier discharge (DBD) air plasma is employed here to treat copper electrode surface. Plasma is generated between the parallel plate electrodes by means of high voltage produced by a high-frequency power supply with transformer. Electrode surface alterations induced by air plasma are investigated by using field emission scanning electron microscope (FE-SEM), X-ray energy dispersion spectroscopy (EDS) and contact angle measurement. The results show that DBD air plasma removes the organic contaminant on surface and causes electrode surface roughness, oxidization and nitridation. In addition, surface wettability is also improved, as concluded from contact angle measurements.     

The influence of vaporization upon the roots of a high current arc. I. Different forms of vaporization in the arc roots

Arc roots at which marked vaporization occur are unstable and therefore in general non-stationary. High speed photography of arc roots using various electrode materials in Ar, SF₆, and N₂ shows that the appearance of the arc roots results from the superposition of several phenomena. On graphite cathodes in Ar it was possible to observe these phenomena separately by varying the cooling of the electrodes. It is shown that distinctions must be drawn between the real current transfer region with relatively weak vaporization, vaporization from the electrode surface outside this region and vaporization from within the body of the electrode. The energy-balance determined experimentally confirms the theoretical prediction that the energy for strong vaporization of the cathode is supplied by an ioncurrent.     

Crystallization of amorphous zirconium thin film using ion implantation by a plasma focus of 1 kJ

In this work preliminary results of amorphous zirconium crystallization using ion beam pulses are presented. Energetic argon- and oxygen-ion beams generated by a plasma focus device were used to promote crystallization on amorphous ZrO₂-2.5 mol% Y₂O₃ film deposited by chemical solution deposition onto silica glass substrate. The films were burnt at 370 °C for 1 h in normal atmosphere previous to plasma irradiation. The irradiation was performed by means of successive pulses of ion beams. The evolution of the surface morphology and crystallization was followed by AFM and X-rays diffraction in a grazing incidence asymmetric Bragg geometry (GIAB), respectively. Argon-irradiated films showed highly nucleated cubic zirconia after 10 pulses. On the other hand, oxygen-irradiated films showed a delayed and less extensive cubic nucleation, but a more ordered structure and well-defined grains.     

The influence of vaporization upon the roots of a high current arc. II

The root of an argon are was stabilized by strong cooling of the graphite cathode; both the composition and the temperature of the plasma at the arc root were determined spectroscopically. The measurements of the absolute intensities of two CI and two CII lines revealed that the plasma is composed almost entirely of atomic carbon. Immediately in front of the cathode a temperature of 12000 K was measured and the degree to which the gas was ionized was found to be 30%. The velocity of the plasma was 300 m/s. This work is based upon material presented in the final report “Basic research programme for plasma technology, high-pressure arcs in SF₆” to the Federal Department of Research and Technology, Fed. Rep. Germany.     

The effect of surface modification by nitrogen plasma on photocatalytic degradation of polyvinyl chloride films

The solid-phase photocatalytic degradation of poly(vinyl chloride) (PVC) films was investigated under the ambient air in order to assess the feasibility of developing photodegradable polymers. Nitrogen plasma was used to modify PVC films to enhance the photocatalytic degradation of PVC with nano-sized anatase TiO₂. The plasma parameter varied in this study is discharge power from 30 to 120 W for a constant treatment time of 60 s and a constant gas pressure of 10 Pa. The photodegradation of the plasma-treated PVC-TiO₂ films was compared with that of pure PVC films and PVC-TiO₂ films performing weight loss monitoring, scanning electron microscopy (SEM) analysis, contact angle measurements, electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The wettability of the plasma-treated PVC is improved significantly. ESR revealed that the signal of radicals on the surface of the plasma-treated PVC film was enhanced after the treatment. Furthermore, the weight loss indicated that TiO₂ speeds up the photocatalytic degradation of PVC chains. The SEM image of the plasma-treated PVC-TiO₂ film showed a lot of crack on the film surface after irradiation. XPS indicated that the C and Cl atomic concentration reached minimum values on the surface of plasma-treated PVC-TiO₂ under identical photocatalytic condition. The experimental results reveal that plasma treatment can obviously enhance the photocatalytic degradation of PVC.     

Study on the surface of fluorosilicone acrylate RGP contact lens treated by low-temperature nitrogen plasma

In order to improve the surface hydrophilicity of fluorosilicone acrylate rigid gas permeable (RGP) contact lens, low temperature nitrogen plasma was used to modify the lens surface. Effects of plasma conditions on the surface structures and properties were investigated. Results indicated that the surface hydrophilicity of RGP contact lens was significantly improved after treatment. X-ray photoelectron spectroscopy (XPS) results showed that the nitrogen element was successfully incorporated into the surface. Furthermore, some new bonds such as NCO, F⁻ and silicate were formed on the lens surface after nitrogen plasma treatment, which could result in the improvement of the surface hydrophilicity. Scanning electronic microscope (SEM) results indicated that nitrogen plasma with moderate power could make the surface smoother in some degree, while plasma with higher power could etch the surface.     

Investigations on ionic processes and dynamics in the sheath region of helium and hydrogen discharges by laser spectroscopic electric field measurements

Temporally and spatially resolved measurements of the electric field distribution in the sheath region of RF and dc discharges provide a detailed insight into the sheath and ion dynamics. The electric field is directly related to the sheath ion and electron densities, the sheath voltage, and the displacement current density. Under certain assumptions also the electron and ion conduction current densities at the electrode, the ion current density into the sheath from the plasma bulk, the ion energy distribution function, and the power dissipated in the discharge can be inferred. Furthermore, the electric field distribution can give an indication of the collision-induced conversion between different ion species in the sheath. Laser spectroscopic techniques allow the noninvasive in situ measurement of the electric field with high spatial and temporal resolution. These techniques are based on the spectroscopic measurement of the Stark splitting of Rydberg states of helium and hydrogen atoms. Two alternative techniques are applied to RF discharges at 13.56 MHz in helium and hydrogen and a pulsed dc discharge in hydrogen. The measured electric field profiles are analyzed, and the results discussed with respect to the ion densities, currents, energies, temporal dynamics and species composition. Received: 26 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

Space and time resolved discharge evolution of a large volume X-ray triggered XeCl laser system

The spatial distribution and the temporal development of the net gain have been measured in a ten liter active volume switchless discharge XeCl laser. The experimental results are compared with both zero-dimensional and two-dimensional kinetic code predictions. The comparison between the results of the kinetic codes and of some measurements relevant to the time-dependent discharge homogeneity allows a deeper insight into the influence of the streamer evolution on the discharge characteristics.ENEA StudentENEA Guest     

Two-channel waveguide modulator based on surface wave propagating in a semiconductor-metal thin-film structure

The results of theoretical investigations of two-channel waveguide modulator based on Surface Wave (SW) propagation are presented. The structure studied consists of twon-type semiconductor waveguide channels separated from each other by a dielectric gap and coated by a metal. The SW propagates at the semiconductormetal interface across an external magnetic field which is parallel to the interface. An external de voltage is applied to the metal surface of one channel to provide a small phase shift between two propagating modes. In a coupled mode approximation, two possible regimes of operation of the structure, namely as a directional coupler and as an electro-optical modulator, are considered. Our results suggest new applications in millimeter and submillimeter wave solid-state electronics and integrated optics.     

Spatio-temporal dynamics of plasma spots in helium surface barrier discharge

The experimental study of plasma spots formation in planar surface barrier discharge system at atmospheric pressure in helium gas is presented. Spatio-temporal patterns of plasma spots are followed by varying the applied voltage and operating gas pressure. These spots melt together at high applied voltage and results in uniform glow discharge. Reduction in operating pressure also results in similar effect. Dynamics of these patterns are discussed in detail.     

Study on the transition from filamentary discharge to diffuse discharge by using a dielectric barrier surface discharge device

Discharge characteristics have been investigated in different gases under different pressures using a dielectric barrier surface discharge device. Electrical measurements and optical emission spectroscopy are used to study the discharge, and the results obtained show that the discharges in atmospheric pressure helium and in low-pressure air are diffuse, while that in high-pressure air is filamentary. With decreasing pressure, the discharge in air can transit from filamentary to diffuse one. The results also indicate that corona discharge around the stripe electrode is important for the diffuse discharge. The spectral intensity of N电介质 表面放电 扩散放电 发射光谱学dielectric barrier surface discharge, diffuse discharge, optical emission spectroscopyProject supported by the National Natural Science Foundation of China (Grant Nos 10575027 and 10647123), the National Science Foundation of Hebei Province, China (Grant No A2007000134), the Education Department of Hebei Province, China (Grant No 2006106),2006-10-24Discharge characteristics have been investigated in different gases under different pressures using a dielectric barrier surface discharge device. Electrical measurements and optical emission spectroscopy are used to study the discharge, and the results obtained show that the discharges in atmospheric pressure helium and in low-pressure air are diffuse, while that in high-pressure air is filamentary. With decreasing pressure, the discharge in air can transit from filamentary to diffuse one. The results also indicate that corona discharge around the stripe electrode is important for the diffuse discharge. The spectral intensity of N＋ （391.4nm） relative to N2 （337.1 nm） is measured during the transition from diffuse to filamentary discharge. It is shown that relative spectral intensity increases during the discharge transition. This phenomenon implies that the averaged electron energy in diffuse discharge is higher than that in the filamentary discharge.     

Highly oriented (1 0 0) ZnO thin films by spray pyrolysis

Undoped ZnO thin films have been deposited onto glass substrates by spray pyrolysis. The structural, electrical and optical properties were studied on thin films, prepared from precursor solutions with varying the ethanol concentrations. X-ray diffraction studies have shown polycrystalline nature of the films with a hexagonal wurtzite-type structure. The preferential orientation plane (1 0 0) of the ZnO thin film is found to be sensitive to ethanol concentration. The texture coefficient (TC) and grain size value have been calculated. Also ethanol concentration was found to have significant effect on sheet resistivity of the films.     

Biological response of stainless steel surface modified by N2O/O2 glow discharge plasma

Stainless steel wafers were treated with the glow discharge plasma of mixed N₂O and O₂ at different molar ratios at a certain discharge condition to create desirable biological characteristics to the surfaces. It was found that the molar ratio of N₂O to O₂ in the mixture at 1:1 used for plasma surface modification caused high apoptotic percentage. Contact angle measurement showed that the surface of stainless steel samples became very hydrophilic after the plasma modification with a value of 15°-30°. The control stainless steel chips without plasma treatment had a contact angle of 40 ± 2°. The data of Electron Spectroscopy for Chemical Analysis (ESCA) indicated that there was a certain amount of oxynitrites formed on the plasma treated surfaces, which was considered to play an important role to cell apoptosis and anti-clot formation in cell culture tests. The ESCA depth profile of up to 250 Å from the top surface showed the change of elemental compositions within 40-50 Å of the surface by the plasma treatment. The decreased platelet attachment, combined with increased apoptosis in fibroblasts is a distinct combination of biological responses arising from the mixed gas plasma treatment. These initial results suggest it may be of particular use relative to stainless steel stents where decreased platelet attachments are advantageous and induction of apoptosis could limit in-stent restenosis.     

SR-PES and STM observation of metastable chemisorption state of oxygen on Si(1 1 0)-16 × 2 surface

Initial adsorption of oxygen molecules on the Si(1 1 0)-16 × 2 surface and subsequent modification of the bonding states induced by mild (300 °C) annealing have been studied by synchrotron-radiation photoemission spectroscopy and scanning-tunneling microscopy. It has been shown that upon annealing, the intensity and the energy positions of the Si 2p suboxide components shift towards the values characteristic for the thermal oxide. This indicates the presence of a metastable chemisorption state of oxygen on the Si(1 1 0)-16 × 2 surface.     

Effect of electron emission and potential perturbations of a hot filament in high voltage pulsed glow discharge

The high voltage dc pulsed glow discharge can be ignited earlier by putting an electron emitting filament in the plasma chamber. The electrons emitted from the filament act as a seed and can cause earlier ignition. The potential of the hot filament shows some periodic positive perturbations (electron loss signals) when it is kept floating in the plasma chamber. It is observed that the positive perturbations disappear as potential difference between the plasma and the filament is made smaller by directly connecting the filament to the grounded chamber.     

Formation and stabilisation of single current filaments in planar dielectric barrier discharge

In the experimental part we report on a typical bifurcation scenario of the current distribution in the discharge plane of a planar dielectric barrier discharge system. Increasing the amplitude of the sinusoidal driving voltage after breakdown a large number of dynamic solitary filaments is observed and the subsequent decrease of results in a pronounced hysteresis with decreasing number of filaments. In this way isolated single stationary filaments can be generated. In the theoretical part the latter are modeled by a reaction-drift-diffusion equation that is solved in three dimensional space numerically without any fitting procedure. As a result we obtain well defined stationary filaments of which size an shape essentially are independent of the initial conditions and having a width and an amplitude that agree with experiment rather well. On the basis of the numerical results we consider mechanisms of filament stabilisation. This includes the discussion of the well known surface charges as well as an additional focusing effect of volume charges.     

Structure of the SiC (0 0 0 1) 3 × 3 reconstruction studied by surface X-ray diffraction

The surface structure of the 3 × 3 reconstruction of the 4H-SiC (0 0 0 1) surface was investigated with surface X-ray diffraction (SXRD).Of the studied models, the twist model proposed by Starke et al. [U. Starke, J. Schardt, J. Bernhardt, M. Franke, K. Reuter, H. Wedler, K. Heinz, J. Furthmuller, P. Kackell, F. Bechstedt, Phys. Rev. Lett. 80 (1998) 758] gave the best fit to the experimental data. The structural parameters were determined accurately.     

Adsorption structure of germanium on the Ru(0 0 0 1) surface

Coverage-dependent adsorption energy of the Ge/Ru(0 0 0 1) growth system and the geometrical distortions of the most stable adsorption structure are investigated through first-principles calculations within density functional theory. A local minimum in adsorption energy is found to be at a Ge coverage of 1/7 monolayer with a Ru(0 0 0 1)- symmetry. Based on this stale superstructure, the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) images are simulated by means of surface local-density of states (LDOS). The results are consistent well with the STM measurements on the phase for Ge overlayer on Ru(0 0 0 1). From this stimulation, the relations between the STM images and the lattice distortion are also clarified.