Low Discharge Power Research Articles

Enhancement in ion beam current with layered-glows in a constricted dc plasma ion source

High current mode has been discovered and investigated in a constricted dc plasma ion source. As discharge currents exceed a certain threshold, voltage to sustain the constricted dc plasma suddenly falls down to almost half of the value. In this sense, constricted dc plasmas can be sustained at much higher current than in conventional mode operation at a fixed discharge voltage. Phenomenally, several discrete layered-glows are created between an anode glow and a cathode glow. The layers are thin and divided by dark spaces where charged particles can be accelerated. In this high current mode, ion beam current density is about 100 times higher than in conventional mode at the same voltage. It is noteworthy that lower gas pressure is desirable to sustain the layered-glow mode, which is also profitable for ion source in terms of differential pumping. Ion current density exceeds 300 mA/cm(2) at low discharge power of 175 W where ion density of plasma ball is estimated to be over 3.7x10(12) cm(-3).

Water treatment with pulsed discharges generated inside bubbles

AbstractThe parallel operation of pulsed discharges generated inside bubbles is successfully demonstrated by applying a fast rising voltage to a multielectrode system immersed in treated water. A 10 ppm solution of acetic acid, which cannot be decomposed by ozone, was used as a persistent material and the acetic acid decomposition efficiency was evaluated by measuring the total organic carbon (TOC) values of the solution. The electric conductivity of the solution affected decomposition efficiency because the solution resistance, which was inversely proportional to the conductivity, limited the magnitude of the discharge current flowing along the surface of the bubbles generated by the feeding of oxygen or argon gas. With a nine‐hole electrode system, the discharge power deposited in one discharge was lower, and the acetic acid decomposition efficiency was higher, than the values obtained with a single‐hole electrode system. Lower discharge power seemed to minimize the self‐quenching of OH radicals, and resulted in the efficient decomposition of acetic acid. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 1–7, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20918

Study of Nanoparticles Formation in a Pulsed Magnetron Discharge in Acetylene

AbstractThe aim of this work is to study in a pulsed magnetron discharge of acetylene at 10−1 Torr, the influence of tOFF parameter on roughness and morphology of films deposited on silicon substrates. By using a low power discharge (long tOFF and short tON for a given power), a coating with unique morphology is deposited. This film is formed of nanoparticles and particular agglomerates called ‘flowers’ of micrometric size. To the best of our knowledge, it's the first time that such ‘flowers’ structures have been observed for a pulsed plasma polymerization of acetylene. According to the obtained results in mass spectrometry of plasma, nanoparticles and ‘flowers’ are probably formed in gas phase. A growth mechanism in several steps is proposed.

PECVD in-situ growth of silicon quantum dots in silicon nitride from silane and nitrogen

Silicon nanostructures have interesting possible applications in new generation photovoltaics. The fabrication techniques usually involve a high-temperature post-deposition annealing. Here we report on the spontaneous growth of silicon quantum dots in silicon nitride films by plasma enhanced chemical vapour deposition (PECVD) using silane and nitrogen as reactant gas sources. The growth rate was kept low by working at low discharge power, and a low deposition temperature was selected (300 °C). This approach is particularly interesting because in principle it allows for use of low cost substrates and application of typical device structures adopted in thin film silicon photovoltaics. Photoluminescence and optical properties have been investigated. The evolution of the photoluminescence emission with nitrogen flow rate has been correlated to the change of the dot size. The effect of the strongly absorbing Si nanostructures in the silicon nitride matrix on the absorption properties has been investigated.

Structural and dielectric properties of conjugated polynitrile thin films deposited by plasma polymerization

Plasma-polymerized 4-biphenylcarbonitrile (PPBPCN) thin films have been deposited by plasma polymerization technique. The effect of the discharge power on the chemical structure, surface composition and morphology of the PPBPCN thin films were investigated by Fourier transform infrared, UV–Visible absorption spectra, X-ray photoelectron spectroscopy, and atomic force microscopy. Structural and morphology characterizations show that a conjugated PPBPCN thin film with a high retention of the aromatic ring structure of the starting monomer can be deposited at a low discharge power. The plasma-synthesized film is homogeneous and quite suitable for the measurement of dielectric properties. The dielectric measurement shows that the dielectric constant of PPBPCN thin films decreased with frequency and increased with temperature.

A novel low k thin film based on plasma-polymerized 1- cyano isoquinoline

AbstractA novel low dielectric constant polymer, plasma-polymerized 1-cyano isoquinoline (PPCIQ) was prepared by plasma polymerization for the first time. The structure and surface compositions of the deposited PPCIQ thin films were investigated by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 15 W was used during film formation. In the case of higher discharge power of 35 W, more severe monomer molecular fragmentation can be observed. The dielectric properties measurements show that a low dielctric constant of 2.62 can be obtained for PPCIQ thin film deposited at 15 W.

Deposition of Plasma‐Polymerized 1‐Cyanoisoquinoline Thin Films and Their Dielectric Properties

AbstractA novel plasma‐polymerized 1‐cyanoisoquinoline (PPCIQ) thin film of desired thickness was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure, surface composition and morphology of the PPCIQ thin films were investigated by Fourier Transform Infrared (FTIR) Spectroscopy, X‐ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and deposition rate measurements. A high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained at a low discharge power of 15 W. The plasma‐synthesized films are homogeneous and quite suitable for the measurement of dielectric properties. The dielectric measurements show that a low dielectric constant of 2.62 has been obtained for the PPCIQ thin films for the first time.magnified image

Towards improved artificial lungs through biocatalysis

Inefficient CO 2 removal due to limited diffusion represents a significant barrier in the development of artificial lungs and respiratory assist devices, which use hollow fiber membranes (HFMs) as the blood–gas interface and can require large blood-contacting membrane area. To offset the underlying diffusional challenge, “bioactive” HFMs that facilitate CO 2 diffusion were prepared via covalent immobilization of carbonic anhydrase (CA), an enzyme which catalyzes the conversion of bicarbonate in blood to CO 2, onto the surface of plasma-modified conventional HFMs. This study examines the impact of enzyme attachment on the diffusional properties and the rate of CO 2 removal of the bioactive membranes. Plasma deposition of surface reactive hydroxyls, to which CA could be attached, did not change gas permeance of the HFMs or generate membrane defects, as determined by scanning electron microscopy, when low plasma discharge power and short exposure times were employed. Cyanogen bromide activation of the surface hydroxyls and subsequent modification with CA resulted in near monolayer enzyme coverage (88%) on the membrane. The effect of increased plasma discharge power and exposure time on enzyme loading was negligible while gas permeance studies showed enzyme attachment did not impede CO 2 or O 2 diffusion. Furthermore, when employed in a model respiratory assist device, the bioactive membranes improved CO 2 removal rates by as much as 75% from physiological bicarbonate solutions with no enzyme leaching. These results demonstrate the potential of bioactive HFMs with immobilized CA to enhance CO 2 exchange in respiratory devices.

The Influence of argon gas pressure on co-sputtered calcium phosphate thin films

A series of Ca–P coatings have been co-deposited by RF magnetron sputtering from hydroxyapatite targets at a range of different argon gas pressures (1–5 Pa) at a low discharge power level. The resultant surfaces were analysed both as-deposited and after annealing at 500 °C using fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and stylus profilometry. The deposition rate increased with increasing argon gas pressure up to 2 Pa, but decreased significantly as the pressure increased up to 5 Pa. The Ca/P ratios of the as-deposited coatings were lower than expected, and decreased significantly at the higher argon gas pressures. The corresponding FTIR and XRD data showed that the as-deposited surfaces were poorly hydroxylated and were mostly amorphous in nature. By comparison, the annealed surfaces had Ca/P ratios of between 3.38 ± 0.11 (1 Pa) and 1.82 ± 0.06 (5 Pa). The FTIR and XRD data for the annealed samples were indicative of HA, however, as the gas pressure increased above 3 Pa, these surfaces were most likely transformed into dehydroxylated HA. This study has shown the utility of varying the argon gas pressure whilst co-sputtering HA in order to modify the resultant surface conditions.

Design and electrical charaterization of a low current–high voltage compact arc plasma torch

A new compact plasma torch associated with a resonance power supply allows the generation of low power discharges (typically 100 W–1 kW) under high voltage (>1 kV) low current (<1 A) conditions. The resonance power supply allows continuous control of the discharge current, which is a major improvement with respect to the traditional dc power source based on a high voltage transformer. In addition, this system is characterized by a high conversion efficiency that is crucial when it comes to industrial applications. It has been shown that different regimes ranging from streamer over gliding arc to continuous discharges were obtained depending on the operating conditions. The objective of this paper is a better understanding of the different observed behaviour through the determination of the main torch and power supply parameters.

Plasma needle for in vivo medical treatment: recent developments and perspectives

In this paper we describe the hitherto unravelled facts on the interactions of a cold atmospheric plasma with living cells and tissues. A specially designed source, plasma needle, is a low-power discharge, which operates under the threshold of tissue damage. When applied properly, the needle does not cause fatal cell injury which would result in cell death (necrosis). Instead, it allows precise and localized cell removal by means of the so-called cell detachment. In addition, plasma can be used for bacterial disinfection. Because of mild treatment conditions, plasma disinfection can be performed in vivo, e.g. on wounds and dental cavities. Presently, one strives to obtain a better control of the operating device. Therefore, plasma has been characterized using a variety of diagnostics, and a smart system has been designed for the positioning of the device with respect to the treated surface.

Temporal Variations in Densities of Y, Ba, and Cu Atoms in Magnetron Sputtering Plasmas with YBaCuO Target

In this study, we used optical emission spectroscopy (OES) for examining the temporal variations in the densities of Y, Ba, and Cu atoms sputtered from a YBaCuO target in a magnetron plasma source. It was found that the densities of Y and Cu changed with the discharge period. In a low-pressure, low-power discharge, the temporal variations in the Y and Cu densities were small, whereas they became significant at a high pressure and a high power. Ten minutes after the initiation of the discharge, Y density decreased to 8% of the initial value at an rf power of 70 W and a gas pressure of 300 mTorr. On the other hand, the optical emission intensities from Ar and Ba were roughly constant during the same discharge period. The roughly constant Ar intensity indicates that electron density and electron temperature were almost constant. The discovery of temporal variations in the Y and Cu densities is important for optimizing the discharge parameters for the deposition of high-quality, high-critical-temperature (high-Tc) superconductor films.

Deposition of plasma conjugated polynitrile thin films and their optical properties

The plasma polymerization of 4-phenylbenzonitrile was carried out with the objective of synthesizing a novel conjugated polynitrile thin film with a better optical property. The structure, compositions and morphology of the plasma-polymerized 4-phenylbenzonitrile (PPBPCN) thin films were investigated by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). A fine, homogenous PPBPCN film with a large π-conjugated system and a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 30 W was used during film formation. For the first time, a blue emission with relatively high photoluminescence intensity for PPBPCN thin films was observed.

Preparation of plasma poly(1-isoquinolinecarbonitrile) thin film and its ultrafast nonlinear optical property

How to get a uniform, defect-free, and reproducible conjugated polymer thin films is now becoming the main fabrication problem for the practical application of these materials as the fast switches and modulators in opto-electronic devices. In this research, a novel plasma-polymerized 1-isoquinolinecarbonitrile (PPIQCN) thin film was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the deposited PPIQCN films was investigated by Fourier transform infrared (FTIR), UV-Visible absorption spectra and X-ray photoelectron spectroscopy (XPS). The results show that a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 10 W was used during film formation. In the case of higher discharge power of 30 W, more severe monomer molecular fragmentation can be observed, which results in a decrease in the effective conjugation length of PPIQCN film. The morphology characterized by atomic force microscopy (AFM) indicates that a fine, homogenous PPIQCN film could be obtained under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect technique at a wavelength of 820 nm has been applied to investigate the third-order nonlinearity of the plasma PPIQCN film. For the first time, a non-resonant optical Kerr effect and ultrafast response of the PPIQCN film was observed.

Hydrogenated microcrystalline silicon films prepared by VHF-PECVD and single junction solar cell

Intrinsic microcrystalline silicon films have been prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) from silane/hydrogen mixture at 180°C. The effect of silane concentration and discharge power on the growth of silicon films was investigated. Samples were investigated by Fourier transform infrared spectroscopy, Raman scattering and X-ray diffraction. The Raman spectrum shows that the morphological transition from microcrystalline to amorphous occurs under conditions of high silane concentration and low discharge power. X-ray diffraction spectra indicate a preferential growth direction of all microcrystalline silicon films in the (111) plane. In addition, a solar cell with an efficiency of 5.1% has been obtained with the intrinsic microcrystalline layer prepared at 10W.

Spectroscopic determination of the cold electron population in very low pressure ECR discharges in N2/He mixtures

We describe a spectroscopic study of the electron distribution functions (EDFs) in two types of electron cyclotron resonance (ECR) discharges at very low pressure: a discharge in a simple magnetic mirror trap (ECRD) and a discharge in a sheared minimum-B-trap used as ion source for multiply charged ions (ECRIS). The discharges were run in mixtures of helium and nitrogen at about 7 mPa. Special attention was paid to electrons with kinetic energies below 10 eV. Their contributions were attained by a quantitative analysis of the vibrational structures in the emission spectra of nitrogen, the analysis of processes of step-wise excitation or an analysis of the rotational populations of nitrogen. The models for evaluating the EDFs are discussed in detail. Besides collision processes in the volume of the discharge processes occurring at the chamber walls contribute significantly to the particle balance and are included in the model. In all cases considered low energy electrons contribute more than 90% to the electron population of the discharges. For every discharge EDFs are measured for two benchmark conditions at low and high discharge power. For the ECRIS other conditions are covered by a measurement of the plasma potential, which turned out to be below 30 V for the conditions considered. This low value is a good indicator for the presence of low energy electrons. The plasma potential was obtained from a retarding field analysis of the energy of ion beams extracted from the plasma.Besides the EDFs, our study yields insight into the important collision and wall processes in these low-pressure discharges, including the first observation of rotational cooling of desorbing N2 molecules in an ECRIS.

Preparation, characterization and electronic and optical properties of plasma-polymerized nitriles

Conjugated polymers are among the most promising organic materials for optoelectronic devices. In such applications, the main fabrication challenge is to get uniform, defect-free and reproducible thin films of these materials. In this research, a series of novel plasma-polymerized 4-cyanopyridine (PPCPD) thin films of desired thickness were prepared through plasma polymerization under different glow discharge conditions. They were transparent, pinhole-free and uniform. The effect of the discharge power on the chemical structure and surface compositions of the plasma-polymerized 4-cyanopyridine (PPCPD) films was investigated by Fourier transform infrared (FTIR), UV-visible absorption spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS) and the deposition rate measurements. A high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 3 to 10 W was used during film formation. A red shift in the maximum absorption wavelength ( λ max) for all the plasma-deposited films was observed as compared with the monomer absorption spectrum. The atomic force microscopy (AFM) measurement shows that the PPCPD film with quite smooth surface could be grown under a relatively low discharge power.

Ultrafast third-order optical nonlinearity of polycyanopyridine

A novel plasma-polymerized 4-cyanopyridine (PP4CPD) thin film of desired thickness was prepared by plasma polymerization under different glow discharge conditions. The effect of the discharge power on the chemical structure and surface compositions of the PP4CPD films was investigated by FT-IR, UV–Vis and X-ray photoelectron spectroscopy (XPS). A high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained at a low discharge power. A red shift in the maximum absorption wavelength ( λ max) for PP4CPD films was observed as compared with the monomer absorption spectrum. The atomic force microscopy (AFM) measurement shows that the PP4CPD film with quite a smooth surface could be grown under a relatively low discharge power. A femtosecond time-resolved optical Kerr effect (OKE) technique has been applied to investigate the third-order nonlinearity of the plasma PP4CPD film. For the first time, a non-resonant optical Kerr effect and ultrafast response of polycyanopyridine was observed.

Novel low-frequency oscillation in a radio-frequency inductively coupled plasma with tuned substrate

The rf self-bias on the substrate in a rf inductively coupled plasma is controlled by varying the impedance of an external tuning inductor and capacitor network inserted between the substrate and the ground. In term of variations of tuned substrate self-bias (Vtsb) with tuning capacitance (Ct), three characteristic regions, namely continuous, instable, and bistable regions are found, corresponding to low, moderate, and high discharge power at a constant gas pressure, respectively. A novel self-oscillation observed in the instable region occurs only within a limited domain of Ct. With the increment in Ct, the self-oscillation frequency increases while its amplitude decreases. Near the boundary of the instable and bistable regions, the self-oscillations shift downward and upward at lower and higher Ct, respectively. The possible mechanism for the self-oscillation is discussed.

Overview of steady state tokamak plasma experiments in TRIAM-1M

An overview of steady state tokamak studies in TRIAM-1M (R0 = 0.8 m, a × b = 0.12 m × 0.18 m and B = 8 T) is presented. The current ramp-up scenario without using centre solenoid coils is reinvestigated with respect to controllability of the current ramp-up rate at the medium density region of (1–2) × 1019 m−3. The plasma is initiated by ECH (fundamental o-mode at 170 GHz with 200 kW) at B = 6.7 T, and the ramp-up rate below the technical limit of 150 kA s−1 for ITER can be achieved by keeping the LH power less than 100 kW during the current ramp-up phase. The physics understanding of the enhanced current drive (ECD) mode around the threshold power level has progressed from a viewpoint of transition probability. A transition frequency, ftrans, for the ECD transition is determined as a function of PCD. At ∼70 kW no transition occurs for an ftrans value of ∼0.017 Hz, meaning almost zero transition probability. With increasing PCD > Pth, ftrans increases up to 10 Hz, and the transition tends to occur with high probability. The record value of the discharge duration is updated to 3 h 10 min in a low and low power (<10 kW) discharge. The global particle balance in long duration discharges is investigated, and the temporal change in wall pumping rate is determined. Although the density was low, the gas supply had to be stopped at 30 min after the plasma initiation to maintain the density constant. After that the density was sustained by the recycling flux alone until the end of the discharges. In addition to the recycling problem, in the high power and high density experiments, the localized PWI affects the SSO of the tokamak plasma. The effects of enhanced influx of metal impurities (Fe, Cr, Ni, Mo) on sustainment of the high performance ECD plasma are investigated. In order to evaluate the helium bombarding effects on the plasma facing component and hydrogen recycling in the future burning plasma, microscopic damage of metals exposed to long duration helium discharges was studied. The total exposure time was 128 s. From thermal desorption experiments for the specimens the amount of retained helium was evaluated as 3.9 × 1020 He m−2 and the scale length to be ∼1 mm in the SOL.