Bipolar Voltage Pulses Research Articles

A comparative analysis of a-C:H films deposited from five hydrocarbons by thermal desorption spectroscopy

Thermal induced gas evolution studies were performed on hydrogenated amorphous carbon (a-C:H) films deposited by plasma enhanced chemical vapour deposition (PECVD). The hydrocarbon–argon discharges were powered by asymmetric bipolar voltage pulses. Five different hydrocarbons (acetylene C2H2, isobutene C4H8, cyclopentene C5H8, toluene C7H8 and cycloheptatriene C7H8) were compared as film growth precursors.The films were heated in vacuum upto 1000 °C and at the same time the gaseous effusion products were measured with a quadrupole mass spectrometer (QMS). The release of hydrogen, water, argon and different hydrocarbons from CH4 upto C7H8 was proved. Large hydrocarbons were detected only when heating up soft films. When annealing hard films, they almost only lost hydrogen – mainly as H2 but also in remarkable portion as H2O. Possibly, the water in the a-C:H films contains the main fraction of hydrogen unbounded to carbon.The characteristic temperatures for the onset of gas evolution of the molecular gases and of argon were found to be strictly correlated with the film hardness – independent of the film growth precursor. The threshold temperature for the release of the dominating effusion product, molecular hydrogen, is significantly higher than that of argon only for films with hardness below about 13 GPa.

High-power sources of ultra-wideband radiation with subnanosecond pulse lengths

Sources of high-power ultra-wideband electromagnetic pulses of nanosecond duration are described. A bipolar voltage pulse with a length of 0.5 ns and an amplitude of ∼200 kV is fed to the input of a radiating system (a 16-element array antenna or a single antenna). The values of the effective radiation potential EpR = 260 kV for a source with a single antenna and EpR = 690 kV for a source with a 16-element antenna array were obtained at a pulse repetition frequency of 100 Hz.

Effect of Substrate Bipolar Pulse Voltage on the Properties of Cu Films on the Paper Substrate Using Magnetron Sputtering with Multipolar Magnetic Plasma Confinement Assisted by Inductively Coupled Plasma

We have deposited Cu thin films on a water-resistant paper substrate using magnetron sputtering with multipolar magnetic plasma confinement assisted by inductively coupled plasma and investigated the effects of the substrate negative pulse voltage (Vs) and pulse frequency on the properties of the films. The X-ray diffraction results showed that the intensities of the Cu(111) and Cu(200) peaks depended strongly on both Vs and the pulse frequency. In addition, atomic force microscopy of the surface morphology revealed that increasing Vs in the range from 0 to −120 V resulted in a decrease in the root-mean-square roughness from 13.7 to 9.48 nm.

The Degradation of Thin Silicon Dioxide Films Subjected to Pulse Voltage Stresses at Nanoscale

In this paper, we report the observation of the degradation and breakdown of thin silicon dioxide films subjected to both the unipolar and bipolar pulse voltage stresses at nanoscale by using conductive atomic force microscopy. It is found that the unipolar pulse voltage stress produces more severe damage than does the bipolar pulse voltage stress. We also notice that hard breakdown is always preceded by soft breakdown for thin silicon dioxide subjected to either unipolar or bipolar pulse voltage stress, and the soft breakdown is always accompanied with random current fluctuation in the I-t characteristics. The influence of varying frequency of the pulse voltage stresses on the oxide breakdown is also investigated in this work.

Optimization of sustain pulse parameters for luminous efficacy improvement in an AC plasma display panel

In this paper, we report the experimental findings for improving the luminance and luminance efficacy in an AC plasma display panel using a new sustain waveform. The original waveform consists of bipolar sustain pulses of equal amplitudes and widths on both the sustain and scan electrodes. The proposed waveform modifies the pulse width and amplitude of the conventional bipolar voltage pulses. On reducing the pulse width of one of the applied sustains pulse; we observe the increase in luminance by 17% and luminance efficacy by 36% which is independent of the pulse polarity. The application of negative wider pulse (2.1 μs) of high amplitude (180 V) and positive shorter pulse (0.5 μs) of low amplitude (30 V) yields additive enhancement of the luminance by 26% and luminance efficacy by 19%. This new sustain waveform can be used to develop new generation high efficacy plasma displays.

Investigation of discharge mechanisms in helium plasma jet at atmospheric pressure by laser spectroscopic measurements

We have measured spatiotemporal structures of excited species by laser spectroscopic methods in a plasma jet, which was driven by a bipolar impulse voltage pulse train of the order of kilohertz repetition rate applied across a pair of electrodes wrapped around a glass tube with a helium gas flow. We noticed the differences between the positive and the negative phases of the voltage applied to the front-side electrode placed closer to the tube exit while the back-side electrode was grounded. The experimental results showed that the radial distribution of the excited species had a hollow shape at the centre in the positive voltage phase, while it had a more uniform shape in the negative phase. The peak density of the helium metastable atom in the positive phase was almost constant irrespective of the peak applied voltage. However, it increased with the increase in the peak applied voltage in the negative phase. The mechanism causing these differences was argued from the respects of positive and negative corona discharges. We have also investigated the property of the plasma plume under conditions similar to material processing with a conductive substrate placed in front of the plasma jet. In this case, the plasma production by electron impact ionization became dominant near the substrate as was revealed from the spatiotemporal distributions of helium metastable atom and nitrogen ion densities.

Effect of Substrate Bipolar Pulse Voltage on the Properties of Cu Films Using Magnetron Sputtering with Multipolar Magnetic Plasma Confinement Assisted by Inductively Coupled Plasma

Effects of substrate bipolar pulse voltage (Vs), pulse frequency and duty ratio on the properties of Cu thin films using magnetron sputtering with multipolar magnetic plasma confinement assisted by inductively coupled plasma (MMPC-ICP) were demonstrated. Results from X-ray diffraction (XRD) show that the intensities of the Cu(111) and Cu(200) peaks depend strongly on the Vs. The intensity of the XRD peak for Cu(111) increased when the Vs was increased from 0 V to −120 V. It is shown that the Cu film deposited at Vs=−120 V has a maximum grain size of about 42.6 nm; this value is about 1.5 times higher than that at Vs=0 V.

Mode Change Observed on Spatial Distribution of Microplasma Emission in a Microdischarge Cell with a Floating Electrode

A microplasma device fabricated on a silicon substrate with a floating electrode inside the microdischarge space was investigated to determine the dependences of discharge properties in neon gas on the gas pressure p and the characteristic dimension D. With a decrease in p towards the condition of the minimum ignition voltage, the spatial emission distribution in the negative phase of the applied bipolar pulsed voltage changed from a hollow pattern with a bright periphery to a concentrated bright pattern in the central area above the floating electrode, which was similar to that in the positive phase. This observation encourages us to make this device structure to provide a brighter light source at the microscales for various photonic applications.

Effects of cathodic voltage pulse duty cycle on characteristics of microarc oxidation coatings of titanium alloy

Under the condition of keeping the bipolar pulse voltage constant, the effect of cathodic pulse voltage duty cycle （dc） on characteristics of microarc oxidation coatings of titanium alloy have been studied by using a multifunction microarc oxidation power supply. Experimental results show that the variations of cathodic and anodic currents with treatment time show obviously several stages, and the beginning and ending time of various stages are closely related to dc. The coating consists mainly of rutile and anatase phases, and there is a sudden change in the rutile phase content at dc=50%. The thickness, morphology and microhardness of the coating strongly depend on dc change. The microhardness valucs of the coatings prepared at dc=50% and dc=70% are the minimum （4.96 GPa） and the highest （6.1 GPa）, respectively. In general, the MAO coatings prepared in the range of 65%≤dc≤80% have higher growth rate and quality.

Miniature conductivity wire-mesh sensor for gas-liquid two-phase flow measurement

A miniature conductivity wire-mesh sensor for gas-liquid two-phase flow measurement in small channels is presented. The sensor design is similar to the conventional wire-mesh sensor for larger flow cross sections with wire electrodes stretched across the flow channel in two adjacent planes and with perpendicular wire orientation between planes. Conductivity measurement is performed by special electronics which consecutively applies bipolar voltage pulse excitation to the sender wires and measures electrical current flow in the wire crossings at the receiver wires. The new design is based on printed circuit board technology. A prototypical sensor made of 2×16 stainless steel wires each of 50 μm diameter was manufactured and applied to two-phase flow measurement inside the mixing chamber of an effervescent atomizer. Accuracy of the sensor was studied for static liquid distributions using microphotography and for dynamic two-phase flow by comparison of wire-mesh sensor data with radial gas fraction profiles obtained from X-ray microtomography measurements.

Resistive Switching in Organic Memories with a Spin-Coated Metal Oxide Nanoparticle Layer

Resistive switching is demonstrated in diodes based on spin-coated layers of nanoparticles of Al2O3, CeO2, TiO2, ZrO2, Y2O3, or ZnO and a semiconducting polymer sandwiched between two electrodes. Inclusion of the metal oxide nanoparticles results in nonvolatile electronic memory characteristics that are similar to those observed for the corresponding “bulk” oxide. The major difference is that the nanoparticulate layers do not require a forming step. ZnO and TiO2 can be switched between a high and low resistance state using voltages pulses of opposite polarity, and Al2O3, CeO2, ZrO2, Y2O3 can be switched with both bipolar and unipolar voltage pulses.

Self-patterned aluminium interconnects and ring electrodes for arrays of microcavity plasma devices encapsulated in Al2O3

Automatic formation of Al interconnects and ring electrodes, fully encapsulated by alumina, in planar arrays of Al2O3/Al/Al2O3 microcavity plasma devices has been accomplished by electrochemical processing of Al foil. Following the fabrication of cylindrical microcavities (50–350 µm in diameter) in 127 µm thick Al foil, virtually complete anodization of the foil yields azimuthally symmetric Al electrodes surrounding each cavity and interconnects between adjacent microcavities that are produced and simultaneously buried within a transparent Al2O3 film without the need for conventional patterning techniques. The diameter and pitch of the microcavities prior to anodization, as well as the anodization process parameters, determine which of the microcavity plasma devices in a one- or two-dimensional array are connected electrically. Data presented for 200 µm diameter cavities with a pitch of 150–225 µm illustrate the patterning of the interconnects and electrode connectivity after 4–10 h of anodization in oxalic acid. Self-patterned, linear arrays comprising 25 dielectric barrier devices have been excited by a sinusoidal or bipolar pulse voltage waveform and operated in 400–700 Torr of rare gas. Owing to the electrochemical conversion of most of the Al foil into Al2O3, the self-formed arrays exhibit an areal capacitance ∼82% lower than that characteristic of previous Al/Al2O3 device arrays (Park et al 2006 J. Appl. Phys. 99 026107).

Active Integrated Antenna Based on Planar Dielectric Resonator With Tuning Ferroelectric Varactor

Design of tunable Gunn diode-based active antenna module including a new type of planar dielectric resonator (PDR) tuned by a ferroelectric (FE) varactor is presented. The module is designed in such a way that the PDR acts both as a stabilizing resonator and as a radiator. Microwave properties of FE elements used for voltage-controlled oscillator (VCO) tuning are considered. The module operates at a frequency around of 17 GHz and demonstrates the radiated power of 8.8plusmn0.1 dBm over the 130-MHz tuning range and a phase-noise level of -80 dBc/Hz at 100-kHz offset. 65deg width of the radiation pattern in both the E-and H-planes corresponding to a gain of 5.1 dBi was measured. The VCO module has been tested in the regime of the frequency modulation. The output signal spectra measured and simulated for modulating bipolar voltage pulses of repetition frequency f=2 MHz are presented.

Impedance spectroscopy characterisation of PEO process and coatings on aluminium

Impedance spectroscopy is a comprehensive technique that operates with frequency response (FR) to provide useful information about both surface treatments and layers produced. In this paper, two FR types were obtained for the aluminium samples during treatment by plasma electrolytic oxidation (PEO). The first was obtained in-situ during PEO, using a frequency sweep of bipolar voltage pulses between 20 Hz and 20 kHz. The modulus and phase angle components of the frequency response were analysed as functions of voltage and treatment time. With increased frequency, the impedance modulus and phase angle were found to decrease from 10 4 to 10 Ω and from 0 to − 80° respectively. The second FR was obtained using electrochemical impedance spectroscopy (EIS) of PEO coatings, at open-circuit potential. The samples were found to exhibit an active-capacitive load behaviour, whereby the impedance decreased from 10 6 to 10 2 Ω, and phase angle varied between − 20° and − 80° with the frequency increase. Both FRs show similar behaviour within the frequency range from 5 to 20 kHz. This approach allows estimations of the frequency response of the PEO microdischarges, to justify the optimal frequency for the pulsed bipolar PEO and also suggests concepts for feedback process control.

Multichannel Microchip Electrophoresis Device Fabricated in Polycarbonate with an Integrated Contact Conductivity Sensor Array

A 16-channel microfluidic chip with an integrated contact conductivity sensor array is presented. The microfluidic network consisted of 16 separation channels that were hot-embossed into polycarbonate (PC) using a high-precision micromilled metal master. All channels were 40 microm deep and 60 microm wide with an effective separation length of 40 mm. A gold (Au) sensor array was lithographically patterned onto a PC cover plate and assembled to the fluidic chip via thermal bonding in such a way that a pair of Au microelectrodes (60 microm wide with a 5 microm spacing) was incorporated into each of the 16 channels and served as independent contact conductivity detectors. The spacing between the corresponding fluidic reservoirs for each separation channel was set to 9 mm, which allowed for loading samples and buffers to all 40 reservoirs situated on the microchip in only five pipetting steps using an 8-channel pipettor. A printed circuit board (PCB) with platinum (Pt) wires was used to distribute the electrophoresis high-voltage to all reservoirs situated on the fluidic chip. Another PCB was used for collecting the conductivity signals from the patterned Au microelectrodes. The device performance was evaluated using microchip capillary zone electrophoresis (mu-CZE) of amino acid, peptide, and protein mixtures as well as oligonucleotides that were separated via microchip capillary electrochromatography (mu-CEC). The separations were performed with an electric field (E) of 90 V/cm and were completed in less than 4 min in all cases. The conductivity detection was carried out using a bipolar pulse voltage waveform with a pulse amplitude of +/-0.6 V and a frequency of 6.0 kHz. The conductivity sensor array concentration limit of detection (SNR = 3) was determined to be 7.1 microM for alanine. The separation efficiency was found to be 6.4 x 10(4), 2.0 x 10(3), 4.8 x 10(3), and 3.4 x 10(2) plates for the mu-CEC of the oligonucleotides and mu-CZE of the amino acids, peptides, and proteins, respectively, with an average channel-to-channel migration time reproducibility of 2.8%. The average resolution obtained for mu-CEC of the oligonucleotides and mu-CZE of the amino acids, peptides, and proteins was 4.6, 1.0, 0.9, and 1.0, respectively. To the best of our knowledge, this report is the first to describe a multichannel microchip electrophoresis device with integrated contact conductivity sensor array.

Sub‐millisecond transient vertical chevron formation during the electroclinic effect in the smectic A* phase

X‐ray diffraction studies are carried out in order to probe the smectic layer structure in liquid crystal devices filled with FLC mixture SCE8 and AFLC mixture CS4001, at a temperature just above the SmA*–SmC* phase transtion. The data gathered are time‐resolved in synchronization with a bipolar voltage pulse applied across the device. The layers are observed to move dynamically and reversibly with voltage application and removal, giving evidence for temporary vertical chevron formation due to the electroclinic effect on a timescale consistent with this phenomenon.

Interferon-γ Down-regulates Adenosine 2b Receptor-mediated Signaling and Short Circuit Current in the Intestinal Epithelia by Inhibiting the Expression of Adenylate Cyclase

Adenosine is an endogenous signaling molecule that is highly up-regulated in inflammatory states. Adenosine acts through the A2b receptor, a G protein-coupled receptor that couples positively to Galpha(s) and activates adenylate cyclase. This leads to cAMP-mediated electrogenic chloride secretion in intestinal epithelia. To better understand the regulation of the A2b receptor in intestinal epithelia, we studied the effects of interferon-gamma (IFN-gamma), a potent immunomodulatory cytokine, in the T84 cell line. Pretreatment of cells with 500 units/ml IFN-gamma for 12 h inhibited an adenosine-induced short circuit current (Isc) without affecting the transepithelial resistance. Under these conditions, IFN-gamma did not inhibit the protein expression or membrane recruitment of the A2b receptor, shown to be essential for its function. Interestingly, IFN-gamma inhibited cAMP levels as well as its downstream signaling pathway as shown by the inhibition of adenosine-induced phosphorylation of cAMP response element-binding protein and protein kinase A activity. Similar studies with forskolin, a direct activator of adenylate cyclase, also demonstrated inhibition of cAMP and its downstream response by IFN-gamma. However, IFN-gamma did not affect secretory responses to the calcium-dependent secretagogue carbachol or cAMP analog 8-bromo-cAMP, indicating that normal secretory responses to adequate second messengers in IFN-gamma-treated cells are achievable. Moreover, IFN-gamma inhibited the expression of adenylate cyclase isoforms 5 and 7. In conclusion, we demonstrate that IFN-gamma down-regulates adenosine-mediated signaling possibly through the direct inhibition of adenylate cyclase expression. We propose that IFN-gamma may acutely affect global cAMP-mediated responses in the intestinal epithelia, thereby decreasing secretory responses, which may consequently aggravate inflammatory processes.

Pt/LiNbO3/AlN/Si(100) 구조를 이용한 MFIS 커패시터의 전기적 특성

Metal-ferroelectric-insulator-semiconductor(WFIS) capacitors using rapid thermal annealed LiNbO<TEX>$_3$</TEX>/AlN/Si(100) structure were fabricated and demonstrated nonvolatile memory operations. The capacitors on highly doped Si wafer showed hysteresis behavior like a butterfly shape due to the ferroelectric nature of the LiNbO<TEX>$_3$</TEX> films. The typical dielectric constant value of LiNbO<TEX>$_3$</TEX> film in the MFIS device was about 27, The gate leakage current density of the MFIS capacitor was 10<TEX>$^{-9}$</TEX> A/cm<TEX>$^2$</TEX> order at the electric field of 500 kV/cm. The typical measured remnant polarization(2P<TEX>$_{r}$</TEX>) and coercive filed(Ec) values were about 1.2 <TEX>$\mu$</TEX>C/cm<TEX>$^2$</TEX> and 120 kV/cm, respectively The ferroelectric capacitors showed no polarization degradation up to 10<TEX>$^{11}$</TEX> switching cycles when subjected to symmetric bipolar voltage pulses of 1 MHz. The switching charges degraded only by 10 % of their initial values after 4 days at room temperature.e.

Field-induced modifications of hydrogenated diamond-like carbon films using a scanning probe microscope

Low-conducting hydrogenated diamond-like carbon (a-C:H) films were examined for the purpose of nanometer-scaled modifications under the action of local electrical field. To create the modifications, a series of voltage pulses (either positive or negative, or bipolar) was applied between the sample and the cantilever at regular points along a given line while scanning the probe in contact mode under ambient conditions. It was established that both geometrical and electrical properties of the obtained nano-objects strongly depended on the pulse shape. A nanocavity with a well-conducting bottom was reproducibly formed under the bipolar voltage pulses. Otherwise, the actions mostly resulted in the formation of poorly conducting nanoprotrusions. Evidence was obtained that, in the case of monopolar voltage pulse actions, local heating of the surface layer underneath the probe is a dominant process in the mechanism of the nanoprotrusion formation. We consider that the bipolar pulse actions additionally involve the tip-surface electrostatic interaction which plays an important role in the formation of nanocavities.

Utilizing bipolar pulsed PACVD for the deposition of alumina hard coatings

In the present investigation, a commercially available PACVD system suited for the deposition of titanium nitride (TiN) was adapted in order to allow alumina (Al 2O 3) deposition up to substrate temperatures of 800 °C. Besides a modification of the gas supply system, an additional heating system inserted into the reactor was needed. Bipolar voltage pulses were applied to the substrate holder whereas the grounded reactor wall served as counter electrode. In order to achieve a uniform discharge across the substrate holder, it was necessary to place an additional grounded counter electrode above the substrate holder. The alumina deposition was investigated on TiN-coated boron-doped silicon (100) substrates and austenitic steel plates placed on the substrate holder. It turned out that the coating thickness decreased strongly with the distance from the central gas inlet. The coatings were analysed by XRD for phase composition, by micro-indentation for hardness, by XPS for chemical composition and by SEM for morphology. At a temperature of 800 °C, only two crystalline modifications of alumina, the α- and the γ-phase, were observed. The γ-phase was stable up to a temperature of 1000 °C.