Negative Voltage Pulses Research Articles

Gate-Voltage-Controlled Threading DNA into Transistor Nanopores.

We present a simple method for DNA translocation driven by applying AC voltages, such as square and sawtooth waves, on an embedded thin film as a gate electrode inside of a dielectric nanopore, without applying a conventional bias voltage externally across the pore membrane. Square waveforms on a gate can drive a single DNA molecule into a nanopore, which often returns from the pore, causing an oscillation across the membrane. An optimized sawtooth-like negative voltage pulse on the gate can thread a fraction of a DNA molecule into a pore after a single pulse. This trapped DNA molecule continues to finish its translocation slowly through the pore. The DNA's slow speed was comparable to previous findings of the escaping DNA speed from a nanopore estimated by the Smoluchowski equation with excluded-volume interactions of a long-chain molecule and electrophoresis by extremely low electric fields. This simple scheme, controlling DNA molecules only by gate potential modulation at a nanopore, will provide an additional method to thread, translocate, or oscillate a single biomolecule at a gated nanopore.

Marx Multilevel Bipolar Modulator Dynamic Models for Load Transient Analysis

This paper presents generalized dynamic models for Marx derived multilevel half-bridge bipolar modulators. This high-voltage topology uses modular Marx multilevel converter diode (M3CD) cells to generate positive and negative (bipolar) pulses or unipolar (positive or negative voltage pulses). The developed models are tested in transient studies of pulse voltages and currents in the load. Simulation and experimental results are presented and compared.

Plasma action on helium flow in cold atmospheric pressure plasma jet experiments

In this work, helium flow modifications, visualized by schlieren imaging, induced by the plasma generated in a plasma jet have been studied in conditions used for biomedical treatments (jet being directed downwards with a low helium flow rate). It has been shown that the plasma action can shift up to few centimeters downstream the effects of buoyancy, which allows to the helium flow to reach a target below in conditions for which it is not the case when the plasma is off. This study reveals the critical role of large and long lifetime negative ions during repetitive operations in the kHz regime, inducing strong modifications in the gas propagation. The cumulative added streamwise momentum transferred to ambient air surrounding molecules resulting from a series of applied voltage pulses induces a gradual built up of a helium channel on tens of millisecond timescale. In some conditions, a remarkable stable cylindrical helium channel can be generated to the target with plasma supplied by negative polarity voltage pulses whereas a disturbed flow results from positive polarity operation. This has a direct effect on air penetration in the helium channel and then on the reactive species production over the target which is of great importance for biomedical applications. It has also been shown that with an appropriate combination of negative and positive polarity pulses, it is possible to benefit from both polarity features in order to optimize the plasma plume propagation and plasma delivery to a target.

Electrooptical effect in the plasmon structure glass–In2O3: Sn–ferroelectric–Al with a subwavelength grating

The spectral features of the electrooptical effect, in which an applied voltage changes the refractive index of a ferroelectric copolymer, are studied. Three nanostructures are investigated: two nanostructures play an auxiliary role, and the basic structure consists of a glass substrate, a transparent ITO (In2O3: Sn) layer, active copolymer layer, and an Al layer with a nanograting. This grating with a period of 400 nm meets the conditions of excitation of plasmon resonances. The light transmission coefficients of all structures are analyzed in the spectral range 400–900 nm. The transmission spectra have two characteristic plasmon dips, one of which is related to the copolymer–ITO interface and the other, to the copolymer–Al interface. The aluminum and ITO layers play the role of electrodes, which supply voltage pulses (from 0 to 15 V) to the copolymer layer. When studying the electrooptical effect, we detected spectral shifts in plasmon resonance bands when the amplitudes of both positive and negative voltage pulses (quadratic effect) increase. These shifts change the effective refractive indices (n eff) of the structural elements, reaching the minimum negative increment Δeff =–0.06.

Experimental Observation of Negative Susceptance in HfO2-Based RRAM Devices

Negative susceptance is experimentally measured in the low resistance state of TiN/Ti/HfO2/W resistive RAM memories. A meminductive-like behavior appears along with the memristive effects. A detailed study of small-signal parameters measured at 0 V after applying positive and negative voltage pulses is presented. A simple model for the conductive filaments consisting in a resistance in series with an inductance is used. In the equivalent circuit, both elements are in parallel with the geometrical capacitance of the structure. Both resistance and inductance show two clearly differentiate states. Positive voltages switch the device to the ON state, in which the resistance value is low and the inductance value is high. By applying appropriate negative voltages, the device switches to the OFF state, in which resistance value is high and inductance becomes negligible. The negative susceptance could be related to lags between current and electric field due to transport mechanisms occurring in the ON state.

Solution-processed field-effect transistors based on polyfluorene –cesium lead halide nanocrystals composite films with small hysteresis of output and transfer characteristics

We have designed and investigated electrical and optical properties of solution-processed organic field-effect transistors (OFETs) based on conjugated polymer PFO and perovskite –cesium lead halide nanocrystals (CsPbI3) composite films. It was shown that OFETs based on PFO:CsPbI3 films exhibit current-voltage (I-V) characteristics of OFETs with dominant hole transport and saturation current behavior at temperatures 200–300 K. It was found that PFO:CsPbI3 OFETs have a negligible hysteresis of output and transfer characteristics especially at temperatures below 250 K. The values of the hole mobility estimated from I-Vs of PFO:CsPbI3 OFETs were found to be ∼2.4 10−1 cm2/Vs and ∼1.9 10−1 cm2/Vs in saturation and low fields regimes respectively at 300 K; the hole mobility dropped down to ∼6 10−3 cm2/Vs and 2.8 10−3 cm2/Vs respectively at 200 K, and then down to 5.5 10−5 cm2/Vs at 100 K (in low field regime), which is characteristic of hopping conduction. The effect of sensitivity to light and light-emitting effect were found under application of negative source-drain and gate pulse voltages to PFO:CsPbI3 OFETs at 300 K. The mechanism of charge carrier transport in OFETs based on PFO:CsPbI3 hybrid films is discussed.

Pulsed Nanosecond Breakdown of a Hollow Cathode Discharge With Pseudospark Geometry

This paper reports the experimental results from the appearance of three discharge modes in a special geometry as a function of applied negative voltage pulses. The geometry is a four-gap pseudospark one with a gap distance of 4 mm, a metallic hollow cathode, and an anode. The applied pulsed voltage $U_{p}$ varies from −20 to −80 kV. The pulse shape is a rectangular one with a pulsewidth of 50 ns and a rise time of 4 ns. There is no breakdown at $U_{p} kV, and at $U_{p} > 27$ kV, a pseudospark discharge starts, which transforms at $U_{p} > 45$ kV into a surface discharge. The working gas is dry air at a constant pressure of 13 Pa. Using these parameters, electric field simulations of the triple point junctions are conducted and time-integrated pictures of the different discharge modes are presented. When the gas pressure is increased from 13 to 35 Pa, the voltage range of the pseudospark discharge mode grows from 13 to 65 kV.

Counter-propagating streamers in an atmospheric-pressure helium plasma jet

This study explores an atmospheric pressure plasma jet impinging on a downstream dielectric surface using a 2D numerical plasma fluid model. It is demonstrated that a counter-propagating discharge ignites at the exposed dielectric surface when the discharge is ignited using negative polarity voltage pulses with fall times in the microsecond range. Two distinct streamer discharges are created, a cathode-directed streamer propagating upstream toward the cathode, and an anode-directed streamer propagating parallel to the dielectric surface facing the gas flow. The surface discharge propagating parallel to the dielectric surface deposits negative surface charge. It is also shown that driving an APPJ with a negative applied potential significantly increases the time-averaged flux to the dielectric surface while decreasing the time-averaged flux.

Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO3 on SrTiO3.

Electric-field (E-field) control of magnetism enabled by multiferroic materials has the potential to revolutionize the landscape of present memory devices plagued with high energy dissipation. To date, this E-field controlled multiferroic scheme has only been demonstrated at room temperature using BiFeO3 films grown on DyScO3, a unique and expensive substrate, which gives rise to a particular ferroelectric domain pattern in BiFeO3. Here, we demonstrate reversible electric-field-induced switching of the magnetic state of the Co layer in Co/BiFeO3 (BFO) (001) thin film heterostructures fabricated on (001) SrTiO3 (STO) substrates. The angular dependence of the coercivity and the remanent magnetization of the Co layer indicates that its easy axis reversibly switches back and forth 45° between the (100) and the (110) crystallographic directions of STO as a result of alternating application of positive and negative voltage pulses between the patterned top Co electrode layer and the (001) SrRuO3 (SRO) layer on which the ferroelectric BFO is epitaxially grown. The coercivity (HC) of the Co layer exhibits a hysteretic behavior between two states as a function of voltage. A mechanism based on the intrinsic magnetoelectric coupling in multiferroic BFO involving projection of antiferromagnetic G-type domains is used to explain the observation. We have also measured the exact canting angle of the G-type domain in strained BFO films for the first time using neutron diffraction. These results suggest a pathway to integrating BFO-based devices on Si wafers for implementing low power consumption and nonvolatile magnetoelectronic devices.

Effect of Ar+ ion assist on the properties of a-C:H films deposited on a trench

In this study, a precursor gas mixture of toluene and Ar was used for the deposition of a-C:H films on a trench (20-mm pitch and 10-mm depth), and the effect of the Ar flow ratio on the film properties was investigated. The a-C:H films were deposited using a bipolar-type plasma based ion implantation and deposition technique under a negative pulse voltage of −2kV. The mechanical properties of the prepared a-C:H films, including internal stress, hardness and adhesion strength, were measured by means of surface profilometry, nanoindentation and a microscratch test, respectively. Furthermore, the microstructure of a-C:H films was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results showed that the thickness uniformity across the trench surface is improved by the addition of Ar, in particular, at an Ar flow ratio of 80%. The film on the top and bottom surfaces of the trench tends to change from a PLC to DLC structure with increasing Ar flow ratio, resulting in a significant improvement of mechanical properties. In the case of the sidewall, the film tends to change to a more GLC structure with increasing Ar flow ratio due to the Ar+ ion bombardment and sputtering effect.

Generators of diffuse plasma at atmospheric pressure

Devices that form low-temperature diffuse nanosecond-discharge plasma in a flow of various gases at the atmospheric pressure are described. To form diffuse plasma, negative voltage pulses with an amplitude of several tens of kilovolts and a duration of 5 ns were fed to a point–plane gap in the pulse–periodic mode. By varying the geometry of the discharge gap, the shape of the cathode, and the composition of the working gas, it is possible to obtain plasma with a wide range of parameters and modify the surfaces of various materials with areas of up to several tens of square centimeters.

Preparation of Titanium-Doped Diamond-Like Carbon Films With Electrical Conductivity Using High Power Pulsed Magnetron Sputtering System With Bipolar Pulse Voltage Source for Substrate

Titanium-doped diamond-like carbon (DLC) films with electrical conductivity are prepared by plasma-enhanced chemical vapor deposition using high-density pulsed Ar/C2H2 plasmas. Those plasmas are produced by high-power pulsed magnetron sputtering (HPPMS) system, whereas the titanium dope into the DLC films is carried out through titanium sputtering. A bipolar pulse voltage source is connected to the substrate and its holder. The HPPMS plasma temporally evolves during a pulse-on time of an HPPMS power source after the discharge is ignited. Then, the negative pulse voltage with a magnitude of 1.5 kV is applied for $10~\mu \text{s}$ before the application of the positive pulse voltage with the magnitude lower than 1 kV and the pulsewidth of 10– $15~\mu \text{s}$ . The fraction of the intensity related to sp2 carbon bond in X-ray photoelectron spectroscopy (XPS) C 1s spectrum is $\sim 80$ % or more for any film. On the other hand, the fraction of the intensity related to sp3 carbon bond is $\sim 20$ %, resulting in the preparation of the films with moderate hardness. The fraction of the intensity related to the titanium component in the overall XPS spectrum is lower than 8%, whereas that of titanium–carbon bond component in the overall XPS spectrum is lower than 1.5%. The conductivity of the prepared films markedly increases to 609 S/cm and its value depends on the amount of titanium–carbon bond. On the other hand, the film hardness ranges between 10 and 15 GPa and it does not strongly depend on the content of titanium.

New possibilities of plasma immersion ion implantation (PIII) and deposition (PIII&D) in industrial components using metal tube fixtures

New possibilities of Plasma Immersion Ion Implantation (PIII) and deposition (PIII&D) for treating industrial components in the batch mode have been explored. A metal tubular fixture is used to allocate the components inside around and along the tube, exposing to the plasma only the parts of each component that will be implanted. Hollow cathode- like plasma is generated only inside the tube filled with the desired gas, by applying high negative voltage pulses to the hollow cylindrical metal fixture which is insulated from the vacuum chamber walls. The metal tube (Me-tube) loaded with workpieces can be set-up inside the vacuum chamber in the standing-up, upside down or lying down arrangements. PIII tests were also run with and without metal sheet lids on the tube as well as with and without the components. Sputtering deposition and carbonitriding are also possible in this scheme by placing carbon tapes inside the tube and running the process with nitrogen PIII. Relatively clean DLC (Diamond Like Carbon) PIII&D deposition is possible by this method also since the plasma occupies mainly the Me-tube interior and not the whole chamber. Furthermore, operating high density PIII and PIII&D systems without additional plasma source, using only the high voltage pulser, is now possible to treat three dimensional parts. These methods are very convenient for batch processing of industrial parts by ion implantation and by ion implantation and deposition, in which a large number of small to medium size components can be treated by PIII and PIII&D, very quickly, efficiently and also at low cost.

Characteristics of Pulsed Heavy Ion Beam Generated in Bipolar Pulse Accelerator

SUMMARYWe have developed a new type of a pulsed ion beam accelerator named “bipolar pulse accelerator” for improvement of the purity of the intense pulsed ion beam. The system utilizes a magnetically insulated accelerate on gap and was operated with the bipolar pulse. A coaxial gas puff plasma gun was used as an ion source, which was placed inside of the grounded anode. Source plasma (nitrogen) of current density of ≈30 A/cm2 and pulse duration of ≈1.0 μs was injected into the acceleration gap. When the bipolar pulse of −114 kV, 70 ns (first pulse) and 85 kV, 62 ns (second pulse) was applied to the drift tube, the ions were successfully accelerated from the grounded anode to the drift tube in the first gap by the negative pulse of the bipolar pulse. The pulsed ion beam with current density of 60 A/cm2 and pulse duration of ≈50 ns was obtained at 48 mm downstream from the anode surface. The energy spectrum of the ion beam was evaluated by a magnetic energy spectrometer. The ion energy was in reasonable good agreement with the acceleration voltage, that is, first pulse (negative pulse) voltage of the bipolar pulse.

Deposition of a-C:H films on inner surface of high-aspect-ratio microchannel

Hydrogenated amorphous carbon (a-C:H) films were prepared on inner surface of 100-μm-width microchannel by using a bipolar-type plasma based ion implantation and deposition. The microchannel was fabricated using a silicon plate, and two kinds of microchannels were prepared, namely, with a bottom layer (open at one end) and without a bottom layer (open at both ends). The distribution of thickness and hardness of films was evaluated by SEM and nanoindentation measurements, respectively, and the microstructures of films were evaluated by Raman spectroscopy. Furthermore, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision and Direct Simulation Monte Carlo to investigate the coating mechanism for the microchannel. It was found that the film thickness decreased as the depth of the coating position increased in the microchannels where it is open at one end. The uniformity of the film thickness improved by increasing the negative pulse voltage because ions can arrive at the deeper part of the microchannel. In addition, the hardness increased as the depth of the coating position increased. This is because the radicals do not arrive at the deeper part of the microchannel, and the incident proportion of ions relative to that of radicals increases, resulting in a high hardness due to the amorphization of the film. The opening area of the microchannel where the aspect ratio is very small, radicals dominate the incident flux, whereas ions prevail over radicals above an aspect ratio of about 7.5. On the other hand, in the microchannels that are open at both ends, there were great improvements in uniformity of the film thickness, hardness, and the film structure. The a-C:H films were successfully deposited on the entire inner surface of a microchannel with an aspect ratio of 20.

Long-term thermal stability of Si-containing diamond-like carbon films prepared by plasma source ion implantation

The long-term stability of silicon-containing diamond-like carbon films was investigated. The samples were prepared by plasma source ion implantation with a mixture of tetramethylsilane (TMS) and acetylene (C2H2) using negative high voltage pulses. The film composition was changed by varying the flow rates of the TMS and C2H2 gases, resulting in a Si content from 0 to 44 at.%. After deposition the films were annealed at temperatures from 523 K to 773 K for 168 h in ambient air. The effect of the Si content on the structure, the mechanical and tribological properties of the DLC films was investigated. A silicon oxide layer is produced on the surface of the film which improves the thermal stability. Mechanical and friction characteristics of the Si-DLC were not much affected by the long-term thermal annealing if the temperature was kept below 573 K.

Effects of AC and pulse voltage combination on surface charge accumulation and decay of epoxy resin

Epoxy resin is widely used in disc-type spacers of gas insulated switchgear (GIS). Surface flashover related to the existence of surface charge often occurs on the spacer, which is a great threat to the application of GIS and the safety of entire grid. Moreover, the influences on surface charge under pulse voltage produced by switch overvoltage, accompanying with the AC voltage, are still unclear. In order to research the comprehensive effect of AC and pulse voltage on surface charge, in this paper, epoxy resin sample was charged by a corona discharge system and the charge distribution was measured by an electrostatic voltmeter. The results are obtained from the research of different pulse amplitudes, pulse numbers and pulse polarities. The surface potential is a negative value after AC voltage applied for a period of time. When AC and negative pulse voltage are applied, smaller pulse voltage would push the original negative charges away. As a result, initial negative surface potential decreases. But bigger pulse voltage could increase the charge accumulation. When the pulse polarity becomes positive, surface potential at the sample center will be positive value at the beginning and then it gradually changes from positive to negative potential. In addition, the influence on surface charge decay rate will be enhanced with the increase of pulse number under the same pulse voltage. Trap energy distributions were used to analyze charge decay process in the last section.

Preparation of hydrogenated diamond-like carbon films using high-density pulsed plasmas of Ar/C2H2 and Ne/C2H2 mixture

Hydrogenated diamond-like carbon films are prepared using reactive high-density pulsed plasmas of Ar/C2H2 and Ne/C2H2 mixture in the total pressure range from 0.5 to 2 Pa. The plasmas are produced using a reactive high-power impulse magnetron sputtering (HiPIMS) system. A negative pulse voltage of −500 V is applied to the substrate for a period of 15 µs in the afterglow mode. The growth rate does not strongly depend on the type of ambient gas but it markedly increases to about 2.7 µm/h at a C2H2 fraction of 10% and a total pressure of 2 Pa with increasing C2H2 fraction. The marked increase in the growth rate means that the HiPIMS system can be regarded as a plasma source for the chemical vapor deposition process. The hardness of the films prepared by Ne/C2H2 plasmas is somewhat higher than that of the films prepared by Ar/C2H2 plasmas under the same operating conditions, and the difference becomes larger as the pressure increases. The hardness of the films prepared by Ne/C2H2 plasmas ranges between 11 and 18 GPa. In the Raman spectra, two very broad overlapping bands are assigned as the G (graphite) and D (disorder) bands. The peak position of the G band is roughly independent of the total pressure, whereas the FWHM of the G peak decreases with increasing total pressure as a whole.

The effect of external visible light on the breakdown voltage of a long discharge tube

The breakdown characteristics of a discharge tube with a configuration typical of gas-discharge light sources and electric-discharge lasers (a so-called “long discharge tube”) filled with argon or helium at a pressure of 1 Torr have been investigated. A breakdown has been implemented using positive and negative voltage pulses with a linear leading edge having a slope dU/dt ~ 10–107 V/s. Visible light from an external source (halogen incandescent lamp) is found to affect the breakdown characteristics. The dependences of the dynamic breakdown voltage of the tube on dU/dt and on the incident light intensity are measured. The breakdown voltage is found to decrease under irradiation of the high-voltage anode of the tube in a wide range of dU/dt. A dependence of the effect magnitude on the light intensity and spectrum is obtained. Possible physical mechanisms of this phenomenon are discussed.

Characteristics of sub-atmospheric pressure glow discharge plasmas for preparation of a-C:H films

A new method of synthesis of a-C:H films using a pulsed glow discharge plasma with a mixed gas of helium and nitrogen at sub-atmospheric pressure of 2 kPa was proposed. Characteristics of the pulsed glow discharge plasma produced with a pair of parallel plate electrodes by applying high-repetition bipolar voltage pulses were investigated using optical emission spectroscopy. The ratio of intensities of the 0–0 transitions of the second positive system of nitrogen molecule (337.1 nm) and the first negative system of ionized nitrogen molecule (391.4 nm) was measured to investigate the electric field strength in the discharge plasma. The spatial structure of the plasma emission was similar with that of a typical glow discharge. It was also found that an intensive electric field appeared near the cathode electrode during negative ripple pulse voltages induced by an inductor added between the electrodes and the power supply. A uniform a-C:H film on a silicon substrate with hardness of 7 GPa was successfully prepared with the pulsed glow discharge plasma with the ripple pulse voltage application, where acetylene was used for the precursor gas. The deposition rate is 0.2 μm/min which is approximately 10 times higher than that of the conventional plasma CVD method under the low gas pressure. It is discussed that a rough estimate of incident ion energy onto the negatively biased substrate using a collisional plasma sheath model indicates the possibility of increase in the incident ion energy that is needed for enhancement of fraction of sp3 carbon bond due to decrease in the neutral gas pressure from 100 kPa to 2 kPa.