Increasing Bias Voltage Research Articles

The effect of duty cycle and bias voltage for graphite-like carbon film coated 304 stainless steel as metallic bipolar plate

Graphite-like carbon films are deposited on 304SS substrates with different duty cycles and bias voltages by unbalanced magnetron sputtering, both the alternating current (AC) twinned and direct current (DC) single graphite targets are used. The microstructures and properties are investigated as bipolar plate for proton exchange membrane fuel cell (PEMFC). It is found that the surface compactness and sp2 fraction are significantly affected by the duty cycle and bias voltage. The electrical resistivity and interface contact resistance (ICR) first decrease and then increase with increasing duty cycle, which is completely dominated by the sp2 fraction. However, although the electrical resistivity and sp3/sp2 ratio monotonously increases with increasing bias voltage, the ICR values show an initial decrease and final increase for appearing a difference between 0 V and −75 V, a mechanism of electronic channels is put forward to explain this result. The lowest ICR of carbon films reaches 8.4 mΩcm2 at a compaction force of 140 N/cm2, which is hopeful to replace commercial graphitic plate. In addition, the corrosion potential and current density are closely related to the surface morphology. The perfect duty cycle and bias voltage are 40% and −75 V respectively in this research, which promotes a most conductive, moderate corrosion resistant and well hydrophobic carbon film to form.

A Theoretical Model for Resonant Frequency and Radiation Pattern on Rectangular Microstrip Patch Antenna on Liquid Crystal Substrate

This paper presents a theoretical model of the rectangular-shaped microstrip patch antennas on liquid crystal (LC) substrates in order to accurately derive the resonant frequencies and radiation performances. The model is based on the solution of the mode matching about an LC loaded cavity. The calculation results of the theoretical model are compared with the experiment and simulation results. The discrepancy between calculation and simulation results is merely 2.7%. In addition, a tuning mechanism of the patch antenna on the LC substrate is verified depending on the strength of a biasing voltage. The calculated results of the theoretical model indicate that the resonant frequency is shifted toward lower direction and 3-dB beamwidth of radiation pattern increases as the bias voltage increases. Although the calculated maximum directivity decreases with the increment of voltage, the realized gain increases due to the radiation efficiency of the antenna.

Structure, morphology and mechanical properties of AlCrN coatings obtained by the method of cathodic arc evaporation

CrAlN coatings have been formed on steel substrates (HS6-5-2) using cathodic arc evaporation. The influence of nitrogen pres-sure and substrate bias voltage on the properties of CrAlN coatings formed from Al80Cr20 cathode, such as: chemical and phase composition of the coatings, their surface morphology, deposition rate, hardness and adhesion to the substrate have been investigated. It has been determined that the rate of the deposition of coatings in the nitrogen atmosphere with the pressure of 3 Pa is the highest and that with the increase of the negative bias voltage of the substrate the deposition rate decreases. The roughness parameter Ra of the coating surface decreases as the nitrogen pressure increases during their formation. Presumably, this is related to the reduction of the amount of macroparticles on the surface of the coating. The hardness of the coatings (taking into account the measurement uncertainty) is independent of the nitrogen pressure, but it increases with the increase of the negative bias voltage of the substrate. The adhesion of the coating increases with the increase of the nitrogen pressure to 3–4 Pa, and then it decreases. The increase in the negative bias voltage of the substrate during the formation of the coating deteriorates its adhesion to the substrate.

Phonon-assisted optical absorption due to Franz–Keldysh effect in 4H-SiC p–n junction diode under high reverse bias voltage

Photocurrent in a 4H-SiC p–n junction diode under illumination with sub-bandgap light was investigated. Under a high reverse bias condition, the photocurrent significantly increased with an increase in the reverse bias voltage. We calculated the photocurrent taking into consideration the phonon-assisted optical absorption due to the Franz–Keldysh effect. The calculated photocurrent showed good agreement with the experimental results. The photocurrent also increased at elevated temperatures, which could be quantitatively explained by the redshift of the 4H-SiC absorption edge (the shrinkage of the bandgap) and the increase in the phonon occupation number with rising temperature.

Expounding Transport Properties of Deoxyribonucleic Acid for Electronic Applications

The scientific interest in field of molecular electronics has raised many folds in last decade to become the centre stage of contemporary research. The community of researchers working in this domain has been continuously exploring newer molecules, which can replace semiconductors of last century and still continue with the same growth. In this research communiqué, we have implemented molecular junctions using NEGF-EHT approach to elucidate the electronic transport properties of two important strands Adenine and Cytosine of Deoxyribonucleic Acid (DNA) sandwiched between with two Au leads under finite bias conditions. Important revelation include non-linear behaviour exhibited with exponential current rise around zero bias due to kondo assisted resonant tunnelling and temperature invariance over a large range of temperature. G–V graph divulges that conductance of the adenine decrease linearly with the increase in bias voltage initially and then becomes dormant for further increase in bias voltage. Contrary to this, the conductance of cytosine is observed to be equal to quantum of conductance (G0) that unambiguously indicates the metallic behaviour of cytosine. The vital information collected through this research work provides vital insight for developing applications as sensors, switches and memory devices.

Effects of Bias Voltage on Microstructure, Hardness and Bonding Strength of TiN Coating Deposited by High Power Pulsed Magnetron Sputtering

Generally, bias voltage exercises a great influence on micro-properties (morphology, preferred orientation, mechanical properties, and so on) of the coatings in the process of coating deposited. In order to more systematically explore the influence of bias voltage on microstructure, hardness and adhesion of TiN coatings, TiN coatings were deposited successfully on the surface of 316 stainless steel by high power pulsed magnetron sputtering (HPPMS). A field emission scanning electron microscopy equipped with energy dispersive spectrometer (FESEM/EDS) and an X-ray diffractometer were employed to analyze the surface morphology, chemical composition and phase structure of coatings, respectively. And a nanoindentation and scratch tester was used to investigate the hardness, elastic modulus and adhesion of TiN coatings. Results showed that bias voltage has a great influence on surface morphology of TiN coatings. Moreover, bias voltage can promote preferential orientation and the phase in TiN coating is mainly TiN with a small amount of Ti2N. The influence of bias voltage on the hardness and modulus of TiN coating is not obvious, however, the binding force increases fast first and then decreases slow with the increase of bias voltage. TiN coating has excellent performance when bias voltage is-100V.

Tuning electronic transport properties of zigzag graphene nanoribbons with silicon doping and phosphorus passivation

Density-functional theory in combination with the non-equilibrium Green’s function formalism is used to study the effect of silicon doping and phosphorus passivation on the electronic transport properties of zigzag graphene nanoribbons (ZGNRs). We study the edge structures passivated by H atoms and by P atoms. In this work, Si atoms are used to substitute C atoms located at the edge of the samples. We consider ZGNRs terminated by H and P atoms with four zigzag carbon chains (4-ZGNRs) in case of six various configurations. Our calculated results determine that the Si doping improves significantly the current of samples by the number of dopants. Moreover, there is dramatical difference in the transmission spectrum of P-passivated ZGNRs and H-passivated ZGNRs i.e. P passivation not only destroys an enhanced transmission at the Fermi level, which is typical for graphene nanoribbons, but also increases considerably the intensity of transmission spectrum with ballistic transport properties. Furthermore, the numerical results illustrate that pristine H-terminated samples have a broadening band gap in transmission spectra when the bias voltage increases. The relationship between the outcomes indicates that such silicon doping and phosphorus passivation are effective and providing a promising way to modulate the properties of ZGNRs for nanoelectronic device applications.

Frequency-tunable metamaterial absorber with three bands

We propose a three-band metamaterial absorber composed of two opposite-trapezoid rings with only one varactor diode. By changing the reverse bias voltage on the varactor diode from 0 V to −15 V, the frequencies at the first and second absorption peaks can be dynamically tuned from 2.77 GHz to 4.36 GHz and 8.11 GHz to 8.41 GHz, respectively. With the increase of the reverse bias voltage, the frequency shift of the first absorption peak may reach 1.59 GHz with the absorptivity from 68.4% to 99.8%; for the second absorption peak, the frequency shift reaches 0.30 GHz with the absorptivity of above 97.4%; while the third absorption peak hardly shifts keeping nearly perfect absorptivity of above 99.9%. The absorption mechanism is analyzed by surface current distributions and the simulation results are verified by the experimental measurement. The proposed metamaterial absorber may be useful in the fields of multi-band electromagnetic stealth, biosensors, reflectors and so on.

Structural and Mechanical Properties of Zr-Si-N Coatings Deposited by Arc Evaporation at Different Substrate Bias Voltages

ZrN and Zr-Si-N coatings were formed using vacuum-arc plasma fluxes deposition system at the substrate bias voltage (UB) ranged from − 50 to − 220 V on HS6-5-2 steel substrates. The structural, mechanical and tribological properties were characterized using x-ray diffraction, atomic force microscopy, scanning electron microscopy, optical microscopy, nanoindentation and ball-on-disk test. The surface roughness parameter Ra of ZrN coatings is lower than Zr-Si-N coatings. Both roughness Ra of Zr-Si-N coatings and the number of surface defects with mainly small dimensions to 1 µm decrease with increasing negative substrate bias voltage. The addition of silicon to ZrN significantly reduces the crystallite size, from about 18.3 nm for ZrN coating to 6.4 nm for Zr-Si-N coating both deposited at the same UB = − 100 V and 7.8 nm for UB = − 150 V. The hardness of Zr-Si-N coatings increases to about 30 GPa with the increase in negative substrate bias voltage (UB = − 220 V). Adhesion of the coatings tested is high, and critical load is above 80 N and reduces with UB increase. Coefficient of friction determined using AFM shows similar trend as surface roughness in microscale.

Microstructure and residual stress of TiN films deposited at low temperature by arc ion plating

Abstract The TiN films were deposited on 316L stainless steel substrates at low temperature by arc ion plating. The influences of substrate bias voltage and temperature on microstructure, residual stress and mechanical properties of the films were investigated by EDS, SEM, XRD and nanoindenter tester, respectively. The results showed that the TiN films were highly oriented in (111) orientation with a face-centered cubic structure. With the increase of substrate bias voltage and temperature, the diffraction peak intensity increased sharply with simultaneous peak narrowing, and the small grain sizes increased from 6.2 to 13.8 nm. As the substrate temperature increased from 10 to 300 °C, the residual compressive stress decreased sharply from 10.2 to 7.7 GPa, which caused the hardness to decrease from 33.1 to 30.6 GPa, while the adhesion strength increased sharply from 9.6 to 21 N.

Micro-stucture and Mechanical Properties of (NbAlSi)N Coatings by Arc Ion Plating with Different Negative Bias

Metastable (NbAlSi)N hard coatings were deposited on 1Cr11Ni2W2MoV steel sheetsby arc ion plating system at different negative pulse bias. The surface morphologies, fractured cross-sections, phase structure, hardness, friction coefficient were characterized using scanning electron microscopy,X-ray diffraction, microindentation and friction tester. All (NbAlSi)N coatings were mainly composed of δ-NbN with minorδ’-NbN. The applicating of negative bias gave rise to the change of preferred orientation, crystal refinement, decreased droplet number and improved structure density. With the increase of negative bias voltage, the hardness increased obviously and the friction coefficient decreased.

Investigation on growth, structural, optical, electrical and X-ray sensing properties of chemically deposited zinc bismuth sulfide (ZnxBi2−xS3) thin films

In the present work, ZnxBi2−xS3 films were synthesized (x = 0.2 M) by a chemical bath deposition (CBD) technique at different bath temperatures (60 °C, 70 °C and 80 °C). The role of bath temperature on the formation of the films has been examined. The crystalline nature, structural parameters and surface morphology of the films were ascertained using x-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS) respectively. These studies confirmed the formation of crystalline Zn0.2Bi1.8S3 films with uniform distribution of homogenous grains. The characterization results revealed that the film deposited at 70 °C has the good crystalline quality than the films deposited at 60 and 80 °C. Further, the optical absorption spectra showed that the bandgap (Eg) of the film deposited at 70 °C was about 2.39 eV which was found to be less than the same film deposited at 60 and 80 °C. The Current-Voltage (I-V) characteristics of all the films were measured under dark condition. This showed that the electrical conductivity of the film deposited at 70 °C was 1.61 × 10−5 S cm−1 which is ten times higher than other films. Further, the I-V characteristics of the film deposited at 70 °C was studied under x-ray radiation. The current under the x-ray radiation was significantly higher compared to the dark current. The x-ray detection sensitivity of the film was found to be maximum at 0.7 V and gradually decreases with increase of bias voltage. This analysis reveals that the film deposited at 70 °C can be used as an x-ray sensor.

Tuning of photodetection properties of V0.5Sn0.5Se2 ternary alloy

In present article, we report the tuning of photodetection properties of V0.5Sn0.5Se2 ternary crystals grown by direct vapour transport technique. The comparison of photodetection under 485 nm, 532 nm and 670 nm periodic illumination is carried out for 0.3 mW cm−2 power intensity and 5 mV bias voltage. The fast response time of 200 ms is realised due to effective absorption of light and device configuration. The detector parameters such as photo-responsivity, specific detectivity and external quantum efficiency are also evaluated. The V0.5Sn0.5Se2 photodetector has shown effective light–matter interaction. The V0.5Sn0.5Se2 photodetector was examined under 670 nm illumination of different power intensity. Besides these, the photo-responsivity is enhanced from 77.67 mA W−1 to 99.67 mA W−1 on increasing bias voltage from 1 mV to 5 mV. The present work on tuning of photodetection can provide novel path for future optoelectronics.

Hydrogen sensing enhancement of zinc oxide nanorods via voltage biasing.

The capability of zinc oxide (ZnO) as a hydrogen sensing element has been pushed to its limits. Different methods have been explored to extend its sensing capability. In this paper, we report a novel approach which significantly improves the hydrogen sensing capability of zinc oxide by applying a bias voltage to ZnO nanorods as the sensing elements. Zinc oxide in the form of aligned nanorods was first synthesized on an Au-coated Si(111) substrate using a facile method via the galvanic-assisted chemical process. The sensing performance of the zinc oxide nanorods was investigated in response to the applied biasing voltage. It was found that the sensitivity, response time and detection limit of the ZnO sensing elements were dramatically improved with increasing bias voltage. A 100% increment in sensing response was achieved for the detection of 2000 ppm hydrogen gas when the bias voltage was increased from −2 to −6 V with 70% reduction in response and recovery times. This remarkable sensing performance is attributed to the reaction of hydrogen with chemisorbed oxygen ions on the surface of the ZnO nanorods that served as the electron donors to increase the sensor conductance. Higher reverse bias voltages sweep the electrons faster across the electrodes. This shortened the response time and, at the same time, depleted the electrons in the sensor elements and weakens oxygen adsorption. The oxygen ions could then be readily removed by hydrogen, leading to a higher sensitivity of the sensors. This, therefore, envisages a way for high-speed hydrogen gas sensing with high detection sensitivities.

Field-effect-dependent thermoelectric power in highly resistive Sb2Se3 single nanowire

In this paper, we report the results of our experiments on and measurements of electrical resistivity and thermoelectric power (Seebeck coefficient) from single-crystalline antimony triselenide (Sb2Se3) single nanowires (NWs) with high resistivity (σ ~ 4.37 × 10−4 S/m). A positive Seebeck coefficient of approximately 661 µV/K at room temperature was obtained using a custom-made thermoelectric power probe with an alternating current lock-in method (the 2ω technique), which indicates that the thermal transport is dominated by holes. The measured Seebeck coefficient of the NWs is a factor of 2–3 lower than their bulk counterparts and is comparable to that of a highly conductive Sb2Se3 single NWs (approximately − 750 µV/K). We observed an increase in the Seebeck coefficients with increased bias voltages by field-effect gating, which cannot be explained by the modulation of the Fermi level in the NWs.

First-principles study on electron transport properties of carbon–silicon mixed chains

In this paper, the transport properties of carbon–silicon mixed chains are studied by using the first-principles. We studied five atomic chain models. In these studies, we found that the equilibrium conductances of atomic chains appear to oscillate, the maximum conductance and the minimum conductance are more than twice the difference. Their I–V curves are linear and show the behavior of metal resistance, M5 system and M2 system current ratio is the largest in 0.9 V, which is 3.3, showing a good molecular switch behavior. In the case of bias, while the bias voltage increases, the transmission peaks move from the Fermi level. The resonance transmission peak height is reduced near the Fermi level. In the higher energy range, a large resonance transmission peak reappears, there is still no energy cut-off range.

Effect of substrate bias voltage on defect generation and their influence on corrosion and tribological properties of HIPIMS deposited CrN/NbN coatings

Substrate bias voltage is one of the most influential deposition parameter for physical vapour deposition processes as it can directly control the adatom mobility during coating growth. It influences the hardness, roughness as well as the microstructure of the coatings. Thus, bias voltage could also affect the defect formation during the coating deposition. High Power Impulse Magnetron Sputtering (HIPIMS) has been proven useful in producing void free and arc droplet free dense coatings. However, such coatings can still suffer from some defects associated with external factors (independent of deposition technique), such as substrate irregularities and the flakes coming from the chamber components. In order to study the effects of bias voltage (Ub) on the defect formation during HIPIMS process, four sets of CrN/NbN coatings were deposited at Ub = −40 V, −65 V, −100 V and −150 V. Microscopic studies revealed that with the increase in bias voltage the coatings morphology was altered and the percentage of surface area covered by optically visible defects was increased from 3.13% to 4.30%. The defects on the coatings deposited at Ub = −100 V and −150 V led to preferential corrosive attack resulting in a sharp increase in corrosion current density during Potentiodynamic polarisation experiments. Room temperature pin-on-disc tribological tests exhibited the influence of defects on the wear behaviour; however, the coefficient of friction (μ) values were mainly influenced by the nature of the oxides formed during the tests. Coating microstructure and bilayer thickness, along with the coating defects determined the coefficient of wear (Kc) values. This study revealed that the coating deposited at Ub = −65 V had the highest wear resistance (Kc = 2.68 × 10−15 m3 N−1 m−1) and the lowest friction (μ = 0.48).

A Tunable Polarization-Dependent Terahertz Metamaterial Absorber Based on Liquid Crystal

In this paper, a tunable polarization-dependent terahertz (THz) metamaterial absorber based on liquid crystal (LC) is presented. The measurement results show that absorption peak is at 239.5 GHz for a TE-polarized wave and 306.6 GHz for a TM-polarized wave, without exerting the bias voltage on the LC layer. An increase in bias voltage affects the orientation of LC molecules and causes redshifted resonant frequencies. By adjusting the bias voltage from 0 to 10 V, frequency tunabilities of 4.7% and 4.1% for TE- and TM-polarized waves, respectively, were experimentally demonstrated. Surface current and power loss distribution was analyzed to explain the physical mechanism of the absorber, while the absorption dependence on geometrical parameters and incident angles was also studied in detail. According to the obtained results, the proposed absorber is shown here to be capable of achieving tunable polarization-dependent absorption, and to have potential application in terahertz polarization imaging, terahertz sensing, and polarization multiplexing.

Diamond-like carbon thin films prepared by pulsed-DC PE-CVD for biomedical applications

In the present research, diamond-like carbon (DLC) thin films were applied on steel substrates by means of pulsed-direct current (DC) plasma-enhanced chemical vapor deposition (PE-CVD). The effects of bias voltage and deposition pressure on the films’ structure and properties were investigated. The Raman spectra of the films revealed features typical of G and D bands, indicating the formation of a DLC phase. The results demonstrate that the sp3 carbon fraction or the so-called diamond-like character of the DLC films increased with increasing bias voltage. Moreover, an increase in the bias voltage resulted in a decrease in the film thickness from 800 to 200 nm. Also, the DLC films prepared at a higher deposition pressure showed a higher fraction of sp2-bonded carbon – that is, graphitic domains. Furthermore, it was found that the variation in the bias voltage and deposition pressure also affected the internal stress values of the DLC films in a way that they increased from 1 to 11 GPa when the bias voltage was increased from 475 to 675 V. The effectiveness of DLC films formed on the steel substrates can pave the way for developing a new class of advanced materials to enhance the performance of stainless steel for biomedical applications.

Adhesive-deformation relationships and mechanical properties of nc-AlCrN/a-SiNx hard coatings deposited at different bias voltages

A series of Al-Cr-Si-N hard coatings were deposited on WC-Co substrates with a negative substrate bias voltage ranging from −50 to −200 V using cathodic arc evaporation system. A Rockwell-C adhesion test demonstrated that excellent adhesion was observed at lower bias voltages of −50 V and −80 V, while further increases in bias voltage up to −200 V led to severe delamination and worsening of the overall adhesion strength. X-ray diffraction and transmission electron microscopy analysis revealed a single phase cubic B1-structure identified as an AlCrN solid solution with a nanocomposite microstructure where cubic AlCrN nanocrystals were embedded in a thin continuous amorphous SiNx matrix. Coatings exhibited a 002-texture evolution that was more pronounced at higher bias voltages (≥−120 V). Stress-induced cracks were observed inside the coatings at high bias voltages (≥−150 V), which resulted in stress relaxation and a decline in the overall residual stresses.