Increasing Bias Voltage Research Articles

Nanoconfinement induced electroluminescence spectrum shift in organic light-emitting diodes

The demands for nanoscale organic light-emitting diodes (OLEDs) have been intensively increased due to theirs’ lightweight, flexibility, which is critical for next-generation displays. Although nanoscale OLEDs are ideal solutions for ultra-high-resolution displays, there are few related researches have been reported. Here we design and fabricate a series of nano-hole array OLEDs (NAOLEDs) with the pixel size from 160 nm to 10,000 nm, based on which, the electroluminescence (EL) spectral properties are systematically studied. It is found that the EL spectral peak produces a red shift and full width at half maximum (FWHM) increases with the decrease of the NAOLED pixel size under the same bias, while a blue shift as well as reduced FWHM are observed with the increase of bias voltage for the same pixel size of the NAOLED. The existence of exciton and exciplex generated from the different combination area is the critical reason of the spectrum change in the NAOLED, which is further verified by multiple fluorescence properties measurement. This research reveals basic principle of nano-confinement induced EL spectral properties change in the NAOLEDs which should heavily impact next-generation OLED and their applications in multi-functional systems, smart sensors, and electronic displays, etc.

Microstructure, mechanical, and wettability properties of Al-doped diamond-like films deposited using a hybrid deposition technique: Bias voltage effects

In this study, Al-doped diamond-like carbon (DLC) films were prepared using a hybrid deposition technique combining high-power impulse magnetron sputtering and pulsed direct current magnetron sputtering. The influence of bias voltage effects on the microstructure and properties of films were investigated. The results showed that the deposition rate of the films decreased after increasing the bias voltage, and the Al content also slightly decreased in the films. All films exhibited a cauliflower-like surface morphology, which was independent of the bias voltage. The maximum values of sp2/sp3 and ID/IG were achieved without bias voltage; the ratios then monotonously decreased with an increase in the bias voltage from −100 V to −400 V, which indicates that the content of sp3-C bonds has improved in films. The mechanical properties and the wettability of the films were also evaluated. The results revealed that the hardness, elastic modulus and residual stress of the films increased with increasing bias voltage. The highest hardness occurred at −400 V, and the high sp3-C fraction and residual stress were beneficial to the hardness enhancement. All films exhibited a water contact angle greater than 100°, implying that the film possessed good hydrophobic performance. Specifically, when deposited at −300 V, the film presented a combination of superior properties, namely, a relatively high hardness and strong hydrophobic behavior.

Structure and mechanical properties of multi-principal-element (AlCrNbSiTi)N hard coating

Multi-principal-element nitride (MPEN) has great potential in the application of cutting tool protective coatings. However, the investigation of the nanostructured MPEN coatings is still insufficient. In this paper, we study (AlCrNbSiTi)N MPEN coatings deposited at various bias voltages ranging from −50 to −200 V, using RF magnetron sputtering technique. The microstructure and mechanical performance e of the coatings are systematically investigated. The results show that the (AlCrNbSiTi)N coating forms an FCC crystal structure and exhibits columnar grains. In the elongated grain, there exists a nanocomposite structure with (AlCrNbTi)N nanograins surrounded with crystallized Si3N4 interfaces. The mechanical performance and wear resistance of the coating is enhanced first and then degraded with the increasing bias voltage. The coating deposited at −150 V exhibits the highest hardness and elastic modulus of 39.8 and 436.7 GPa, respectively, and has the lowest wear rate of 6.7 × 10−6 mm3·N−1·m. These results show that the (AlCrNbSiTi)N coating is a competitive candidate for protective coating applications.

Graphitic regulation of C/Cr composite film for 304 stainless steels bipolar plates

This work aims to deposit conductive and corrosion-resistant protective coatings for bipolar plates in proton exchange membrane fuel cells. The films' graphitization degree is regulated to obtain excellent conductivity and corrosion-resistance. A series of Cr-doped graphite-like carbon films with different substrate bias voltages and deposition times (600 V 2 h, 900 V, 2 h, 900 V, 3 h; and 1200 V, 2 h) were prepared on 304 stainless steels by plasma enhanced chemical vapour deposition method combined with magnetron sputtering technique. The results showed that an increase of substrate bias voltage increased substrate current density. The substrate current density was the highest when the substrate bias voltage was 1200 V at 400 °C. Subsequently high substrate bias voltage caused ID/IG to increase, indicating that the increase of energy contributes to graphitisation of the films. The particle size of the films decreased with increasing bias voltage, and the cross section showed that the prepared films were homogeneous and distinctive. The interface contact resistance (ICR) of the films at 1.4 MPa decreased with an increase of substrate bias voltage, showing that deeper graphitisation improves the conductivity of the films. The coated 304 stainless steels showed a considerable decrease in self-corrosion current density in comparison to the 304 stainless steel substrate. According to the VDI-3198 indentation test, the adhesion of the films and substrate belongs to the HF1 level. After long-term service, chromium oxides, iron oxides, and defects were formed on the surface, leading to an increase in ICR. The study revealed that the optimum technical parameters were 1200 V and 2 h.

Microstructure and tribological properties of CrAlTiN coating deposited via multi-arc ion plating

Developments in engine technologies have led to reduction in engine volume and increase in engine power. Thus, valve seat ring components in engines should have high wear resistance. In this study, a high-performance coating on the surface of valve seat material was investigated. The CrAlTiN coating was prepared on the surface of vermicular graphite cast iron, a common material of valve seat ring, with a multi-arc ion plating technology. Experimental results showed that the distribution of crystal clusters was relatively uniform as bias voltage increased from − 100 V to − 400 V and large droplets appeared at low bias voltage. As bias voltage increased, the sizes and number of droplets decreased, and pits appeared. The increase of bias voltage was beneficial to the formation of new phase of CrAlTiN coating. At bias voltages of − 300 and − 400 V, the phase composition was mainly TiN, AlN, CrN, and small amounts of Al2O3, Cr2O3, Ti2O3, and Cr. The adhesion, nano-hardness, and elastic modulus of the coating increased and then decreased with increasing bias voltage. When the bias voltage was − 300 V, the maximum adhesion was 61 N, the nano-hardness was 26 GPa, and the elastic modulus was 268 GPa. Moreover, the lowest friction coefficient was observed (0.4). The wear mechanism of CrAlTiN at different bias voltages was abrasive wear.

Above-room Curie temperature and barrier-layer-dependent tunneling magnetoresistance in 1T-CrO2 monolayer based magnetic tunnel junctions.

van der Waals (vdW) heterostructures based on two-dimensional (2D) ferromagnetic materials hold great potential applications in spintronics. Using the density functional theory (DFT) method and first-principles quantum transport simulation, we studied the structures, magnetic properties and spin-resolved transport of 1T-CrO2 monolayer (ML) based vdW magnetic tunnel junctions (MTJs). Owing to a high Curie temperature (TC) of 392 K and a moderate magnetic anisotropy energy (MAE) of 94 μeV of the ferromagnetic 1T-CrO2 monolayer, Cu(111)|CrO2|nML-Gr|CrO2|Cu(111) MTJs were built. Our results reveal that their tunneling magnetoresistance (TMR) ratios are dependent on the number of Gr barrier layers within a working bias voltage of 1 V. For the thin barrier layers (n = 1-2), the maintained TMR ratios can reach a giant value of about 1 × 104%, while there appears a decreasing trend with the increasing bias voltage for thick Gr layers (n = 3-5). The barrier-layer-dependent phenomenon is attributed to the decreasing transmission magnitude with increasing bias voltage in a parallel configuration (PC), which is as small as that in an anti-parallel configuration (APC) eventually. Our results would provide some guidance for future experimental fabrications of these 2D materials based MTJs.

Bias-dependent tunneling anisotropic magnetoresistance in antiferromagnetic Pd-doped FeRh-based junctions

We report the bias-dependent tunneling anisotropic magnetoresistance (TAMR) in antiferromagnetic α′-Fe(Rh0.98Pd0.02)/MgO/γ-Fe(Rh0.98Pd0.02) junctions. The TAMR effect is driven by the antiferromagnetic-ferromagnetic phase transition of α′-Fe(Rh0.98Pd0.02) and concomitantly large variation of the density of states (DOS) near the Fermi level. It exhibits polarity reversion behavior with increasing bias voltage, i.e., negative and positive polarities for low and high bias voltages, respectively. Such bias-dependent TAMR is comprehended by first-principle calculations, where a crossing point and subsequent magnitude-reversion emerge between the DOS of antiferromagnetic and ferromagnetic phases of α′-Fe(Rh0.98Pd0.02). Harnessing the tunneling behavior by a feasible bias voltage in an antiferromagnet-based junction is a frontier of great promise in antiferromagnet spintronics.

Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin-filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study of two-dimensional materials has expanded to the field of spintronics. Intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 have received much attention due to their nearly spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design magnetic tunnel junctions (MTJs) of Cu/CrI3/Cu and Cu/CrBr3/Cu with electrodes of Cu(111) and a tunneling barrier of four-monolayer CrI3 or CrBr3. Our first-principle calculations combined with non-equilibrium Green’s function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin-filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that a negative differential resistance effect is observed in the CrBr3-based MTJ. The differences in spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the physics inside the device, including the spin-dependent density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJs.

Unconventional bias dependence of tunnel magnetoresistance induced by the Coulomb blockade effect

In conventional magnetic tunnel junctions (MTJs), the tunnel magnetoresistance (TMR) monotonically decreases with increasing bias voltage, which limits the bias voltage range for the operation of MTJs. In our study, using double-barrier MTJs composed of Fe/MgO/Fe/γ-Al2O3 grown on a Nb-doped SrTiO3 substrate, we demonstrate unconventional bias dependences of the TMR, in which the TMR ratio increases with increasing bias voltage. We reveal that this behavior originates from the sharp giant resistance peak near zero bias likely induced by the Coulomb blockade effect via Fe impurities in γ-Al2O3, which are diffused from the Fe layer. The observed TMR ratio is 23% at a bias voltage of −4 V at 3.5 K, which is a very high value in this large bias voltage range. Our results offer a novel way to improve the bias voltage dependence of TMR.

A Modelling of Tunnelling Current through a Trapezoidal Potential Barrier by Using Exponential Wavefunction Approach

A tunnelling current through a trapezoidal barrier potential has been modelled. The transmittance is determined using the exponential wavefunction approach method. Furthermore, the transmittance is used to calculate the tunnelling current density by applying the Gauss-Laguerre quadrature method. The simulation results show the increasing bias voltage causes the raising tunnelling current, and an increase of temperature is proportional to the tunnelling current.

A Modelling of Tunnelling Current through a Trapezoidal Potential Barrier by Using Exponential Wavefunction Approach

A tunnelling current through a trapezoidal barrier potential has been modelled. The transmittance is determined using the exponential wavefunction approach method. Furthermore, the transmittance is used to calculate the tunnelling current density by applying the Gauss-Laguerre quadrature method. The simulation results show the increasing bias voltage causes the raising tunnelling current, and an increase of temperature is proportional to the tunnelling current.

Effect of bias voltages on microstructure and properties of (TiVCrNbSiTaBY)N high entropy alloy nitride coatings deposited by RF magnetron sputtering

(TiVCrNbSiTaBY)N high entropy alloy nitride (HEAN) coatings have been deposited onto Si (100) and cemented carbide substrates by radio frequency magnetron sputtering. The deposition is carried out at different bias voltages to study its influence on microstructure, morphology, mechanical properties and tribological behaviour of the coatings. Grazing Incidence X-Ray Diffraction (GIXRD) technique shows that all coatings exhibit single NaCl-type face-centered cubic (FCC) crystal structure, while the preferred orientation of the crystal structure is greatly affected by the bias voltages. High resolution transmission electron microscopy (TEM) reveals that the structure of the coatings is a mixture of amorphous-like phase and FCC crystal structure, which is in agreement with GIXRD data. Cross-sectional Scanning Electron Microscopy (SEM) images exhibit that the columnar structure of the coatings gradually transforms into a featureless dense structure with the increase of bias voltage. SEM and Atomic Force Microscopy reveal that the surface morphology become smoother with increasing bias voltage. The (TiVCrNbSiTaBY)N HEAN coating deposited at a specific bias voltage exhibit a high hardness of 32.2 GPa. The friction coefficient is significantly influenced by the variation of the coatings surface roughness. Tribological tests for coating deposited without and at low bias voltage show that the wear behavior of the coatings is severe abrasive wear and adhesive wear, while at high bias voltage the slight abrasive wear appears. By applying the substrate bias voltage, the (TiVCrNbSiTaBY)N coatings exhibit excellent mechanical and tribological performance, which can be a promising candidate for protective coating in cutting tools or components.

Enhanced Dielectric Relaxation in Self-Organized Layers of Polypeptides Coupled to Platinum Nanoparticles: Temperature Dependence and Effect of Bias Voltage

Using alternative current impedance spectroscopy, we investigate the dynamical conductivity of hybrid nanomaterials composed of helical polypeptide layers containing platinum nanoparticles (PtNP). The electrical characteristics of the self-organized poly(γ-benzyl-l-glutamate) (PBGL) in bidimensional lamellar assembly in the presence of Pt nanoparticles are well modeled and described by a single equivalent circuit of parallel resistance and capacitance. The latter are determined using a comparison between the measured and calculated Nyquist plots, which allows extracting the characteristic relaxation time and frequency of the dipolar relaxation process. We found that the relaxation frequency in the PBLG–PtNP hybrid materials is enhanced by 4 orders of magnitudes compared to pure PBLG, which indicates a much faster dielectric relaxation in PBLG–PtNP due to dipole orientation and dipole–dipole interactions. The temperature dependence of the relaxation time is analyzed using Arrhenius plots, from which the activation energy of the relaxation process is found to be around 0.1 eV. Such a value close to the peptide vibration energy of the PBLG indicates a vibration-assisted relaxation process and a polaronic charge transport mechanism. An advantage of the PBLG–PtNP nanocomposite material is that the activation energy can be finely tuned by the PBLG degree of polymerization. Finally, an important outcome of this work is the investigation of the dielectric relaxation process in PBLG–PtNP under applied DC bias. We found that the activation energy decreases with increasing bias voltage for all degrees of polymerization of the PBLG molecule. This effect is interpreted in terms of electric field-induced alignment of the dipoles and of increased mobility of the polaronic charge carriers. The presence of piezoelectricity in the hybrid material gives the possibility to use the DC bias as a simple mean of monitoring the dynamical conductivity involving polaronic states.

Study on Preparation and Properties of TiCrAlN Film on the Surface of H13 Die Steel by Multi-arc Ion Plating

This paper studies the influence of substrate bias on the structure and performance of multi-arc ion plating TiCrAlN film on the surface of H13 die steel. Using multi-arc ion plating technology, by controlling and adjusting the size of the substrate bias, different structures and properties are prepared on the H13 die steel substrate. The research results show that when the substrate bias voltage gradually increases, the number of large particles gradually decreases, the particle distribution becomes more and more uniform, and the density of the film increases. When the substrate bias voltage rises to 100V, the number of large particles on the film surface is the least, the surface structure is evenly distributed, and the surface quality of the film is the best. The micro-hardness and film-base bonding force of the film increase with the continuous increase of the substrate bias voltage. At 100V, the film’s micro-hardness and film-base bonding force reach the maximum value, but when the substrate bias voltage exceeds a certain range, The microhardness of the film and the bonding force of the film base are greatly reduced; with the increase of the bias voltage, the corrosion resistance of the film increase, and the 100V performance reaches the best. The influence mechanism of substrate bias on the corrosion resistance of the film was analyzed.

Corrosion Behavior of Niobium-Coated 316L Stainless Steels as Metal Bipolar Plates for Polymer Electrolyte Membrane Fuel Cells.

Niobium was coated on 316L stainless steel by pulsed direct-current (DC) magnetron sputtering to improve corrosion behavior. The applied bias voltage highly affected the microstructure and crystallographic features, which lead to improved corrosion behavior. Due to the increased bias voltage, the microstructure of the niobium coating layer presented a smaller crystallite size and a densified structure, which obviously reduced the number of pinholes in the coated layer. Additionally, an increase in the degree of orientation toward the (110) plane, the most densely packed plane, lead to reduced dissolution of metal ions. Therefore, a pure niobium coating layer effectively protected the metal bipolar plate from a highly corrosive environment of polymer electrolyte membrane fuel cell (PEMFC) stacks. In particular, higher bias voltages of 600 and 800 V induced improved corrosion resistance, which satisfied the demand for the bipolar plate.

An alternative approach to the tribological analysis of Si-doped DLC coatings deposited with different bias voltages using Raman spectroscopy mapping

A series of diamond-like carbon (DLC) coatings were deposited with increasing bias voltage using magnetron sputtering techniques. Structural changes were observed in the sp2-configuration across the films which were accompanied by a slight increase in the sp3 fraction. With an increasing bias voltage, the thermal stability of the coatings increased from 300 to 450 °C. Oxygen diffusion was observed through the coating as a result of the high-temperature annealing and found to slow down with increasing bias voltage. Coefficients of friction (COF) remained stable with temperature for the individual coatings, with the softer films reporting the lowest COF. Our approach employed Raman spectroscopy to map the wear tracks at different temperatures, providing a deeper understanding of the coating performance and suggested maximum flash temperatures endured during testing.

Study on proton-induced single event effect of SiC diode and MOSFET

Proton-induced degradation and catastrophic failures in 650 V SiC diode and 900 V SiC MOSFET under different bias voltage and different proton energy are investigated. The experimental results show that when the bias voltage of SiC diode and MOSFET reaches 88% of rated voltage, 20 MeV protons will not cause the single event burnout (SEB) of two SiC devices. When SiC devices are burned out, a wave-shaped pulse current appears, the pulse current peak value gradually decreases, and the total pulse current width is within 5 microseconds. With the increase of bias voltage, the SEB fluence of SiC device is significantly reduced. After SiC diode is burned out, its reverse breakdown voltage is lower than 1 V, and the forward current when device has not been turned on is up to 8 orders of magnitude higher than before irradiation; the reverse breakdown voltage of SiC MOSFET is also lower than 1 V after burning out, only some SiC MOSFETs still maintain transfer characteristics under a voltage bias of 700 V, and the gate-source current has increased by 7–8 orders of magnitude compared to before irradiation. The Monte Carlo simulation results show that the linear energy transfer (LET) of 20 MeV proton in the epitaxial layer is lower than 2 MeV·cm2/mg, which is not enough to generate charge required for SEB. And the randomness of interaction between protons and device materials leads to different SEB fluences for SiC devices under different proton energies.

Temperature assessment of Si1-xGex source/drain heterojunction NT-JLFET for gate induced drain leakage ‒ A compact model

In this paper, we have investigated the impact of temperature ( T ) and drain bias voltage ( V ds ) on gate induced drain leakage (GIDL) in SiGe Source/Drain heterojunction silicon-nanotube junctionless field effect transistor (S/D Si-NT JLFET). We developed a temperature dependent model for surface potential, electric field E Z , L-BTBT induced I GIDL and full drain current I ds using 2-D Poison equation with suitable boundary conditions. We have also examined impact of temperature (activation energy) and drain bias voltage (electric field) on L-BTBT induced I GIDL . It is found that the increase in drain bias voltage causes 31.1% rise in I GIDL and elevation in temperature has 29.4% increase in I GIDL . Furthermore, we have examined impact of temperature on transconductance ( g m ) and output conductance ( g d ). The results demonstrated that temperature and drain bias voltage has significant impact on SiGe S/D NTJLFET, however, it is considerably less than the NTJLFET. • A compact model of drain current and impact of temperature along with drain bias has been studied in SiGe source/drain heterojunction NTJLFET. • It is found that the increase in drain bias voltage cause 31.1% rise in I GIDL , however, elevation in temperature increase I GIDL by 29.4%. • The elevation in temperature results in reduced tunnelling width at channel-drain interface and it leads to earlier triggering of L-BTBT induced GIDL. • The higher drain voltage combined with higher temperature has more influence on the L-BTBT induced GIDL.

Effect of Bias Voltage on Microstructure and Properties of Tantalum Nitride Coatings Deposited by RF Magnetron Sputtering

TaNx coatings were deposited by RF magnetron sputtering with different bias voltages. The growth morphology, crystalline structure, chemical bond structure, hardness and elastic modulus, adhesion strength and tribological performance of the coatings were studied as a function of the bias voltage. The results showed that an increasing bias voltage refines the coating grains and facilitates structure densification. Simultaneously, the structure of the TaNx coatings transfers from a composite structure consisting of TaN and Ta2N crystals, through a single composite mainly composed of the Ta2N crystal, to an amorphous structure as the bias voltage increases from low to high, indicating that the phase composition of the TaNx coatings can be varied by the bias voltage. The coating composed of Ta2N crystal showed a good overall performance including enhanced hardness, enhanced adhesive strength, and good tribological performance with enhanced wear resistance and a low friction coefficient of 0.18.

Tunable multiferroic and forming-free bipolar resistive switching properties in multifunctional BiFeO3 film by doping engineering

The advent of multiferroic-based materials has opened the plethora for high tunable multifunctional materials and ultra-fast operation for future non-volatile memory technology. Multifunctional rhombohedral Bi0.94Y0.06Fe0.95Mn0.05O3 (BYFMO) film is grown on fluorine-doped tin oxide to investigate the electromechanical and resistive switching properties in Ag/BYFMO/FTO RRAM configuration. UV–visible absorbance spectra reveal the semiconducting behavior of BYFMO, and the band-gap is found to be 2.37 eV. The magnetic hysteresis curve manifests the soft ferromagnetic nature by suppressing the spiral spin modulated structure, supported by MFM imaging. The Y-Mn co-doped BFO possesses highly tunable piezoelectric and ferroelectric features with maximum domains preferred along 710 and 1090. Lateral domain growth is observed with the increase in tip bias voltage. The Ag/BYFMO/FTO RRAM shows distinct bipolar resistive switching behavior at the SET (ON), and RESET (OFF) processes are obtained at voltage VSET = +1.7V and VRESET = −2.8V, respectively. The memory window (ON/OFF) between high resistance state and low resistance state is about ~ 100, which can be sustained up to 100 testing cycles and 103s without any degradation, indicating that the BYFMO based device exhibits better endurance and retention properties. Moreover, the resistive switching mechanism of the device can be well explained by space charge limited current conduction, which is well supported by conducting a filamentary model. With excellent piezoelectric and resistive switching performance, the multifunctional BYFMO has enough potential for future non-volatile memory technology.