Increasing Bias Voltage Research Articles

Characterization and antibacterial activity of co-sputtered Cu-doped TiO2 coatings deposited on Ti6Al4V alloy

Copper has gained increased interest because of its important role in metabolism and antimicrobial activity. In this study, composite target material of Ti and Cu was used to deposit TiO2 coatings doped with copper on Ti6Al4V alloy. The aim was to examine the influence of the applied bias during the deposition of Cu-doped TiO2 coating by sputtering in a glow-discharge in a pure O2 atmosphere for a deposition time of 240 min. Different substrate values, selected from 0 to -150 V, were used in the process. The increase in bias voltage from -50 to - 150 V decreased the thickness of the oxide coatings and improved their adhesion to the substrate while increasing the Cu2O phase at the expense of a CuO phase decrease. Simultaneously, the increase in bias voltage decreased Cu content from about 32 wt% for the -50 V biased down to around 11 wt% for the -150 V biased specimens. The antimicrobial efficacy against E. coli estimated by direct contact experiments on the top of the uncoated (control) and coated Ti6Al4V alloy revealed about 94% inhibition for the -50V biased down to around 37% for the -150 V biased coatings as opposed to the control.

Enhancing the bond strength of magnetron-sputtered copper layers on polyimide and polyether ether ketone surfaces through surface modification

This study explores the fabrication of composites involving polyimide (PI) and polyether ether ketone (PEEK) resins with Cu using chemical treatment and sandblasting, followed by plasma cleaning in a vacuum environment charged with Ar. To enhance the bonding strength of Cu to PI and PEEK, vacuum magnetron sputtering was used to deposit an intermediate transition layer of titanium and a plated seed layer of Cu onto the resin. For PI/copper composites, the copper layer’s highest bonding strength was achieved through sandblasting and plasma cleaning for 150 s at a bias voltage of 100 V. For PEEK/Cu composites, the optimal bonding strength of the copper layer was observed after 80 s of plasma cleaning. Surface roughness is important in the bonding strength of the copper layer. Additionally, the Ti transition layer strengthens bonding forces between Cu and both PI and PEEK. X-ray photoelectron spectroscopy revealed Ti–O bond formation with oxygen in the resins and Ti–C bonds within the carbon, indicating chemical interactions that bolstered Cu adhesion to resins. Adjusting the bias voltage had varying effects on the bonding strength of resin/Cu. For PI/Cu, the bonding force decreased with increasing bias voltage (20–150 V) owing to excessive bias voltage causing surface defects on the plated Cu layer, which reduced the density of the plated Cu layer. Conversely, the PEEK/Cu bonding force initially increased with increasing bias voltage due to enhanced surface bombardment. Beyond an optimal point, the bonding force in PEEK/Cu decreased due to unfavorable effects on layer density.

Photo-emission electron gun and electron optical simulation for ultrafast scanning electron microscope

Ultrafast scanning electron microscope (USEM) integrates pump-probe technique with microscopic imaging, enabling the visualizing of photon-induced surface charge dynamics with high spatial and temporal resolution. This capability is crucial for high-resolution detection of semiconductor surface states and optoelectronic devices. This work discusses the parametric design of a thermionic emission electron gun that has been modified into a photoemission electron gun, based on a home-built ultrafast scanning electron microscope. Given that the dose of the photoemitting electron beam is usually much lower than that of thermionic emission, the transition to photoemission requires the removal of the self-bias voltage function of the original electron microscope power supply to ensure the normal operation of the Wehnelt electrode. We quantitatively analyze the dependence of bias voltage, cathode, Wehnelt electrode, and anode on the position, size and divergence angle of crossover, which helps to improve the parameter adjustment of the modified electron gun. The analysis results indicate that if the distance between the Wehnelt electrode and the anode is adjusted from 8 to 23 mm, the distance between the filament and wehnelt can be changes from 0.65 to 0.45 mm to cooperate with the bias adjustment, so that the normal use of high-resolution thermionic emission mode, low voltage mode and photoemission mode can be realized. Subsequently, the effect of the mirror’s position on the electron optical path is analyzed. It is found that when the anode is raised 1.4 mm above the mirror, the influence on the electron optical path can be ignored. Additionally, the zero-of-time and temporal broadening of the photo-electron pulse are further simulated. The results indicate that with the increase of bias voltage, the time zero of photoemission will be delayed and the temporal broadening will become larger. This study lays a foundation for the future development of ultrafast electron microscope and the design of photoemission electron sources.

Efficient spin filtering through Fe4GeTe2-based van der Waals heterostructures.

Utilizing ab initio simulations, we study the spin-dependent electronic transport characteristics within Fe4GeTe2-based van der Waals heterostructures. The electronic density of states for both free-standing and device-configured Fe4GeTe2 (F4GT) confirms its ferromagnetic metallic nature and reveals a weak interface interaction between F4GT and PtTe2 electrodes, enabling efficient spin filtering. The ballistic transport through a double-layer F4GT with a ferromagnetic configuration sandwiched between two PtTe2 electrodes is predicted to exhibit an impressive spin polarization of 97% with spin-up electrons exhibiting higher transmission probability than spin-down electrons. Moreover, we investigate the spin transport properties of Fe4GeTe2/GaTe/Fe4GeTe2 van der Waals heterostructures sandwiched between PtTe2 electrodes to explore their potential as magnetic tunnel junctions in spintronic devices. The inclusion of monolayer GaTe as a 2D semiconducting spacer between F4GT layers results in a tunnel magnetoresistance of 487% at a low bias and decreases with increasing bias voltage. Overall, our findings underscore the potential of F4GT/GaTe/F4GT heterostructures in advancing spintronic devices based on van der Waals materials.

Tuning magnetoresistance of chromium chloride tunnel junction through the interface and multi-field effect

<sec>Magnetic tunnel junctions (MTJs) serve as essential platforms for investigating spin transport properties, magnetic phase transitions, and anisotropy in magnetic materials. Recently two-dimensional van der Waals antiferromagnetic insulators like chromium chloride (CrCl<sub>3</sub>) or chromium iodide (CrI<sub>3</sub>) have been used to develop spin-filtering magnetic tunnel junctions (sf-MTJs), improving the device performance for material property exploration and spintronic applications. However, it is crucial to recognize that the spin-filtering effect is not the sole determining factor of tunneling magnetoresistance (TMR) in these junctions; the interface magnetic exchange interactions and adjustable electrode density of states (DOS) fluctuations, response to applied electric or magnetic fields, can also influence the tunneling current.</sec><sec>In this study, we fabricate MTJ devices by using mechanically-exfoliated few-layer CrCl<sub>3</sub> as the tunnel barrier and few-layer graphene (FLG) as electrodes through dry transfer technique. Conducting low-temperature quantum transport measurements, we observe unconventional TMR behaviors, including bias-voltage-dependent TMR, oscillatory tunneling current under high magnetic fields, and tunable tunneling current via gate voltage.</sec><sec>A qualitative model of elastic tunneling current is employed to analyze the spin and band characteristics of the MTJ device. The observed bias-voltage-dependent TMR is attributed to the changes in the tunneling mechanism due to magnetic proximity effect, which induces magnetization in the FLG electrode near the FLG/CrCl<sub>3</sub> interface. The antiparallel alignment of polarized spin to CrCl<sub>3</sub>’s magnetization results in injected charge carriers facing a higher tunnel barrier, leading to negative TMR at lower bias voltages. As the bias voltage increases, the magnetic proximity effect lessens, and the device reverts to its conventional spin-filtering functionality. The oscillatory tunneling current is explained by the graphene electrode’s quantum oscillatory density of states behavior under vertical magnetic fields, which can be controlled by the applied gate voltage.</sec><sec>This study contributes to the understanding of previously unexplored TMR phenomena in two-dimensional MTJs, deepening our insights into carrier transport properties in these heterostructures and broadening avenues for investigating the physical properties of two-dimensional magnetic materials and their spintronic applications.</sec>

Heavy ion single event effect in double-trench SiC metal–oxide–semiconductor field-effect transistors

In this paper, experiments on 208 MeV Ge ion irradiation with different source-drain bias voltages are carried out for the double-trench SiC metal–oxide–semiconductor field-effect transistors, and the physical mechanism of the single event effect is analyzed. The experimental results show that the drain leakage current of the device increases more obviously with the increase of the initial bias voltage during irradiation. When the bias voltage is 400 V during irradiation, the device has a single event burned at a fluence of 9×10<sup>4</sup> ion/cm<sup>2</sup>, and when the bias voltage is 500 V, the device has a single event burned at a fluence of 3×10<sup>4</sup> ion/cm<sup>2</sup>, so when the LET value is 37.3 MeV·cm<sup>2</sup>/mg, the SEB threshold of DUT does not exceed 400 V, which is lower than 34 % of the rated operational voltage. The post gate-characteristics test results show that the leakage current of the device with a bias voltage of 100 V does not change significantly during irradiation. When the bias voltage is 200 V, the gate leakage and the drain leakage of the device both increase, so do they when the bias voltage is 300 V, which is positively related to bias voltage. In order to further analyze the single particle effect mechanism of device, the simulation is conducted by using TCAD tool. The simulation results show that at low bias voltage, the heavy ion incident device generates electron-hole pairs, the electrons are quickly swept out, and the holes accumulate at the gate oxygen corner under the effect of the electric field, which combines the source-drain bias voltage, leading to the formation of leakage current channels in the gate oxygen layer. The simulation results also show that at high bias voltage, the electrons generated by the incident heavy ion move towards the junction of the N<sup>–</sup> drift layer and the N<sup>+</sup> substrate under the effect of the electric field, which further increases the electric field strength and causes significant impact ionization. The local high current density generated by the impact ionization and the load large electric field causes the lattice temperature to exceed the melting point of silicon carbide, causing single event burnout. This work provides a reference and support for studying the radiation effect mechanism and putting silicon carbide power devices into aerospace applications.

Structure and tribological properties of multiphase carbon coatings fabricated by multi-arc ion plating

Carbon coating with excellent wear resistance will play a significant role in protecting metal materials, especially in piston rings. In this work, a series of multiphase carbon coatings were fabricated by multi-arc ion plating under different bias voltages ranging from 0 to 160 V. The microstructures were investigated by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Raman Spectroscopy and X-ray Photoelectron Spectrometry (XPS). The mechanical properties and tribological performances were measured by nanoindentation, scratching tester and reciprocating tribometer. The results demonstrated that the multiphase carbon coatings mainly compose different phases, including amorphous carbon, fullerene-like carbon, nanographite, nanodiamond and C60. The sp2 hybrid bond existed in the form of multi-bent carbon rings and increased from 46.82 % to 52.01 % with the increase of bias voltage. The content of seven-membered carbon rings (7A1) increased first and then decreased, with the highest value of 18.05 %. The hardness values of the coatings ranged from 18.33 ± 3.55 GPa to 33.88 ± 2.26 GPa. When Vickers indenter was pressed into the coating under high load, the coating exhibited good load strength and toughness. Under the load of 10 N, the friction coefficient between the coating and Φ3 mm 316 stainless steel (SS) balls in fresh 5 W-30 oil was about 0.13. In the degraded oil, the highest friction coefficient was 0.20, and the lowest was 0.11. The grinding ball's surface looked to have sustained severe damage, but there was no visible damage to the coating structure at the worn tracks. There was no significant difference in the coating surface profile curves before and after rubbing exhibiting super wear resistance of coatings.

Effect of bias voltage on the erosion performance of TiAlSiN coatings on TC6 substrate by high power impulse magnetron sputtering

TiAlSiN coatings were deposited on TC6 substrates by high power impulse magnetron sputtering at various bias voltages for the improvement of titanium alloy anti-sand erosion performance. The effect of bias voltage on the composition, microstructure and mechanical properties were investigated by X-ray photoelectron spectroscopy, X-ray diffractometer, transmission electron microscopy, scanning electron microscopy, Rockwell-C indentation, scratch testing and nano nanoindentation. The erosion performance was evaluated at the impingent angles of 30° and 90° respectively in a sand blasting tester. With the application and increase in bias voltage, the discharge current increases from ∼87 A to ∼210 A. The coatings exhibit face center cubic structure, mainly composed of the (Ti,Al)N nanocrystallites and Si3N4 matrix. The preferred orientation shifts from (200) to (220) in the range of 0∼−150 V, but goes back to (200) at −200 V. The surface nodular defects and deposition rate are gradually reduced, yet the sectional structure becomes much denser. The residual stress is compressive and continually grows, whereas the adhesion strength, hardness (H), Young's modulus (E) and H/E ratio gradually increase before decreasing, arriving at maximum values of ∼68 N, ∼37.53 GPa, ∼339.9 GPa and 0.11 respectively at −150 V. The erosion resistance of the TiAlSiN coatings is consistent with these mechanical changes at various bias voltages and is also optimal at −150 V, which is ∼14 times that of TC6 substrate. The failure mechanism comes from coating brittleness nature, fractured chips and microcracks, regardless sand erosion angles, yet the driving forces are different.

Reactive remote plasma sputtering of TiOx thin films and controlled growth of textured single-phase rutile using rf substrate biasing

Titanium oxide (TiOx) thin films were deposited by remote plasma sputtering (RPS) with the use of rf substrate bias onto unheated and water-cooled glass, Si, and Kapton substrates. The rf remote plasma power was kept constant (2.0 kW) and the properties of the films were studied as a function of deposition rate and substrate bias voltage. Four different reactive processes at four different deposition rates were developed under zero bias conditions by altering the target bias voltage and the flow of oxygen to give highly transparent TiOx films. These processes were studied with varying substrate bias voltage and the film structural, optical, and surface properties were investigated by GI-XRD, SEM, transmission, and sessile drop measurements. The changes in film structure and properties observed were related to the plasma conditions of the RPS system, investigated by dc electrical probe and OES measurements, and compared with other observations for films deposited under energetic conditions in the literature. All films deposited under zero bias conditions exhibited amorphous structures in GI-XRD and SEM images. Sufficient application of substrate bias was seen to promote columnar growth in cross-sectional SEM images and to crystallise phase pure rutile with no detection of the anatase phase in GI-XRD. Rutile bearing films were noted for their change in optical properties. Further increase of the substrate bias voltage caused a change in the texture of the rutile films from a low-energy [110] preferred orientation to a high-energy [101] and [002] preferred orientation. Contact angles of water with deposited films were found to increase with increasing substrate bias voltage and decreasing deposition rate. Film stress was also found to be influenced mainly by the substrate bias voltage process parameter.

Effects of bias voltage on the structure, mechanical properties and tribological properties of TaBx films at elevated temperatures

Transition metal boride (TMBx) show the potential application as protective films at extreme environment due to their high hardness, but their low toughness limits reliability. In order to achieve both excellent mechanical and high wear resistances of the films, the microstructure of TaBx films deposited by magnetron sputtering were regulated by varing the substrate bias voltages. With the increase of the higher bias voltage, the B content of TaBx films decreases and the crystallinity of the TaBx films is enhanced. Meanwhile, the microstructure of TaBx films transforms from fibrous to dense columnar and then to granular structure with the increase of the bias voltage. The hardness and elastic modulue decrease then increase when the substrate bias voltage increases from 0 V to −240 V. The films exhibit a super high hardness of 86.07 GPa at the bias voltage increases of −180 V. The dislocation motion inhibited by the lattice defects lead to the super high hardness and a mild fracture toughness (KIC = 1.20 MPa m1/2) . For the high hardness and relatively moderate fracture toughness, the TaBx film deposited at a bias voltage of −180 V show a lower wear rate (∼1.86 × 10−6, ∼5.22 × 10−6 mm3/Nm) at room temperature and 600 °C. Meanwhile, the hardness (77.5GPa) and thermal stability of −180 V films were mantained after annealing.

Influence of plasma grid bias on the beam extraction of RF driven negative hydrogen ion source

In the negative hydrogen ion sources, the positive bias of the plasma grid with respect to the discharge chamber is often used to suppress co-extracted electrons. Because most of the co-extracted electrons are magnetically deflected onto the extraction grid, the difference between the extraction and acceleration current (i.e., Iext − Iacc) is commonly used to represent the number of co-extracted electrons. In the single-driver RF negative ion source at ASIPP, the variation of Iext − Iacc with the plasma grid bias voltage was accidentally found to have different trends with and without the Cs seeding. When the current density of Iacc (regarded as JH-) was larger than 120 A/m2 during Cs conditioning, the Iext − Iacc fell first and then rose with the increasing bias voltage. The previous research results from NIFS that the beam optics were changed by the bias voltage can be used to explain the phenomenon. In this paper, the electron temperature (Te) in front of the plasma grid was found to increase from the Langmuir probe measurement, when the bias voltage was higher than a threshold of 4.5 V to the float potential. Interestingly, the bias voltage corresponding to the trough of Iext − Iacc was higher than the float potential—a similar value of 4.1 V to the threshold of Te increasing. Since the negative hydrogen ions are easily destroyed by the high-energy electrons, the increasing of Te may also cause the change of beam optics and the increase in co-extracted electrons. The electron energy distribution function was used to explain the change of plasma parameters in front of the plasma grid.

Effects of Bias Voltage and Substrate Temperature on the Mechanical Properties and Oxidation Behavior of CrWSiN Films

CrWSiN films were prepared through the co-sputtering technique, and the process variables were substrate bias voltage and temperature. The mechanical properties of hardness and elastic modulus of the CrWSiN films were dominantly affected by their average crystallite size and by substrate bias voltage and temperature. Moreover, the effect of substrate temperature was more evident than that of substrate bias. The highest hardness and elastic modulus of 42.6 and 459 GPa, respectively, were obtained for the Cr20W28Si9N43 film fabricated at a substrate temperature of 400 °C, which exhibits an evident advantage over the 25.0 and 323 GPa values for the Cr21W28Si9N42 film fabricated at room temperature. In contrast, an increase in negative bias voltage to −100 V on the substrate decreased the mechanical properties compared to one prepared using a similar process without applying the negative bias voltage. The oxidation resistance of the Cr-enriched Cr37W4Si10N49 and Cr37W5Si10N48 films was superior to that of the Cr20W28Si9N43 films with near-equal Cr and W contents annealed at 900 °C in air. The formation of a surficial Cr2O3 layer plays a vital role in restricting subsequent oxidation for CrWSiN films.

Effects of Bias Voltage and Target Current on Microstructure and Load Measurement Performance of ZnO Piezoelectric Coatings Applied to Bolt in Transformer

Electrical accidents caused by bolt looseness in transformers have been frequently reported in recent years. The monitoring, and warning of, axial force as an indicator of looseness is one of the key issues affecting the operation and maintenance of transformers. Traditional ultrasonic testing and a patch-type ultrasonic method, using piezoelectric probes and coupling agents, showed poor repeatability and accuracy in detecting the bolt pre-tightening force, because of the uncertainty of the contact interface produced via manual operation. A permanent thin-film pressure sensor (PMTS), which provides accurate and in-situ stress detection, is more suitable for bolts, to reveal the pretightening force. The key is depositing a nano-zinc oxide (ZnO) piezoelectric film with an excellent measurement performance, which could be tuned using deposition parameters. This paper investigates the effects of the current and bias voltage on the crystal structure and performance of ZnO piezoelectric films. The results show that the crystallinity degree and resistance decrease with the increase in bias voltage, while the target current could increase the crystallinity. However, a high current also brings large particles in the coating surface, which greatly decrease the resistance. The cause is expected to be related to the ion energy, which could be affected by the bias voltage and current. The PMTS deposited with an optimized bias voltage and current revealed excellent measurement performance, and is expected to be applied to the bolt, to detect the pretightening force.

The achievement of high-performance and allochroic organic light-emitting diodes via nondoped 4CzPN ultrathin emissive layer

The device fabrication process can be simplified by the employment of ultrathin nondoped emission layer (UT-EML). Based on 1,2,3,4-tetrakis(carbazol-9-yl)-5,6-dicyanobenzene (4CzPN) emitter, the influence of the thickness of ultrathin emissive layer on the device properties was systemically investigated. The high-performance nondoped device was fulfilled by utilizing a 0.02 nm ultrathin emissive layer. The nondoped device delivered the maximum efficiencies of 9.0%, 30.0 cd A−1, and 15.0 lm W−1, accompanied by the peak luminance of 30 597 cd m−2, whilst the corresponding properties of the doped device with a similar configuration were 7.4%/23.7 cd A−1/14.9 lm W−1, and 10 072 cd m−2. Moreover, the efficiency roll-off (just 1.5% from peak to the value at 5 000 cd m−2) of nondoped device was much superior to that of doped devices (46%). Besides, the color can be tuned by controlling the thickness of ultrathin emissive layer and applied voltage, exhibiting potential applications in the field of smart lighting and anti-counterfeiting. When the emission layer thickness was increased from 0.02 to 1.0 nm, the CIE coordinates of devices under 6 V shifted from (0.322, 0.603) to (0.436, 0.537). And the device with a 1.0-nm-thick emissive layer showed a ΔCIE of (0.056, 0.023) with the increase of bias voltage from 5 to 12 V. These results shed light on that nondoped ultrathin emission layer holds great potential for high performance and color-tunable TADF OLEDs.

Low frequency noise in β -Ga2O3 based nanoelectronic devices

In this work, low frequency noise in β-Ga2O3 nanowire-based (NW) electronic devices is analyzed, which exhibits different behaviors as the device size scales down. The noise spectrum for the narrower NW (∼80 nm) is closer to 1/f characteristics, whereas it starts to show evident 1/f2 components as the NW size gets thicker (∼200 nm), giving clear signs of distinctive features for the bunch of traps at the NW interface or in the bulk. Our results show that 1/f noise in these NW electronic devices seems predominantly originated from an aggregated effect of the intricate trap states close to the β-Ga2O3 NW surface or interface with a wide range distribution, while finite groups of active deep traps play a critical role in contributing 1/f2components via generation-recombination or random telegraph signal processes. Notably, as the bias voltage increases, the 1/f2 components in the noise spectra get more overwhelming and would shift toward lower frequencies, suggesting that electric ionization effects would screen the shallow traps close to the surface or interface based on the Poole–Frenkel model. The Hooge's constants extracted from the 1/f noise component for these β-Ga2O3 NW-based devices fall in the range of 0.008–0.019, which are comparable to those of the best reported devices based on other wide bandgap semiconductor with nanoscale structures, including GaN, ZnO, and SnO2. This work may give hints of revealing the sophisticated dynamic behaviors of traps in the surface/volume β-Ga2O3 materials and electronic devices in the nanoscale by low frequency noises.

Layer-Dependent Magnetoresistance and Spin-Transfer Torque in MnSe2 -Based Magnetic Tunnel Junctions

The recently synthesized two-dimensional van der Waals (vdW) ferromagnet 1T-${\mathrm{MnSe}}_{2}$ has attracted great attention due to its room-temperature ferromagnetism. By using ab initio quantum transport simulations with noncollinear spins, we demonstrate a monotonic increasing (decreasing) tendency of the angle-resolved tunneling magnetoresistance (spin-transfer torque) with the increasing graphene layer number n in the ${\mathrm{MnSe}}_{2}$/n-layer graphene/${\mathrm{MnSe}}_{2}$ (n = 1--4) vdW magnetic tunnel junctions (MTJs). A surprising tunneling magnetoresistance of around ${10}^{6}$% is obtained when $\ensuremath{\theta}={180}^{\ensuremath{\circ}}$ and n = 4 owing to the nearly perfect spin polarization; this is 3 orders of magnitude larger than that of the commonly used $\mathrm{MgO}$-based MTJ (1000% at 5 K). The maximal linear-response spin-transfer torque of the ${\mathrm{MnSe}}_{2}$/graphene/${\mathrm{MnSe}}_{2}$ MTJ (5260 \textmu{}eV/V) is 2 orders of magnitude larger than that of the $\mathrm{Fe}/\mathrm{MgO}/\mathrm{Fe}$ MTJ. The decay rate of the spin-transfer torkance at zero bias is revealed to be nonmonotonically n dependent. Meanwhile, the total spin-transfer torque in the device changes from linear dependence to nonlinear dependence as the bias voltage increases. Our calculation suggests that the 1T-${\mathrm{MnSe}}_{2}$-based vdW MTJs are promising in next-generation room-temperature nonvolatile memories.

Construction of Cr coatings with different columnar structure on Zircaloy-4 alloys to optimize the high-temperature steam oxidation behavior for accident tolerant fuel claddings

To optimize the oxidation behavior of chromium-coated Zircaloy-4 alloys under 1200 °C high-temperature steam for accident tolerant fuel (ATF) claddings, Cr coatings with different columnar structure are constructed by changing bias voltage using high power impulse magnetron sputtering and corresponding microstructure, mechanical and high-temperature steam oxidation properties are studied systematically. With the bias voltage increase from 0 V to − 150 V, the microstructure of Cr coatings changes from porous columnar structure to compact columnar structure. Especial for bias voltage is − 90 V, the tiny compact grains uniform distribute on the surface micrographs and optimal compact columnar structure are observed on the cross-section micrographs. The hardness and elastic modulus of as-prepared Cr coatings increase firstly and then decrease, the hardness of Cr coatings with optimal compact columnar structure is 8.65 GPa, which is elevated ∼2.28 times than Cr coatings with porous columnar structure. 1200 °C high-temperature steam oxidation test results show an interesting phenomenon that the thickness of Cr layer reduces initial and then increase with the exposure time prolong from 1 h to 4 h. The main steam oxidation mechanism, in the early oxidation stage, is formation the compact Cr2O3 oxide layer. Then, with the exposure time extend, the reduction reaction plays the significant part for steam oxidation mechanism, which is consumption of outmost Cr2O3 oxide layer and formation of subsurface Cr layer. The construction of Cr coatings with compact columnar structure and relevant oxidation mechanism are expected to offer a new idea for improving 1200 °C steam oxidation resistance of chromium-coated Zircaloy-4 alloys.

Nonequilibrium quantum transport properties of tetragonal zinc chalcogenide monolayers

Tetragonal zinc chalcogenide monolayers (TZCM) are emerging as interesting electronic materials with a direct band gap and relatively high carrier mobility. In this work, we report a theoretical investigation of electronic transport properties and photoelectric response properties of TZCM with gold contacts by density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. When there is no gate voltage applied, the current increases nonlinearly as bias voltage increases. Among the four proposed devices, the Au(100)/ZnS/Au(100) device has the best electronic transport performance and is most sensitive to the adjustment of bias voltage and gate voltage. The photocurrent calculation results indicate that the low-frequency oscillatory photocurrent of the Au(100)/ZnSe/Au(100) device in the high photon energy region may have potential applications in ultraviolet light-emitting diodes. The Au(100)/Zn2SeS/Au(100) device has more stable photoelectric response and polarization sensitivity than the Au(100)/Zn2SSe/Au(100) device. The Au(100)/TZCM/Au(100) devices exhibit considerable photocurrent and good extinction ratios. This work could pave the way for the future application of TZCM in the field of optoelectronics and so on.

Increase of the surface recombination velocity at high bias voltage in silicon irradiated by neutrons to extremely high fluences

The upgrading of ionizing radiation detectors is an actual problem especially related to the high energy physics and space research experiments. The simplest way to restore the signal of the irradiation degraded detector is the increase of the detector bias voltage. This method is widely used worldwide, including high energy physics experiments in ATLAS and CMS. This work presents an effect, which was caused by increased bias voltage in detectors irradiated to extreme high neutron fluence at low temperature. The effect could be related to the increase of surface recombination velocity.The intrinsic photoconductivity spectra were exploited in order to investigate the properties of highly irradiated silicon as this effect depends on parameters that are important in radiation detectors. Two characteristic effects were observed in such highly irradiated samples: the increase of photoconductivity quantum yield and the enhancement of surface recombination at higher bias voltages. The increase of the quantum yield was analyzed in Ref. [1]. The increase of the surface recombination with bias electric field was analyzed in this work as an extension of the performed investigation in the same samples as in Ref. [1]. The investigated silicon samples were irradiated by neutrons to wide range fluence up to 1017 n/cm2.The origin of this effect was analyzed and related to the radiation clusters, which decrease the free carrier lifetime.

Resistive switching study on diffusive memristors using electrochemical impedance spectroscopy

Diffusive memristors demonstrate volatile resistive switching powered by the diffusion of silver nanoparticles through the matrix of silicon dioxide. The equivalent circuit of the high resistance state has been studied via electrochemical impedance spectroscopy for two types of devices which demonstrate either analog or abrupt switching characteristics. It was found that the resistance component has a relatively good agreement with the differential resistance obtained from the I–V curves, whereas the capacitance visibly increases in the analog switching devices with increasing bias voltage as its conductive precursor filament starts forming with increasing voltage and redistribution of silver nanoparticles starts to occur at the top electrodes. Such an effect is not observed for abrupt switching device, which rapidly enters its conductive state for a small increase in bias voltage. This experimental approach allows for the identification of different types of electrical circuit behaviors in a memristive device, even before resistive switching takes place.