High Negative Bias Research Articles

One-Step Magneton Sputtering of Crystalline Cu-Doped TiO2 Coatings: Characterization and Antibacterial Activity

Early biofilm formation could be inhibited by applying a thin biocompatible copper coating to reduce periprosthetic infections. In this study, we deposited crystalline Cu-doped TiO2 films using one-step DC magnetron sputtering in an oxygen atmosphere on a biased Ti6Al4V alloy without external heating. The bias voltage varied from −25 V to −100 V, and the resultant substrate temperature was measured. The deposited coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness, scratch and hydrophilicity tests, potentiodynamic polarization measurements, and antibacterial assays against S. aureus and E. coli. The findings demonstrated that when a higher negative bias is applied, the substrate temperature drops, and the anatase to rutile transformation is initiated without indicating obvious Cu-containing phases. The SEM images of the films showed spherical agglomerates with homogeneously distributed Cu with decreasing Cu content as the bias value increased. Higher bias results in the grain refinement of the thinning coatings with more lattice microstrain and more defects, together with an increase in water contact angles and hardness values. Samples biased at −75 V exhibited the highest adhesive strength between coatings and substrate, whereas the specimen biased at −50 V demonstrated higher corrosion resistance. Cu-containing TiO2 coatings with pure anatase phase composition and Cu concentrations of 2.62 wt.% demonstrated excellent bactericidal activity against both S. aureus and E. coli. The layers containing 2.34 wt.% Cu exhibited very good antibacterial properties against S. aureus, only. According to these findings, the produced copper-doped TiO2 coatings have high bactericidal qualities in vitro and may be used to prepare orthopaedic and dental implants in the future.

Evaluation and comparison of MODIS and MISR aerosol products with ground-based monitoring stations in the Amazon Basin

This study evaluates the long-term accuracy of six daily aerosol optical depth (AOD) datasets derived from the Moderate Resolution Imaging Spectroradiometers (MODIS) Dark Target (DT) at 3 and 10 km resolution, Deep Blue (DB), combined DT and DB datasets (DTB) and MODIS Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithms and the Multi-angle Imaging SpectroRadiometer (MISR) Version 23, by comparing them with ground-based AOD observations in 18 Aerosol Robotic Network (AERONET) sites over the Amazon basin between 2000 and 2022. The AOD retrieval accuracy was also assessed under varying seasons, aerosol loading, particle size, elevation and land cover type. Overall results showed that Terra and Aqua-MODIS DB and MISR algorithms perform better, with about 88% of AOD retrievals within the expected error range. However, MISR presented a systematic high negative bias. MODIS DT 3 km overestimated AOD values and indicated unsatisfactory retrieval accuracy in almost all scenarios. MODIS and MISR retrievals showed improved performance under low aerosol loading, whereas Aqua-MODIS MAIAC under intermediate conditions (AOD>0.2). MISR indicated a large dependence on a coarse mode-dominated environment with considerable negative bias. Terra-MODIS MAIAC retrievals exhibited a smaller dependence for aerosol particle size distribution, while Terra-MODIS DB performed better for fine mode and Aqua-MODIS DB for coarse dominance. MAIAC also performed well under polluted scenarios in the dry season in contrast to the majority of satellite-based AOD retrievals, which showed good agreement under clean background conditions in the wet season. Almost all satellite-based retrievals showed higher uncertainty under extremely high altitudes (>3000 m) followed by non-satisfactory correlation and significant biases. Additionally, almost all satellite-based AOD retrievals indicated poor performance as vegetation coverage increases. On the contrary, MISR showed higher accuracy under forest type. In general, MODIS and MISR retrieval accuracy demonstrated distinct levels of dependencies that require further improvement in the Amazon Basin.

Threshold voltage uniformity improvement by introducing charge injection tuning for low-temperature poly-Si thin film transistors with metal/oxide/nitride/oxide/silicon structure

Low-temperature poly-Si thin film transistors (TFTs) with a metal/oxide/nitride/oxide/silicon structure were fabricated to investigate the feasibility of suppressing threshold voltage variations between TFTs. By applying relatively high positive and negative gate bias voltages, threshold voltage could be tuned positively and negatively, respectively, by injecting charges into the charge trap layer. Stability of threshold voltage against positive gate bias at a level close to the actual circuit operation was not degraded compared with the case of an as-fabricated TFT. A uniform threshold voltage distribution could be achieved in a preliminary test using 16 TFTs by converging threshold voltages with a target value by tuning the threshold voltage for each TFT.

Effects of applied negative bias voltage on the optical and structural properties of CaF2 coatings deposited by RF magnetron sputtering

Calcium fluoride (CaF2) is a ceramic material exhibiting versatile properties including broadband transparency, lubrication at high temperature, and mechanical stability. In the current research, aimed at improving optically-driven infrared detection devices, CaF2 coatings were deposited on sapphire. One challenge concerning this CaF2/sapphire system is the significant difference between their coefficients of thermal expansion, which can cause adhesion failure. To avoid such failure, we first studied the behavior of thick CaF2 coatings on silicon substrates where adhesion issues are expected to be more pronounced, then employed thin CaF2 coatings, initially on silicon and subsequently on sapphire substrates.Deposition was carried out by radio frequency magnetron sputtering technique in an argon atmosphere at a fixed power of 4.4 W/cm2. Substrate bias voltage was varied from 0 to - 150 V in order to explore voltage impact on properties of the obtained CaF2 coatings.Coatings deposited with low negative bias voltages presented an inhomogeneous surface with a columnar structure that remained firmly attached to the substrate; optical transmission for these coatings was reduced relative to that for bare sapphire. Alternatively, while coatings deposited with high negative bias voltages became dense and uniform, they were also subjected to high surface reactivity causing formation of CaO/Ca(OH)2 phases and defects, as well as delamination that reduced optical transmission. In contrast, only samples deposited with moderate bias voltages exhibited a sufficiently dense, highly adhesive layer, resulting (relative to that for bare sapphire) in improved optical transmission. Thin CaF2 coatings deposited with −100 V improved transmittance (at a wavelength of 1.9 μm) from almost 88.5 %–92 %, representing approximately a 30 % decrease in radiation loss caused by absorbance, scattering, and reflectance effects. Even though the optical values of transmittance for increased wavelength (up to 5 μm) were reduced, these values still surpassed those obtained for sapphire alone.

A Multicentric Verification of Hereditary and Acquired Thrombophilia Coagulation Assays

Aims: With an ever-growing number of patients being admitted to our University Hospital Sveti Duh (Zagreb, Croatia), there was a need to positively respond to clinicians' demands about hereditary and acquired thrombophilia testing.
 Study Design: An extensive and multicentric verification of coagulation assays included in thrombophilia testing was performed on the BCS XP coagulation analyzer (Siemens Healthineers, Marburg, Germany): antithrombin activity (AT) (Innovance Antithrombin), protein C activity (PC) (Berichrom Protein C), protein S activity (PS) (Protein S Ac), free protein S antigen (free PS:Ag) (Innovance Free PS Ag), activated protein C resistance (APCR) (ProC Ac R and ProC Global + Coagulation Factor V Deficient Plasma), lupus anticoagulant (LA) screening (LA1 and activated partial thromboplastin time by using Dade Actin FSL as reagent) and confirmation test (LA2), factor VIII activity (FVIII) (Dade Actin FS and coagulation FVIII Deficient Plasma).
 Place and Duration of Study: Department of Medical Laboratory Diagnostics, University Hospital Sveti Duh, Zagreb, Croatia, between January 2020 and December 2021.
 Methodology: Verification protocol included: the precision study (CLSI EP15-A3 protocol), trueness estimation by comparison of seventy remnant plasma samples with two large Croatian hospital laboratories with established thrombophilia testing, and verification of reference intervals and cut-off values (CLSI EP28-A3C and CLSI HA-60 guidelines).
 Results: All of the obtained imprecision CVs were within the manufacturer's claims (<5/10/15%). While the observed bias for PC (+1.9%) was within the EFLM performance specifications (6.7%), the average bias for AT was higher than acceptance criteria (+10.8% vs 3.2% allowed). P&B regression revealed a significant positive proportional difference (slope=1.14). Comparison of PS activity yielded a high negative bias (-33.4%) that exceeded the acceptance criteria of 8.1%. Regarding LA testing, the diagnostic accuracy was 99% when compared to Sestre milosrdnice UHC (N=70) and 95% when compared to University Hospital Centre Zagreb (N=19). All manufacturer's reference intervals and cut-offs were verified.
 Conclusion: The verification study confirmed all manufacturer's claims, except for PS which has been replaced with free PS:Ag determinations.

Potential‐induced degradation in bifacial silicon heterojunction solar modules: Insights and mitigation strategies

AbstractPotential‐induced degradation (PID) may be a serious concern in photovoltaic (PV) modules and plants, particularly when approaching high system voltages (1500+ V). Here, we investigate PID occurring in bifacial rear‐emitter silicon heterojunction (SHJ) solar cells encapsulated in a glass/glass (G/G) module configuration with ethylene vinyl acetate (EVA) as an encapsulant. PID testing was performed at 85°C in 85% relative humidity (RH), and the solar cells were subjected to −1 kV and +1 kV for up to 800 h. SHJ cells were found to degrade when subjected to −1 kV, and to a lesser extent when left unbiased in damp heat (DH) conditions, while the application of +1 kV prevented degradation. Although prone to PID after extended test durations, the SHJ mini‐modules investigated in this study noticeably passed the industry standard (IEC 61215:2021) PID test of 96 h. The degradation was primarily characterized by losses in short‐circuit current (ISC) at the front side, followed by fill factor (FF) and open‐circuit voltage (VOC). A cross‐sectional transmission electronic microscopy analysis of the laminates subjected to −1 kV highlighted a transport of sodium (Na) through the transparent conductive oxide (TCO), reaching the amorphous Si/TCO interface. The samples tested in DH conditions and with positive PID test conditions did not exhibit such a migration of Na. To account for these observations, we updated a previously proposed model describing the sensitivity of SHJ cells to water. In our degradation model, moisture in the module corrodes the glass, creating sodium hydroxide (NaOH) that then percolate through the EVA before reaching the SHJ cell. The application of a high negative bias amplifies the previous mechanism by increasing the availability of Na+ and also enhances the drift of Na+ through the EVA to the cell. Finally, we demonstrate that PID can be mitigated or suppressed at the module level by using a high‐volume resistivity encapsulant with a low water vapor transmission rate (WVTR) or by encapsulating SHJ solar cells in a configuration impermeable to water (e.g., using an edge sealant).

Effects of deposited particle energy on the structure and properties of diamond-like carbon films

Using plasma-enhanced chemical vapor deposition (PECVD), a series of diamond-like carbon (DLC) films were prepared on YG8 carbide substrate by changing the enhancement mode and the negative bias voltage of the substrate. The structure and properties of the deposited films were tested by a series of analytical and testing instruments.During the deposition of DLC films, the ability of electrons to collide and ionize the gas is enhanced by increasing the number of electrons and extending the movement path of electrons, which is called electron-assisted enhanced gas ionization. Four different experimental modes (A mode, B mode, C mode, D mode) were set up. Different experimental modes have different degrees of electron-assisted enhancement ability of gas ionization, so different experimental modes are called different enhancement modes. The ions ionized by the electrons participate in the deposition of the film under the traction of the negative bias voltage of the substrate. The results show that: when depositing diamond-like carbon films, the energy of the ion beam is indirectly affected by electron collisions in different enhancement modes and directly affected by the negative bias voltage of the substrate. The higher the enhancement mode, the higher the ion beam energy. The higher the substrate negative bias voltage, the higher the ion beam energy generated by gas source discharge. Under the dual action of enhancement mode and substrate negative bias voltage, the total energy of ions involved in deposition should not be too high or too low, and the synergy of the two makes the properties and quality of the deposited film reach a better value. For industrial large-scale production of tool protection film for cutting aluminum alloy, it is more suitable for high enhancement mode and low negative bias voltage production.Through a series of process optimization to improve and enhance the comprehensive performance of DLC film, it is further applied to the actual processing application field, which has great industrial and social value to realize the large-scale application of DLC film in the field of hard to cut metal processing.

High transparent and stability indium praseodymium oxide thin-film transistors with tungsten doping by solution method

Indium-oxide-based thin-film transistors are widely investigated and exhibit higher carrier mobility than amorphous silicon. Lanthanide-doped Indium oxide TFTs show relatively high negative bias illumination stress (NBIS) stability but at the cost of mobility. To improve the NBIS stability by the solution method, we doped Tungsten (W) into Praseodymium-doped Indium oxide (InPrO) and fabricated InPrWO TFT. We proposed that W doping could densify the films and suppress oxygen vacancy. With the increase of W doping concentration from 0 to 3 mol%, the contact angle of precursor solutions first decreased and then increased, reaching minimums of ∼13° at 1 mol%. When the W doping concentration increased from 0 to 1 mol%, the density of films increased from 6.155 to 6.479 g/cm3. While doping concentration increased from 1 to 3 mol%, the density of films decreased. Transmittance of InPrWO films was higher than 90 % from 300 to 800 nm. The localized defects of InPrWO films were investigated by μ-PCD. With 1 mol% W doping, deep-level and shallow-level defects were relatively the least. XPS result revealed that W was successfully doped into the films. Besides, the oxygen vacancy ratio first decreased and then increased when the W doping concentration increased. InPrWO film with 1 mol% W doping had the least oxygen vacancy ratio, resulting in the highest stability. The TFT fabricated with optimal 1 mol% W doped InPrWO film showed excellent electrical characteristics (μsat = 5.4 cm2/Vs, Vth = -0.3 V, Ion/Ioff = 8.0 × 105, and SS = 0.30 V/dec). With the W doping concentration increased, the NBIS stability first increased and then decreased, having minimum shift ΔVth = -2.1 V at 1 mol%. We improved the quality of films and NBIS stability of TFT by doping W into InPrO and appropriate post-processing, satisfying the development trend of high transparency and high stability TFTs for future displays.

Patterns of attentional biases in children and emotional symptoms during the COVID-19 pandemic: a two-wave longitudinal study

BackgroundIt is unknown how the patterns of negative and positive attentional biases in children predict fear of COVID-19, anxiety symptoms, and depression symptoms during the COVID-19 pandemic. The study identified profiles of negative and positive attentional biases in children and examined their association with emotional symptoms during the COVID-19 pandemic.Method264 children (girls: 53.8% and boys: 46.2%) of 9–10 years born in Hong Kong or mainland China from a primary school in Shenzhen, People’s Republic of China were involved in a two-wave longitudinal study. Children completed the COVID-19 Fear Scale, the Revised Child Anxiety and Depression Scale, and the Attention to Positive and Negative Information Scale to measure fear of COVID-19, anxiety and depression symptoms, and negative and positive attentional biases in classrooms. After six months, they completed the second assessment of fear of COVID-19, anxiety symptoms, and depression symptoms in classrooms. Latent profile analysis was conducted to reveal distinct profiles of attentional biases in children. A series of repeated MANOVA was performed to examine the association of profiles of attentional biases to fear of COVID-19, anxiety symptoms, and depression symptoms across 6 months.ResultsThree profiles of negative and positive attentional biases were revealed in children. Children with a “moderate positive and high negative attentional biases” profile had significantly higher fear of the COVID-19 pandemic, anxiety symptoms, and depression symptoms than children with a “high positive and moderate negative attentional biases” profile. Children with a “low positive and negative attentional biases” profile were not significantly different in fear of COVID-19, anxiety symptoms, and depression symptoms than those with the other two profiles.ConclusionsPatterns of negative and positive attentional biases were related to emotional symptoms during the COVID-19 pandemic. It might be important to consider children's overall patterns of negative and positive attentional biases to identify children at risk of higher emotional symptoms.

A new method to explicitly estimate the shift of optimum along gradients in multispecies studies

A new method to explicitly estimate the shift of optimum along gradients in multispecies studies

Unraveling the electric field effect on the grain‐boundary migration in alumina through phase field modeling

AbstractIt is experimentally demonstrated that the electric field drives the grain‐boundary (GB) migration in ceramics, but this has not been interpreted mechanistically. This work develops a phase field model to study the GB migration in alumina (Al2O3) and validate through the comparison with previous experiments. Results show that the GBs move to the small grain domain. Under an electric field in the positive bias direction, GB migration is enhanced, whereas the migration to the small grain domain is inhibited under the electric field in the negative bias direction. The enhancement or inhibition effect becomes more pronounced with increasing the electric field. The high negative bias induces decrease in the GB migration velocity even with the migration direction altering. It is revealed that GB migrations are dominated by the competitive effect between the curvature and electric field driving forces, and an analytical expression of the critical electric field is derived.

Effect of Water Adsorption Layers on the Friction Properties of Fluorinated Amorphous Carbon Films in Ambient Air.

Fluorinated amorphous carbon (a-C:F) films with different microstructures were prepared with bipolar-type plasma-based ion implantation and deposition method by changing the negative bias voltage, and the tribological properties were investigated in ambient air. Their surface chemistry and water adsorption properties were investigated to determine their friction properties. Microstructural analysis results showed that, as the negative bias voltage increased, the density of the films decreased with the promotion of graphitization. The water adsorption properties evaluated using a quartz crystal microbalance showed that a large adsorbed water weight was observed for the films deposited at high negative bias voltages. In contrast, these films exhibited thin water adsorption layers from the measurements with an ellipsometer. These results indicate that water molecules are adsorbed on the film surface and permeate into the films, particularly for the films deposited at high negative bias voltages. The friction properties in ambient air depend significantly on their microstructure and relative humidity (RH). Regardless of the RH, the higher the negative bias voltage during film deposition, the lower the friction coefficient. Since several water molecules existed on the surface of the film deposited with a low negative bias voltage, its surface was oxidized during sliding, which increased the friction coefficient. In addition, the friction coefficient of the films increased at high RH. The number of water molecules adsorbed on the film increased as the RH increased, causing a high shear force owing to many hydrogen bonds and/or high capillary force at the friction interface.

(Digital Presentation) Instability of α-Si:H TFTs under Simultaneous Ultraviolet Light Illumination and Different Bias Stresses

The threshold voltage degradation and recovery phenomena of the α-Si:H TFTs stressed by DC or AC biases under with or without UV light illumination are investigated. For the negative DC bias stress, the threshold voltage shift of the stressed α-Si:H TFTs measured in the reverse sweep mode is smaller than that in the forward sweep mode, but the threshold voltage recovery is opposite, owing to the different increment of subthreshold swing of the α-Si:H TFTs after stressing. For the AC biases stresses, there are no significant difference of threshold voltage shift between the stressed α-Si:H TFTs measured by forward sweep and reverse sweep modes due to the less increment of subthreshold swing of the α-Si:H TFTs after stressing. There are more threshold voltage degradation but less recovery of the α-Si:H TFTs stressed by lower AC frequency with the higher negative bias in a cycle than those stressed by higher AC frequency.

Assessing extreme precipitation from a regional climate model in different spatial–temporal scales: A hydrological perspective in South America

AbstractGlobal and regional climate models (GCM and RCM respectively) are the current mathematical tools used to project alterations on precipitation regimes given different greenhouse gases emissions scenarios. However, these models have specific resolutions, physical equations and numerical approaches that provide a diverse set of performances across different regions and spatial–temporal scales. In South America, most hydrological impact studies have used the Eta RCM to yield precipitation projections without a proper uncertainty analysis. It is important to acknowledge its uncertainties prior to any hydrological assessment to adequately support climate change investigations and related water decision making. Therefore, we aim to investigate how Eta extreme precipitation biases vary in different spatial–temporal scales from a hydrological perspective. Thus, we evaluate the extreme precipitation generated by the Eta RCM driven by four different GCMs. It is investigated Eta biases across different temporal (3 hr–5 days) and spatial scales (0.2–1.0°) and how those errors affect river streamflow simulations. It is used local intensity–duration–frequency (IDF) curves and gridded precipitation datasets (MSWEP and ERA5‐Land) as references for Eta assessment. In general, Eta underestimates subdaily extreme precipitation across South America, regardless of the driven GCM. The median bias of a 10‐year return period daily precipitation is −36 mm (1st and 3rd quantiles −58 and −17 mm) compared to MSWEP and −26 mm (1st and 3rd quantiles −45 and −11 mm) compared to ERA5‐Land. However, the relative errors reduce with temporal and spatial aggregation. For example, the average bias of extreme precipitation decreases 8.4 and 5.4 percentage points from 1‐ to 5‐day duration compared to MSWEP and ERA5‐Land, respectively. The negative biases observed for precipitation (20%) are propagated to the flood discharges (40%), and these errors reduce with the drainage area. In general, there are greater biases in extreme discharges for small basins, but these errors considerably reduce for basins larger than 30,000 km2 compared to MGB‐MSWEP simulations. Compared to MGB‐ERA5‐Land simulations, MGB‐Eta presents relatively similar errors for basins of different sizes, probably due to the high negative bias for not only extreme but average precipitation as well.

High Voltage Solar Array Development for Space and Thruster-Plume Plasma Environments

High-power solar arrays are in development by the National Aeronautics and Space Administration (NASA) for near-term high-power solar electric propulsion (SEP) missions. These high-voltage (HV) solar arrays use deployable flexible blanket configurations and need to be able to operate in the plasma environment of high-power Hall thrusters operating at tens of kilowatts of power. Array voltages of 300–800 V are desired both to minimize the copper bus mass in the system and to potentially operate the SEP Hall thrusters directly at high specific impulse without an in- series power processing unit. Coupons with multiple strings of solar cells (SCs) have been tested to high positive and negative biases in a plasma environment representative of the edge of Hall thruster plumes. Proper encapsulation of the exposed metals and triple points is required to avoid excessive current collection and arc initiation. Fully encapsulated test coupons have been successfully been tested at highest anticipated thruster plume plasma densities at voltages from 600 to 1000 V, which enables both very high power arrays and direct drive configurations for SEP missions.

Neurocomputational mechanism of controllability inference under a multi-agent setting.

Controllability perception significantly influences motivated behavior and emotion and requires an estimation of one’s influence on an environment. Previous studies have shown that an agent can infer controllability by observing contingency between one’s own action and outcome if there are no other outcome-relevant agents in an environment. However, if there are multiple agents who can influence the outcome, estimation of one’s genuine controllability requires exclusion of other agents’ possible influence. Here, we first investigated a computational and neural mechanism of controllability inference in a multi-agent setting. Our novel multi-agent Bayesian controllability inference model showed that other people’s action-outcome contingency information is integrated with one’s own action-outcome contingency to infer controllability, which can be explained as a Bayesian inference. Model-based functional MRI analyses showed that multi-agent Bayesian controllability inference recruits the temporoparietal junction (TPJ) and striatum. Then, this inferred controllability information was leveraged to increase motivated behavior in the vmPFC. These results generalize the previously known role of the striatum and vmPFC in single-agent controllability to multi-agent controllability, and this generalized role requires the TPJ in addition to the striatum of single-agent controllability to integrate both self- and other-related information. Finally, we identified an innate positive bias toward the self during the multi-agent controllability inference, which facilitated behavioral adaptation under volatile controllability. Furthermore, low positive bias and high negative bias were associated with increased daily feelings of guilt. Our results provide a mechanism of how our sense of controllability fluctuates due to other people in our lives, which might be related to social learned helplessness and depression.

High-speed deposition of graphite-like carbon film by Ar/C6H6 surface-wave plasma with high-voltage pulse biasing

A method for graphite-like carbon (GLC) deposition using Ar/C6H6 surface-wave plasma (SWP) is proposed. Characteristic of the SWP, i.e., high plasma density with wide spatial uniformity realized uniform carbon film deposition at high deposition rates. To increase sp2 ratio in carbon films, a pulsed negative bias voltage up to ~2 kV is applied to a substrate. Conductive carbon films of low sheet resistances below ~102 Ω/sq is achieved at high deposition rates up to ~6 nm/s with good spatial uniformity (±5%) in an area of ~18×3 cm2. Film structure is evaluated by Raman spectroscopy, Fourier-transform infra-red spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning transmission electron microscopy and electron energy loss spectroscopy. At high negative bias voltages, sp2-rich with reduced hydrogen content of the film is observed.

Nano-Topographical Control of Ti-Nb-Zr Alloy Surfaces for Enhanced Osteoblastic Response.

Nano-scale surface roughening of metallic bio-implants plays an important role in the clinical success of hard tissue reconstruction and replacement. In this study, the nano-topographical features of titanium-niobium-zirconium (TNZ) alloy surfaces were controlled by using the target-ion induced plasma sputtering (TIPS) technique to improve the in vitro osteoblastic response. The TIPS technique is a novel strategy for etching the surface of metallic bio-implants using bombardment of target metal cations, which were accelerated by an extremely high negative bias voltage applied to the substrates. The nano-topography of the TNZ surfaces was successfully controlled by modulating experimental variables (such as the ion etching energy and the type of substrate or target materials) of TIPS. As a result, various nanopatterns (size: 10–210 nm) were fabricated on the surface of the TNZ alloys. Compared with the control group, experimental groups with nanopattern widths of ≥130 nm (130 and 210 nm groups) exhibited superior cell adhesion, proliferation, and differentiation. Our findings demonstrate that TIPS is a promising technology that can impart excellent biological functions to the surface of metallic bio-implants.

Microstructure, erosion and tribological behaviour of thick DLC coatings by the filtered cathodic vacuum arc combined with a high-voltage pulse power

Hydrogen-free diamond-like carbon (DLC) films with thickness of 36 μm and 50 μm have been prepared on Si and AISI 304L stainless steel substrates, respectively, by filtered cathodic vacuum arc (FCVA) together with a high-voltage pulse power. The structure, chemical bonding state, mechanical properties and wear, corrosion resistance and anti-erosion performance were evaluated. The thick DLC films with compressive stress of 0.71 GPa and hardness of 3160 HV were obtained. The preparation of the low stress but high hardness coating mainly due to the appropriate high negative bias and short pulse duration, which could result in an alternate ion bombardment and deposition. The 50 μm-thick coating showed corrosion resistance with high polarization resistance of 4.69 × 108 Ω·cm2 and low corrosion current density of 5.47 × 10−8 A·cm−2. Thick coating exhibited outstanding sand particle erosion resistance with low average mass loss rate of 0.035 mg g−1. Under high-speed sand erosion conditions, the coating remains unbroken, without peeling or cracking were observed on the erosion center. In addition, DLC coatings showed good tribological performance under dry, water- and oil-lubricated condition.

Fabrication and characterization of CrNbSiTiZr high-entropy alloy films by radio-frequency magnetron sputtering via tuning substrate bias

CrNbSiTiZr high-entropy alloy films with different substrate bias voltages (from 0 V to–200 V) were fabricated on 304 stainless steel and Si substrates by radio-frequency magnetron sputtering. The microstructure, mechanical properties, tribological performance, and corrosion resistance were investigated in detail. Results show that all the as-fabricated films exhibit an amorphous phase. The columnar structure becomes featureless with the increase substrate bias due to re-sputtering effects and densification of the film. The film deposited at the bias of –50 V has a high residual compressive stress of –0.82 ± 0.04 GPa and a high hardness of 12.4 ± 0.3 GPa. The wear mechanism of the film is adhesive and slightly abrasive at low negative bias (0, –50, and –100 V), and that at high negative bias (–150 and –200 V) is abrasive. Polarization and electrochemical impedance spectrum measurements reveal that all films have a superior electrochemical corrosion resistance to the 304 stainless steel in 3.5 wt% NaCl solution, which indicates that the film can effectively protect substrate from corrosion. The values of Ecorr, icorr, and Rpo of the film deposited at the bias of –50 V are −283 mV, 0.0178 μA/cm2, and 2.084 × 106 Ω‧cm2, respectively.