Higher Substrate Bias Voltage Research Articles

Effect of Graphene Sheets Embedded Carbon Films on the Fretting Wear Behaviors of Orthodontic Archwire-Bracket Contacts.

Carbon films were fabricated on the orthodontic stainless steel archwires by using a custom-designed electron cyclotron resonance (ECR) plasma sputtering deposition system under electron irradiation with the variation of substrate bias voltages from +5 V to +50 V. Graphene sheets embedded carbon (GSEC) films were fabricated at a higher substrate bias voltage. The fretting friction and wear behaviors of the carbon film-coated archwires running against stainless steel brackets were evaluated by a home-built reciprocating sliding tribometer in artificial saliva environment. Stable and low friction coefficients of less than 0.10 were obtained with the increase of the GSEC film thickness and the introduction of the parallel micro-groove texture on the bracket slot surfaces. Particularly, the GSEC film did not wear out on the archwire after sliding against three-row micro-groove textured bracket for 10,000 times fretting tests; not only low friction coefficient (0.05) but also low wear rate (0.11 × 10−6 mm3/Nm) of the GSEC film were achieved. The synergistic effects of the GSEC films deposited on the archwires and the micro-groove textures fabricated on the brackets contribute to the exceptional friction and wear behaviors of the archwire-bracket sliding contacts, suggesting great potential for the clinical orthodontic treatment 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.

The influence of residual stress on the properties and performance of thick TiAlN multilayer coating during dry turning of compacted graphite iron

TiAlN is one of the most widely used physical vapour deposition (PVD) coatings in the manufacturing industry. Naturally, the performance of this coating is dependent on its properties, which can be tuned and optimized according to the application. Residual stress is one of the properties which affects hardness, fracture toughness, and adhesion of the coating. Although it is difficult to make a general recommendation for desirable residual stress values, individual recommendations can be made based on a specific workpiece material and tool wear mechanism. In this regard, adhesion wear and the formation of built-up edge were identified as the dominant wear mechanism during dry turning of compacted graphite iron and a coating's residual stress should be adjusted to minimize the damage from adhesion wear. Therefore, the present work investigates cutting performance and related coating properties of multilayer thick TiAlN coatings with different residual stress designs. For this purpose, residual stress was adjusted by varying the substrate bias voltage during the deposition process. The effect of residual stress on properties such as hardness, yield strength, and adhesion were studied by nanoindentation and scratch tests. Moreover, the dominant wear pattern, especially on the rake face and cutting edge, was thoroughly studied using a scanning electron microscope (SEM). The results showed increased mechanical properties such as hardness and yield strength with higher substrate bias voltages and therefore higher residual stresses. However, the coating with the lowest compressive residual stress outperformed the other coatings during machining due to a combination of high adhesion to the substrate and low as-deposited defects which effectively delayed cutting-edge exposure.

Microstructures and mechanical properties of AlCrN/TiSiN nanomultilayer coatings consisting of fcc single-phase solid solution

AlCrN/TiSiN nanomultilayer coatings, basically consisting of single-phase fcc-AlCrTiSiN solid solution, were prepared by co-deposition method with Al30Cr70 and Ti72Si18 targets. With substrate negative bias voltage increase from 50 V to 110 V, the hardness of nanomulitlayer coatings is increased from 32.1 GPa to 36.5 GPa, and the growth behavior changes from (2 0 0)fcc preferred orientation to coexistence of both (2 0 0)fcc and (1 1 1)fcc preferred orientation. Low interfacial energy supports the epitaxial growth, resulting in an increase in strain energy of coating systems due to the lattice misfit between neighboring sublayers. Increased strain energy is overcompensated by the formation of interfacial dislocations and dislocation loops as well as fcc-AlCrTiSiN nano-twins and hcp-AlN clusters at twin boundaries. Additionally, the Cr-ion etching induces to form a thin amorphous loose layer (LL) between coating and steel substrate during the pretreatment process. High substrate bias voltage promotes the transformation of amorphous phase to the (Cr,Fe)N solid solution during the coating deposition process, resulting in a notable increase in adhesion strength.

DEPOSITION OF TiN-BASED COATINGS USING VACUUM ARC PLASMA IN INCREASED NEGATIVE SUBSTRATE BIAS VOLTAGE

The paper presents the results of the study on the influence of a high substrate bias voltage from 300 up to 1300 V on the titanium nitride coating deposition under nitrogen pressure of 2 Pa. The deposition rate, phase and chemical composition, adhesion and mechanical properties of coatings, macroparticle number and size distribution were investigated.

The effect of the H2/(H2 + Ar) flow-rate ratio on hydrogenated amorphous carbon films grown using Ar/H2/C7H8 plasma chemical vapor deposition

To produce hydrogenated amorphous carbon (a-C:H) films with high mass density at a high deposition rate and low substrate bias voltage, we deposited these films on a Si substrate by plasma chemical vapor deposition, using toluene as a source compound and varying the gas flow-rate ratio of H2/(H2 + Ar). By decreasing the gas flow-rate ratio from 55% to 11%, the hydrogen content in the films decreased, and the density of sp3 carbon atoms in the films increased, whereas their surface roughness increased. At the gas flow-rate ratio of 11%, we produced a-C:H films with a high bulk density of 1830 kg/m3 at a high deposition rate of 81.1 nm/min.

Influence of bias voltage on sputter deposited V2O5 films

Vanadium pentoxide (V2O5) thin films were deposited over thoroughly cleaned silicon dioxide (SiO2)-coated silicon (Si) (100) substrates by reactive dc magnetron sputtering technique at various substrate bias voltages keeping the other deposition parameters constant. The thickness value of the films measured using stylus probe technique was in the range of 200 to 230 nm. The films were characterized for their structural, morphological, optical and electrical properties using X-ray diffractometry, field emission scanning electron microscopy, UV-Vis spectroscopy and four-point probe method, respectively. The crystallinity of the films was improved at higher substrate bias voltages, which in turn had influence on the optical bandgap value and electrical resistivity. The optical bandgap of the deposited films were decreased to 2·68 eV from 2·71 eV as a result of removal of defects. The temperature coefficient of resistivity value of V2O5 films deposited at −100 V was found to be −1·9%/K. The results obtained are correlated to the substrate bias voltage.

Preparation and characterization of CrAlN/TiAlSiN nano-multilayers by cathodic vacuum arc

Superhard CrAlN/TiAlSiN nano-multilayers deposited at various substrate bias voltages were produced on the surface of Si (100) wafers and high-speed steels by cathodic vacuum arc. The microstructures of these coatings were investigated systematically by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM), in association with mechanical property characterization. The HRTEM observation shows that these coatings have a nano-multilayer structure containing alternatively fcc-(Cr,Al)N sublayer and amorphous sublayer with some nanocrystalline fcc-(Ti,Al)N phases embedded in this amorphous matrix. The coherent epitaxial growth structure is observed along the {100} crystal plane of the fcc-(Cr,Al)N phase and the {100} crystal plane of the fcc-(Ti,Al)N phase. The orientation relationship between them is as follows: {100}(Cr,Al)N//{100}(Ti,Al)N and [001](Cr,Al)N//[001](Ti,Al)N. Mechanical property characterization shows that the coating hardness is dependent on the substrate bias voltages, and the friction coefficients of these coatings with a higher substrate bias voltage are found to be much lower than those of the coatings deposited at a lower substrate bias voltage. The improvement of the friction coefficient is attributed mainly to the formation of tribochemical reaction films. In addition, the much lower friction coefficient can also be related to the higher hardness and fracture toughness.

Effect of substrate biasing and temperature on AlN thin film deposited by cathodic arc ion

Aluminum nitride (AlN) films have been grown in pure N2 plasma using cathodic arc ion deposition process. The films were prepared at different substrate bias voltages and temperatures. The aim was to investigate their influence on the Al macro-particles, structural and optical properties of deposited films. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscope (SEM) and Rutherford backscattering spectrometry (RBS) were employed to characterize AlN thin films. XRD patterns indicated the formation of polycrystalline (hexagonal) films with preferential orientation of (002), which is suppressed at higher substrate bias voltage. FTIR and Raman spectroscopic analysis were used to assess the nature of chemical bonding and vibrational phonon modes of AlN thin films respectively. FTIR spectra depicted a dominant peak around 850cm−1 corresponding to the longitudinal optical (LO) mode of vibration. A shift in this LO mode peak towards higher wavenumbers was observed with the increase of substrate bias voltage and temperature, showing the upsurge of nitrogen concentration in the deposited film. Raman spectra illustrated a peak at 650cm−1 corresponding to E2 (high) phonon mode depicting the c-axis oriented (perpendicular to substrate) AlN film. SEM analysis showed the AlN film deposited at higher substrate bias voltage contains fewer amounts of Al macro-particles.

Influence of Plasma Treatments on the Frictional Performance of Rubbers

The frictional performance of several rubbers after pulsed-DC plasma treatments has been examined. In all cases, the treated rubbers showed better performance than the corresponding untreated ones. Stronger treatments, in terms of longer process time and/or higher substrate bias voltage, led to larger reductions of coefficient of friction and wear. The addition of hydrogen to the argon plasma did not show any additional positive effect. Nevertheless, different degrees of improvement were observed for different rubbers. In fact, the energy consumed during the tribotest scales with the maximum working temperature of the rubbers, indicating that the plasma treatment is more effective in the case of more sensitive rubbers.

Device Design for a 12.3-Megapixel, Fully Depleted, Back-Illuminated, High-Voltage Compatible Charge-Coupled Device

A 12.3-megapixel charge-coupled device (CCD) that can be operated at high substrate-bias voltages has been developed in support of a proposal to study dark energy. The pixel size is 10.5 mum, and the format is 3512 rows by 3508 columns. The CCD is nominally 200 mum thick and is fabricated on high-resistivity n-type silicon that allows for fully depleted operation with the application of a substrate-bias voltage. The CCD is required to have high quantum efficiency (QE) at near-infrared wavelengths, low noise and dark current, and an rms spatial resolution of less than 4 mum. In order to optimize the spatial resolution and QE, requirements that have conflicting dependences on the substrate thickness, it is necessary to operate the CCD at large substrate-bias voltages. In this paper, we describe the features of the CCD, summarize the performance, and discuss in detail the device-design techniques used to realize 200-mum-thick CCDs that can be operated at substrate-bias voltages in excess of 100 V.

Development of X-Shaped Filtered-Arc-Deposition (X-FAD) Apparatus and DLC/Cr Film Preparation

An X-shaped filtered-arc-deposition (X-FAD) apparatus was developed in order to prepare hydrogen-free tetrahedral amorphous carbon (ta-C), which is a kind of diamond-like carbon (DLC), and metal film as a binding interlayer on the superhard alloy using a plasma beam irradiated from the same direction. First of all, the droplet-reduction performance was verified, and then, the appropriate duct-bias voltages and deposition rate were measured. Optima of duct biases for chromium (Cr) and DLC were found to be 25 and 15 V, respectively. From the result of X-ray diffraction analysis, it was found that Cr film that is prepared at a higher substrate-bias voltage was well crystallized and has less internal stress. The appropriate substrate bias for preparing ta-C was -100 to -200 V. DLC film was also prepared with substrate heating. It was found that ta-C could be prepared at a substrate temperature of less than 200degC, and the film was graphitized at higher temperature. By following these results, 2.5-mum-thick ta-C film was prepared on a superhard alloy with an interlayer by X-FAD.

Effect of implanted argon on hardness of novel magnetron sputtered Si–B–C–N materials:experiments and ab initio simulations

Amorphous silicon–boron–carbon–nitrogen alloys were deposited by reactivemagnetron sputtering in nitrogen–argon gas mixtures, and their structure andresulting mechanical properties were investigated using a combined approach ofexperiment and molecular-dynamics simulations. We show a difference betweenstructures of the materials deposited with a low substrate bias voltage of−100 V leading to a 2% content of implanted Ar atoms, and a high substrate bias voltage of−500 V, resulting in a 6% content of implanted Ar atoms. We find that, while at the higher Arcontent the material is practically homogeneous, at the low Ar content there are similarvolumes of Si-rich (around the implanted Ar atoms) and Si-poor zones. This can increasematerial hardness. We examine a temperature dependence of this phenomenon in the lightof experimental results.

Effect of high-voltage sheath electric field and ion-enhanced etching on growth of carbon nanofibers in high-density plasma chemical-vapor deposition

The results of a parametric study on the growth of vertically aligned carbon nanofibers (CNFs) by high-density inductively coupled plasma (ICP) chemical-vapor deposition are reported. We investigated the mechanisms that cause the detachment of CNFs during the growth process by high-density plasma-enhanced chemical-vapor deposition with high substrate bias voltage and atomic hydrogen concentration. A simplified model, combining the Child law for sheath field, floating sphere model for field enhancement at the fiber tip and electric-field screening effect, was employed to estimate the detachment electrostatic force on individual CNFs induced by plasma sheath electric field. The force was found to increase with substrate bias voltage, bias current, and lengths of CNFs, consistent with the experimental observations that CNFs density decreases with ICP power, bias power, and growth time. However, the magnitude of the electrostatic force per se cannot explain the detachment phenomena. The other factor is believed to be the ion-assisted etch of CNFs by atomic hydrogen during the growth process since it was observed that the lower end of CNFs formed earlier in the synthesis process became thinner than the tip end.

Biosensing properties of nanocrystalline diamond film grown on polycrystalline diamond electrodes

Micron-sized polycrystalline diamond electrode typically exhibits poor and sluggish response to ascorbic acid (L-AA) and cannot resolve voltammetrically mixtures of biomolecules (e.g. L-AA, dopamine (DA) and uric acid (UA)). This paper investigates a simple re-growth strategy to modify the polycrystalline diamond surfaces for making an active biosensing electrode. A thin, nominally undoped nanocrystalline diamond (NCD) layer has been grown on the surface of boron-doped polycrystalline diamond substrate using a high substrate bias voltage (−200 V) and a 12% hydrocarbon-in-hydrogen gas feed. We found that the over-potential for L-AA oxidation has been reduced from 400 to 60 mV and that voltammetric differentiation of DA and UA, or UA and L-AA, is possible on the NCD-modified diamond electrode.

Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (VB) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (H) and Young’s modulus (Y) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100–250 V. Films deposited at |V B| = 250 V exhibited hardness as high as 3300 kg/mm2. This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure.

Tribological properties and adhesive strength of DLC coatings prepared under different substrate bias voltages

An investigation has been carried out to study the effect of high substrate bias voltages on the morphological, mechanical, adhesive and tribological properties of diamond-like carbon (DLC) films. The morphological study shows that the film has a tendency to be rougher, when it is prepared with increased substrate bias voltages. Relatively lower hardness and poor wear resistance (the coefficient of friction remains almost same) are characteristics of the films that are prepared with higher substrate bias voltages. Improved adhesion is observed for the films that are prepared under high substrate bias voltage, and is due to the formation of increased intermixed layer thickness.

Tribological and mechanical properties of carbon nitride films deposited by ionised magnetron sputtering

Tribological and mechanical properties were evaluated for carbon nitride films deposited by an ionised d.c. magnetron sputtering system in which an inductive plasma was generated between the graphite target and the substrate. Steady-state mean coefficients of friction against hard steel in ball-on-rotating disc tests were from 0.44 to 0.81 for films deposited with the inductive plasma, and from 0.36 to 0.60 without the inductive plasma. In each case, the friction increased with increasing nitrogen content in the sputtering gas and then reached a constant value. The elastic modulus of the films was deduced from nanoindentation experiments, and the residual strains in the films were estimated from specimen curvature measurements. The modulus of the films with no inductive plasma reached a maximum with 10 vol.% nitrogen in the sputtering gas, and decreased markedly with the inductive plasma. The modulus also decreased at higher pressures and higher substrate bias voltages. The strains in the films were always compressive, and increased when nitrogen was present in the sputtering gas.

Cavitation-resistant TiNi films deposited by using cathodic arc plasma ion plating

TiNi intermetallic compound with superelasticity and corrosion resistance could have potential use in resisting sliding wear, rolling fatigue, corrosion, or erosion environments. TiNi is, however, expensive. A thin film coating of TiNi may enable low-cost materials such as plain steel to be used in the above applications. Thus, a study on the uses of TiNi coating is necessary. A cathodic arc plasma (CAP) ion plating process was used to deposit TiNi films onto plain steel using Ti 50Ni 50 target material. The substrate's bias voltage was changed to optimize the properties of the deposited film. Experimental results show that the deposited films have approximately the stoichiometry of Ti 40Ni 60. The nickel-rich composition may be caused by the ease of scattering of the titanium atoms or the thermalization of the background gas atoms during their flight to the substrate. Due to the higher migration ability of the surface adatoms, the films deposited at high substrate bias voltage possess a higher crystallinity. The major phase in such films is TiNi-B2. TiNi 3 and TiNi-B19′ coexist as the minor phases. Cavitation resistance of the specimen in freshwater was significantly increased to a 3-fold value in comparison with the uncoated plain steel. These promising results suggest that CAP ion plating is suitable for preparing cavitation-resistant TiNi films, if high substrate bias voltage is employed. The highly aggressive electrolyte develops a perfect Galvanic cell around the pits and the electrolyte accelerates the electrochemical dissolution of the anodically polarized substrate.

Sheath expansion in a drifting, nonuniform plasma

A model is proposed for the sheath expansion into a nonuniform plasma with substantial drift velocity. We refer in particular to the streaming metal plasma produced by a vacuum arc discharge; this kind of plasma is characterized by its spatial nonuniformity and high ion drift velocity. It is shown that for a nonuniform plasma and high substrate bias voltage (>10 kV), the sheath thickness is significantly smaller than in a uniform plasma. High drift velocity also leads to a decrease in sheath thickness. For plasma immersion ion implantation carried out in a nonuniform plasma, the increase in ion implantation current with increasing voltage is different from that of a uniform plasma where the ion current is constant with voltage. This effect was found to be quantitative agreement with experiment. The decrease in sheath thickness with increasing plasma drift velocity can explain qualitatively the experimentally observed existence of a stable high-voltage sheath for a relatively long time.