Reactive Unbalanced Magnetron Sputtering Research Articles

Effect of bias voltage on the properties of CeO2−x coatings prepared by magnetron sputtering

In this study, cerium oxide (CeO2−x) coatings were deposited onto silicon substrates by reactive unbalanced magnetron sputtering in an Ar-O2 gas mixture. The effect of substrate negative bias voltage on the surface morphology, wetting behavior, microstructure, mechanical and tribological properties of CeO2−x coatings were systematically investigated. It was found that the surface morphology and the root mean square (RMS) roughness of the coatings exhibited a non-linear evolution. The smoothest surface with a RMS roughness of about 3.3nm was obtained at a bias voltage of −60V. All deposited coatings exhibited a hydrophobic feature with the water contact angle around 100°, which was close to the value obtained from Teflon surface. X-ray diffraction (XRD) analyses revealed the best crystallinity of CeO2−x coatings in cubic CeO2 phase at a critical value of −80V bias. Cross-sectional scanning electron microscope (SEM) images displayed typical columnar-type structures with a relatively large column grain for the coating deposited at −20V and a dense, fine-grained microstructure obtained at −80V. The microstructure improvement at the optimized bias (−80V) contributed further to the enhancement in the hardness, reaching a maximum value of ~18.0GPa. The average friction coefficients of as-deposited coatings prepared between −40 and −120V were measured to be around ~0.40, whereas the coating prepared at −80V showed the best anti-wear performance. The wear volumes were two orders of magnitude lower than that of 316 stainless steel (SS) and three orders of magnitude lower than that of Teflon.

Plasmonic Properties of Nanostructured Diamond Like Carbon/Silver Nanocomposite Films with Nanohole Arrays

Plasmonic properties of the diamond like carbon nanocomposite films with embedded silver nanoparticles with patterned nanohole arrays were analyzed in this study. The films were deposited by unbalanced reactive magnetron sputtering of silver target. Nanopatterning of the films was performed by combining electron beam nanolithography and ion beam etching techniques. Modeling of plasmonic properties was done using the classical Maxwell-Garnett theory. Modeling data and experimental results were in good accordance. Formation of the nanohole pattern in diamond like carbon films doped with silver resulted in decreased intensity of the surface plasmon resonance absorbance peak. No new absorbance or transmittance peaks were observed after the nanopattering. It was explained by extraordinary transmission effect in nanostructured DLC : Ag film films due to plasmon polariton resonance inside of the nanoholes. DOI: http://dx.doi.org/10.5755/j01.ms.22.4.13193

Friction and wear response of nitride coating deposited through PVD magnetron sputtering

Surface engineering with applied coating plays a vital role in any industrial application. These coatings are meant for better mechanical and tribological characteristics when applied on to the materials. The major challenge in selecting a suitable coating strategy is their input process parameters. There are several parameters which influences the coating properties, but it is hard to choose one of them and ignoring others. Multilayers of tungsten nitride are attracting great interest to modulate their tribological and mechanical properties through physical vapour deposition process due to their wide application range. These multilayer nitride films were deposited through unbalanced reactive magnetron sputtering technique. The tribological tests were performed on a pin-on-disc tribometer at room temperature and it has been observed that friction and wear values reduce drastically while applying multilayer coatings. Later, artificial neural network (ANN) is employed to optimize the tribological properties of sputtered coatings.

Optimization of process parameters to achieve spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO high temperature solar absorber coating

TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber was deposited on stainless steel substrate by using four cathode reactive direct current unbalanced magnetron sputtering system. The reactive gas flow rates (C2H2, N2 and O2) and thicknesses of each individual layers were varied to obtain the selective properties of the tandem absorber. The detailed effects of reactive gas flow rates and thicknesses of the individual layers on the optical properties were studied by using UV–vis–NIR spectrophotometer. Guiding factor in optimizing various process parameters was to achieve low reflectance in the solar spectrum region and high reflectance in the infrared region. The change in growth rate of the tandem absorber with reactive gas flow rate was studied using the thickness data, target voltage and target current. These results indicate a decrease in the growth rate of each individual layer of the tandem absorber with an increase in the flow rates of the reactive gases. The changes in bonding structure and chemical composition with reactive gas flow rates were studied by X-ray photoelectron spectroscopy. The optimized tandem absorber deposited on stainless steel substrate shows absorptance of 0.960 and emittance of 0.15. The thicknesses of the optimized individual layers were ∼62, 18, 20, 16, 27nm, respectively.

An experimental investigation on the machining characteristics of Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills

We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (vc) of 13m/min and a feed rate (fz) of 6mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation.

Improved thermal stability, mechanical and tribological properties of reactively sputtered Si doped TiAlC nanostructured hard coatings

The influence of different Si contents on TiAlSiC nanocomposite coatings deposited on stainless steel and silicon (100) substrates using reactive unbalanced direct current magnetron sputtering has been studied. A comprehensive study of microstructure, mechanical, tribological and thermal stability of Si doped TiAlC has been carried out. X-ray diffraction (XRD) analysis reveals that the TiAlSiC coating exhibits fcc NaCl type TiC phase. The presence of a-AlC and a-Si phases was observed by correlating the X-ray photoelectron spectroscopy and XRD data. Moreover, micro-Raman spectroscopy studies indicate the existence of graphitic rich layer of a-C in the coating which limits the columnar growth on account of a-Si. Friction coefficient, adhesion, toughness and mechanical properties of the TiAlSiC coatings were characterized by nanoscratch tester and nanoindentation measurements. A high hardness ~ 28 GPa and a friction co-efficient of ~ 0.49 was achieved for TiAlSiC coatings prepared at a Si contents of 8 at.%. The maximum toughness of 2.14 MPa m1/2 was obtained for the optimized coating due to grain boundary strengthening. Although, increase in the Si content deteriorates the mechanical and tribological performance, but it improves the thermal stability of the coatings. A remarkable thermal stability up to 1000 °C in air for 4 h has been observed for higher Si contents (> 12 at.%).

Structural, chemical and nanomechanical investigations of SiC/polymeric a-C:H films deposited by reactive RF unbalanced magnetron sputtering

Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C2H2 precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C2H2 concentration during deposition. A higher C2H2 flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H3/E2. The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp3 bond content shows the highest elastic recovery during scratching.

Multilayer nitride coating performance optimized by an artificial neural network approach

One of the most important problems occurred in many industries is due to friction and wear process. Over the years, minimizing friction and controlling wear is one of the difficult tasks for the researchers. Both properties can be minimized by the application of adequate coating technology. Many coating deposition technologies have been employed to limit friction and wear but only few succeeded, those are directly affected by the nature of the material under investigation and process parameters. A suitable coating strategy varying from single layer to multilayer should be applied to the materials whose superficial properties such as low friction, improved wear resistance, and adhesion are the prime interest. Multilayer coatings possess high hardness, ductility and fracture strength compared to single layer coatings. The advantageous properties of these multilayers can be preciously tailored according to specific application. For this purpose Physical Vapour Deposition (PVD) coatings have been developed considerably due to increasing industrial demands. In the present research, friction and wear study of multilayer PVD-nitride coating deposited on tool steel by unbalanced reactive magnetron sputtering technique have been discussed. Later on an Artificial Neural Network approach was used to predict the tribological properties of multilayer nitride films. Bias voltage, total gas flow rate, lap, time, velocity and load were considered as controllable factors. The regression and performance curve analysis is used to assess the optimized outcome of deposited film properties such as friction and wear. The analyzed results shows that experimented and predicted values are in a good agreement.

Titanium oxide films with vacuum thermal treatment for enhanced hemocompatibility

Blood compatibility is a key property of biomaterials contacting blood. Titanium oxide film has been deposited on Si wafers (110) by unbalanced reactive magnetron sputtering and successive vacuum annealing. The structure, chemical composition, hydrophilicity and surface energy of the films have been investigated by X-ray diffraction, X-ray photoelectron spectroscopy and contact angle measurement respectively. The results revealed that high vacuum annealing increased the surface energy, hydrophilicity and the rate of of Lewis base in the film. In vitro evaluation of hemocompatibility, including platelet adhesion, fibrinogen denaturation, activated partial thromboplastin time and thrombin time test, proved that the hydrophilic titanium oxide films have excellent blood compatibility.

Insight into Al existing form and its role on microstructure and properties of Cr1−xAlxN films

A series of Cr 1−x Al x N (where x denotes the atom fraction of Al in Cr 1−x Al x N film) films with different Al contents have been deposited by unbalanced reactive magnetron sputtering technique. The chemical composition, microstructure, surface morphology, cross-sectional structure, mechanical properties, thermal stability and tribological properties of the deposited films were studied by means of different techniques. It is found that with the increase of Al doping, the Al atoms either substitute the Cr atoms or occupy the interstitial sites in the CrN crystal lattice firstly, and when the Al doping content exceeds the solid solubility, superfluous Al atoms then exist in the form of amorphous or nanocrystal state in the films. Meanwhile, the grain size becomes smaller, and the microstructure gets denser because the Al doping leads to multiple crystal orientations and inhibits the grain growth. The Al doping induced solid solution hardening and grain boundary effects contribute to the high hardness of CrAlN films, and the dense structure as well as interstitial solid solution of Al, which can block the diffusion channel, endows the CrAlN films good oxidation resistance. Besides, a small amount of free Al existing in the films is favorable to improve the thermal stability without obvious loss of hardness. Finally, the relatively high hardness and good thermal stability make the Cr 0.29 Al 0.71 N film has relatively good tribological properties than CrN film under a wide temperature range, which extends the operating temperature of the CrN films in some fields.

Relationship between bias voltage and microstructure as well as properties of CrAlYN films**Project supported by the National Basic Research Program of China (Grant No. 2013CB632302) and the National Natural Science Foundation of China (Grant No. 51175491).

In this work, a series of CrAlYN films doped with 1 at.% yttrium were deposited by unbalanced reactive magnetron sputtering under different bias voltages. The effects of bias voltage on microstructure and properties of the CrAlYN films were subsequently investigated. It is found that all the as-deposited films have similar chemical composition and crystalline structure. However, the bias voltage has significant impact on the mechanical properties and oxidation resistance of the resulting films. Namely, the film deposited at 100 V has the highest hardness and best oxidation resistance, which are mainly attributed to its denser structure and higher Al content than others. In addition, the film obtained at 100 V exhibits superior oxidation resistance even at 1000 °C, and good friction and wear properties at 600 and 800 °C, and the latter two are mainly ascribed to the formation of compact transfer layer on the worn surfaces. However, this film experienced obvious wear loss at low testing temperatures (i.e., 200 and 400 °C) due to the serious abrasive wear.

Study on reactive sputtering of yttrium oxide: Process and thin film properties

This paper investigates the influence of deposition conditions on the properties of yttrium oxide thin films. The paper focuses on the texture, optical and mechanical properties. With this objective, a series of yttrium oxide thin films with different thicknesses were deposited by direct current (DC) unbalanced reactive magnetron sputtering at high and low pumping speed. By changing the oxygen flow, depositions were performed in the three characteristic deposition modes for reactive magnetron sputtering, i.e., metallic, transition and poisoned mode. By using an oxygen flow directed to the substrate, full oxidation of the samples, as shown by X-ray photoelectron spectroscopy (XPS), in the three modes is obtained. Crystallographic characterization by X-ray diffraction (XRD) shows that films crystallize in the cubic phase with a strong (222) out-of-plane orientation at low oxygen flow. As the oxygen flow increases a mixture of cubic and monoclinic phase is obtained. In poisoned mode, the films consist of the cubic phase with preferred (420) orientation. Scanning electron microscopy (SEM) cross sections show, with increasing oxygen flow, a loss of the columnar structure. As the oxygen flow rates increase through the metallic, transition, and the poisoned mode, the grain size becomes gradually smaller. An overview diagram of all experimental results uncovers that the textural changes are closely linked to the oxygen partial pressure rather than the oxygen flow. The optical properties of films were investigated by spectroscopic ellipsometry (SE). The films with a columnar structure demonstrate superior hardness and modulus as well as the high plasticity.

Structural and mechanical properties of reactively sputtered TiAlC nanostructured hard coatings

TiAlC nanostructured hard coatings have been deposited on Si(100) substrates by four-cathode reactive pulsed direct current unbalanced magnetron sputtering at various process conditions. The effects of Al and C on the compositional, mechanical and micro-structural properties of TiAlC coatings have been investigated using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy and nanoindentation hardness tester. Furthermore, the effect of substrate bias on the surface morphology, micro-structure and mechanical properties of TiAlC coatings is examined in detail. Formation of Ti3AlC(111) phase along with inclusion of TiC and amorphous carbon phases has been confirmed by XRD and micro-Raman spectroscopy studies. The optimized TiAlC coating exhibited a maximum hardness of ~30GPa and elastic modulus of 288GPa. Analysis of the nanoindentation data indicated that the resistance to plastic deformation (H3/E*2) and elastic strain to failure (H/E*) decrease with C and Al contents in the TiAlC coatings, whereas, these properties increase with an increase in the substrate bias due to grain size refinement. Lastly, fracture toughness of TiAlC coating has also been calculated using a cube corner indenter and the optimized coating exhibited a maximum toughness of ~1.38MPam1/2 at a load of 50mN.

Novel hard, tough HfAlSiN multilayers, defined by alternating Si bond structure, deposited using modulated high-flux, low-energy ion irradiation of the growing film

Hf1−x−yAlxSiyN (0 ≤ x ≤ 0.14, 0 ≤ y ≤ 0.12) single layer and multilayer films are grown on Si(001) at 250 °C using ultrahigh vacuum magnetically unbalanced reactive magnetron sputtering from a single Hf0.6Al0.2Si0.2 target in mixed 5%-N2/Ar atmospheres at a total pressure of 20 mTorr (2.67 Pa). The composition and nanostructure of Hf1−x−yAlxSiyN films are controlled by varying the energy Ei of the ions incident at the film growth surface while maintaining the ion-to-metal flux ratio constant at eight. Switching Ei between 10 and 40 eV allows the growth of Hf0.78Al0.10Si0.12N/Hf0.78Al0.14Si0.08N multilayers with similar layer compositions, but in which the Si bonding state changes from predominantly Si–Si/Si–Hf for films grown with Ei = 10 eV, to primarily Si–N with Ei = 40 eV. Multilayer hardness values, which vary inversely with bilayer period Λ, range from 20 GPa with Λ = 20 nm to 27 GPa with Λ = 2 nm, while fracture toughness increases directly with Λ. Multilayers with Λ = 10 nm combine relatively high hardness, H ∼ 24 GPa, with good fracture toughness.

Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for high-temperature solar thermal power applications

A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for high-temperature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82°C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325°C in air for 400h and up to 650°C in vacuum for 100h, thus demonstrating its suitability for high-temperature solar thermal power generation applications.

Semiconducting WO3 thin films prepared by pulsed reactive magnetron sputtering

WO3 crystalline semiconductor thin films for water-splitting applications were prepared by pulsed unbalanced reactive magnetron sputtering with W target and Ar + O2 gas mixture. Postdeposition annealing at temperature of 450 °C was applied to the WO3 samples to improve their crystallinity and semiconductor properties. Various pulsing modes were tested in deposition experiments with different pulsing frequencies, discharge power applied in pulse, and average applied power. To determine the influence of the plasma parameters on the deposition process, the pulsed and average ion flux density on the substrate were measured using an ion probe. The WO3 films had monoclinic crystalline structure after the annealing process. Different crystallite orientations were found for different modes of discharge pulsing. Preferential orientation of the (200) plane parallel to the substrate surface was identified for higher frequency of discharge pulsing with lower substrate pulsed ion flux but higher average substrate ion flux. The WO3 films with this type of texture had the highest photocurrents in photoelectrochemical (PEC) measurements.

Microstructures, mechanical properties and oxidation behavior of vacuum annealed TiZrN thin films

The purpose of this study was to investigate the effects of vacuum heat treatments on microstructures, associated mechanical behavior and oxidation behavior of TiZrN films. The films with three Zr/(Zr + Ti) ratios of 0.3, 0.5 and 0.7 were prepared using a DC reactive unbalanced magnetron sputter system. The annealing temperatures ranged from 700 to 1000 °C. X-ray diffraction (XRD) and microstructural examination revealed that both the as-deposited and heat-treated films exhibited a single TiZrN phase with columnar grains at the annealing temperature below 900 °C. At 1000 °C, ZrO2 phase appeared. In a temperature range from 700 to 900 °C in vacuum for 3 h, the heat-treated films showed a 15% drop in hardness, as compared with the as-deposited films. The slight decrease in hardness suggested that the heat-treated TiZrN films with a hardness level of application interest could be attributed to solid solution strengthening. Stress state of the films was found to be compressive. Substantial decrease in the magnitude of the residual compressive stresses could be achieved via heat treatment. At 1000 °C, the volume expansion arising from the oxidation of zirconium within the film may lead to an increase in residual compressive stresses of the films. The Ti0.7Zr0.3N film exhibited a lowest oxidation rate in the TiZrN coatings at 1000 °C in vacuum.

Plasmonic properties of silver nanoparticles embedded in diamond like carbon films: Influence of structure and composition

In the present study optical properties of hydrogenated diamond like carbon nanocomposite films containing silver nanoparticles (DLC:Ag) deposited by direct current (DC) unbalanced reactive magnetron sputtering were studied in 180–1100nm range. Different substrate bias was used during deposition of the films. Structure of the films was investigated by multiwavelength Raman scattering spectroscopy and X-ray diffractometry (XRD). Chemical composition of the samples was studied by X-ray photoelectron spectroscopy (XPS), surface morphology was investigated by atomic force microscopy (AFM). Red shift of the surface plasmon resonance peak of DLC:Ag films with the increase of Ag atomic concentration was observed. It was found that high atomic concentration of oxygen in DLC:Ag films results in some redshift of the plasmonic peak, too. Such a behavior is explained by increase of the refractive index of the dielectric medium surrounding silver nanoparticle due to possible presence of the silver oxide interlayer at the Ag nanocluster and diamond like carbon matrix interface. It was demonstrated that influence of the increased Ag atomic concentration on position of the surface plasmon resonance peak of DLC:Ag films clearly prevails influence of the increased sp3/sp2 ratio of the diamond like carbon matrix. Correlation between the structure of Ag nanocrystallites studied by XRD and position of the surface plasmon resonance peak position was observed.

Effect of bias voltage on compositional, mechanical and corrosion property of ZrNbAlN multilayer films by unbalanced magnetron sputtering

Nano-scaled ZrNbAlN films with different negative bias voltages (Vb) were deposited on bronze substrate and Si (100) wafers by a reactive unbalanced magnetron sputtering technique. Composition and structure properties were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. It is found that mole concentrations of Zr and Nb are affected by Vb, which leads to the increase of binding energy of N 1s and Al 2p and decrease of binding energy of Zr 3d5/2 and Nb 3d5/2. Surface morphologies evolution controlled by Vb could be observed. Furthermore, X-ray diffraction patterns reveal that these films show a (111) preferred orientation. Moreover, mechanical property and corrosion behavior of ZrNbAlN films were characterized by nanoindentation test and corrosion test, respectively. A maximum value of 21.85 GPa at −70 V occurs in the ZrNbAlN- bronze system, which outperforms uncoated bronze. Corrosion experiments in 0.5 mol/L NaCl and 0.5 mol/L HCl solution show that corrosion potential and corrosion current are dependent on Vb, and better anti-corrosion property could be obtained at −90 V.

Tailored Mechanical Properties and Residual Stresses of a-C:H:W Coatings

In this study, three different a-C:H:W coatings with predefined hardness values, ranging from 10 up to 16 GPa, were deposited by adjusting bias voltage according to a previously created regression model. For this purpose, the influence of the main process parameters of the used reactive unbalanced magnetron sputtering process on the mechanical properties of the a-C:H:W coating was investigated previously by nanoindentation. For a systematical evaluation of the single effects, parameters were varied according to a central composite design. The three coating variants of this study were investigated in terms of microstructure, mechanical properties and residual stresses. It turned out, that by the use of the regression model, a-C:H:W coatings with tailored mechanical properties can be deposited. Residual stresses were measured by means of focused ion beam milling of a double-slit geometry, which causes the internal stresses to relax, and mapping of the resultant relief strain by digital image correlation. A linear relation between the applied bias voltage and the hardness, the modulus of the coating as well as the determined relief strain was observed. Thus, residual stresses of the coatings increase disproportionately with applied bias voltage. The obtained results can be helpful for tailored coating design and further optimization of a-C:H:W coatings.