Pulsed DC Magnetron Sputtering Research Articles

Sputter deposited p-NiO/n-SnO2 porous thin film heterojunction based NO2 sensor with high selectivity and fast response

In this work, we report fabrication and characterization of porous, single layer n-SnO2, p-NiO and bilayer thin film heterojunction devices developed using pulsed DC magnetron sputtering for NO2 detection. Template-free, NiO/SnO2 heterojunction devices were deposited both in top-bottom and in-plane electrode configurations. All the devices showed an optimum sensing temperature of 200 °C. Systematic comparison of the fabricated devices revealed that the heterojunction devices with top-bottom electrodes improved performance. Electrical characterization confirmed the formation of heterojunction across the interface. The response values of the heterojunction sensor ranged from 57 to 144 % for the NO2 concentration range of 2–10 ppm. The heterojunction device showed high selectivity against CO and NH3 with selectivity coefficients of 90 and 26, respectively. The heterojunction sensor exhibited fast response and recovery times of 37 and 98 s, respectively. The device showed excellent stability with < 2 % variation in response for 10 cycles of transient response characteristics. The I–V characteristics of heterojunctions with top-bottom and in-plane electrodes were explained by an equivalent circuit model. The observed enhancement in various parameters can be ascribed to the formation of distributed p-n nano-heterojunctions across the interface. The developed NiO/SnO2 heterojunction sensor by the simple and reproducible sputtering technique is found to be a promising candidate for the detection of NO2.

A simple route to prepare anatase TiO2 film onto polyimide substrate by DC pulsed magnetron sputtering

TiO2 film was deposited onto polyimide substrate by DC pulsed magnetron sputtering with different sputtering power densities. XRD results showed that with increasing the sputtering power density from 0.83 W/cm2 to 5.00 W/cm2, the crystallinity of as-deposited TiO2 film improved monotonously. And 5.00 W/cm2 was determined as the critical sputtering power density in which the highest temperature the substrate could withstand. Then, XRD and TEM results showed that the as-deposited TiO2 film could have a better anatase structure by providing an auxiliary heating to the substrate at the highest temperature during TiO2 film deposition. Combining the sputtering parameters, as well as DC pulsed voltage waveform, the reason for as-deposited TiO2 film crystallization was investigated systematically.

Experimental and theoretical study of thermoelectric properties of rhombohedral GeSb5Te10 thin films

Rhombohedral GeSb5Te10 thin films are synthesized onto Al2O3 substrate by a pulsed-DC magnetron sputtering method using a target prepared by hot-pressing method. Thermoelectric properties of these films are studied as a function of temperature from room temperature to 773 K and correlated to the microstructural and surface properties. It is found that the phase transformation from amorphous to rhombohedral phase of GeSb5Te10, observed in temperature range 473–773 K, involved lattice-swelling and atomic diffusion within the crystalline structure. The completion of phase transformation at annealing temperature 673 K minimized the average crystallite size of thin film and enhanced the Seebeck coefficients (~140 μVK−1) and thermoelectric power factor (~4.5 mWm−1 K−2). Molecular orbital simulations of small cluster model, performed using linearly decreasing scattering variable along with the temperature dependent Fermi energy for onto determining the electrical and thermoelectric properties, were found in agreement to the experimental results.

Hard yet tough CrN/Si3N4 multilayer coatings deposited by the combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering

Hard yet tough coatings with simultaneously high hardness and toughness represent a new class of high-performance coatings, which are vital for tribological applications due to the enhanced surface/interface properties. In this work, CrN/Si3N4 multilayer coatings with various Si content were reactively deposited by the combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering. The as-deposited coatings exhibit smooth surface morphology, well-defined nc-CrN/a-Si3N4 interfaces, uniform thickness and highly dense architecture. Microstructure evolution is induced by Si content changing from scaly nanocolumnar to densely packed fibrous grains to tapered crystallites. These features allow the achievement of the increased properties in terms of high hardness of 30.6 GPa, H/E* of 0.099, H3/E*2 of 0.387, elastic recover We of 58.5% and fracture toughness KIC of 3.69 MPa·m1/2. Hard yet tough CrN/Si3N4 multilayer coatings show excellent tribological properties by enhanced cooperative deformability through energy dissipation and stress relaxation at well-arranged nc-CrN/a-Si3N4 interfaces to reduce crack initiation and propagation, and adhesion failure, thanks to the enhanced H, H/E*, H3/E*2, We and KIC. Meanwhile, under limited normal load conditions, uniform tribolayers (Cr2O3, FeO(OH), Fe2O3 and Fe3O4) caused by tribochemical reaction on the worn surface also act to make contributions towards reducing friction and wear as a lubricant.

Influence of plasma excitation power on mechanical property and biocompatibility of titania/alumina composite thin films for medical implant prepared by magnetron sputtering

In present study, titania-alumina composite films were deposited using pulsed DC magnetron sputtering system for various plasma excitation powers (100 W to 200 W). The composition of films was examined through x-ray diffractometer (XRD), whereas Scanning electron microscope (SEM) and Atomic force microscope (AFM) were carried out to investigate the surface morphology. The mechanical properties such as strength and hardness of deposited films were determined by using universal testing machine and Vickers hardness tester. It was observed that the yield strength (YS), ultimate tensile strength (UTS) and hardness of treated samples were increased. The stability of deposited films was investigated using scratch test. The biocompatibility of deposited films was studied by culturing the MC3T3-E1 cells for three days. The micrographs of cells culture showed better cells growth/proliferation (elongated morphology) on film prepared at 150 W. Our results exhibit that titania-alumina composite films enhance the surface roughness, mechanical properties and biocompatibility of titanium. Therefore, Ti is also a better choice for load barring applications as compared to Ti6Al4V which contain the toxic element.

Influence of sputtering power and Ar–N2 flow on the structure and optical properties of indium nitride films prepared by magnetron sputtering

ABSTRACTThis paper discusses the deposition of indium nitride (InN) thin films on Si (100) substrates by using pulsed DC magnetron sputtering. Effects of varying sputtering power and Ar–N2 flow ratio on the structural, morphological, and optical properties of indium nitride (InN) films were investigated. The structural characterization indicated nanocrystalline InN film with preferred orientation towards (101) plane that exhibited the optimum crystalline quality at 130 W and for 40:60 Ar–N2 ratio. The surface morphology of InN, as observed through FESEM, contained irregularly shaped nanocrystals with size that increases with higher sputtering power and Ar:N2 flow ratio. The optical properties of InN films were studied using ellipsometer at room temperature. The band gap of InN was decreased with the increase of sputtering power to 130 W, whereas an increase in the band gap was noticed with the increase of the Ar:N2 flow ratio.

Study of W-B-C thin films prepared by magnetron sputtering using a combinatorial approach

X-B-C materials, where X is a transition metal such as Mo, W or Ta, have recently gained attention as possible materials for protective coatings used in material machining. In this study, a combinatorial approach was used to deposit a total of 182 coatings with a wide composition range using pulsed-DC magnetron sputtering. The coatings were prepared either in conditions, where a comparatively lower energy was delivered onto the growing coating, i.e. at ambient temperature and without applied bias, or in conditions where the coating received higher energy, i.e. at 500 °C with a bias voltage of −100 V, to study the effect of energy flow on the coating structure and properties. The coating structure was examined and four different types of diffractograms have been observed: amorphous, short range ordered, crystalline W and nanocrystalline WB2. No other crystalline phases were detected. The measured hardness of the coatings was between 9.7 and 29.7 GPa and was independent of the carbon content, however, it increased with the boron content and decreased with the tungsten content in the composition region studied. The hardest coatings exhibited an amorphous structure. The effective elastic modulus ranged from 170 to 340 GPa and increased with the boron and tungsten contents. The highest moduli were obtained for coatings exhibiting a crystalline W phase. Coatings deposited at high energy flow to the growing coating generally exhibited higher hardness and comparable elastic modulus to their counterparts with a similar composition prepared without heating or bias.

Tribological behaviors in air and seawater of CrN/TiN superlattice coatings irradiated by high-intensity pulsed ion beam

Surface integrity and interface structure of coating materials play a key role in tribological and corrosion behaviors in harsh working environments in nuclear power plants. In this work, we focus on the investigations of tribological behaviors in air and seawater of CrN/TiN superlattice coatings deposited by the combined deep oscillation magnetron sputtering with pulsed dc magnetron sputtering, which were irradiated by high-intensity pulsed ion beam (HIPIB) with ion energy density of 1–3 J/cm2 and shot number of 1–5. At 1 J/cm2, the increased shot number leads to a broaden (111) peak of face-centered cubic crystal structure, indicating grain size refinement. At 3 J/cm2, the increased shot number results in the coarsening grain, and superlattice structure gradually disappeared at 2 shots, finally the coatings fell off from substrate at 5 shots. The highest hardness (H), H/E* (E*, effective Young’s modulus) and H3/E*2 of the coatings irradiated at 1 J/cm2 and 5 shots are achieved at 38.7 GPa, 0.1 and 0.387, respectively. The increased ion energy density and shot number result in the decrease in Rockwell C HF adhesion level from HF1 to HF6. At 1 Jcm−2 and 1 shot, tribological behavior of irradiated coatings in air was dominated by oxidative wear with coefficient of friction (COF) of 0.51 and specific wear rate of 4.2 × 10−7mm3N−1m−1. The irradiated coatings show excellent tribocorrosion properties in seawater with high open circuit potential of 0.32 V, low COF of 0.14 and specific tribocorrosion rate of 6.1 × 10−8mm3N−1m−1 without pitting corrosion under moderate HIPIB irradiation due to high surface integrity and stability of well-defined interfaces and dense microstructure. With an increase of energy density and shot number, wear mechanism in air changes to severe adhesive and oxidative wear, while tribocorrosion mechanism is gradually dominated by plough wear coupled with pitting corrosion.

Tailoring of TiO2 film microstructure by pulsed-DC and RF magnetron co-sputtering

In current study unconventional method of TiO2 film deposition by co-sputtering from two symmetrically placed inclined pulsed-DC and RF powered magnetrons has been tested. The differences in crystallinity, crystal texture and surface morphology of the films deposited by single magnetron and two magnetron co-sputtering process were investigated. For most of the practical applications anatase phase TiO2 with high fraction of {001} facets is desired. However, it was demonstrated that at maximum nominal power without sample heating/calcination single pulsed-DC magnetron sputtering tends to form smooth amorphous TiO2 films. On the other hand, due to the higher energetics of physical vapour condensation under similar conditions single RF magnetron sputtering deposits relatively rough films with highly oriented crystalline rutile and anatase TiO2 phases (phase orientations (110) and (101) respectively). By introducing pulsed-DC and RF magnetron co-sputtering approach it was possible to tailor the nucleation and growth of TiO2 crystalline domains and to form purely anatase phase TiO2 films with relatively high fraction of photocatalyticaly the most active {001} facets. Main insights into the advantages of the two magnetron co-sputtering process as well as general guidelines on promotion of specific crystal phases with different crystallographic orientation are provided.

Influence of power frequency on the performance of SiC thin films deposited by pulsed DC magnetron sputtering

Because of its high stability, good wear resistance, and high mechanical hardness, SiC is widely used in various mechanical parts as a protective film. However, there have been few reports published on the preparation of SiC films by pulsed DC magnetron sputtering. In this work, SiC films were deposited onto glass and ceramic substrates from a sintered SiC target through pulsed DC magnetron sputtering. The influence of the variation of the power pulse frequency (0 kHz, 50 kHz, 150 kHz, 250 kHz, and 300 kHz) on the film’s performance was studied. The surface morphology, structural characteristics, hardness, and adhesion strength of the deposited SiC films were investigated here. The results show that all the deposited films adhered well to the substrate. They were smooth, compact, and presented an amorphous structure. The film hardness was found to increase as the pulse frequency was increased. When the pulse frequency was 250 kHz, the resulting SiC film possessed optimal mechanical properties with a hardness of 25.74 GPa (measured using a nanometer indentation instrument) and an adhesion strength of about 36 N (measured by scratch tester).

Solid solution hardening in nanolaminate ZrN-TiN coatings with enhanced wear resistance

Coating architectures with a microstructure controlled on nanoscale enables the attainment of enhanced mechanical, tribological and other properties. In the present study, we fabricated nanolaminate ZrN/TiN systems with various modulation periods, L, ranging from 1 to 100 nm using pulsed DC magnetron sputtering. It was observed that a modulation period of L = 10 nm is a threshold value for the transition from a periodic to a solid solution structure. We demonstrate that the coatings with L<10 nm displayed a single-phase solid solution with a Zr-rich composition of Ti0.35Zr0.65N. This indicates the effect of mixing and/or diffusion between the two phases that occurred during the film growth. The crystallite size was found to vary with the modulation periodicity: we obtained 11–12.5 nm for the Ti0.35Zr0.65N solid solution, and 14.5–25 nm for the laminate structure. The solid solution and interface strengthening were found to be the main cause of the hardening of the nanolaminate structure presenting a hardness of 32–35 GPa, significantly higher than for the individual TiN (21 GPa) and ZrN (16 GPa) single-layer coatings. The hard, solid solution system was found to exhibit the highest wear resistance corresponding to the highest values of the H/E and H3/E2 ratios related to a high resistance to plastic deformation and a high toughness. Finally, a model for the Ti0.35Zr0.65N solid solution phase formation related to internal residual stress is proposed.

The effect of stress state on AlN thin films and AlN/Finemet magnetoelectric composite device

Piezoelectric aluminum nitride (AlN) thin films with high c-axis oriented were deposited on Fe73.5Cu1Nb3Si13.5B9 (Finemet) substrates using a pulsed DC magnetron sputtering system. The influences of stress state on piezoelectric properties of AlN thin films, and magnetoelectric (ME) coupling properties of AlN/Finemet device have been investigated. The result shows that samples with flat state have a good piezoelectric property of 1.71 pm/V, which is higher than samples with compressive state and tensile state. It has been found that the stress state of the sample has a significant effect on magnetoelectric coupling coefficient. The ME coupling coefficient αME of samples were measured as 212.5 V/cm Oe (flat state), 167.5 V/cm Oe (compressive state), 141.6 V/cm Oe (tensile state), which is potential for weak magnetic field measurement.

Structural and Photoelectric Properties of Epitaxially Grown Vanadium Dioxide Thin Films on c-Plane Sapphire and Titanium Dioxide

Vanadium dioxide (VO2) is one of the most extensively studied materials in the strongly correlated electron family capable of sustaining an insulator-to-metal transition. Here we present our studies of high-quality thin films of epitaxially grown VO2 on c-Al2O3(0001) and TiO2(001) via reactive DC pulsed magnetron sputtering. We present the structural transition probed via Reflection High Energy Electron Diffraction (RHEED) for the first time and we correlate the surface microstructure measurements with simulations before, during, and after the thermally induced transition. We also study the photoelectric conversion of VO2 on TiO2(001) and c-Al2O3(0001) under 405 nm light and demonstrate up to a 2000% increase in quantum efficiency as the power of the light is varied for VO2 on TiO2(001).

The Effects of Annealing Temperature on the Structural Properties of ZrB2 Films Deposited via Pulsed DC Magnetron Sputtering

Zirconium diboride (ZrB2) thin films were deposited on a Si(100) substrate using pulsed direct current (dc) magnetron sputtering and then annealed in high vacuum. In addition, we discussed the effects of the vacuum annealing temperature in the range of 750 to 870 °C with flowing N2 on the physical properties of ZrB2 films. The structural properties of ZrB2 films were investigated with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns indicated that the ZrB2 films annealed at various temperatures exhibited a highly preferred orientation along the [0001] direction and that the residual stress could be relaxed by increasing the annealing temperature at 870 °C in a vacuum. The surface morphology was smooth, and the surface roughness slightly decreased with increasing annealing temperature. Cross-sectional TEM images of the ZrB2/Si(100) film annealed at 870 °C reveals the films were highly oriented in the direction of the c-axis of the Si substrate and the film structure was nearly stoichiometric in composition. The XPS results show the film surfaces slightly contain oxygen, which corresponds to the binding energy of Zr–O. Therefore, the obtained ZrB2 film seems to be quite suitable as a buffer layer for III-nitride growth.

AZO (Al:ZnO) thin films with high figure of merit as stable indium free transparent conducting oxide

This work presents a broad study of transparent and conducting Al-doped ZnO (AZO) thin films that could replace indium tin oxide (ITO) as transparent electrode in optoelectronic devices. AZO thin films are deposited by pulsed DC magnetron sputtering at a sputtering power of 80 W with different pulse frequencies in the range 50–100 kHz. Diffraction data confirm formation of doped ZnO and AZO thin films exhibit preferred orientation in the c-direction. The crystallite sizes of Al:ZnO are in the range 16–21 nm. The field emission scanning electron microscopy and atomic force microscopy of AZO thin films reveal nucleation and growth of uniform and dense films with better quality films deposited at a pulse frequency 75 kHz. A simple and non-destructive optical method is adopted to determine thickness and dispersion parameters such as dispersion energy, carrier concentration to effective mass ratio, and plasma frequency. AZO thin films offer excellent visible light transparency and limited transparency in the near-infrared region due to free carrier absorption. The sheet resistance of AZO thin films is recorded in the range 9–45 Ω/sq making these transparent conducting oxides (TCOs) suitable for optoelectronic applications. The figure of merit as high as 1.99 × 10−2 Ω−1 is achieved for AZO thin film deposited at a pulse frequency of 75 kHz. AZO thin film sputtered with a pulse frequency of 75 kHz is quite stable in ambient oxidizing environment and surface adsorption sites might govern the initial oxidation of films when exposed to atmosphere. Excellent figure of merit and good stability of sputtered AZO thin films as TCO fulfill the requirements of a transparent electrode in photovoltaics.

Corrosion-protection of moulded graphite conductive plastic bipolar plates in PEM electrolysis by plasma processing

Proton exchange membrane electrolysis is one of the key technologies for the implementation of renewable energy. The main advantage is the conversion of electrical energy into storable chemical energy. The objective of this work is to enhance our understanding of protective coatings for carbon-polymer composite compound materials used as bipolar plates in acidic electrolysis cells. A two-step plasma process was developed to deposit a corrosion protection. As a first step, the composite compound surface was roughened by applying RF high voltage and using it as a powered electrode. As a second step, titanium coatings were deposited by pulsed DC magnetron sputtering. The plasma process was monitored by in-situ temperature measurements. The corrosion resistance of the coated compound surface was evaluated by cyclic voltammetry and chronoamperometry at 2 V vs. SHE as well as light microscopy. Furthermore, we analysed the activation effect by SEM; the titanium coatings were analysed by the van-der-Pauw method and SEM.

The Properties of Multi-Layered Optical Thin Films Fabricated by Pulsed DC Magnetron Sputtering

The Properties of Multi-Layered Optical Thin Films Fabricated by Pulsed DC Magnetron Sputtering

Aluminum Oxide Waveguides for Improved Transmission in the Visible and Near-Infrared Spectrum

Planar waveguides were fabricated from amorphous aluminum oxide (AlOx) for the visible and near-infrared spectra. AlOx films with the nominal thickness of $1~\mu \text{m}$ were deposited on glass substrates using pulsed-dc magnetron sputtering with RF substrate bias without substrate heating. Films were deposited using various combinations of pulsed-dc power and RF substrate bias to study the dependence of optical properties under a range of controlled ion energy and ion-to-neutral ratio. To observe changes in waveguide performance, samples were further annealed at 550 °C for 1 h in air. Optical properties of the waveguides were assessed using spectroscopic ellipsometry and lateral transmission measurements with prism coupling. Results show that by using high pulsed-dc power at the target, it is possible to achieve 1.5-dB/cm transmission loss without post-deposition annealing, enabling the deposition of AlOx films at high deposition rates with low transmission loss in applications with a low thermal budget.

The adhesion strength and mechanical properties of SiC films deposited on SiAlON buffer layer by magnetron sputtering

Herein, SiC films were prepared by DC pulse magnetron sputtering on ceramic substrates using SiAlON as buffer layer. The influence of SiAlON buffer layer thickness on the structural, morphological, and mechanical properties of the SiC/SiAlON bilayers was discussed. The result show that SiAlON buffer layer can effectively improve the adhesion strength of SiC films, while the hardness of the SiC/SiAlON bilayers isn't suppressed a lot. With increase in the buffer layer thickness, the film's adhesion strength gradually increases from 66 N to 83 N, which is much higher than 36 N of single SiC layer. Meanwhile, all the SiC/SiAlON films maintain great hardness between 20 GPa and 25 GPa.

Effect of bonding structure on hardness and fracture resistance of W-B-C coatings with varying B/W ratio

Low ductility and brittle deformation behaviors are major drawbacks of currently used commercial hard ceramic-based protective coatings. Recent ab-initio calculations revealed that the coexistence of metallic, boride and carbide bonds in a nanolaminate structure of crystalline W2BC system provides a combination of high hardness together with moderate ductility. The present paper deals with coatings containing W, B and C with different compositions and investigates the effect of the boron to tungsten ratio (B/W) on the structural and mechanical properties of W-B-C coatings prepared by pulsed-DC magnetron sputtering at a moderate temperature. Coatings with low B/W were deposited in a nanocomposite structure, whereas coatings with high B/W ratios were near-amorphous. The structure of the coatings was not a decisive factor in determining their mechanical properties. These were, however, directly correlated with the chemical bonds present. All the coatings exhibited high fracture resistance. These properties together with good adhesion to cemented tungsten carbides make W-B-C coatings promising candidates for the future protective coatings of tools which undergo large deformation in their working cycle.