Current–voltage characteristics and impedance spectroscopy of LiNbO<Subscript>3</Subscript> films grown by RF magnetron sputtering

Polycrystalline LiNbO₃ films with random orientation of grains on (001)Si substrates have been grown by RF magnetron sputtering method. Electrical conductance of the formed (001)Si–LiNbO₃ heterostructures is defined through hopping mechanism by charge localization centers (CLC) in the band gap of LiNbO₃ with concentration N _t  = 2.3 × 10²⁴ m⁻³. Analysis of the impedance frequency spectrum has disclosed two relaxation processes of Maxwell–Wagner type with relaxation times τ₁ = 0.1 s and τ₂ = 1 × 10⁻⁴ s. Thermal annealing at T = 650 °C leads to an increase in the average grain size from 50 to 95 nm; it also leads to a decrease in the CLC concentration down to N _t  = 2.8 × 10²⁰ m⁻³. Electrical conductance of (001)Si–LiNbO₃ heterostructures after thermal annealing is determined by space charge limited conduction mechanism. There have been defined parameters of dielectric hysteresis loops. It has been demonstrated that thermal annealing leads to a decrease in values of remanent polarization and coercive field.     

Dielectric relaxation and ac conductivity of polyaniline–zinc ferrite composite

In situ polymerization of aniline is carried out in the presence of zinc ferrite to synthesize polyaniline/ZnFe₂O₄ composites (PANI/ZnFe₂O₄) by chemical oxidation method. The composite has been synthesized with various compositions (10, 20, 30, 40 and 50 wt.%) of zinc ferrite in PANI. From the infrared spectroscopy (FTIR) studies on polyaniline/ZnFe₂O₄ composites, the peak at 1140 cm^?1 is considered to be measure of the degree of electron delocalization. The surface morphology of these composites is studied with scanning electron micrograph (SEM). The ac conductivity and dielectric properties are studied in the frequency range from 10² to 10⁶ Hz. The results obtained for these composites are of scientific and technological interest.     

Effect of carbon content on the microstructure and properties of W–Si–C–N coatings fabricated by magnetron sputtering

A series of W–Si–C (4–5 at.%)–N nanocomposite coatings with different C contents have been deposited on Si wafer substrates by reactive magnetron sputtering of W–Si–C composite target in Ar + N₂ mixed atmosphere. Microstructure characteristics and mechanical properties of W–Si–C–N coatings were investigated in this paper. Results exhibited that W–Si–C–N coatings possess nanocomposite microstructure where nano-crystallites W₂(C, N) embedded in amorphous matrix of Si₃N₄/CNx/C. As the C content increased, the hardness and Youngs’ modulus of the W–Si–C–N coatings first increased and then decreased, reaching the maximum value of approximate 36 GPa and 382 GPa, respectively, for coatings containing 11.1 at.% C. All the coatings are in compressive stress state, ranging from 0.8 to 2.0 GPa. In addition, friction coefficient of the W–Si–C–N coatings considerably decreased with the increase of C content.     

Anisotropic I–V characteristics of spontaneously emerged periodic stripes of superconducting NbN thin films on Si trench sidewall by RF magnetron sputtering

To realize a highly integrated thin film superconductive coil, sputter-deposition of NbN on a trench sidewall of Si substrate was examined. A trench of 0.2 mm in depth was fabricated by Si Deep-RIE. A Nb target was sputtered in Ar/N₂ mixed gas flow. Thanks to the periodic corrugated structure formed by repeated Deep-RIE process, it was found that NbN superconducting lateral stripes connected with each other with thinner NbN thin film were spontaneously emerged. The superconducting properties along and across the stripes were completely different. Along the stripes, the I–V curves showed supercurrent. Additionally, the undulations were observed in I–V curves below Tc indicating the existence of the inhomogeneity of such as thickness, having different J_c depending on the position in the stripes. The normal conductivity along the stripes is almost five times higher than that across the stripes. Across the stripes, clear supercurrent was observed in the films formed in N₂ flow rate lower than 12%, indicating the stripes were connected with a thin superconductive layer in between. In the films formed in N₂ flow rate over 14%, no supercurrent was observed but the conductance increased with temperature indicating tunneling conduction. The obtained novel structure can be looked upon as a spontaneously emerged multifilamentary superconducting wire possibly applicable to produce high magnetic field.     

Corrosion resistance of nanocrystalline Mg–Cr alloys deposited by magnetron sputtering

Nanocrystalline Mg–Cr alloys were formed by dc magnetron sputtering in a wide range of concentrations. Structure, composition and grain sizes of the deposits were studied by XRD and XPS. EIS and dc-voltammetry showed that small chromium concentrations (2–8 at.%) had detrimental effect, while high corrosion resistance was observed when chromium content reached one third or so. Chromium refinement effect on alloy crystalline structure was found by XRD. The values of grain sizes were determined as follows: Mg–3Al (chromium-free) – over 100 nm, Mg–2Cr – 60.5 nm, Mg–8Cr – 44.6 nm, Mg–20Cr – 31.0 nm, Mg–45Cr, Mg–53Cr – ∼11.0 nm and ∼15 nm for sputtered Cr. Mott–Schottky plots showed that the spontaneous oxide layers formed on the alloys with high Cr content (Mg–36Cr, Mg–53Cr) were highly doped semiconductors of n-type. A conductivity change n–p was observed at E = 0.0 V (Ag/AgCl) in a buffer solution (pH 9.9). The conductivity change was also confirmed by photo-electrochemical measurements. Surface enrichment by chromium during initial stages of corrosion was determined, which promote corrosion resistance and provides an opportunity of surface auto-protection (self-healing) in damaged locations.     

Effects of RF magnetron sputtering power density on NTC characteristics of Mn–Co–Ni thin films

Thin film NTCR (negative temperature coefficient resistance), based on Mn–Co–Ni oxide, was prepared by reactive RF magnetron sputtering with various sputtering power density (0.95–3.82 W/cm²). The crystalline structure and surface morphology of the NTC thin film were analyzed by XRD and AFM. The NTC characteristics, as a function of sputtering power density, were investigated. The values of B, α ₂₅ and R ₂₅ were in the range of 3,740–3,847 K, ?4.328 to ?4.207 %/K and 8.7–2,082.5 KΩ, respectively. With the increasing power density, the standard resistance (R ₂₅ ) decreased and the consistency of R₂₅ increased. Thin film NTCR with stable B value (3,740 K), low R ₂₅ (10⁴ Ω) and excellent consistency could be fabricated in mass production with about 3.82 W/cm² sputtering power density.     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

Properties of coatings of the Al–Cr–Fe–Co–Ni–Cu–V high entropy alloy produced by the magnetron sputtering

It has been found that coatings from an Al–Fe–Co–Ni–Cu–Cr–V high entropy equiatomic alloy produced by the magnetron sputtering have nanocrystalline microstructures, are textured, and present a solid two-phase solution, which crystallizes in the bcc (a = 2.91 Å) and fcc (a = 3.65 Å) phases. The ion bombardment of a growing coating caused by the bias voltage (0–(–200) V), which has been applied to the substrate, decreases the growth rate of a condensate and affects its composition and structure. It has been shown that the composition of coatings deposited without an ion bombardment coincides with the target composition, whereas an increase of the ion bombardment intensity leads to the depletion of the coating composition in Al, Cu, and Ni and increase the microhardness. The anisotropy of the coating produced has been revealed.     

Structure and ac conductivity of sodium–lead–cadmium metaphosphate glasses

Sodium–lead–cadmium phosphate glasses having a mol% composition (40−y)Na₂O–yCdO–10PbO–50P₂O₅ (0≤y≤40) were prepared by using the melt–quench technique. They have been characterised by infrared spectroscopy, Raman spectroscopy and ³¹P magic angle spinning nuclear magnetic resonance (MAS-NMR). Infrared and Raman spectroscopies reveal the formation of P–O–Pb and P–O–Cd bonds, which replace P–O–⁺Na bonds. MAS-NMR spectroscopy shows that no metaphosphate network depolymerisation occurs when y increases. Thus, both PbO and CdO act as the network modifiers. Systematic variations of the glass transition temperature, density, and molar volume observed are in agreement with these results. Ionic conductivity is correlated to the structural model.     

Effect of Si/Fe ratio on the boron and phosphorus doping efficiency of β-FeSi2 by magnetron sputtering

Boron-doped or phosphorus-doped β-FeSi₂ thin films have been prepared on silicon substrate by magnetron sputtering. Effects of Si/Fe ratio on the boron and phosphorus doping efficiencies have been studied from the resistivities of doped β-FeSi₂ thin films and current-voltage characteristics of doped β-FeSi₂/Si heterojunctions. The experimental results reveal that the carrier concentration and doping efficiency of boron or phosphorus dopants at the Fe-rich side are higher than that at the Si-rich side. The effect of Si/Fe ratio can be deduced from the comparison of the formation energies under two extreme conditions. At the Fe-rich limit condition, the formation energy of boron or phosphorous doping is lower than that at the Si-rich condition. Therefore, the activation of impurities is more effective at the Fe-rich side. These results demonstrate that the boron-doped and phosphorous-doped β-FeSi₂ thin films should be kept at the Fe-rich side to avoid the unexpected doping sites and low doping efficiency.     

Ti3SiC2-formation during Ti–C–Si multilayer deposition by magnetron sputtering at 650 °C

Titanium Silicon Carbide films were deposited from three separate magnetrons with elemental targets onto Si wafer substrates. The substrate was moved in a circular motion such that the substrate faces each magnetron in turn and only one atomic species (Ti, Si or C) is deposited at a time. This allows layer-by-layer film deposition. Material average composition was determined to Ti_0.47Si_0.14C_0.39 by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy and Raman spectroscopy were used to gain insights into thin film atomic structure arrangements. Using this new deposition technique formation of Ti₃SiC₂ MAX phase was obtained at a deposition temperature of 650 °C, while at lower temperatures only silicides and carbides are formed. Significant sharpening of Raman E_2g and A_g peaks associated with Ti₃SiC₂ formation was observed.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

Shape memory behavior of Fe–Pd alloy thin films prepared by dc magnetron sputtering

Fe–Pd films have been deposited onto fused quartz and silicon substrates by dc magnetron sputtering. When an arc-melted and homogenized Fe–30at.% Pd alloy disk was used as a sputtering target, Fe–Pd films fabricated was shown to contain about 24 at.% Pd under the deposition condition used. The target configuration was then modified by placing Pd wires on the target so as to control the Pd content of films with an accuracy of 1 at.% Pd. Fe–Pd films containing 28.5 at.% Pd underwent a thermoelastic fcc-to-fct martensite transformation after annealing at 900 °C followed by quenching into iced water. Apparently, the reverse transformation was also thermoelastic and the thermoelastic transformations occurred repeatedly upon thermal cycling. Some of the Fe–28.5at.% Pd films were peeled off from the quartz substrate and they showed SM effects upon heating after deformation. A diaphragm-shaped free-standing film was also fabricated on a thin Si substrate. This film showed attractive transformation characteristics, including a narrow transformation hysteresis loop of about 4 °C and a small temperature difference between M_f and A_f (about 10 °C) in addition to M_s (43 °C) close to room temperature. This diaphragm-shaped film showed a reversible ballooning behavior with a maximum strain of about 0.05% upon thermal cycling.     

Deposition of thin titanium–copper films with antimicrobial effect by advanced magnetron sputtering methods

The antibacterial effect of thin titanium–copper (Ti–Cu) films combined with sufficient growth of human osteoblastic cells is reported in the paper. Thin Ti–Cu films were prepared by three different plasma-assisted magnetron sputtering methods: direct current magnetron sputtering (dc-MS), dual magnetron sputtering (dual-MS) as well as dual high power impulse magnetron sputtering (dual-HiPIMS). The antimicrobial effect is caused by copper released from the metallic Ti–Cu films, which was measured by atomic absorption spectroscopy (AAS). The copper release is influenced by the chemical and physical properties of the deposited films and was investigated by X-ray diffractometry and X-ray reflectometry (GIXD and XR) techniques. It was found that, within the first 24 h the amount of Cu released from dual-HiPIMS films (about 250 μg) was much higher than from dc-MS and dual-MS films. In vitro planktonic growth tests on Ti–Cu surfaces for Staphylococcus epidermidis and S. aureus demonstrated the killing of both bacteria using the Ti–Cu films prepared using the dual-HiPIMS technique. The killing effects on biofilm bacteria were less obvious. After the total release of copper from the Ti–Cu film the vitality of exposed human osteoblast MG-63 cells increased significantly. An initial cytotoxic effect followed by the growth of osteoblastic cells was demonstrated. The cytotoxic effect combined with growth of osteoblastic cells could be used in joint replacement surgery to reduce the possibility of infection and to increase adoption of the implants.     

Physical properties of amorphous Mo-doped In–Ga–Zn–O films grown by magnetron co-sputtering technique

Amorphous thin films of In–Ga–Zn–O (a-IGZO) doped with Mo have been fabricated by using magnetron co-sputtering technique. The Mo concentration in a-IGZO films was modulated by varying the sputtering power applied on the Mo target. The electrical, optical and magnetic properties of Mo-doped a-IGZO films grown on glasses were investigated. The carrier density and mobility of a-IGZO films can be remarkably enhanced by low concentration Mo doping. On the other hand, the optical bandgap of a-IGZO films is not significantly affected by Mo doping. However, the transmission is decreased with increasing the Mo doping. Moreover, all Mo-doped films exhibit room-temperature ferromagnetism.     

Silicon-rich oxynitride hosts for 1.5 μm Er emission fabricated by reactive and standard RF magnetron sputtering

This study compares the erbium emission from different Si-rich silicon oxynitrides matrices fabricated by magnetron sputtering. The Er-doped layers were grown by two different sputtering configurations: (i) standard co-sputtering of three confocal targets (Er₂O₃, Si₃N₄ and SiO₂) under Ar plasma, and (ii) reactive co-sputtering under Ar + N₂ plasma of either three (Er₂O₃, pure Si and SiO₂) or two targets (Er₂O₃ and pure Si). The last reactive configuration was found to offer the best Er³⁺ PL intensity at 1.5 μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide.     

Effects of Nb doping on microstructure and properties of Bi4Ti3?xNbxO12 thin films prepared by magnetron sputtering

Bi₄Ti_3−xNb_xO₁₂ ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure and properties of Bi₄Ti_3−xNb_xO₁₂ films were investigated. Bi₄Ti_3−xNb_xO₁₂ films had the same structure as Bi₄Ti₃O₁₂ with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi₄Ti_3−xNb_xO₁₂ films were improved by Nb doping. Bi₄Ti_3−xNb_xO₁₂ films have better dielectric and ferroelectric properties with P _r = 16.5 μC/cm², E _C < 100 kV/cm, ε _r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive Nb doping would lead to bad dielectric and ferroelectric properties.     

Effect of ZrN coating by magnetron sputtering and sol–gel processed silica coating on titanium/porcelain interface bond strength

In this study, a coating technique was applied to improve the bond strength of titanium (Ti) porcelain. ZrN coating was prepared by magnetron sputtering, and silica coating was processed by a sol–gel method. The treated surfaces of the specimens were analyzed by X-ray diffraction, and the Ti/porcelain interface was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy. The coated specimens appeared fully coherent to the Ti substrate. The fractured bonding surface was also investigated by SEM. The residual porcelain on the metal surface could be observed in the ZrN group and silica group, but there was no obvious porcelain remaining in the control group. A three-point-bending test showed that the bonding strength of the ZrN group (45.99 ± 0.65 MPa) was higher than the silica group (37.77 ± 0.78 MPa) (P < 0.001) and control group (29.48 ± 1.01 MPa) (P < 0.001), while that of the silica group was significantly higher than the control group (P < 0.001). In conclusion, conditioning the ceramic surface with ZrN and silica coatings resulted in a stronger Ti/porcelain bond. ZrN coating by magnetron sputtering was a more effective way to improve the bond strength between Ti and porcelain compared with sol–gel processed silica coating in this study.