Direct Current Magnetron Sputtering Research Articles

Refractory high entropy TiTaZrHfW-N/Si3N4 nano-layered alloy thin film’s oxidation resistance

Refractory high entropy TiTaZrHfW-N/Si3-N4 nano-layered alloy thin films are investigated to study the effect of nano-layered architecture and silicon (Si) mean content on their structural, mechanical, thermal properties and oxidation behavior. The films are deposited using direct current (DC) magnetron sputtering of separate Si and TiTaZrHfW targets. The Si mean content is controlled by tailoring the power discharge applied to the Si target. The deposition process led to a nano-layered architecture where Si3N4 (amorphous) and TiTaZrHfW-N (nano-crystalized NaCl FCC type structure) are alternated. By increasing the thickness of Si3N4 nano-layers, the Si mean content increases. All coatings are found to have good thermal stability after annealing under vacuum at 900 °C. Increasing Si mean content reduces the film’s hardness; however, the annealing treatment at 900 °C improves it. A super-hardness of 41 GPa is found for the post-annealed Si-free film. Si3N4 nano-layers enhance the oxidation resistance at elevated temperatures of 600, 700, and 800 °C. This oxidation resistance is further enhanced by increasing the nano-layer’s period and also by increasing the density of the films.

Evolution of TiAlSi thin film coatings under varying target power in DC magnetron sputtering

This study, for the first time, presents the growth, nucleation, and characteristics of TiAlSi thin films sputtered from a partially sintered Ti30Al16Si10 (at. %) composite target under controlled conditions of target power. The TiAlSi thin films were grown on soda-lime glass substrates through Direct Current (DC) sputtering at varying levels of the target power: 73.2 W, 151.2 W, and 269.5 W. The other deposition parameters: the deposition temperature, time, argon mass flow rate, substrate rotation, and deposition pressure, were kept constant at 23 °C, 150 min, 25 sccm, 5 rpm, and 10−3 mbar, respectively. The pre-sputter power, argon flow rate, and time were also kept constant at 73.2 W, 20 sccm, and 5 min, respectively. The physical properties, microstructure, crystal structure, topography, and mechanical properties of the thin film coatings were analysed. The thickness and rate of deposition of the TiAlSi thin films increased with an increase in the target power (73.2 W – 269.5 W) from 414.6 nm and 0.046 nm/s to 1358.8 nm and 0.151 nm/s, respectively. The chemical composition of all the thin films remained constant, with the formation of a uniform TiAlSi alloy with no segregation of elements. However, a thin (wetting) interlayer consisting of Si and O elements was observed between the TiAlSi layer and the glass substrate. Further, the structure sizes and roughness values of the TiAlSi thin films increased with an increase in the target power, with a maximum of 75.4 nm for the size and 4.78 nm for the RMS roughness of thin films deposited at the maximum target power (269.5 W). Lastly, mechanical analysis of the TiAlSi thin films depicted an increase in the hardness as the target power increased, with the highest hardness at maximum power (269.5 W) obtained as 4.76 GPa. Despite having the lowest elastic modulus (50.5 GPa), the coating deposited at the highest power exhibited the highest plasticity index (H/E) and plastic deformation factor (H3/E2) of 0.094 and 0.042 GPa, respectively, which indicated the high resistance to abrasive wear, cracking, and deformation, compared to thin films deposited at the lowest target power (H/E = 0.066 and H3/E2 = 0.015 GPa). This study demonstrates that target power is a significant factor in determining the growth of TiAlSi thin films during the sputtering process and can be used for better control of their physical, structural, and mechanical properties.

Investigating Gold Deposition with High-Power Impulse Magnetron Sputtering and Direct-Current Magnetron Sputtering on Polystyrene, Poly-4-vinylpyridine, and Polystyrene Sulfonic Acid.

Fabricating thin metal layers and particularly observing their formation process in situ is of fundamental interest to tailor the quality of such a layer on polymers for organic electronics. In particular, the process of high power impulse magnetron sputtering (HiPIMS) for establishing thin metal layers has sparsely been explored in situ. Hence, in this study, we investigate the growth of thin gold (Au) layers with HiPIMS and compare their growth with thin Au layers prepared by conventional direct current magnetron sputtering (dcMS). Au was chosen because it is an inert noble metal and has a high scattering length density. This allows us to track the growing nanostructures via grazing incidence scattering. In particular, Au deposition on the polymer polystyrene (PS) with the respective structural analogues poly-4-vinlypyridine (P4VP) and polystyrene sulfonic acid (PSS) is studied. Additionally, the nanostructured layers on these different polymer films are further probed by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray reflectometry (XRR), and four-point probe measurements. We report that HiPIMS leads to smaller island-to-island distances throughout the whole sputter process. Moreover, an increased cluster density and an earlier percolation threshold are achieved compared to dcMS. Additionally, in the early stage, we observe a significant increase in coverage by HiPIMS, which is favorable for the improvement of the polymer-metal interface.

Measurement and Analysis of Surface Temperature Gradients on Magnetron Sputtered Thin Film Growth Studied Using NiCr/NiSi Thin Film Thermocouples.

In the general analysis of thin-film growth processes, it is often assumed that the temperature of the film growth surface is the same as the temperature of the film growth substrate. However, a temperature gradient exists between the film growth surface and film growth substrate. Using the growth surface of TiO2 thin films as an example, the temperature gradient of the film growth surface is tested and analyzed. A NiCr/NiSi thin-film thermocouple is fabricated using the direct-current pulse magnetron sputtering method. A three-layer NiCr/NiSi thin-film thermocouple temperature measurement system is established to measure the temperature gradient of the film growth surface. The growth surface temperature and substrate temperature of the TiO2 thin films are measured. For a sputtering power density of 0.83W cm- 2, the temperature difference between the first and second layers is 104.79°C, while the temperature difference between the second and third layers is 39.92°C. A standard K-type thermocouple is used to measure the substrate temperature, which is recorded to be 132.05°C, consistent with common measurements of substrate temperature. The heat conduction on the film growth surface in the vacuum chamber is examined and a model for the temperature measurement device during film growth is constructed.

INFLUENCE OF THE RATIO OF GASE CONSUMPTION N<sub>2</sub>/Ar AND MAGNETRON POWER ON THE DENSITY AND STOICHIOMETRIC COMPOSITION OF TIN<sub>X</sub> FILMS SYNTHESIZED BY MAGNETRON SPUTTERING METHOD

The films of titanium nitride were deposited by direct current magnetron sputtering on the surface of singlecrystalline silicon samples in an Ar-N2 atmosphere for use as a diffusion barrier. The thickness and density of films were measured by X-ray reflectometry. The design of the MAGNA TM-200-01 installation has been changed to increase the supply of nitrogen into the chamber. The influences of sputtering conditions, including the flow rate of nitrogen and argon gases and their N2 /Ar ratios in the range of 1–60 in the chamber, magnetron power of 690–1400 W on the formation of TiNx films, their density and stoichiometric composition, were studied. It is shown that the value of x is affected not only by the N2 /Ar gas flow rate ratio, but also by the magnetron power. At the sputtering parameters 1200 W, N2 /Ar = 30, 0.8 Pa, 320 s and 100°C, a maximum density of 5.247 g/cm3 of a film was achieved, which corresponds to the composition TiN0.786 = Ti56N44. The presence of nanocrystalline film of titanium nitride and the absence of a nanocrystalline titanium phase were confirmed by photographic X-ray diffraction. It was found that for the synthesis of titanium nitride as close as possible to the stoichiometric composition TiN0.770 - TiN0.786, it is necessary to use magnetron power in the range of 900–1200 W, nitrogen rate of 30 cm3 /min with low argon flows of 1–5 cm3 /min.

Diffusion mechanisms and corrosion resistance of nanostructured ZrN-Cu coating obtained by hybrid HiPIMS-DCMS

Globalisation has brought numerous benefits regarding the cost-effective transportation of goods. Still, the shipping industry faces challenges such as corrosion, biofouling, and restrictions on heavy pollutant products used in paintings. This study proposes a solution using a multifunctional coating based on zirconium nitride and copper nano-structured coating, applying high-power impulse and direct current magnetron sputtering processes (i.e., HiPIMS and DCMS, respectively). The coating’s morphological, structural, and chemical features were analysed using advanced characterisation techniques (SEM, EDX, STEM, SAED and EELS). Potentiodynamic polarisation (PP) and Electrochemical Impedance Spectroscopy (EIS − up to 30 days) were employed to study the corrosion resistance in saline solution (3.5 wt% NaCl). Besides, activated ZrN-Cu exhibited a corrosion rate decrease from ∼ 354 x 10−4 to 52 x 10−4 mm/yr when compared to its inactivated counterpart. Besides, a ∼ 3.5-fold impedance increasing was exhibited by activated ZrN-Cu after 30 days of exposure to saline solution, meaning an increase in corrosion resistance compared to the non-activated ZrN-Cu. SEM micrographs revealed that the copper diffusion in ZrN-Cu can be provoked by a strong oxidising agent (NaOCl) or by an electrical potential. Based on the chartered evidence, a diffusion mechanism is proposed for the biocidal release (Cu) in the obtained ZrN-Cu films. The present study depicts a solution that offers a controlled biocide release and corrosion resistance, opening the possibility of its application in the maritime industry.

Analysis of pulsed direct current reactive magnetron sputtering on a silicon target

Reactive sputtering is a very useful technique, particularly, for producing inhomogeneous interference filters, where the refractive index changes smoothly during deposition. In such a context, precise control of deposition parameters is crucial for replicating the desired optical properties. This study employed a pulsed DC power source to investigate the influence of a duty cycle on target poisoning, sputtering plasma characteristics, electric signals, and optical and morphological properties of synthesized films. Reactive pulsed DC magnetron sputtering was characterized by analyzing the behavior of plasma emission via optical emission spectroscopy and voltage-current signals, while modulating parameters such as the oxygen content within the vacuum chamber. A set of thin films was coated on glass substrates under different system conditions. These films underwent characterization employing spectroscopic ellipsometry to ascertain their optical constants, atomic force microscopy for surface morphology analysis, and x-ray diffraction for the determination of crystalline structures. The results indicate that longer duty cycles required higher oxygen levels to poison the target. Additionally, a detailed analysis of electrical signals revealed nonsquare waveforms, whose characteristics were influenced by both the duty cycle and the oxygen content within the sputtering chamber, resulting in higher effective voltages during the on-time of the voltage pulse. Grown films via reactive pulsed DC magnetron sputtering were also compared to films grown via conventional DC magnetron sputtering at equivalent conditions of target poisoning.

Investigation of thermally induced surface composition and morphology variation of magnetron sputtered Sb2Se3 absorber layer for thin film solar cells

One of the most promising semiconductor materials for the development of sustainable thin-film solar cell technology is antimony selenide (Sb2Se3). Its excellent optical and electrical properties have drawn attention lately for potential application in thin-film solar cells. In this study, Sb2Se3 films deposited using the direct current (DC) magnetron sputtering technique have been subjected to a post-annealing process without an extra selenium supply at temperatures between 150 and 450 °C. Without an extra selenium supply, the impact of post-annealing temperature on the surface composition as well as the physical properties of the fabricated films was investigated. The overall evaluations revealed that the post-annealing temperature is highly efficient in altering the physical properties of the Sb2Se3 absorber thin films. We further observed that the post-annealing process improved the crystallization and the heat treatment temperature quite affected preferential orientation. The surface morphology of films exhibited structural deformation at high post-annealing temperatures (> 350 °C). According to optical and electrical characterizations, respectively, the optical energy gap and the resistivity of Sb2Se3 films reduced with an increment in the post-annealing temperature. Based on the XPS result, the variation in temperature of post-annealing led to a change in the surface composition of the films. The findings on the growth of Sb2Se3 thin films indicate the existence of an intermediate growth temperature that permits the growth of Sb2Se3 films to be optimized. The study’s conclusions can serve as a guide to the growth of Sb2Se3 thin films with the desired crystallinity, surface morphology, and composition for thin film solar cell applications.

Tailoring Mechanical and Optical Properties of Sputtered SiNx/BN Coatings.

The swift evolution of contemporary electronics products, such as flexible screens and wearable electronic devices, highlights the significance of flexible protective coatings, which combine superior mechanical and optical properties. Even though the recently developed polymer protective coatings can satisfy requirements for flexibility and transparency, their intrinsic nature often results in a hardness below 1 GPa, rendering them susceptible to scratches. On the other hand, traditional inorganic coatings, known for their high hardness and transparency, fall short of meeting flexibility requirements. In the present study, a SiNx/BN periodical nanolayered coatings (PNCs) structure has been tailored to achieve high mechanical durability, transparency, and flexibility. In SiNx/BN PNCs, the optical and mechanical properties of the single-layer SiNx film are crucial to the overall performance of the PNCs. Therefore, pulse direct current (DC) magnetron sputtering was optimized first to enhance the ionization efficiency of Si and N, thereby promoting their reaction and diminishing the presence of elemental silicon in SiNx. The effects of the pulse frequency and duty cycle on SiNx were evaluated. Additionally, the influence of the thickness ratio and modulation periods on the overall performance of the SiNx/BN PNCs was investigated. As a result, a SiNx/BN coating with sapphire-grade hardness, almost no optical absorption in the visible-near-infrared (vis-NIR) range, high wear resistance, and exceptional flexibility was demonstrated.

Studies on the Morphological and Mechanical Properties of TiZrHfNiCuCo Metallic Coatings Deposited by DC Magnetron Sputtering

This research aimed to investigate the effects of input power and gas flow rate on the composition, microstructure, and mechanical properties of TiZrHfNiCuCo metallic coatings. These metallic coatings were deposited on a p-type Si wafer using a direct current magnetron sputtering system with varying input powers (100–300 W) and Ar flow rates (5–20 sccm). It was observed that increasing input power and decreasing Ar flow rate led to TiZrHfNiCuCo metallic coatings with higher hardness and smoother surfaces. The experiment resulted in the formation of a metallic amorphous coating. This study describes the mechanism by which the mechanical properties of the TiZrHfNiCuCo coating change according to sputtering parameters. Based on these results, the effects of sputter variables, such as input power and gas flow rate properties, on the properties of coatings are discussed.

Laser scanning patterns induced surface properties variations of Ti-V-Hf-Zr non-evaporable getter film with 316L stainless steel substrates

The effects of laser treatment scanning patterns on the properties of Ti-V-Hf-Zr non-evaporable getter (NEG) film on 316L stainless steel (316L SS) substrates were analyzed. 316L SS substrates were laser-treated with different patterns, which resulted in spherical structure and protrusions on the surface of the substrates. Subsequently, Ti-V-Hf-Zr NEG films were deposited on ultrasonically cleaned laser-treated 316L SS by a direct current (DC) magnetron sputtering machine. Based on the XPS results of Ti-V-Hf-Zr, it has been revealed that the atomic proportions of film elements on the surface of samples #1-1∼#3–1 were about 2.2 (Ti):1.7 (Zr):0.9 (V):1.0 (Hf). In this paper, the Ar+-induced secondary electron yield (SEY) and surface resistivity of Ti-V-Hf-Zr NEG are discussed for the first time, and it has been observed that the laser treatment leads to an increase of the substrate surface roughness, which decreases the SEY and increases the surface resistivity.

SERS detection of dopamine in artificial cerebrospinal fluid and in Parkinson’s disease-induced mouse cortex using a hybrid ZnO@Ag nanostructured platform

Rapid, direct, and sensitive detection of metabolites or clinically relevant biomarkers in complex biological samples is still challenging. We report a label-free surface-enhanced Raman scattering (SERS)-based approach for highly sensitive detection of dopamine (DA) in artificial cerebrospinal fluid (aCSF) and mouse brain tissue samples. The hybrid SERS-active sensing platform was designed to maximize the hot spot distribution. It encompasses a network of flexible and polymeric nanotrenches and nanogaps fabricated by nanoimprint lithography (NIL) covered by thin films of zinc oxide (ZnO) and silver (Ag) deposited using pulsed laser deposition (PLD) and direct current magnetron sputtering (DC-MS), respectively. The growth of the ZnO and Ag thin films was assessed by scanning electron microscopy (SEM) technique. The proposed SERS substrate benefits from the interlayered semiconductor–metal contribution in SERS enhancement, leading to a versatile sensing platform with improved detection sensitivity through the increased hot spots distribution. Using this strategy, the proposed assay can achieve an ultralow DA determination at the nM level, a short testing time (<30 min), and high signal reproducibility (RSD 11 %). We also assessed the sensing attributes of our in house developed SERS platform to detect DA in spiked aCSF samples, and a limit of detection (LOD) of 10 μM was achieved. Additionally, after in vivo inducing Parkinson’s disease (PD) in mice, relevant biological samples (striatum and cortical brain tissue) were investigated by SERS and ELISA. Given its good stability and accuracy in complex samples, the SERS-ELISA analysis has great potential to be a powerful tool for the reliable detection of DA in remote conditions.

Electrically pumped random laser device based on Pd/SiO2/ZnO nanorods MIS structure

Electrically pumped random lasing based on Pd/SiO2/ZnO nanorods (NRs) structures is demonstrated. Chemical bath deposition (CBD) technique was used to synthesize the ZnO NRs. Then, an insulating layer of SiO2 was deposited via radio frequency (RF) magnetron sputtering. After that, direct current (DC) magnetron sputtering was used to deposit palladium (Pd) metal contacts on the sample through a shadow mask. The electrical, morphological as well as optical characteristics of the ZnO NRs were analyzed. The device exhibits typical Schottky diode current–voltage (I-V) characteristics at a turn-on voltage of 6.18 V. The electroluminescence (EL) spectra shows good random lasing behavior with lasing peaks centered at approximately 380 nm and exhibited a threshold current of 37.5 mA. This report reveals Pd as a relatively cheaper material and low-cost CBD fabrication method is sufficient to fabricate electrically pumped random laser devices. Furthermore, this report also present a new way to interpret the mechanism of random lasing in the device.

Effect of sputtering power and thickness ratios on the materials properties of Cu–W and Cu–Cr bilayer thin films using high power impulse magnetron and DC magnetron sputtering

This study investigates the influence of Cu thickness ratios on the structural, morphological, and mechanical properties of sputtered Cu–W and Cu–Cr bilayer thin films. Employing high power impulse magnetron sputtering (HiPIMS), five distinct thickness ratios of 1:3, 3:5, 1:1, 5:3, and 3:1 were analyzed and compared to bilayer films developed using direct current magnetron sputtering (DCMS). The microstructural and surface characteristics of these films were evaluated using x-ray diffraction (XRD), atomic force microscopy, and scanning electron microscopy. Electrical properties were measured using a four-point probe, while mechanical properties were assessed through nanoindentation. Results reveal that increasing Cu thickness in Cu–W and Cu–Cr bilayers inversely affects hardness, grain size, and roughness, highlighting the influence of thickness ratios on film properties. Films with a higher Cu thickness ratio in both Cu–W and Cu–Cr bilayer systems deposited by HiPIMS exhibited lower hardness, smaller grain size, and reduced average roughness. Cross-sectional analysis and XRD confirmed the impact of thickness ratio on crystal phase and microstructure, indicating smoother columnar structures. Specifically, the HiPIMS-deposited Cu–Cr 3-1 film exhibited the lowest resistivity, at 4.77 μΩ cm, and hardness, measuring 8.26 GPa. Moreover, the 1:1 ratio films of Cu–W and Cu–Cr demonstrated hardness values of 13.81 and 11.37 GPa, respectively, which were 1.39 times higher than the films grown by DCMS. Additionally, variations in the bilayer thickness ratio significantly affected the electrical properties of the films. The enhanced properties of HiPIMS films are attributed to the higher peak power density of the target, leading to increased ion energy and deposition of dense grain structures.

Multicoated Flexible Indium Tin Oxide Electrodes Fabricated Using Magnetron Sputtering and Arc Plasma Ion Plating for Flexible Perovskite Solar Cells.

High-performance flexible Sn-doped In2O3 (indium tin oxide, ITO) electrodes were fabricated using a multicoating process on colorless polyimide (CPI) substrates for flexible perovskite solar cells (FPSCs). The effects of different coating sequences on the electrical, optical, and mechanical properties of the flexible ITO electrodes were thoroughly investigated after preparing them with direct-current magnetron sputtering (DMS) and arc plasma ion plating (APIP). Although both the sputtered ITO (SITO)/arc ion-plated ITO (AITO) film and the AITO/SITO film showed similarly low sheet resistance (18.69-25.29 Ω/sq) and high optical transmittance (94.96-96.85%), the coating sequence significantly affected the mechanical flexibility of the multicoated ITO films. The 120 nm-thick SITO/AITO electrode exhibited small outer and inner critical bending radii (3 mm and 3 mm, respectively) compared to the AITO/SITO electrode (4 and 5 mm, respectively). Owing to better adhesion of the arc-ion-plated ITO bottom layer and the amorphous structure of the top SITO layer, the SITO/AITO electrode exhibited excellent mechanical flexibility and durability. In addition, an FPSC using the SITO/AITO electrode achieved a higher power conversion efficiency (15.09%) than that with the AITO/SITO electrode (13.22%). This improvement was attributed to its high transmittance, low sheet resistance, smooth surface morphology, and enhanced hole collection efficiency. These findings highlight the efficacy of the combined DMS and APIP multicoating process for fabricating high-quality flexible ITO electrodes for high-performance FPSCs.

Impact of fractal dimension and lateral correlation length on surface plasmon resonance activity in sputtered silver layers

Fractal and optical characteristics of self-affine surfaces of silver(Ag) thin films deposited through direct current (dc) magnetron sputtering as a function of thickness are investigated and explored here. The surface morphology of Ag thin films is characterized by field emission electron microscopy, and atomic force microscopy technique. The cube counting algorithm is used to extract the fractal dimension of Ag thin film. The surface roughness (interface width) shows monotonic increases with film thickness, while the other parameters, such as lateral correlation length, roughness exponent, and fractal dimension exhibit linear variation with thickness. Our findings reveal distinctive scaling behaviors, with scaling exponents α, β, and 1/z indicating unique growth characteristics. The interface width w increases as a power law of thickness t, w(t)∝tβ, with β=0.39± 0.007, and the lateral correlation length ξ grows as ξt∝t1/z with 1/z=0.14± 0.002. The roughness exponent extracted from height-height correlation analysis is α=0.61–0.41. The self-affine nature of the Ag thin films is further confirmed by the autocorrelation function. X-ray photoelectron spectroscopy (XPS) is used to the confirm the growth of Ag thin film. Additionally, we have studied the role of fractal dimensions and lateral correlation length (ξ) on the surface plasmon resonance (SPR) of Ag thin film. Our results indicate a red-shifting behavior of SPR with increasing interface width (w), lateral correlation length (ξ), and fractal dimensions. This study suggests the significance of not only the roughness exponent and fractal dimension but also the local surface slope in SPR activity in Ag thin films.

The key role in the structure and properties of a novel CrNiTiMo high-entropy alloys films prepared by magnetron sputtering: Bias voltage

In this study, CrNiTiMo high-entropy alloys films were prepared on 304 stainless steel and silicon wafer substrates by direct current magnetron sputtering and the effects of bias voltages (0 to −200 V) on microstructure, chemical composition, hardness and corrosion resistance were investigated. The results showed that the surface of the CrNiTiMo HEAs films exhibited equiaxed nanoparticles and are composed of uniformly distributed Cr, Ni, Ti, and Mo elements. Meanwhile, the films developed a columnar structure and formed a biphasic structure with body-centered cubic solid solution and amorphous phases. The roughness decreased and then increased with increasing bias voltage, and the film deposited at −50 V had the lowest roughness (1.02 ± 01 nm), which also had a maximum hardness of approximately 9.52 ± 0.2 GPa and a maximum elastic modulus of approximately 187 ± 6 GPa. In addition, all films showed better corrosion resistance compared to 304 stainless steel substrates at 3.5 wt% NaCl solution. The corrosion current density (icorr) of the films decreased and then increased with increasing bias voltages and reached the lowest icorr of about 2.49 × 10−8A/cm2, indicating that the films deposited at a bias voltage of −50 V had the best corrosion resistance. These was attributed to the formation of the passivation films mainly composed of TiO2 and Cr2O3 and the improvement of the surface quality of the film as well as the refinement of the columnar structure and particles.

Investigating the growth behavior of titanium dioxide film prepared with direct current pulsed–magnetron sputtering technology

The direct current pulsed magnetron sputtering technology is employed to deposit TiO2 film onto the glass and Si(100) substrates. After annealing treatment, TiO2 film displays anatase (001) preferential orientation. The growth behavior of deposited and annealed TiO2 films is investigated. The results show that in the original stage, TiO2 film growth behavior is in Volmer–Weber mode, which is dominated by the diffusion effect. Considering the rivalry between TiO2 crystal nuclei, both crystallographic orientation and diffusion effects jointly dominate the film growth behavior in the rest stage. More importantly, the annealing treatment resulted in the coalescence of TiO2 crystal nuclei, as well as the growth of TiO2 crystal nuclei. Most importantly, after coalescence and growth of TiO2 nuclei, the anatase [001] crystal orientation of TiO2 grains remains the same as the normal direction of TiO2 film. Finally, after annealing treatment, TiO2 films comprise anatase (001) preferential orientation.

Oxidation characteristics of copper oxide thin films deposited by direct current sputtering under substrate temperature and post-deposition copper-ion implantation

The oxidation and structural, optical and morphological properties of copper oxide thin films deposited by direct current magnetron sputtering under different substrate temperatures and oxygen (O2) partial pressures, and subsequent 200 keV Cu ion implantation are investigated. The colour of the films progressively changed from yellowish brown to dark brown and oxide phase from Cu2O to Cu4O3 to CuO through mixed phases with increase in oxygen partial pressure from 20 to 90 % of the working pressure and substrate temperature from room temperature (27 °C) to 350 °C. The rate of oxidation and crystallinity of the films substantially increased with increase in substrate temperature. The ion implantation in the room temperature deposited films produced significant crystallization and decrystallization with respect to the ion fluence, and that in 350 °C substrate temperature deposited films instigated Cu-rich phase. The substrate temperature and ion implantation engendered distinctive red shift of the absorption edge and prevalent changes in the interference patterns in the optical spectra of the films. The calculated direct band gap values of the films are in the range of 1.7 to 2.42 eV, which decreased to the range of 1.65 to 2.17 eV on ion implantation. The indirect band gap of the films with predominant Cu4O3 and CuO phases are in the range of 1.23 to 1.49 eV. The refractive index and extinction coefficient of the films at 1100 nm are in the range of 2.1 to 2.5 and 0.03 to 0.12, which increased to the range of 3 to 7 and 0.2 to 0.45, respectively, on ion implantation. The films displayed agglomeration of the particles and directional growth of the agglomerates with respect to O2 partial pressure and substrates temperature, and increase in the size of the particles / agglomerates, and rough surface morphology on ion implantation.

Effect of bias voltage on the structure and properties of CoCrFeNi high entropy alloy thin films prepared by magnetron sputtering

In this study, CoCrFeNi high entropy alloy thin films were prepared on 304 stainless steel and single crystal Si substrates using the direct-current magnetron sputtering process under different bias voltages. The effects of these bias voltages on the film micrographs, phase structure, surface roughness, corrosion resistance, and mechanical characteristics of thin films were studied by a scanning electron microscope, transmission electron microscope, X-ray diffractometer, atomic force microscope, electrochemical workstation and nanoindentation tester, respectively. The results indicated that all films exhibited equiaxed nano-scale grains and developed a columnar structure. Fe, Co, Cr, and Ni were uniformly dispersed in all films and all films displayed face centered cubic solid solution (FCC). At a bias voltage of 0 V, the CoCrFeNi HEAs film formed a FCC single phase. With increasing bias voltage, the crystallinity decreased and then increased, reaching the worst crystalline state at bias voltage of −200 V due to the fact that the structure of the film was composed of FCC nanocrystalline and amorphous biphasic structure. Meanwhile, the surfaces of the film prepared at bias voltage of −200 V exhibited the densest structures and the least roughness, with grain sizes reaching a minimum value of approximately 10 nm. In addition, columnar grains of the film prepared at a bias voltage of −200 V displayed the densest state and had the least size, thus this film displayed the best corrosion resistance of a minimum value 1.51 × 10−7 A/cm2, a maximum hardness of approximately 11.18 ± 0.2 GPa and a maximum elastic modulus of approximately 193 ± 2.8 GPa. The passivation films of CoCrFeNi HEAs films were mainly composed of Cr2O3.