Direct Current Sputtering Research Articles

Solar Light-Induced Decolorization of Safranin O Using Unmodified and Gold-Modified Semiconductor Oxides

Unmodified and gold-modified semiconductor oxides were used for the complete decolorization of non-buffered aqueous safranin O solutions. Photocatalytic properties of commercially available ZnO and TiO2 (anatase nanopowder) were compared with those of gold-modified ZnO (Au/ZnO). Au/ZnO was obtained from commercial ZnO powder through direct current sputter coating. ZnO-based catalysts show significantly higher decolorization power in comparison with TiO2. Au/ZnO show slightly higher activity than unmodified ZnO. Decolorization of safranin O using Au/ZnO was additionally tested in different types of mineral water. The decolorization efficiency in mineral waters was negatively correlated with the dry residue content (180 °C) and in all cases was less than in distilled water. The inhibiting effect of hydrogen carbonate was additionally investigated.

Fabrication and characterization of NiO films for energetic nano-multilayers by direct current reactive sputtering

NiO films were fabricated by reactive direct current magnetron sputtering on glass and alumina substrates for the application in energetic nano-multilayers. The structural and thermal properties of the films were investigated with the volume ratio of oxygen to argon ranging from 1:9 to 3:2, and the optimized ratio value is obtained as 1:3, which was confirmed by X-ray diffraction (XRD), atomic force microscopy and ultrafast measurement system. The effect of the film thickness, varying from 150 to 900 nm, on the structural properties was characterized by XRD and scanning electron microscopy (SEM). XRD analysis reveals that the (111) lattice plane is the preferred orientation. The intensities of preferential peaks and the grain sizes increase as the film thicknesses increase.

A novel OTA-based circuit model corroborated by an experimental semiconductor memristor

A semiconductor memristor device based on a 300-nm ZnO thin film was fabricated by direct-current reactive sputter. The memristive behavior of this device was confirmed by time dependent current–voltage (I-V-t) measurements, and the distinctive pinched hysteresis I-V loops of the memristor were observed. Structural analysis of the ZnO memristor was carried out using both X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). After physical implementation of the memristor, an operational transconductance amplifier (OTA) based memristor circuit was designed to emulate the ZnO-based semiconductor memristor for use in memristor-based circuit applications. All simulations were in good agreement with experimental results. In addition, a comparison of the proposed circuit with other memristor emulators was presented.

Structural, electrical and optical properties of SnOx films deposited by use of atmospheric pressure plasma jet

Structural, electrical and optical properties of undoped tin oxide thin films (SnOx) deposited on silicon and glass slides by use of an atmospheric pressure plasma jet at substrate temperatures varying between 300 °C and 500 °C were determined. One role of the used plasma is the promotion of SnO2 formation and reduction of organic residues from the tetra-n-butyltin (IV) precursor by supplying a highly reactive oxygen-containing atmosphere. Moreover, film properties were compared to SnOx films prepared by a vacuum direct current sputtering procedure. Scanning electron microscopic investigations showed high specific surface area and porous films at 300 °C substrate temperature. With increasing this temperature a decrease in film thickness and roughness of the films could be observed. These experiments were supplemented by transmission electron microscopy and showed the formation of a dense layer close to the substrate with a more porous layer on top of it. Spectral ellipsometry further supported these results and allowed to determine the thickness of the films as well as the thickness of the dense and porous part. X-ray diffraction pattern indicated the presence of a predominantly crystalline film structure (SnO2, cassiterite) at 500 °C substrate temperature with an average grain size of ~4 nm. Comparing to this, film deposited by vacuum sputtering method were more crystalline with average grain sizes of ~12–14 nm. Additionally, the presence of SnO2 on the surface was demonstrated by X-ray photoelectron spectroscopy. Films with an average transmittance of >85% and low resistivities of 7.2 × 10−2 Ωcm even at lower substrate temperatures of 300 °C could be achieved, whereby electrical film properties (conductivity) were superior to those of films prepared by sputter deposition. First attempts to show gas sensing properties were conducted and revealed a response toward ammonia gas atmospheres.

A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering

Indium tin oxide (ITO) film was deposited by the traditional direct current (DC) pulsed magnetron sputtering technology. With the increase of reverse time from 0 to 4.0 μs, the crystal structure of ITO film changed from the polycrystalline structure without preferred orientation to (1 0 0) preferred orientation. ITO film with (1 0 0) preferred orientation showed the satisfactory optical and electrical properties, such as the band gap in 4.15 eV and carrier concentration in 4.25 × 1020/cm3. Based on DC pulsed voltage waveform, the formation of (1 0 0) preferred orientation, as well as the change of optical and electrical properties of ITO film, were analyzed logically.

Plasma emission spectroscopy and its relation to the refractive index of silicon nitride thin films deposited by reactive magnetron sputtering

In this work, we present a thorough study on the relation between the plasma emission and the change of the silicon nitride thin films refractive index. Thin films were grown by reactive magnetron direct current sputtering technique and deposited onto silicon wafers at different fluxes of Ar and N2 and at different working pressures. This procedure, at certain deposition parameters, produced poor quality films, i.e. films with refractive index other than pure Si3N4 films. The emission of the plasma was interrogated in real time by means of optical emission spectroscopy (OES) observing at the vicinity of the trget location. In addition, optical properties of the films were measured by in situ ellipsometric-spectroscopy and then correlated with OES observations. Changes in the film refractive index could be deduced from changes in plasma emission applying a principal component analysis.

Hydrogen Permeation, and Mechanical and Tribological Behavior, of CrNx Coatings Deposited at Various Bias Voltages on IN718 by Direct Current Reactive Sputtering

In the current work, the microstructure, hydrogen permeability, and properties of chromium nitride (CrNx) thin films deposited on the Inconel 718 superalloy using direct current reactive sputtering are investigated. The influence of the substrate bias voltage on the crystal structure, mechanical, and tribological properties before and after hydrogen exposure was studied. It was found that increasing the substrate bias voltage leads to densification of the coating. X-ray diffraction (XRD) results reveal a change from mixed fcc-CrN + hcp-Cr2N to the approximately stoichiometric hcp-Cr2N phase with increasing substrate bias confirmed by wavelength-dispersive X-ray spectroscopy (WDS). The texture coefficients of (113), (110), and (111) planes vary significantly with increasing substrate bias voltage. The hydrogen permeability was measured by gas-phase hydrogenation. The CrN coating deposited at 60 V with mixed c-CrN and (113) textured hcp-Cr2N phases exhibits the lowest hydrogen absorption at 873 K. It is suggested that the crystal orientation is only one parameter influencing the permeation resistance of the CrNx coating together with the film structure, the presence of mixing phases, and the packing density of the structure. After hydrogenation, the hardness increased for all coatings, which could be related to the formation of a Cr2O3 oxide film on the surface, as well as the defect formation after hydrogen loading. Tribological tests reveal that hydrogenation leads to a decrease of the friction coefficient by up to 40%. The lowest value of 0.25 ± 0.02 was reached for the CrNx coating deposited at 60 V after hydrogenation.

Quasi van der Waals epitaxy of copper thin film on single-crystal graphene monolayer buffer

Quasi van der Waals epitaxial growth of face-centered cubic Cu (~100 nm) thin films on single-crystal monolayer graphene is demonstrated using thermal evaporation at an elevated substrate temperature of 250 °C. The single-crystal graphene was transferred to amorphous (glass) and crystalline (quartz) SiO2 substrates for epitaxy study. Raman analysis showed that the thermal evaporation method had minimal damage to the graphene lattice during the Cu deposition. X-ray diffraction and electron backscatter diffraction analyses revealed that both Cu films are single-crystal with (1 1 1) out-of-plane orientation and in-plane Σ3 twin domains of 60° rotation. The crystallinity of the SiO2 substrates has a negligible effect on the Cu crystal orientation during the epitaxial growth, implying the strong screening effect of graphene. We also demonstrate the epitaxial growth of polycrystalline Cu on a commercial polycrystalline monolayer graphene consisting of two orientation domains offset 30° to each other. It confirms that the crystal orientation of the epitaxial Cu film follows that of graphene, i.e. the Cu film consists of two orientation domains offset 30° to each other when deposited on polycrystalline graphene. Finally, on the contrary to the report in the literature, we show that the direct current and radio frequency flip sputtering method causes significant damage to the graphene lattice during the Cu deposition process, and therefore neither is a suitable method for Cu epitaxial growth on graphene.

Simple Fabrication and Characterization of an Aluminum Nanoparticle Monolayer with Well-Defined Plasmonic Resonances in the Far Ultraviolet

Currently, aluminum plasmonics face technical challenges for the manufacture of reproducible structures by simple and low-cost techniques. In this work, we used a direct current (DC) sputtering system to grow a set of quasi-spherical aluminum nanoparticles with diameters below 10 nm. Our particles are uniformly distributed over the surface of quartz and nitrocellulose substrates. We review in detail the methodology for the determination of adequate deposition parameters to allow great reproducibility in different production runs. Likewise, we carry out an exhaustive nanostructural characterization by means of scanning and transmission electron microscopy. The latter allowed us to identify that our depositions are nanoparticle monolayers with thicknesses equal to the average particle diameter. Finally, by means of absorbance spectra we identify the presence of a very well-defined plasmonic resonance at 186 nm that is associated with the dipolar mode in particles smaller than 10 nm. Due to the sharpness of their plasmonic resonances as well as their great manufacturing simplicity and high reproducibility, our aluminum nanoparticles could be used as optical sensors.

Lithium storage performance of copper nitride films deposited by reactive DC magnetron sputtering

Copper nitride (Cu3N) films were deposited on copper foil substrates by reactive direct current (DC) unbalance magnetron sputtering. The Cu3N films with DC sputtering powers of 110, 205, 280 and 373 W under the mixture of argon (Ar) and nitrogen (N2) gases were investigated. The dependence of crystalline structure and film thickness of Cu3N on the sputtering powers was evaluated. Exclusively, the electrochemical measurements of the films in 1M LiCl as electrolyte were also carried out. The good performance of lithium ion storage was observed. These results demonstrate that Cu3N film on copper foil could be further explored as high capacity material for flexible lithium ion battery development.

Surface morphology and wettability for thin films of beta-iron disilicide produced through direct-current sputtering utilizing a pair of facing targets

In the current work, beta-FeSi2 films were epitaxially produced onto Si(111) wafer substrates via usage of facing-targets direct-current sputtering (FTDCS). The temperature for substrate heating was maintained at 600 °C and the sputtering pressure was set at 1.33 × 10-1Pa. The surface morphology and contact angles of the beta-FeSi2films were explored consistently in this research. Images of three-dimensional AFM and FESEM for the beta-FeSi2 film surface revealed a smooth surface with a root mean square roughness of 1.31 nm and a porous area. The average contact angle between the dropped water and beta-FeSi2film surface was found to be 98.7°, establishing that the surface of the beta-FeSi2films was hydrophobic. The acquired experimental results revealed the commencement of the hydrophobic surface feature of the beta-FeSi2films produced via FTDCS approach.

Impact of Plasma Electron Flux on Plasma Damage-Free Sputtering of Ultrathin Tin-Doped Indium Oxide Contact Layer on p-GaN for InGaN/GaN Light-Emitting Diodes.

The origin of plasma‐induced damage on a p‐type wide‐bandgap layer during the sputtering of tin‐doped indium oxide (ITO) contact layers by using radiofrequency‐superimposed direct current (DC) sputtering and its effects on the forward voltage and light output power (LOP) of light‐emitting diodes (LEDs) with sputtered ITO transparent conductive electrodes (TCE) is systematically studied. Changing the DC power voltage from negative to positive bias reduces the forward voltages and enhances the LOP of the LEDs. The positive DC power drastically decreases the electron flux in the plasma obtained by plasma diagnostics using a cutoff probe and a Langmuir probe, suggesting that the repulsion of plasma electrons from the p‐GaN surface can reduce plasma‐induced damage to the p‐GaN. Furthermore, electron‐beam irradiation on p‐GaN prior to ITO deposition significantly increases the forward voltages, showing that the plasma electrons play an important role in plasma‐induced damage to the p‐GaN. The plasma electrons can increase the effective barrier height at the ITO/deep‐level defect (DLD) band of p‐GaN by compensating DLDs, resulting in the deterioration of the forward voltage and LOP. Finally, the plasma damage‐free sputtered‐ITO TCE enhances the LOP of the LEDs by 20% with a low forward voltage of 2.9 V at 20 mA compared to LEDs with conventional e‐beam‐evaporated ITO TCE.

Structural, optical and electrical properties of DC sputtered indium saving indium-tin oxide (ITO) thin films

Amorphous indium tin oxide (ITO) thin films with reduced to 50 mass% indium oxide content were prepared by direct current (DC) sputtering of ITO target in mixed argon-oxygen atmosphere onto glass substrates preheated at 523 K. The films were subsequently heat-treated in air at different temperatures in the range of 523–923 K for 60 min. The use of oxygen during deposition resulted in highly transparent (>80%) in visible and infrared ranges of spectra films. It has been found from the electrical measurements that as-deposited films under optimum sputtering conditions at working gas flow rate of Q(Ar)/Q(O2) = 50 sccm/0.5 sccm showed minimum volume resistivity of about 694 μΩcm. As-deposited thin films obtained under the optimum condition showed amorphous structure. Improving of crystallisation has been observed with increasing heat treatment temperature. It has been found that DC sputtered films with decreasing amount of indium oxide have smooth surface in contrast to typical ITO (90 mass% indium oxide).

Development of sensitive impedimetric urea biosensor using DC sputtered Nano-ZnO on TiO2 thin film as a novel hierarchical nanostructure transducer

3D hierarchical Nano-ZnO/TiO2 on conductive fluorinated-tin oxide (FTO) layer was fabricated by reactive direct current (DC) magnetron sputtering of ZnO, at the optimized instrumental deposition conditions, on a pre-covered TiO2 surface with Polyvinyl Alcohol (PVA) as an omissible polymer in a pattern of parallel strips (Nano-ZnO/PVA/TiO2/FTO) following by PVA omission via annealing process, which resulted in an efficient porous media for urease (Urs) enzyme immobilization (Urs/Nano-ZnO/TiO2/FTO) designed for urea biosensing. The criteria for TiO2 selection as substrate was based on: (i) its ability to promote electron transfer between ZnO to FTO substrate, (ii) affording high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents at the biological media, and (iii) enhancement of urea biosensing by the formation of heterojunctions with ZnO. Characterization of the surface morphology of 3D hierarchical Nano-ZnO/TiO2 film by field emission-scanning electron microscopy (FE-SEM) exhibits cavities of nanoporous ZnO film as an effective biosensing area for Urs enzyme immobilization. Step by step monitoring of Urs/Nano-ZnO/TiO2/FTO biosensor fabrication was performed using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fabricated Urs/Nano-ZnO/TiO2/FTO biosensor was used for urea determination using impedimetric assessment. The impedimetric results show high sensitivity for urea detection within 5–205mgdl−1 and limit of detection as 2mgdl−1. A fast response of fabricated biosensor can usually allow a real-time analysis.

DC sputtering of highly c-axis AlN films on top of 3C-SiC (111)-on-Si (111) substrates under various N2 concentrations

This article reports on the direct current sputtering of AlN thin films on top of a cubic-silicon carbide (111) on silicon (111) substrates. The authors varied the nitrogen (N2) concentrations, while keeping other process parameters fixed at the power of 1200 W, the substrate temperature of 350 °C, the target to substrate distance of 20 cm, and the sputtering pressure of 2 mT. The total N2/Ar gas flow is 50 sccm, and the poison mode starts at 40%. The x-ray diffraction results show that the AlN films are highly oriented along the (002) orientation at various N2 concentrations. The values of the three parameters support this observation, namely, (1) the extracted full width at half maximum (FWHM) of (002) diffraction peaks with the median of 0.28° and the standard deviation of 0.012°, (2) the area of AlN (002) under the curve is between 92% and 97%, and (3) the grain sizes are between 30.11 and 32.3 nm. The omega scan rocking curve of two samples at 40% and 80% N2 concentrations depicts good quality AlN (002) films with the FWHM values of 1.5° and 2°, respectively. The relationship between the N2 concentrations and the film's properties is elucidated. Finally, the authors discuss the effect of the lattice mismatch of 1% between AlN (002) and 3C-SiC (111).

Role of sputtering power on the microstructural and electro‐optical properties of ITO thin films deposited using DC sputtering technique

The effects of sputtering power on the deposition rate as well as the microstructural, electrical, and optical properties of indium tin oxide (ITO) thin films are investigated in this paper. ITO thin films were deposited on glass substrates using direct current (DC) magnetron sputtering of different DC powers, ranging from 60 to 140 W, onto externally unheated glass substrates. All samples were grown at the minimum sustainable plasma pressure to reduce the destructive role of pressure. The microstructural, electrical, and optical properties of the sputtered ITO films were systematically characterized by X‐ray diffraction (XRD), atomic force microscopy (AFM), four‐probe electrical conductivity, and optical spectroscopy. XRD studies confirmed the cubic bixbyite ITO structure, and the main preferred orientations of the prepared thin films were (222), (400), (440), and (622). AFM analysis showed a minimum surface roughness of 1.37 nm for the films deposited at 140 W, while the average size of the grains was 65 ± 5 nm. The deposition time was fixed at 10 min for all samples, and the AFM characterization of the films showed 170, 230, and 250 nm thickness for the samples deposited at 60, 100 and 140 W, respectively. From the variations of the sheet resistance and the XRD patterns of the ITO thin films, it was concluded that, as the ratio I222/I400 of a sample approaches unity, the sheet resistance of the layer reduces. A minimum sheet resistance 16 Ω/square, transmittance 85% with the thickness of 230 nm, and optical bandgap 4.09 eV were found for the thin film grown on the externally unheated substrates at 100 W DC power and 32 mTorr working pressure. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Controllable Formation of (004)-Orientated Nb:TiO2 for High-Performance Transparent Conductive Oxide Thin Films with Tunable Near-Infrared Transmittance.

A niobium-doped titanium dioxide (Nb:TiO2, NTO) film is a promising candidate material for indium-free transparent conductive oxide (TCO) films. It is challenging and interesting to control (004)-oriented growth to decrease resistivity. In this work, NTO films with different fractions of preferential (004) orientation (η(004)) were controllably prepared by direct current sputtering. Notably, the direction of local-ordering of ions-packing could be adjusted by slightly changing the angle between the sputtering source and the glass substrate, which is identified as a key factor to determine the growth direction of a columnar crystal as well as the η(004) of films. Hall effect measurements indicate that NTO films with the highest η(004) present the lowest resistivity (6.4 × 10-4 Ω cm), which originates from super-high carrier concentration (2.9 × 1021 cm-3) and mobility (3.4 cm2 V-1 s-1). The corresponding low sheet resistance (10.3 Ω sq-1) makes it a potential material for commercial TCO films. We also observe that films with higher η(004) show lower transmittance in the near-infrared region.

Nanoscale silver depositions inhibit microbial colonization and improve biocompatibility of titanium abutments

Although titanium dental implants are biocompatible, exhibit excellent corrosion resistance and high mechanical resistance, the material fails in providing resistance to infection because it exhibits poor antimicrobial activity. To address these issues, we deposited silver onto titanium abutments (Grade 5 titanium discs) using direct current (DC) sputtering and assessed the antimicrobial activity and biocompatibility of the modified implant material. Atomic absorption spectrometry and X-ray photoelectron spectroscopy were employed to investigate the concentration and elemental composition of the deposited silver. As expected, silver deposited using DC plasma was uniform and good control over the deposition could be achieved by varying the sputtering time. Moderate biocompatible responses (up to 69% viability) were observed in primary human gingival fibroblast cells incubated in the presence of Ti sputtered with Ag for 5min. Silver deposited titanium (Ti-Ag) showed excellent antibacterial effects on Pseudomonas aeruginosa and Streptococcus mutans at a very low concentration (Ag content 1.2 and 2.1μg/mm2). However, higher concentration of silver (6μg/mm2) was required to achieve a reduction in cell viability of Staphylococcus aureus and Candida albicans. The silver sputtered Ti abutments could maintain a long-term antibacterial activity as evidenced by the release of silver up to 22days in simulated body fluid. Our study illustrates that silver deposited titanium is indeed a promising candidate for soft tissue integration on dental abutments and prevents initial microbial adhesion.

Vital Role of Oxygen for the Formation of Highly Rectifying Schottky Barrier Diodes on Amorphous Zinc-Tin-Oxide with Various Cation Compositions.

We present electrical properties of Schottky barrier diodes on room-temperature deposited amorphous zinc-tin-oxide (ZTO) with Zn/(Zn + Sn) contents between 0.12 and 0.72. A combinatorial approach with continuous composition spread pulsed laser deposition is used to achieve the wide range of compositions with four samples each on 50 × 50 mm2 glass substrates. The Schottky barrier contacts were fabricated by the reactive direct-current sputtering of platinum. Best diode properties (rectification ratio SV = 2.7 × 107, ideality factor η = 1.05, and effective barrier height ϕB,eff = 1.25 eV) are obtained for a composition of 0.63 Zn/(Zn + Sn). Aging on the timescale of days and months is observed that leads to improved device properties (higher rectifications and lower ideality factors). In particular, the diodes with the lowest performance in the as-prepared state show the biggest improvements. The best diode properties after the aging process (SV = 3.9 × 107, η = 1.12, and ϕB,eff = 1.31 eV) were also observed for 0.63 Zn/(Zn + Sn).

Effect of moving speed during in-line pulsed direct-current magnetron sputtering deposition on the structural and optical properties of Al-doped ZnO films

Aluminum-doped zinc oxide (AZO) films were deposited on glass substrates with pulsed direct current (DC) magnetron sputtering. Deposition was carried out in both static and dynamic modes. The pulsed DC sputtering process provided a stable deposition of AZO films without arcing, resulting in good crystallinity, unlike simple DC magnetron sputtering. The growth characteristics of the films sputtered on various moving speeds of the in-line dynamic mode are investigated and compared to those of the static mode. AZO films deposited at a moving speed of 120cm/min showed a dominant (002) orientation, a smooth surface roughness, and a higher figure of merit (FOM), of which properties are similar to those of the static mode. Comparisons of the characteristics obtained at several moving speeds showed that better crystallinity was obtained at the higher moving speed of 120cm/min. This improvement could be attributed to an averaging effect, which is due to more frequent interruption and initiation of the growth at the higher moving speed. Optical transmission characteristics were compared between the static and dynamic modes, and analyzed in terms of the complex indices of refraction and interference effects of light.