Rf Diode Sputtering Research Articles

Diagnostics of phase composition of lithium niobate films on sapphire by principal component analysis using Raman spectra

Thin films of lithium niobate were deposited by RF diode sputtering of a LiNbO3 single-crystal target on a heated sapphire substrate (R-cut, 650 °C). Radial distributions of the phase composition of the films along the substrate were obtained by principal component analysis (PCA) using Raman spectra. It was found that at small target-substrate distances (12 mm is the distance between the target and the substrate, 76 mm is the diameters of the target and the substrate holder, 30 mm is the size of the film deposition area in axial geometry), the effects of resputtering of the deposited film do not lead to a considerable decrease in the lithium content: no phases other than LiNbO3 are formed in the extended central part of the film, the edge of the film contains no more than 2 % of the undesirable LiNb3O8 phase, and the difference in the measured values of deviation of LiNbO3 phase composition from stoichiometry in the film compared to the target is 0.7 mol% Li2O. These results indicate that the technology for depositing of lithium niobate films can be improved since there is no need to produce a target additionally enriched with Li2O.

Predictive modelling of the dielectric response of plasmonic substrates: application to the interpretation of ellipsometric spectra

A predictive modelling of plasmonic substrates appropriate to read ellipsometric spectra is presented in this work. We focus on plasmonic substrates containing a single layer of silver nanoparticles (AgNPs) embedded in silica matrices. The model uses the Abeles matrix formalism and is based on the quasistatic approximation of the classical Maxwell-Garnett mixing rule, however accounting for the electronic confinement effect through the damping parameter. It is applied on samples elaborated by: (i) RF-diode sputtering followed by Plasma Enhanced Chemical Vapor Deposition (PECVD) and (ii) Low Energy Ion Beam Synthesis (LE-IBS), and represents situations with increasing degree of complexity that can be accounted for by the model. It allows extraction of the main characteristics of the AgNPs population: average size, volume fraction and distance of the AgNPs layer from the matrix free surface. Model validation is achieved through comparison with results obtained from transmission electron microscopy approving for its applicability. The advantages and limitations of the proposed model are discussed after eccentricity-based statistical analysis along with further developments related to the quality of comparison between the model-generated spectra and the experimentally-recorded ellipsometric spectra.

Magnetic Properties and Microstructure of Co Thin Films by RF-diode Sputtering Method

Magnetic Properties and Microstructure of Co Thin Films by RF-diode Sputtering Method

Formation and possible growth mechanism of bismuth nanowires on various substrates

In this work, we report results of a study of bismuth nanowires growth on various substrates, including Fe, Ni, Co, W, Pt, Au thin films on oxidized Si, Si (111), oxidized Si (100), and fused quartz. The nanowires (NW) were prepared by RF diode sputtering of Bi onto a substrate heated to about 200 °C. The structure of the wires was studied by a scanning and transmission electron microscopy. The NWs are monocrystalline up to a length of several micrometers and possess a very thin (less than 2 nm) oxide layer. A major influence of the substrate type on the quantity and the length of the obtained nanowires is observed. Based on the above studies, we propose a possible mechanism of a bismuth nanowire growth.

Tungsten oxide thin film photo-anodes by reactive RF diode sputtering

Tungsten oxide (WO3) thin films were deposited both on silicon, soda-lime glass and W foils by Ar/O2 plasma diode sputtering process from a W metal target. The influence of O2 content percentage on the structural and optical properties of the films, as well as the effects of post treatment annealing both in vacuum (400°C) and in air (600°C) have been investigated. X-ray diffraction studies revealed that the as-grown films are amorphous-like regardless of the oxygen percentage. The degree of crystallinity of films is increased by a post-growth thermal-annealing procedure. With respect to other plasma sputtering recipes, here a lower stress state is favoured by the slower deposition rate and the multi-step deposition. The optical band gap deduced from the absorbance spectra ranges from 3.1–3.3eV for the amorphous samples and it decreases to 2.3–2.5 for the more crystalline films. The photoelectrochemical activity of WO3 samples annealed at 600°C in air have been investigated as a function of the O2 content.

Efficient Detection of SO2 Gas Using SnO2 Based Sensor Loaded with Metal Oxide Catalysts

A novel sensor structure using SnO2 thin film matrix integrated with nano-clusters of metal oxide modifiers were fabricated with the help of rf-diode sputtering for low level (500 ppm) detection of SO2 gas at lower operating temperature of 180 °C. Ultrathin dotted clusters (10 nm thick and 600 μm dia.) of various metal oxide catalysts (PdO, CuO, NiO, MgO, V2O5) were loaded over the SnO2 surface. Due to the difference in work function of the SnO2 layer with respect to the integrated metal oxide catalyst, all prepared sensor structures exhibited high resistance in air. SnO2 film with NiO nano-clusters is found to exhibit a maximum sensing response of ∼56 at a low operating temperature of 180 °C towards 500 ppm of SO2 gas with a fast response time of 80 s. The rough and porous morphology of the SnO2 thin film with the formation of hetero- interface favours the sensing of SO2.

THE STRUCTURE AND MECHANICAL PROPERTIES OF ALUMINA FILM PREPARED BY RF DIODE SPUTTERING

Alumina (Al2O3) films were prepared on Al2O3-TiC substrates by RF diode sputtering. The target sputtering power was varied from 4 to 8 kW. The effects of target sputtering power on the structure and mechanical properties of alumina films were investigated. The results show that the structure of the alumina films deposited at all the target sputtering powers is amorphous. However, under the exposure to the electron beam during the Transmission Electron Microscopy (TEM) measurements, the structure of alumina films becomes crystalline. The hardness and elastic modulus of alumina films were found to increase as the target sputtering power was increased.

Stress Induced in Al<sub>2</sub>O<sub>3</sub> Films as Deposited onto Al<sub>2</sub>O<sub>3</sub>TiC Substrate by RF Diode Sputtering

Al2O3 films were deposited onto Al2O3-TiC substrates by RF diode sputtering. The Al2O3 films were deposited at various substrate bias voltages from -80 to -180 V, sputtering powers from 4 to 8 kW and operating pressures from 20 to 30 mTorr. The stress induced in Al2O3 films was measured. The results show that the stress induced in all prepared Al2O3 films is tensile stress. The stress slightly increased with increasing substrate bias voltage whereas it increased linearly with increasing operating pressure. However, the stress was almost constant as the sputtering was increased from 5 to 8 kW and significantly decreased as the sputtering power was decreased below 5 kW.

Characteristics of SAW hydrogen sensors based on InOx/128°YX-LiNbO3 structures at room temperature

Abstract A new kind of SAW hydrogen sensors based on 128°YX-LiNbO 3 SAW delay lines covered by InO x sensing layers is presented, in which the InO x layers are prepared by RF diode sputtering method and Pt films are deposited on the surfaces of the sensing layers as catalysts. The experimental results indicate that an apparent frequency shift of 11.83 kHz of the sensor towards 400 ppm hydrogen mixed in natural air is observed at room temperature, which displays very high sensing characteristics. By using XRD, AFM and XPS analyses, it is found that the InO x sensing layers deposited by RF diode sputtering method have small and uniform nano-grains (∼16 nm in diameter), high oxygen vacancies and high ratios of the chemisorbed oxygen to that in the lattice, which make the response properties of the sensors greatly improved.

A comparative study of ultraviolet photoconductivity relaxation in zinc oxide (ZnO) thin films deposited by different techniques

Photoresponse characteristics of ZnO thin films deposited by three different techniques namely rf diode sputtering, rf magnetron sputtering, and electrophoretic deposition has been investigated in the metal-semiconductor-metal (MSM) configuration. A significant variation in the crystallinity, surface morphology, and photoresponse characteristics of ZnO thin film with change in growth kinetics suggest that the presence of defect centers and their density govern the photodetector relaxation properties. A relatively low density of traps compared to the true quantum yield is found very crucial for the realization of practical ZnO thin film based ultraviolet (UV) photodetector.

Characterization of Aluminum Oxide Films Deposited on Al2O3-TiC by RF Diode Sputtering

In magnetic head recording storage, Al2O3 film was deposited onto Al2O3-TiC substrate, as insulating and protection layers, using RF diode sputtering. Pure Al2O3 (99.5%) with a dimension of 43.2cm × 43.2cm × 2.0cm was used as a sputtering target. The base pressure for all depositions was 1 × 10-6 m Torr and the deposition time was 12.2min. The target sputtering power and substrate bias voltage were varied from 4 to 8kW and 80 to 180V, respectively. The surface morphology of Al2O3 films was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). It was found that the roughness of deposited Al2O3 films depends on sputtering power. SEM cross-sectional image clearly showed good adhesion between substrate and Al2O3 film. The mechanical properties, including elastic modulus and hardness, of Al2O3 films were performed on nanoindentator. The results showed that both elastic and hardness of Al2O3 films increased with the increase of target sputtering power.

Effect of annealing on properties of sputtered and nitrogen-implanted ZnO:Ga thin films

Thin films of gallium-doped zinc oxide (ZnO:Ga) were deposited on Corning glass substrates by rf diode sputtering and then implanted with 180 keV nitrogen ions in the dose range of 1 × 1015 ÷ 2 × 1016 cm-2 . After the ion implantation, the films were annealed under oxygen and nitrogen ambient, at different temperatures and time, and the effect on their microstructure, type and range of conductivity, and optical properties was investigated. Post-implantation annealing at 550 °C resulted in n -type conductivity films with the highest electron concentration of 1.4 × 1020 cm-3 . It was found that the annealing parameters had a profound impact on the film’s properties. A p -type conductivity (a hole concentration of 2.8 × 1019 cm-3 , mobility of 0.6 cm2 /V s) was observed in a sample implanted with 1 × 1016 cm-2 after a rapid thermal annealing (RTA) in N2 at 400 °C. Optical transmittance of all films was >84% in the wavelength range of 390–1100 nm. The SIMS depth profile of the complex 30 NO− ions reproduces well a Gaussian profile of ion implantation. XRD patterns reveal a polycrystalline structure of N-implanted ZnO:Ga films with a c -axis preferred orientation of the crystallites. Depending on the annealing conditions, the estimated crystallite size increased 25 ÷ 42 nm and average micro-strains decreased 1.19 × 10-2 ÷ 6.5 × 10-3 respectively.

Carrier Control in Polycrystalline ZnO:Ga Thin Films via Nitrogen Implantation

The electrical characteristics of gallium-doped zinc oxide (ZnO:Ga) thin films prepared by rf diode sputtering were altered via nitrogen implantation by performing two implants at 40 keV and 80 keV with doses of 1×1015 and 1×1016 cm−2 to achieve a p-type semiconductor. An implantation of 1×1015 cm−2 N+-ions yielded a p-type with hole concentrations 1017–1018 cm−3 in some as-implanted samples. The films annealed at temperatures above 200°C in O2 and above 400°C in N2 were n-type with electron concentrations 1017–1020 cm−3. The higher nitrogen concentration (confirmed by SRIM and SIMS), in the films implanted with a 1×1016 cm−2 dose, resulted in lower electron concentrations, respectively, higher resistivity, due to compensation of donors by nitrogen acceptors. The electron concentrations ratio n(1×1015)/n(1×1016) decreases with increasing annealing temperature. Hall measurements showed that 1×1016 cm−2 N-implanted films became p-type after low temperature annealing in O2 at 200°C and in N2 at 400°C with hole concentrations of 3.2×1017 cm−3 and 1.6×1019 cm−3, respectively. Nitrogen-implanted ZnO:Ga films showed a c-axes preferred orientation of the crystallites. Annealing is shown to increase the average transmittance (>80%) of the films and to cause bandgap widening (3.19–3.3 eV).

Oblique Angle Sputtering of ZnO:Ga Thin Films

Abstract RF diode sputtering of ZnO:Ga thin films by three types of deposition at constant oblique-angle (80°) configuration is presented: simple oblique deposition, oblique depositions by substrate sequential turning around the substrate normal - double by an 180° angle and four-times by 90°. XRD patterns and azimuthal line profiles confirmed their inclined (002) texture and SEM/TEM cross-section analyses indicated the columnar crystallic structures: tilted by about 11°, 2D- and 3D- “pseudo-zigzag” ones. Both inclined texture and tilted columnar structure of the films increased their optical transmittance and widened their direct optical band-gap.

Influence of deposition regime on physical properties of gallium doped zinc oxide films

Zinc oxide films doped by gallium were deposited using RF diode sputtering from a ceramic ZnO + 2% Ga2O3 target on Corning glass in argon atmosphere. Samples were supported in three different positions against a substrate holder – horizontal, and at 60 and 80° to the horizontal position. Two series of samples 700–1000 nm in thickness were prepared: one at room temperature (RT) and the second at 200 °C. XRD, optical and electrical experiments indicated that the films are polycrystalline having average crystallite sizes from 30 to 80 nm, integrated transmittances in the range of 400–1000 nm increased from 85 to 90 per cent and optical band-gap values increased from 3 to 3.2 eV with higher deposition temperature. The resistivity of the obliquely sputtered samples positioned at 80° to the substrate holder was one order lower than the horizontally positioned samples. No significant changes were observed in case of optical properties of the films in dependence on the tilt-angle.

Characterization of gallium–nitrogen co-doped zinc oxide thin films prepared by RF diode sputtering

We investigated the possibility of achieving p-type zinc oxide (ZnO) by RF diode sputtering and gallium–nitrogen co-doping. ZnO:Ga:N thin films were prepared with a different N2 content in Ar/N2 working gas, ranging from 0 to 100%, and at a varying substrate temperature, from room temperature (RT) to 300 °C. A hole conduction with maximum carrier concentration of 2.6 × 1018 cm−3, mobility of 2 cm2/Vs and resistivity of 1.5 Ω cm resulted from deposition at RT with 100% N2. It arose from N incorporation and formation of NO acceptors. In the secondary ion mass spectrometry (SIMS) depth profiles of the co-doped films were observed NO/NO2 negative ions. Average transmittance (including Corning glass substrate) across the visible spectrum varied (60 ÷ 66%) with increasing nitrogen content (50 ÷ 100% N2). As the substrate temperature increased (RT – 300 °C), highly transparent (T ∼72–83%) and conductive (electron concentrations of 1017–1019 cm−3) n-type ZnO:Ga:N films were attained. Reduction of optical band gap (Eg) (∼3.13–3.08 eV) was observed for co-doped ZnO films. Atomic force microscopy (AFM) images revealed that the films grown at RT have roughness of approximately 5.3 nm while roughness of those grown at 300 °C is approximately 3.9 nm.

Electrical properties of nickel electrodes for high-k MOS structures

Together with high-κ dielectric films, metal gate electrodes have to be employed in advanced CMOS technologies. The metal gate material should be carefully selected with respect to work function, stability of metal-dielectric stack and compatibility with the CMOS process. In our investigation Ni gate electrodes grown on thermal SiO2, atomic-layer deposition HfO2 and Al2O3 dielectric films have been analyzed by means of high-frequency capacitance–voltage measurement on MOS capacitors. Ni gate materials were prepared by RF diode sputter deposition. Work function of the investigated gate material and density of effective defect charge of the gate oxide film were extracted from the measurements. These properties are discussed with regard to application of Ni metal gates in CMOS technology.

Ion sputter etching of ZnO:Ga thin film surfaces

In this article the modification of surface morphology of ZnO:Ga (GZO) thin films by ion sputter etching is presented. GZO thin films were prepared at room temperature on Corning glass substrates by both normal and oblique angle RF diode sputtering from ZnO:2%Ga ceramic target in Ar gas. Ion sputter etching was performed by RF re-sputtering of GZO thin films on substrates. During RF sputter etching, Ar pressure of 1.3Pa and RF power of 250W were kept constant, only the time of sputter etching was changed. Ion sputter etching had remarkable influence on surface morphology of GZO thin films: increase of roughness Rq and the “homogenization” of film surfaces, i.e. skewness (Rsk) and spikiness (Rku) parameters (Rsk≈0/Rku≈3).Surface root-mean-square roughness (Rq) increased from 15.3nm (after sputter deposition) to 29.1nm (after ion sputter etching). For obliquely thin films increased from 16.5nm (after sputter deposition) to 38.2nm. Changes of these parameters Rq, Rsk, Rku influenced optical properties of GZO films, increased Haze parameter up to values 7.7% and width of optical band gap 3.44eV, respectively.

Influence of Doping and Co-Doping on the Behavior of Sputtered ZnO Thin Films

A co-dopand approach was used to investigate influence of gallium-nitrogen co-doping on the microstructure and electrical parameters of ZnO. ZnO:Ga:N thin films were deposited by rf diode sputtering at varying nitrogen content (0÷100%) in Ar/N2 gas. ZnO:Ga films (0% N2) showed minimum resistivity of 0.12 Ωcm, electron concentration of 2.5x1019 cm-3 and mobility of 2 cm2/Vs. A hole concentration of 2.6x1018 cm-3, a mobility of 2 cm2/Vs and a resistivity of 1.5 Ωcm in ZnO:Ga:N resulted from the deposition with 100% N2 in Ar/N2 gas. XRD patterns revealed a profound impact of Ga-N co-doping on film orientation. The estimated crystallite size varied from 234 to 41 nm, depending on the N2 content. TEM images of the co-doped films along with the corresponding selected area diffraction pattern indicated a polycrystalline, columnar layer with a c-axis preferred orientation. AFM images demonstrated the different crystalline structure and grain formation depending on nitrogen content.

Survival of Staphylococcus aureus exposed to UV radiation on the surface of ceramic tiles coated with TiO2

The aim of this study was to determine and compare the antimicrobial activity of UV radiation of wavelength 253.7 nm (used in typical germicidal lamps) against Staphylococcus aureus on the surfaces of conventionally produced white ceramic wall tiles (matt and shiny) and the same tiles coated with TiO2 using three different methods: RF diode sputtering, atmospheric pressure chemical vapour deposition (APCVD) and spray pyrolysis deposition (SPD). Results clearly indicate that the bactericidal action of UV radiation is much stronger on the surfaces of tiles coated with TiO2 than on the tiles uncovered. The strongest bactericidal effect of UV radiation was found for film prepared by APCVD. Results of experiments for shiny and matt tiles did not differ statistically. The use of ceramic wall tiles coated with TiO2 films in hospitals, veterinary clinics, laboratories, food processing plants and other places where UV radiation is applied for disinfection should greatly improve the efficiency of this treatment.