Effect of oxygen concentration and system geometry on the current-voltage relations during reactive sputter deposition of titanium dioxide thin films

Current-voltage relations at different magnetron sputtering systems and gas mixtures were studied during reactive sputter deposition of titanium dioxide thin films. The main goal of this work was to investigate the influence of reactive gas mixture (Ar + O₂) and system geometry on the electrical characteristics of the discharge. The geometries utilized were the conventional magnetron sputtering, hollow cathode magnetron sputtering and triode magnetron sputtering. A change in the system geometry leads to a change in the electric field distribution, which alters the working range of the discharge voltage and magnetron efficiency. It is noticed that the discharge voltage at constant current can be reduced when the geometry is altered from conventional magnetron to hollow cathode magnetron or triode magnetron, at the same time the magnetron efficiency is increased when hollow cathode magnetron or triode magnetron are used instead of conventional magnetron sputtering.     

Structural and mechanical characterization of BCxNy thin films deposited by pulsed reactive magnetron sputtering

BC_xN_y thin films deposited at 250 °C by pulsed reactive magnetron sputtering of a B₄C target in an Ar/N₂ plasma were studied by elastic recoil detection analysis, Fourier transform infrared, Raman, and photoelectron spectroscopy, electron microscopy, and nanoindentation. In the concentration range of 6% to 100% N₂ in the sputter plasma the segregation into nanocrystalline hexagonal boron nitride and amorphous sp² carbon is the dominant process during the film growth. The stoichiometric ratio and structural details of the major phases depend on the N₂ concentration in the plasma and have significant influence on the Young′s modulus and the elastic recovery of the BC_xN_y thin films.     

XPS analysis of WxCy thin films prepared by sputter deposition

W_xC_y thin films with different compositions were studied in order to correlate their properties with the thin-film composition and chemical bonding of C and W atoms. Three W_xC_y thin films with C concentrations in the range 40-80 at% were deposited on WC-Co substrates by the plasma beam sputtering technique. The composition of the thin films and chemical states of elements were analysed by X-ray photoelectron spectroscopy (XPS) depth profiling. The C and W concentrations in the films were quantified using XPS intensities from a WC-Co substrate with a known composition. The C1s peaks in the high energy resolution XPS spectra of thin films allowed identification of the WC phase and the amorphous carbon phase as a function of the film composition. The results show that the amorphous carbon a-C phase is present in those films with composition x<y. The measured hardness of the films decreases with a decrease of the WC concentration.     

Mechanical properties of superhard TiB2 coatings prepared by DC magnetron sputtering

Superhard titanium diboride (TiB₂) coatings (H_v> 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB₂ target using an unbalanced direct current (d. c.) magnetron. Polished Si (0 0 1), stainless steel, high-speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, U_s, and substrate temperature, T_s, on mechanical properties of TiB₂ coatings was studied. X-ray diffraction (XRD) analysis showed hexagonal TiB₂ structure with (0 0 01) preferred orientation. The texture of TiB₂ coatings was dependent upon the ion bombardment (U_s increased from 0 to −300 V) and the substrate heating (T_s increased from room temperature (RT) to 700 °C). All TiB₂ coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness H_v up to 34 GPa, effective Young's modulus E*=E/(1-ν) ranging from 450 to 600 GPa; here E and ν are the Young's modulus and Poisson's ratio, respectively, and elastic recovery W_e≈80%. TiB₂ coating with a maximum hardness H_v≈73 GPa and E*≈580 GPa was sputtered at U_s=−200 V and T_s=RT. Macrostresses of coatings σ were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB₂ coatings exhibited compressive macrostresses.     

Variations of microstructure, conductivity and transparency of Al-doped ZnO thin films prepared by radio frequency magnetron sputtering with target-substrate distances

Al-doped ZnO films were deposited at different target-substrate distances by radio frequency magnetron sputtering. The crystallite size of the films is reduced with increasing the target-substrate distance, but the (002) preferential orientation of ZnO is observed for all the films. It is found that the target-substrate distance has a great influence on the carrier concentration in the films. Reduction of the target-substrate distance is favorable to obtain higher carrier concentrations. The lowest resistivity of 1.1 × 10⁻³ Ω cm is obtained for the film at target-substrate distance of 55 mm. The optical transmittance in the visible range remains higher than 90% for all the films, and the absorption edge shifts towards the shorter wavelength side with decreasing the target-substrate distance. The band gap was widened by 0.11 eV due to the Burstein-Moss (BM) shift from 3.33 eV to 3.44 eV with the reduction of the target-substrate distance from 60 mm to 55 mm.     

Evolution of the properties of ZnO thin films subjected to heating treatments

Structural and optical properties of ZnO thin films (200 nm thickness) deposited using magnetron sputtering technique are influenced by structural defects. Therefore, we applied various heating treatments in order to control and improve the crystallinity of the samples. These treatments were realized in air at temperatures of 350 °C, 550 °C and 700 °C respectively, each for a duration of 1 h. The properties of the samples were investigated both before and after the heating treatment. Modern methods like X-ray Diffraction, Atomic Force Microscopy and Scanning Electron Microscopy were used to analyze the structure and morphology of the heated ZnO thin films. These heating treatments may be held responsible for rearrangements in the morphology of the thin films. Thus, it was observed that an increase of porosity and agglomeration of the crystallites is followed by an increase in the size of the crystallites. Inter-crystalline borders will migrate determining a coalescence of several crystallites during the heating process, as well. As a consequence, an increase of the band gap width from 3.26 eV to 3.30 eV (at 350 °C) and 3.32 eV (at 550 °C) respectively, occurred.     

Microstructure of ZnO thin films produced by magnetron sputter oblique deposition

ZnO films deposited at different oblique angles of 40, 60 and 80°, under different Ar pressures 0.27, 0.67, 1.33 and 2.67 Pa, DC currents of 0.15 and 0.25 A, and distances of 10-15 cm from the target were studied. It was found that the film grains grow at an angle to the substrate when deposition angle is above 40°. It was shown that the grains consisted of a number of small crystals growing one on top of the other and shifted towards the target with the crystal orientation not along the grain growth but perpendicular to the substrate. Crystal size decreased with the deposition angle and internal stress disappeared when α = 80°. It was found that 1.33 Pa pressure provided the best balance between the deposition parameters. Growth rate reached maximum, samples had the biggest crystal size and high crystal density. However, crystal spatial alignment changed gradually with pressure and distance.     

Characterization of nanocrystalline indium tin oxide thin films prepared by ion beam sputter deposition method

Indium tin oxide (ITO) thin films were deposited on glass substrates by ion beam sputter deposition method in three different deposition conditions [(i) oxygen (O₂) flow rate varied from 0.05 to 0.20 sccm at a fixed argon (1.65 sccm) flow rate, (ii) Ar flow rate changed from 1.00 to 1.65 sccm at a fixed O₂ (0.05 sccm) flow rate, and (iii) the variable parameter was the deposition time at fixed Ar (1.65 sccm) and O₂ (0.05 sccm) flow rates]. (i) The X-ray diffraction (XRD) patterns show that the ITO films have a preferred orientation along (400) plane; the orientation of ITO film changes from (400) to (222) direction as the O₂ flow rate is increased from 0.05 to 0.20 sccm. The optical transmittance in the visible region increases with increasing O₂ flow rate. The sheet resistance (R_s) of ITO films also increases with increasing O₂ flow rate; it is attributed to the decrease of oxygen vacancies in the ITO film. (ii) The XRD patterns show that the ITO film has a strong preferred orientation along (222) direction. The optical transmittance in the visible spectral region increases with an increase in Ar flow rate. The R_s of ITO films increases with increasing Ar flow rate; it is attributed to the decrease of grain size in the films. (iii) A change in the preferred orientations of ITO films from (400) to (222) was observed with increasing film thickness from 314 to 661 nm. The optical transmittance in the visible spectral region increases after annealing at 200 °C. The R_s of ITO film decreases with the increase of film thickness.     

Low resistivity transparent conducting CdO thin films deposited by DC reactive magnetron sputtering at room temperature

Transparent conducting cadmium oxide (CdO) films were deposited on PET (polyethylene terephthalate) substrate by DC reactive magnetron sputtering at room temperature. All the films deposited at room temperature were polycrystalline in rock-salt structure. Dependences of the physical properties of the CdO films on the oxygen partial pressure were systematically studied. The films deposited at low oxygen flow rate were (200) oriented, while the films deposited at an oxygen flow rate greater than 20 sccm were (111) oriented. The average grain size of the CdO films decreased as the oxygen flow rate increases as determined by XRD and SEM. The Hall effect measurement showed that CdO films have high concentration, low resistivity, and high mobility. Both the mobility and the concentration of the carrier decreased with the increase of the oxygen flow rate. A minimum sheet resistance of 36.1 Ω/□, or a lowest resistivity of 5.44 × 10^− 4 Ω cm (6.21 × 10²⁰/cm³, μ = 19.2 cm²/Vs) was obtained for films deposited at an oxygen flow rate of 10 sccm.     

Al-Mg-B thin films prepared by magnetron sputtering

Hard, nanocomposite aluminum magnesium boride thin films were prepared on Si (100) substrates with a three target magnetron sputtering system. The films were characterized by X-ray diffraction, atomic force microscope, electron micro-probe, Fourier transform infrared spectroscopy and nanoindentation. The results show that the maximum hardness of the as-deposited films is about 30.7 GPa and these films are all X-ray amorphous with smooth surfaces. The influences of substrate temperature and boron sputtering power on the quality of the films are discussed. From the results of this work, magnetron sputtering is a promising method to deposit Al-Mg-B thin films.     

Mechanical properties of gradient and multilayered TiAlSiN hard coatings

Multicomponent coatings based on different metallic and non-metallic elements possess the combined benefit of individual components leading to further improvement of coating properties. In this study, monolayered Ti-Al-N, multilayered Ti-Al-N/TiN, gradient Ti-Al-Si-N, and multilayered Ti-Al-Si-N/TiN coatings were synthesized by using a cathodic-arc evaporation (CAE) system. In addition to Ti, Ti₃₃Al₆₇ and Al₈₈Si₁₂ cathodes were used for the deposition of Ti-Al-N, and Ti-Al-Si-N coatings, respectively. The gradient Ti_0.50Al_0.43Si_0.07N, and multilayered Ti_0.50Al_0.43Si_0.07N/TiN with nanograins separated by disordered grain boundaries possessed lower residual stress (− 2.8 ~ − 4.8 GPa) than that of monolayered Ti-Al-N (− 6.8 GPa) and multilayered Ti-Al-N/TiN coatings (− 5.7 GPa). The highest hardness was obtained for the gradient Ti_0.50Al_0.43Si_0.07N (38 ± 2 GPa) with Ti/(Ti + Al + Si) content ratio being 0.5. On the contrary, the multilayered Ti_0.50Al_0.43Si_0.07N/TiN possessed the highest H³/E^?2 ratio of 0.182 ± 0.003 GPa, indicating the best resistance to plastic deformation, among the studied coatings.     

The effect of sputtering power on the structure and photocatalytic activity of TiO2 films prepared by magnetron sputtering

TiO₂ films were fabricated by direct current reactive magnetron sputtering. The effect of the sputtering power on the film structures, morphologies, and properties was investigated in detail. It is found that the concentration of oxygen impurities increased with increasing sputtering power accompanied by the bandgap (E_g) narrowing and broadening of photoluminescence (PL) peaks. The oxygen impurities were found to mainly play the role of recombination centers, leading to the decrease of photocatalytic activity. Furthermore, the photoconductivity to dark conductivity ratio could be used to evaluate and even predict photocatalytic activity to some extent.     

Preferentially oriented vanadium nitride films deposited by magnetron sputtering

Because of solid state lubricious properties of vanadium oxides, wear resistant coatings based on nitrides and carbides of that metal are still of interest for research teams. The aim of this report is to show phase composition evolution from metallic vanadium through intermediate phases up to δ-VN phase supersaturated with nitrogen in thin films deposited by reactive, pulsed magnetron sputtering from vanadium target. This analysis is completed by remarks on preferential orientation, lattice constant and crystallite size. Presented work is a part of research on composite hard coatings for woodworking tools where vanadium nitrides and carbides are considered as a component reducing friction.     

溅射气压对碳化钒薄膜微结构与力学性能的影响

采用碳化钒靶的磁控溅射方法在不同的Ar气压下制备了一系列碳化钒薄膜,利用能量分析光谱仪,X射线衍射,扫描电子显微镜,原子力显微镜和微力学探针研究了气压对薄膜成分、相组成、微结构以及力学性能的影响。结果表明磁控溅射VC陶瓷靶可以方便地制备晶体态的单相碳化钒薄膜,并且溅射气压对薄膜的化学成分、相组成、微结构以及相应的力学性有较大的影响。在溅射气压为2.4~3.2 Pa的范围内,可获得结晶程度好和硬度与弹性模量较高的碳化钒薄膜,其最高硬度和弹性模量分别为28,269 GPa。低的溅射气压(0.32~0.9 Pa)下,所得薄膜结晶较差且硬度较低;过高的溅射气压(>4.0 Pa),薄膜的溅射速率降低,结晶变差,其硬度和弹性模量亦随之降低。低气压下薄膜碳含量较高和高气压下溅射原子能量降低可能是薄膜结晶程度降低的主要原因。     

Switching properties of vanadium doped TiO2 thin films prepared by magnetron sputtering

In the present work thin films of Ti-Me (where Me: V, Nb, Ta) were deposited onto glass substrates by magnetron sputtering of mosaic target in reactive oxygen plasma. The properties of the prepared thin films were studied by X-ray diffraction (XRD), electron dispersive spectroscopy, temperature-dependent electrical and optical transmission spectroscopy measurements. The structural investigations indicate that thin films were XRD-amorphous. Reversible thermoresistance effect, recorded at 52 ± 1 °C was found from electrical measurements. The prepared coatings were well transparent in the visible part of the light spectrum from ca. 350 nm.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Structural and optical properties of CdS thin films grown by chemical bath deposition

Cubic cadmium sulphide (CdS) thin films with (111) preferential orientation were prepared by chemical bath deposition (CBD) technique, using the reaction between NH₄OH, CdSO₄ and CS(NH₂)₂. The films properties have been investigated as a function of bath temperature and deposition time. Structural properties of the obtained films were studied by X-ray diffraction analysis. The structural parameters such as crystallite size have been evaluated. The transmission spectra, recorded in the UV visible range reveal a relatively high transmission coefficient (70%) in the obtained films. The transmittance data analysis indicates that the optical band gap is closely related to the deposition conditions, a direct band gap ranging from 2.0 eV to 2.34 eV was deduced. The electrical characterization shows that CdS films' dark conductivities can be controlled either by the deposition time or the bath temperature.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.     

Synthesis and characterization of indium phosphide films prepared by co-evaporation technique

Polycrystalline indium phosphide films were successfully deposited on glass and Si substrates by co-evaporating indium and phosphorus from appropriate crucibles. Microstructural studies indicated the average crystallite size to be ∼78 nm. X-ray diffraction pattern indicated reflections from (111), (220) and (311) planes only. The surface roughness of the films was estimated to be 30 nm and the band gap as determined from the transmittance versus wavelength traces was found to be ∼1.42 eV. The PL spectrum measured at 300 K was dominated by a strong peak located ∼1.41 eV. The intensity of this peak increased significantly when recorded at lower (10 K) temperatures and shifted towards higher energy (∼1.54 eV). XPS studies indicated two peaks ∼444.5 eV and ∼451.9 eV, corresponding to peaks of 3d_5/2 and 3d_3/2 of In 3d core while the P 2p peak at ∼128.8 eV was assigned to only P in InP. Characteristics Raman peaks for InP at ∼303 cm⁻¹ (TO) and ∼342 cm⁻¹ (LO) were observed.