Influence of ZnO buffer layer on AZO film properties by radio frequency magnetron sputtering

Transparent conductive films of Al-doped zinc oxide (AZO) were deposited on glass substrates under various ZnO buffer layer deposition conditions (radio frequency (r.f.) power, sputtering pressure, thickness, and annealing) using r.f. magnetron sputtering at room temperature. This work investigates the influence of ZnO buffer layer on structural, electrical, and optical properties of AZO films. The use of grey-based Taguchi method to determine the ZnO buffer layer deposition processing parameters by considering multiple performance characteristics has been reported. Findings show that the ZnO buffer layer improves the optoelectronic performances of AZO films. The AZO films deposited on the 150-nm thick ZnO buffer layer exhibit a very smooth surface with excellent optical properties. Highly c-axis-orientated AZO/ZnO/glass films were grown. Under the optimized ZnO buffer layer deposition conditions, the AZO films show lowest electrical resistivity of 6.75 × 10⁻⁴ Ω cm, about 85% optical transmittance in the visible region, and the best surface roughness of R_a = 0.933 nm.     

Influence of N2/Ar gas mixture ratio and annealing on optical properties of SiCBN thin films prepared by rf sputtering

Optical properties of amorphous thin films of silicon carbon boron nitride (Si–C–B–N) obtained by reactive sputtering has been studied. Compositional variations were obtained by changing the nitrogen and argon gas mixture ratio in the sputtering ambient. The effect of gas ratios and annealing on the optical properties was investigated. It was found that the transmittance of the films increases with nitrogen incorporation. Annealing at higher temperatures leads to considerable increase in transmittance. Optical energy gap (Tauc gap) calculated from absorption data is influenced by annealing temperatures and reactive process gas mixture. Changes in optical properties were correlated to the chemical modifications in the films due to annealing, through X-ray photoelectron spectroscopy. Studies reveal that the carbon and nitrogen concentrations in the films are highly sensitive to temperature. Annealing at higher temperatures leads to broken C–N bonds which results in the loss of C and N in the films. This is believed to be the primary cause for variations in optical properties of the films.     

Gallium oxide films deposition by RF magnetron sputtering; a detailed analysis on the effects of deposition pressure and sputtering power and annealing

In this study, gallium oxide (Ga₂O₃) thin films were deposited on sapphire and n-Si substrates using Ga₂O₃ target by radio frequency magnetron sputtering (RFMS) at substrate temperature of 300 °C at variable RF power and deposition pressure. The effects of deposition pressure and growth power on crystalline structure, morphology, transmittance, refractive index and band gap energy were investigated in detail. X-ray diffraction results showed that amorphous phase was observed in all the as-deposited thin films except for the thin films grown at low growth pressure. All the films showed conversion to poly-crystal β-Ga₂O₃ phase after annealing process. When the deposition pressure increased from 7.5 mTorr to 12.20 mTorr, change in the 2D growth mode to 3D columnar growth mode was observed from the SEM images. Annealing clearly showed formation of larger grains for all the thin films. Lower transmission values were observed as the growth pressure increases. Annealing caused to obtain similar transmittance values for the thin films grown at different pressures. It was found that a red shift observed in the absorption edges and the energy band gap values decrease with increasing growth pressure. For as-deposited and annealing films, increasing sputtering power resulted in the increase refractive index.     

Effect of substrate temperature on the structural,electrical, and optical properties of GZO/ZnO films deposited by radio frequency magnetron sputtering

Ga-doped ZnO (GZO)/ZnO bi-layered films were deposited on glass substrates by radio frequency magnetron sputtering at different substrate temperatures of 100, 200 and 300 °C to investigate the effects of substrate temperature on the structural, electrical, and optical properties of the films. Thicknesses of the GZO and ZnO buffer layer were kept constant at 85 and 15 nm by controlling the deposition times.     

Influence of a Ni interlayer on the optical and electrical properties of trilayer GZO/Ni/GZO films

Trilayer GZO/Ni/GZO films were deposited onto polycarbonate (PC) substrates with RF and DC magnetron sputtering, and then the influence of a Ni interlayer on the optical and electrical properties of the films was investigated. A 2-nm-thick Ni interlayer decreased the resistivity to 6.4×10⁻⁴ Ω cm and influenced the optical transmittance.Although optical transmittance deteriorated with Ni insertion, the films showed a relatively high optical transmittance of 74.5% in the visible wavelength region. The figure of merit (FOM) of a GZO single layer film was 1.2×10⁻⁴ Ω⁻¹, while that of the GZO/Ni/GZO films reached a maximum of 8.2×10⁻⁴ Ω⁻¹.Since a higher FOM results in higher quality transparent-conductive oxide (TCO) films, it is concluded that GZO films with a 2 nm Ni interlayer have better optoelectrical performance than single-layer GZO films.     

Electrical properties of annealed MPCVD grown vertically aligned carbon nanotube films

Vertically aligned multiwalled carbon nanotubes (MWNTs) were grown on silicon substrate at a low temperature (<520 °C) using microwave plasma-enhanced chemical vapor deposition (MPCVD). From the Raman spectra, it was found that the I_D/I_G ratio of MWNTs decreased after annealing, indicating that more graphenes were formed by the annealing process. Nevertheless, a strong Si signal was found in Raman spectra after annealing at a high-temperature (600 °C). From X-ray photoelectron spectroscopy (XPS) analysis it was observed that the ratio of the oxygen to carbon (O/C) signal intensity was from 0.15 to 1.88 for the increasing annealed temperatures of MWNTs, and a Si signal was found nearby the surface of MWNTs after annealing at 600 °C. Moreover, from the I–V measurement, the less symmetric I–V characteristic was found for the metal/MWNTs/metal (MIM) sandwich structure of unannealed MWNTs. After 300 °C annealing process, the positive current was increase and the negative current was decrease. It was conjectured that the MWNTs could obtain more graphenes structure by the 300 °C annealing process. Moreover, the I–V trace of the sample annealed by 600 °C exhibited rapid current descent, indicating the oxygenated and partly silicided phenomena might cover outer graphite layer of MWNTs. The equivalent circuit for the MIM sandwich structure could be represented as two Schottky barrier diodes in a back-to-back configuration. From the data fitting, it was found that the Schottky barrier height (_B0) decreased and the current density (J) increased from unannealing to 300 °C annealing temperature. However, the Schottky barrier height (_B0) was increased from 300 to 600 °C annealing temperature. Comparison with the XPS, this may due to the oxygenated and partly silicided phenomenon on the surface of the MWNTs.     

Influence of postdeposition annealing on the properties of ZnO films prepared by RF magnetron sputtering

ZnO films were prepared on unheated silicon substrate by RF magnetron sputtering technique. Postdeposition annealing of ZnO films in vacuum were found to improve film structure and electrical characteristics, such as dense structure, smooth surface, stress relief and increasing resistivity. Suitable annealing temperature also reduced loss factor. The correlation between annealing conditions and the physical structure of the films (crystalline structure and microstructure) was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The preferred annealing condition has been found to improve ZnO film characteristics for piezoelectric applications. An over-mode acoustic resonator using the ZnO film after annealing at 400 °C in vacuum circumstance for 1 h showed a large return loss of 42 dB at the center frequency of 1.957 GHz.     

Improved physical properties of Al-doped ZnO thin films deposited by unbalanced RF magnetron sputtering

Room temperature Al-doped ZnO (AZO) thin films with improved crystalline and optical properties were grown on normal glass substrates using unbalanced RF magnetron sputtering technique. To modify the plasma density towards the substrate and enhance the crystalline nature, an additional magnetic field ranging from 0 to 6.0 mT has been applied to the AZO target by proper tuning of solenoid coil current from 0 to 0.2 A respectively, which plays a significant role for controlling the physical properties of AZO films. The results from XRD studies indicate that all AZO films were composed of hexagonal wurtzite structure with better crystal quality through the applied magnetic field, ZnO (002) plane as a preferred growth. Furthermore, XPS studies suggested that symmetric chemical shifts in the binding energies for the Zn 2p and O1s levels with applied magnetic field. SEM analysis revealed the formation of a smooth, homogeneous and dense morphological surface with applied magnetic field. From AFM analysis, it was observed that the applied magnetic field strongly influenced the grain size and the films showed decreasing tendency in electrical resistivity. Films exhibited superior optical transmittance more than 94% in the visible region essentially due to the formation of better crystalline nature. The results indicate that improved band gap from 3.10 to 3.15 eV with additional magnetic field varied from 0 to 6.0 mT respectively.     

Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

Silicon-rich Al₂O₃ films (Si_x(Al₂O₃)_1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.     

Multi-response optimization of mechanical properties for ZrWN films grown using grey Taguchi approach

ZrWN nitride films are prepared using direct current (dc) reactive magnetron sputtering. Grey Taguchi analysis is used to determine the effect of deposition parameters (substrate plasma etching time, N₂/(N₂+Ar) flow rates, deposition time, and substrate temperature) on the microstructure and the tribological properties. An orthogonal array, signal-to-noise ratio and analysis of variance are used to determine the effects of deposition parameters. The substrates are pretreated using oxygen plasma etching. The resulting ZrWN coatings are homogeneous, very compact and completely adhered to the substrate. In the confirmation runs, using grey Taguchi analysis, the coefficient of friction decreases from 0.45?±?0.02 to 0.35?±?0.02, the corrosion potential increases from ??0.201?±?0.01 to ??0.072?±?0.01?V, the Vickers hardness increases from 23.63?±?0.07 to 24.65?±?0.05?GPa, and reduced modulus increases from 115.82?±?1.13 to 136.17?±?1.18?GPa. The ZrWN films are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rockwell C indentation and scratch testing. The TEM pattern for the ZrWN films corresponds to the (111), (200) and (220) planes of the face center cubic structure. Samples with a ZrWN film coating are classified as HF1 and exhibit good adhesive strength. The signal of friction and the associated acoustic emission signal are analyzed, and the scratch profile is analyzed using an optical microscope. Results show that the adhesive force for the critical load Lc2 is about 76.2?±?0.5?N.     

Microwave dielectric properties of the BaTi5O11 thin film grown on the poly-Si substrate using rf magnetron sputtering

BaTi₅O₁₁ thin films were grown on the poly-Si/SiO₂/Si substrate using rf magnetron sputtering. The BaO-TiO₂ thin film deposited on the poly-Si substrate had an amorphous phase even though the growth temperature was high at 550 °C. The amorphous film was crystallized into the BaTi₅O₁₁ phase when the film was post annealed above 800 °C. The post annealing temperature is one of the most important factors for the formation of the crystalline BaTi₅O₁₁ thin film. The homogeneous BaTi₅O₁₁ thin film was obtained when the film was grown at 550 °C and rapid thermal annealed (RTA) at 900 °C for 3 min. The dielectric constant (ɛ_r) of the BaTi₅O₁₁ film measured at 100 kHz was about 35 and the dissipation factors of all the films were smaller than 4.0%. The dielectric properties of the BaTi₅O₁₁ thin film were also measured at microwave frequencies. For the BaTi₅O₁₁ thin film grown at 550 °C and RTA at 900 °C for 3 min, the ɛ_r of 34–30 and dielectric loss of 0.025 ± 0.005 were obtained at 1–6 GHz.     

Influence of radio frequency magnetron sputtering parameters on the structure and performance of SiC films

Amorphous SiC films fabricated by Radio frequency (RF) magnetron sputtering have been widely used due to their excellent properties including high strength, good hardness and outstanding abrasion resistance. However, most researches set a lower target-substrate distance, which limits its large-scale coating for practical industrial application. In this work, the distance between the target and substrate was enlarged to 120 mm, and the effective coating area was about four to ten times than other researches. Furthermore, the effects of sputtering power, deposition pressure, substrate temperature and bias voltage on the structure and performance of SiC films were also investigated. Finally, SiC films with high elasticity modulus (310.8 GPa) and hardness (35.6 GPa) are obtained by RF magnetron sputtering.     

Influence of annealing atmosphere on the structure, resistivity and transmittance of InZnO thin films

Dependence of the electrical and optical properties of In₂O₃–10 wt% ZnO (IZO) thin films deposited on glass substrates by RF magnetron sputtering on the annealing atmosphere was investigated. The electrical resistivities of indium zinc oxide (IZO) thin films deposited on glass substrate can be effectively decreased by annealing in an N₂ + 10% H₂ atmosphere. Higher temperature (200 °C) annealing is more effective in decreasing the electrical resistivity than lower temperature (100 °C) annealing. The lowest resistivity of 6.2 × 10⁻⁴ Ω cm was obtained by annealing at 200 °C in an N₂ + 10% H₂ atmosphere. In contrast, the resistivity was increased by annealing in an oxygen atmosphere. The transmittance of IZO films is improved by annealing regardless of the annealing temperature.     

Effect of annealing on structure and properties of Ta–O–N films prepared by high power impulse magnetron sputtering

High power impulse magnetron sputtering of a Ta target in various $\mathrm{Ar}+{\mathrm{O}}_2+{\mathrm{N}}_2$ gas mixtures was utilized to prepare amorphous tantalum oxynitride (Ta–O–N) films with a finely controlled elemental composition in a wide range. We investigate the effect of film annealing at $900°\mathrm{C}$ in vacuum on structure and properties of the films. We show that the finely tuned elemental composition in combination with the annealing enables the preparation of crystalline Ta–O–N films exhibiting a single TaON phase with a monoclinic lattice structure, refractive index of $2.65$ and extinction coefficient of $2.0\times {10}^2$ (both at the wavelength of $550\mathrm{nm}$), optical band gap width of $2.45\mathrm{eV}$ (suitable for visible light absorption up to $505\mathrm{nm}$), low electrical resistivity of $0.4\text{Ω}\mathrm{cm}$ (indicating enhanced charge transport in the material as compared to the as-deposited counterpart), and appropriate alignment of the band gap with respect to the redox potentials for water splitting. These films are therefore promising candidates for application as visible-light-driven photocatalysts for water splitting.     

Effect of Fe-doping on the structural,optical and magnetic properties of ZnO thin films prepared by RF magnetron sputtering

In this paper, we report the fabrication and systematic characterization of Fe Doped ZnO thin Films. Fe_xZn_1−x O (x=0<0.05) films were prepared by RF magnetron sputtering on Si (400) substrate. Influence of Fe doping on structural, optical and magnetic properties has been studied. The X-ray diffraction (XRD) analysis shows that Fe doping has affected the crystalline structure, grain size and strain in the thin films. The best crystalline structure is obtained for 3% Fe Doping as observed from Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). The magnetic properties studied using Vibrating Sample Magnetometer reveals the room temperature ferromagnetic nature of the thin films. However, changing the Fe concentration degrades the magnetic property in turn. The mechanism behind the above results has been discussed minutely in this paper.     

Influence of plasma nitriding treatment on the adhesion of DLC films deposited on AISI 4140 steel by PVD magnetron sputtering

Duplex surface treatments composed of diamond like carbon (DLC) coating followed by plasma nitriding have drawn attention for a while. In this study, AISI 4140 steel substrates were plasma nitrided at different treatment temperatures and times. Then, DLC films were deposited on both untreated and plasma nitrided samples using PVD magnetron sputtering. The effect of different plasma nitriding temperatures and times on the structural, mechanical and adhesion properties of DLC coatings was investigated by XRD, SEM, microhardness tester and scratch tester, respectively. It was found that surface hardness, intrinsic stresses, layer thickness values and phase distribution in modified layers and DLC coating were the main factors on adhesion properties of duplex coating system. The surface hardness and residual stress values of AISI 4140 steel substrates significantly increased with both DLC coating and duplex surface treatment (plasma nitriding + DLC coating). Increasing plasma nitriding temperature and time also increased the diffusion depth and the thickness of modified layers. Hard surface layers led to a significant improvement on load bearing capacity of the substrate material. However, it was also determined that the process parameters, which provided lower intrinsic stresses, improved the adhesion properties of the duplex coating system.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Microstructural and optical properties of Ta-doped ZnO films prepared by radio frequency magnetron sputtering

Ta-doped ZnO films with different doping levels (0–5.02 at%) were prepared by radio frequency magnetron sputtering. The effects of the doping amount on the microstructure and the optical properties of the films were investigated. The grain size and surface roughness first significantly decrease and then slowly increase with the increase of Ta doping concentration. Both the grain size and the root mean square (RMS) roughness reach their minimum values at the doping content of 3.32 at%. X-ray Diffraction (XRD) patterns confirmed that the prepared Ta-doped ZnO films are polycrystalline with hexagonal wurtzite structure and a preferred orientation along the (002) plane. X-ray photoelectron spectroscopy (XPS) analysis reveals that Ta exists in the ZnO film in the Ta⁵⁺ and Ta⁴⁺ states. The average optical transmission values of the Ta-doped ZnO films are higher than those of the un-doped ZnO film in the visible region. The band gap energy extracted from the absorption edge of transmission spectra becomes large and the near band edge (NBE) emission energy obtained from PL spectra blueshifts to high energy when the Ta doping content grows from 0 at% to 5.02 at%, which can be explained by the Burstein–Moss shift.     

Mechanical properties and thermal stability of tungsten boride films deposited by radio frequency magnetron sputtering

Tungsten and boron compounds belong to the group of superhard materials since their hardness could exceed 40?GPa. In this study, the properties of the tungsten boride WB_x coatings deposited by radio frequency magnetron sputtering were investigated. The sputtering was performed from specially prepared targets that were composed of boron and tungsten mixed in a molar ratio of 2.5 and sintered in Spark Plasma Sintering (SPS) process. WB films were deposited on silicon (100) and stainless steel 304 substrates at temperatures of 23 ÷ 770?°C. Microstructure, chemical and phase composition were investigated by using Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD), respectively. The mechanical properties like Vickers hardness and Young's modulus were obtained by using nanoindentation test at a load of 5 ÷ 100 mN. The friction coefficient and wear resistance of αWB coatings were investigated in scratch test and reciprocal sliding wear instrumentation. Moreover, in order to investigate thermal properties, the αWB films were annealed at 1000?°C in argon/air for 1?h and at 250?°C for 2?h in air atmosphere. Results of our research confirm that αWB coatings can be considered as an alternative to superhard materials in the production of wear resistant, long-lasting tools.