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.     

Effect of Cu dopant on microstructure and phase transformation of ZnTiO3 thin films prepared by radio frequency magnetron sputtering

Cu doped zinc titanate (ZnTiO₃) films were prepared using radio frequency magnetron sputtering. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that the as-deposited films were amorphous and contained 0.84 at.% Cu. This was further confirmed by the onset of crystallization that took place at annealing temperatures 600 °C. The phase transformation for the as-deposited films and annealed films was investigated in this study. The results showed that Zn₂Ti₃O₈, ZnTiO₃, and TiO₂ can coexist at 600 °C. When annealed at 700 °C, the results revealed that mainly the hexagonal ZnTiO₃ phase formed, accompanied by minority amounts of TiO₂ and Zn₂Ti₃O₈. Unlike pure zinc titanate films, this result showed that the Zn₂Ti₃O₈ phase can be stable at temperatures above 700 °C. Moreover, Cu addition in zinc titanate thin film could result in the decomposition of hexagonal (Zn,Cu) TiO₃ phase at 800 °C. When the Cu content was increased in zinc titanate thin films from 0.84 at.% to 2.12 at.%, there were only two phases; Zn₂Ti₃O₈ and ZnTiO₃, coexisting at temperatures between 700 and 800 °C. This result indicated that a greater presence of Cu dopants in zinc titanate thin films leads to the existence of the Zn₂Ti₃O₈ phase at higher temperatures.     

Microstructure of Co2CrxFe1−xAl thin films for magneto-electronic applications

Thin films of the Heusler alloy Co₂Cr_0.6Fe_0.4Al have been prepared by means of magnetron sputtering under varying conditions (sputter power, sputter pressure and substrate temperature). All the films are polycrystalline with the cubic B2 structure. The extent of Co-Al antisite defects, lattice constants, internal stress states are influenced by the sputter conditions which is related to differences in the saturation magnetization. The magnetic moment can be increased by additional annealing up to an optimum temperature of 400 °C, but does not reach the theoretically predicted value. Above 600 °C the metastable B2 phase transforms into either (ε)-Co/Cr or (α)-Co/Cr.     

Initial study on the structure and optical properties of Zn1−xFexO films

Zn_1−xFe_xO (x = 0, 0.052, 0.103, 0.157 and 0.212) films were prepared by the radio-frequency magnetron sputtering technique on Si (111) substrates and the microstructure of which was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The samples had a preferential c-axis orientation and the position of (002) diffraction peak shifted to the lower degree side with increasing Fe component. In order to investigate the optical transmittance properties of Zn_1−xFe_xO films, we prepared the films on Al₂O₃ (001) substrates simultaneity and the UV-VIS optical transmittance spectra showed that the band gap energy of Zn_1−xFe_xO films decreased with increase of Fe concentration. Photoluminescence spectra of the samples were observed at room temperature.     

Nd-substituted SrBi2Ta2O9 ferroelectric thin films prepared by radio frequency magnetron sputtering

Nd-substituted SrBi₂Ta₂O₉ (SNBT) thin films are sputtered on Pt/Ta/SiO₂/Si substrates. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate that Nd³⁺ is substituted into the bismuth layered perovskite structure, preferentially at the Sr²⁺ site. The annealed thin film is polycrystalline with plate/needle-like grain microstructure. Secondary ion mass spectrometry results show that elements in SNBT thin film homogeneously distribute along film depth and interfacial diffusion takes place during post annealing. The Nd substitution leads to enhanced remnant polarization (2P_r = 18 μC/cm²) and reduced coercivity (2E_c = 64 kV/cm) at 180 kV/cm measured at 25 °C. After 10¹⁰ switching cycles, around 9% remnant polarization is decreased.     

Electrical properties of AlNxOy thin films prepared by reactive magnetron sputtering

Direct current magnetron sputtering was used to produce AlN_xO_y thin films, using an aluminum target, argon and a mixture of N₂ + O₂ (17:3) as reactive gases. The partial pressure of the reactive gas mixture was increased, maintaining the discharge current constant. Within the two identified regimes of the target (metallic and compound), four different tendencies for the deposition rate were found and a morphological evolution from columnar towards cauliflower-type, ending up as dense and featureless-type films. The structure was found to be Al-type (face centered cubic) and the structural characterization carried out by X-ray diffraction and transmission electron microscopy suggested the formation of an aluminum-based polycrystalline phase dispersed in an amorphous aluminum oxide/nitride (or oxynitride) matrix. This type of structure, composition, morphology and grain size, were found to be strongly correlated with the electrical response of the films, which showed a gradual transition between metallic-like responses towards semiconducting and even insulating-type behaviors. A group of films with high aluminum content revealed a sharp decrease of the temperature coefficient of resistance (TCR) as the concentration ratio of non-metallic/aluminum atomic ratio increased. Another group of samples, where the non-metallic content became more important, revealed a smooth transition between positive and negative values of TCR. In order to test whether the oxynitride films have a unique behavior or simply a transition between the typical responses of aluminum and of those of the correspondent nitride and oxide, the electrical properties of the ternary oxynitride system were compared with AlN_x and AlO_y systems, prepared in similar conditions.     

Formation and transformation of ZnTiO3 prepared by sputtering process

Zinc titanate (ZnTiO₃) films were prepared using RF magnetron sputtering at substrate temperatures ranging from 30 to 400 °C. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that all as-deposited films were amorphous, as confirmed by XRD. This was further confirmed by the onset of crystallization that took place at annealing temperatures 600 °C. The phase transformation for the as-deposited films and annealed films were investigated in this study. The results revealed that pure ZnTiO₃ (hexagonal phase) can exist, and was obtained at temperatures between 700 and 800 °C. However, it was found that decomposition from hexagonal ZnTiO₃ to cubic Zn₂TiO₄ and rutile TiO₂ took place with a further increase in temperature to 900 °C.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on In2O3 layer deposited on Si (111) substrates

GaN nanorods were synthesized by ammoniating Ga₂O₃/In₂O₃ thin films deposited on Si (111) with magnetron sputtering. X-ray diffraction, Scanning electronic microscope and high-resolution TEM results show that they are GaN single crystals, the sizes of which vary from 2 to 7 μm in length and 200 to 300 nm in diameter. In₂O₃ middle layer plays an important role in the GaN nanorod growth.     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

The effect of heat treatment on physical properties of nanograined (WO3)1-x-(Fe2O3)x thin films

Thin films of (WO₃)_1-x-(Fe₂O₃)_x composition were deposited by thermal evaporation on glass substrates and then all samples were annealed at 200-500 °C in air. Optical properties such as transmittance, reflectance, optical bangap energy, and the optical constants of the “as deposited” and the annealed films were studied using ultraviolet-visible spectrophotometry. It was shown that the annealing process changes the film optical properties which were related to Fe₂O₃ concentration. Moreover, using X-ray photoelectron spectroscopy, we have indicated that WO₃ is stoichiometric, while iron oxide was in both FeO and Fe₂O₃ compositions so that the FeO composition converted to Fe₂O₃ after the annealing process. Using atomic force microscopy, it was observed that surface of the “as deposited” films were smooth with a nanometric grain size. The film surface remained unchanged after annealing up to 300 °C. Surface roughness and the grain size of the films with x = 0, 0.05, and 0.75 highly increased at higher annealing temperatures (400 and 500 °C), but were nearly unchanged for medium x-values (0.3 and 0.4).     

Thickness dependent microstructural changes in La0.5Ca0.5MnO3 thin films deposited on (111) SrTiO3

The epitaxial strain can modify the physical properties of complex oxide thin films considerably. The strain effect is expected to be less pronounced for relatively thick films and the physical properties should resemble to the bulk material. However, it has been recently observed that the electronic and magnetic properties of La_0.5Ca_0.5MnO₃ thin films deposited on (111) SrTiO₃ substrates thicker than a threshold value differ considerably from the bulk material. This observation is a hint for some interesting microstructural features in these films. In the present study, the microstructure of La_0.5Ca_0.5MnO₃ thin films on (111) SrTiO₃ substrates is investigated by X-ray diffraction and high resolution transmission electron microscopy.     

Photoluminescence of Eu-doped TiO2 thin films prepared by low pressure hot target magnetron sputtering

In this work Eu-doped TiO₂ thin films prepared by reactive magnetron co-sputtering of Ti-Eu metallic target have been studied. The results of photoluminescence (PL) and its correlation with microstructure have been described. Structural properties were examined by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). XRD studies have shown that thin films consisted of TiO₂-anatase and AFM images display their high quality and dense nanocrystalline structure. PL spectra, measured at room temperature, show a dominating strong red luminescence corresponding to ⁵D₀-⁷F₂ transition at ∼ 617 nm and ∼ 623 nm. The evolution of photoluminescence and microstructure of the thin films has been examined as they were additionally annealed in an air ambient.     

Structural properties of epitaxial SrCuO2 thin films on SrTiO3 (001) substrates

Thin films of SrCuO₂ with tetragonal structure have been epitaxially grown on SrTiO₃ (001) substrates by high-oxygen pressure sputtering technique. The interface structure between SrCuO₂ and SrTiO₃ and configuration of defects in SrCuO₂ thin films have been characterized by means of high-resolution transmission electron microscopy. Two types of film-substrate interface structure coexist and are determined as bulk-SrO-TiO₂-Sr(O) -CuO₂-Sr-bulk and bulk-SrO-TiO₂-SrO-Sr(O) -CuO₂-Sr-bulk. The planar faults with double SrO atomic layers in {100} planes in SrCuO₂ thin films are observed, which mainly arise from the coalescence of these two types of film-substrate interface structure. Meanwhile, planar faults in {110} planes are observed in thin films and structural models are proposed.     

Sputtering deposited ternary Zn1−xCdxO crystal films on Si(111) substrates

Using the d.c. reactive magnetron sputtering method we have successfully deposited completely (002)-oriented ternary Zn_1−xCd_xO (0≤x≤0.6) alloy crystal films without Cd segregation on Si(111) substrates. X-Ray photoelectron spectroscopy measurements show that Cd/Zn ratios in the films are nearly consistent with those in the targets. The Zn and Cd exist only in oxidized states, no evidence of metallic Zn or Cd was observed. The O/(Cd+Zn) atomic ratios of the films are in the range of 0.89-0.98. Transmission electron microscopy measurements show that for the (002)-oriented films the grains are columnar structures with the c-axis perpendicular to the Si substrate. By post-annealing treatments in O₂ ambient, the crystal quality of the Zn_1−xCd_xO films can be improved. For the sample of x=0.2, the optimal annealing temperature is 500 °C.     

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.     

Structure and dielectric properties of highly (100)-oriented PST thin films deposited on MgO substrates

High-quality Pb_0.4Sr_0.6TiO₃ (PST) thin films have been epitaxially grown on MgO (100) substrates at various substrate temperatures by the pulsed laser deposition (PLD) technique. Their crystalline phase structures and surface morphology were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their in-plane orientation was observed by the Phi scans on the (111) plane. Their dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in PST thin film. The crystalline phase formation of the thin film depended on the deposition temperature. The phase formation ability and (100)-orientation of these films were increased with increasing deposition temperature. Both of the high tunabilities and low dielectric loss of the thin films show that the (100)-oriented PST is a potential material that can be used for tunable applications.     

Microstructure and electric properties of (104)/(014)-oriented Bi3.15Nd0.85Ti3O12 films on Pt (111)/Ti/SiO2/Si by sol-gel method

Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films with predominant (104)/(014) orientation were fabricated directly on (111)Pt/Ti/SiO₂/Si substrates through a sol-gel process. The volume fraction of (104)/(014)-oriented grains in the film was estimated to be about 65% according to X-ray pole figure. The BNdT film is dense and uniform and consists of columnar grains penetrating the whole film thickness. The (104)/(014)-oriented BNdT film capacitors showed excellent ferroelectric properties with 2P_r = 46.4 μC/cm² and E_c ≈ 140 kV/cm. The films also exhibit excellent piezoelectric property, with high piezoelectric coefficient d₃₃ ≈ 17 pm/V.     

Structural properties of RF-magnetron sputtered Cu2O thin films

Cuprous oxide thin films were produced on soda-lime glass substrates using reactive RF-magnetron sputtering. The influence of deposition parameters and temperature on composition and structural properties of the single layers was extensively studied using X-ray diffraction. The control over microstructure and residual stresses is possible by changing reactive gas pressure and deposition temperature. Fiber textured Cu2O films showing a [100] preferred orientation and a fraction of untextured domains can be obtained: suitable modeling taking this microstructure into account shows the presence of a strong compressive stress decreasing with the temperature. Highly reproducible films can be obtained, whose microstructure is preserved when sputtering on tungsten and zinc oxide substrates.     

Characteristics of highly orientated BiFeO3 thin films on a LaNiO3-coated Si substrate by RF sputtering

BiFeO₃ (BFO) films were grown on LaNiO₃-coated Si substrate by a RF magnetron sputtering system at temperatures in the range of 300-700 °C. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. For a substrate temperature below 300 °C and at 700 °C only partially crystalline films and completely randomly polycrystalline films were grown, whereas highly (001)-orientated BFO film was obtained for a substrate temperature in the range of 400-600 °C. The crystalline quality of BFO thin films increase as the deposition temperature increase except for the film deposited at 700 °C. The fitted result from X-ray reflectivity curves show that the densities of the BFO films are slightly less than their bulk values. For the BFO films deposited at 300-600 °C, the higher the deposition temperature, the larger the remnant polarization and surface roughness of the films present.     

Ion conducting properties of hydrogen-containing Ta2O5 thin films prepared by reactive sputtering

Hydrogen-containing Ta₂O₅ (Ta₂O₅:H) thin films are considered to be a candidate for a proton-conducting solid-oxide electrolyte. In this study, Ta₂O₅:H thin films were prepared by reactively sputtering a Ta metal target in an O₂ + H₂O mixed gas. The effects of sputtering power and post-deposition heat treatment on the ion conducting properties of the Ta₂O₅:H thin films were studied. The ionic conductivity of the films was improved by decreasing the RF power and a maximum conductivity of 2 × 10⁻⁹ S/cm was obtained at an RF power of 20 W. The ionic conductivity decreased by heat-treatment in air, and no ion-conduction was observed after treatment at 300 °C due to the decrease in hydrogen content in the films.