Fabrication of Y2O3-doped BaZrO3 thin films by electrostatic spray deposition

Electrostatic spray deposition (ESD) technique was used to fabricate dense Y₂O₃-doped BaZrO₃ (BYZ) thin films, which have been extensively studied for the protonic ceramic fuel cell electrolyte. Effects of the ESD process parameters (i.e. substrate temperature, type of precursor, flow rate and applied voltage) on the microstructure of as-deposited films were studied. The uniform as-deposited films were obtained using a mixture of zirconium acetylacetonate, barium chloride dihydrate and yttrium chloride hexahydrate precursors in a solvent mixture of butyl carbitol and deionized water at a volume ratio of 50:50. The optimum deposition parameters were obtained at the substrate temperature of 250 °C with the applied voltage and flow rate in a range of 10-12 kV and 1.4-2.8 ml/h, respectively. The as-deposited films were subsequently annealed at 1350 °C for 10 h to ensure the complete chemical reactions of the precursors. X-ray diffraction patterns reveal the perovskite structures of the annealed BYZ films (deposited on yttria stabilized zirconia substrates) with only traces of Y₂O₃ phase, which could arise from the loss of BaO at high annealing temperatures.     

Effect of annealing on molybdenum doped indium oxide thin films RF sputtered at room temperature

Thin films of molybdenum doped indium oxide (IMO) were deposited on glass at room temperature using an in-built three-source RF magnetron sputtering. The films were studied as a function of oxygen volume percentage (O₂ vol. %; ranging from 0.0 to 17.5%) in the sputtering chamber. The as-deposited amorphous films were crystallized on post-annealing. The as-deposited films are low conducting and Hall coefficients were undetectable; whereas post-annealed films possess fairly high conductivity. The lowest transmittance (11.96% at 600 nm) observed from the films deposited without oxygen increased to a maximum of 88.01% (3.5 O₂ vol. %); whereas this transmittance was decreased with the increasing O₂ vol. % to as low as 81.04% (15.6 O₂ vol. %); a maximum of 89.80% was obtained from the films annealed at 500 °C in open air (3.5 O₂ vol. %). The optical band gap of 3.80 eV obtained from the films deposited without oxygen increased with increasing O₂ vol. % to as high as 3.91 eV (17.5 O₂ vol. %). A maximum of 3.92 eV was obtained from the films annealed at 300 °C in N₂:H₂ gas atmosphere (17.5 O₂ vol. %).     

Basal plane-oriented gallium nitride films on fused silica via acetate dip coating

c-axis-oriented gallium nitride (wurtzite GaN) thin films were fabricated by nitridation of acetate derived precursor films deposited on fused silica substrates without any buffer layer on the top of the substrate. The acetate derived precursors were obtained by (i) preparing a gallium-acetate sol by reacting Ga metal with acetic acid, (ii) coating cleared fused silica substrate with the sol and (iii) after drying the coated films at 100 °C, annealing them in air at 300°, 500° and 900 °C. Only films showing crystallization of α-GaO(OH) (300 °C) and (α + β)-Ga₂O₃ (500 °C) were selected for nitridation. In spite of the amorphous nature of the substrate, the GaN films showed a strong preferred orientation for the basal plane (002) under selected conditions of precursor annealing (300°, 500 °C) and subsequent nitridation (under flowing NH₃) temperature and time. In other cases formation of an additional plane, i.e. (101) was indicated as a weaker peak in X-ray diffraction (XRD) patterns. The precursors and nitride films were characterized by Fourier transform infrared spectroscopy, UV-Visible spectroscopy, XRD, high resolution transmission electron microscopy and atomic force microscopy analyses.     

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.     

Synthesis of the nanocrystalline CoFe2O4 ferrite thin films by a novel sol-gel method using glucose as an additional agent

Polycrystalline and nanometer-sized CoFe₂O₄ ferrite thin films are successfully synthesized using glucose as an addition agent. The thermal gravimetric/differential thermal analyzer, X-ray diffractometer, electron diffraction, scanning electron microscope, atomic force microscope and vibrating sample magnetometer are used to characterize the effects of the calcination temperature on the crystalline structure, morphology and magnetic properties of the Co-ferrite thin films. CoFe₂O₄ ferrite thin films have a single phase inverse spinel structure and are crystallized at and above 300 °C which is much lower than the required temperature in the traditional ceramic method (about 500-600 °C). Co-ferrite thin films annealed at relative low temperature of 400 °C show very small particle size with average of 32 nm and excellent magnetic properties for information storage applications.     

Temperature dependence of the microstructure and resistivity of indium zinc oxide films deposited by direct current magnetron reactive sputtering

Indium zinc oxide (IZO) films were deposited as a function of the deposition temperature using a sintered indium zinc oxide target (In₂O₃:ZnO = 90:10 wt.%) by direct current (DC) magnetron reactive sputtering method. The influence of the substrate temperature on the microstructure, surface roughness and electrical properties was studied. With increasing the temperature up to 200 °C, the characteristic properties of amorphous IZO films were improved and the specific resistivity was about 3.4 × 10^− 4 Ω cm. Change of structural properties according to the deposition temperature was also observed with X-ray diffraction patterns, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. IZO films deposited above 300 °C showed polycrystalline phases evolved on the amorphous IZO layer. Very flat surface roughness could be obtained at lower than 200 °C of the substrate temperature, while surface roughness of the films was increased due to the formation of grains over 300 °C. Consequently, high quality IZO films could be prepared by DC magnetron sputtering with O₂/Ar of 0.03 and deposition temperature in range of 150-200 °C; a specific resistivity of 3.4 × 10^− 4 Ω cm, and the values of peak to valley roughness and root-mean-square roughness are less than 4 nm and 0.5 nm, respectively.     

Atomic layer deposition and characterization of zirconium oxide-erbium oxide nanolaminates

ZrO₂ and Er₂O₃ thin films and nanolaminates were grown by atomic layer deposition from tris(2,2,6,6-tetramethyl-3,5-heptanedionato)erbium, bis(methylcyclopentadienyl)methoxymethylzirconium and ozone as precursors at 350 °C. Nanolaminates consisted of 3-8 nm thick ZrO₂ and Er₂O₃ layers alternately deposited on planar substrates and on three-dimensional substrates with aspect ratio 1:20. The erbium content was 5-15 at.%. ZrO₂-Er₂O₃ films crystallized already in as-deposited states. Upon annealing at 650 °C, the films were stabilized in the form of cubic or tetragonal ZrO₂ polymorph and cubic Er₂O₃. Dielectric properties of the nanolaminates were comparable to those of the constituent oxides.     

In-situ growth of oriented PbTiO3 thin films by low temperature metalorganic chemical vapor deposition

Oriented PbTiO₃ thin films were successfully grown on (200)-oriented Pt/SiO₂/Si by metalorganic chemical vapor deposition at low temperature range from 350°C to 400°C, using -diketonate complex of Pb(tmhd)₂ and titanium isopropoxide as source precursors. Dependences of orientation and formation of crystalline PbTiO₃ phase on Pb/Ti ratio and substrate temperature was investigated. Crystalline phases and preferred orientations were determined by X-ray diffraction technique, and surface morphology was identified with scanning electron microscopy. As the deposition temperature was raised from 350°C to 400°C at two fixed Pb/Ti ratios of 3.3 and 5.0, structures of PbTiO3w₃ films transformed from amorphous to polycrystalline and preferred orientation changed from random to [100] parallel to the surface. Similar results were also observed in the films deposited at 400°C with the increase of Pb/Ti ratio from 1.1 to 5.0. As the Pb/Ti ratio increased, the dielectric constant and current density increased due to crystallization of the PbTiO₃ films. It is found that the control of excess Pb precursor amount through Pb/Ti ratio change is the key process parameter for the formation of crystalline PbTiO₃ phase in the low temperature MOCVD process.     

Dielectric properties of DC reactive magnetron sputtered Al2O3 thin films

Alumina (Al₂O₃) thin films were sputter deposited over well-cleaned glass and Si < 100 > substrates by DC reactive magnetron sputtering under various oxygen gas pressures and sputtering powers. The composition of the films was analyzed by X-ray photoelectron spectroscopy and an optimal O/Al atomic ratio of 1.59 was obtained at a reactive gas pressure of 0.03 Pa and sputtering power of 70 W. X-ray diffraction results revealed that the films were amorphous until 550 °C. The surface morphology of the films was studied using scanning electron microscopy and the as-deposited films were found to be smooth. The topography of the as-deposited and annealed films was analyzed by atomic force microscopy and a progressive increase in the rms roughness of the films from 3.2 nm to 4.53 nm was also observed with increase in the annealing temperature. Al-Al₂O₃-Al thin film capacitors were then fabricated on glass substrates to study the effect of temperature and frequency on the dielectric property of the films. Temperature coefficient of capacitance, AC conductivity and activation energy were determined and the results are discussed.     

The effect of annealing on Al-doped ZnO films deposited by RF magnetron sputtering method for transparent electrodes

In this study, transparent conducting Al-doped zinc oxide (AZO) films with a thickness of 150 nm were prepared on Corning glass substrates by the RF magnetron sputtering with using a ZnO:Al (Al₂O₃: 2 wt.%) target at room temperature. This study investigated the effects of the post-annealing temperature and the annealing ambient on the structural, electrical and optical properties of the AZO films. The films were annealed at temperatures ranging from 300 to 500 °C in steps of 100 °C by using rapid thermal annealing equipment in oxygen. The thicknesses of the films were observed by field emission scanning electron microscopy (FE-SEM); their grain size was calculated from the X-ray diffraction (XRD) spectra using the Scherrer equation. XRD measurements showed the AZO films to be crystallized with strong (002) orientation as substrate temperature increases over 300 °C. Their electrical properties were investigated by using the Hall measurement and their transmittance was measured by UV-vis spectrometry. The AZO film annealed at the 500 °C in oxygen showed an electrical resistivity of 2.24 × 10^− 3 Ω cm and a very high transmittance of 93.5% which were decreased about one order and increased about 9.4%, respectively, compared with as-deposited AZO film.     

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO₂/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La_0.5Sr_0.5CoO₃ (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Temperature effects on the growth and electrical properties of Er2O3 films on Ge substrates

Er₂O₃ films were grown on Ge (001) substrates at different temperatures by molecular beam epitaxy using metallic Er and molecular oxygen sources with otherwise identical conditions. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the microstructures and compositions of the films. The film deposited at room temperature is found to be composed of an Er₂O₃ layer and an ErGe_xO_y interface layer with a thickness of 5.5 nm; the film grown at 300 °C has a mixed structure of Er₂O₃ and ErGe_xO_y and the thickness was found to be reduced to 2.2 nm; the film grown at 450 °C becomes much rougher with voids formed underneath the film, having a mixed structure of three compounds of Er₂O₃, GeO and ErGe_xO_y. The growth mechanisms of the films at different temperatures are suggested. Current images obtained by tunneling atomic force microscopy show that the film grown at 450 °C has much more leaky spots than those grown at RT and 300 °C, which may arise from the formation of volatile GeO in the film.     

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.     

Dip coated 12CaO·7Al2O3 thin films through sol-gel process using metal alkoxide

Transparent nanostructured 12CaO·7Al₂O₃ thin films with cubic structure have been prepared on soda lime glass substrates via the sol-gel dip coating using the precursor sol solution at low temperature. The structural, compositional, morphological and optical properties of the 12CaO·7Al₂O₃ films and powder were studied using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy. Optical properties of 12CaO·7Al₂O₃ films have been investigated using UV-visible spectroscopy. Two different precursor sols were prepared using calcium-2-ethyl hexonate and aluminium isopropoxide as precursor materials in isopropanol and ethylene glycol monomethyl ether solvents. Dip coated gel like films were dried at 120 °C for 15 min and subsequently heat-treated at 450 °C for 1 h in air atmosphere. The influence of films thickness and optical transparency with use of different solvent and sol concentration on microstructure of the films were established. In addition, XRD patterns revealed that 12CaO·7Al₂O₃ films have been composed of cubic phase. SEM observations exhibited that the films structure becomes more homogeneous using isopropanol as compared to ethylene glycol monomethyl ether solvent. The 12CaO·7Al₂O₃ films prepared using 2 (wt.%) sol in isopropanol had high transparency nearly 88% in wide visible range with maximum of 90% at 600 nm wavelength.     

Electric-field-induced strain and piezoelectric properties of a high Curie temperature Pb(In1/2Nb1/2)O3-PbTiO3 single crystal

The temperature dependence of dielectric and piezoelectric properties, electric-field-induced strains of 0.66 Pb(In_1/2Nb_1/2)O₃-0.34 PbTiO₃ single crystals, which were grown directly from melt by using the modified Bridgman technique with the allomeric Pb(Mg_2/3Nb_1/3)O₃-PbTiO₃ seed crystals, were determined as a function of crystallographic orientation with respect to the prototypic (cubic) axes. Ultrahigh piezoelectric response (d₃₃∼2000 pC/N, k₃₃∼94%) and strain levels up to 0.8%, comparable to rhombohedral (1−x)Pb(Mg_2/3Nb_1/3)O₃-xPbTiO₃ and (1−x)Pb(Zn_2/3Nb_1/3)O₃-xPbTiO₃ single crystals, were observed for the 〈0 0 1〉-oriented crystals. Strain levels up to 0.47% and piezoelectric constant d₃₃∼1600 pC/N could be achieved being related to an electric-field-induced rhombohedral-orthorhombic phase transition for the 〈1 1 0〉-oriented crystals. In addition, high electromechanical coefficients k₃₃ (∼88%) can be achieved even heating to 110 °C. High T_C (∼200 °C), large electromechanical coefficients k₃₃ (∼94%) and low dielectric loss factor (∼1%), along with large strain make the crystals promising candidates for a wide range of electromechanical transducers.     

Atomic layer deposition of Ru films from bis(2,5-dimethylpyrrolyl)ruthenium and oxygen

Ru thin films were grown on hydrogen terminated Si, SiO₂, Al₂O₃, HfO₂, and TiO₂ surfaces by atomic layer deposition from bis(2,5-dimethylpyrrolyl)ruthenium precursor and oxygen. The 4-20 nm thick films on these surfaces consisted of nanocrystalline hexagonal metallic ruthenium, regardless of the deposition temperature. At the lowest temperatures examined, 250-255 °C, the growth of the Ru films was favored on silicon, compared to the growth on Al₂O₃, TiO₂ and HfO₂. At higher temperatures the nucleation and growth of Ru became enhanced in particular on HfO₂, compared to the process on silicon. At 320-325 °C, no growth occurred on Si-H and SiO₂-covered silicon. Resistivity values down to 18 μΩ·cm were obtained for ca. 10 nm thick Ru films.     

Preliminary studies on molybdenum-doped indium oxide thin films deposited by radio-frequency magnetron sputtering at room temperature

Thin films of molybdenum-doped indium oxide (IMO) were prepared by a 3-source, cylindrical radio-frequency magnetron sputtering at room temperature. The films were post-annealed and were characterized by their structural (X-ray diffraction) and optical (UV-VIS-NIR spectrophotometer) properties. The films were studied as a function of oxygen volume percentage (O₂ vol.%) ranging from 3.5 to 17.5. The structural studies revealed that the as-deposited amorphous films become crystalline on annealing. In most cases, the (222) reflection emerged as high intensive peak. The poor visible transmittance of the films as-deposited without oxygen was increased from ∼ 12% to over 80% on introducing oxygen (3.5 O₂ vol.%). For the films annealed in open air, the average visible transmittance in the wavelength ranging 400-800 nm was varied between 77 and 84%. The films annealed at high temperatures (> 300 °C) decreased the transmittance to as low as < 1%. The optical band gap of the as-deposited films increased from the range 3.83-3.90 to 3.85-3.98 eV on annealing at different conditions.     

A study on the electrical properties of Pb(Zr, Ti)O3 thin films crystallized by the electrical resistive heating of Pt thin film

The electrical properties of Pb(Zr, Ti)O₃ thin films annealed by Pt thin film heater were investigated. By the thin film heater, we successfully crystallized Pb(Zr, Ti)O₃ thin films at a high temperature above 750 °C in a few seconds. The thin film heater has some advantages, such as a low thermal budget, little Pb-loss and enhanced surface morphology compared with the conventional furnace because it has a fast heating rate. The electrical properties of the Pb(Zr, Ti)O₃ thin film crystallized by thin film heater improved considerably comparing to those crystallized in conventional furnace. The remanent polarization, breakdown field, and leakage current density measured to be 22.7 μC/cm², 853 kV/cm, and 6.93 × 10⁻⁷ A/cm², respectively.     

Solvothermal approach for low temperature deposition of aluminium oxide thin films

At elevated pressure, stoichiometric and high quality Al₂O₃ thin films are fabricated at 65-105 °C. By using pre-organised single source precursor aluminium(III) diisopropylcarbamate, Al₂O₃ were deposited on the surface of a Si substrate in a single step in the liquid phase. Comprehensive removal of large carbamate ligands by proposed β-elimination during decomposition of precursor led to an effective delivery of enshrouded Al-O fragments. Scanning electron microscopy revealed dense and grainy surface morphology. The thicknesses of the films were measured to be 150-300 nm and independent to reaction temperatures or reaction times. Through the use of near edge X-ray absorption fine structure spectroscopy, Al absorption peaks suggest a short range crystalline formation in a film deposited at 105 °C.