Atomic layer deposition of TiO2 from tetrakis-dimethylamido-titanium and ozone

Ozone (O₃) was employed as an oxygen source for the atomic layer deposition (ALD) of titanium dioxide (TiO₂) based on tetrakis-dimethyl-amido titanium (TDMAT). The effects of deposition temperature and O₃ feeding time on the film growth kinetics and physical/chemical properties of the TiO₂ films were investigated. Film growth was possible at as low as 75 °C, and the growth rate (thickness/cycles) of TiO₂ was minimally affected by varying the temperatures at 150–225 °C. Moreover, saturated growth behavior on the O₃ feeding time was observed at longer than 0.5 s. Higher temperatures tend to provide films with lower levels of carbon impurities. The film thickness increased linearly as the number of cycles increased. With thicker films and at higher deposition temperatures, surface roughening tended to increase. The as-deposited films were amorphous regardless of the substrate temperatures and there was no change of crystal phase even after annealing at temperatures of 400–600 °C. The films deposited in 0.5 mm holes with an aspect ratio of 3: 1 showed an excellent conformality.     

Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO₂ films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO₂ films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO₂ film growth. The TiO₂ films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO₂ surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO₂ film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO₂ could not be deposited on the substrate and a cloudy TiO₂ film was formed due to the increase of surface roughness, respectively.     

The effects of deposition temperature on structure and dielectric properties of Ba0.6Sr0.4TiO3 thin films produced by pulsed laser deposition

The effects of deposition temperature on orientation, surface morphology and dielectric properties of the thin films for Ba_0.6Sr_0.4TiO₃ thin films deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition were investigated. X-ray diffraction patterns revealed a (2 1 0) preferred orientation for all the films. With rising substrate temperature from 650 °C to 700 °C, the crystallinity and crystal grain size of the films increase, the relative dielectric constant increases, but the dielectric losses have not obvious difference. The film deposited at 350 °C and annealed at 700 °C has strongly improved roughness and dielectric permittivity compared with the film only deposited directly at 700 °C. Three distinct relaxation processes within tan(δ) were found for the Ba_xSr_1?xTiO₃ film: a broadened process of the film relaxation, an intermediate peak which originates from Maxwell–Wagner–Sillars polarization, and an extremely slow process ascribed to leak current. The complex dielectric permittivity and loss can be fitted by an improved Cole–Cole model corresponding to a stretched relaxation function.     

Selective formation of crystal polymorphs in Er3+-doped Bi2O3 thin films and their photoluminescence properties

The process conditions for selectively forming crystal polymorphs in Er³⁺-doped Bi₂O₃ films deposited on Si, SiO₂, and C-plane sapphire substrates were systematically investigated. Bi₂O₃:Er films were deposited at either room temperature or 300 °C and subsequently post annealed to promote crystallization. The critical factor controlling the crystal polymorphs was Er content. When the Er content was less than 1.5 at.%, only α-Bi₂O₃ phase nucleated upon post annealing. Deposition at 300 °C somewhat lowered the oxidization state, under which β-Bi₂O₃ structure appeared at lower temperatures and α-Bi₂O₃ structure appeared at higher temperatures. When the films were doped with over 2 at.% Er³⁺ ions, the excess Er₂O₃ stabilized the δ-Bi₂O₃ structure as the lowest temperature phase. The universal phase transition scheme with increasing annealing temperature was δ-Bi₂O₃ → β-Bi₂O₃ → α-Bi₂O₃. The δ → β transition proceeded through splitting each diffraction peak of δ-Bi₂O₃ into two components of β-Bi₂O₃, indicating a correlation between the structures of β-Bi₂O₃ and δ-Bi₂O₃. The γ-Bi₂O₃ phase appeared only in films on Si(100) substrates and after vacuum annealing, suggesting the formation of sillenite (Bi₁₂SiO₂₀). Deposition on C-plane sapphire by using H₂O as the oxygen source gas produced a highly (111)-oriented δ-Bi₂O₃ structure, whereas deposition with O₂ yielded a randomly oriented δ-Bi₂O₃ structure. At Er content exceeding 4 at.%, δ-Bi₂O₃ was the primary phase in the films on SiO₂. The photoluminescence (PL) activity of dopant Er³⁺ under excitation at a wavelength of 532 nm strongly depended on the crystal polymorphs. α-Bi₂O₃:Er exhibited intense and stable PL spectra consisting of eight Stark splitting lines. PL from γ-Bi₂O₃:Er exhibited much weaker two emission lines. δ-Bi₂O₃:Er and β-Bi₂O₃:Er films were not emission-active at all. However, δ-Bi₂O₃:Er film on SiO₂ with an Er content of 4 at.% exhibited an intense and broad emission at 1530 and 1560 nm.     

Atomic layer deposition of TiO2 films on particles in a fluidized bed reactor

Atomic layer deposition (ALD) of controlled-thickness TiO₂ films was carried out on particle substrates in a fluidized bed reactor for the first time. Films were deposited on 550 nm SiO₂ spheres and 65 nm ZnO nanoparticles for enhanced optical properties. Nanoparticles were fluidized with the assistance of a magnetically-coupled stirring unit. The metalorganic precursor titanium tetraisopropoxide was used here followed by either H₂O or H₂O₂ to deposit TiO₂ at various substrate temperatures. Growth rates of 0.01 nm/cycle and 0.04 nm/cycle were achieved when using H₂O and H₂O₂ as the oxidizer, respectively. These conformal TiO₂ films were verified using HRTEM, ICP-AES, XPS and UV absorbance measurements. The specific surface area changed appropriately after the particle size increased by the deposition of films with a given density, which showed that primary particles were not agglomerated together due to the coating process. In situ mass spectrometry was used to monitor reaction progress throughout each ALD reaction cycle. Bulk quantities of powder were successfully functionalized by TiO₂ nanofilms without wasting excess precursor.     

Characteristics of aluminum films prepared by metalorganic chemical vapor deposition using dimethylethylamine alane on the plasma-pretreated TiN surfaces

Aluminum films were prepared on H₂-plasma pretreated TiN substrates at deposition temperatures of 60-250 °C by metallorganic chemical vapor deposition using dimethylethylamine alane as a precursor. The films were highly pure and the growth rates were 3-50 nm/min, where the lowest deposition temperature was 60 °C. The resistivity was as low as 2.8 μΩcm. High substrate temperatures tended to favor a low resistivity and smooth surface morphology of the films, compared to films with a low temperature at a given thickness. Numerous empty pores appeared in the Al films deposited at a temperature below 150 °C when the film thickness exceeded 200 nm. The number of these pores tended to increase with decrease in temperature. However, in films deposited at temperatures above 200 °C, there were no pores and the large grains were interconnected to a high degree. Higher deposition temperatures yielded a greater preference of the (111) orientation of Al films.     

Epitaxial growth of LaMnO3 thin films on different single crystal substrates by polymer assisted deposition

Structure of epitaxial LaMnO₃ thin films grown on different single crystal substrates by unconventional polymer assisted deposition (PAD) method was investigated. Epitaxial films were prepared from lanthanum manganite water based solutions deposited by spin coating on single crystal MgO (001), SrTiO₃ (001) and SrTiO₃ (110) substrates, and the influence of substrate type on the film structure was analysed. Better uniformity of the epitaxial LaMnO₃ films on SrTiO₃ substrates was obtained, but a non-stoichiometric La_1-xMnO₃ phase was formed after the heat treatment at 750 °C. In addition, the prepared thin films were multiple annealed at different temperatures up to 900 °C, in order to investigate importance of post-annealing treatment. Epitaxial nature of the prepared films was preserved after annealing at up to 900 °C and the structure rearrangement through formation of cell closer to bulk stochiometric LaMnO₃ phase was observed.     

The phase formation process of Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared using the sol-gel method

Lead-free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ (abbreviated as BNKT) thin films were grown on Pt(111)/Ti/SiO₂/Si substrates using a sol-gel/spin coating technique and were then annealed at different temperatures (350 °C, 550 °C, 750 °C and 850 °C). Analysis of the XRD patterns and FT-IR spectra were used to determine the main reactions and the phase formation process of BNKT thin films during the sol-gel process. The results show that the dielectric constant of the thin films attains a maximum at a set temperature and then decreases at higher annealing temperatures, which can be attributed to phase formation and transformation. Moreover, the morphologies of the BNKT thin films improve with the increase in grain size and the formation of distinct grain boundaries. Furthermore, through increasing the pH of the precursor solutions, the size of the sol-gel colloidal particles increases slightly and the grains formed from the corresponding solutions tend to be small and uniform.     

The Effect of Deposition Temperature and Postanneal on the Bi3.63Pr0.3Ti3O12 thin Films Prepared by RF-Magnetron Sputtering Method

Praseodymium doped Bi₄Ti₃O₁₂ (BTO) thin films with composition Bi_3.63Pr_0.3Ti₃O₁₂ (BPT) were successfully prepared on Pt/Ti/SiO₂/Si substrates by RF-magnetron sputtering method at substrate temperatures ranging between 500° and 750°C. The structural phase and orientation of the deposited films were investigated in order to understand the effect of the deposition temperature on the properties of the BPT films. As the substrate temperature was increased to 700°C, the films started showing a tendency of assuming a c -axis preferred orientation. At lower temperatures, however, polycrystalline films were formed. The Pt/BPT/Pt capacitor showed an interesting dependence of the remnant polarization (2 P _r) as well as dc leakage current values on the growth temperature. The film deposited at 650°C showed the largest 2 P _r of 29.6 μC/cm². With the increase of deposited temperature, the leakage current densities of films decreased at the same applied field and the film deposited at 750°C exhibited the best leakage current characteristics. In addition, the ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BPT films. It was revealed that the BPT film postannealed in air exhibited the weakest fatigue-resistance characteristics and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in this film.     

Seed layer mediated growth of high dielectric and low leakage BaTiO3 thin film using two-step sputtering process

In this study, we demonstrated the seed layer mediated growth of high-quality BaTiO₃ (BTO) thin films using a two-step radio frequency (RF) magnetron sputtering process. Since the as-grown BTO thin films obtained by RF magnetron sputtering at the deposition temperatures of 300–500 °C were amorphous with a low dielectric constant of 20, it is necessary to develop a fabrication process for obtaining crystalline high-k BTO thin films without sacrificing other film properties such as morphology and leakage current. First, it was revealed that ex-situ post-deposition annealing (PDA) at high temperatures in the 700–800 °C range led to the crystallization of BTO films and a high dielectric constant of 121. However, the film morphology deteriorated significantly during PDA, and consequently, a high leakage current was observed due to the rough and discontinuous surface containing voids and micro-cracks. To achieve an excellent leakage current characteristic as well as a high dielectric constant for a crystalline BTO thin film, in-situ crystallization was carried out through local epitaxial growth using a crystalline seed layer. The crystalline BTO seed layer was formed by annealing a 5-nm-thick amorphous BTO film at 700 °C on which the in-situ crystallized BTO main layer was deposited at 500 °C. The in-situ crystallization method resulted in a smooth and uniform surface and a high dielectric constant of 113. In addition, the in-situ crystallized BTO film exhibited a low leakage current density of 10⁻⁶ A/cm² (at 0.8 V) displaying an improvement by a factor of 10³ compared to the ex-situ crystallized BTO film.     

Effect of Heat Treatment on Micromechanical Properties of Sprayed TiO2 Film on Ce-Doped Glass

Abstract

Anatase TiO₂ films were deposited on unheated Ce-doped soda–lime–silicate glass substrates by a spray technique from an anatase sol made in the laboratory. In order to investigate the micromechanical properties of TiO₂ films, the deposited films were heated treated at: 350, 500 and 550°C, each for 1 h. X-ray diffraction spectra revealed a crystalline structure with an anatase phase and the average diameter of the grains increased from 21.4 to 31.2 nm as the temperature in the heat treatment rose from 20 to 550°C. The films as-deposited and heat-treated at 350°C were found to be smooth and relatively dense. Cracks appeared in TiO₂ films when the heating temperature increased to 550°C. The results of nano-indentation test showed that when the heating temperature rose to 500°C, the TiO₂ films were found to have nano-hardness and elastic modulus values of 1.1 and 30.8 GPa, respectively. These were the highest values recorded in this work. When the temperature reached 550°C, the nano-hardness and elastic modulus decreased due to the presence of cracks in the films.     

Effect of Annealing Temperature on TiO2 Nanorod Films Prepared by dc Reactive Magnetron Sputtering for Dye-Sensitized Solar Cells

Anatase TiO₂ nanorod films have been prepared on ITO coated glass substrates at room temperature by dc reactive magnetron sputtering technique. The nanorods are highly ordered and are perpendicular to the substrate. XRD measurements show that the anatase nanorods have a preferred orientation along the [110] direction. The prepared nanorods were annealed at different temperatures (200?C500 °C) in air for 1 h. The dye-sensitized solar cells (DSSC) have been made using the as-deposited and annealed TiO₂ nanorods as working electrodes. It has been found that annealing improves the efficiency of the DSSC. An optimum conversion efficiency of 2.13%, at 100 mW/cm² light intensity has been achieved with TiO₂ nanorods annealed at 300 °C.     

Low temperature deposition of titanium oxide containing thin films in trench features from titanium diisopropoxide bis(dipivaloylmethanate) in supercritical CO2

We studied supercritical carbon dioxide fluid deposition of titanium oxide (TiO₂) in trench features on Si substrates using a flow-type deposition apparatus from titanium diisopropoxide bis(dipivaloylmethanate), aiming at fabricating conformal films at a relatively low temperature. We investigated the deposition rate and step coverage under a fluid temperature from 40 to 60 °C, a pressure from 8.0 to 10.0 MPa, and a substrate temperature from 80 to 120 °C. They were dependent on the fluid density, indicating that the solubility difference between the bulk fluid and the neighborhood of the substrate surface plays a decisive role for the deposition. An excellent conformal filling of the trench features was achieved from the fluid of 60 °C under 8 MPa on the substrate kept at 80–100 °C. The XPS spectra of the deposited film suggested partial formation of TiO₂, and the XRD spectra showed the existence of some crystalline TiO₂ (anatase).     

Influence of growth temperature on the microstructure and electrical transport properties of epitaxial NiCo2O4 thin films

In the work reported here, NiCo₂O₄ films were grown epitaxially on LaAlO₃ (111) substrates at temperatures between room temperature and 700?°C. The effects of the substrate temperature (T_sub) on the structural, electrical and magnetic properties and on the Hall effect of the film were investigated. T_sub has a great influence on the cation disorder. High T_sub makes substitution of Ni (Oh) for Co (Td) easier, and changes the relative Ni³⁺/Co³⁺ concentration. The film grown at 400?°C had a relatively larger concentration of Ni³⁺, which lowers the resistivity and enhances the ferrimagnetism of the NiCo₂O₄ film. In addition, a sign change in the Hall coefficient from negative to positive was observed with increasing measurement temperature for each of the samples grown at different substrate temperatures.     

Volume expansion during reaction sintering of γ-Bi12SiO20

Preparation of γ-Bi₁₂SiO₂₀ from a compacted mixture of α-Bi₂O₃ and SiO₂ powders is described. A very large volume expansion, related to the phase formation, is observed during heat treatment at 600°C. It is shown that the dedensification results from a preferential diffusion of bismuth and oxygen ions towards SiO₂, through the layer of γ-Bi₁₂SiO₂₀ which forms around a silica grain. The expansion begins when γ-Bi₁₂SiO₂₀ grains form a continuous skeleton. When bismuth oxide grains are isolated in the skeleton, expansion and reaction rates are proportional. A quantitative model is proposed to describe this situation assuming an isotropic matter transfer and no coalescence between the γ-Bi₁₂SiO₂₀ grains.     

Enhanced gyromagnetic properties of NiCuZn ferrite ceramics for LTCC applications by adjusting MnO2-Bi2O3 substitution

The demand for high performance microwave devices is increasingly promoting the development of miniaturization, integration and multifunctionalization. Here, a uniform and dense NiCuZn ferrite ceramic with high saturation magnetization and low ferromagnetic resonance linewidth was obtained at 950?°C by adjusting the MnO₂-Bi₂O₃ composite additives. The MnO₂-Bi₂O₃ composite additives were composed of 0.5?wt% MnO₂ and x wt% Bi₂O₃ (x?=?0.0, 0.5, 1.0, 1.5, 2.0, and 3.0). The phase structure, microstructures and magnetic properties were systematically studied by means of modern measurement techniques. SEM images reveal that appropriate MnO₂-Bi₂O₃ additions can promote grain growth and reduce sintering temperatures, which is very advantageous for LTCC technology. In addition, the content of MnO₂-Bi₂O₃ additives can significantly reduce ferromagnetic resonance linewidth (FMR) by promoting grain growth and densification at low temperatures. Finally, a uniform and compact NiCuZn ferrite ceramic with an improved 4πM_s (~?3812.5 Gauss), a narrow ΔH (~?144.6?Oe), and a reduced H_c (~?85.2?A/m) were obtained (at 950?°C) by adding the optimal volume of Bi₂O₃ additive. It is expected that the improved gyromagnetic performances will allow the NiCuZn ferrite ceramics to be promising candidates for X-band microwave devices.     

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2 films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO₂ thin films using dc dual magnetron (DM) sputtering in Ar + O₂ mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature T_surf measured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency f_r was investigated in detail. It was found that the increase of f_r from 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate a_D of sputtered TiO₂ films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO₂ films can be sputtered on unheated glass substrates at a_D = 80 nm/min, T_surf < 180 °C when high value of f_r = 350 kHz was used. Properties of a thin hydrophilic TiO₂ film deposited on a polycarbonate substrate are given.     

Photocatalytic enamel/TiO2 coatings developed by electrophoretic deposition for methyl orange decomposition

The aim of this study was to obtain photocatalytic coatings, capable to decompose organic pollutants, through Electrophoretic Deposition (EPD) of enamels containing respectively 0%, 5%, 10%, 15% (in wt%) of TiO₂ onto carbon steel substrates. High quality and homogeneous coatings were obtained by applying 12.5?V during 10?s, as the best EPD conditions. The layers were subsequently heat treated at 740?°C for 10?min, in order to obtain dense glazes.Rietveld refinement of XRD patterns and Raman results show that, after the heat treatment at 740?°C, TiO₂ mostly exists as anatase, responsible of the photocatalytic effect. Semi-quantitative chemical analysis indicate segregation of TiO₂ on the coatings surface, reaching saturation in the sample with 10?wt% TiO₂. FEG-SEM observations reveal rod-like and spherical Ti-rich phases along the cross section of the coatings; some Ti was also dissolved into the enamel. 3D topographical mapping shows that, by adding TiO₂, surface roughness increases significantly.Photocatalytic tests were carried out using a 2?×?10^?5 M aqueous solution of Methyl Orange (MO) as an organic pollutant. By comparing the decomposition rate of MO achieved with the pure enamel (0% of TiO₂) and with the sample with 10% of TiO₂, it was shown that the addition of 10% of TiO₂ results in 90% photocatalytic efficiency.Moreover, the permeation of organic compounds and their UV degradation were studied by measuring the water contact angle onto the enamel surface directly after dipping into oleic acid and after various UV irradiation times. The longer the UV irradiation time, the lower the contact angle, down to a minimum of 14.54° after 8?h of UV irradiation. This means, the compound was initially adsorbed on the enamel/TiO₂ coating surface (10?wt% TiO₂) but was efficiently decomposed upon UV irradiation.     

Characterization of single crystalline a-TiO2 films on MgAl2O4(100) substrates by MOCVD

Anatase phase TiO₂ (a-TiO₂) films have been deposited on MgAl₂O₄(100) substrates at the substrate temperatures of 500–650 °C by the metal organic chemical vapor deposition (MOCVD) method using tetrakis-dimethylamino titanium (TDMAT) as the organometallic (OM) source. The structural analyses indicated that the TiO₂ film prepared at 600 °C had the best single crystalline quality with no twins. The out-of-plane and in-plane epitaxial relationships of the film were a-TiO₂(001)||MgAl₂O₄(100) and TiO₂[100]||MgAl₂O₄[100], respectively. A uniform and compact surface with stoichiometric composition was also obtained for the 600 °C-deposited sample. The average transmittance of all the TiO₂ films in the visible range exceeded 91% and the optical band gap of the films varied from 3.31 to 3.41 eV.     

Synthesis and electrical properties of lead-free piezoelectric Bi0.5Na0.5TiO3 thin films prepared by Sol-Gel method

Lead-free Bi_0.5Na_0.5TiO₃ (BNT) piezoelectric thin films were deposited on Pt/TiO_x/SiO₂/Si substrates by Sol-Gel method. A dense and well crystallized thin film with a perovskite phase was obtained by annealing the film at 700 °C in a rapid thermal processing system. The relative dielectric constant and loss tangent at 12 kHz, of BNT thin film with 350 nm thickness, were 425 and 0.07, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 9 μC/cm² and a coercive field of 90 kV/cm. Piezoelectric measurements at the macroscopic level were also performed: a piezoelectric coefficient (d_33effmax) of 47 pm/V at E = 190 kV/cm was obtained. The piezoresponse force microscopy data confirmed that BNT thin films present ferroelectric and piezoelectric behavior at the nanoscale level.