The properties of the Y2O3 films exposed at elevated temperature

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (1 1 1) substrates by RF magnetron sputtering. The influences of thermal exposure at high temperature in air on the structure, the surface morphology, roughness, and the refractive index of the Y₂O₃ thin film were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). The results indicate that chemical composition of the as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio, and it has a cubic polycrystalline structure but the crystallinity is poor. The monoclinic and cubic phases can coexist in the Y₂O₃ film after thermal exposure to 900 °C, and the monoclinic phase disappears completely after 300 s exposure to 950 °C. The changes of the surface morphology, roughness, and the refractive index of the Y₂O₃ film are closely related to the crystal structure, the internal stress, and various defects influenced by thermal exposure temperature and time.     

Influence of Different Substrates on Laser Induced Damage Thresholds at 1064nm of Ta2O5 Films

Ta2O5 films are prepared on Si, BK7, fused silica, antireflection （AR） and high reflector （HR） substrates by electron beam evaporation method, respectively. Both the optical property and laser induced damage thresholds （LIDTs） at 1064 nm of Ta2O5 films on different substrates are investigated before and after annealing at 673 K for 12 h. It is shown that annealing increases the refractive index and decreases the extinction index, and improves the O/Ta ratio of the Ta2O5 films from 2.42 to 2.50. Moreover, the results show that the LIDTs of the Ta2O5 films are mainly correlated with three parameters： substrate property, substoichiometry defect in the films and impurity defect at the interface between the substrate and the films. Details of the laser induced damage models in different cases are discussed.     

Deposition and characterization of La2Ti2O7 thin films via spray pyrolysis process

Thin films of La₂Ti₂O₇ have been deposited on fused silica and Si substrates by a spray pyrolysis method using ethylene glycol solution of La(III)-Ti(IV)-citrate complexes as starting material and O₂ as a carrier gas. The composition, crystal structure and morphology of the films are studied.     

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi₄Ti₃O₁₂ (BTO) and Bi_3.25In_0.75Ti₃O₁₂ (BTO:In) thin films were prepared on fused quartz and LaNiO₃/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E₀, the dispersion energy E_d, the average interband oscillator wavelength λ₀, the average oscillator strength S₀, the refractive index dispersion parameter (E₀/S₀), the chemical bonding quantity β, and the long wavelength refractive index n_∞ were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E₀/S₀) increases and the chemical bonding quantity β decreases in the BTO and BTO:In films compared with those of bulk.     

Optical and electrical properties of Y2O3 thin films prepared by ion beam assisted deposition

Y₂O₃ thin films were deposited by ion beam assisted deposition (IBAD) and the effects of fabrication parameters such as substrate temperature and ion energy on the structure, optical and electrical properties of the films were investigated. The results show that the deposited Y₂O₃ films had less optical absorption, larger refractive index, and better film crystallinity with the increase of substrate temperature or ion energy. The as-deposited Y₂O₃ films without ion-beam bombardment had larger relative dielectric constant (?_r) and the ?_r decreased with time even over by 40%, while the ?_r of films prepared with high ion energy had less changes, only less than 3%. Also, with the increase of ion energy, the electrical breakdown strength and the figure of merit increased.     

Refractive index behavior of SiO2-P2O5 glass in optical fiber application

The refractive index of SiO₂-P₂O₅ glass prepared by a modified chemical vapor deposition method is measured using an interference microscope. It is found that the refractive index in bulk form increases linearly at 9.5×10^-4 (mol.%)^-1 as the P₂O₅ concentration increases. It is also found that quenching at extremely high speed reduces the refractive index over 2 mol.% P₂O₅. The wavelength dispersion of the refractive index dn/dλ is constant up to 5 mol.% P₂O₅ producing a refractive index difference of 5×10^-3 compared with fused silica. Consequently, this glass materials is thought to be suitable for wide band-width optical fiber applications.     

Femtosecond Z-scan measurement of third-order optical nonlinearities in anatase TiO2 thin films

Anatase phase TiO₂ films have been grown on fused silica substrate by pulsed laser deposition technique at substrate temperature of 750 °C under the oxygen pressure of 5 Pa. From the transmission spectra, the optical band gap and linear refractive index of the TiO₂ films were determined. The third-order optical nonlinearities of the films were measured by Z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. The real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ were determined to be −7.1 × 10⁻¹¹esu and −4.42 × 10⁻¹²esu, respectively. The figure of merit, T, defined by T=βλ/n₂, was calculated to be 0.8, which meets the requirement of all-optical switching devices. The results show that the anatase TiO₂ films have great potential applications for nonlinear optical devices.     

Analysis of codeposited Gd2O3/SiO2 composite thin films by phase modulated spectroscopic ellipsometric technique

Tailoring of the refractive index of optical thin films has been a very fascinating as well as challenging topic for developing new generation optical coatings. In the present work a novel Gd₂O₃/SiO₂ composite system has been experimented and probed for its superior optical properties through phase modulated spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The optical parameters of the composite films have been evaluated using Tauc-Lorentz (TL) formulations. In order to derive the growth dependent refractive index profiles, each sample film has been modeled as an appropriate multilayer structure where each sub-layer was treated with the above TL parameterizations. All codeposited films demonstrated superiority with respect to the band gap and morphological measurements. At lower silica mixing compositions such as in 10-20% level, the composite films depicted superior spectral refractive index profile, band gap as well as the morphology. This aspect highlighted the fact that microstructural densifications in composite films can override the chemical compositions while deciding the refractive index and optical properties in such thin films.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

Microstructural investigations of Y2O3 thin films deposited by laser ablation on MgO

The epitaxial relationships and the microstructure of thin Y₂O₃ film, in situ grown by laser ablation at 700 °C under 0.5 mbar oxygen pressure on MgO substrate, are studied by X-ray and HRTEM investigations. X-ray φ-scanexperiments show that Y₂O₃ exhibits two different crystallographic growing directions <111> and <100> on (100) single-crystalline MgO substrate. The <111> growing direction appears with four different epitaxial relationships where the <110> Y₂O₃ in-plane direction is parallel to the <110> in-plane direction of MgO. The <100> growing direction appears with one epitaxial relationship, cube Y₂O₃ on cube MgO. The HRTEM experiments show the columnar aspect of the Y₂O₃ thin film. Both (111) and (100) Y₂O₃-oriented grains are observed in good agreement with the X-ray experiments. Received: 16 May 2000 / Accepted: 22 May 2000 / Published online: 13 September 2000     

On the spray-drying deposition of TiO2 photocatalytic films

The photocatalytic activity of TiO₂ films deposited on different substrates by the spray-drying method using suspensions of commercially available TiO₂ (Degussa P25 or Tronox) as starting material was studied. The influence of the type of the initial TiO₂, preparation conditions (temperature of the substrate during the film deposition, temperature of the post-deposition annealing), substrate material (glass, fused silica, stainless steel and graphite), the presence of additives in the spraying suspension (polyethylene glycol, ethylene glycol and acetylacetone) and its sonication before spraying on the morphology, size of crystallites and phase composition (rutile/anatase ratio) was studied. Optimal conditions for spray deposition of the films are suggested.     

Laser Induced Damage Threshold at 355 and 1064nm of Ta2O5 Films of Different Phases

Ta2O5 films axe deposited on fused silica substrates by conventional electron beam evaporation method. By annealing at different temperatures, Ta2 O5 films of amorphous, hexagonal and orthorhombic phases are obtained and confirmed by x-ray diffractometer （XRD） results. X-ray photoelectron spectroscopy （XPS） analysis shows that chemical composition of all the films is stoichiometry. It is found that the amorphous Ta2 O5 film achieves the highest laser induced damage threshold （LIDT） either at 355 or 1064nm, followed by hexagonal phase and finally orthorhombic phase. The damage morphologies at 355 and 1064nm are different as the former shows a uniform fused area while the latter is centred on one or more defect points, which is induced by different damage mechanisms. The decrease of the LIDT at 1064nm is attributed to the increasing structural defect, while at 355nm is due to the combination effect of the increasing structural defect and decreasing band gap energy.     

A comparative study on Zn0.8Cd0.2O films deposited on different substrates

Highly (0 0 2)-oriented Zn_0.8Cd_0.2O crystal films were prepared on different substrates, namely, glass, Si(1 1 1) and α-Al₂O₃(0 0 1) wafers by the dc reactive magnetron sputtering technique. The Zn_0.8Cd_0.2O/α-Al₂O₃ film has the best crystal quality with a FWHM of (0 0 2) peak of 0.3700°, an average grain size of about 200 nm and a root-mean-square surface roughness of about 70 nm; yet the Zn_0.8Cd_0.2O/glass holds the worst crystal quality with a much larger FWHM of 0.6281°. SIMS depth profile shows that the Zn and O compositions change little along the film depth direction; the Cd incorporation also almost holds the line towards the top surface other than an accumulation at the interface between the film and the substrate. The Cd content in the film is nearly consistent with that in target.     

Fabrication and magnetic properties of Ce1Y2Fe5O12 thin films on GGG and SiO2/Si substrates

Microstructure and magnetic properties of crystalline Ce₁Y₂Fe₅O₁₂ thin films prepared on GGG and on SiO₂/Si substrates by pulsed laser deposition were studied. The results show that highly textured Ce₁Y₂Fe₅O₁₂ film with (4 4 4) preferred orientation prepared on GGG (1 1 1) shows strong paramagnetism superimposed by a weak ferromagnetism. However, polycrystalline Ce₁Y₂Fe₅O₁₂ thin films on SiO₂/Si, which can only be obtained after post-annealing, show strong ferromagnetism with easy axis of magnetization lying in the plane of the film. With post-annealing temperature increasing, CeO₂ segregates from Ce₁Y₂Fe₅O₁₂; then YIG continues to be decomposed, forming Fe₂O₃. Consequently, the saturation magnetization of Ce₁Y₂Fe₅O₁₂ films decreases first and then increases correspondingly, which indicates that the magnetic properties of Ce₁Y₂Fe₅O₁₂ films are mainly related to the microstructure.     

Optical and structural studies on Ba(Mg1/3Ta2/3)O3 thin films obtained by radiofrequency assisted pulsed plasma deposition

Single-phase Ba(Mg_1/3Ta_2/3)O₃ thin films were prepared by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) starting from a bulk ceramic target synthesized by solid state reaction. Atomic force microscopy, X-ray diffraction and spectroscopic ellipsometry were used for morphological, structural and optical characterization of the BMT thin films. The X-ray diffraction spectra show that the films exhibit a polycrystalline cubic structure. From spectroscopic ellipsometry analysis, the refractive index varies with the thin films deposition parameters. By using the transmission spectra and assuming a direct band to band transition a band gap value of ≈4.72 eV has been obtained.     

Effect of Al content on the properties of Cr1−xAlxC films prepared by RF reactive magnetron sputtering

Cr_1−xAl_xC films were deposited on high-speed steel by RF reactive magnetron sputtering. In this study, we aimed to identify the effect of the Al content on the properties of Cr_1−xAl_xC films. We found that Cr_1−xAl_xC films exhibited a fine columnar grain microstructure with some special characteristics, such as high hardness of Hv 1426, a low friction coefficient of 0.29, and a large contact angle of 90° for x = 0.18. Furthermore, an increase in Al content resulted in a decrease in film hardness and an increase in contact angle. Moreover, on annealing at 923 K, the mechanical properties of the films improved and a dense protective film of complex Cr₂O₃ and Al₂O₃ oxides was formed on the surface for better wear resistance, which will ultimately increase the lifetime of the high-speed steel substrate.     

Laser-induced voltage characteristics of Bi2Sr2Co2Oy thin films on LaAlO3 substrates

We report the laser-induced voltage (LIV) effects in c-axis oriented Bi₂Sr₂Co₂O_y thin films grown on (0 0 1) LaAlO₃ substrates with the title angle α of 0°, 3°, 5° and 10° by a simple chemical solution deposition method. A large open-circuit voltage with the sensitivity of 300 mV/mJ is observed for the film on 10° tilting LaAlO₃ under a 308 nm irradiation with the pulse duration of 25 ns. When the film surface is irradiated by a 355 nm pulsed laser of 25 ps duration, a fast response with the rise time of 700 ps and the full width at half maximum of 1.5 ns is achieved. In addition, the experimental results reveal that the amplitude of the voltage signal is approximately proportional to sin 2α and the signal polarity is reversed when the film is irradiated from the substrate side rather than the film side, which suggests the LIV effects in Bi₂Sr₂Co₂O_y thin films originate from the anisotropic Seebeck coefficient of this material.     

Silica-coated Y2O3:Eu nanoparticles and their luminescence properties

Crystalline Y₂O₃:Eu is of paramount significance in rare earth materials and research on luminescence spectra. In this work, the nanocrystalline Y₂O₃:Eu was coated with silica by a facile solid state reaction method at room temperature. The transmission electron microscope (TEM) photographs showed that the prepared Y₂O₃:Eu particle is polycrystalline with the size of 20 nm, the size of silica-coated particle is about 25 nm. The XPS spectra indicated that the silica layer is likely to interact with Y₂O₃:Eu by a Si-O-Y chemical bond. The luminescence spectra showed that the intensity of ground samples is lower than that of unground ones, the intensity of silica-coated phosphors is higher than that of the ground samples, while almost the same as that of the unground ones. Therefore, the silica coating decreases the surface defects of nanoparticles of the nanocrystalline Y₂O₃:Eu, thus increasing their luminescent intensity.     

Optical parameters in SnO2 nanocrystalline textured films grown on p-InSb (111) substrates

Spectroscopic ellipsometry and photoluminescence (PL) measurements on SnO₂ nanocrystalline textured films grown on p-InSb (111) substrates by using radio-frequency magnetron sputtering at low temperature were carried out to investigate the dependence of the optical parameters on the SnO₂ thin film thickness. As the SnO₂ film thickness increases, while the energy gap of the SnO₂ film decreases, its refractive index increases. The PL spectra show that the broad peaks corresponding to the donor-acceptor pair transitions are dominant and that the peak positions change with the SnO₂ film thickness. These results can help improve understanding for the application of SnO₂ nanocrystalline thin films grown on p-InSb (111) substrates in potential optoelectronic devices based on InSb substrates.     

The Validity of the Results of High-Performance Modeling of SiO<Subscript>2</Subscript> Film Growth

This work is devoted to checking of the validity of the results of high-performance modeling of SiO₂ film growth. Modeling of the high-energy deposition process shows that the refractive indices of deposited SiO₂ films exceed the refractive index of a fused silica substrate. This is entirely supported by the analysis of spectrophotometric data obtained for practical thin films deposited using the respective deposition technique.