Influences of oxygen partial pressure on structure and related properties of ZrO2 thin films prepared by electron beam evaporation deposition

ZrO₂ thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on structure and related properties of ZrO₂ thin films were studied. Transmittance, thermal absorption, structure and residual stress of ZrO₂ thin films were measured by spectrophotometer, surface thermal lensing technique (STL), X-ray diffraction and optical interferometer, respectively. The results showed that the structure and related properties varied progressively with the increase of oxygen partial pressure. The refractive indices and the packing densities of the thin films decreased when the oxygen partial pressure increased. The tetragonal phase fraction in the thin films decreased gradually as oxygen partial pressure increased. The residual stress of film deposited at base pressure was high compressive stress, the value decreased with the increase of oxygen partial pressure, and the residual stress became tensile with the further increase of oxygen pressure, which was corresponding to the evolution of packing densities and variation of interplanar distances.     

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.     

Investigation on properties of TiO2 thin films deposited at different oxygen pressures

TiO₂ thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on optical, mechanical and structural properties of TiO₂ thin films were studied. The results showed that with the increase of oxygen partial pressure, the optical transmittance gradually increased, the transmittance edge gradually shifted to short wavelength, and the corresponding refractive index decreased. The residual stresses of all samples were tensile, and the value increased as oxygen partial pressure increasing, which corresponded to the evolutions of the packing densities. The structures of TiO₂ thin films all were amorphous because deposition particles did not possess enough energy to crystallize.     

Preparation and characterization of upconversion luminescent LaF3:Yb,Er/LaF3 core/shell nanocrystals

LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals were successfully synthesized using solvothermal method. The crystal structure, morphology and photoluminescence properties of as-prepared nanocrystals were investigated in detail. XRD patterns show that the obtained LaF₃:Yb³⁺,Er³⁺ core and LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals exhibit hexagonal structure. The average particle size is about 9.3 nm and 11.4 nm for core and core/shell nanocrystals, respectively. Compared with LaF₃:Yb³⁺,Er³⁺ nanocrystals, both the upconversion emission intensity and the lifetime increase in LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals. The enhancement can be attributed to the LaF₃ shell which can eliminate the nonradiative centers on the surface of LaF₃:Yb³⁺,Er³⁺ nanocrystals.     

Structural and DC conduction studies on vacuum evaporated BaTiO3 thin films prepared from BaTiO3 nano particles synthesised by wet chemical method

BaTiO₃ nanoparticles prepared by wet chemical method were thermally grown onto well cleaned glass substrates under the vacuum of 2 × 10⁻⁵ Torr, using 12A4 Hind Hivac coating unit. An Al–BaTiO₃–Al sandwich structure has been used for electrical conduction properties in the temperature range 303–423 K. The composition of nanoparticles and thin films were identified by EDS spectrum. The structural studies have been performed by the X-ray diffraction (XRD) technique. The X-ray analysis showed that the nano particle has a tetragonal structure and deposited films at a lower thickness amorphous in nature, whereas the crystallinity increases with increase of thickness. In the DC conduction studies, the current–voltage characteristics of the films showed ohmic conduction in the low voltage region. In the higher voltage region, a space charge limited conduction (SCLC) takes place due to the presence of the trapping level. The activation energy was estimated and the values found to decrease with increasing applied voltage. The zero field value of the activation energy is found to be 0.31 eV. The free carrier mobility, carrier density and trap density values were calculated and reported in this paper.     

Spray pyrolytic deposition of transparent aluminum oxide (Al2O3) films

Optically transparent Al₂O₃ films has been synthesized, on quartz substrates at 500, 600 and 700 °C, from 0.02 M aluminum acetyl acetonate (Al(acac)₃) in ethanol, by using ultrasonic spray pyrolysis technique. The films synthesized at 500, 600 and 700 °C are amorphous having average particle sizes 27 ± 6, 18 ± 3 and 14 ± 3, respectively. The films are found to be 95% optically transparent in the visible region. The optical transparency of the films in the ultraviolet region is found to increase with increase in deposition temperature. The observed increase in optical band gap and decrease in refractive index is attributed to the decrease in particle size with increase in deposition temperature. The stoichiometry and chemical bonding of the amorphous film studied using XPS and FTIR spectroscopy revealed the presence chemisorbed oxygen.     

Oblique angle deposition of TiO2 thin films prepared by electron-beam evaporation

Optical, structural and photocatalytic properties of TiO₂ thin films obliquely deposited on quartz glass substrate using an electron-beam evaporation method were investigated. The photocatalytic activity of the films was evaluated by photodecomposition of methylene blue. An increase in incident deposition angle increased the porosity and surface roughness of the TiO₂ films. As a result, the photocatalytic activity was enhanced with incident deposition angle up to 60°. However, a further increase in incident deposition angle to 75° reduced the photocatalytic activity due to a lack of the crystalline phase.     

Study of effect annealing temperature on the structure, morphology and photocatalytic activity of Si doped TiO2 thin films deposited by electron beam evaporation

Transparent Si-doped TiO₂ thin films (Si-TiO₂) were deposited on quartz glasses using electron beam evaporation (EBE) and annealed at different temperature in an air atmosphere. The structure and morphology of these films were analyzed by X-ray diffraction (XRD), Raman microscopy (Raman), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Meanwhile the photocatalytic activity of the films has also been evaluated on the basis of the degradation degree of rhodamine B in aqueous solution. Our experimental results suggest that the annealing temperature impact a strong effect on the structure, morphology and photocatalytic activity of Si-TiO₂ thin films. Furthermore the enhanced thermal stability of Si-TiO₂ films enabled them to elevate the phase transformation temperature of TiO₂ from anatase to rutile and enhanced the photocatalytic efficiency.     

Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

High-quality SrRuO₃ (SRO) thin films and SrTiO₃/SRO bilayer were grown epitaxially on SrTiO₃ (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction ϑ-2ϑ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΘ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials. Supported by the National Natural Science Foundation of China (Grant No. 10334070)     

The photoemission study of NdNiO3/NdGaO3 thin films, through the metal-insulator transition

The electronic structure of thin films NdNiO₃/NdGaO₃ with various thicknesses (from 17 nm to 150 nm), have been studied by photoemission spectroscopy at 300 K and 169 K. The XPS results are consistent with the literature ab initio calculations of the NdNiO₃ electronic structure. A noticeable variation attributed to the metal-insulator (MI) transition has been found only for the films with relatively high thickness (150 nm). Furthermore, the photoemission spectra and their temperature dependence have been discussed with regard to the results of dc electrical resistivity measurements which also exhibit large thickness dependence. Finally, these new results support a possible large hetero-epitaxial effect on the thinnest sample (17 nm) which could stress the NdNiO₃ structure and consequently makes its electronic structure nearly stabilized.     

Magnetic field annealing effects on self-oriented BiFeO3 thin films prepared by chemical solution deposition

Self-oriented BiFeO₃ (BFO) thin films are prepared via chemical solution deposition method with magnetic field in-situ annealing process. The effects of magnetic annealing on the microstructure, magnetic and dielectric properties as well as magnetoelectric coupling effect of the BFO thin films are investigated. With increasing the annealing magnetic field, the crystallization quality, texture, grain boundary connectivity and densification of the films are enhanced, which is attributed to the improvement of connection and diffusion of components. The magnetization of the field-annealing films and dielectric constant as well as remanent polarization increases with increasing the strength of annealing magnetic field. In addition, it is observed that magnetocapacitance value of the magnetic-field-annealing BFO thin film is higher than the non-field-annealing one. Moreover the BFO thin films annealed at 3 kOe magnetic field show the magnetoelectric effect with 4% under 2 kOe at room temperature.     

Chemical bath deposition of hausmannite Mn3O4 thin films

A low-temperature chemical bath deposition (CBD) technique has been used for the preparation of Mn₃O₄ thin films onto glass substrates. The kinetic behavior and the formation mechanism of the solid thin films from the aqueous solution have been investigated. Structure (X-ray diffraction and Raman), morphological (atom force microscope), and optical (UV-vis-NIR) characterizations of the deposited films are presented. The results indicated that the deposited Mn₃O₄ thin films of smooth surface with nanosized grains were well crystalline and the optical bandgap of the film was estimated to be 2.54 eV.     

VO2-WO3 nanocomposite thin films synthesized by pulsed laser deposition technique

Pure VO₂ and VO₂-WO₃ composite thin films were grown on quartz substrate by pulsed laser deposition (PLD) technique. The influence of varying WO₃ molar concentration in the range from x = 0.0 to x = 0.4 on structural, electrical and optical properties of VO₂-WO₃ nanocomposite thin films has been systematically investigated. X-ray diffraction studies reveal the single crystalline monoclinic VO₂ phase (m-VO₂) up to 10% of WO₃ content whereas both m-VO₂ as well as h-WO₃ (hexagonal WO₃) phases were present at higher WO₃ content (0.2 ≤ x ≤ 0.4). Optical transmittance spectra of the films showed blue shift in the absorption edge with increase in WO₃ content. Temperature dependence of resistivity (R-T) measurements indicates significant variation in metal-insulator transition temperature, width of the hysteresis, and shape of the hysteresis curve. Cyclic Voltammetry measurements were performed on VO₂-WO₃ thin films. A direct correlation between V/W ratio and structure-property relationship was established. The present investigations reveal that doping of WO₃ in VO₂ is effective to increase the optical transmittance and to reduce the semiconductor to metal phase transition temperature close to room temperature.     

Characterization of LaF3 coatings prepared at different temperatures and rates

LaF₃ thin films were prepared by thermal boat evaporation at different substrate temperatures and various deposition rates. X-ray diffraction (XRD), Lambda 900 spectrophotometer and X-ray photoelectron spectroscopy (XPS) were employed to study crystal structure, transmittance and chemical composition of the coatings, respectively. Laser-induce damage threshold (LIDT) was determined by a tripled Nd:YAG laser system with a pulse width of 8 ns. It is found that the crystal structure became more perfect and the refractive index increased gradually with the temperature rising. The LIDT was comparatively high at high temperature. In the other hand, the crystallization status also became better and the refractive index increased when the deposition rate enhanced at a low level. If the rate was super rapid, the crystallization worsened instead and the refractive index would lessen greatly. On the whole, the LIDT decreased with increasing rate.     

Structural, optical and magnetic properties of Nd-doped BiFeO3 thin films prepared by pulsed laser deposition

Nd-doped BiFeO₃ thin films were grown by pulsed laser deposition on quartz substrate and their structural, optical and magnetic properties have been studied. X-ray diffraction analysis revealed that Nd addition caused structural distortion even with 5% of Nd concentration, additional secondary phase appeared in all samples but its intensity was greatly reduced with Nd addition. Doping-induced variations in texture and structure modifying both magnetic and optical properties of BiFeO₃ thin films. The energy band gap decreases while the refractive index increases with addition of Nd³⁺ in BiFeO₃ for Bi³⁺. These variations in energy band gap and refractive index have been explained on the basis of density of states and increase in disorders in the system. All the samples were found to exhibit ferromagnetism at room temperature and the saturation magnetization increases with the increase in structural distortion with addition of Nd. Finally, Nd-doping modifies the physical properties of BiFeO₃ in comparison to undoped BiFeO₃ thin films.     

Ferromagnetism in epitaxial orthorhombic YMnO3 thin films

Epitaxial orthorhombic YMnO₃ thin films, (0 0 1) oriented, have been grown by pulsed laser deposition on (0 0 1)SrTiO₃ substrates. Their crystal structure and magnetic response have been studied in detail. Although bulk o-YMnO₃ is antiferromagnetic, our magnetic measurements reveal intriguing thermal hysteresis between the zero-field-cooled and field-cooled curves below the onset of the antiferromagnetic ordering temperature, thus signaling a more complex magnetic structure with net ferromagnetic moments. We discuss on the possible origin of this net magnetization and we have found a correlation of the magnetic response with the strain state of the films. We propose that substrate-induced strain modifies the subtle competition of magnetic interactions and leads to a non-collinear magnetic state that can thus be tuned by strain engineering.     

Influence of [S2O3]/[Sm] on Sm2S3 thin films deposited by liquid phase deposition method on self-assembled monolayers

Sm₂S₃ thin films were prepared on Si (1 0 0) substrates using SmCl₃ and Na₂S₂O₃ as precursors by liquid phase deposition method on self-assembled monolayers. The influence of the molar concentration ratio of [S₂O₃²⁻]/[Sm³⁺] on the phase compositions, surface morphologies and optical properties of the as-deposited films were investigated. The as-deposited Sm₂S₃ thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-vis) and photoluminescence spectrum (PL). Results show that it is important to control the [S₂O₃²⁻]/[Sm³⁺] during the deposition process and monophase Sm₂S₃ thin films with orientation growth along (0 1 1) direction can be achieved when [S₂O₃²⁻]/[Sm³⁺] = 2.0, pH 3.0, with citric acid as a template agent. The as-deposited thin films exhibit a dense and crystalline surface morphology. Good transmittance in the visible spectrum and excellent absorbency of ultraviolet light of the thin films are observed, and the band gap of the thin films first decrease and then increase with the increase of the [S₂O₃²⁻]/[Sm³⁺]. The as-deposited thin films also exhibit red photoluminescence properties under visible light excitation. With the increase of the [S₂O₃²⁻]/[Sm³⁺] in the deposition solution, the PL properties of Sm₂S₃ thin films are obviously improved.     

Chemical bath deposition of Bi2S3 films by a novel deposition system

Bismuth sulfide (Bi₂S₃) films were chemically deposited by a novel deposition system in which ammonium citrate was used as the chelating reagent. Two sulfur source thioacetamide (TA) and sodium thiosulfate (Na₂S₂O₃) were used to prepare Bi₂S₃ films. Both the as-prepared films have amorphous structure. However, annealing can improve the crystallization of the films. The composition of the films prepared by TA and Na₂S₂O₃ are all deviate from the stoichiometric ratio of Bi₂S₃. The Bi₂S₃ films are all homogeneous and well adhered to the substrate. The optical properties of the Bi₂S₃ films are studied. The electrical resistivity of the as-prepared films are all around 7 × 10³ Ω cm in dark, which decreases to around 1 × 10³ Ω cm under 100 mW/cm² tungsten-halogen illumination. After the annealing, the dark resistivity of the Bi₂S₃ film prepared by TA decreases by four magnitudes. In contrast, the dark resistivity of the Bi₂S₃ film prepared by Na₂S₂O₃ only decreases slightly.     

Oxygen pressure dependent electroresistance in La0.9Sr0.1MnO3 thin films grown by laser molecular beam epitaxy

We report here studies on the influence of oxygen pressure on the electroresistance behavior of La_0.9Sr_0.1MnO₃ thin films fabricated by laser molecular beam epitaxy. It was found that the film deposited at lower oxygen pressure shows larger c-axis parameter, higher resistance, and more distinct electroresistance. These results reveal that the electroresistance of manganite thin films can be tuned by the conditions of film fabrication. Supported by the National Natural Science Foundation of China (Grant No. 10334070) and the National Key Basic Research Program of China (Grant No. 2004CB619004)     

Characteristics of electron beam evaporated nanocrystalline SnO2 thin films annealed in air

Tin oxide (SnO₂) thin films (about 200 nm thick) have been deposited by electron beam evaporation followed by annealing in air at 350-550 °C for two hours. Optical, electrical and structural properties were studied as a function of annealing temperature. The as-deposited film is amorphous, while all other annealed films are crystalline (having tetragonal structure). XRD suggest that the films are composed of nanoparticles of 5-10 nm. Raman analysis and optical measurements suggest quantum confinement effects that are enhanced with annealing temperature. For instance, Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk SnO₂. Blue shift becomes more pronounced with annealing temperature. Optical band gap energy of amorphous SnO₂ film is 3.61 eV, which increases to about 4.22 eV after crystallization. Two orders of magnitude decrease in resistivity is observed after annealing at 350-400 °C due to structural ordering and crystallization. The resistivity, however, increases slightly with annealing temperature above 400 °C, possibly due to improvement in stoichiometry and associated decrease in charge carrier density.