Influence of Hf→Zr substitution on optical and refractometric parameters of Hf1−xZrxO2 thin films

Ellipsometric and spectroscopic investigations of Hf_1−xZr_xO₂ thin films were performed. Dispersion dependences of refractive indices and extinction coefficients in the wavelength interval 0.2-0.7 μm were obtained by optical-refractometric synthesis of absorption spectra. Optical-refractometric relation is applied to describe the dispersion of the refractive indices. Compositional behaviour of optical pseudogap and refractive indices of HfO₂-ZrO₂ thin films is studied.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Optical characterization of vacuum evaporated a-Se80Te20−xCux thin films

Thin films of a-Se₈₀Te_20−xCu_x (where x=2, 6, 8 and 10) were deposited on glass substrates by vacuum evaporation technique. The absorbance, reflectance and transmittance of as-deposited thin films were measured in the wavelength region 400-1000 nm. The optical band gap and optical constants of amorphous thin films have been studied as a function of photon energy. The optical band gap increases on incorporation of copper in Se₈₀Te_20−xCu_x system. The value of refractive index (n) decreases while the value of the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states.     

Structural and optical properties of Er-doped Y2Ti2O7 thin films by sol-gel method

Er³⁺-doped Y₂Ti₂O₇ and Er₂Ti₂O₇ thin films were fabricated by sol-gel spin-coating method. A well-defined pyrochlore phase Er_xY_2-xTi₂O₇ was observed while the annealing temperature exceeded 800 °C. The average transmittance of the Er_xY_2-xTi₂O₇ thin films annealed at 400 to 900 °C reduces from ∼ 87 to ∼ 77%. The refractive indices and optical band gaps of Er_xY_2-xTi₂O₇ (x = 0-2) annealed at 800 °C/1 h vary from 2.20 to 2.09 and 4.11 to 4.07 eV, respectively. The ∼ 1.53 μm photoluminescence spectrum of Er³⁺ (5 mol%)-doped Y₂Ti₂O₇ thin films annealed at 700 °C/1 h exhibits the maximum intensity and full-width at half maximum (∼ 60 nm).     

Influences of carbon content and power density on the uniformity of PECVD grown a-Si1−x:Cx:H thin films

Large area electronics require large size thin films whose eventual inhomogeneities arise as a problem. Hydrogenated amorphous silicon carbide thin films (a-Si_1−xC_x:H) for four different source gas mixtures at two power densities were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The degree of film homogeneity was investigated through measurements of deposition rate, refractive index and optical energy gap along the radial direction of bottom electrode. Both ellipsometer at various incident angles and optical transmittance at normal incidence were used in mutual control as diagnosing tools. It seems there is a critical power density beyond which inhomogeneities of the deposited films along the radial direction of the electrode are unavoidable.     

Microfabrication of dilute magnetic semiconducting Ti1−xCoxO2 films using photosensitive sol-gel method

Photosensitive Ti_1−xCo_xO₂ gel films are prepared by chemical modification with benzoylacetone, and then their Fourier transform infrared spectra and ultraviolet visible spectra are measured. Results show that the chelate rings of benzoylacetone with Ti ions are formed in the Ti_1−xCo_xO₂ gel films. With irradiation of UV light, the chelate rings are photolyzed, which leads to a change of the solubility of the Ti_1−xCo_xO₂ gel films in methanol. Based on this, the micro-patterns of Ti_1−xCo_xO₂ gel films are obtained. After the patterned gel films are dried at 200 °C and are fired at 550 °C for 1 h, negative patterned Ti_1−xCo_xO₂ inorganic films are obtained. The Ti_1−xCo_xO₂ films have an anantase structure and exhibit a room temperature ferromagnetic property.     

Composition dependence of optical constants in ferroelectric Ba(Ti1 − x,Nix)O3 thin films by optical transmittance technique

Ba(Ti_1 − x,Ni_x)O₃ ferroelectric thin films with perovskite structure are prepared on fused quartz substrates by a sol-gel process. Optical transmittance measurements indicate that Ni-doping has an obvious effect on the energy band structure of BaTiO₃. It has been found that the refractive index n, extinction coefficient k, and band gap energy E_g of the films are functions of the film composition. The E_g of Ba(Ti_1 − x,Ni_x)O₃ decreases approximately linearly as the Ni content increases, which is attributed to the decline of conduction band energy level with increasing the Ni content. On the other hand, n and k both increase linearly with increasing the Ni content because of the increase of packing density. These results indicate that thin films might have potential applications in BaTiO₃-based thin-film optical devices.     

Magnetic and photoconductive properties of the CoxPt1−x-Pt-TiO2 nanocomposite films prepared by reactive sputter-deposition

Co-Pt-Ti-O films were prepared on SiO₂ glass substrate by sputtering of a Co-Pt-Ti composite target in Ar+O₂ atmosphere with the total pressure of 4 Pa and then in situ annealed at an elevated temperature T_a to form the Co_xPt_1−x-TiO₂ films. It is found that the ferromagnetic films grow in the form of fiber-like columnar grain about 10 nm in diameter when sputtered in the pressure ratio of O₂/Ar=1/133 followed by in situ annealing at The films contain Pt and amorphous anatase-type TiO₂ phases besides the ferromagnetic fcc-Co_xPt_1−x phase. Thus, such nanocomposite films show photoconductive properties due to the anatase-type TiO₂ phase as well as ferromagnetic properties due to the Co_xPt_1−x phase.     

Locating the normal to relaxor phase boundary in Ba(Ti1−xHfx)O3 ceramics

In this article, we report our studies on the relaxor behavior of Ba(Ti_1−xHf_x)O₃ ceramics, made with close compositions between 0.20 ≤ x ≤ 0.30, to locate the hafnium concentration boundary for the normal to relaxor crossover. X-ray diffraction followed by Rietveld refinement shows the occurrence of single-phase cubic structure for the synthesized Ba(Ti_1−xHf_x)O₃ ceramics. Temperature and frequency dependence of the real (?′) and imaginary (?″) parts of the dielectric permittivity has been studied in the temperature range of 90-350 K at frequencies of 0.1, 1, 10, and 100 kHz. A diffuse phase transition accompanying frequency dispersion is observed in the permittivity versus temperature plots revealing the occurrence of relaxor ferroelectric behavior. The T_m verses Hf concentration plot shows a discontinuous jump and change in the slope at x = 0.23. Quantitative characterization based on phenomenological models has also been presented. The plausible mechanism of the relaxor behavior has been discussed. Substitution of Hf⁴⁺ for Ti⁴⁺ in BaTiO₃ reduces the long-range polar ordering yielding a diffuse ferroelectric phase transition.     

Microstructure and electrical properties of Ba0.7Sr0.3(Ti1 − xZrx)O3 thin films prepared on copper foils with sol-gel method

Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0, 0.1, 0.2) (BSZT) thin films have been prepared on copper foils using sol-gel method. The films were annealed in an atmosphere with low oxygen pressure so that the substrate oxidation was avoided and the formation of the perovskite phase was allowed. The X-ray diffraction results show a stable polycrystalline perovskite phase, with the diffraction peaks of the BSZT films shifting toward the smaller 2θ with increasing Zr content. Scanning electron microscopy images show that the grain size of the BSZT thin films decreases with increasing Zr content. High resolution transmission electron microscopy shows the clear lattice and domain structure in the film. The dielectric peaks of the BSZT thin films broaden with increasing Zr content. Leakage current density of Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0.1) thin film is the lowest over the whole applied voltage.     

Influence of laser-irradiation on the optical constants Se75S25 − xCdx thin films

Amorphous thin films of glassy alloys of Se₇₅S_25 − xCd_x (x = 2, 4 and 6) were prepared by thermal evaporation onto chemically cleaned glass substrates. Optical absorption and reflection measurements were carried out on as-deposited and laser-irradiated thin films in the wavelength region of 500-1000 nm. Analysis of the optical absorption data shows that the rule of no-direct transitions predominates. The laser-irradiated Se₇₅S_25 − xCd_x films showed an increase in the optical band gap and absorption coefficient with increasing the time of laser-irradiation. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The value of refractive index increases decreases with increasing photon energy and also by increasing the time of laser-irradiation. With the large absorption coefficient and change in the optical band gap and refractive index by the influence of laser-irradiation, these materials may be suitable for optical disc application.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Structural characterization and optical properties of Cd(1−x)MnxSe thin films

Stoichiometric bulk ingot materials of the ternary mixture Cd_(1−x)Mn_xSe (0.05 ≤ x ≤ 0.9) were prepared by direct fusion of the constituent elements in vacuum sealed silica tubes. X-ray diffraction studies indicate that the investigated samples exhibited a hexagonal structure. The lattice parameters varied linearly with Mn content, following Vegard's law. Thin films were deposited by thermal evaporation from the pre-synthesized ingot material, onto glass substrates. X-ray and electron diffraction studies on the as-deposited and annealed films revealed an amorphous-to-crystalline phase transition at T_a ≈ 423 K. EDAX studies on the prepared films show that the as-deposited films are nearly stoichiometric. The transmittance and reflectance of the deposited Cd_(1−x)Mn_xSe films were measured at normal light incident in the wavelength spectral range 500-2500 nm. Analysis of the transmittance spectra in the entire wavelength range allowed the determination of the refractive index. The dispersion parameters have been calculated, from which the static refractive index as well as static dielecric constant were calculated. Analysis of the absorption coefficient of the investigated films revealed the existence of both the allowed direct and forbidden direct optical transition mechanisms. The corresponding energies were estimated.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Refractive index measurement of cerium-doped LuxY2−xSiO5 single crystal

Principal refractive indices of the biaxial cerium-doped Lu_xY_2−xSiO₅ (LYSO) crystal were determined with high accuracy at seven different wavelengths between 400 and 700 nm using the classical minimum angle of deviation method. The reliability of the measured data permitted to deduce parameters of a common dispersion formula, by which the refractive indices can be extrapolated for wavelengths up to 1100 nm, an important range for laser applications. The extent of axial dispersion was precisely measured by ellipsometry, its effects on the anisotropic refractive index has been calculated. Examples are given to demonstrate the influence of anisotropy on the operation of optical devices.     

Mechanical and environmental properties of Ge1−xCx thin film

Ge_1−xC_x thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ as precursors and its mechanical and environmental properties were investigated. The samples were measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum, FT-IR spectrometer, WS-92 testing apparatus of adhesion and FY-03E testing apparatus of salt and fog. The results show that the infrared refractive index of Ge_1−xC_x thin film varies from 2 to 4 with different x values. The adhesion increases with increasing gas flow ratio of GeH₄/CH₄ and decreases with increasing film thickness. The nanoindentation hardness number decreases with increasing germanium content. Three series films exhibit the best anti-corrosion property when the RF power is about 80 W, or substrate temperature is about 150 °C, or DC bias is about −100 V. Furthermore, increasing the gas flow ratio of GeH₄/CH₄ improves the anti-corrosion property of these films.     

Studying trivalent/bivalent metal ion doped TiO2 as p-TiO2 in bipolar heterojunction devices

Trivalent/bivalent metal ions doped TiO₂ thin films (M_xTi_1−xO₂, M = Cr³⁺, Fe³⁺, Ni²⁺, Co²⁺, Mn²⁺ and x = 0.01, 0.05, 0.1, 0.15, 0.2) were deposited on Indium–tin oxide (ITO) coated glass substrates by spin coating technique. X-ray photoelectron spectroscopy (XPS) showed Ti⁴⁺ oxidation state of the Ti2p band in the doped p-TiO₂. The homogenous M_xTi_1−xO₂ was used to support n-ZnO thin films with thickness ∼40–80 nm and vertically aligned n-ZnO nanorods (NR) with length ∼300 nm and 1.5 μm. Current (I)–voltage (V) characteristics for the Ag/n-ZnO/M_xTi_1−xO₂/ITO/glass assembly showed rectifying behavior with small turn-on voltages (V₀) < 1 V. The ideality factor (η) and the resistances in both forward and reverse bias were calculated. The temperature dependence performance of these bipolar devices was performed and variation of the parameters with temperature was studied.     

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

Single-crystalline Ti_1−xNb_xO₂ (x = 0.2) films of 40 nm thickness were deposited on SrTiO₃ (100) substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction measurement confirmed epitaxial growth of anatase (001) film. The resistivity of Ti_1−xNb_xO₂ films with x ≥ 0.03 is 2-3 × 10^− 4 Ω cm at room temperature. The carrier density of Ti_1−xNb_xO₂, which is almost proportional to the Nb concentration, can be controlled in a range of 1 × 10¹⁹ to 2 × 10²¹ cm^− 3. Optical measurements revealed that internal transmittance in the visible and near-infrared region for films with x = 0.03 was more than 97%. These results demonstrate that the presently developed anatase Ti_1−xNb_xO₂ is one of the promising candidates for the practical TCOs.     

Synthesis, structure and dielectric characterization of Ln2Ti2−2xM2xO7(Ln=Gd, Er; M=Zr, Sn, Si)

The progress in wireless communications and information access has demanded the use of electronic ceramics exhibiting desired properties. To further our understanding of these properties, compounds in the Ln₂Ti_2-2xM_2xO₇ (Ln=Gd, Er; M=Zr, Sn, Si) systems were synthesized by ceramic methods and characterized by powder X-ray diffraction. The ZrO₂-doped Gd₂Ti_2−2xZr_2xO₇ compounds adopt the pyrochlore structure type and form a complete solid solution. Er₂Ti_2−2xZr_2xO₇ forms a pyrochlore solid solution for x<0.1. However, stoichiometric Er₂Zr₂O₇ does not form; instead Er₄Zr₃O₁₂ forms a with defect fluorite structure. The Sn-doped Ln₂Ti_2−2xSn_2xO₇ (Ln=Gd, Er) compounds form complete solid solutions, and the Si compounds adopt the pyrochlore structure up to x=0.05. At ambient temperature, dielectric constants range from 10 to 61 for Er₂Ti_2−2xZr_2xO₇ and 16-31 for Gd₂Ti_2−2xZr_2xO₇ with low dielectric loss (1×10⁻³) at 1 GHz.