Structural,electrical and optical properties of boron doped ZnO thin films using LSMCD method at room temperature

Zn_1−x B _x O (0≤x≤0.04) thin films were deposited by the liquid source misted chemical vapor deposition (LSMCD) method. The thin films were polycrystalline with grain sizes of 16 nm to 22 nm. The structural, optical, and electrical properties were investigated by X-ray diffraction, UV-visible spectrophotometry, Raman spectroscopy, and Hall effect measurement. Also scanning electron (SEM) and atomic force microscopy (AFM) techniques were used in order to determine the morphological and topological characteristics of the films. The optimal result of Zn_1−x B _x O films was obtained at x=0.02, with a low resistivity of ≈10⁻² Ω cm, and a high transmittancy of 85% in the visible light spectrum (300 nm ∼ 800 nm).     

Influence of samarium on optical absorption in thin films of the solid electrolyte RbAg4I5

The fundamental optical absorption of films of the solid electrolyte RbAg₄I₅ electrolyte films decreases (by approximately 25%) after vacuum evaporation of Sm films onto them, and a broad strong-absorption band with a maximum at 2.4 eV appears within the bad gap. The films bleach after 5–10 days in dry air. The observed phenomena are attributed to a high concentration (∼3×10²⁰ cm⁻³) of point defects, including F-centers, in nonstoichiometric RbAg₄I₅:Sm, and also to the oxidation of Sm. In colored films the ionic conductivity is σ⋍0.9σ ₀, and in bleached films it is close to the initial value σ ₀. Fiz. Tverd. Tela (St. Petersburg) 39, 1544–1547 (September 1997)     

Investigation of the optical properties of AgGaTe2 films obtained by laser deposition

We obtain thin films of AgGaTe₂ by laser vaporization of starting crystals. The compositions of the starting crystals and of the films obtained are determined by x-ray spectral analysis, with their structure and the parameters of the crystal lattice being determined by the x-ray method. The energies of interband transitions and crystalline (Δ _cr ) and spin-orbit (Δ _so ) splitting are calculated from transmission spectra in the region of the main absorption band. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 793–796, November–December, 1997.     

Surface plasmon resonance response of Au–WO3?x composite films

Surface plasmon resonance of metal–dielectric composite thin films formed by noble metal nanoparticles embedded in a dielectric matrix offers a high degree of flexibility and enables many applications such as surface enhanced spectroscopes, and biological and chemical sensing. In this article, Au–WO_3−x composite films of various Au contents and thicknesses were prepared by the pulsed laser deposition technique, and their SPR responses were measured in the Kreschmann geometry, using a polarized light beam at 640 nm wavelength. Theoretical calculation of SPR responses based on the Bruggeman or Maxwell–Garnett model with the MacLeod general characteristic matrix method is in obvious discrepancy with experimental measurements but it is able to predict the trend in term of the dependence of SPR responses on Au content and thickness of the Au–WO_3−x films. The SPR responses of the Au–WO_3−x films when exposed to NO gas molecules were measured and the preliminary results indicated that gas sensing using the SPR responses of metal–dielectric composite films is feasible.     

Precise determination of?optical properties of?pentacene thin films grown on various substrates: Gauss–Lorentz model with effective medium approach

Spectroscopic ellipsometry measurements are performed on thin pentacene films grown on glass, SiO₂, and n-Si substrates. The Gauss–Lorentz oscillator model is shown to be effective in modeling the π–π ^∗ transitions found in organic compounds. The effective medium approximation that considers the surface roughness of the films, which can be significant in case of pentacene, is also shown to be a key factor in precisely determining their dielectric functions. The proposed method reveals that there are some quantitative differences in the optical properties of the pentacene films prepared on different substrates.     

Variations in the electrical resistivity of La0.67Ca0.33MnO3 films and induced interconversions of ferromagnetic and nonferromagnetic inclusions in their bulk

A significant (∼1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion (a _⊥/a _‖ ≈ 1.04) and reduction in the volume of the unit cell of La_0.67Ca_0.33MnO₃ films (15 nm) quasicoherently grown on the (001) surface of a LaAlO₃ substrate. The films consist of single-crystal blocks with the lateral size of 30–50 nm. The atomically smooth LaAlO₃-La_0.67Ca_0.33MnO₃ interphase boundary has no misfit dislocations. At T = 4.2 K, the transformation of nonferromagnetic phase inclusions into ferromagnetic ones in a constant magnetic field H is accompanied by a stable reduction in the electrical resistivity ρ of manganite films with time, so that the curve ρ(t) is well approximated by the relationship ρ(t) ∼ ρ₁(t − t ₀)^1/2, (where t ₀ is the time for establishment of the specified value (μ₀ H = 5 T) of the magnetic field and ρ₁ is a coefficient independent of H). The magnetocrystalline anisotropy due to the elastic deformation of films by the substrate and stratification of electronic phases are the reasons of the distinct hysteresis in the dependences ρ(μ₀ H, T < 100 K) obtained on μ₀ H scanning in the sequence 5 T → 0 → −5 T → 0 → 5 T. At T = 50 K and μ₀ H = 0.4 T, the magnetoresistance MR = 100% [ρ(μ₀ H) − ρ(μ₀ H = 0)]/ρ(μ₀ H = 0) of LCMO films attains 150%.     

Determination of the degree of crystallinity of poly(vinyl alcohol) by FTIR spectroscopy

Quantitative correlations between the intensity of the crystalline band at 1144 cm⁻¹ (A ₁₁₄₄) normalized to the intensity of the C–O stretching band at 1094 cm⁻¹ (A ₁₀₉₄) in IR spectra of PVA films and the degree of crystallinity (α) of these films measured by an x-ray diffraction method were investigated. It was found that α and A ₁₁₄₄/A ₁₀₉₄ were related by the linear dependence α (%) = a + b(A ₁₁₄₄/A ₁₀₉₄) with correlation coefficient 0.999 for α values in the range 18–60%.     

The development of the physical and electrical characteristics of multi-layer TiO<Subscript>2</Subscript>–W–TiO<Subscript>2</Subscript> thin films

In this study, two different thin films, TiO₂ thin film and TiO₂–W–TiO₂ multi-layer thin films (W, tungsten), are prepared by RF magnetron sputtering onto glass substrates. The crystal structure, morphology, and transmittance of TiO₂ and TiO₂–W–TiO₂ multi-layer thin films are investigated by X-ray diffraction, SEM, and UV-Vis spectrometer, respectively. The amorphous, rutile, and anatase TiO₂ phases are observed in the TiO₂ thin film and in the TiO₂–W–TiO₂ multi-layer thin films. The deposition of tungsten as the inter-layer will have large effect on the transmittance and phase ratios of rutile and anatase phases in the TiO₂–W–TiO₂ multi-layer thin films. The crystal intensities of amorous TiO₂ will decrease as the tungsten is used as the middle layer in the multi-layer structure. The band gap energy values of TiO₂ thin film and TiO₂–W–TiO₂ multi-layer thin films are evaluated from (αhν)^1/2 versus energy plots, and the calculated results show that the energy gap decreases from 3.21 eV (TiO₂ thin film) to 3.08∼3.03 EV (TiO₂–W–TiO₂ multi-layer thin films).     

Anisotropic magnetoresistance of partially relaxed SrRuO3 films

The SrRuO₃ films (50 nm thick) grown by laser evaporation on (001)(LaAlO₃)_0.3 + (Sr₂AlTaO₆)_0.7 substrates were under partially relaxed biaxial compressive mechanical stresses. The films consisted of crystallites with lateral dimensions of 40–100 nm and a relative azimuthal misorientation of about 0.9°. Ferromagnetic ordering of spins in the SrRuO₃ films was manifested by a change in the slope of the temperature dependence of their electrical resistivity ρ at T ≈ 155 K. For a magnetic field H parallel to the measuring current, the maximum values (∼7.5%) of the magnetoresistance MR = [ρ(μ₀ H = 5 T) − ρ(μ₀ H = 0)]/ρ(μ₀ H = 0) were observed at temperatures of about 100 K. At T = 95 K (μ₀ H = 5 T), the anisotropic magnetoresistance of the films was 8% and increased by a factor of approximately 1.5 with decreasing temperature to 4.2 K.     

Persistent spin splitting of a two-dimensional electron gas in tilted magnetic fields

The effect of atomic disorder on the electron transport and the magnetoresistance (MR) of Co₂CrAl Heusler alloy (HA) films has been investigated. We show that Co₂CrAl films with L2₁ order exhibit a negative value for the temperature coefficient of resistivity (TCR) in a temperature range of 10 < T < 290 K, and the temperature dependence of electric conductivity varies as T ^3/2 similarly to that of the zero-gap semiconductors. The atomic or the site disorder on the way of L2₁ → B2 → A2 → amorphous state in Co₂CrAl HA films causes the deviation from this dependence: reduction in the absolute value of TCR as well as decrease in the resistivity down to ϱ(T = 293 K) ∼ 200 μΩ cm in comparison to ϱ(T = 293 K) ∼ 230 μΩ cm typical for the Co₂CrAl films with L2₁ order. The magnetic-field dependence of MR of the Co₂CrAl films with L2₁ order is determined by two competing contributions: a positive Lorentz scattering and a negative s-d scattering. The atomic disorder in Co₂CrAl films drastically changes MR behavior due to its strong influence on the magnetic properties.     

Long-term evolution of photoinduced light absorption in C60 films

It is found that photoinduced absorption in the energy range 0.6–2.1 eV in C₆₀ films grown by the same method can differ by a factor of 100. This change is attributable a 10⁶-fold increase in the relaxation time τ of electron-hole photoexcitations after working with the films for several months. It is established that the bimolecular recombination mechanism for photoexcitations (triplet excitons and polarons), which is typical of as-prepared and partially aged films, is superseded in fully aged films by thermally activated tunneling of localized photoexcitations. An investigation of the film transmission spectra in the photon energy range 0.2–5.0 eV shows that the long-time variations of the optical properties are associated with a decrease in the concentration of defects forming shallow tails of the density of states. An abrupt decrease of the relaxation time τ and the photoinduced absorption is observed in both types of films at T⩾80 K. Fiz. Tverd. Tela (St. Petersburg) 39, 1303–1309 (July 1997)     

Large optical nonlinearity in CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully prepared on LaAlO₃ substrates by pulsed laser deposition technique. We measured the nonlinear optical susceptibility of the thin films using Z-scan method at a wavelength of 532 nm with pulse durations of 25 ps and 7 ns. The large values of the third-order nonlinear optical susceptibility, χ ⁽³⁾, of the CCTO film were obtained to be 2.79×10⁻⁸ esu and 3.30×10⁻⁶ esu in picosecond and nanosecond time regimes, respectively, which are among the best results of some representative nonlinear optical materials. The origin of optical nonlinearity of CCTO films was discussed. The results indicate that the CCTO films on LaAlO₃ substrates are promising candidate materials for applications in nonlinear optical devices.     

Nonlinear optical absorption in Bi3TiNbO9 thin films using Z-scan?technique

Bi₃TiNbO₉ (BTN) thin films with layered perovskite structure were fabricated on fused silica by pulsed laser deposition. The XRD pattern revealed that the films are single-phase perovskite and highly (00l) textured. Their fundamental optical constants, such as band gap, linear refractive index, and linear absorption coefficient, were obtained by optical transmittance measurements. The dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The nonlinear optical absorption of the films was investigated by single beam Z-scan method at a wavelength of 800 nm with laser duration of 80 fs. We obtained the nonlinear absorption coefficient β=1.44×10⁻⁷ m/W. The results show that the BTN thin films are promising for applications in absorbing-type optical devices.     

Excimer laser deposited CuO and Cu<Subscript>2</Subscript>O films with third-order optical nonlinearities by femtosecond <Emphasis Type="Italic">z</Emphasis>-scan measurement

By controlling the oxygen pressure, single-phase CuO and Cu₂O thin films have been obtained on quartz substrates using a pulsed laser deposition technique. The structure properties and linear optical absorption of the films were characterized by X-ray diffraction and UV–VIS spectroscopy. By performing z-scan measurements using a femtosecond laser (800 nm, 50 fs), the real and imaginary parts of the third-order nonlinear susceptibility, Re χ ⁽³⁾ and Im χ ⁽³⁾, of the films were determined. Both CuO and Cu₂O films exhibited large optical nonlinearities, which is comparable to those in some representative semiconductor films such as ZnO and GaN films using femtosecond laser excitation. Compared with Cu₂O films, the CuO films showed larger third-order nonlinear optical effects under off-resonance excitation. Furthermore, the mechanisms of the optical nonlinearities in CuO and Cu₂O films are explained in the main text. It was suggested that the reasons of the difference in their nonlinear refractive effects may be related to the different electronic structure in CuO and Cu₂O materials.     

Thin sol-gel bismuth silicate films

The sol-gel method is used to obtain thin films with the composition Bi₁₂SiO₂₀. The characteristic features of the technology for obtaining the films are presented. Diffractometry confirmed that the films possess γ-Bi₂O₃-type structure. The transmission spectra of the films were investigated. The spectral dependence of the absorption coefficient of the films matches well with the spectra determined using bulk Bi₁₂SiO₂₀ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1003–1005 (June 1999)     

Synthesis of nanometric iron oxide films by RPLD and LCVD for thermo–photo sensors

Iron oxide films were deposited on <100> Si substrates by reactive pulsed laser deposition (RPLD) using a KrF laser (248 nm). These films were deposited too by laser (light) chemical vapor deposition (LCVD) using continuous ultraviolet photodiode radiation (360 nm). The deposited films demonstrated semiconducting properties. These films had large thermo-electromotive force (e.m.f.) coefficient (S) and high photosensitivity (F). For films deposited by RPLD the S coefficient varied in the range 0.8–1.65 mV/K at 205–322 K. This coefficient depended on the band gap (E _g ) of the semiconductor films, which varied in the range 0.43–0.93 eV. The largest F value found was 44 V_c/W for white light at power density I≅0.006 W/cm². Using LCVD, iron oxide films were deposited from iron carbonyl vapor. For these films, the S coefficient varied in the range −0.5 to 1.5 mV/K at 110–330 K. The S coefficient depended on E _g of the semiconductor films, which varied in the range 0.44–0.51 eV. The largest F value of these films was about 40 V_c/W at the same I≅0.006 W/cm². Our results showed that RPLD and LCVD can be used to synthesize iron oxide thin films with variable stoichiometry and, consequently, with different values of E _g . These films have large S coefficient and high photosensitivity F and therefore can be used as multi-parameter sensors: thermo–photo sensors.     

Magnetic, electrical, and crystallographic properties of thin La1−x SrxMnO3 films

A study is reported of the magnetic, electrical, and crystallographic properties of La_1−x Sr_xMnO₃ (0.15⩽x⩽0.23) epitaxial films grown on single-crystal substrates of (001)ZrO₂(Y₂O₃) having the fluorite structure and (001)LaAlO₃ having the perovskite structure. It was found that films with close compositions for x=0.15 and 0.16, grown on different substrates, have different properties, namely, the film on a fluorite substrate is semiconducting and has a coercive strength 30 times that of the film on a perovskite substrate; the temperature dependence of electrical resistance of the latter film has a maximum around the Curie point T _C and follows metallic behavior for T<T _C. These differences are explained as due to different structures of the films. The x=0.23 film on the perovskite substrate has been found to exhibit a combination of giant magnetoresistance at room temperature with a resistance of ≈300 Ω which is useful for applications. The maxima in resistance and absolute value of negative magnetoresistance are accounted for by the existence of two-phase magnetic states in these films. Fiz. Tverd. Tela (St. Petersburg) 40, 290–294 (February 1998)     

Use of surface acoustic waves for analysis of gases and surface processes induced by them

An analytical expression for the magnitude of the “response” of surface acoustic waves (SAWs) to gases is obtained. It is tested experimentally. The main features of the detection of gases by means of SAWs are predicted theoretically and confirmed experimentally. The SAWs in coated and uncoated gas sensors are compared. A technique for using SAWs to determine the relative changes in the density (Δρ/ρ) and the elastic moduli (ΔC ₁₁/C ₁₁ and ΔC ₄₄/C ₄₄) of films upon the adsorption (desorption) of gases is proposed. The possibility of using this technique to analyze adsorption and desorption processes is demonstrated. The adsorption properties of polycrystalline, thermally deposited palladium films before and after low-temperature vacuum annealing, as well as unannealed Pd and Pd:Ni films, are compared. The prospects of using SAWs to detect gases and to study surface processes induced by them are discussed. Zh. Tekh. Fiz. 68, 73–81 (February 1998)     

Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method

In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction (XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90% in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T _s = 450°C and thickness of the thin films t = 110–130 nm.     

Synthesis and characterization of electron beam evaporated LiCoO<Subscript>2</Subscript> thin films

LiCoO₂ thin films were prepared by electron beam evaporation technique using LiCoO₂ target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10⁻⁴ mbar. The films prepared at substrate temperature T _s < 573 K were amorphous in nature, and the films prepared at T _s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–e_g absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t_2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006