Structural,electrical and optical properties of Cd1−xZnxO thin films and alloying effects on Kβ/Kα intensity ratios

Cd_1?xZn_xO thin films were prepared by spray pyrolysis in air atmosphere on a glass substrate at 250 °C. The Zn content in Cd_1?xZn_xO films was varied from x = 0 to 0.60. Structural, electrical and optical properties of Cd_1?xZn_xO films were investigated by x‐ray diffraction, electrical resistivity and optical transmittance spectra, respectively. As the Zn content in Cd_1?xZn_xO thin films increased, the preferred orientation of the films did not change, only the peak intensity of the planes decreased. In addition to the peaks of CdO, peaks of ZnO were observed in the film with x = 0.6. The resistivity of Cd_1?xZn_xO thin films increased with increasing Zn content. Transmittance spectra studies of films were carried out in the 190‐1100 nm wavelength range and the results showed that the bandgap energy range varied from 2.42 to 3.25 eV. In addition, alloying effect on the Kβ/Kα intensity ratio in Cd_1?xZn_xO semiconductor thin films was studied. It was found that the Kβ/Kα intensity ratio is changed by alloying effects in Cd_1?xZn_xO semiconductor thin films for different composition of x. The results were compared with the theoretical values. Copyright © 2006 John Wiley & Sons, Ltd.     

Electromechanical properties of Ba(Ti1-xZrx)O3 thin films

The electromechanical properties of thin films of barium titanate zirconate were studied with the help of a double-beam interferometer. Thin films of barium titanate zirconate (Ba(Ti_1-xZr_x)O₃) of various compositions (x=0, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4) were deposited by chemical solution deposition on Pt/TiO₂/SiO₂/Si substrates. The thin films show a strain of around 0.05 (at 200 kV/cm) for the unsubstituted BaTiO₃ thin films. For higher Zr substitutions up to 5% the strain increases slightly and subsequently falls to 0.01 at 200 kV/cm for even higher Zr content. The d₃₃ values were found to vary between 30 pm/V and 10 pm/V for 0x0.4. PACS 77.65.-j; 77.55.+f; 77.84.Dy     

Optical constants for Ge30− x Se70Ag x (0 ≤ x ≤ 30 at%) thin films based only on their reflectance spectra

In this paper, different homogenous compositions of Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30 at%) thin films were prepared by thermal evaporation. Reflection spectra, R(λ), for the films were measured in the wavelength range 400–2500?nm. A straightforward analysis proposed by Minkov [J. Phys. D: Appl. Phys. 22 (1989) p.1157], based on the maxima and minima of the reflection spectra, allows us to derive the real and imaginary parts of the complex index of refraction and the film thickness of the studied films. Increasing Ag content at the expense of Ge atoms is found to affect the refractive index and the extinction coefficient of the films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing Ag content, the refractive index increases while the optical band gap decreases. The compositional dependence of the optical band gap for the Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30) thin films is discussed in terms of the chemical bond approach.     

Effect of oxygen partial pressure and VO<Subscript>2</Subscript> content on hexagonal WO<Subscript>3</Subscript> thin films synthesized by pulsed laser deposition technique

We report on the effect of oxygen partial pressure and vacuum annealing on structural and optical properties of pulsed laser-deposited nanocrystalline WO₃ thin films. XRD results show the hexagonal phase of deposited WO₃ thin films. The crystallite size was observed to increase with increase in oxygen partial pressure. Vacuum annealing changed the transparent as-deposited WO₃ thin film to deep shade of blue color which increases the optical absorption of the film. The origin of this blue color could be due to the presence of oxygen vacancies associated with tungsten ions in lower oxidation states. In addition, the effects of VO₂ content on structural, electrochemical, and optical properties of (WO₃)_1−x (VO₂) _x nanocomposite thin films have also been systematically investigated. Cyclic voltammogram exhibits a modification with the appearance of an extra cathodic peak for VO₂–WO₃ thin film electrode with higher VO₂ content (x ≥ 0.2). Increase of VO₂ content in (WO₃)_1−x (VO₂) _x films leads to red shift in optical band gap.     

Crystallization of lead zirconate titanate films by laser annealing

The structure of lead zirconate titanate Pb(Zr _x Ti_{1 ? x} )O₃ thin films grown by chemical solution deposition on Si-SiO₂-Ti-Pt substrates has been studied using transmission electron microscopy and energy-dispersive analysis. Films crystallization has been performed using laser annealing. It has been found that, in contrast to isothermal annealing where nucleation on the platinum layer dominates, crystallization and growth of spherical perovskite crystals occur in the film bulk. The perovskite phase crystal size increases from 10 to 120 nm with increasing laser beam energy.     

Study of aluminium-modified Ge2Sb2Te5 thin films for the applicability as phase-change storage device material

Electrical and optical studies have been carried out on aluminium-modified Ge₂Sb₂Te₅ thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Al_x(Ge₂Sb₂Te₅)_1?x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge–Sb–Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge–Sb–Te alloy films.     

Blue luminescence from Ce-doped ZnO thin films prepared by magnetron sputtering

The photoluminescence properties of undoped and Ce-doped ZnO thin films that were prepared by DC magnetron sputtering were investigated. It was found that the incorporation of Ce could intensively affect the structural, optical, and photoluminescence properties of the ZnO thin films. The undoped ZnO thin films showed a sharp UV luminescence, whereas the Ce-doped ZnO thin films showed a broad blue luminescence. The effects of excitation wavelength and annealing atmosphere on the photoluminescence properties of Ce-doped ZnO thin films were also studied. After post-annealing in air and oxygen atmospheres, the blue emissions of the prepared films were drastically suppressed. Our results indicate that the blue emissions of Ce-doped ZnO thin films are related to zinc interstitials and the intrinsic transition of Ce³⁺ ions.     

Characterization of new quaternary chalcogenide As–Ge–Se–Sb thin films

This paper reports the effect of replacement of selenium by antimony on the optical gap and some other physical parameters of new quaternary chalcogenide As₁₄Ge₁₄Se_{72? x} Sb _x (where x = 3, 6, 9, 12 and 15 at%) thin films. Thin films with thickness 200–220 nm of As₁₄Ge₁₄Se_{72? x} Sb _x were prepared by thermal evaporation of the bulk samples. Increasing antimony content was found to affect the average heat of atomization, the average coordination number, number of constraints and cohesive energy of the As₁₄Ge₁₄Se_{72 ?x} Sb _x alloys. Optical absorption measurements showed that the fundamental absorption edge is a function of composition. Optical absorption is due to allowed, non-direct transition and the energy gap decreases with the increasing antimony content. The chemical bond approach has been applied successfully to interpret the decrease in the optical gap with increasing antimony content.     

Determination of the thickness and optical constants of amorphous Ge–Se–Bi thin films

The effect of varying bismuth concentration on the optical constants of amorphous Ge₂₀Se_{80? x} Bi _x (where x = 0, 3, 6, 9 and 12 at%) thin films prepared by thermal evaporation has been investigated. The transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. An analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 16 (1983) p.1214], based on the use of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing bismuth content was found to affect the refractive index and extinction coefficient of the Ge₂₀Se_{80? x} Bi _x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing bismuth content, the refractive index increases while the optical band gap decreases.     

Electrical resistivity of liquid Sb–Zn alloys

Using the DC four-probe method, temperature dependence of the electrical resistivity (ρ???T) of Sb_{100? x} Zn _x (x?=?25,?40,?50,?57,?61,?80 at%) alloys was investigated in the temperature range of 500–860°C. The results showed that resistivity of each liquid alloy decreased non-linearly with temperature increasing above their liquidus (T _L) until reaching critical temperature, at which the resistivity–temperature coefficients dρ/dT–T converts from negative into positive. The phenomena of liquid phase transformation might relate with the dissociation of covalent bonds, chemical orders and associations in Sb–Zn melts.     

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

The effect of laser irradiation on the optical properties of thermally evaporated Se_100?x Te _x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.     

Phase formation and dielectric properties of (Pb0.925Ba0.075)(Zr1− x Ti x )O3 ceramics prepared by the solid-state reaction method

Lead barium zirconate titanate [(Pb_0.925Ba_0.075)(Zr_{1? x} Ti _x )O₃] ceramics with 0?≤?x?≤?1 were prepared by the solid-state reaction method. The calcination temperatures were between 800°C and 1000°C for 1?h and the sintering temperature was 1200°C for 3?h. It was found that the structure of the calcined powders and sintered pellets was in an orthorhombic phase for x?=?0; a rhombohedral phase for x?=?0.25 and a tetragonal phase for 0.5?≤?x?≤?1. The c/a ratio increased with an increase in the x content. The average particle size and density slightly decreased with an increase in the x content, while the average grain size, linear shrinkage, and Curie temperature increased when the x content increased.     

Theoretical and experimental study on the photoluminescence in BaTiO3 amorphous thin films prepared by the chemical route

A polymeric precursor method was used to synthesize BaTiO₃ amorphous thin film processed at low temperature. The luminescence spectra of BaTiO₃ amorphous thin films at room temperature revealed an intense single-emission band in the visible region. The visible emission band was found to be dependent of the thermal treatment history. Photoluminescence (PL) properties for different annealing temperatures were investigated. It was concluded that the intensity of PL is strongly dependent on both the heat treatment of the films and the presence of an inorganic disordered phase. Experimental optical absorption measurements showed the presence of a tail. These results are interpreted by the nature of these exponential optical edges and tails, associated with defects promoted by the disordered structure of the amorphous material. We discuss the nature of visible PL at room temperature in amorphous barium titanate in the light of the results of recent experimental and quantum mechanical theoretical studies. Our investigation of the electronic structure involved the use of first-principle molecular calculations to simulate the variation of the electronic structure in the barium titanate crystalline phase, which is known to have a direct band gap, and we also made an in-depth examination of amorphous barium titanate.     

Compositional dependence of the optical properties of the amorphous GexTe1−x system

Optical absorption at room temperature of vacuum evaporated Ge_xTe_1−x (0.125?x?0.225) amorphous thin films has been studied as a function of composition. It was found that the optical absorption is due to a direct transition. The real and imaginary parts of the dielectric constant were determined. The single-oscillator energy (E_o) and the energy dispersion parameter (E_d) have been calculated and discussed in terms of the Wemple and Di-Domenico model. The relationship between the optical gap, the average heat of atomization and the coordination numbers has been determined. The optical properties of the amorphous thin films do not change monotonically with increasing Ge content. The observed behavior of the optical properties in the range of compositions studied are explained on the basis of the Bond Constraint Theory (BCT) and rigidity theory, which provide a powerful framework for understanding the structure and properties of amorphous materials. The non-monotonic variation of the optical properties indicates that a transition from floppy to rigid occurs in the Ge_xTe_1−x films.     

Electrical,optical and mechanical properties of PS/GNP composite films

In this study, the electrical, optical and mechanical properties of polystyrene (PS) thin films added graphene nanoplatelet (GNP) have been investigated. Surface conductivity (σ), absorbance intensity (A) and tensile modulus of these composite films have increased with increasing the content of GNP in the composite. The increase in the electrical and optical properties of the PS/GNP composite films has been interpreted by site and classical percolation theory, respectively. The electrical and the optical percolation thresholds of PS/GNP composite films were determined as R_σ?=?23.0?wt.% and R_op?=?13.0?wt.%, respectively. While the conductivity results have been attributed to the classical percolation theory, the optical results have attributed to the site percolation theory. The electrical (β_σ) and the optical (β_op) critical exponents were calculated as 2.54 and 0.40, respectively. The tensile modulus and the tensile strength of the PS/GNP composites increased with the increasing of GNP content in the PS. But, the toughness of the composites fluctuated with GNP addition.     

Electromechanical properties of lanthanum-doped lead hafnate titanate thin films for integrated piezoelectric MEMS applications

This paper focuses on the deposition and electromechanical characterization of lanthanum-doped lead hafnate titanate (PLHT) thin films as key material in piezoelectric microelectromechanical systems (pMEMS). PLHT (x/30/70) and PLHT(x/45/55) films with a thickness between 150 nm and 250 nm were deposited by chemical solution deposition (CSD). Thereby x varies between 0 and 10% La content. The electrical characterization shows that undoped (x=0) PLHT exhibit ferroelectric behavior similar to PZT of the same composition. La doping results in reduced ferroelectric properties and also affects the electromechanical properties. Measurements using a double beam laser interferometer yield a piezoelectric coefficient d ₃₃ of 60 pm/V, which stays constant with an increasing electric field. This leads to a linear displacement compared to undoped PLHT or conventional PZT films used for MEMS applications.     

Effect of composition and thermal annealing on the absorption and electrical conduction of Se85−xTe15Sbx glasses

The optical absorption of the as-prepared and thermally annealed Se_85−xTe₁₅Sb_x (0≤x≤9) thin films was measured. The mechanism of the optical absorption follows the rule of non-direct transition. The optical energy gap (E₀) decreased from 1.12 to 0.84 eV with increasing Sb content of the as-prepared films from 0 to 9 at.%. The as-prepared Se₇₆Te₁₅Sb₉ films showed an increase in (E₀) with increasing the temperature of annealing in the range above T_g (363 K). The electrical conductivity of the as-prepared and annealed films was found to be of Arrhenius type with temperature in the range 300-360 K. The activation energy for conduction was found to decrease with increasing both the Sb content and temperature of annealing. The results were discussed on the basis of the lone-pair electron effect and of amorphous crystalline transformation.     

Effects of high-energy ion-beam irradiation on structural and optical properties of (Mg0.95Co0.05)TiO3 thin films

We report the structural and optical properties of high-energy ion-beam irradiated Co-doped magnesium titanate thin films. (Mg_0.95Co_0.05)TiO₃ (MCT) thin films were deposited on quartz substrates using radio frequency magnetron sputtering. Subsequently, the films were annealed for crystallinity and were irradiated with 100?MeV Ag ions by varying the ion fluence. The X-ray diffraction patterns of the films before and after the irradiation were refined using the Rietveld refinement and the variations in the lattice parameters were correlated with the ion fluence. Although, annealing of thin films results in an enhancement in refractive index and optical bandgap, the ion fluence induces significant changes in the refractive index and optical bandgap. Atomic force microscopy is employed to study the surface morphology of the films. The impact of ion fluence on structural and optical properties of MCT thin films has been investigated.     

Structural,optical, and electrical properties of boron-doped ZnO1-xSx thin films deposited by MOCVD

Boron-doped ZnO_1-xS_x (ZnO_1-xS_x:B) thin films were fabricated by metalorganic chemical vapor deposition (MOCVD). We investigated the structural, optical, and electrical properties of the ZnO_1-xS_x:B thin films. X-ray diffraction patterns showed that, except for the ZnO:B (x?=?0) and ZnS:B (x?=?1) thin films, the ZnO_1-xS_x:B thin films exhibit amorphous characters. Optical transmittance spectra were analyzed to estimate the band gaps of the thin films with different S content. All thin films showed direct band gaps ranging from 3.34?eV (ZnO:B) to 3.49?eV (ZnS:B). The influence of sulfur content on carrier concentration, electrical resistivity, and Hall mobility of the ZnO_1-xS_x:B thin films were analyzed from Hall effect measurements measured at temperatures ranging from liquid nitrogen temperature to room temperature. The ZnO_1-xS_x:B thin films exhibited n-type electrical conductivity except for ZnS:B, which was not measurable in this study due to its high resistivity (>100?Ω?cm).     

Superconducting and magnetic properties of Nb/Pd 1-xFex/Nb triple layers

The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers with constant Nb layer thickness d_Nb=200 ? and different interlayer thicknesses 3 ?≤ d_PdFe ≤ ? are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows that for small iron concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x ≥ 0.13. The parallel critical field B_c2||(T){B_{c2||}}(T) exhibits a transition from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a 2D behavior of decoupled Nb films with increasing d_PdFeand/or x. This transition allows a determination of the penetration depth x_F{\xi _F} of Cooper pairs into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic interlayer x_F{\xi _F} is found to be independent of x.