Crystalline structure and magnetic and magneto-optical properties of MnSbBi thin films

Mn–Sb–Bi thin films were prepared by successive r.f. or d.c. sputter deposition of elements in a trilayer configuration with either Bi or Sb as the first layer. In-situ transmission electron microscopy (TEM) observations were conducted to investigate the morphology and structure of the films, both as-deposited and after annealing at 623 K for 5 h in a high vacuum furnace. The morphology and structure of all the films are highly dependent on the first-deposited layer. For the annealed film in the configuration of Mn/Bi/Sb// a well-defined hexagonal Mn–Sb–Bi NiAs type structure with the c-axis perpendicular to the film surface was observed. The grain size (100 nm) was two times larger than that of the film having Bi as the first layer. In both kinds of film the easy direction of magnetisation was very close to the film plane. The polar Kerr rotation from the two film structures was approximately 1.0°.     

Sol-gel法制备(BiAl)DyIG石榴石磁光记录薄膜

采用柠檬酸络合物型溶胶 凝胶法首次制备得到了具有垂直各向异性的(BiAl)DyIG石榴石磁光记录薄膜,并对材料结构和磁光性质进行了研究,结果得到石榴石磁光记录薄膜磁滞回线具有较好的矩形比,在430nm和520nm的品质因子为2°和1.5°,最佳晶化温度为675℃。     

Nonlinear optical and optical limiting properties of phthalocyanines in solution and thin films of PMMA at 633 nm studied using a cw laser

We present our results on nonlinear optical (NLO) and optical limiting properties of Tetra tert-butyl phthalocyanine and Zinc tetra tert-butyl phthalocyanine studied at 633 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. We have observed low power optical limiting, with low limiting thresholds, based on nonlinear refraction in both the samples. We also present results on the NLO properties of the same dyes doped in Polymethylmethacrylate (PMMA). These studies indicate that both the phthalocyanines are potential candidates for low power optical limiting applications.     

Modeling the optical properties of tin oxide thin films

Searching the many papers reporting on the optical characteristics of tin oxide thin films, an obvious question arises: what is the origin of the very large differences in the reported optical and electrical properties of these films? The objective of the present work is to resolve this question by applying a modeling approach, simulating the refractive index of SnO, SnO₂, SnO + SnO₂, and porous tin oxide films in the visible range of the spectrum under various structure and composition conditions. Using the semi-empirical model of Wemple and DiDomenico for the dielectric function below the interband absorption edge of ionic and covalent solids, and the effective-medium theory of Bruggeman, the refractive indices of SnO, SnO₂, several mixtures of SnO and SnO₂ and various porous tin oxide films were calculated. The resulting data are compared with some published data to suggest the compositional and structural characteristics of the reported oxides. The correlation between the optical properties of the studied thin films and film composition is also indicated. It is proposed that the large spread in reported optical data is possibly a spread in the composition of the samples.     

Electrical and optical properties of copper-complexes thin films grown by the vacuum thermal evaporation technique

In this work, the synthesis and characterization of molecular materials formed from K₂[Cu(C₂O₄)₂], 1,8-dihydroxyanthraquinone and its potassium salt are reported. These complexes have been used to prepare thin films by vacuum thermal evaporation. The synthesized materials were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), fast atomic bombardment (FAB+) mass and ultraviolet–visible (UV–vis) spectroscopy. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.36–0.65 eV, were calculated from their Arrhenius plots. Optical absorption studies in the 100–1100 nm wavelength range at room temperature showed thin films' optical band gaps in the 2.3–3.9 eV range for direct transitions. On the other hand, strong visible photoluminescence (PL) at room temperature was noticed from the thermally-evaporated thin solid films. The PL of all investigated samples were observed with the naked eye in a bright background. The PL and absorption spectra of the investigated compounds are strongly influenced by the molecular structure and nature of the organic ligand.     

Structural, optical and electrical properties of In doped CdO thin films for optoelectronic applications

Thin films of indium doped cadmium oxide were deposited on quartz substrate using pulsed laser deposition technique. The effect of growth temperature and partial oxygen pressure on structural, optical and electrical properties was studied. We find that the optical transparency of the films largely depends on the growth temperature, while partial oxygen pressure has virtually no effect on the transparency of the films. Electrical properties are found to be sensitive to both the growth temperature and oxygen pressure. It is observed that conductivity and carrier concentration decreases with temperature. The film grown at 200 °C under an oxygen pressure of 5.0 × 10^− 4 mbar shows high mobility (155 cm²/V s), high carrier concentration (1.41 × 10²¹ cm³), and low resistivity (2.86 × 10^− 5 Ω cm).     

Structural and optical properties of CdS thin films grown by chemical bath deposition

Cubic cadmium sulphide (CdS) thin films with (111) preferential orientation were prepared by chemical bath deposition (CBD) technique, using the reaction between NH₄OH, CdSO₄ and CS(NH₂)₂. The films properties have been investigated as a function of bath temperature and deposition time. Structural properties of the obtained films were studied by X-ray diffraction analysis. The structural parameters such as crystallite size have been evaluated. The transmission spectra, recorded in the UV visible range reveal a relatively high transmission coefficient (70%) in the obtained films. The transmittance data analysis indicates that the optical band gap is closely related to the deposition conditions, a direct band gap ranging from 2.0 eV to 2.34 eV was deduced. The electrical characterization shows that CdS films' dark conductivities can be controlled either by the deposition time or the bath temperature.     

Electrodeposition and optical properties of silver infiltrated photonic nanostructures

In this work we report about the preparation and optical characterization of technologically relevant silver based nanostructures by metal infiltration of monolayered or opal-like templates of polystyrene (PS) latex spheres. Low toxicity electrolytic baths present obvious advantages and facilitate the synthesis, and are therefore, desirable methods for this kind of processes. Silver was reduced from an environmentally friendly solution based on ethylendiaminetetraacetic acid or EDTA using pulse plating electrochemical methods. The morphology of the deposits may be controlled by the pre-treatment process performed before the electrodeposition. Optical reflectance spectroscopy analysis shows that high quality films may be obtained by this method.     

Effect of cadmium oxide incorporation on the microstructural and optical properties of pulsed laser deposited nanostructured zinc oxide thin films

CdO doped (doping concentration 0, 1, 3 and 16 wt%) ZnO nanostructured thin films are grown on quartz substrate by pulsed laser deposition and the films are annealed at temperature 500 °C. The structural, morphological and optical properties of the annealed films are systematically studied using grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Micro-Raman spectra, UV–vis spectroscopy, photoluminescence spectra and open aperture z-scan. 1 wt% CdO doped ZnO films are annealed at different temperatures viz., 300, 400, 500, 600, 700 and 800 °C and the structural and optical properties of these films are also investigated. The XRD patterns suggest a hexagonal wurtzite structure for the films. The crystallite size, lattice constants, stress and lattice strain in the films are calculated. The presence of high-frequency E₂ mode and the longitudinal optical A₁ (LO) modes in the Raman spectra confirms the hexagonal wurtzite structure for the films. The presence of CdO in the doped films is confirmed from the EDX spectrum. SEM and AFM micrographs show that the films are uniform and the crystallites are in the nano-dimension. AFM picture suggests a porous network structure for 3% CdO doped film. The porosity and refractive indices of the films are calculated from the transmittance and reflectance spectra. Optical band gap energy is found to decrease in the CdO doped films as the CdO doping concentration increases. The PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. The 16CdZnO film shows an intense deep green PL emission. Non-linear optical measurements using the z-scan technique indicate that the saturable absorption (SA) behavior exhibited by undoped ZnO under green light excitation (532 nm) can be changed to reverse saturable absorption (RSA) with CdO doping. From numerical simulations the saturation intensity (I_s) and the effective two-photon absorption coefficient (β) are calculated for the undoped and CdO doped ZnO films.     

Surface morphology and optical properties of magnetron - sputtered ultrathin Al films

Ultrathin Al films with different thicknesses were deposited on glass substrates by DC magnetron sputtering. The effects of film thickness on morphology and optical properties of the films were investigated in detail. When film thickness increases from 7.0 to 84.0 nm, the average grain size and surface roughness enlarges from 27.6 to 94.2 nm and from 0.25 to 1.87 nm, respectively. Below critical thickness of 28.0 nm, which is the thickness that Al films form continuous film, the optical properties vary significantly with thickness increasing and then tend to be stable. In the absorptance spectra, all films exhibit distinct broad peaks which can be attributed to the absorption due to the interband transition. The possible reasons for the shift in the peak position are due to the quantum size effects and internal stress in the ultrathin Al films.     

Effect of thermal annealing time on optical and structural properties of TeO2 thin films

TeO₂ thin films were deposited on quartz substrates by rf reactive sputtering technique from a Te metal target. The obtained samples were annealed in an argon atmosphere at 450 °C for different annealing times up to 90 min. X-ray diffraction studies revealed that the as-grown samples were amorphous and there was no appreciable change in structure for a short annealing time. Thin films became polycrystalline with the tetragonal (α-phase) structure of tellurium dioxide crystal with the increase of the thermal annealing time. The refractive index and optical energy gap of the films were calculated by modelling transmittance spectra. The optical energy gap decreased continuously from 3.83 eV to 3.71 eV with increasing thermal annealing time.     

Doping effects on the optical properties of evaporated a-Si:H films

Thin films of a-Si:H are deposited on substrates at 300°C by a conventional thermal evaporation technique. The electrical conductivity of these films is modified by the addition of antimony giving n-type films. The optical properties of the films are investigated using spectrophotometric measurements of the transmittance and reflectance in the wavelength range 200–3000 nm. Both the refractive index n and the absorption coefficient increase when the Sb content is increased. The absorption edge shifts to lower energies for doped films. The optical gap E_g is evaluated using three different plots for comparison, namely; (hν)^1/2, (/hν)^1/2 and (hν)^1/3. The value of E_g decreases with doping for the three expressions. The Urbach parameter E₀ is calculated and found to increase with doping from 74 meV for the undoped film to 183 meV for concentrations of 9.4 at.% Sb.     

Structural and optical properties of yttria-stabilized-zirconia films grown by MOCVD

The morphology of yttria doped zirconia thin films deposited by metal organic chemical vapour deposition (MOCVD) in two different substrate materials, glassy quartz and sapphire single crystals has been examined. The Y₂O₃ doping concentration has been varied from 3 to 12 mol percent. Structural characterization has been realized by X-ray diffraction, raman spectroscopy and scanning electron microscopy. The structure of the films corresponds to that of bulk crystals of the same composition. Refractive index has been determined by the optical transmission method. Refractive index close to those of bulk crystals are obtained for epitaxially grown zirconia on sapphire substrates, whereas low refractive index values, related with low packing densities, are obtained for thin films in the glassy substrate.     

Spectroscopic ellipsometry investigations of the optical properties of manganese doped bismuth vanadate thin films

The optical properties of Bi₂V_1−xMn_xO_5.5−x {x = 0.05, 0.1, 0.15 and 0.2 at.%} thin films fabricated by pulsed laser deposition on platinized silicon substrates were studied in UV-visible spectral region (1.51-4.17 eV) using spectroscopic ellipsometry. The optical constants and thicknesses of these films have been obtained by fitting the ellipsometric data (Ψ and Δ) using a multilayer four-phase model system and a relaxed Lorentz oscillator dispersion relation. The surface roughness and film thickness obtained by spectroscopic ellipsometry were found to be consistent with the results obtained by atomic force and scanning electron microscopy. The refractive index measured at 650 nm does not show any marginal increase with Mn content. Further, the extinction coefficient does not show much decrease with increasing Mn content. An increase in optical band gap energy from 2.52 to 2.77 eV with increasing Mn content from x = 0.05 to 0.15 was attributed to the increase in oxygen ion vacancy disorder.     

Effect of Al dopants on the structural,optical and gas sensing properties of spray-deposited ZnO thin films

Undoped and Al-doped ZnO thin films were deposited on glass substrates by the spray pyrolysis method. The structural, morphological and optical properties of these films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, photoluminescence (PL) and photoconductivity (PC) measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the crystallite size has been found to be in the range 20–40 nm. SEM and AFM analyses reveal that the films have continuous surface without visible holes or faulty zones, and the surface roughness decreases on Al doping. The Al-doped films have been found to be highly transparent (>85%) and show normal dispersion behavior in the wavelength range 450–700 nm. The doped films show only ultraviolet emission and are found to be highly photosensitive. Among all the films examined, at 300 °C the 1.0 at% Al-doped film shows the selective high response (98.2%) to 100 ppm acetone concentration over to methanol, ethanol, propan-2-ol, formaldehyde and hydrogen.     

Effect of high-temperature annealing on the optical and photoluminescence properties of nanocrystalline SiC films

The optical and photoluminescence (PL) properties of nanocrystalline 3C-SiC films and the effect of the boundary regions between the nanocrystals were studied for two sets of films: (a) films with 10-15 nm nanocrystal size obtained by direct ion deposition method and (b) similar films annealed in oxygen at 850-950 °C. It was shown that annealing of the nanocrystalline SiC films resulted in weaker absorption in a broad spectral range, and to the increase of the optical band gap from 1.8 to 2.2 eV. On the contrary, the edge PL bands in the UV range (2.2 to 2.4 eV) remained similar. In the IR range, three maxima absent in the as-grown films, appeared at 1.52 eV, 1.56 eV and 1.63 eV. Measurement of the intensity of PL maxima as a function of the excitation power showed a nonlinear dependence that was attributed to the onset of stimulated emission.     

Grain size dependent optical band gap of CdI2 films

The thermally evaporated stoichiometric CdI₂ films show goodc-axis alignment normal to substrate plane for film thickness up to 200 nm. The optical absorption data indicate an allowed direct interband transition across a gap of 3.6 eV in confirmation with earlier band structure calculations. However, part of the absorption data near band edge can be fitted to an indirect band gap of 3 eV. The dependence of band gap on film thickness (> 200 nm) can be explained qualitatively in terms of decreasing grain boundary barrier height with grain size.     

Facile synthesis and large third-order optical nonlinearity of Manganese-loaded mesoporous silica thin films

An in-situ reduction method is adopted to incorporate MnO₂ nanoparticles into mesochannels of silica thin films by using KMnO₄ as the oxidizing agent and manganese precursor. As the reduction time in KMnO₄ solution increases, the ordered mesostructure collapses, and the loaded MnO₂ nanoparticles become bigger in size, resulting in a narrower band gap. Z scan measurement demonstrates a large third-order nonlinear susceptibility of the composite films under the picosecond Nd:YAG laser excitation. A sign reversion of the third-order nonlinear refractive index coefficient in the sample with longer reduction time is also observed, which can be attributed to the variation in the band gap energy.     

Intrinsic optical and structural properties of SrS thin films

SrS thin films were deposited by electron beam evaporation on heated silica substrates. The optical properties of the layers – complex refractive index and optical band gap –were derived from optical transmission spectra, measured by means of UV-VIS-NIR spectrophotometry. The influence of post-deposition annealing by rapid thermal processing (RTP) was studied. X-ray powder diffraction (XRD) was used to study the film crystal structure and preferential orientation.