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.     

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.     

Effect of Zr (IV) doping on the optical properties of sol–gel based nanostructured indium oxide films on glass

Zr (IV) doped indium oxide thin films (55 nm) were deposited onto pure silica glass by the sol–gel dip coating technique utilizing the precursors of 6 wt% equivalent oxide content. Three different Zr (IV) oxide (ZrO₂) dopant concentrations (5.0, 10.0 and 15.0 wt% w.r.t. total oxides) were chosen. XRD patterns suggested the films were of distinct cubic symmetry of In₂O₃. Nanostructured surface feature was revealed by FESEM images. Average cluster size decreased with increasing dopant concentration as evidenced from TEM study. Blue shift of band gap and UV cut off wavelength (lambda-50) occurred with increase in dopant concentration. The refractive index gradually increased with doping. Baking atmosphere plays an important role in tailoring the refractive index (RI) of the films and relatively high RI was obtained in the case of baking in pure oxygen. Presence of both free and bound excitons was detected by the photoluminescence (PL) study. The 5 wt% doped film exhibited relatively high PL intensity at 380 nm responsible for free exciton. The PL emissions gradually quenched with increase in dopant concentration. Similar behaviour was also observed when the film was baked in pure oxygen atmosphere.     

Stability,UV shielding properties,and light conversion behavior of Eu(BMDM)3@polysiloxane nanoparticles in water and polyurethane films

Bifunctional Eu(BMDM)₃@polysiloxane nanoparticles were prepared through reprecipitation–encapsulation methods using 1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione (BMDM) ligand and octyltrimethoxysilane (OTS) precursor and embedded into waterborne polyurethane (PU) coatings to fabricate transparent optical composite films. The photostability and thermostability of the nanoparticles in water and their ability to block UV and convert light when embedded in PU films were investigated. In comparison with the control Eu(BMDM)₃ nanoparticles, the Eu(BMDM)₃@polysiloxane nanoparticles, especially those prepared at a Eu(BMDM)₃/OTS mole ratio of 1:2, exhibited far superior stability under storage conditions, UV irradiation, and heating. They also showed excellent UV-shielding and highly efficient light conversion properties because of the protective polysiloxane.     

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.     

Poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (3,4-ethylenedioxythiophene)-few walled carbon nanotube (PEDOT-FWCNT) nanocomposite based thin films for Schottky diode application

Transparent, conductive films of poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (3,4-ethylenedioxythiophene)-few walled carbon nanotube (PEDOT-FWCNT) nanocomposite were synthesized by in-situ oxidative polymerization and investigated for their Schottky diode property. The prepared films were characterized by UV–Vis spectroscopy, thermal gravimetric analysis (TGA), surface resistivity, cyclic voltametery, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). SEM reveals the formation of homogeneous and adhesive polymer films while HRTEM confirms the uniform wrapping of polymer chains around the nanotube walls for PEDOT-FWCNT film. Improved thermal stability, conductivity and charge storage property of PEDOT in the presence of FWCNT is observed. Among different compositions, 5 wt. % of FWCNT is found to be optimum with sheet resistance and transmittance of 500 Ω sq⁻¹ and 77%, respectively. Moreover, the electronic and junction properties of polymer films were studied and compared by fabricating sandwich type devices with a configuration of Al/PEDOT or PEDOT-FWCNT nanocomposite/indium tin oxide (ITO) coated glass. The measured current density-voltage characteristics show typical rectifying behavior for both configurations. However, enhanced rectification ratio and higher forward current density is observed in case of PEDOT-FWCNT based Schottky diode. Furthermore, reliability test depicts smaller hysteresis effect and better performance of PEDOT-FWCNT based diodes.     

Preparation of mixed (Cd,Bi)S composite thin films via surfactant facilitated electrodeposition process and their photoelectrochemical characterization

In the present investigation we explored possibilities of preparing mixed CdS–Bi₂S₃ composite thin films of nanodimensions using a single step surfactant facilitated electrochemical process from aqueous solutions containing different colloidal concentrations of CdS and Bi₂S₃ particles. As deposited composite thin films has been characterized on the basis of SEM, AFM and XRD studies for determination of their surface morphology, surface roughness and grain size. Photoelectrochemical characterization of these composite materials has been carried out on the basis of photopotential, current–voltage (I–V) characteristics under dark and illumination conditions and photoaction spectral studies. Attempt has also been made to estimate the resistance of these composite materials towards their electrochemical corrosion. As prepared mixed (Cd,Bi)S composite semiconductor film exhibits substantial improvement in their photoelectrochemical properties.     

The effect of aggregation on the nonlinear optical absorption performance of indium and gallium phthalocyanines in a solution and co-polymer host

The nonlinear optical properties (NLO) of Pcs can be modified by substituting different metal atoms into the ring or altering peripheral and axial functionalities. In this study, nonlinear optical absorption properties of tetra-substituted gallium and indium phthalocyanine complexes both in solution and polymeric film have been investigated by open aperture Z-scan measurements with nanosecond pulses at 532 nm. All investigated compounds exhibited reverse saturable absorption for both solution and film experiments. The investigated compounds in the solution showed better nonlinear optical absorption properties than polymeric films. The observed nonlinear optical absorption differences depending on the aggregation are discussed using the ultrafast dynamics and decay processes of excited states found from femtosecond pump-probe spectroscopy with white light continuum experiments.     

Novel transparent and flexible nanocomposite film prepared from chrysotile nanofibres

In the present study, chrysotile nanofibres, obtained from physicochemical dispersion of natural chrysotile, were used to prepare nanofibre sheets by vacuum filtration. As-prepared sheets were then impregnated by UV-curable resin and cured by ultraviolet light to fabricate the flexible and transparent nanocomposite films. Observed from SEM, the transparent films showed a smooth surface and a typical sandwich structure in cross section, viz. nanofibre sheet filled with resin was sandwiched by two layers of resin. XRD patterns indicated the amorphous nature of cured resin and characteristic crystallographic structure of chrysotile in nanocomposite films. Though the nanofibre sheets were white in colour, and nanofibre contents in nanocomposites were as much as 43.4 wt%, the nanocomposite films displayed an excellent optical transparency with about 85% light transmittance in the visible light range. Tensile tests showed that the addition of nanofibres resulted in a great improvement in mechanical strength of the nanocomposite films; with the increase of nanofibre contents, the modulus and tensile strength of nanocomposite films increased gradually.     

Cu2O nanorod thin films prepared by CBD method with CTAB: Substrate effect,deposition mechanism and photoelectrochemical properties

Cuprous oxide (Cu₂O) films with different nanostructures are deposited on different substrates of fluorine-doped SnO₂ (FTO) glass, Cu and Ti foil respectively by using chemical bath deposition (CBD) technique with the presence of cetyltrimethylammonium bromide (CTAB). The samples are characterized by X-ray diffractmeter, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The results show that the prepared Cu₂O films are composed of nanorod arrays when there is CTAB in reaction system. Without CTAB, Cu₂O films with nanospheres are formed. The concentration of CTAB is crucial for the controllable synthesis of nanorod structured Cu₂O films with different length to diameter ratio and nanorod array density is dependent on both substrates and CTAB. A possible mechanism for the formation of Cu₂O nanorods is discussed. Additionally, the UV–vis absorption property for Cu₂O nanorods is much better than that for nanospheres. The photovoltage produced under visible light for Cu₂O nanorod films is higher than that for the nanospheres. Although Cu₂O nanorods on Ti foil can absorb the most visible light, those on Cu foil demonstrate better and more stable photoelectrochemical property than those on any other substrates. This study may be extremely useful for Cu₂O based device with nanostructures.     

Preparation and characterization of CuO nanostructures on copper substrate as selective solar absorbers

Selective solar absorber coatings of copper oxide (CuO) on copper substrates are prepared by room temperature oxidation of copper at different alkaline conditions. The surface morphology and structural analyses of the CuO coatings are carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Raman spectroscopy techniques. XRD and Raman studies indicated the single phase nature and high crystallinity of the prepared CuO nanostructures. Different CuO nanostructures, viz., nanoneedles, nanofibers and nanoparticles are formed at different alkaline conditions. The influence of reaction time on morphology of the CuO nanostructures is also studied. The thermal emittance values of these nanostructured CuO samples are found to be in the range of 6–7% and their solar absorptances are ranged between 84 and 90%. The observed high solar selectivity values (>12.7) suggest that these coatings can be used as selective absorbers in solar thermal gadgets.     

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.     

Novel transparent ternary nanocomposite films of trialkoxysilane-capped poly(methyl methacrylate)/zirconia/titania with incorporating networks

Novel ternary nanocomposite trialkoxysilane-capped poly(methyl methacrylate)/zirconia/titania optical films were successfully prepared through a nonaqueous in situ sol–gel method. The acrylic monomers used were methyl methacrylate (MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). PMMA/ZrO₂–TiO₂ incorporating networks formed from alcoholysis of poly(MMA-co-MSMA), zirconium n-butoxide and titanium isoproproxide. The structure, morphology and property of the obtained nanocomposite films were investigated by X-ray photoelectron spectra, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, scanning probe microscopy, thermogravimetric analyses, UV–vis spectrum and spectro-ellipsometer. The nanoparticle size, roughness, thermal stability, UV-shielding property, and refractive index of nanocomposite films increase with the increasing of inorganic contents. The formation mechanism and reason of such improvements were examined and interpreted in a theoretical model. The nanocomposite films possess interesting properties in thermal stability and optical response due to the uniform incorporating networks between organic polymer chains and inorganic clusters.     

Facile synthesis and optical band gap calculation of Mn3O4 nanoparticles

Mn₃O₄ nanoparticles were prepared by a simple solid state decomposition method. Four manganese benzoic acid complexes were synthesized through semi-solid phase reaction method as precursors for the preparation of Mn₃O₄ nanoparticles. The calcination temperature of the precursors was determined from thermal gravimetrical analyses (TGA). The resulting nanoparticles were characterized by XRD, SEM, STM and HRTEM. The obtained particle size is in the range 39–90 nm. HRTEM indicated the formation of spherical nanoparticles. The optical absorption measurements for the obtained nanoparticles showed that the fundamental absorption edge obeys Tauc's relation for the allowed direct transition. It was found that, the optical band gap (E_g) increases with the decrease of the particle size of the Mn₃O₄ nanoparticles.     

Sub-nanomolar sensing of ionic mercury with polymeric electrospun nanofibers

Ethyl cellulose (EC) based electrospun nanofibers were exploited for sub-nanomolar level optical chemical sensing of ionic mercury. An azomethine ionophore was used as Hg (I) and Hg (II) sensing material. Ethyl cellulose nanofibers with varying amounts of the ionic liquid; 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) were prepared and characterized. The nanofibers were fabricated by electrospinning technique. The offered chemosensor allow determination of mercury ions in a large linear working range between 1.0 × 10⁻¹⁰ and 1.0 × 10⁻⁴ mol L⁻¹. Limit of detection was found to be 0.07 nM which makes this technique alternative to cold-vapor atomic absorption spectrometry (CV-AAS), flame emission methods and to inductively coupled plasma-mass spectrometry (ICP-MS).     

Absorption and photoreflectance spectroscopy of zinc phthalocyanine (ZnPc) thin films grown by thermal evaporation

Optical properties of the as-deposited and annealed ZnPc layers have been investigated using absorption, reflectance and modulated photoreflectance methods. The absorption coefficient of ZnPc layers was directly determined from the transmission and reflection spectra. The absorption spectra were analyzed in terms of the mixed Lorentz–Lorenz model. We found that annealing thin layers at 580 K caused a structural transformation, which results in the decrease of the absorption coefficient and the shifting of all peak position to lower energies except for the peak of the N-band. Photoreflectance spectroscopy confirmed that there exist three transitions in the Q-band region of the studied material. Complex refractive index and dielectric constants of the ZnPc layer were directly found from the spectral data.     

光学材料和光学薄膜的光热表征(英文)

光热技术用来测量样品的光学和热特性。简要介绍了光热技术及其在光学薄膜测量和钛蓝宝石激光晶体表征中的应用。光热技术可以提供纯光学光谱学所无法提供的、类似光-热能量转换效率之类的信息。光热技术已被用作质量测试和改善现代光学制造的有用工具。     

VO2 thin films deposited on silicon substrates from V2O5 target: Limits in optical switching properties and modeling

Thermochromic VO₂ thin films presenting a phase change at T_c = 68 °C and having variable thickness were deposited on silicon substrates (Si-001) by radio-frequency sputtering. These thin films were obtained from optimized reduction of low cost V₂O₅ targets. Depending on deposition conditions, a non-thermochromic metastable VO₂ phase might also be obtained. The thermochromic thin films were characterized by X-ray diffraction, atomic force microscopy, ellipsometry techniques, Fourier transform infrared spectrometry and optical emissivity analyses. In the wavelength range 0.3 to 25 μm, the optical transmittance of the thermochromic films exhibited a large variation between 25 and 100 °C due to the phase transition at T_c: the contrast in transmittance (difference between the transmittance values to 25 °C and 100 °C) first increased with film thickness, then reached a maximum value. A model taking into account the optical properties of both types of VO₂ film fully justified such a maximum value. The n and k optical indexes were calculated from transmittance and reflectance spectra. A significant contrast in emissivity due to the phase transition was also observed between 25 and 100 °C.     

Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film

Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter.