Influence of MgO and ZrO2 buffer layers on dielectric properties of Ba(Zr0.20Ti0.80)O3 thin films prepared by sol-gel processing

Ba(Zr_0.20Ti_0.80)O₃ (BZT) thin films are deposited on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel process. The BZT thin films directly grown on Pt(1 1 1)/Ti/SiO₂/Si substrates exhibit highly (1 1 1) preferred orientation, while the films deposited on Pt(1 1 1)/Ti/SiO₂/Si substrates with MgO and ZrO₂ buffer layers show highly (1 1 0) preferred orientation. At 100 kHz, dielectric constants are 417, 311 and 321 for the BZT thin films grown on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates, respectively. The difference in dielectric properties of three BZT films can be attributed to the series capacitance effect, interface conditions and their orientations.     

Pure UV photoluminescence from ZnO thin film by thermal retardation and using an amorphous SiO2 buffer layer

ZnO/SiO₂ thin films were fabricated on Si substrates by E-beam evaporation with thermal retardation. The as-prepared films were annealed for 2 h every 100 °C in the temperature range 400-800 °C under ambient air. The structural and optical properties were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL). The XRD analysis indicated that all ZnO thin films had a highly preferred orientation with the c-axis perpendicular to the substrate. From AFM images (AFM scan size is 1 μm×1 μm), the RMS roughnesses of the films were 3.82, 5.18, 3.65, 3.40 and 13.2 nm, respectively. PL measurements indicated that UV luminescence at only 374 nm was observed for all samples. The optical quality of the ZnO film was increased by thermal retardation and by using an amorphous SiO₂ buffer layer.     

Preparation of sol-gel ZrO2-SiO2 highly reflective multilayer films and laser-induced damage threshold characteristic

Sol-gel (ZrO₂/SiO₂)¹² ZrO₂ films were prepared by spin coating method. The reflectivity spectrum of the films was measured with a Lambda 900 spectrometer. In order to investigate laser-induced damage threshold (LIDT) characteristic of highly reflective films, one-layer ZrO₂ and SiO₂ films, two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were also prepared by spin coating method. LIDT of each film was measured. Damage morphology after laser irradiation was characterized by optical microscopy (Nikon E600K). The experimental results showed that the reflectivity of (ZrO₂/SiO₂)¹² ZrO₂ film at 1064 nm and 355 nm wavelength is 99.7%. The LIDT results decreases as the number of layer of films increases. All the films have similar damage morphology. The experimental results are explained by the different temperature profiles of the films.     

Synthesis and fine patterning of organic-inorganic composite SiO2-Al2O3 thick films

Organic-inorganic composite SiO₂-Al₂O₃ films have been prepared by sol-gel using methacryloxypropyl trimethoxysilane and aluminum sec-butoxide as the precursors. By introduction of organic groups into the inorganic backbone, the smooth and crack-free films could be readily achieved by a one-step dip-coating process, with the thickness up to 4.6 μm after being post-baked at 200 °C for 2 h. The films presented in an amorphous phase with an acceptable chemical homogeneity. Owing to the formation of chelate rings, the gel films showed a strong photosensitivity to ultraviolet light at 325 nm. The uniform fine patterns of SiO₂-Al₂O₃ thick films could be well defined by ultraviolet light imprinting simply using a mask. These performances of SiO₂-Al₂O₃ films indicate the potential for integrated optical systems.     

IR laser ablation of doped poly(methyl methacrylate)

We investigate the TEA CO₂ laser ablation of films of poly(methyl methacrylate), PMMA, with average M_W 2.5, 120 and 996 kDa doped with photosensitive compounds iodo-naphthalene (NapI) and iodo-phenanthrene (PhenI) by examining the induced morphological and physicochemical modifications. The films casted on CaF₂ substrates were irradiated with a pulsed CO₂ laser (10P(20) line at 10.59 μm) in resonance with vibrational modes of PMMA and of the dopants at fluences up to 6 J/cm². Laser induced fluorescence probing of photoproducts in a pump and probe configuration is carried out at 266 nm. Formation of naphthalene (NapH) and phenanthrene (PhenH) is observed in NapI and PhenI doped PMMA, respectively, with relatively higher yields in high M_W polymer, in similarity with results obtained previously upon irradiation in the UV at 248 nm. Above threshold, formation of photoproducts is nearly complete after 200 ms. As established via optical microscopy, bubbles are formed in the irradiated areas with sizes that depend on polymer M_W and filaments are observed to be ejected out of the irradiated volume in the samples made with high M_W polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies.     

Low cost fabrication of SiO2 optical waveguides by laser direct writing on Ti-doped Sol-Gel films

A commercial direct laser writing (DLW) system operating at 1070 nm was used to fabricate SiO₂ optical waveguides on silicon wafers. A Ti-doped SiO₂ Sol-Gel film was deposited on the SiO₂/Si substrate by the dip-coating technique, based on which SiO₂ optical waveguides were patterned by DLW using a Ytterbium fiber laser and followed by chemical etching. The effects of laser parameters and the preheated temperature of Sol-Gel films on the dimensions of optical waveguides were studied systematically. The differences of etching rate between laser irradiated and non-irradiated areas in Sol-Gel films preheated at various temperatures are characterized by measuring the thickness of the films. Results demonstrate that the available laser power density range for laser densification and the width of the patterned optical waveguides are influenced strongly by the preheated temperature of the Sol-Gel films. The width of the optimized optical waveguide in this work is 25 μm. The minimum propagation loss of the fabricated optical waveguides is 1.7 dB cm⁻¹ at the wavelength of 1550 nm.     

Experimental study of Love-wave immunosensors based on ZnO/LiTaO3 structures

Experimental study of Love-mode immunosensors based on structures of ZnO/36°YX-LiTaO₃ is presented, in which the ZnO films with c-axis (0 0 2) orientation have been successfully grown on the 36°YX-LiTaO₃ substrates by RF magnetron sputtering technique. Then the Love-mode immunosensors based on the ZnO/36°YX-LiTaO₃ structures and monitoring antibody-antigen immunoreactions in aqueous solutions in real time are fabricated. The experimental results show that the optimal thickness of ZnO layers is about 1.20 μm in the structures deposited on 36°YX-LiTaO₃ substrates, which is much less than that of SiO₂ overlayers about 6 μm. The antibody-antigen immunoreaction experiments also show that the frequency shifts of the sensors with 1.33 μm ZnO films are proportional to the concentration of antigen in solution as the concentration range less than 100 μg/ml.     

硅基光波导芯层材料及波导分束器的制备

本文采用溶胶－凝胶法制备了具有紫外感光性的SiO2/ZrO2/H有机无机复合薄膜,利用分光式椭偏仪测得该薄膜在光纤的常用通信窗口0.85 μm、1.31 μm和1.55 μm波长附近折射率分别为1.556 9、1.548 9和1.547 2,与下包层SiO2的折射率（1.46）相比,其折射率差比δ分别为6.64％,6.09％和5.97％,可作为芯层材料用于光波导的制备.通过控制提拉速率可以制作出厚度分别为1.29,2.20,4.00,5.44和6.82 μm的SiO2/ZrO2/H芯层薄膜,以满足0,1,2,3和4阶导模的传输要求.进而利用该薄膜自身的感光特性结合紫外掩模法,制备出相应厚度的1×8Y分支光功率分配器.通光实验表明,该光功分器能够将1.53～1.56 μm波长的光限制在波导内,实现光的传输和分束功能.     

Enhanced dielectric properties of lead barium zirconate thin films by manganese doping

(Pb_0.5Ba_0.5)ZrO₃ (PBZ) and 1 mol% Mn-doped (Pb_0.5Ba_0.5)ZrO₃ (Mn-PBZ) sol were successfully fabricated, and corresponding thin films were deposited on Pt(1 1 1)/TiO₂/SiO₂/Si(1 0 0) substrates by spin-coating method. Effects of Mn doping on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction patterns showed that both films had a polycrystalline perovskite structure, and that the degree of (1 1 1) orientation were increased by Mn doping. Dielectric measurements illustrated that Mn-doped PBZ thin films not only had a larger dielectric constant, but also possessed a smaller dielectric loss. Accordingly, the tunability and the figure of merit of PBZ films were improved by Mn doping.     

Synthesis of bamboo-leaf-shaped ZnO nanostructures by oxidation of Zn/SiO2 composite films deposited with radio frequency magnetron co-sputtering

Bamboo-leaf-shaped ZnO nanostructures were synthesized by oxidation of metal Zn/SiO₂ matrix composite thin films deposited on Si(1 1 1) substrates with radio frequency magnetron co-sputtering. The synthesized bamboo-leaf-shaped ZnO are single crystalline in nature with widths ranging from 30 to 60 nm and lengths of up to 5-10 μm, room temperature photoluminescence spectrum of the nanostructures shows a strong and sharp UV emission band at 372 nm and a weak and broad green emission band at about 520 nm which indicates relatively excellent crystallization and optical quality of the ZnO nanostructures synthesized by this novel method.     

Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OⁱPr)₂(tbaoac)₂] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has -CH₃ terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO₂ and ZrO₂ were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300-500 °C and deposition pressure of 1×10⁻³-3×10⁻² Torr. N₂ gas (5 sccm) was used as a carrier gas during film depositions. TiO₂ and ZrO₂ thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO₂ or Si-OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.     

Microstructure of microwave dielectricthin films by RF magnetron sputtering

The article describes the microstructure and morphological properties of microwave dielectric ceramic thin films. These thin films were successfully prepared on SiO₂ (1 1 0) single-crystal substrates by radio frequency magnetron-sputtering system. The microstructure and morphology of the thin films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The results show that the main phase is Ba_0.5Sr_0.5Nb₂O₆,which has a tetragonal perovskite structure, a long strip pattern, and uniform crystal-grain size of about 2-3 μm in length when annealed under 1150 °C for 30 min in an O₂ atmosphere. These thin films are of excellent crystallization quality, with a polycrystalline and dense structure.     

XPS investigation of diffusion of two-layer ZrO2/SiO2 and SiO2/ZrO2 sol–gel films

Two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO₂/SiO₂ and SiO₂/ZrO₂ films. To explain the difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films, porous ratio and surface morphology of monolayer SiO₂ and ZrO₂ films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO₂/SiO₂ films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO₂/ZrO₂ films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO₂ layer had diffused through the entire SiO₂ layer. The difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films was influenced by the microstructure of SiO₂ and ZrO₂.     

Effects of substrates on the structure and dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were grown on Pt(1 1 1)/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The BTS thin films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si and annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates exhibited strong (1 1 1) and perfect (1 0 0) orientations, respectively. The BTS thin films grown on un-annealed Pt(1 1 1)/Ti/SiO₂/Si substrates showed random orientation with intense (1 1 0) peak, while the films deposited on un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate exhibited random orientation with intense (1 0 0) peak, respectively. The dielectric constant of the BTS films deposited on annealed Pt(1 1 1)/Ti/SiO₂/Si, annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si, un-annealed Pt(1 1 1)/Ti/SiO₂/Si and un-annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates was 512, 565, 386 and 437, respectively, measured at a frequency of 100 kHz. A high tunability of 49.7% was obtained for the films deposited on annealed LNO/Pt(1 1 1)/Ti/SiO₂/Si substrate, measured at the frequency of 100 kHz with an applied electric field of 200 kV/cm. The high tunability has been attributed to the (1 0 0) texture of the films and larger grain sizes.     

Fabrication of TiO2 μ-donuts by sol-gel spin coating using a polymer mask

TiO₂ μ-donuts have been fabricated on glass and silicon substrates using polymer masks in combination with a sol-gel technique. Cylindrical poly(methyl methacrylate) (PMMA) nanopillars have been created using a composite polymer of polystyrene (PS) and PMMA followed by careful removal of the PS. Atomic force microscopy (AFM) analyses show that the height and diameter of the PMMA cylinders used as the mask are 440 ± 5 nm and 2.1 ± 0.2 μm, respectively. The cylindrical PMMA nanopillars have been coated with the sol of the TiO₂ precursor by a spin coating technique and annealed in air at elevated temperature to remove the PMMA mask. Removal of the PMMA mask has resulted in the formation of well ordered μ-donuts of TiO₂ on silicon surfaces. The interior and exterior heights of the TiO₂ μ-donuts are found to be 373 ± 152 nm and 457 ± 136 nm, respectively; and the interior and exterior diameters of the TiO₂ μ-donuts are found to be 1.33 ± 0.63 μm and 2.82 ± 0.50 μm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of the TiO₂ μ-donuts as well as the smooth TiO₂ thin film showed signals from Ti and O confirming the presence of TiO₂ with Ti 2p_3/2 and O 1s peaks at 458.8 eV and 530.4 eV, respectively. The O 1s peak of the TiO₂ μ-donuts shows another peak at binding energy 532.0 eV due to SiO₂, as during annealing, the PMMA evaporates and the Si substrate is exposed. The X-ray diffractometer (XRD) pattern of the smooth TiO₂ thin film indicates that the anatase phase is present, with the characteristic peaks observed at 2θ values of 25.4°, 37.4°, and 48° corresponding to (1 0 1), (0 0 4), and (2 0 0) planes, respectively. UV-vis absorption spectra of TiO₂ μ-donuts on glass showed an unusual absorption of light in the visible region at ∼524 nm in addition to the usual UV absorption at ∼337 nm.     

Infrared optical properties of Ba(Zr0.20Ti0.80)O3 and Ba(Zr0.30Ti0.70)O3 thin films prepared by sol-gel method

Ba(Zr_xTi_1−x)O₃ (BZT) (x = 0.20 and 0.30) thin films are deposited on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrate by sol-gel method. X-ray diffraction patterns show that the thin films have a good crystallinity. Optical properties of the films in the wavelength range of 2.5-12 μm are studied by infrared spectroscopic ellipsometry (IRSE). The optical constants of the BZT thin films are determined by fitting the IRSE data using a classical dispersion formula. As the wavelength increases, the refractive index decreases, while the extinction coefficients increase. The effective static ionic charges are derived, which are smaller than that in a purely ionic material for the BZT thin films.     

The structure and optical properties of evaporated Samarium fluoride films

Samarium fluoride (SmF₃) films have been deposited on quartz, silicon and germanium substrates by vacuum evaporation method. The crystal structure of the films deposited on silicon substrate is examined by X-ray diffraction (XRD). The films deposited at 100 °C, 150 °C and 250 °C have the (1 1 1) preferred growth orientation, but the film deposited at 200 °C has (3 6 0) growth orientation. The surface morphology evolution of the films with different thickness is investigated with optical microscopy. It is shown that the microcrack density and orientation of thin film is different from that of thick film. The transmission spectrum of SmF₃ films is measured from 200 nm to 20 μm. It is found that this material has good transparency from deep violet to far infrared. The optical constants of SmF₃ films from 200 nm to 12 μm are calculated by fitting the transmission spectrum of the films using Lorentz oscillator model.     

Texture development and magnetic properties of [ZrO2/CoPt]n/Ag nanocomposite films

The L1₀ CoPt films with (0 0 1) preferred orientation are achieved by fabricating on the glass substrates and post annealing at 600° C for 30 min. The preferred orientation of [ZrO₂/CoPt]_n/Ag films dependence of the Ag underlayer thickness, ZrO₂ and CoPt interlayer thickness is investigated. A large perpendicular magnetic anisotropy and a nearly perfect L1₀ CoPt (0 0 1) texture are obtained in the [ZrO₂ (3 nm)/CoPt (5 nm)]₃/Ag (10 nm) film. The existence of ZrO₂ plays an important role in reducing the intergranular interactions and in determining the size of CoPt grains. Magnetic reversal in textured CoPt films are close to a Stoner-Wolfarth rotation.     

Effect of indium doping on photoelectrochemical properties of Cd0.9Zn0.1Se photosensitive films

Indium doped Cd_0.9Zn_0.1Se films have been synthesized by chemical bath deposition method. The deposited films act as photoanode in photoelectrochemical (PEC) cells. The varying concentration of indium from 0.01 to 1.0 mol% was used. The film thickness increases from 0.72 to 0.80 μm as doping concentration increases up to 0.1 mol%, thereafter it decreases. The cell configuration is n-Cd_0.9Zn_0.1Se:In|NaOH (1 M)+S (1 M)+Na₂S (1 M)|C_(graphite). The various performance parameters were examined with respect to doping concentration of indium. It is found that fill factor and efficiency is maximum for 0.1 mol% indium photosensitive films. This is due to low resistance, high flat band potential, maximum open circuit voltage as well as maximum short-circuit current. The barrier height was examined from the temperature dependence of the reverse saturation current. The lighted ideality factor was found to be minimum for 0.1 mol% indium photosensitive films. A cell utilizing doping photosensitive films showed a wider spectral response. The utility of this work is in improving efficiency of the PEC cell.     

Optical and gas sensing properties of thick TiO2 films grown by laser deposition

In this work the optical and the gas sensing properties of thick TiO₂ waveguide films, produced by pulsed laser deposition, were investigated by m-line spectroscopy. The films were deposited on (0 0 1) SiO₂ substrates at temperature of 100 °C. The thickness of the films was measured to be in the range from 650 to 1900 nm and the roughness increases from 5 to 14.6 nm. High quality mode spectra, consisted of thin and bright TE and TM modes, were observed in the films with thickness up to 1200 nm. All the films revealed anisotropic optical properties. Gas sensitivity of the films to CO₂ was examined at room temperature on the basis of the variations of the refractive index. CO₂ concentration of 3 × 10⁴ ppm was detected, which corresponds to a refractive index variation of about 1 × 10⁻⁴. The crystal structure and the optical transmittance of the films were also presented and discussed.