Nanostructured Silicon Oxide–Nickel Oxide Sol–Gel Films with Enhanced Optical Carbon Monoxide Gas Sensitivity

Sol–gel derived silica (SiO₂) films doped with nickel oxide (NiO) nanocrystals were fabricated. A bifunctional ligand was used, bearing amine groups capable of coordinating the nickel ions and hydrolysable siloxane groups for anchoring the metal complex moiety to the silicate matrix. Nickel oxide nanocrystals precipitated at 500°C while the film was still porous. The nanocomposite films showed a reversible change in the optical transmittance in the VIS-NIR range when exposed to carbon monoxide gas. The effects of residual porosity, testing temperature, and carbon monoxide gas concentration on optical transmittance were studied.     

Chemical Solution Deposition of Columnar-Grained Metallic Lanthanum Nitrate Thin Films

Columnar and (100)-oriented LaNiO₃ thin films were prepared on silicon substrates by a chemical solution deposition (CSD) process using a 0.05 M solution. By reducing the individual layer thickness to 10 nm, columnar LaNiO₃ films with a lateral grain size of ∼120 nm were obtained. The success of this approach required restricting the individual layer thickness to a value below the grain size observed for equiaxed films. This change in microstructure resulted in an improvement in conductivity. The columnar LaNiO₃ film with a thickness of 300 nm showed a resistivity of 4.5 × 10⁻⁵Ω·cm, which is lower by one order of magnitude than that of fine-grain equiaxed films that typically result from CSD methods.     

Large Piezoelectricity and Ferroelectricity in Mn‐Doped (Bi0.5Na0.5)TiO3‐BaTiO3 Thin Film Prepared by Pulsed Laser Deposition

Mn‐doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (MnBNBT) thin films were prepared on SrRuO₃ (SRO)‐coated (001) SrTiO₃ (STO) single crystal substrates by pulsed laser deposition under different processing conditions. Structural characterization (i.e., XRD and TEM) confirms the epitaxial growth of STO/SRO/MnBNBT heterostructures. Through the judicious control of deposition temperature, the defect level within the films can be finely tuned. The MnBNBT thin film deposited at the optimized temperature exhibits superior ferroelectric and piezoelectric responses with remanent polarization P_r of 33.0 μC/cm² and piezoelectric coefficient d₃₃ of 120.0 ± 20 pm/V.     

Sol-gel route to nanocrystalline Eu2Ti2O7 films with tailored structural and optical properties

We present a generic sol-gel approach for the preparation of highly transparent europium titanate Eu₂Ti₂O₇ films with tailored structural and optical properties. The films were prepared by a sol-gel process and thermally treated in a rapid thermal annealing furnace. We determined the effects of the annealing temperature on structural, morphological, and optical properties of the films. We evaluated film's optical constants. The size of the primary nanocrystals and the film's refractive index were tailored by the annealing temperature. The crystallization of Eu₂Ti₂O₇ started at 800°C and the nanocrystals grew with increasing annealing temperature reaching the size from 20 nm to 100 nm. The energy of nanocrystal growth was 21 ± 3 kJ·mol⁻¹. Increasing nanocrystal size caused the regular growth of the refractive index recorded at 632 nm from 2.07 to 2.17 for the films annealed at 800°C and 1200°C, respectively. These results provide fundamental information about the effects of the structure and the morphology of the films on their optical properties. The presented approach can be extended to other rare earth-doped titanates and these films can be used as passive protective coatings as well as active materials suitable for photonic and spintronic applications.     

Control of Crystal Orientation and Piezoelectric Response of Lead Zirconate Titanate Thin Films Near the Morphotropic Phase Boundary

PbZr_0.53Ti_0.47O₃ (PZT) thin films with various preferred crystallographic orientations were synthesized on various substrates using pulsed laser deposition techniques. Larger piezoelectric displacement, which involved the bending vibration of the PZT film/substrate, was observed in randomly oriented PZT thin film than that in (100)- and (111)-preferred texture films. This result was discussed by correlation with the number of effective spontaneous polarization axes in the morphotropic phase boundary of the PZT system. Moreover, polarization fatigue was found to lower the electric-field-induced displacement significantly, indicating a large contribution of ferroelectric domain motion to the piezoelectric response of PZT thin films under bipolar drive.     

薄膜厚度对Al掺杂ZnO薄膜性能的影响

采用直流磁控溅射技术,以氧化锌铝陶瓷靶为靶材,在玻璃衬底上制备了ZnO：Al（ZAO）薄膜样品。在其他参数不变的情况下,由不同溅射时间得到了不同厚度的薄膜,研究了薄膜的结构性质、电学和光学性质随薄膜厚度的变化关系。实验结果表明：在薄膜厚度为500 nm时,ZAO薄膜具有最优化的光电性能,电阻率为1.68×10-3Ω.cm,可见光区平均透射率为90.3%。     

Visible Frequency Thin Film Photonic Crystals from Colloidal Systems of Nanocrystalline Titania and Polystyrene Microspheres

This work describes a simple and novel ceramic processing technique to form periodic ordered structures in ceramic materials with a uniform pore size distribution. This material shows photonic gaps at visible/near-IR wavelengths. Monodisperse colloidal polystyrene microspheres are self-organized into a crystalline structure of close-packed spheres in a suspension of nanocrystalline titania. The nanoparticle titania fills the intersphere region simultaneously during colloidal crystallization. Removal of the polystyrene microspheres by calcination at a temperature of 520°C results in a periodic porous structure with a high refractive index background material. Crystals having ordered regions, a few millimeters across with typical grain sizes of 50–70 μm, are grown as thin films on substrates including glass and silicon. Optical reflectivity measurements indicate peaks at the stop band wavelengths that scale with the pore size. Visual inspection and optical microscopy reveal uniform colored regions for crystals with periodicity comparable to visible wavelengths. Despite the presence of cracks resulting from drying and heat treatment as well as numerous grain boundaries, optical characterization clearly demonstrates a photonic band gap. Reflectance peaks due to a pseudogap can be shifted by application of high pressure. In the following sections we will describe the experimental procedure and discuss optical reflectance and transmission measurements that can reveal information about the crystals, namely, the lattice constant, the refractive index, and the filling fraction of the background material.     

Metastable Tantalum Oxide Formation During the Devitrification of Amorphous Tantalum Thin Films

Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright‐field imaging, and electron‐diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO₂ phase. While the appearance of these phases indicated the films were evolving to the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. New insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide‐based dielectric materials for novel memristor designs.     

Amorphous Ge‐Sb‐Se thin films fabricated by co‐sputtering: Properties and photosensitivity

Amorphous Ge–Sb–Se thin films were fabricated by a rf‐magnetron co‐sputtering technique employing the following cathodes: GeSe₂, Sb₂Se₃, and Ge₂₈Sb₁₂Se₆₀. The influence of the composition, determined by energy‐dispersive X‐ray spectroscopy, on the optical properties was studied. Optical properties were analyzed based on variable angle spectroscopic ellipsometry and UV‐Vis‐NIR spectrophotometry. The results show that the optical bandgap range 1.35‐2.08 eV with corresponding refractive index ranging from 3.33 to 2.36 can be reliably covered. Furthermore, morphological and topographical properties of selenide‐sputtered films studied by scanning electron microscopy and atomic force microscopy showed a good quality of fabricated films. In addition, structure of the films was controlled using Raman scattering spectroscopy. Finally, irreversible photoinduced changes by means of change in optical bandgap energy and refractive index of co‐sputtered films were studied revealing the photobleaching effect in Ge‐rich films when irradiated by near‐bandgap light under Ar atmosphere. The photobleaching effect tends to decrease with increasing antimony content.     

In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

有序介孔二氧化硅薄膜的制备及性能

以十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯为无机前驱体,在酸性条件下,采用溶胶-凝胶技术,用蒸发诱导自组装(EISA)工艺制备了二氧化硅透明介孔薄膜. 透射电子显微镜图显示热处理后的薄膜具有高度有序的六方相结构孔道;由椭偏仪测得热处理后薄膜的折射率低至1.18,厚度在180 nm左右;阻抗分析仪测得薄膜的介电常数为2.14. 薄膜经过六甲基二硅胺烷(HMDS)表面修饰后具有良好的疏水性能和热稳定性,作为低介电材料能更好满足工业需求.     

Optical and Mechanical Properties of Thin PTFE Films,Deposited from a Gas Phase

Thin polytetrafluoroethylene (PTFE) films are produced by deposition from a gas phase by two methods: electron-enhanced vacuum deposition (EVD) and EVD + low-temperature plasma (LTP). Structure, morphology, and composition of the films are studied by IR spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. They are close to the structure of bulk PTFE. The roughness of the films’ surface is changed with gas pressure and LTP power variations. Films are transparent from UV to near-infrared regions. Refractive and extinction indices and their anisotropy are measured by spectral ellipsometry. They are tuned by variations of deposition conditions. Hardness and Young modulus of the films are increased if EVD + low power LTP is used for film deposition. Use of EVD + LTP also increases thermal stability of the films. Contact angle of the films corresponds to the bulk PTFE. The PTFE molecules oriented are preferentially in perpendicular direction to the substrate surface.     

铁电薄膜的材料系统与功能性质

集成铁电体把铁电材料与集成半导体技术联合起来,以发展出一批新的电子器件.铁电薄膜在其中发挥着非挥发性记忆、热释电、压电、光折变、抗辐射、声学的和/或介电的功能性质.在不同的器件应用中,铁电薄膜的材料体系是不相同的.在非挥发性存贮器(NVRAM)中,PZT薄膜面临着SrBi2Ta2O9(SBT)系列铁电体的强力挑战;Ba1-xSrxTiO3(BST)则可能出现在下一代高密度动态随机存贮器(DRAM)中.金属氧化物电极和/或过渡层可以克服Pt电极面临的一些问题,并有助于铁电薄膜的外延生长.     

Thickness‐dependent domain wall reorientation in 70/30 lead magnesium niobate‐ lead titanate thin films

Continued reduction in length scales associated with many ferroelectric film‐based technologies is contingent on retaining the functional properties as the film thickness is reduced. Epitaxial and polycrystalline lead magnesium niobate‐lead titanate (70PMN‐30PT) thin films were studied over the thickness range of 100‐350 nm for the relative contributions to property thickness dependence from interfacial and grain‐boundary low permittivity layers. Epitaxial PMN‐PT films were grown on SrRuO₃/(001)SrTiO₃, while polycrystalline films with {001}‐Lotgering factors >0.96 were grown on Pt/TiO₂/SiO₂/Si substrates via chemical solution deposition. Both film types exhibited similar relative permittivities of ~300 at high fields at all measured thicknesses with highly crystalline electrode/dielectric interfaces. These results, with the DC‐biased and temperature‐dependent dielectric characterization, suggest irreversible domain wall mobility is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films, the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The temperature at which a peak in the relative permittivity is observed was the only measured small signal quantity which was more thickness‐dependent in polycrystalline than epitaxial films. This is attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. Finally, the effective interfacial layers are found to contribute to the measured thickness dependence in the longitudinal piezoelectric coefficient.     

Thermal Softening Behavior and Application to Transparent Thick Films of Poly(benzylsilsesquioxane) Particles Prepared by the Sol–Gel Process

Thick films of poly(benzylsilsesquioxane) (BnSiO_3/2) particles, prepared by the sol–gel process, were deposited onto indium-tin-oxide-coated glass substrates by electrophoresis for the application to the micropatterning of the films. BnSiO_3/2 particles were thermally softened and sintered at ∼50°C, which was above the glass transition temperature of the particles. The films prepared by the electrophoretic sol–gel deposition consisted of aggregates of particles with diameters of 0.2–1 μm and were opaque. The film shrank from 2.5 μm to 1.4 μm in thickness and became transparent upon sintering of the particles during heat treatment at temperatures >100°C.     

结构优化的异质Ca(Mg1/3Ta2/3)O3/CaTiO3薄膜介电性能

采用Pechini方法,在Pt/Ti/SiO₂/Si(100)基板上沉积了均质Ca(Mg1/3Ta2/3)O3 (CMT),CaTiO₃(CT)和堆叠次序不同以及摩尔比不同的异质Ca(Mg_1/3Ta_2/3)O₃/CaTiO₃(CMT/CT)薄膜。结果表明:以CT为底层的异质CMT/CT薄膜可以形成单一的钙钛矿结构,以CMT为底层的异质薄膜则有杂相产生。对于以CT为底层的不同摩尔比的异质CMT/CT薄膜,随着CMT含量的增加,异质薄膜中CT的衍射峰逐渐减小至消失,而CMT的结晶度变得更强,这说明以CT为缓冲层将有助于上层的CMT形成钙钛矿相。介电性能研究表明:异质CMT/CT薄膜的介电常数高度依赖于CMT的含量,而介电损耗不但与CMT含量有关,还与异质薄膜中界面数有关。当n(CMT):n(CT)=1:1 (摩尔比)时,异质的CMT/CT薄膜的介电常数和损耗分别为56和0.038。     

Application of the Island Blister Test for Thin Film Adhesion Measurement

The island blister test has recently been proposed as an adhesion test which allows the peel of thin, well-adhered films without exceeding the tensile strength of the film. The island blister test site is a modification of the standard blister test site, consisting of a suspended membrane of film with an “island” of substrate at the film center. The membrane support and island are secured to a rigid plate and the film is pressurized, peeling the film inward off the island. A model for this inward or “annular” peel indicates that even for systems of good adhesion, peel can be initiated at low enough pressures to prevent film failure by making the center island sufficiently small relative to the size of the film.

We have fabricated island blister test sites using micromachining techniques and have used them to measure the debond energy of polymer films on various substrates. The peel data obtained from these island sites match well to the behavior predicted by a simple fracture mechanics analysis. This paper reports the fabrication of the island test sites, the experimental verification of the test, and the results of application of the test to polyimide films on metallic and polymeric substrates.     

Application of the Island Blister Test for Thin Film Adhesion Measurement

The island blister test has recently been proposed as an adhesion test which allows the peel of thin, well-adhered films without exceeding the tensile strength of the film. The island blister test site is a modification of the standard blister test site, consisting of a suspended membrane of film with an “island” of substrate at the film center. The membrane support and island are secured to a rigid plate and the film is pressurized, peeling the film inward off the island. A model for this inward or “annular” peel indicates that even for systems of good adhesion, peel can be initiated at low enough pressures to prevent film failure by making the center island sufficiently small relative to the size of the film.

We have fabricated island blister test sites using micromachining techniques and have used them to measure the debond energy of polymer films on various substrates. The peel data obtained from these island sites match well to the behavior predicted by a simple fracture mechanics analysis. This paper reports the fabrication of the island test sites, the experimental verification of the test, and the results of application of the test to polyimide films on metallic and polymeric substrates.     

TEM Characterization of Single- and Multilayer Triol-Based Sol–Gel PZT (53/47) Thin Films

Integrated lead zirconate titanate thin films deposited on Pt/Ti/SiO₂/Si substrates using a novel triol-based route were characterized using X-ray diffraction and transmission electron microscopy. Crack-free single-layer PZT films of up to 200 nm thick were prepared by triol-based sol–gel processing onto Pt/Ti/SiO₂/Si substrates. Films ∼75 nm thick exhibited a microstructure free of pores and second phase. As film thickness increased, film texture changed from {100} to {111} perovskite. Essentially, single-phase multilayer films could be prepared by the deposition and pyrolysis of several 75 nm layers, followed by a single crystallization step. The influence of heat-treatment schedule on the microstructure and orientation of the multilayer films is discussed. Comparison has been made between multilayer films prepared using the triol-based sol and an inverted mixing order/acetic acid-based sol.