Raman Spectroscopy of Nanocrystalline Ceria and Zirconia Thin Films

The results of Raman-scattering studies of nanocrystalline CeO₂ and ZrO₂:16% Y (YSZ) thin films are presented. The relationship between the lattice disorder and the form of the Raman spectra is discussed and correlated with the microstructure. It is shown that the Raman line shape results from phonon confinement and spatial correlation effects and yields information about the material nonstoichiometry level.     

Characterization and Investigation of the Tribological Properties of Sol–Gel Zirconia Thin Films

Sol–gel zirconia thin films were prepared by dip coating in an ethanol solution of zirconium oxychloride. The zirconia films consisted of a completely tetragonal phase and exhibited nanoscale uniformity. They displayed excellent antiwear and friction-reduction performance in sliding against steel. The friction coefficient (0.13–0.15) and the wear life over 5000 sliding cycles were recorded for the films at a sliding speed of 90 mm/min and a load of 0.5 N. The film was characterized by slight scuffing and abrasion at low loads and sliding speeds.     

Microstructure Development in Unsupported Thin Films

To better understand the role of the substrate in the microstructural evolution of thin films, unsupported nanocrystalline yttrium-stabilized zirconia (ZrO₂:16%Y or YSZ) films were examined as a function of temperature and annealing time. Grain growth, texturing, and pinhole formation were measured using transmission electron microscopy (TEM) and electron diffraction. Films were produced and subsequently annealed on metallic grids using a previously developed technique that results in near full density films at low annealing temperatures. Microstructural evolution in these films was unique compared with constrained films. Grains were found to spheroidize much more readily, ultimately resulting in the formation of porosity and pinholes. Grain growth was found to stagnate at a size particular to each annealing temperature, presumably due to the effects of Zener pinning. It is proposed that the lack of substrate strain and confinement effects allows for the dominance of surface energetics with respect to microstructural evolution.     

Microstructural Characterization of Ferroelectric Thin Films in Transverse Section

A technique has been developed for the TEM examination of ferroelectric thin films in transverse section. Some preliminary results are reported for three different thin-film/substrate systems. The microstructures of thin films of lead scandium tantalate deposited onto sapphire and MgO, and lead titanate deposited onto AIN, have been examined, with particular attention being paid to the quality of the thin-film/substrate interfaces and to the changes in the nature of the microstructures of the thin films as a function of distance from their substrates. It is demonstrated that the technique successfully produces adequate electron transparent regions for the characterization of the thin-film/substrate interface of all the samples examined and that it is possible to prepare transverse sections of ferroelectric thin films routinely.     

Production of Dense Yttria-Stabilized Zirconia Thin Films by Dip-Coating for IT-SOFC Application

Yttria-stabilized zirconia (YSZ) thin films were prepared by conventional and modified dip-coating techniques followed by heating to an appropriate temperature in air. Scanning electron microscopy showed that films of the thickness ranging from 20 to 30 m were dense and crack-free. The electrical properties of the films were investigated by ac impedance spectroscopy. La_0.8Sr_0.2MnO₃ paste was printed on to a YSZ electrolyte/anode assembly to create single fuel cells which were tested in the temperature range 650–800 °C. The results showed that both open circuit voltage (OCV) and maximum power density values of the cells with electrolytes produced by the modified dip coating were higher than those fabricated by conventional processing. At 800 °C, the OCV reached 0.98 V and a maximum power density of 190 mW cm^–2 was attained, demonstrating that the modified dip coating process is a simple and cost-effective fabrication technique for IT-SOFCs, though further improvement is necessary.     

Synthesis and Characterization of Zirconia Nanorods

ZrO₂ nanorods are prepared by annealing precursor powders produced in the novel inverse microemulsion system. The length and diameter of ZrO₂ nanorods are a few micrometers and 40–100 nm, respectively. The microstructure of the resultant nanorods are studied by XRD, TEM, selected area electron diffraction, and Raman spectroscopy. The ZrO₂ nanorods are single crystalline and have monoclinic structure. The formation of ZrO₂ nanorods is discussed.     

纳米晶TiO2多孔薄膜的研究进展

综述了近年来纳米晶TiO2多孔薄膜材料的研究进展情况,对纳米晶TiO2多孔薄膜材料的各种制备方法及其特点进行了归纳和分析,并时纳米晶TiO2多孔薄膜材料的应用现状作了简要介绍.     

Nanocrystalline Tin Oxide Thin Films via Liquid Flow Deposition

Nanocrystalline films of SnO₂ were deposited by liquid flow deposition (LFD), i.e., by flowing aqueous solutions of SnCl₄·5H₂O and HCl over single-crystalline silicon substrates at 80°C. The substrates were either oxidized and fully hydrolyzed (bare silicon) or oxidized, hydrolyzed, and then coated with siloxy-anchored organic self-assembled monolayers (SAMs). Continuous, adherent films formed on sulfonate- and thioacetate-functionalized SAMs; adherent but sometimes discontinuous films formed on bare silicon and methyl-functionalized SAMs. The films contained equiaxed cassiterite crystals, ∼4–10 nm in size. The film thickness increased linearly with deposition time. The maximum growth rate observed was 85 nm·h⁻¹ on sulfonate SAM, and the maximum film thickness obtained was 1 μm. A new dimensionless parameter, the normalized residence time, τ, was introduced for the purpose of interpreting the influence of solution conditions (i.e., degree of supersaturation, as controlled via pH, and tin concentration) and flow characteristics (flow rate and the configuration of the deposition chamber) on the growth rate in LFD processes. The results were consistent with a particle attachment mechanism for film growth and inconsistent with heterogeneous nucleation on the substrate.     

Synthesis of Niobium(V)-Stabilized Tetragonal Zirconia Nanocrystalline Powders

The polymer precursor method is very useful to prepare Nb⁵⁺-stabilized nanocrystalline powders of t -ZrO₂. The precursor solution is composed of zirconium oxalate, niobium tartrate, and poly(vinyl alcohol), which help to form a network matrix to disperse the metal ions homogeneously. Nb⁵⁺ is an effective agent to stabilize t -ZrO₂, and ease of formation of the tetragonal phase increases with increasing dopant concentration. Thermal stability of t -phase is found up to 1700°C having 15 mol% Nb⁵⁺, prepared at 600°C with particle sizes of 35 ± 5 nm.     

Hydrothermal Synthesis of Thin Films of Barium Titanate Ceramic Nano-Tubes at 200°C

A novel, low-temperature synthesis method for producing BaTiO₃ thin films patterned in the form of nano-tubes ("honeycomb") on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (∼200–300-nm thickness) of amorphous titanium oxide nano-tube (∼100-nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)₂, where the nano-tube arrays serve as templates for their hydrothermal conversion to polycrystalline BaTiO₃ nano-tubes. This opens the possibility of tailoring the nano-tube arrays and of using various precursor solutions and their combinations in the hydrothermal bath, to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic device applications but also in biomedical applications, where patterned thin films are also desirable.     

Ceramic Oxygen Generators with Thin-Film Zirconia Electrolytes

Ceramic oxygen generators (COGs) based on stabilized zirconia electrolytes are being developed for oxygen generation from air and other gases, e.g., carbon dioxide. In zirconia-based COG cells, it is desirable to use thin-film electrolytes to minimize ohmic resistance losses, thus permitting reduced operating temperatures (600°–800°C vs 900°–1000°C). The tape calendering process developed by Honeywell is a simple, cost-effective process for fabrication of thin-film electrolytes supported on a substrate electrode. In combination with optimized electrodes, thin-film electrolytes allow significantly high performance in COG cells. Performance characteristics of COG cells and stacks made by tape calendering for oxygen generation from air and CO₂ are discussed.     

Nanocrystalline Zirconia Surface-Doped with Alumina: Chemical Vapor Synthesis, Characterization, and Properties

Nanocrystalline zirconia with a grain size of ∼5 nm was surface-doped with 3 and 30 mol% alumina by chemical vapor synthesis using two sequential hot-wall reactors. The powders were characterized by high-resolution transmission electron microscopy, X-ray diffractometry (XRD), and nitrogen adsorption. Aqueous dispersions were studied by zeta-potential measurements and photocorrelation spectroscopy. Green and sintered ceramic bodies were investigated by high-resolution scanning electron microscopy, XRD, and nitrogen adsorption. Zirconia surface-doped with 3 mol% of alumina displays substantial changes in dispersability and sinterability compared with pure nanocrystalline zirconia.     

Hydrothermal Synthesis of Weakly Agglomerated Nanocrystalline Scandia-Stabilized Zirconia

A pure cubic phase of weakly agglomerated, nanocrystalline, 8-mol%-Sc₂O₃-stabilized zirconia (8ScSZ) was synthesized by a two-step hydrothermal treatment in the presence of urea: a stock solution of metal nitrates and urea was heated at 80°C for 48 h and then at 180°C for 72 h. The omission of the first low-temperature treatment resulted in more monoclinic phase. The effects of urea concentration and calcining temperature on the crystallization of the as-synthesized nanocrystalline 8ScSZ are also discussed.     

The Synthesis of Discrete Colloidal Crystals of Zeolite Beta and their Application in the Preparation of Thin Microporous Films

Stable colloidal suspensions containing discrete crystals of zeolite Beta with particle sizes less than 150 nm were synthesized within a wide composition range. Crystallization of colloidal zeolite Beta was facilitated by low water and sodium contents and by high TEAOH contents. Solid samples obtained after drying were characterized using XRD and FT-IR. Thin (ca. 130 nm) films of zeolite Beta were grown on a Ta-substrate using colloidal crystals of zeolite Beta as seeds.     

Synthesis and Colloidal Processing of Zirconia Nanopowder

Nanosized tetragonal 3 mol% Y₂O₃-doped ZrO₂ powder was produced by hydrothermal precipitation from metal chlorides and urea sol followed by a washing–drying treatment and calcination. The effects on powder properties of powder washing by water and ethanol with subsequent centrifuging, with possible deagglomeration using microtip ultrasonication, were experimentally shown. Ultrasonic irradiation induced pressure waves, which generated cavities that could violently collapse, producing intense stress. This induced stress was effective in minimizing secondary particle size, deagglomerating the powder, redispersing the ZrO₂ after all the washing–centrifuging cycles, and minimizing mean aggregate size after final calcination. A uniformly aggregated tetragonal ZrO₂ nanopowder with a mean secondary particle size of ∼45 nm and without hard agglomerates was prepared. The properties of the nanopowders produced by colloidal processing and CIP were studied. Determination of the best suspension parameters allowed for low-temperature sinterability, which resulted in a nanograined ∼95 nm ceramic.     

CeO_2纳米薄膜的制备

以 Ce(NO3) 3· 6H2 O为前驱物 ,加入火棉胶作为粘度调节剂 ,采用 sol-gel提拉法制备了均匀透明的 Ce O2 纳米薄膜 ,对其性能进行了研究 ,并用光声光谱确定了 Ce O2 纳米薄膜的透明区间     

自组装膜引导合成二氧化钛薄膜

采用巯丙基三甲氧基硅烷的分子自组装膜层对基材表面进行修饰,利用低温下氟钛酸铵的配位交换反应,制备出与基底结合紧密的二氧化钛晶态薄膜.磺酸基修饰的基材能够对TiO2膜的沉积产生明显的诱导作用,当(NH4)2TiF6与HBO3的摩尔比为0.05:0.10时,薄膜晶型主要为金红石型;比例增大为0.05:0.15时,薄膜晶型主要为锐钛矿型.沉积的TiO2晶态薄膜具有良好的透光性.     

Microstructural Characterization of C60-Doped Zirconia

Zirconia powders doped with C₆₀ molecules were prepared from an aqueous solution of zirconium oxynitrate dihydrate, C₆₀ and C₁₆TMA, and sintered at 600°C under 5.5 GPa for 2 h. C₆₀ was found to be retained in the sintered specimens by HRTEM, and carbon was observed to be uniformly dispersed by the SEM-EDX analysis. HRTEM observations of the sintered specimens exhibited the formation of ZrO₂ crystal grains covered with thin graphitic or amorphous carbon films.     

Synthesis and Optical Properties of Poly(BPDA-ODA)/Silica Hybrid Thin Films

Poly(BPDA-ODA)/silica hybrid optical thin films were synthesized using a sol-gel reaction combined with spin coating and multi-step baking. The hybrid thin films were prepared by the precursors of aminoalkoxysilane capped poly(BPDA-ODA) amic acid and tetramethoxysilane (TMOS). Highly transparent hybrid thin films were obtained at a silica content of 0–51.9 wt%. The prepared hybrid thin films showed homogeneous structures and excellent surface planarity. The refractive index of the prepared hybrid thin films decreased linearly with increasing the silica content while the Abbe number showed the opposite trend. The prepared hybrid films also exhibited a much smaller optical birefringence than the parent poly(BPDA-ODA) because of the reduction of the rigid backbone by incorporating the silica moiety. Optical planar waveguides were prepared from the prepared hybrid thin films. The optical losses of the planar waveguides at 1310 nm were in the range of 0.5–1.3 dB/cm, which were reduced significantly by increasing the silica moiety. The reduction of the C–H bonding density and excellent surface planarity by incorporating the silica moiety explain the trend of optical loss. These results suggest that the prepared polyimide-silica hybrid thin films have potential applications for optical devices.     

Characterization and Tribological Investigation of Sol–Gel Titania and Doped Titania Thin Films

Titania (TiO₂) and doped TiO₂ ceramic thin films were prepared on a glass substrate by a sol–gel and dip-coating process from specially formulated sols, followed by annealing at 460°C. The morphologies of the original and worn surfaces of the films were analyzed with atomic force microscopy (AFM) and scanning electron microscopy. The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of TiO₂ and doped TiO₂ thin films sliding against Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The AFM analysis shows that the morphologies of the resulting films are very different in nanoscale, which partly accounts for their tribological properties. XPS analysis reveals that the doped elements exist in different states, such as oxide and silicate, and diffusion took place between the film and the glass substrate. TiO₂ films show an excellent ability to reduce friction and resist wear. A friction coefficient as low as 0.18 and a wear life of 2280 sliding passes at 3 N were recorded. Unfortunately, all the doped TiO₂ films are inferior to the TiO₂ films in friction reduction and wear resistance, primarily because of their differences in structures and chemical compositions caused by the doped elements. The wear of the glass is characteristic of brittle fracture and severe abrasion. The wear of the TiO₂ thin film is characteristic of plastic deformation with slight abrasive and fatigue wear. The doped TiO₂ thin films show lower plasticity than the TiO₂ thin film, which leads to large cracks. The propagation of the cracks caused serious fracture and failure of the films.