Microstructure and Ionic Conductivity of Yttria‐Stabilized Zirconia Thin Films Deposited on MgO

A number of reports have suggested that nanometric thin films of yttria‐stabilized zirconia (YSZ) deposited on MgO can support high ionic conductivity, but the results remain controversial and difficult to repeat. In this work, sub‐100‐nm‐thick YSZ films have been deposited on single‐crystal MgO substrates with different crystallographic orientations and sourced from different companies. The growth of YSZ on MgO (100) was found to be unstable: both (111)‐oriented films with polycrystalline structure and (100)‐oriented films with cube‐on‐cube epitaxy were observed despite seemingly identical deposition conditions. On MgO (110) and MgO (111) substrates, the growth of YSZ was more stable with high degrees of texture in the (110) and (111) film directions, respectively. Ionic conductivities of the films were measured with impedance spectroscopy, and conductivity values were consistently near or slightly below that of a YSZ single crystal.     

Microstructure, Orientation, and Properties of Sol-Gel-Derived KTiOPO4 Thin Films

Dense and crack-free thin films of potassium titanyl phosphate (KTP) were synthesized using a sol-gel process. The decomposition of the organic precursors and the formation of the KTP were studied using thermal analysis, DRIFT, and XRD. Several processing parameters such as the nature of the precursors, the aging of the alkoxide solution, the firing atmosphere, time, and temperature were found to affect the final film microstructure. Thin films were deposited on single-crystal KTP, LaGaO₃, MgO, and sapphire substrates to promote crystallographic orientation. SEM and XRD studies reveal that films deposited on KTP and LaGaO₃ single crystals are highly oriented. The films deposited on MgO or sapphire were found to detach or chemically degrade. The orientation as well as the degradation mechanisms were examined in detail.     

Highly-oriented proton conducting BaZr0.9Y0.1O3−x ceramic thin films prepared by chemical solution deposition

In this work, the parameters for the formation of 10% yttrium-doped barium zirconate (BZY) thin films were investigated systematically using the low-cost and scalable chemical solution deposition method. By modifying the chemistry of the precursor solution and applying different thermal treatment schedules, the key parameters of controlling microstructure and growth orientation were unraveled. Films with porous and lamellar, granular, and dense columnar structures, respectively, were obtained at a relatively low annealing temperature (950 ℃). Particularly, the film with a highly (200) preferred orientation was attained by employing a seed layer approach, in combination with a butyrate-based precursor coating solution. The decomposition of the precursors was surveyed through thermal analysis. The in-plane conductivity of BZY films was investigated by electrochemical impedance spectroscopy and the corresponding activation energy was evaluated. The relationship between microstructures and electrochemical properties was discussed and concluded that the denser BZY film with larger grains shows better performance.     

Crystallization Behavior of Sol–Gel-Derived Strontium Barium Niobate Thin Films

The crystallization of sol–gel-derived strontium barium niobate (SBN) thin films on various substrates is enhanced by a two-step heating process. Also, SBN films with c -axis preferred orientation are obtained on MgO (100) substrates. The crystallized phase and the degree of orientation are dependent on crystallization temperature and film composition. The crystallization temperature required to form a single tetragonal tungsten bronze (TTB) SBN phase increases with an increase of Sr content due to the distorted SBN structure. However, in the case of the film on MgO substrate, the oriented crystallization which forms the single tetragonal phase occurs at a lower crystallization temperature than those of polycrystalline films because of lattice matching between the film and the substrate. Its optical and ferroelectric properties were also investigated. They vary depending on film composition, due to the effect of the distorted SBN structure.     

Highly Oriented, Chemically Prepared Pb(Zr, Ti)O3 Thin Films

We have fabricated highly oriented, chemically prepared thin films of Pb(Zr_0.04Tio._0.60)O₃ (PZT 40/60) on both insulating and conducting substrates. While (100) MgO single crystals were used as the insulating substrates, the conducting substrates. were fabricated by RF magnetron sputter deposition of 100-nm-thick (100) Pt films onto (100) MgO substrates. For comparison, we also fabricated PZT 40/60 films that had no significant preferential orientation on platinized MgO substrates. Sputter deposition of an underlying amorphous Pt film was used to fabricate randomly oriented PZT 40/60 films. Highly (001) oriented PZT 40/60 films had higher remanent polarization (61 μC/cm² compared to 41 μC/cm²) and lower relative dielectric constant (368 compared to 466) than PZT 40/60 films that were randomly oriented.     

Glass‐Like Thermal Conductivity of (010)‐Textured Lanthanum‐Doped Strontium Niobate Synthesized with Wet Chemical Deposition

We have measured the cross‐plane thermal conductivity (κ) of (010)‐textured, undoped, and lanthanum‐doped strontium niobate (Sr_2?xLa_xNb₂O_7?δ) thin films via time‐domain thermoreflectance. The thin films were deposited on (001)‐oriented SrTiO₃ substrates via the highly‐scalable technique of chemical solution deposition. We find that both film thickness and lanthanum doping have little effect on κ, suggesting that there is a more dominant phonon scattering mechanism present in the system; namely the weak interlayer‐bonding along the b‐axis in the Sr₂Nb₂O₇ parent structure. Furthermore, we compare our experimental results with two variations of the minimum‐limit model for κ and discuss the nature of transport in material systems with weakly‐bonded layers. The low cross‐plane κ of these scalably‐fabricated films is comparable to that of similarly layered niobate structures grown epitaxially.     

Growth of CeO2 Films on Sapphire and MgO by rf Magnetron Sputtering

pitaxial CeO₂ films on (1102) sapphire and (100) MgO were grown by rf magnetron sputtering. Substrate temperature, total pressure, and oxygen-to-argon mole ratio were varied to explore the optimal deposition condition. The X-ray diffraction spectra indicate that the degree of crystallinity of the deposited CeO₂ films depends on the oxygen- to-argon mole ratio and the substrate temperature. Atomic force microscopy images of the films on sapphire and MgO showed that substrate temperature and total pressure affect surface roughness. The best film surface is smooth with a 0.89 nm root-mean-square roughness. The quality of the films on MgO showed a strong dependence on substrate pretreatments. Epitaxial CeO₂ films could be grown on pre- annealed or pre-etched MgO if substrate temperatures reached higher than 790^deg;C. Additionally, the effect of ion bombardment at low total pressures on the crystallinity of the films was examined by growing the films outside the plasma region. Experimental results indicate that the ion bombardment does not prevent the films from preferred orientation.     

Deposition of Pb(Zr,Ti)O3 Thin Films by Metal-Organic Chemical Vapor Deposition Using β-diketonate Precursors at Low Temperatures

Lead zirconate titanate (PZT) thin films were deposited by metal-organic chemical vapor deposition (MOCVD) using β-diketonate precursors and 0₂ at temperatures below 500°C on variously passivated Si substrates. PZT thin films could not be deposited on bare Si substrates, owing to a serious diffusion of Pb into the Si substrate during deposition. Pt/SiO₂/Si substrates could partially block the diffusion of Pb, but a direct deposition of PZT thin films on the Pt/SiO₂/Si substrates resulted in a very inhomogeneous deposition. A TiO₂ buffer layer deposited on Pt/SiO₂/Si substrates could partially suppress the diffusion of Pb and produce homogeneous thin films. However, the crystallinity of PZT thin films deposited on the TiO₂-buffered Pt/SiO₂/Si substrate was not good enough, and the films showed random growth direction. PZT thin films deposited on the PbTiO₃-buffered Pt/SiO₂/Si substrates had good crystallinity and a- and c-axis oriented growth direction. However, the PZT thin film deposited at 350°C showed fine amorphous phases at the grain boundaries, owing to the low chemical reactivities of the constituent elements at that temperature, but they could be crystallized by rapid thermal anneaiing (RTA) at 700°C. PZT thin film deposited on a 1000-å PbTiO₃,-thin-film-buffered Pt/SiO₂/Si substrate at 350°C and rapid thermally annealed at 700°C for 6 min showed a single-phase perovskite structure with a composition near the morphotropic boundary composition.     

Flame Spray Synthesis of BaZr0.8Y0.2O3–δ Electrolyte Nanopowders for Intermediate Temperature Proton Conducting Fuel Cells

Flame Spray Synthesis (FSS) technique has been used for the preparation of BaZr_0.8Y_0.2O_3–δ (BZY20) nanoprecursors. The nanoprecursors were composed of a perovskite phase mixed with doped Zirconia and barium nitrate. Pure phase powder could be obtained after calcining the precursors at 1,200 °C. Both nanoprecursors and pure phase powder were then sintered at 1,600 °C to obtain dense specimen. AC impedance spectroscopy performed on the sintered samples allowed correlation of the electrical properties of the samples to their microstructures. The sintered nanoprecursors compared with the sintered pure phase powders showed enhanced grain growth associated with higher grain boundary conductivity. The influence of the reactive sintering on the enhanced grain growth and electrical properties in the nanoprecursors is discussed. The high total proton conductivity measured (7.7·10⁻³ S cm⁻¹ at 450 °C) promotes FSS as an effective powder synthesis method for the preparation of BZY20 electrolyte material for proton conducting fuel cells operating in the intermediate temperature range.     

Electrophoretic Deposition Kinetics and Characterization of Ni–La1.95Ca0.05Zr2O7−δ Particulate Thin Films

Suspensions of NiO–La_1.95Ca_0.05Zr₂O_7?δ (NiO–LCZ) composite material have been prepared in isopropanol medium using iodine and acetylacetone as dispersants. The effect of iodine concentration on suspension stability, electrical conductivity, and suspension pH are studied in detail to optimize the suspension chemistry. Electrophoretic deposition has been successfully conducted on conducting substrate (steel plate) to fabricate NiO–LCZ thin particulate films. Deposition kinetics have been studied in detail to optimize the process parameters. Good quality particulate films of such composite on steel plates are obtained at an applied voltage of 60 V for 3 min. The optimized suspension chemistry and process parameters thus obtained are then used to fabricate NiO–LCZ composite films onto nonconducting porous ceramic substrate by placing a conducting plate at the reverse side of the porous substrate. The deposited films along with the ceramic substrates are co‐fired at 1400°C for 6 h in reducing atmosphere (5% hydrogen in argon) to produce a good quality dense Ni–LCZ film of thickness ~40 μm. The hydrogen permeation flux of the developed cermet membrane has been measured and it reveals that Ni–LCZ could be used as a potential membrane for hydrogen separation at high temperature.     

Characterization of the biaxial textures of MgO thin films grown by E-beam evaporation

The biaxial textures of MgO thin films with thicknesses 4500–5500 Å deposited by electron beam evaporation on glass substrates have been characterized. The surface normal to the amorphous soda-lime glass substrate was placed parallel to the MgO vapor flux, i.e., at zero degree with respect to the MgO vapor source. The MgO thin films showed biaxial texture regardless of the deposition parameters. XRD and SEM have been used to characterize the crystal structure and thin film surface morphology. In this study we devised a novel method for the characterization of the biaxial texture of MgO thin films with thicknesses ≤5000 Å, for which the X-ray pole figure method cannot be used due to the low scattering intensity from the MgO film containing only low atomic X-ray scattering ions. We report the biaxial texture development in MgO thin films grown by E-beam evaporation on the amorphous glass substrate inclined at zero degree with respect to the MgO vapor source.     

Layer‐by‐layer films based on charge transfer interaction of ϕ‐conjugated poly(dithiafulvene) and incorporation of gold nanoparticles into the films

Layer‐by‐layer (LBL) self‐assembled ultrathin films were prepared via consecutively alternating immersion of substrates into solutions of electron donor, poly(dithiafulvene) (PDF), and electron acceptor, poly(hexanyl viologen) (6‐VP). The charge transfer (CT) interaction formed at solid–liquid interfaces between the backbones of the electron acceptor and donor polymers was the driving force of the alternative deposition. The sandwich heterostructure of the LBL film led to electrical anisotropy in the directions parallel and perpendicular to the film surfaces. Incorporation of gold nanoparticles into the LBL films was investigated by reducing gold ions with the PDF layers already deposited on the film surfaces, or depositing PDF‐protected gold colloidal solution as the electron donor layers directly. The influence of the gold nanoparticles on the electrical anisotropy of the LBL films was also illustrated in this research. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1608–1615, 2007     

Direct synthesis and characterization of optically transparent conformal zinc oxide nanocrystalline thin films by rapid thermal plasma CVD

We report a rapid, self-catalyzed, solid precursor-based thermal plasma chemical vapor deposition process for depositing a conformal, nonporous, and optically transparent nanocrystalline ZnO thin film at 130 Torr (0.17 atm). Pure solid zinc is inductively heated and melted, followed by ionization by thermal induction argon/oxygen plasma to produce conformal, nonporous nanocrystalline ZnO films at a growth rate of up to 50 nm/min on amorphous and crystalline substrates including Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), gold, titanium, and polyimide. X-ray diffraction indicates the grains of as-deposited ZnO to be highly textured, with the fastest growth occurring along the c-axis. The individual grains are observed to be faceted by (103) planes which are the slowest growth planes. ZnO nanocrystalline films of nominal thicknesses of 200 nm are deposited at substrate temperatures of 330°C and 160°C on metal/ceramic substrates and polymer substrates, respectively. In addition, 20-nm- and 200-nm-thick films are also deposited on quartz substrates for optical characterization. At optical spectra above 375 nm, the measured optical transmittance of a 200-nm-thick ZnO film is greater than 80%, while that of a 20-nm-thick film is close to 100%. For a 200-nm-thick ZnO film with an average grain size of 100 nm, a four-point probe measurement shows electrical conductivity of up to 910 S/m. Annealing of 200-nm-thick ZnO films in 300 sccm pure argon at temperatures ranging from 750°C to 950°C (at homologous temperatures between 0.46 and 0.54) alters the textures and morphologies of the thin film. Based on scanning electron microscope images, higher annealing temperatures appear to restructure the ZnO nanocrystalline films to form nanorods of ZnO due to a combination of grain boundary diffusion and bulk diffusion.PACS: films and coatings, 81.15.-z; nanocrystalline materials, 81.07.Bc; II-VI semiconductors, 81.05.Dz.     

Surface morphology of PECVD fluorocarbon thin films from hexafluoropropylene oxide, 1,1,2,2‐tetrafluoroethane,and difluoromethane

Atomic force microscopy (AFM) measurements have been made on a series of fluorocarbon films deposited from pulsed plasmas of hexafluoropropylene oxide (HFPO), 1,1,2,2‐tetrafluoroethane (C₂H₂F₄), and difluoromethane (CH₂F₂). All of the films give images showing nodular growth (cauliflower‐like appearance), with the size and distribution of the nodules dependent on both the precursor, the degree of surface modification to which the growing film is exposed, and the substrate surface. Films deposited from C₂H₂F₄ showed clusters of smaller nodules around larger nodules, whereas films deposited from CH₂F₂ were characterized by a uniform distribution of smaller nodules, and films deposited from HFPO had the largest observed nodules. Movchan and Demchishin's structure zone model was applied to the observed films, which were all found to be zone 1 structures, indicating that film growth is dominated by shadowing effects. Increased substrate temperature and incident power per nm of film deposited results in decreased rms roughness, consistent with greater atomic mobility during deposition. Larger nodules in the fluorocarbon films developed on silicon wafer substrates than on rougher Al‐coated substrates. Advancing contact angles for all of the films were found to be higher than that of PTFE (108°), indicating both hydrophobic and rough surfaces. Specifically, contact angles of films deposited from HFPO were found to increase with pulse off‐time, the same trend observed for both the CF₂ fraction of the film and the rms roughness. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2439–2447, 1999     

Transparent and conductive indium tin oxide/polyimide films prepared by high‐temperature radio‐frequency magnetron sputtering

A highly transparent and thermally stable polyimide (PI) substrate was prepared and used for the fabrication of indium tin oxide (ITO)/PI films via radio‐frequency magnetron sputtering at an elevated substrate temperature. The effect of the deposition conditions, that is, the oxygen flow rate, substrate temperature, sputtering power, and working pressure, on the optical and electrical properties of the ITO/PI films were investigated from the microstructural aspects. The results indicate that the optical and electrical properties of ITO were sensitive to the oxygen. Moreover, it was beneficial to the improvement of the ITO conductivity through the adoption of a high substrate temperature and sputtering power and a low working pressure in the deposition process. A two‐step deposition method was developed in which a thick bulk ITO layer was overlapped by deposition on a thin seed ITO layer with a dense surface to prepare the highly transparent and conductive ITO/PI films. The ITO/PI film after annealing at 240°C gave a transmittance of 83% and a sheet resistance of 19.7 Ω/square. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42753.     

Preparation of Highly Dense PZN–PZT Thick Films by the Aerosol Deposition Method Using Excess-PbO Powder

Lead zinc niobate–lead zirconate titanate thick films with a thickness of 50–100 μm were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as-deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 μm thick films annealed at 900°C were 43.1 μC/cm² and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process.     

Preparation of KTaO3 and KNbO3 Solid Solutions through Sol–Gel Processing

Potassium tantalate–niobate solid-solution (KTN) powders and thin films were prepared from metallo–organic compounds through sol–gel processing. The KTN precursors were chemically modified and then prehydrolyzed with various concentrations of water. The stability of the modified solutions and the effects of prehydrolysis on the crystallization are discussed. Powder gels were obtained by exposing the solution to the atmospheric water, hydrolyzing the solutions. Alternatively, thin films were deposited on fused silica, silicon, sapphire, MgO, and SrTiO₃, using the spinning technique. The pyrolysis and crystallization of KTN powders and films were investigated by differential thermal analysis, theromogravimetric analysis, and X-ray diffraction. The effects of substrate and other processing parameteres on the crystal structure of the KTN phases were also investigated. KTN powders crystallized into a perovskite phase regardless of the processing conditions. The crystal structure of the KTN thin films had a strong dependency on the crystal structure of the substrates, while other processing parameters played smaller roles. Pyrochlore KTN was the major phase that crystallized on fused silica and silicon, whereas oriented perovskite KTN was obtained on single-crystal MgO and SrTiO₃.     

Effects of time-dependent substrate biasing and gas composition on the nucleation of cubic boron nitride thin films

Boron nitride (BN) thin films were deposited on silicon and sapphire substrates by an inductively coupled plasma chemical vapor deposition technique with time-dependent control of the substrate dc bias (Vdc). Turbostratic BN films were deposited on sapphire when the bias reduction rate, ·Vdc, was optimized specifically for cBN growth on silicon. This difference depending on the substrates was explained by a potential drop in the dielectric substrate. By reducing ·Vdc at the early stage of deposition, the cBN phase was successfully deposited on both substrates. We also found that the chemical composition of BN varied from B/(B + N) = 0.48 to 0.57 upon changing the gas ratio of diborane to nitrogen. The gas ratio for film nonstoichiometry resulted in a thicker initial layer, i.e., the delayed nucleation of cBN.     

Synthesis and Microstructure of Highly Oriented Lead Titanate Thin Films Prepared by a Sol-Gel Method

Thin films of PbTiO₃ were deposited on fused silica, resistor-grade alumina, and single-crystal (100) MgO by a sol–gel processing method. Whereas the films deposited on silica and alumina substrates were randomly oriented and polycrystalline, highly {100} oriented PbTiO₃ films were grown on the MgO single crystals. The perovskite-type structure was observed with films deposited on the single-crystal MgO and annealed at temperatures as low as 470°C, whereas a pyrochlore-type strcuture was observed with films on fused silica and alumina processed in a similar manner. All films heat-treated at temperatures in excess of 570°C showed significant formation of a second PbTi₃O₇ phase. The films were characterized by electron microscopy and glancing-incidence-angle X-ray diffraction.     

Influence of Deposition Parameters and Substrate on the Quality of Pulsed-Laser-Deposited Pb1-xCaxTiO3 Ferroelectric Films

Pb_{1- x} Ca _x TiO₃ (PCaT) thin films have been prepared by pulsed laser deposition (PLD) on Pt/TiO₂/SiO₂/(100)Si, (100)MgO, and Pt/(100)MgO substrates. A Pb deficiency with regard to the target composition occurs in films prepared on heated substrates, while the Ca concentration in the film remains congruent with the target composition. The onset temperature for the Pb loss changes from 250°C using nonsintered targets to 450°C if sintered targets are used; moreover, the sintered targets also produce a low particle density on the film surface (0.4 µm⁻²). Increasing the laser fluence to about 10 J/cm² improves the crystalline quality of the films. PCaT ( x = 0.24) films obtained by PLD on Si-based substrates have a lattice tetragonality c / a = 1.014, lower than the value obtained in films prepared by other methods. The film tetragonality can be slightly increased to c / a = 1.022 by using MgO substrates and much more efficiently by reducing the Ca concentration, up to reach c / a = 1.048 in Ca free films. The increase of the film tetragonality induces an enhancement of the film orientation with the [001] axis perpendicular to the substrate surface; moreover, the typical values of the spontaneous and remanent polarizations increase up to P _r similar/congruent 34 µCcm⁻².