Thickness Of CeO2 Research Articles

Insights into the structure-performance relationship of CuOx-CeO2 catalysts for preferential oxidation of CO: Investigation on thermally induced copper migration process

A series of CuOx-CeO2 catalysts is designed by coating composite copper-ceria precursor with different thickness of CeO2, followed by thermal treatment at 500 and 700 °C respectively to investigate the outward migration phenomenon of Cu species induced by high temperature thermal treatment. For the CuOx-CeO2 catalysts calcined at 500 °C, the coating of CeO2 covers the active surface Cu entities and degrades the low temperature catalytic performance for preferential oxidation of CO (CO-PROX). However, thermal treatment at 700 °C induces the migration of large amounts of Cu entities from bulk to the surface of CeO2 nanoparticles and recovers the low temperature catalytic performance. In addition, 700 °C thermal treatment of CuOx-CeO2 catalyst without CeO2 coating causes excessive outward migration of Cu species and severe CuO agglomeration, which decreases the catalytic performance at low reaction temperature, but broadens the high temperature operation window on account of the formation of inverse CeO2-CuO structure. This work provides deeper insight into the regime of thermally induced Cu migration phenomenon, and illuminated the structure-performance relationship of copper-ceria based catalysts for CO-PROX.

Investigation of cerium oxide thin film thickness using THz spectroscopy for non-destructive measurement

Through time of non-destructive measurement of individual layer of materials or paint layers at nano-scale, non-contact terahertz technique is a very good approach. In this research work, the cerium oxide (CeO2) thin film is deposited on sapphire (c-Al2O3) substrate having thickness of 430 µm by using RF magnetron sputtering technique. A terahertz pulses incident on the CeO2 film, layer of CeO2 interface with substrate. Some amount of incident pulse transmits and rest will reflect with respect to transmission mode and reflection mode, respectively. In the reflection mode, the time elapsed between the arrival and departure of cerium oxide layer is directly proportional to the thickness of the layer as a function of wavelength. The thickness of CeO2 is measured about 35.83 µm using terahertz spectroscopy. This study shows that terahertz spectroscopy is an experimental approach and possible to measure thickness of thin film for non-destructive measurement.

Facile construction of Mn2O3@CeO2 core@shell cubes with enhanced catalytic activity toward CO oxidation

Heterogeneous core@shell nanostructures bring unique synergetic catalytic properties in comparison with their single-component materials, because the two-phase interface could render hybrid junctions with rich redox reactions. Herein, a series of Mn2O3@CeO2 core@shell cubes with tunable CeO2 shell thickness have been controllably synthesized by a facile multi-step process, which involved the annealing treatment of MnCO3 precursor to produce Mn2O3 microcubes, followed by a refuxing process to deposit a uniform CeO2 layer on the Mn2O3 surface. The CeO2 shell was assembled by nanoparticles with sizes in the range of 2–10 nm, and the thickness could be facilely manipulated by changing the Mn/Ce molar ratios of reactants used in the synthetic process. The Mn2O3@CeO2 core@shell cubes exhibited enhanced catalytic activity toward CO oxidation compared with both pure CeO2 and Mn2O3, which was attributed to the synergistic interaction between CeO2 and Mn2O3. Impressively, Mn2O3@CeO2-0.1 sample with a proper CeO2 thickness exhibited the highest catalytic performance, attaining 100% CO conversion at 220 °C.

A comparison of the influence of CeO2 and In doped CeO2 interlayer on the properties of the YGBCO/interlayer/YGBCO tri-layer films deposited by pulsed laser deposition

High critical current (Ic) has long been proved important to REBa2Cu3O7−δ (REBCO or RE123) superconductor for the practical applications. To achieve high Ic values, the primary way is to increase the thickness of superconducting layer and to enhance high critical current density (Jc). However, Jc drops precipitously with increasing the thickness of the films. This phenomenon is called the thickness effect, which can be effectively inhibited by fabricating superconductor/interlayer/superconductor tri-layer structure. In this study, a series of YGBCO/CeO2/YGBCO and YGBCO/In doped CeO2 (CeO2 + In)/YGBCO tri-layer films with different interlayer thickness were fabricated. The microstructure, surface morphology and superconducting property of these samples were measured. It was found that all the tri-layer films had pure c-axis orientation. When using CeO2 film as an interlayer, the two YGBCO layers in the tri-layer films were almost completely isolated, resulting in the low Ic values, which were equivalent to the Ic of a single YGBCO layer. While using CeO2 + In film as an interlayer, the Ic values of all the YGBCO/CeO2 + In/YGBCO trilayers were almost double the Ic of a single YGBCO layer, and the Ic values of the trilayers firstly slow increased and then decreased with increasing the thickness of CeO2 + In interlayer. Under the optimal experimental parameters, the Ic value was much higher than that of the a double YGBCO layer without interlayer. The thickness effect of superconducting layer can be effectively inhibited by inserting CeO2 + In interlayer with wide thickness range.

Nanostructured TiO2 thin films sensitized by CeO2 as an inexpensive photoanode for enhanced photoactivity of water oxidation

Nanostructured CeO2/TiO2 bilayer thin films were fabricated by sequential deposition of CeO2 on TiO2 with varying the thickness of CeO2 using sol–gel spin-coating method. All samples were characterized by XRD, SEM, and UV–Visible absorption spectroscopy with an inspiration to use them as photoanode in photoelectrochemical splitting of water. The CeO2/TiO2 bilayer with the optimized thickness of CeO2 and TiO2 showed enhanced photoelectrochemical response of 2.1 mA cm-2 at 0.95 V/Ag/AgCl as compared to pristine CeO2 and TiO2. The improved photocurrent density of CeO2/TiO2 bilayer probably due to rapid transfer of charge carriers or electrical gradient at CeO2/TiO2 interface. This scalable and cost effective work with stable PEC performance of CeO2/TiO2 also shows the potential for realistic PEC applications.

Influence of CeO2 layer thickness on the properties of CeO2/Gd2O3 multilayers prepared by pulsed laser deposition

CeO2/Gd2O3 multilayers were prepared on Si (100), quartz and inconel-783 substrates by pulsed laser deposition technique at an oxygen partial pressure of 2 Pa and substrate temperatures of 300 and 873 K. The layer thickness of CeO2 was varied from 5 to 30 nm, whereas Gd2O3 layer thickness was kept constant (∼10 nm). The phase and crystallite size of the films were characterized by X-ray diffraction (XRD), X-ray reflectivity (XRR), Raman spectroscopy, atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) techniques. The layer thicknesses, measured by XRR as well as from HRTEM micrographs were in good agreement with each other. The CeO2/Gd2O3 multilayers show transmittance of ∼70%. Nanoindentation measurements indicated that the hardness values of the multilayers were higher than that of single layers of CeO2 and Gd2O3 thin films.

High-performance ZnCo₂O₄@CeO2₂₄ core@shell microspheres for catalytic CO oxidation.

In this paper, we report a self-assembly method to synthesize high-quality ZnCo2O4@CeO2 core@shell microspheres with tunable CeO2 thickness. ZnCo2O4 spheres were first synthesized as the core, followed by a controlled CeO2 shell coating process. The thickness of CeO2 shell could be easily tuned by varying the feeding molar ratio of Ce/Co. Transmission electron microscope (TEM) images and scanning transmission electron microscope (STEM) image have identified the core@shell structure of these samples. In CO oxidation tests these ZnCo2O4@CeO2 core@shell microspheres exhibited promising catalytic performance, and the catalytic activity of the best sample is even close to the traditional noble metal-CeO2 system, attaining 100% CO conversion at a relatively low temperature of 200 °C. Cycling tests confirm their good stability of these core@shell microspheres besides activity. Their high catalytic performance should be attributed to the core@shell structure formation, and moreover further H2-temperature-programmed reduction (TPR) results revealed the possible synergistic effects between the two components of ZnCo2O4 and CeO2.

The Influence of the Microstructure and Morphology of CeO 2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape

YBa2Cu3O7−δ films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Δω, of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Δω vs. buffer thickness and T c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00 l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00 l) texture) and other defects generated by agglomeration supply a low fraction of (00 l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.

Effects of CeO2 buffer layer on the dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel processing

The Ba0.6Sr0.4TiO3 (BST60) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by a sol–gel method. The thickness of CeO2, serving as a buffer layer, was varied from 0 to 75 nm, in order to optimize the dielectric tunable property. X-ray patterns analysis indicates that all the thin films exhibit good crystalline quality with a pure perovskite phase and insertion of the CeO2 buffer layer does not change the crystal structure of BST60. Dielectric properties of the thin films were investigated as a function of both temperature and direct current electric field. The results show that dielectric constant and loss are modified by insertion of the CeO2 buffer layer. The BST60 thin films with 25 nm thickness CeO2 buffer layer have the highest figure of merit, low dielectric loss, and suitable dielectric constant, which render them attractive for the tunable microwave device applications.

One-pot synthesis of core–shell Au@CeO2−δ nanoparticles supported on three-dimensionally ordered macroporous ZrO2 with enhanced catalytic activity and stability for soot combustion

A series of multifunctional catalysts of three-dimensionally ordered macroporous (3DOM) ZrO2-supported core–shell structural Au@CeO2−δ nanoparticles were successfully synthesized by the one-pot method of gas bubbling-assisted membrane reduction–precipitation (GBMR/P). All the catalysts possess a well-defined 3DOM structure with interconnected networks of spherical voids, and the Au@CeO2−δ core–shell nanoparticles with different molar ratios of Au/Ce are well dispersed and supported on the inner wall of the uniform macropore. 3DOM support facilitates the contact efficiency between solid reactant and catalyst, and the Au@CeO2−δ core–shell nanoparticles with strong metal-oxides interaction improve the amount of active oxygen species and the sintering resistance of supported Au nanoparticles due to the optimization of the interface area by formation of the metal-oxides core–shell (MOCS) nanostructure particles. 3DOM Au@CeO2−δ/ZrO2 catalysts exhibit high catalytic activity and stability for diesel soot oxidation. Among the as-prepared catalysts, 3DOM Au@CeO2−δ/ZrO2-2 catalyst with the moderate thickness of CeO2−δ nanolayer shell shows the highest catalytic activity for soot combustion, i.e., its T50 is 364 °C. In summary, 3DOM Au@CeO2−δ/ZrO2 catalysts are excellent systems for catalytic combustion of solid particles or macromolecules, and the design concept and facile synthesis method of 3DOM oxide-supported MOCS nanoparticle catalysts can be extended to other metal/oxide compositions.

Nanostructured Pt–CeO2 thin film catalyst grown on graphite foil by magnetron sputtering

Layers of different thickness of CeO2 doped by Pt were prepared by magnetron sputtering on different substrates: Si (100) and a graphite foil. The structure and chemical composition of the Pt–CeO2 catalysts have been investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES). SEM showed that the layers prepared on different substrates had very different morphology. XPS and HAXPES studies demonstrated that Pt was dispersed only in Pt2+ and Pt4+ oxidation states in CeO2. Intensity of Pt2+- and Pt4+-peaks was affected by the plasma substrate interaction effects showing that carbon substrate played an active role by determining the film structure. The Pt2+/Pt4+ and Ce3+/Ce4+ ratios depend on the layer thickness and increases in the case of the graphite substrate. The reduced character of porous layer was explained by a general effect of formation of defects and oxygen vacancies at oxide edges and steps, and oxygen reaction with carbon which is responsible of formation of oxygen deficient cerium oxide at the interface.

Improvement of IBAD-MgO texturing for high throughput of buffered substrate

The requirements from the market on two important factors of performance and cost need to be satisfied for commercialization of the coated conductors. Highly biaxially grain texturing with high production rate should be realized from the perspective of buffer layers processing. IBAD-MgO process is one of the major techniques which are possible to satisfy those requirements. The structure of our buffered substrate is IBS-GZO/IBAD-MgO/RFsputter-LaMnO3/PLD-CeO2. The PLD-CeO2 process is the rate limiting and cost dominant one in this architecture. It is proposed that the self-texturing CeO2 layer thickness could be reduced by optimization of the MgO processing due to higher MgO texturing and/or effective growth of self-texturing CeO2. Influence of the IBAD beam conditions and deposition time has been studied to optimize the IBAD conditions. Optimized IBAD conditions were decided from the viewpoints of in-plane grain texturing and the stability to obtain high texturing on fabrication. The Δϕ value of CeO2 layer was improved from 4–5° to 3–3.5° by the optimization. This buffered substrate gave high and uniform Ic values of 524–565A/cm-width for 50m long GdBCO (1.5μm) tape, indicating uniform distribution of Δϕ(CeO2). This improvement of Δϕ(CeO2) enables to reduce the CeO2 thickness down to 300nm without making Δϕ(CeO2)>5°, which improves CeO2 throughput from 10m/h to 30m/h. A 50m long patch sample showed more uniform Δϕ distribution around 4° even by high speed of 30m/h as CeO2 through-put. Highly and uniformly textured CeO2 buffered substrate was obtained in 100m long cost-effectively by optimization of IBAD-MgO processing.

RE (RE = Sm, Eu, Gd)‐doped CeO2 single buffer layers for coated conductors prepared by chemical solution deposition

AbstractTextured RE (RE = Sm, Eu, Gd)‐doped CeO2 single buffer layers for coated conductors were prepared by a polymer assisted chemical solution deposition (PACSD) approach. The as‐grown buffer layers on biaxially textured NiW(5%) alloy tapes were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM) as well as atomic force microscopy (AFM). The thicknesses of these buffer layers have been determined to be over 150 nm, on which a YBCO film has been deposited with an onset transition temperature above 90 K and a critical current density of 1 MA cm–2. These results indicate that RE doping can increase the critical thickness of CeO2 and PACSD may be a cost‐effective way to deposit CeO2. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of growth and property of YBa2Cu3O7-x coated conductors on the thickness of CeO2 buffer layer

Biaxially textured MgO templates were grown on un-textured metal substrates by inclined-substrate-deposition and YBa2Cu3O7-x films were epitaxially grown on these substrates by pulsed laser deposition. Yttria-stablized-zirconia and CeO2 were deposited in turn as buffer layers prior to YBa2Cu3O7-x growth. The biaxial alignment features of the films were examined by X-ray diffraction 2θ-scan，pole-figure，-scan and rocking curve of Ω angles. The Raman spectroscopy，scanning electron microscopy and atomic force microscopy were used to characterize the orientation order，morphology and surface roughness of the YBa2Cu3O7-x films，respectively. The influence of the thickness of CeO2 on the properties of the YBa2Cu3O7-x films were investigated and the singnificant and unique dependence of the properties of YBa2Cu3O7-x films on the thickness of CeO2 were revealed. The possible mechanisms for this dependence were discussed.

Research on CeO 2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition (PLD) under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel (SS) tapes coated by IBAD-YSZ (IBAD-YSZ/SS), and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density (Jc) of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.

Effective thickness of CeO2 buffer layer for YBCO coated conductor by advanced TFA-MOD process

YBCO films were fabricated on PLD-CeO2/IBAD-Gd2Zr2O7/Hastelloy substrates using the advanced TFA-MOD process. The effective thickness of the CeO2 buffer layer for obtaining high Ic was investigated in short samples of YBCO films. The CeO2 buffer layer was epitaxially grown on an IBAD-Gd2Zr2O7 template tape with 18° of Δϕ by a reel-to-reel PLD system. The in-plane grain alignment of PLD-CeO2 buffer layers rapidly improved with the thickness and saturated at a critical thickness of 0.8μm. The size of CeO2 grains was about 1μm at the saturated thickness of Δϕ. YBCO films with the thickness of 1μm were deposited by the TFA-MOD on the CeO2 buffer layer with different thickness films. Improvement of the CeO2 in-plane grain alignment resulted in increase of Ic. The Ic values of 250–290A were obtained with the CeO2 layer thicker than 0.8μm. The CeO2 thickness, at which the intensity ratio of the BaCeO3 was saturated, corresponded to the critical thickness. From the view points of achieving higher production rates and to obtain the CeO2 Δϕ value of 5° as well as considering the reaction between YBCO and CeO2, the optimum thickness of the CeO2 buffer layer on the IBAD-Gd2Zr2O7 with 18° of Δϕ was found to be at least 0.8μm.

Controllable capacitance–voltage hysteresis width in the aluminum–cerium-dioxide–silicon metal–insulator–semiconductor structure: Application to nonvolatile memory devices without ferroelectrics

The Al/CeO2/Si metal–insulator–semiconductor (MIS) structure showed a capacitance–voltage (C–V) hysteresis, which could be controlled by variation of the CeO2 thickness. For a sample with 3000 Å CeO2, hysteresis width as high as ∼1.8 V was obtained. For nonvolatile field-effect transistors, the Al/CeO2/Si MIS structure with a reliable and controllable C–V hysteresis could be an alternative to metal–ferroelectric–semiconductor structures containing unstable, multicomponent ferroelectric materials.

Studies on the Surface Morphology and Orientation of CeO2 Films Deposited by Pulsed Laser Ablation

We studied the surface morphology and orientation of CeO2 films grown by pulsed laser ablation (PLA) on r-cut (1102) Al2O3 substrates and evaluated the effects of predeposition annealing conditions of Al2O3 and film thickness of CeO2. The annealing of Al2O3 substrates improves the smoothness of the surface and performing this in high vacuum leads to better crystallinity and orientation of deposited CeO2 films compared to those annealed in oxygen. A critical value of the film thickness was found beyond which the surface roughness increases abruptly. Atomic force microscopy (AFM) study showed that the surface of CeO2 films is characterized by a mazelike pattern. Increasing the film thickness leads to the formation of larger islands which cause the increase in the surface roughness of the films. The areal density and height of these islands increased with film thickness.