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Bulk Values (bulk + value)
Selected AbstractsSurface morphology of sputtered Ta2O5 thin films on Si substrates from X-ray reflectivity at a fixed angleJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2008Hsin-Yi Lee The temporal variation of the surface morphology of Ta2O5 films on Si substrates has been measured using X-ray reflectivity at a fixed angle during radio-frequency magnetron sputtering. During an early stage of growth of polycrystalline Ta2O5, the variation of surface roughness revealed a morphology of island nucleation and island coalescence. For a thickness greater than 7,nm, the surface roughness increased, to more than 2,nm at a thickness of 80,nm. For crystalline Ta2O5 films, the density of sputtered Ta2O5 films increased and attained the bulk value for a film only at a thickness greater than 80,nm. For an amorphous sputtered film, the surface was less rough and the density was less than that for a crystalline film. [source] A comprehensive investigation of the structural properties of ferroelectric PbZr0.2Ti0.8O3 thin films grown by PLDPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009David Walker Abstract X-Ray diffraction investigations were made of high-quality epitaxial thin films of the ferroelectric material lead zirconate titanate, PbZr0.2Ti0.8O3 (PZT), grown by pulsed laser deposition (PLD). Layers from 7 to 200,nm in thickness were studied, deposited on a 30,nm SrRuO3 (SRO) electrode on a [001] oriented SrTiO3 (STO) substrate. The out-of-plane lattice parameters of the PZT films were measured by high-resolution X-ray diffraction using CuK,1 radiation. A significant enhancement of the c lattice parameter with film thickness was observed, the maximum value of 4.25,Å reached in the 30,50,nm thick films. For film thicknesses greater than 100,nm, the c lattice parameter is relaxed, towards the bulk value of 4.13,Å at this composition. The in-plane lattice parameters were studied by Grazing incidence X-ray scattering (GIXS), using 15,keV synchrotron radiation at I16, Diamond. The a lattice parameter of domains with [001] oriented normal to the sample surface was effectively lattice matched to the SRO layer in the 7,nm ultra-thin film, but relaxed compared to the SRO in thicker films. The tetragonality of the [001] oriented domains decreases with increasing film thickness, approaching the bulk value of 1.05 in the thickest films. Evidence for the presence of [100] oriented a -domains was found in PZT films as thin as 30,nm, the proportion of which increased with increasing film thickness, suggesting they grow in order to relieve stresses that would prevent the epitaxial growth of thicker PZT films. The a -domains in the thicker films were found to be located nearer to the PZT/SRO interface than to the top surface of the PZT. [source] Liquid-Injection MOCVD of ZrO2 Thin Films using Zirconium Bis(diethlyamido)-bis(di- tert -butylmalonato) as a Novel Precursor,CHEMICAL VAPOR DEPOSITION, Issue 5 2006R. Thomas Abstract The stabilization of highly reactive amide complexes of zirconium diethylamide with malonates as chelating ligands leads to a stable six-coordinated monomeric complex which shows promise for CVD applications. This novel precursor, zirconium bis-(diethylamido)bis(di- tert -butylmalonato) zirconium, [Zr(NEt2)2(dbml)2], has been characterized and tested in a production-type MOCVD reactor for ZrO2 thin-film deposition. Up to 450,°C, the ZrO2 films are amorphous, and above 475,°C films they are crystalline. Atomic force microscopy (AFM) shows a lower roughness (,2.5Å) for as-deposited amorphous films compared to crystalline films (,6.0,Å); however, smooth crystalline films can be obtained by post-deposition annealing of amorphous films. Electrical properties are investigated for Pt/ZrO2/SiOx/Si capacitor structures. Relative dielectric permittivity reaches a bulk value of 24, and leakage currents for typically 4,nm thick films are below 10,4,A,cm,2 at a bias of ,1,V. Hence, the precursor shows promising properties for possible application in the deposition of high- k gate oxide (MIS) and high- k dielectric (MIM) structures. [source] Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin filmsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2005H. OGI ABSTRACT This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in-plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement,amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions. [source] Increased gas solubility in nanoliquids: Improved performance in interfacial catalytic membrane contactorsAICHE JOURNAL, Issue 2 2009Marc Pera-Titus Abstract The kinetics of gas-liquid catalytic reactions can be strongly promoted when these are performed in interfacial catalytic membrane reactors instead of other three-phase reactors such as slurry stirrers or trickle beds. The well-defined gas-liquid-catalyst contact in this system avoiding diffusional limitations is usually argued as the main reason for such enhancement. In this work, using nitrobenzene hydrogenation as a model reaction, we propose that this increased catalytic performance might also be attributed, at least partially, to increased gas solubilities in mesoconfined solvents (or simply "nanoliquids") in interfacial contactors overcoming the values predicted by Henry's Law. To support this hypothesis, we provide experimental evidence of a dramatic increase of H2 solubility in confined ethanol using mesoporous ,-Al2O3 as confining solid. Gas-liquid solubilities can be enhanced up to five times over the corresponding bulk values for nanoliquid sizes lower than 15 nm as long as the gas-liquid interface is confined in a mesoporous array. In such a situation, the volume of the gas-liquid interface is no longer negligible compared to the total volume of the confined liquid, and the high surface excess concentrations of the gas adsorbed on the liquid surface make solubility grow up dramatically. According to these measurements, we discuss how nanoliquids might form in catalytic membrane contactors, which gas-liquid configuration in the reactor appears to be more appropriate, and how the structure of the mesoporous catalytic layer contributes to their increased gas solubilization performance. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Elastic properties of nanowiresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2010Claus-Christian Röhlig Abstract The elastic properties of metallic and semiconducting nanowires were analyzed by different techniques employing static and dynamic loads. The reliability of the methods is verified by analyzing well defined microstructures and a good agreement for the values of the Young's modulus determined by the different methods was achieved. For the investigated materials systems (Au, W, Si, InN), basically no differences in the Young's moduli were observed between microstructures, bulk material, and nanowires with radii of 20,300,nm. Microstructure, morphological undulation, defects, and contaminations, however, can drastically change the apparent Young's moduli of nanowires. Examples are given, where an apparent increasing or decreasing of the Young's modulus with decreasing diameter is caused by such effects. The same effects have also influence on the fracture strength in nanowires. While perfect Au nanowires exhibit fracture strengths exceeding the bulk values up to two orders of magnitude, any anomaly causes earlier failure. In addition, failure mechanisms are observed to be dependent on the microstructure. While single crystalline Au nanowires have shown a pure elastic deformation upon load, polycrystalline nanowires show a remarkable plastic deformation before breaking. [source] Preparation and electrical characterization of amorphous BaO, SrO and Ba0.7Sr0.3O as high-k gate dielectricsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010D. Müller-Sajak Abstract We report on the measurement of band offsets and electrical characterizations of amorphous BaO, SrO and Ba0.7Sr0.3O as alternative gate oxides grown on n-Si(001) at room temperature without further treatments. These materials provide relative dielectric constants close to those expected from bulk values even for ultra-thin films (equivalent oxide thicknesses below 1 nm) and posess very low rechargeable trap densities. Interface defect densities are comparable to other high-k materials for BaO and SrO films, but an order of magnitude lower for Ba0.7Sr0.3O. This demonstrates the importance of both chemical and structural interface effects (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry's LawCHEMPHYSCHEM, Issue 12 2009Marc Pera-Titus Dr. Abstract The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H2 in a series of solvents (CHCl3, CCl4, n -hexane, ethanol, and water) when confined in the cavities of mesoporous solids (,-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H2 still increases linearly with increasing pressure in the range 1,5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility. [source] | ||||||||||||||||