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Preparation and structural characterisation of Pd/MgO(001) model catalysts
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
1995 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Palladium films with nominal thicknesses varying between 0.5 and 40 nm have been grown by electron beam evaporation on polished MgO(OO1) wafers, kept at substrate temperatures, Ts, of 100, 300 and 600 °C. Microstructure, strain and orientation of the Pd films were studied using a combination of x-ray diffraction (XRD) and transmission electron microscopy (TEM).

Two types of TEM samples were prepared: MgO substrates chemically thinned to electron transparency prior to growth, using phosphoric acid (H3P04), and carbon lift-off samples, where a thin conductive amorphous carbon coating containing the palladium particles, was stripped off the MgO wafer substrates and collected on microscope grids. The lift-off samples proved to be the most suited ones for nucleation and growth studies.

The method of grazing incidence XRD (GIXRD) using a standard laboratory x-ray source was explored in the case of very thin films. By GIXRD, epitaxial Pd was detected for films with a nominal thickness 0.5 nm for films grown at 600 °C, ≥ 1 nm for films grown at 300 °C and ≥ 2.5 nm for films grown at 100 °C. In a few cases, also four 111-oriented Pd domains rotated 90 degrees with respect to each other were detected using GIXRD.

The growth morphology, observed in TEM, showed nucleation and initial three­ dimensional particle growth, for all Ts values. The Pd particles started to coalesce at a nominal film thickness ≤ 1 nm. For Ts = 300 and 600 °C, the coalescence was liquid-like, and secondary nucleation was observed from nominal film thicknesses of 2.5 nm. Increasing growth temperature resulted in a decreased substrate coverage. Continuous film formation was obtained at thickness 10 nm and 20 nm for Ts = 100 and 300 °C, respectively.

The average Pd particle sizes, calculated from the GIXRD 2θ peak broadening, were comparable to the particle sizes seen in TEM. For Ts = 600 °C, the lateral Pd d020 plane distance was expanded ~0.8 % for nominal film thicknesses < 2.5 nm, whereas thicker films showed bulk Pd lattice spacing. Ts = 300 °C, an average lattice expansion for nominal thicknesses ≤ 2.5 nm, and for Ts = 100 °C for film thicknesses ≤ 10 nm

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 1995. , p. 65.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 514
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-145883Local ID: LiU-TEK-LIC-1995:46ISBN: 9178716012 (print)OAI: oai:DiVA.org:liu-145883DiVA, id: diva2:1201227
Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2018-10-30Bibliographically approved

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Total: 6 hits
CiteExportLink to record
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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
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  • Other style
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  • nn-NB
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Output format
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