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HREM imaging of small Pt clusters dispersed in Y-zeolites (1990)

Pan, M. ; Cowley, J. M. ; Chan, I. Y.

Springer

Catalysis letters 5 (1990), S. 1-11

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ISSN: 1572-879X

Keywords: HREM ; small Pt clusters ; zeolites

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract High resolution electron microscopy (HREM) has been used to study dispersed Pt clusters in NaY- and USY-zeolites. All the samples contained 0.8% Pt and were reduced at temperatures of 300 ° C, 500 ° C and 650 ° C. The size of the Pt clusters ranged from a few å up to ∼ 30 å. When the incident electron beam was sufficiently strong, it caused some of the extremely small metal clusters to sinter. This was usually accompanied by zeolite damage. This in-situ sintering must be taken into consideration when interpreting the particle size distribution results obtained solely by TEM, especially for particles that are smaller than 10 å. The minimum phase contrast imaging condition is demonstrated to be more appropriate than optimum defocus for detecting the extremely small Pt clusters inside the zeolite structures.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00772087

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Geometric analysis of surface resonance conditions in reflection high energy electron diffraction (1987)

Peng, L. M. ; Cowley, J. M.

New York, NY : Wiley-Blackwell

Journal of Electron Microscopy Technique 6 (1987), S. 43-53

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ISSN: 0741-0581

Keywords: Ewald sphere ; Refraction ; Specular reflection ; Double diffraction ; Diffraction geometry ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Natural Sciences in General

Notes: A three-dimensional analysis in reciprocal space is used to analyse reflection high energy electron diffraction (RHEED) patterns. Particular emphasis is placed on investigating the surface resonance phenomenon, the resonance conditions, and the diffraction mechanisms. The surface resonance regions defined by the resonance beam threshold conditions are related to the limits for the specular reflection spot in the diffraction pattern. The introduction of an Ewald sphere of varying radius is shown to be useful in understanding the surface phenomenon. Simulations based on the geometric theory, taking account of the surface refraction effect, describe very well the RHEED pattern geometry from the (111) surface of a platinum single crystal.

Additional Material: 11 Ill.