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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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Characterization of the annealed (0001) surface of sapphire (α-al2o3) and interaction with silver by reflection electron microscopy and scanning reflection electron microscopy (1992)

Ndubuisi, Godfrey C. ; Liu, J. ; Cowley, J. M.

New York, NY [u.a.] : Wiley-Blackwell

Microscopy Research and Technique 20 (1992), S. 439-449

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ISSN: 1059-910X

Keywords: Single-crystal sapphire ; Oxygen-annealing ; RHEED ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Natural Sciences in General

Notes: Annealed (0001) surfaces of single-crystal sapphire (α-Al2O3) rod have been studied in the electron microscope using reflection electron microscopy (REM), scanning reflection electron microscopy (SREM), and reflection high energy electron diffraction (RHEED). Annealed surfaces of (0001) sapphire are vicinal and characterized by close-packed (0001)-oriented terraces separated by faceted multiple-height steps, with edges parallel to energetically preferred low-index directions (〈101―0〉 and 〈112―0〉). These structural features are not seen on cleaved surfaces or polished surfaces treated at temperatures 〈 1,250°C. Oxygen-annealing produces clean surfaces which prove useful for investigating the interaction of deposited metals with the (0001) sapphire. Both REM and SREM (with microdiffraction spots) techniques have been used to observe fine structure of flat Ag islands on the scale of 1 - 100 nm on the (0001)-oriented terraces as well as aggregations at the steps. A preliminary result on interaction with Cu is also included.

Additional Material: 11 Ill.