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Microanalysis on the (200) diffraction intensity to determine the Al concentrations for AlGaAs-GaAs multiple-quantum-well structures (1990)

Ou, H.-J. ; Cowley, J. M. ; Chyi, J. I. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 67 (1990), S. 698-704

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: By using a nanoprobe electron beam 4 A(ring) in diameter, the [001] nanodiffraction patterns of AlGaAs-GaAs multiple-quantum-well structures have been formed and the epitaxial relationship between AlGaAs and GaAs is confirmed. The intensities of the (200) diffraction disk, monitored by a spot detector, are displayed in two ways: (1) the (200) dark-field scanning transmission electron microscopy (STEM), which shows the layers of AlGaAs and GaAs in contrast, and (2) the (200) line-scan profile, which reveals the (200) intensity distribution of a specimen region of uniform thickness. The thickness and the absolute Al concentration of AlGaAs layers are, respectively, determined from the contrast of, and the (200) thickness contour position in, the (200) dark-field STEM images. The microanalysis on the (200) line-scan profile is used to find the local Al concentrations in AlGaAs layers and to study the interface boundary between the layers of AlGaAs and GaAs. Diffusion of the Al atoms from the AlGaAs layer into the GaAs layer is also reported.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.345774

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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.