A B
Figures 3: (A) Platinum-carbon replica TEM micrograph and (B) SEM micrograph of cuprite, Cu
2
O.
proportional to the d-values of the compounds. face of the specimen. But all this can be sharpened up if
An alternative to this was to use reflected, instead of need be.
transmitted, electrons. I learned this interesting technique It is interesting to compare the carbon replica and SEM
on a Phillips 300 TEM. Delivered with that microscope was images of these copper oxides. Figure 3 shows replica and
one of the few reflection diffraction stages in this country. SEM micrographs of Cu
2
O, and Figure 4 shows similar
It mounted low in the column above the final lens. Figure 1 micrographs of CuO.
is a crude diagram showing how it relates to the beam and Electron diffraction did help my professional work.
the screen. The idea was to simply present the beam to the The only Science publication of my career came from
sample in grazing incidence and use the final lens to suitably transmission electron diffraction carried out on the
enlarge the diffraction pattern. I could never understand high-resolution diffraction stage of that old HU11A. The
why this technique did not catch on because it’s far easier venerable George Brindley, of clay-mineralogy fame, had
than struggling to get x-ray diffraction patterns from tiny me determine the lattice constants of a special form of
samples. kaolinite to three decimal places, far better precision than is
Figure 2 compares reflection electron diffraction usually possible by “selected area diffraction” in the normal
patterns from cuprite (Cu
2
O) and tenorite (CuO), the red sample position.
and black copper oxides. For purists, the electrons aren’t Editor: Reflection high-energy electron diffraction
truly reflected. They pass through atomic-level asperities (RHEED) was revived in the 1980s and became the basis for
that exist on the surface of almost everything. The beam the technique of reflection electron microscopy (REM) that
streams down the surface of the sample, partly passing can reveal fine surface steps and reconstructions. For more
through these little protrusions, and is diffracted when details see the special issue on REM in T. Hsu (ed.) J. Elect.
Bragg’s law is satisfied. The d-values are quite low-precision Microsc. Tech. 20 (1992) part 4.
because the pattern originates at different points down the
A B
Figures 4: (A) Platinum-carbon replica TEM micrograph and (B) SEM micrograph of tenorite, CuO, corrosion deposit on copper coupon.
2009 September •
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