Procedure for Cleaving Single Crystals
Easy preparation for freshly cleaved surfaces
All that is needed is a new single edged razor blade and small "hammer"
and of course, a clean, lint free work surface and a relatively dry
environment.
The procedure is to place the blade parallel to one of the existing
edges, and then tap lightly with the small hammer. Cleaving occurs
instantly and the only time there is a problem is when the razor blade
being used gets dull (it should be changed after every several
cleavings). In practical terms, a 2 mm thick slab is probably the lower
limit in thickness that can be obtained this way.
One note of caution: It just would not make sense to "pre-cleave" into
desired thicknesses since you would then lose the benefit of a surface
that was "freshly cleaved". That is also the reason why our firm does not
offer smaller cleaved pieces, we believe it would result in inferior
results.
Never lose sight of the fact that the advantage of the use of these
freshly cleaved substrates is that the cleaving produces a very flat,
relatively clean surface. However, it must be prepared immediately and then
placed in the vacuum chamber of the system being used for the deposition,
followed by an immediate pump down, which is then followed by the deposition
of one or more thin film coatings.
If all of this is not done quickly and as described some of the benefit of
the freshly cleaved surface could be lost.
For those researchers using the freshly cleaved surface as a smooth substrate
for crystal growth, there is often times asked the question "can't we make a
surface without any cleavage steps" and the answer is, probably not.
However there are some tricks that have been reported to help reduce the
number of steps formed and we present some of them here:
1. Irradiate the entire crystal before cleaving with a Co60 source, which
tends to set up point defects in the crystal making it easier to cleave, and
presumably more homogeneously as well. However, one of our best resources
for information on single crystal NaCl says that not only is radiation not
going to help anyone, but adds that for NaCl it is absolutely not necessary,
since the crystal cleaves so readily anyhow. Those comments would not apply
however for LiF.
2. After cleaving, take a piece of SPI Lens Cleaning Tissue,
place it on a smooth surface, wet the lens tissue with a small amount of water,
and then rub in a circular motion in the middle of the water wet area. Now we
have not tried this particular suggestion out in our own laboratory but we
present it as a suggestion, one that was presented on the Microscopy Listserver.
But we do add this caveat: But for good quality single crystal NaCl, the
flattest surface is produced by cleaving the sample. It is our opinion and
experience that polishing it will only make the surface worse! So we
present this second suggestion only as a historical reference, but is not
something we ourselves recommend
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Saturday July 05, 2008
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