SPI MgO Magnesium Oxide Single Crystal Substrates
Information for cleaving and polishing MgO single crystals
Cleaving the MgO single crystals:
The MgO single crystal material supplied by SPI Supplies is normally cleaved
very easily by using either a small knife (or better still, a
single edge GEM type razor blade)
and a small hammer. This should always be done
on 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.
However, obtaining a perfectly cleaved (100) block is not easy without first
some practice and certainly it is not easy doing the cleaving without
generating at least some "chips". The MgO crystals are grown with (100)
orientation, so this kind of cleaving along the (100) plane is usually not
all that difficult by the method described above.
However, a multiwire sawing machine is used when processing to wafer form
from the MgO boule in order to achieve far superior tolerances for the cut.
Information for polishing MgO:
Some uses of MgO requires polishing and the polishing of MgO is fairly
similar to that used for other crystals of electronic materials. But the
cleaning and packing steps do require much more attention to detail and care
than most of the other materials.
If one sees a white haze on the MgO surface, it is usually because it has
been exposed to air for more than three days, in humid environments, the
exposure time to haze being less. The material is moisture sensitive, so
must be handled (and stored) under dry conditions. Clearly, one must use
a non-aqueous polishing media should one want to polish away water spots
from the surface of the MgO crystal.
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