Appearance: Semi clear to gray translucent sheets, strips, and discs
CAS#: 12001-26-2
Specific Gravity (water = 1.0): 2.7
Chemical Formula: K
2O·Al
2O
3·SiO
2
Hardness on Mohs scale of hardness: 2 - 2.25
It is important to know that the material we know as "mica" is not just a
generic kind of item, that is, that all mica "is the same". All mica most
definitely is
not the same.
First,
there are a number of different
minerals known as part of the Mica Group. And within that Group, is a
classification scheme that can be used to specify the quality of a particular
piece of mica. We believe it important for the researcher to understand these
differences, both in terms of the type of mica being used and also, the quality
of that particular type of mica.
Our interest is strictly in the
muscovite form of mica. And as a result, the only mica offered by SPI
Supplies is of the muscovite type and indeed, we offer only the highest
qualities of the mineral because of the applications of our typical customer. SPI Supplies mica, cut
into mica strips, discs, and sheets is used widely by researchers worldwide.
What is not generally known is that there is a
classification scheme of different qualities. Measurements are performed
as described and defined by ASTM Standard D351. And as with most other
things encountered in life, the higher the quality, the higher the cost.
One should be cautious if not also skeptical when a vendor offers
"EM quality mica" or "AFM quality mica"
without disclosing the precise mica grade. It has been our experience that persons offering mica in
that way are not offering the best mica (otherwise why would they not be
disclosing the grade according to the ASTM grading scheme?).
If you are reading this page, then there is a good chance that you are or will be
using mica for either a substrate for the making of carbon support films, in thin film
coatings research or as a substrate for AFM studies. There is also the possibility that
you are using mica in part because of its dielectric properties,
which can vary from
Grade V-1 on down to V-5 and beyond.
We believe that for carbon support film production and even thin film
coatings research, grade V-5 is more than adequate. It is low cost,
readily available and persons who have used it seem to have obtained
satisfactory results. It is also popular as a substrate for dispersing
fine colloidal particles prior to microscopic preparation or Pt/C shadowing.
Just remember that we are, at all times talking about freshly cleaved surfaces,
not the "as received" surfaces, so
some
thought has to be given to your cleaving technique.
Applications:
For AFM studies, and for those making either carbon films or doing thin
film coating research and wanting a higher quality mica as defined as
having fewer "steps" on a freshly cleaved surface, we would recommend grade
V-4. This grade is also great for use with AFM where a polar substrate is
desired or where polarity of the substrate just does not matter. From the
standpoint of pricing, V-4 may be somewhat more costly than V-5, but it is still
much lower in price than
HOPG when used for
this same purpose.
For AFM calibration studies or perhaps the ultimate substrate for carbon
film production, we offer the generally unavailable grade V-1. We know that
its relatively high cost, in comparison to the other grades, will ensure it
will not see general use as a substrate material. However, we believe that
nothing should be spared in terms of calibrating a SPM instrument.
Mica can also be used as a substrate for binding cells to be characterized
by TEM. It is generally best to
"silanize" the mica before doing the actual experiments. With this
approached, the plastic can be peeled away from the mica, however sometimes
a thin layer of mica will remain. However it has been the experience of
persons following this procedure that such thin adhering mica does not
adversely affect the sectioning when being done with a diamond knife
(although we will concede that such a clinging thin layer could result in
adding some fine striations to the edge of the knife).
Note: The point is not to confuse but to clarify. We believe it
important that a researcher know what kind of mica is in fact being used in
their experiments. We do not believe that "high quality mica" or "high
quality muscovite" or even "High Grade" or "EM Grade" properly and fairly
explains the differences in mica qualities.
Keep in mind that SPI Supplies is one of the largest suppliers of mica to
the microscopy and thin film coatings research market. If you do not see
your size or thickness or grade listed, let us know what you need. We can
generally make whatever is required. And without gigantic minimum
quantities either.
But whatever the grade selected, you can be sure that all of these mica
products cleave into fresh, clean surfaces, ready for immediate use. The
kinds of applications for high quality mica in a typical EM or SPM
laboratory are numerous. For example, the SPI mica strips can be used as
a substrate for the production of the very finest carbon films. Or it can
be used as a substrate for small particle dispersions where a completely
structureless and featureless background is needed. Or as a substrate
for AFM studies where a structured and polar substrate is needed.
The force needed for the cleaving depends on the mica grade selected.
Why you don't see Grade V-3 being offered:
The main difference in properties between Grade V-3 and V-4 is the
air inclusion content.
And, it is much more complicated than it being
strictly a matter of voids, or microholes or microspheres in the final
cleaved mica. But for reference, Grade V4 has 25% air content whereas
V1 has zero %. For some workers this is an important difference, but
for others it would not make any difference at all.
There are numerous deposits of mica around the world but only one or two have
the highest quality and most defect free mica and it is one of these very
scarce "ultimate sources" that is the origin of the SPI mica. We therefore
feature only muscovite mica from this one particular source, resulting in
superior cleavability and the most defect free possible surface. As our
customer you are also assured of a continuous reproducible supply of mica,
for whatever grade you are using so that experiments of the past can be
reliably reproduced in the future. But as is the case with most other
things in life, nothing is really that simple and
we have accumulated some additional information that might be of interest
to the user of mica from SPI Supplies. But just remember, whatever grade
you are going to be using, the SPI mica sheets, after cleavage, require no
further surface preparation, no cleaning and no exposure to solvents. The
surfaces are expected to be used "as cleaved".
Presence of surface charge:
Mica is a dielectric materials and therefore, on its own, can not hold a
charge.
Quality is also in the cutting:
It might not be generally recognized, but another factor affecting the
quality of the final mica product is its freedom from particulates. Cutting
mica is, in a sense, like cutting steel, and if the mica is contaminated
with particulates, this could wreak all kinds of havoc in a clean room
environment.
SPI Supplies goes to great lengths to minimize the presence of particulates
on the SPI supplied mica. We have had many years of experience cutting mica into all kinds
of custom shapes and thicknesses and have composed a
summary of methods for cutting that might be employed by customers of SPI Supplies mica.
Publishing your results?
When reporting on results using mica from SPI Supplies, be sure to mention
the grade used, thereby making it easier for some future researcher to
reproduce your results. Remember that vendors who do not report the "grade" of the
mica they are selling are invariably offering one of the lower quality
grades, most likely V-5 or worse.
Standard tolerances for SPI Supplies mica products:
Lateral dimensions: 0.005" (127 µm, 0.127 mm)
Thickness dimension: 0.0005" (12.7 µm, 0.012 mm)
Thickness variation: Not more than 5% across the flat surface
Grade V-1 Muscovite
(highest possible quality)
Each mica sheet is individually wrapped in order to preserve the V-1
quantity of each piece.
Squares
Grade V-4 Muscovite
Premium research quality
Squares and Rectangles
Discs
Grade V-5 Muscovite
Research quality
Squares and Rectangles
Round Discs
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Saturday July 04, 2009
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