SPI-Chem Mica Grade V-4 3 mm Discs, CAS# 12001-26-2 with Grid Box
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Grade V-4 Muscovite
Premium research quality
Appearance: Semi clear to gray translucent sheets, strips, and discs
Specific Gravity (water = 1.0): 2.7
Chemical Formula: K2O·Al2O3·SiO2
Hardness on Mohs scale of hardness: 2 - 2.25
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
Thickness = 0.05 mm (0.002")
Diameter = 3.05 mm diameter
Designed to fit into a standard TEM grid holder
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.
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.