SPI Supplies® Brand of TEM grids
How to decide which grids are going to be best for your particular application
Introduction to TEM grids offered by SPI Supplies:
A new user, when confronted with the huge selection of grid possibilities,
can find the experience to be almost overwhelming. But if the following is kept in mind,
one can quickly find some "order" in the "confusion". Try to remember the following:
- Most popular grids: 95% of all grids sold are copper.
- Most popular mesh sizes: 80+% of all grids sold are 200, 300, or 400 mesh.
- Immunogold tagging: Nickel (or gold) grids should be used because electrochemical
reactions occur with copper when doing immunogold labeling. On the other hand, the residual magnetism in
nickel, if ordinary antimagnetic stainless steel tweezers are being used
instead of SPI Miracle Tip or Dumostar tweezers,
can cause such grids to "stick" to the tweezer tips, in which cases gold grids are recommended.
But gold is soft and to some degree fragile, so some don't like gold either for
that reason. The point is, the selection of the "right" grid for your work
can involve a series of trade offs, and there is no one grid that is always
going to be the "right" grid.
- Custom coated grids: The purchase of "coated" vs "uncoated" grids. Some samples are
self-supporting and do not require any kind of additional "support film".
If you can get away without the use of a support film, you will in general,
have the best results. Sometimes this could mean that using a higher mesh
grid, for example 1000 mesh instead of 400 mesh, you can get away without
using a support film. But if a support film is necessary, as it is for a
huge percentage of all TEM users, the question is, do you make them yourself
or do you have someone make them for you, like SPI Supplies. This is a
somewhat personal kind of decision since it strikes at the heart of the
question of how you want to be spending your time. However, if you did
decide to purchase grids already coated by the experts at SPI Supplies,
you can be sure that you are receiving the very best possible coated grids.
- High temperature studies: High temperature studies require are more specialized grid, either
silicon nitride membrane window grids
or for some applications, carbon
coated molybdenum grids. For work on nanoparticles, especially those that
are really "nano", ones that are on the order of 1-3 nm in size, since that
size is also the size of the carbon grain in a carbon coating, carbon coated
grids might not be the best choice. We would suggest 20 nm thick silicon
nitride membrane window grids should be considered.
- Holey and lacey filmed grids: These are preferred by those who need a
support but just the same, want to have areas from which observations can be
made without any support film being present. Unfortunately, when talking
about any TEM image, one also has to talk about the "drift rate", that is,
the rate of drift of the image in the beam which is never ever "zero". It
is always some finite number. Any carbon film is fragile and holey and
lacey are even more so. For most users, however, the drift rate is small
enough that it does not detract too much from the resolution in the
resulting images. But for those needing something better, we can suggest the
perforated silicon nitride membrane window grids.
- Index or "Finder" grids: These grids are
preferred by those who once making a particular observation, want to come
back for further examination on the same identical features. Some times
these grids are preferred by those who want certain features to be examined
by others.
- Special application grids: Some types of work,
for example, those asbestos analysis work, require grids of a very special
design and those should be using exclusively, the SPI Asbestos Index Grids,
which are made to a specification (for quantitative EM) that has an almost
immeasurable standard deviation in area, grid square to grid square.
- Low EDS background grids: For those doing EDS
work, and not wanting to have unwanted x-rays from the grid itself, we can
offer grids constructed of
beryllium,
diamond,
and
composite carbon. Unfortunately, these
low background grids also in general have a lower percent open area (e.g. %
transmission).
No sag" TEM support films: All support films to one degree or another, exhibit "grid sag"
as they go across a grid square. Since the position in the z direction is what determines
magnification, and since the z position is an unknown variable, the use of conventional
grids in cases where one is making precision measurements is not the optimum experimental
approach. This is where one should consider using the
SPI Supplies® Brand Silicon Nitride Membrane Window grids
or the Perforated Silicon Nitride Membrane window grids.
You will be assured of a far more precise measurement experience using these new types
of grids because when compared to conventional grid support films, grid sag is virtually zero.
The above is not meant to be an all-inclusive listing of some of the
trade-offs and different possibilities for the selection of their grids. It
is meant to give the beginner a "start". SPI Supplies is part of
Structure Probe, Inc, an internationally know independent testing and
analytical laboratories doing electron microscopy studies for others. Some
of us trace our "beginnings" in electron microscopy back to the early
1960's. If you have a special need that is not being addressed above,
let us know what kinds of samples you are trying to examine and we will do our
best to give you a recommendation based on our own years of experience with
both materials as well as life sciences samples.
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Tuesday May 13, 2008
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