SPI Supplies® TEM Grid Collection
Why some grids are more likely to require cleaning before use
We wish to share some information about the grid making process that is not
generally known, however, we release it here in order to minimize the
"cleaning" of grids that really don't have to be cleaned at all!
Quite simply put, the copper grids offered by SPI Supplies are passivated
with a passivation layer, it is a proprietary anti-tarnishing treatment of
primarily organic composition. The amount of layer present is measured in
terms of molecular dimensions, and its presence should be detectable only
with XPS or Auger.
Such passivation coatings to reduce or eliminate tarnishing (e.g. oxidation)
of the grid surface is not necessary and therefore is not applied to the
grids made from Ni or Au.
The vast majority of users of copper grids find no real need to "clean" this
passivation layer from the surfaces of their grids before use. However,
there are some who have found that this extra cleaning step does result in
better results. So clearly, there could be reasons for the cleaning of
copper grids before use.
To the degree we can determine, at least some of those engaging in this
cleaning process picked up and carried over the cleaning step from a time
that they were using copper grids. But for most users of the SPI nickel or
gold grids, such a cleaning step really is not necessary. The final
cleaning step given the SPI grids should render such further cleaning
unnecessary.
Cleaning to improve adhesion:
Some users report better section adhesion to grids that have been cleaned.
However, the way one picks up their sections on the grids can have an even
far greater impact on section adhesion to a grid. Putting it another way,
you want to take full advantage of surface tension effects to hold the
sections to your grids, thereby avoiding the use of so-called "grid pens".
If the sections are picked up from underneath, that is, the grid is lowered
into the water first, and the approach to the section is from underneath,
there will be experienced maximum surface tension forces holding the section
in place on the grid. Those who approach the grid from above, pushing the
grid down on the section, seem to experience less of the surface tension
forces, perhaps because the grid never really was completely wet by the
water.
But if you think that your grids should be cleaned no matter what the
composition, we do make available a suggested grid cleaning protocol.
We hope that this message has not been too confusing, but this is a
controversial topic amount EM users and we are just trying to bring a bit
more "light" to the discussion.
We would welcome comments from customers of SPI grids who might
want to share their own experiences with grid cleaning.
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Tuesday February 09, 2010
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