SPI Supplies® Brand TEM Grids
The Fountain of Youth for grids!
In days of shrinking research and other budgets, old grids found in a drawer
are being looked at more and more frequently as to whether they can or can
not "still" be used. Remember we are talking about those grids that have
reached their senior citizen years, and we are not talking about the kinds
of routine cleaning done by some,
even for grids newly purchased.
Basically there are several types of "aging" of grids:
A) Adsorption of organics from the air, especially true for copper grids
because of their more reactive nature.
B) Reaction of grids with oxygen creating oxides, especially true for Ni.
Only on very rare occasions have we ever seen discolorations on gold grids,
but remember, in the end, different makers of grids use different production
and final cleaning and inspection procedures, so while it would be
extraordinary to have discolored SPI grids, we do know that from some
sources, this kind of condition is more likely.
Organics:
Depending on the organics being adsorbed, usually the best way is to put the
grids into a petri dish, and then expose them to an oxygen plasma, 100 watts,
in an SPI Plasma Prep II plasma
etcher, for five minutes.
The oxygen radicals so formed are highly reactive to all organics and will
leave the copper or nickel surface completely clean and free or any sorbed
organics. Not all grid manufacturing processes are the same, and some in
fact leave more organics than others on the grids just from the manufacturing
process. Hence a plasma cleaning treatment this way, even on newly purchased
grids can result is substantial increases in the adhesion levels of sections
to grids.
Oxides or other reaction products:
One hears far more about the cleaning of copper grids than other (e.g. Ni)
grids, perhaps because any kind discoloration is far more easily seen on
copper than anything else. There are several "recommended" procedures for
the cleaning of copper grids and we present both without preference:
Hydrochloric acid approach:
A 10% HCl solution is used for the cleaning of the grids.
Allow the girds time to "clean", perhaps ten minutes, and at the end of
the cleaning time the grids should have an ultra shinny appearance to them.
Remove the HCl from the beaker holding the grids, and wash several times with
distilled water (with the grids still in the beaker). Then remove the distilled
water and add acetone and allow the grids to stand for one day. Then pour the
acetone and grids out onto a clean glass Petri dish filled with filter paper.
Remove the top filter paper with the grids and put into another clean glass
Petri dish and allow to dry by allowing the acetone to evaporate."
In the case of Ni grids, the oxides can have a bluish green color, and such
discoloration is not going to be removed by an oxygen plasma in the Plasma
Prep II unit. However such oxides will generally be removed through the use
of argon. And in the event Ar does not remove the discoloration, then
CF4 gas will.
Another approach for Ni grids is clean for 10 minutes with acetic acid. The
protocol is to rinse with water, followed by drying, preferably in an oven.
When this treatment is done, there is invariably a marked improvement of the
adhesion of sections to grids. But the point is that the real benefit is
not so much due to a "cleaning" from a contamination standpoint but from
an adhesion standpoint of the sample to the grid.
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Sunday October 12, 2008
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