SPI Plasma-Prep™ II
Plasma Etcher/Asher/Cleaner

Although the many SEM applications for the SPI Plasma-Prep™ II Plasma Etcher/Asher/Cleaner are in general, far more widely known and appreciated than TEM applications, there are nevertheless some exciting new possibilities.

The above micrograph was the result of the following sample preparation procedure:

1. Bacterial sample was not dehydrated but was infiltrated with the SPI Chem Low Acid GMA (for TEM) where the GMA acts as its own dehydrator, so that no additional dehydration is necessary. For immunogold work, for example, this approach to sample preparation ensures the maximum preservation of antigenicity within the sample.


2. Sections are picked up on a silicon dioxide supported grid prepared using SPI-Chem silicon monoxide chips.


3. Prepared grids with sections are placed in the SPI Plasma Prep II plasma etcher and exposed to the oxygen plasma for time periods as short as ten seconds. The oxygen plasma removes all organics from the section, and at the same time, since oxygen will not effect the SiO₂the support film remains intact, unlike the situation that would exist if a Formvar^® or other organic based support film was used.


4. By eliminating the organics from the section, the inorganic constituents of the section are left behind, resulting in an easy way to "see" the original structure by way of a form of "ghost" image.


5. For EDS work, the sensitivity and lower limits of detection are improved considerably, since the primary source for the Bremsstrahlung radiation is now removed.

a) Of the two fundamentally different plasma reactor geometries available, and we refer now to "barrel" vs. "parallel plate" geometry, in order to achieve the best removal of organics , one should use an etcher with a barrel type geometry since only the barrel is capable of giving isotropic etching. A parallel plate etcher, which produces anisotropic etching, while desirable in some instances, would most definitely not be desirable in this application since it would result in organics being left behind underneath the mineral deposits. b) We do not know for sure whether the composition of the resulting thin film support that we have called "silicon dioxide" really is pure silicon dioxide but it is the end result of the evaporation of silicon monoxide via a tungsten basket in a vacuum evaporator.

There has been some discussion as to just what really is the final composition of a film produced this way, and we don't know any more than anyone else, however, we did want to disclose the way such films should be made so that anyone trying to do this themselves should have minimum difficulty (although there is some "art" that is needed just the less!).

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