Apertures

Platinum Melting Point: 1768°C (3214.4°F)
Molybdenum Melting Point: 2610°C (4730°F)
Tungsten Boat Melting Point: 3422°C (6191.6°F)
(With coated ceramic Al2O3 tabs)

Aperture contamination occurs when it is exposed to the electron beam, in which case regular cleaning or replacement is required. The smaller the hole, the more quickly contamination builds up and astigmatism increases. Dirty aperture systems make alignment difficult due to beam deflection caused by dirt charging up.

Platinum/Iridium apertures may be cleaned by flaming them and applying temperature where the aperture does not exceed a color of cherry-red (not white-heat). Bunsen burner or small flame devices (alcohol, butane) have been used for this procedure. About 10-15 seconds should be sufficient for this procedure. "Flamers" for this purpose are described below. The entire surface will reach the same color when completely clean.

Molybdenum apertures must be heated in a vacuum below 10-4 mbar. After proper vacuum is reached and current applied, a color of cherry-red is achieved. Use a tungsten boat. This will require about 20-30 seconds. Molybdenum apertures can be successfully cleaned more frequently and used again, than Platinum/Iridium.

Platinum/Iridium disc apertures can be flamed in our platinum gauze "Aperture Flamer" (No. 60001) for cleaning purposes. Other Aperture Flamers (No. 60003, 60004) are shown for Platinum/Iridium discs, small and large, and for hanging strip Platinum/Iridium apertures.

The cleaned aperture(s) should be inspected on a clean glass slide at 30-40X. The hole should be clean and round. Misshapen apertures should be rejected.
 

Platinum Gauze cup and stem, with handle. Length 190mm; basket 8mm dia. x 9mm high.