AN INVESTIGATION OF THE USE OF CHROMIUM, PLATINUM AND GOLD COATING FOR SCANNING ELECTRON-MICROSCOPY OF CASTS OF LYMPHOID-TISSUES

Resin casts replicate the internal structure of organs and provide a t hree-dimensional representation of the arrangement of vessels and inte rcellular spaces. Casting media are insulators and must be coated with a conductor to prevent sample charging and to allow the adequate prod uction of secondary electrons from the specimen to generate sufficient signal to form a clear image. Visualization of surface structures dep ends largely on the metal coating. The use of gold or platinum, deposi ted on Mercer casts of lymphoid tissues using plasma-magnetron sputter ing, and of chromium coating of casts by Penning ion-beam coating, was investigated. Casts were examined using a field emission scanning ele ctron microscope at 3-3.5 kV. Thick coatings of gold were necessary to reduce cast charging but they obscured fine structural information. C harging effects were less pronounced when casts were coated with plati num, but charge lines were present at slow scan rates. The dimensions of cast impressions for both platinum and chromium coatings were simil ar to those described in fixed tissues. Negligible charging and maxima l cast thermal stability and structural information was obtained from casts which were tumbled during chromium coating.