Hydration Stages—Achievements and Obstacles
As we have previously reported our laboratory has developed and perfected a dynamically pumped hydration stage. The stage consists of four collinear apertures: two 100μ and two 200μ. The two 100μ apertures straddle the specimen and define the specimen chamber. The two 200μ apertures define the intermediate chamber which is independently pumped by a normal cryotrapped forepump. The whole stage is translated in order to move the apertures collinear with the beam by the normal specimen translation mechanism, through the bore of the upper polepiece. The specimen may be moved within its 1.2mm gap by an independent translation mechanism thereby allowing the full area of the grid to be examined. Water vapor evaporates from the source and continuously flows out of the apertures thereby providing a very effective anticontamination device.