uses of metal for shadowing freeze fracture techniques and ultramicrotomes
... To be observed by EM, cells and tissues have to be prepared with techniques that differ considerably from those used for light microscopy, although the steps are comparable. ... As they are very fragile, the sections have to be floated on water after being cut and are collected on small circular metal grids for viewing. As contrast depends on atomic number of atoms on specimen (higher atomic number atoms scatter more electrons) EM stains consist of heavy metal salts, usually uranyl acetate and lead citrate. ... Specimens have to be fixed, dried and coated with a thin layer of heavy metal (gold, platinum or palladium). ... Special TEM techniques There are special techniques of preparation of specimens for TEM that are of relevance for this course. ... Metal shadowing. ... A metal is sprayed on the specimen, under vacuum, at an oblique angle so that a coating that is thicker in some places than in others is created. This procedure is named shadowing as a shadow effect is produced upon observation.