Sputter coating

Sputter coating in microscopy is a process of covering a specimen with a very thin layer of heavy metal, generally a gold/palladium (Au/Pd) mixture. This coating increases the ability of a specimen to conduct electricity and emit secondary electrons when in a scanning electron microscope, acting as a "stain" for electron microscopy. Biological specimens, composed largely of carbon compounds, are usually poor emitters of secondary electrons due to the low atomic number of carbon. Rather than absorbing electrons from the electron source of the microscope and then emitting electrons for detection, carbon compounds tend to collect a charge.