The Effects of Osmium Coating and Chemical Cleaning on SEM Images of Dispenser Cathode Surface Porosity

Most tungsten dispenser cathodes are coated with a thin refractory metal layer to lower the work function and enhance emission. The coating must not interfere with the dispensation of barium from the tungsten matrix onto the emitting surface. Cathode manufacturers and users have long discussed the possible effects of the coating being either too thin or too thick and masking the pores in the tungsten matrix. SEM inspection is often used to evaluate the surface porosity of a dispenser cathode