Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas at low pressure (i.e. in a vacuum system). The main application of glow discharge in electron microscopy (EM) is to convert naturally hydrophobic (‘water-hating’) carbon-coated transmission electron microscopy (TEM) support grids into a hydrophilic (‘water-loving’) condition. Glow discharge treatment with air will make film surfaces negatively charged and hydrophilic and allow the easy spread of aqueous solutions.
Other treatments include:
Hydrophilic-positive treatment in air with magnesium acetate post-treatment to allow nucleic acid adhesion to carbon films.
Hydrophobic-positive treatment with alkylamine for proteins, antibodies and nucleic acids.
Hydrophobic-negative treatment in air for positively charged protein molecules, (e.g. ferritin and cytochrome c).
Glow discharge can also be used for modifying surface, for example, to increase bond strength of polymers.
For further information please see the GloQube – a dedicated glow discharge system.
Glow discharge is also available on other coating systems (e.g. the SC7620, Q150R, Q150T and Q300 series with optional attachment) or add-ons to larger vacuum evaporators (e.g. the K975X).
NB: Glow discharges are sometimes considered to be ‘imperfect’ plasmas and cannot be used to plasma etch or plasma ash specimens their use mainly being confined to altering surface energies, not the removal of bulk material. For these applications the K1050X RF Plasma Barrel Reactor is recommended.