In more recent developments known as field ionization (FI) and field desorption (FD), the ion source consists of an anode (emitter) which may be a thin wire, a sharp edge or blade, or, more recently, 10µm tungsten wires coated with carbon fibre microneedles about 30µm long, and a cathode which is a plate with a fine slit or hole according to the shape of the emitter.