Observation of Ions Emitted from Hot Graphite, Including Excited Molecular Ions

Thermal desorption of K ions from positively biased graphite (grafoil) containing K impurities has been investigated by measuring the energies of the emitted ions with a hemispherical electrostatic analyzer and the masses with a residual gas analyzer under ultra‐high vacuum conditions. Potassium ions are seen to be emitted at temperatures above 800°C. The present data provide evidence for the emission of K+ ions for sample bias voltages from 1V to 6V and the emission of K2+ ions for biases above 10V. The emission of excited K2+ ions are inferred from the measurement of the K+ ion energies which for sample biases above 10 volts with energies which correspond to approximately half of the bias (accelerating) voltage. From this it is deduced that the K2+ ions are produced and disassociate after leaving the surface. The K ion emission can be greatly enhanced by prior bombardment with an ion beam (not K ions) and quenched by ion beam doses that amorphize the graphite surface. This would appear to indicate the e...