Study of the properties of Ga beam from the nozzle source

A nozzle source, similar in principle to those used for ionized cluster beam deposition has been built and studied. The apparatus has been designed for both thin film deposition and the measurements of ion beam energy by the retarding potential method. Its unique features include a two filament electron emitter for heating a graphite crucible, which enables the control of the temperature gradient along the crucible axis. Good thermal and electrical shielding of both the crucible and the ionizer sections has been provided. The crucible is held at ground potential and its temperature is measured by a thermocouple. Multiple grid electrodes positioned in front of an ion collector help to discriminate against ion and electron background. Results obtained with Ga show the presence of energetic ions only when the crucible temperature is 1700 °C or higher. The measured ion energies are consistent with the presence of clusters of hundreds of atoms ejected from the nozzle with thermal velocities. The current of the high energy component of the beam is only 0.1 % of the total ion current and the measurement accuracy is limited by the background of charged particles present in the vacuum chamber and the accuracy of its determination limited by the background inherent in retarding potential measurements.