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Determination of the angular distribution of backscattered particles at the ion accumulation experiment

Categories:
  • Fundamentals of Metrology
26.09.2006

A monitor was developed for the measurement of sputtered and reflected particles to determine the mass contribution of particles which are backscattered through the entry hole of the collector at the ion accumulation experiment.

Weighable masses between 50 mg and 100 mg can be accumulated currently during one beam session at the ion accumulation experiment. A singly charged Bi-ion beam with an energy of 25 keV is caught in a cylindrical collector made of aluminium with a length of 20 cm and a diameter of 8 cm by the method presently used. Atoms are sputtered and reflected when the ion beam encounters the collector bottom. A part of this sputtered - mainly neutral - atoms get lost through the entry hole of the collector. Therefore, a special monitor was developed to measure the angular distribution of the backscattered particles. The monitor consists of a central aluminium target which is circularly surrounded by special stainless steel catchers. Thereby the backscattered particles are collected on the circular surfaces of the catchers.
Depending on the angular position of the catcher a different mass was collected and determined through weighing of the catcher (see Fig.1). The various accumulated layer thicknesses can visually be seen by taking notice of the different colours that originate from light interference (see Fig.2).

Determination of the angular distribution of backscattered particles at the ion accumulation experiment

Figure 1: Mass of the accumulated layers as a function of the scattering angle. Schematic set up (right corner).

Photograph of the monitor showing some catchers with different colours

Figure 2: Photograph of the monitor showing some catchers with different colours

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Ch. Schlegel, FB 1.2, AG 1.24, Christian.Schlegel@ptb.de

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