Influence of electronic charge compensation on Rutherford backscattering spectra of biased insulators
On irradiating quartz targets with 2 MeV 4He + ions the spectra show a drastic shift of the RBS edge towards higher energies. This shift depends strongly on the biasing voltage applied to the target holder. For positive biasing up to 200 V no significant shift of the edges compared to the theoretical RBS edges of SiO 2 is observed. On the other hand, negative biasing up to - 200 V shifts the edges by 120 keV. This effect can be explained by a negative (electronic) charge compensation of the positive charge on the irradiated insulator. This charge compensation is affected by the potential of the holder, the positive potential of the target and the potential of the space charge in front of the target. The experimental results are explained according to this model with realistic parameters, i.e. mean electron energy and electron density.