Observation by scanning electron microscopy of radiation damage produced in LiF by ionic bombardments

A scanning electron microscope supplied with a discharge system for : nsulating materials has been used to observe LiF crystals bombarded with 2 MeV protons, 60 MeV oxygen ions and 56 MeV chlorine ions. The damaged zone gives a clear contrast which allows a direct measure of the penetration depth of the incident ions. This contrast has been attributed to the defects which were also revealed by means of optical absorption measurements. The bleaching of defects during thermal annealings allows the observation of the stopping zone of the incident ions. In this case, the observed contrast is due to the variation of the mean atomic number in the implanted zone. This permits a direct measure of straggling. For light implanted ions (2 MeV protons) the contrast of the stopping zone can be attributed to an escape of fluorine atoms from this heavily damaged zone. For heavy implanted ions (56 MeV chlorine ions) the chemical contrast is due to the implanted ions themselves.