Ion-beam modification of SnO₂: Predictions and observations

Abstract

The response of crystalline SnO2 to heavy-ion impact has apparently never been studied in spite of the importance of this substance as a transparent electronic conductor when O deficient or doped. We present here both predictions and explicit results. The question of amorphizability can in general be answered either in terms of the ratio Tc/Tm = (crystallization temp.)/(melting temp.) or in terms of the ionicity. The values for SnO2 (e.g. Tc/Tm = 0.41 or 0.52) suggest the possibility of amorphization and this is observed to occur for heavy-ion doses beyond ∼ 3×1015 ions/cm2. Randomization should not occur with SnO2 in view of the fundamental differences between the structures of SnO2 and β-Sn. The question of whether sputtering is congruent can, at least with oxides, be treated semiempirically in terms of decomposition pressures. The values for SnO2 (e.g. 2 atm of O2 at 3000 K) are sufficiently low compared with other oxides as to suggest that the sputtering is congruent and this agress both with electron diffraction and with the lack of bombardment-induced electrical conductivity. The question of whether the rate of sputtering is normal or high is found with oxides to relate semiempirically to the pressure for congruent vaporization, thence to whether collisional sputtering is supplemented by an implied thermal component or related process. The experimental vapor pressures for SnO2 (e.g. 350 atm of SnO+ 1 2 O2 at 3000 K) are amongst the highest for all known metallic oxides, in agreement with the experimental rate of sputtering being the highest known for metallic oxides. © 1983.