Role of carrier concentration in swift heavy ion irradiation induced surface modifications

摘要

Highly conducting SnO2 thin films were prepared by chemical spray pyrolysis technique. One set of as-deposited films were annealed in air for 2 h at 850 degrees C. These as-deposited and annealed SnO2 thin films were irradiated using gold ions with energy of 120 MeV at different fluences ranging from 1 x 10(11) to 3 x 10(13) ions/cm(2). Electrical measurement shows that as-deposited SnO2 films are in conducting state with n = 3.164 x 10(20) cm(-3) and annealed SnO2 films are in insulating state. The amorphized latent tracks are created only above a certain threshold value of S-e which directly depends on the free electron concentration (n). The electronic energy loss (S-e) of 120 MeV Au9+ ions in SnO2 is greater than the threshold energy loss (S-eth) required for the latent track/molten zone formation in annealed SnO2 thin film, but is less than S-eth required for as-deposited SnO2 film. Therefore, the latent tracks/molten zones are formed in the annealed SnO2 film and not in the as-deposited SnO2 film. Thermal spike model is used for the calculation of threshold energy loss and radius of melted zone. The possible mechanism of the structural changes and surface microstructure evolutions is briefly discussed in the light of ion's energy relaxation processes and target's conductivity. The atomic force microscopy (AFM) study of films shows that the morphologies of irradiated films are linked with carrier concentration of target materials. (C) 2017 Elsevier B.V. All rights reserved.