Negative-charged ion energy spectra of the Fe_3O_4 (001) and (111) surface revealed large peaks attributed to the O^- recoils from a binary collision. Under Ar^+ ion bombardments such an emission was largely affected by the screening effect of the Fe ions. A distinguished peak related to the O^+ recoil ions was observed under Ne^+ ion bombardments, while such a peak was merged into the high background in the case of Ar^+ ion ones. A weak effect from the Verwey transition was found on oxygen emissions. For the (111) surface a small peak characteristic of the O^+ recoils from double collisions appeared in the energy spectra around 140-170 K and a minimum was observed in both R^+(T) and R^-(T) curves under 6 keV Ne^+ ion beam.
The (100) surface of magnetite Fe_3O_4 thin film was studied by a UHV low-temperature scanning tunneling microscope and by an ion scattering spectroscopy. The tunneling spectra revealed a widening of the gap with decreasing temperature, which may be related to the metal-insulator phase transition in this material. A strong effect of this phase transition on ion scattering from such a surface was observed. The temperature dependence of the scattered ion yield, R^+(T), revealed two minima at around 100 K and at 125 K under Ne^+ bombardment with the primary energy up to 6 keV. The disappearance of the high-temperature minimum at a bombarding energy of 6.5 keV gave a further evidence for the ion velocity dependence of the character of the R^+(T) curve, which has been first observed for a MBE Fe_3O_4 (111) film surface.
Surfaces of three selected materials were investigated by means of low-energy ion-scattering technique: (1) the magnetite (Fe_3O_4) exhibiting the so-called Verwey transition (T_V(bulk)=125 K) accompanied by a small cubic-monoclinic crystal distortion, (2) the intermetallic compound NdMn_2 undergoing an antiferromagnetic-paramagnetic phase transition (T_N=104 K) accompanied by a large crystal distortion with a volume change of 1%, and (3) the typical insulator BaTiO_3 with two structural transitions below 300 K. The primary energy of the (Ne^+, Ar^+) ion beam was in the range of 4-8 keV, and the low-energy ion-scattering spectra were collected in the temperature range of 85-300 K. A large influence from the Verwey transition on the neutralization and re-ionization of scattered ions from magnetite surface was observed, while no visible change at the magnetic phase transition in NdMn_2 was revealed in the low-energy ion-scattering spectra. A strong dependence of the characteristics of the low-energy ion-scattering spectra on the irradiated time was observed for BaTiO_3 indicating that this surface was heavily charged by ion bombardments.
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