  We have investigated the effects of low-energy ion beam irradiations using
argon clusters on the chemical and electronic properties of LaAlO3/SrTiO3
(LAO/STO) heterointerfaces by combining X-ray photoelectron spectroscopy (XPS)
and electrical transport measurements. Due to its unique features, we show that
a short-time cluster ion irradiation of the LAO surface induces indirect
modifications in the chemical properties of the buried STO substrate, with (1)
a lowering of Ti atoms oxidation states (from Ti4+ to Ti3+ and Ti2+) correlated
to the formation of oxygen vacancies at the LAO surface and (2) the creation of
new surface states for Sr atoms. Contrary to what is observed by using higher
energy ion beam techniques, this leads to an increase of the electrical
conductivity at the LAO/STO interface. Our XPS data clearly reveal the
existence of dynamical processes on the titanium and strontium atoms, which
compete with the effect of the cluster ion beam irradiation. These relaxation
effects are in part attributed to the diffusion of the ion-induced oxygen
vacancies in the entire heterostructure, since an increase of the interfacial
metallicity is also evidenced far from the irradiated area. These results
demonstrate that a local perturbation of the LAO surface can induce new
properties at the interface and in the entire heterostructure. This study
highlights the possibility of tuning the electronic properties of LAO/STO
interfaces by surface engineering, confirming experimentally the intimate
connection between LAO surface chemistry and electronic properties of LAO/STO
interfaces.
