Tuning the Electronic Properties of LAO/STO Interfaces by Irradiating LAO Surface with Low-Energy Cluster Ion Beams

摘要

We have investigated the effects of low-energy ion beam irradiations usingargon 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 thata short-time cluster ion irradiation of the LAO surface induces indirectmodifications in the chemical properties of the buried STO substrate, with (1)a lowering of Ti atoms oxidation states (from Ti4+ to Ti3+ and Ti2+) correlatedto the formation of oxygen vacancies at the LAO surface and (2) the creation ofnew surface states for Sr atoms. Contrary to what is observed by using higherenergy ion beam techniques, this leads to an increase of the electricalconductivity at the LAO/STO interface. Our XPS data clearly reveal theexistence of dynamical processes on the titanium and strontium atoms, whichcompete with the effect of the cluster ion beam irradiation. These relaxationeffects are in part attributed to the diffusion of the ion-induced oxygenvacancies in the entire heterostructure, since an increase of the interfacialmetallicity is also evidenced far from the irradiated area. These resultsdemonstrate that a local perturbation of the LAO surface can induce newproperties at the interface and in the entire heterostructure. This studyhighlights the possibility of tuning the electronic properties of LAO/STOinterfaces by surface engineering, confirming experimentally the intimateconnection between LAO surface chemistry and electronic properties of LAO/STOinterfaces.