Figure 5

Cationic intermixing A-sites vs B-sites.

(a–c) Diffusion profiles of Ti and La from EELS analyses for the (a) 3 u.c. (c) 5 u.c. sample. The x coordinates locate the cations by the number of unit cells to the interface (+1 = first u.c. in STO, −1 = first u.c. in ). Ti diffused up to the film surface for both samples. Assuming a full occupancy of B-sites, Al would diffuse down to 3/4 u.c. into the substrate of the LAO(3 u.c.)/STO sample and slightly deeper (4/5 u.c.) into the substrate of the LAO(5 u.c.)/STO sample. La atoms diffused down to about 5 u.c within the substrate of the 3 u.c. sample whereas it was found deeper (6/7 u.c.) into the thicker sample STO. The shallower diffusion depth of B cations compared to A cations results in La_Sr. donor dopants that are not fully compensated by Al_Ti’ acceptor dopants and can provide charge carriers. It can be noticed that La cations are detected at deeper depth by EELS than by MEIS. This is explained by the straggling of He⁺ particles that decreases the sensibility of this ion beam analysis with the depth of the analyzed region. (b–d) EELS fine structure of the O-K edge recorded in the first u.c. under the film surface of the (b) 3 u.c. (d) 5 u.c. sample. The observed O-K pre-peak, between 529 and 531 eV, is characteristic of the Ti-O π* hybridization⁴¹ which confirmed the presence of Ti atoms within the very first unit cell of each samples.