Low Energy Ions Scattering (LEIS) analysis of surface atomic terminations in SrTiO3, LaAlO3 and NdGaO3 single crystals

Research in thin film materials has recently focus its attention on the role of interfaces in the enhancement or, in some cases, in the appearance of new unexpected properties. For example, the 2D electron gas generated at the interface between the insulating SrTiO3 and LaAlO3 perovskites 1. A more precise knowledge of the interface chemical composition between single crystals and inorganic thin film oxides is then a step towards a better comprehension of some of the mass and charge transport properties in functional thin films. Generally the most of the superficial analytical techniques probe an average of many atomic layers, LEIS instead gives a very accurate atomic composition of the outer atoms of the surface. In this work we analyzed by LEIS the surface termination of LaAlO3 (100), SrTiO3 (100) and NdGaO3 (110) single crystals. Samples have been studied both as received and after a specific thermal treatment distinct for each kind of material. These processes, already reported in literature, are used to obtain a fully single A-cation surface terminated. LEIS analysis is an unique tool to confirm the preciseness of some of these controversial methods 2. By the use of a sequential low energy Ar+ sputtering with primary ion LEIS analysis, a 3D reconstruction of the chemical composition of approximately each atomic layer has been possible. A frequent contamination of the single crystal surface during the thermal treatments has also been pointed out. 1 A. Ohtomo and H. Y. Hwang, Nature, 2004, 427, 423–426. 2 R. Gunnarsson, A.S. Kalabukhov, D. Winkler, Surface Science 603 (2009) 151–157