ATOMIC CONTROL OF LAYER-BY-LAYER EPITAXIAL-GROWTH ON SRTIO3(001) - MOLECULAR-DYNAMICS SIMULATIONS

Molecular-dynamics simulations were performed to clarify the structure s of SrO and BaO layers on a SrTiO3(001) substrate at the atomic level , and to predict an appropriate buffer layer for YBa2Cu3O7-x/SrTiO3 he terojunction. The atomic structure of these layers grown on a SrTiO3(0 01) substrate terminated on the TiO2 atomic plane was investigated. Fr om the analysis of the angle distribution of Sr-O-Sr and the radial di stribution between Sr and O, the first single SrO layer on the SrTiO3( 001) substrate was found to keep a perfect NaCl-type structure. Howeve r, the structure of the second SrO layer deviated from a NaCl-type str ucture. This result suggests that only a single SrO layer is able to g row epitaxially and uniformly on the SrTiO3(001) substrate terminated on the TiO2 atomic plane. Since a BaO layer is one component of the YB a2Cu3O7-x layered structure, a detailed understanding of the BaO/SrTiO 3(001) heterojunction has been desired. Here, the stress induced by th e lattice mismatch of the BaO/SrTiO3(001) and BaO/SrO/SrTiO3(001) hete rojunction was evaluated. The BaO/SrTiO3(001) gained 1.2 GPa stress, w hile surprisingly the BaO/SrO/SrTiO3(001) did not have any stress. Mor eover, the BaO layer was found to grow epitaxially and uniformly on th e SrO/SrTiO3(001). Note that YBa2Cu3O7-x is expected to grow epitaxial ly on a BaO layer since the BaO layer is a part of the YBa2Cu3O7-x lay ered structure. Hence, we suggest that BaO/SrO is a suitable buffer la yer for the YBa2Cu3O7-x/SrTiO3 heterojunction.