激光分子束外延BaTiO_3/SrTiO_3超晶格的晶格应变研究

Lattice Strains in BaTiO_3/SrTiO_3 Superlattice Prepared with Laser Molecular Epitaxy

采用脉冲激光分子束外延(PLMBE)方法,通过优化的工艺参数,在SrTiO3(100)单晶基片上外延结构为(8/8)的BaTiO3/SrTiO3超晶格薄膜。综合利用反射式高能电子衍射系统(RHEED)、高分辨率X射线衍射(HRXRD)以及高分辨率透射电镜选区电子衍射(SAED)技术,研究超晶格薄膜的晶格应变现象和规律。研究结果表明,在制备的BaTiO3/SrTiO3超晶格薄膜中,BaTiO3晶胞面外晶格增大,面内晶格减小;而SrTiO3晶胞面内及面外方向晶格都被拉伸,但面外晶格拉伸程度较大,SrTiO3晶胞产生了与BaTiO3晶胞方向一致的四方相转变。

The high-quality BaTiO3/SrTiO3 supertattice with a periodicity of （8/8） structure has been prepared on SrTiO3（100） substrate by pulsed laser molecular epitaxy under optimum parameters. The lattice strain in as-prepared BaTiO3/SrTiO3 superlatfiee was analyzed with reflective high energy electronic diffraction（RHEED）,X-ray diffraction（XRD） and selective area electron diffraction（SAED）. As expected,out-of-plane lattice in BaTiO3 layer increased while in-plane lattice decreased. However, surprisingly, SrTiO3 layer, in which out-of-plane lattice in- creased much more than in-plane lattice,demonstrates an out-of-plane euhie-tetragonal transition,which is consistent with that in BaTiO3 layer. Our results are helpful to explain the polarization enhancement in BaTiO3/SrTiO3 superlattice.