激光分子束外延BaTiO3/SrTiO3超晶格的晶格应变研究

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.

Lattice Strains in BaTiO3/SrTiO3 Superlattice Prepared with Laser Molecular Epitaxy

The high-quality BaTiO_3/SrTiO_3 superlattice with a periodicity of (8/8) structure has been prepared on SrTiO_3(100) substrate by pulsed laser molecular epitaxy under optimum parameters.The lattice strain in as-prepared BaTiO_3/SrTiO_3 superlattice 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 BaTiO_3 layer increased while in-plane lattice decreased.However,surprisingly,SrTiO_3 layer,in which out-of-plane lattice increased much more than in-plane lattice,demonstrates an out-of-plane cubic-tetragonal transition,which is consistent with that in BaTiO_3 layer.Our results are helpful to explain the polarization enhancement in BaTiO_3/SrTiO_3 superlattice.