PZT/NFO/LSMO多层磁电外延薄膜微观结构研究

Microstructure of PZT/NFO/LSMO multi-layer magnetoelectric epitaxial thin films

用脉冲激光沉积法在(110)取向的SrTiO3(STO)单晶衬底上制备了Pb(Zr0.52Ti0.48)O3/NiFe2O4/La0.7Sr0.3MnO3(PZT/NFO/LSMO)磁电复合外延薄膜,并用X射线衍射和透射电镜技术研究了外延薄膜的物相和显微结构。原子力显微镜结果表明PZT、NFO和LSMO薄膜表面均平整,晶粒尺寸分布均匀,表面粗糙度分别为1.8,1.7和0.2 nm。X射线衍射、选区电子衍射和高分辨透射电子显微镜(HRTEM)测试结果均证明各层薄膜沿(110)STO衬底外延生长,其外延关系为(110)PZT//(110)NFO//(110)LSMO//(110)STO和[001]PZT//[001]NFO//[001]LSMO//[001]STO。HRTEM结果显示,NFO/LSMO界面和LSMO/STO界面平整外延性好,无缺陷,而PZT/NFO界面较粗糙;NFO薄膜表面呈锯齿状,锯齿状面为立方NFO的能量最低{111}面,而PZT薄膜表面呈岛状,进一步的显微结构分析认为PZT薄膜为层状-岛状生长模式。

Pb(Zr0.52Ti0.48)O3/NiFe2O4/La0.7Sr0.3MnO3(PZT/NFO/LSMO)epitaxial thin films on(110)-oriented SrTiO3(STO)single crystal substrates were fabricated by pulsed laser deposition.The phase and microstructure of the prepared epitaxial films were investigated by X-ray diffraction,atomic force microscopy(AFM)and transmission electron microscopy(TEM).AFM images indicate that all the surfaces of the PZT,NFO and LSMO thin films are flat with uniform grain size,and their surface roughness are measured to be 1.8 nm,1.7 nm and 0.2 nm,respectively.X-ray diffraction,selected area electron diffraction and high resolution TEM(HRTEM)results confirm that the films are epitaxially grown on the(110)-oriented STO substrate.The epitaxial relationships of the three layers are(110)PZT//(110)NFO//(110)LSMO//(110)STO and[001]PZT//[001]NFO//[001]LSMO//[001]STO.HRTEM images show that both the NFO/LSMO interface and the LSMO/STO interface are very flat without any defects.However,the PZT/NFO interface exhibits a zig-zag structure.The zig-zag top surface is the{111}planes of cubic NFO with the lowest surface energy.Islands-like structure can be observed on the top surface of the PZT film by high magnification bright field image.Further detailed analysis reveals that PZT layer follows the layered-island growth mode.And a reasonable growth mechanism was proposed.