Raman光谱研究厚度对La_(0.9)Sr_(0.1)MnO_3/Si薄膜结构的影响

Thickness dependence of microstructure for La_(0.9)Sr_(0.1)MnO_3/Si films determined by micro-Raman spectroscopy

通过溶胶-凝胶旋涂方法结合后退火工艺在Si(100)上制备了不同厚度的La0.9Sr0.1MnO3(LSMO)薄膜,利用X射线衍射(XRD)和共焦显微拉曼散射(Raman)研究了LSMO/Si(100)薄膜的微结构.研究结果表明90nm厚的LSMO薄膜具有正交相结构,当厚度大于150nm时,薄膜具有菱方相结构.150nm厚的薄膜的Raman图谱中,490cm-1和602cm-1正交结构中的Jahn-Teller特征峰和670cm-1附近菱方相中MnO6八面体的反对称伸缩模式振动特征峰非常明显,表明薄膜为两相共存结构.随着薄膜厚度的增加,薄膜的晶格常数发生变化,a增大,c减小.这是由于在较厚的薄膜中,相邻MnO6八面体间的夹角变大,Mn—O键长增长.通过使用不同波长的激光Raman散射证实,LSMO/Si薄膜的确具有两相共存结构.由于LSMO和Si衬底间晶格失配,衬底与薄膜的界面处产生了应力,薄膜具有在衬底与薄膜的界面处为正交相、表面为菱方相的双层结构.利用不同波长激发的Raman散射,可以很容易的研究LSMO/Si薄膜的界面结构.

La0.9Sr0.1MnO3 films on Si （100） substrate of different thickness were prepared by sol-gel routine, and the microstructure of LSMO/Si was studied by XRD and confocal micro Raman spectroscopy. Both XRD and Raman results show different structures in LSMO films of different thickness. There are two strong peaks around 490 cm-1and 600 cm-1 that is characteristic of Jahn-Teller distortion in spectra and characteristic peak of rhombohedral structure of the film with thickness of 90 nm, which show the coexistence of two phases. Lattice constants of LSMO film vary with film thickness. Lattice constants vary as film thickness increases, which is because the tilting angle of MnO6 octahedron and the bond length of Mn-O increase as film thickness increases. Raman spectra of 532 nm-laser and 325 nm-laser show, that there are two phases existing in LSMO/Si film, namely the phase in LSMO/Si interface, and the rhombohedral phase in the surface.