钛酸锶钡薄膜中微观结构缺陷及其形成机理

采用脉冲激光沉积方法,在(001)单晶铝酸镧(LaAlO3)衬底上成功制备出钛酸锶钡(Ba0.75Sr0.25TiO3)外延薄膜.利用高分辨电子显微学对其微观结构进行了详细研究,并探讨了其微观结构缺陷的形成机理.研究发现,在钛酸锶钡外延薄膜中存在失配位错和穿透位错,且存在直线型和锯齿型的两种反相畴界.失配位错是由于钛酸锶钡薄膜与LaAlO3单晶衬底之间存在较大的晶格失配形成的,可分解为不全位错;穿透位错可以分解为不全位错伴随有堆垛层错的形成.反相畴界的形成是由于衬底表面存在台阶,直线型反向畴界是由于形核点离台阶处较近产生的,而锯齿型反向畴界是由于形核点离台阶处较远而形成.研究结果可为其它钙钛矿型外延薄膜中微观结构缺陷的形成机理提供理论指导.

Microstructural Defects and Their Formation Mechanisms in Ba0.75Sr0.25TiO3 Epitaxial Film

Ba0.75Sr0.25TiO3 film was epitaxially grown on a(001) LaAlO3 substrate using single-target pulsed laser deposition.The microstructure of the epitaxial film was investigated by high-resolution transmission electron microscope(HRTEM),and the formation mechanism of microstructural defects was explored.It was shown that misfit and threading dislocations existed in the epitaxial Ba 0.75 Sr 0.25 TiO 3 film.Apart from the dislocations,two different kinds of antiphase boundaries,straight and zig-zagged,were observed.For misfit dislocations,they were formed due to the lattice mismatch between LaAlO 3 and Ba 0.75 Sr 0.25 TiO 3 which could dissociate into several partial dislocations.For the threading dislocations,it was found that their dissociation usually coexists with stacking faults.The formation mechanism of the antiphase boundaries is attributed to the terrace or step on the surfaces of LaAlO 3 substrate.If the nucleation site is just on the terrace,straight antiphase boundaries will be formed.However,if the nucleation site is not just on the terrace but a little far away from the terrace,zig-zagged antiphase boundaries will be produced.The results could shed light on the microstructural defects in other perovskite epitaxial films.