高氧压下氧化物薄膜同质和异质外延的RHEED实时监测

我们自行研制了具有三级差分气路可以在高气压下工作的RHEED系统(High-pressure RHEED),并利用本系统实时监测了(001)SrTiO3基片上SrTiO3:Nb、Ba0.5Sr0.5TiO3、YBa2Cu3O7单层薄膜,及Ba0.5Sr0.5TiO3/SrTiO3:Nb双层膜的生长过程.研究结果表明当镀膜室氧压高达21Pa时该系统仍然可以正常工作,并且能够获取较清晰的衍射图样.通过分析衍射图样我们发现,所有这些薄膜都是外延生长且晶体质量良好,但薄膜生长模式及表面平整度受沉积条件影响较大.在真空下薄膜基本上以层状模式生长,具备纳米级光滑的表面,且其表面平整度并不因膜厚的改变而变化;而在10Pa量级氧压下薄膜更倾向于以岛状模式生长,膜表面平整度较差,并且随膜厚的增加粗糙度上升.此外对多层薄膜而言,底层薄膜的表面和结构直接影响到顶层薄膜的质量和品质.

IN SITU MONITORING OF THE GROWTH OF COMPLEX OXIDE THIN FILMS AT HIGH OXYGEN PRESSURES USING A THREE-STAGE PUMPING RHEED SYSTEM

We have successfully developed a high-pressure RHEED accessory with a three-stage differential pumping system for the PLD equipment in our laboratory. It can be used for in situ monitoring during the deposition of complex oxides at standard PLD conditions. Oxygen pressure in the deposition chamber can be increased to as high as 21Pa while fairly clear RHEED patterns are observable. We monitored the deposition of SrTiO_3:Nb,Ba_ 0.5 Sr_ 0.5 TiO_3,and YBa_2Cu_3O_7 single layers,as well as Ba_ 0.5 Sr_ 0.5 TiO_3/SrTiO_3:Nb heterostructure on (001) SrTiO_3 substrates. Pattern analyses suggest that all the films are epitaxy with good crystallinity; however the growth mode and film morphology are greatly affected by the ambient during film deposition. In high vacuum,the film tends to grow in the layer-by-layer mode,and the surface roughness is within nanometers; in an oxygen pressure of 5Pa or above,however,the film tends to grow in the island mode with less smooth surface. It is revealed that,in the case of multilayer growth,the crystallinity and surface smoothness of the top layer are limited by the quality of the bottom layer.