VO2薄膜表面氧缺陷的修复:F4TCNQ分子吸附反应  

Healing of oxygen defects on VO_2surface: F_4TCNQ adsorption

作　　者：王凯[1] 张文华[1] 刘凌云[1] 徐法强[1] 

机构地区：[1]中国科学技术大学,国家同步辐射实验室,合肥230029

出　　处：《物理学报》2016年第8期347-353,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11175172,U1232137,u1332133);中国科学院合肥大科学中心科学研究项目(批准号:2015SRGHSC032)资助的课题~~

摘　　要：VO_2表面氧缺陷的存在对VO_2材料具有显著的电子掺杂效应,极大地影响材料的本征电子结构和相变性质.通过2,3,5,6-四氟-7,7’,8,8’-四氰二甲基对苯醌(F_4TCNQ)分子表面吸附反应,可以有效消除表面氧缺陷及其电子掺杂效应.利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应,发现这种方式使得VO_2薄膜样品氩刻后得到的V^(3+)失去电子成功地被氧化成原先的V^(4+),同时F_4TCNQ分子吸附引起电子由衬底向分子层转移,界面形成带负电荷的分子离子物种.受电化学性质的制约,(F_4TCNQ)分子吸附反应修复氧缺陷较氧气氛退火更安全有效,不会引起表面过度氧化形成V_2O_5.Oxygen-defect vacancies that routinely exist in wet production of VO2 material or on the surface of VO2 single crystal after surface treatment have significant influence on the metal-insulator phase transition features mainly due to their enhanced effect of doping on V 3d electronic structure. The removal of the surface oxygen defects is highly desired for investigating the VO2 intrinsic electronic properties. In this work, we propose a charge transfer doping method by using strong electric affinity molecule tetrafluorotetracyanoquinodimethane（F4TCNQ） adsorption rather than the normal thermal annealing in oxygen atmosphere to heal the surface oxygen defects of VO2 crystalline film. The healing effect is probed by the electronic structure evolution at the （F4TCNQ）/VO2 interface. The VO2 crystalline film is grown by an oxygen plasma assisted molecular beam epitaxy method on an Al2O3（0001） substrate. Surface oxygen defects on VO2 film are produced after a mild sputtering with an ionic energy of 1 ke V and a thermal annealing in vacuum at 100？C. The influence of F4 TCNQ molecule adsorption on the electronic structure of the sputtered VO2 film is studied by using in-situ synchrotron-based photoelectron spectroscopy（XPS） and X-ray absorption spectroscopy（XAS）. XPS and XAS results demonstrate convincingly that V^（3＋）species of sputtered VO2 are oxidized into the V^4＋ and simultaneously negative molecular ions form at （F4TCNQ）/VO2 interface resulting from the electron transfer from VO2 to the F4 TCNQ layer.The preferred adsorption on surface defects and the strong electron withdrawing function of F4 TCNQ molecules may account for the effective elimination of the electron doping effect of oxygen defects on VO2 surface. This charge transfer effect at interface recovers the electronic properties of VO2. Compared with thermal annealing in oxygen environment,the healing of oxygen defects by the molecular adsorption can prevent the surface from over oxidating VO2 into V2O5,which opens a new ro

关 键 词：二氧化钒薄膜 氧缺陷 F4TCNQ 同步辐射 

分 类 号：O484[理学—固体物理] O483[理学—物理]