Co离子掺杂金红石TiO2晶体的正电子湮没

Vacancy identification in Co^+ doped rutile TiO_2 crystal with positron annihilation spectroscopy

室温稀磁半导体是自旋电子器件研究的关键途径,但其室温铁磁性的内禀性及其起源的研究有争议。正电子湮没谱学方法(PAS)是研究材料缺陷的重要实验手段。为了建立缺陷结构与材料铁磁性之间的相互关系,用离子注入法制备了注入剂量不同的Co离子掺杂金红石TiO2晶体薄膜,在北京慢正电子束流装置上以不同的入射电子能量测量了样品的正电子湮没多普勒展宽能谱(DBS)和正电子符合多普勒展宽谱(CDB),分析样品的缺陷浓度和缺陷类型。DBS谱的S参数和W参数分析表明,Co离子的注入使样品出现了新的湮没机制。CDB谱的商谱分析说明,Co离子注入TiO2晶体后产生了Ti-Co-VO型和Ti-VO型氧空位复合体,样品中空位浓度随Co离子注入剂量有所增加,它是由氧空位周围过剩的Ti原子的3d电子所引起。

Room temperature Diluted Magnetic Semiconductor （DMS） is a critical path in the study of spin-electronic devices, but there are many disputes in the intrinsic properties and origin of the room temperature ferromagnetism. Positron annihilation spectroscopy （PAS） is a powerful technique for evaluating vacancy-type defects. Purpose： We aim to establish the relationship between the defect structure and ferromagnetism of the materials by analyzing the parameters of positron annihilation. Methods： Co-doped rutile TiO2 films weresynthesized by ion implantation and extensively studied by variable energy positron annihilation Doppler broadening spectroscopy （DBS） and coincidence Doppler broadening （CDB） measurements with variable energy slow positron beam for identification of the vacancies. Results： The results of DBS showed that a newly formed type of vacancy could be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy （Vo） complex Ti-Co-Vo and/or Ti-Vo were formed with Co ions implantation and the vacancy concentration increased with increasing dopant dose. Conclusion： We identify that the generation of Ti-Vo and/or Ti-Co-Vo vacancy complex are induced by the existence of excess Ti 3d electrons around the oxygen vacancy.