分子团簇负离子束沉积超薄BiSe二维拓扑绝缘体

This project develops molecular cluster ion beam technology for preparation of two-dimensional ultrathin materials. Molecular ion beams of BiSe and BiFeSe will be generated by using a celsium sputtering negative ion source equipped on a tandetron accelerator. An electric scanner will be installed between the two 45-degree analytical magnets, and the sample stage in the cluster beam chamber will be biased with a negative voltage to decelerate the ion beams to 1-10 keV. Ultrathin films of BiSe films will be formed on Si(111)and GaAs(111) by using the low-energy cluster beams. The morphology, structure, and defects will be measured by atomic force microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and grazing-incidence X-ray diffraction, and their resistivity, carrier concentration and mobility will be studied by Hall effect. The preparation process will be optimized by tuning the ion beam energy, dose, and process temperature, with a goal of preparing 3-7 nm thick toplogical insulators. The formation of the ultrathin layers will be interpreted by cluster-solid interaction and crystal growth theories, to lay a foundation for development of the molecular cluster beam technology in preparation of novel low-dimensional materials.

本项目发展适用于二维超薄材料制备的分子团簇负离子束技术，用串列加速器的铯溅射负离子源产生BiSe,FeSe和BiFeSe等化合物离子束，在两个45度分析磁铁之间安装电扫描装置，团簇离子束靶室中的样品台外接负偏压使离子减速，获得能量1-10keV的化合物离子束，在Si(111)和GaAs(111)表面形成超薄BiSx薄膜。用原子力显微镜、扫描电镜、高分辨透射电镜和掠入射X射线衍射等方法测定薄层的形貌、结构和缺陷特性，用Hall效应测定薄膜的电阻率、载流子浓度和迁移率。改变团簇离子能量、剂量、退火温度等参数，系统研究制备工艺对BiSe超薄层的结构和物理性质的影响，获得优化的制备工艺条件。通过精确控制团簇离子剂量，制备3-7nm厚的拓扑绝缘体薄膜。用离子-固体相互作用理论、晶体生长理论等探讨超薄层形成的物理机制，为分子团簇离子束制备二维纳米材料提供科学依据。

BiFeSe是重要的拓扑绝缘体材料，本项目发展团簇负离子束制备BiFeSe技术，用串列加速器的铯溅射负离子源产生分子团簇离子束，经减速后能量达到1-10keV，在单晶Si和GaAs表面形成超薄BiSe薄膜，获得二维Bi2Se3超薄层的结构和物性等基本信息。. 对铯溅射离子源进行了改进设计，增加了静电扫描和团簇离子注入靶室，获得了原子数1-10的B, C, F, Si, Fe, Bi, Se等的团簇离子束及其分子团簇，且为负离子束，其中Fe离子束流10nA，而C、Si团簇束流达到10nA-50微安，利用这些团簇进行了离子注入制备单层与少层石墨烯、硅烯、过渡金属离子注入制备磁性半导体的实验研究，减速后则用于离子束沉积制备铋铁硒二维纳米材料。. 用激光脉冲沉积法制备了BiSe和BiFeSe膜层，结构测试表明膜层的主要结构为Bi2Se3:Fe，其中Fe的含量为5-8 at.%，用XRD, XPS和内转换电子穆斯堡尔谱(CEMS)对材料的结构、Fe原子价态、超精细结构及沉积温度的影响进行了系统研究，测得Fe原子价态为三价，Fe原子位于Bi的替位，磁性测试观察到材料以顺磁性为主，较低温度沉积的样品由于表面氧化而呈现弱的磁性，高温沉积的样品氧化则更为显著。. 在本项目支持下已发表论文9篇，在国际学术会议报告研究工作2次，培养博士研究生1名，硕士研究生1名。