Xie Sen, Ouyang Yujie, Liu Wei, Yan Fan, Luo Jiangfan, Li Xianda, Wang Ziyu, Liu Yong, Tang Xinfeng
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.
International School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China.
Nanomaterials (Basel). 2022 Dec 12;12(24):4429. doi: 10.3390/nano12244429.
MgSb-based compounds are one type of important room-temperature thermoelectric materials and the appropriate candidate of type-II nodal line semimetals. In MgSb-based films, compelling research topics such as dimensionality reduction and topological states rely on the controllable preparation of films with high crystallinity, which remains a big challenge. In this work, high quality MgSb films are successfully grown on mismatched substrates of sapphire (000), while the temperature-driven twin structure evolution and characteristics of the electronic structure are revealed in the as-grown MgSb films by in situ and ex situ measurements. The transition of layer-to-island growth of MgSb films is kinetically controlled by increasing the substrate temperature (), which is accompanied with the rational manipulation of twin structure and epitaxial strains. Twin-free structure could be acquired in the MgSb film grown at a low of 573 K, while the formation of twin structure is significantly promoted by elevating the and annealing, in close relation to the processes of strain relaxation and enhanced mass transfer. Measurements of scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) elucidate the intrinsic p-type conduction of MgSb films and a bulk band gap of ~0.89 eV, and a prominent Fermi level downshift of ~0.2 eV could be achieved by controlling the film growth parameters. As elucidated in this work, the effective manipulation of the epitaxial strains, twin structure and Fermi level is instructive and beneficial for the further exploration and optimization of thermoelectric and topological properties of MgSb-based films.
基于MgSb的化合物是一类重要的室温热电材料，也是II型节线半金属的合适候选材料。在基于MgSb的薄膜中，诸如维度降低和拓扑态等引人注目的研究课题依赖于高结晶度薄膜的可控制备，而这仍然是一个巨大的挑战。在这项工作中，高质量的MgSb薄膜成功生长在蓝宝石（000）的不匹配衬底上，同时通过原位和非原位测量揭示了生长态MgSb薄膜中温度驱动的孪晶结构演变和电子结构特征。通过提高衬底温度（），MgSb薄膜从层状生长到岛状生长的转变受到动力学控制，这伴随着孪晶结构和外延应变的合理调控。在573 K的低温下生长的MgSb薄膜中可以获得无孪晶结构，而提高温度和退火显著促进了孪晶结构的形成，这与应变弛豫和增强的质量传输过程密切相关。扫描隧道谱（STS）和角分辨光电子能谱（ARPES）测量阐明了MgSb薄膜的本征p型导电性和~0.89 eV的体带隙，并且通过控制薄膜生长参数可以实现约0.2 eV的显著费米能级下移。如本工作所示，对外延应变、孪晶结构和费米能级的有效调控对于进一步探索和优化基于MgSb的薄膜的热电和拓扑性质具有指导意义和益处。
