新型二维硫化铬的化学气相沉积法制备及其电、磁性能探索

Our modern information society relies on the development of optical, electronic, and magnetic materials. With their own advantages and disadvantages, typical two-dimensional (2D) materials such as graphene and MoS2 have unique optical and electronic properties. However, of all the types of condensed-matter behavior that have been observed in 2D materials, intrinsic magnetism has been notably absent. As recently published in Nature, clear signatures of ferromagnetism in two chromium-based 2D materials, i.e. mechanically exfoliated Cr2Ge2Te6 and CrI3, have been observed and unexpected new effects have been uncovered. Furthermore, very limited theoretical studies have shown that 2D CrS2 not only has unique optical and electronic properties, but exhibits outstanding magnetic properties. However, there is few report on experimental study of 2D CrS2 so far. Here, on the basis of our preliminary study of 2D CrS2, we will develop methods for 2D CrS2 synthesis based on chemical vapor deposition and explore its fundamental electronic and magnetic properties. We will systematically investigate the influence of topological structure and chemical component of substrates on the synthesis of 2D CrS2. By combining theoretical study, we will experimentally study its fundamental electronic and magnetic properties of 2D CrS2 as functions of the phase and the layer number of CrS2 under applied magnetic field. Based on our study, we aim to reveal the dominant factors which control the nucleation and growth of 2D CrS2 and establish appropriate protocols for the fabrication of 2D CrS2, and to elucidate the relationships between the phase and the layer number of 2D CrS2 and its electronic and magnetic properties such as energy band structure, carrier transport, and ferromegnetism. Our study will help us to comprehensively understand how to experimentally create 2D CrS2 and the fundamental electronic and magnetic properties of 2D CrS2. Combined with their rich electronics and optics, the emergence of magnetism in chromium-based 2D materials, if possible, could open up numerous opportunities for 2D magnetic, magnetoelectric, and magneto-optic applications.

信息社会与光、电、磁材料息息相关。石墨烯、MoS2等已有二维材料在光、电等方面具有优异性能，各自也存在优缺点；最近研究表明二维Cr2Ge2Te6和CrI3具有新颖磁性，然而具有本征磁性的二维材料还很缺乏。有限的理论研究表明二维CrS2具有优异光、电、磁性能，但实验研究鲜有报道。在申请人前期研究基础上，本项目研究二维CrS2的化学气相沉积法制备技术及探索其基本电、磁性能。将重点研究衬底表面拓扑结构和化学组分对合成二维CrS2的影响，进而揭示影响其成核生长的关键因素；结合理论研究，实验上重点研究在外加磁场下二维CrS2的相结构和层数对其能带结构、载流子输运、铁磁相转变等基本电、磁性能的影响。通过本项目研究，揭示控制二维CrS2成核生长的关键因素，建立可控制备技术；揭示二维CrS2的相结构和层数与其能带结构、载流子输运、铁磁相转变等之间的内在关联性，为认识具有潜在重要性的CrS2提供基础数据。

集成电路微缩化、多功能异质集成、低功耗是未来芯片发展趋势。室温下温度的二维本征磁性材是磁存储技术基础，至今稳定的在室温下具有铁磁特性的二维材料聊聊无几。本项目从0到1制备出室温下稳定且具有室温铁磁特性的二维层状CrS2材料、成果制备出晶圆级纯1T相CrS2薄膜，建立了不同相的CrS2材料的基本原子结构、Raman谱图特征等数据库；实验和理论上发现，2H- CrS2表现为半导体特性，单层的禁带宽度约0.95 eV，1T- CrS2为金属特性、具有室温铁磁特性【M. S. Xu, et al., Nanoscale 11, 20123 (2019)、Adv. Mater. Interfaces 9, 2201353 (2022)】，这在芯片技术不断发展中为发展小型化、低能耗的磁存储具有重要意义。研究了2H-CrS2与金属（Ag, Au, Pd, Pt, Sc和 Ti）接触界面特性，发现不同肖特基结存在不同的接触势垒、轨道耦合、隧穿势垒等，对于电子输运而已，Ti是所研究的金属中最好的接触金属【Phys. Status Solidi B 256, 1800597(2019)】。在本项目的支持下，也展开了二维层状材料及其器件相关的研究。与Si基CMOS工艺兼容，制备了晶圆级二维PtSe2薄膜及其与硅的异质结高性能高性能、空气稳定、自驱动、室温宽带光电探测器，该光电探测器表现出超高的响应度(8.06 A W-1)和比探测率、极低的暗电流(0.12 pA)以及优秀的开关比；研制的PtSe2/超薄SiO2/Si异质结光电探测器件具有对于硅基异质集成的弱光探测等方面具有重要的实用价值【Science China Materials 66, 193 (2023)】。构筑了一系列基于有机半导体和二维MoS2的异质结，发现尽管都是type-II型异质结，DIP/MoS2、PTCDI-Ph/MoS2、SnCl2Pc/MoS2出现荧光淬灭现象，而PTCDA/MoS2出现荧光增强现象；在VOPc/MoS2异质结出现不同于以往报道的层间激子发光现象【Mater. Horiz. 9, 1253 (2022)】，即该异质结层间发光峰的能量在构成VOPc和MoS2的禁带宽度之间，研究认为异质结的电荷转移、能量转移不仅仅依赖于异质结是type-II还是是type-I，而与界面结构有关。