Key Laboratory of Materials Physics and Center for Energy Matter in Extreme Environments, Institute of Solid State Physics, Chinese Academy of Sciences, 350 Shushanghu Road, Hefei, Anhui 230031, China.
Istituto Nazionale di Ottica (CNR-INO) and European Laboratory for non Linear Spectroscopy (LENS), Via N. Carrara 1, 50019 Sesto Fiorentino, Italy.
J Chem Phys. 2018 Jan 7;148(1):014503. doi: 10.1063/1.5011333.
Dichalcogenides are known to exhibit layered solid phases, at ambient and high pressures, where 2D layers of chemically bonded formula units are held together by van der Waals forces. These materials are of great interest for solid-state sciences and technology, along with other 2D systems such as graphene and phosphorene. SiS is an archetypal model system of the most fundamental interest within this ensemble. Recently, high pressure (GPa) phases with Si in octahedral coordination by S have been theoretically predicted and also experimentally found to occur in this compound. At variance with stishovite in SiO, which is a 3D network of SiO octahedra, the phases with octahedral coordination in SiS are 2D layered. Very importantly, this type of semiconducting material was theoretically predicted to exhibit continuous bandgap closing with pressure to a poor metallic state at tens of GPa. We synthesized layered SiS with octahedral coordination in a diamond anvil cell at 7.5-9 GPa, by laser heating together elemental S and Si at 1300-1700 K. Indeed, Raman spectroscopy up to 64.4 GPa is compatible with continuous bandgap closing in this material with the onset of either weak metallicity or of a narrow bandgap semiconductor state with a large density of defect-induced, intra-gap energy levels, at about 57 GPa. Importantly, our investigation adds up to the fundamental knowledge of layered dichalcogenides.
二硒化物在常压和高压下表现出层状固态相，其中二维的化学结合单元层由范德华力保持在一起。这些材料对于固态科学和技术以及其他二维系统（如石墨烯和磷烯）具有重要意义。SiS 是该组合中最基本兴趣的典型模型系统。最近，理论上预测了具有 Si 以 S 配位的八面体的高压（GPa）相，并且在该化合物中也已实验发现了这些相的存在。与 SiO 中的 stishovite 不同，SiO 是 SiO 八面体的 3D 网络，SiS 中的具有八面体配位的相是二维层状的。非常重要的是，理论上预测这种半导体材料在数十 GPa 的压力下具有连续的带隙关闭，变成较差的金属态。我们在 7.5-9 GPa 的金刚石砧细胞中通过激光加热在 1300-1700 K 下的元素 S 和 Si 合成了具有八面体配位的层状 SiS。实际上，高达 64.4 GPa 的拉曼光谱与该材料的连续带隙关闭兼容，其起始点要么是微弱的金属性，要么是具有大量缺陷诱导的带隙内能级的窄带隙半导体状态，约为 57 GPa。重要的是，我们的研究增加了对层状二硒化物的基础知识。
