Fang Yuqiang, Hu Xiaozong, Zhao Wei, Pan Jie, Wang Dong, Bu Kejun, Mao Yuanlv, Chu Shufen, Liu Pan, Zhai Tianyou, Huang Fuqiang
State Key Laboratory of High Performance Ceramics and Super fine Microstructure , Shanghai Institute of Ceramics, Chinese Academy of Sciences , Shanghai 200050 , China.
University of Chinese Academy of Sciences , Beijing 100049 , China.
J Am Chem Soc. 2019 Jan 16;141(2):790-793. doi: 10.1021/jacs.8b12133. Epub 2019 Jan 4.
Noncentrosymmetric MoS semiconductors (1H, 3R) possess not only novel electronic structures of spin-orbit coupling (SOC) and valley polarization but also remarkable nonlinear optical effects. A more interesting noncentrosymmetric structure, the so-called 1T‴-MoS layers, was predicted to be built up from [MoS] octahedral motifs by theoreticians, but the bulk 1T‴ MoS or its single crystal structure has not been reported yet. Here, we have successfully harvested 1T‴ MoS single crystals by a topochemical method. The new layered structure is determined from single-crystal X-ray diffraction. The crystal crystallizes in space group P3m with a cell of a = b = 5.580(2) Å and c = 5.957(2) Å, which is a √3 a × √3 a superstructure of 1T MoS with corner-sharing Mo triangular trimers observed by the STEM. 1T‴ MoS is verified to be semiconducting and possesses a band gap of 0.65 eV, different from metallic nature of 1T or 1T' MoS. More surprisingly, the 1T‴ MoS does show strong optical second-harmonic generation signals. This work provides the first layered noncentrosymmetric semiconductor of edge-sharing MoS octahedra for the research of nonlinear optics.
非中心对称的二硫化钼半导体（1H、3R）不仅具有自旋轨道耦合（SOC）和谷极化的新型电子结构，还具有显著的非线性光学效应。一种更有趣的非中心对称结构，即所谓的1T‴-MoS层，理论学家预测它是由[MoS]八面体基序构成的，但尚未报道块状1T‴ MoS或其单晶结构。在此，我们通过一种拓扑化学方法成功制备出了1T‴ MoS单晶。新的层状结构由单晶X射线衍射确定。该晶体属于空间群P3m，晶胞参数a = b = 5.580(2) Å，c = 5.957(2) Å，它是1T MoS的√3 a × √3 a超结构，通过扫描透射电子显微镜（STEM）观察到其具有角共享的钼三角形三聚体。1T‴ MoS被证实为半导体，带隙为0.65 eV，这与1T或1T' MoS的金属性质不同。更令人惊讶的是，1T‴ MoS确实显示出强烈的光学二次谐波产生信号。这项工作为非线性光学研究提供了首个由边共享的MoS八面体构成的层状非中心对称半导体。
