Wu Kedi, Torun Engin, Sahin Hasan, Chen Bin, Fan Xi, Pant Anupum, Parsons Wright David, Aoki Toshihiro, Peeters Francois M, Soignard Emmanuel, Tongay Sefaattin
School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA.
Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerpen B-2020, Belgium.
Nat Commun. 2016 Sep 22;7:12952. doi: 10.1038/ncomms12952.
Transition metal trichalcogenides form a class of layered materials with strong in-plane anisotropy. For example, titanium trisulfide (TiS) whiskers are made out of weakly interacting TiS layers, where each layer is made of weakly interacting quasi-one-dimensional chains extending along the b axis. Here we establish the unusual vibrational properties of TiS both experimentally and theoretically. Unlike other two-dimensional systems, the Raman active peaks of TiS have only out-of-plane vibrational modes, and interestingly some of these vibrations involve unique rigid-chain vibrations and S-S molecular oscillations. High-pressure Raman studies further reveal that the A S-S molecular mode has an unconventional negative pressure dependence, whereas other peaks stiffen as anticipated. Various vibrational modes are doubly degenerate at ambient pressure, but the degeneracy is lifted at high pressures. These results establish the unusual vibrational properties of TiS with strong in-plane anisotropy, and may have relevance to understanding of vibrational properties in other anisotropic two-dimensional material systems.
过渡金属三硫属化物形成一类具有强烈面内各向异性的层状材料。例如，三硫化钛（TiS）晶须由弱相互作用的TiS层构成，其中每层由沿b轴延伸的弱相互作用准一维链组成。在此，我们通过实验和理论方法确定了TiS不同寻常的振动特性。与其他二维系统不同，TiS的拉曼活性峰仅具有面外振动模式，有趣的是，其中一些振动涉及独特的刚性链振动和S-S分子振荡。高压拉曼研究进一步表明，A S-S分子模式具有非常规的负压依赖性，而其他峰则如预期那样变硬。各种振动模式在常压下是双重简并的，但在高压下简并性消失。这些结果确定了具有强烈面内各向异性的TiS不同寻常的振动特性，并且可能与理解其他各向异性二维材料系统中的振动特性相关。
