Lipatov Alexey, Loes Michael J, Lu Haidong, Dai Jun, Patoka Piotr, Vorobeva Nataliia S, Muratov Dmitry S, Ulrich Georg, Kästner Bernd, Hoehl Arne, Ulm Gerhard, Zeng Xiao Cheng, Rühl Eckart, Gruverman Alexei, Dowben Peter A, Sinitskii Alexander
Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588 , United States.
Department of Physics and Astronomy , University of Nebraska , Lincoln , Nebraska 68588 , United States.
ACS Nano. 2018 Dec 26;12(12):12713-12720. doi: 10.1021/acsnano.8b07703. Epub 2018 Nov 30.
Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals' thickness. These results could be used to distinguish between TiS crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.
准一维（quasi-1D）材料因其独特的物理性质以及在微型电子器件方面的应用前景而备受关注。然而，与传统层状晶体的剥离相比，将准一维材料机械剥离成薄片和纳米带的研究受到的关注要少得多。在本研究中，我们研究了代表性准一维晶体TiS晶须的微机械剥离，并证明它们通常会分裂成边缘非常光滑、笔直且具有明显一维TiS链特征的窄纳米带。理论计算表明，破坏二维（2D）层之间以及层内一维链之间的弱相互作用所需的能量相当，并且反过来，远低于破坏链内共价键所需的能量。我们还通过使用原子力显微镜（AFM）探针尖端在不同晶体学方向对TiS晶体施加局部剪切力，在纳米尺度上模拟了宏观剥离实验。在AFM实验中，可以使二维TiS层相互滑动，也可以从层中去除选定的一维链。我们通过拉曼光谱系统地研究了剥离后的TiS晶体，并确定了光谱位置最依赖于晶体厚度的拉曼峰。这些结果可用于区分厚度从单层到约七层的TiS晶体。本研究中关于剥离后的TiS晶体得出的结论可以扩展到各种过渡金属三硫属化物材料以及其他准一维晶体。将TiS剥离成边缘光滑的窄（几纳米宽）晶体的可能性对于未来实现电荷载流子边缘散射减少的微型器件通道可能很重要。
