Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
Nanoscale. 2017 May 18;9(19):6417-6426. doi: 10.1039/c7nr01127j.
We use electron-beam nanofabrication to create sub-nanometer (sub-nm) pores in 2D monolayer MoS with fine control over the pore size down to 0.6 nm, corresponding to the loss of a single Mo atom and surrounding S atoms. The sub-nm pores are created in situ with 1 nm spatial precision in the MoS lattice by control of the angstrom sized probe in an aberration corrected scanning transmission electron microscope with real time tracking of the pore creation. Dynamics of the sub-nm pore creation are captured at the atomic scale and reveal the mechanism of nanopore formation at accelerating voltages of 60 and 80 kV to be due to displacing a Mo atom from the lattice site onto the surface of the MoS. This process is enabled by the destabilization of the Mo bonding from localized electron beam induced S atom loss. DFT calculations confirm the energetic advantage of having the ejected Mo atom attach on the sheet surface rather than being expelled into vacuum, and indicate sensitivity of the nanopore potential as a function of the adsorption position of the ejected Mo atom. These results provide detailed atomic level insights into the initial process of single Mo loss that underpins the nucleation of a nanopore and explains the formation mechanism of sub-nm pores in MoS.
我们使用电子束纳米光刻技术在二维单层 MoS 中制造亚纳米（sub-nm）孔，可对孔径进行精细控制，最小可达 0.6nm，相当于损失一个 Mo 原子和周围的 S 原子。通过在具有原子级空间分辨率的校正像差扫描电子显微镜中的纳米探针控制，在 MoS 晶格中以 1nm 的空间精度原位制造亚纳米孔，并实时跟踪孔的形成。在 60kV 和 80kV 的加速电压下，以原子尺度捕捉到亚纳米孔形成的动力学过程，揭示了纳米孔形成的机制是由于 Mo 原子从晶格位置被推到 MoS 的表面。这种过程是由于局部电子束诱导的 S 原子损失导致 Mo 键的不稳定而得以实现。密度泛函理论（DFT）计算证实了被逐出的 Mo 原子附着在片层表面而不是被驱逐到真空中的能量优势，并表明纳米孔势作为被逐出的 Mo 原子的吸附位置的函数的敏感性。这些结果提供了对支撑纳米孔成核的单个 Mo 损失的初始过程的详细原子级见解，并解释了 MoS 中亚纳米孔形成的机制。
