Autonomous Beam Fabrication of 1D-2D Nano Hetero-structures within 2D Materials

One of the central goals of nanotechnology is to directly fabricate nanoscale architectures with atomic-scale precision. With recent advancements in aberration corrected scanning transmission electron microscopy (STEM), the sub-Å sized electron beam can be used to manipulate the atomic structure of materials. Previous work has shown the electron beam is capable of locally and controllably creating defect structures within 2D materials such as nanopores and atomic edge configurations that have enhanced electronic, magnetic, optical and catalytic properties. In the model MoS₂ materials system, several such defect structures can be fabricated through the localized irradiation of sulfur sites within the lattice through the knock-on process. In this work, an emphasis was placed on the controlled fabrication and characterization of two distinct defect structures. First, the sulfur vacancy line (SVL) defect structure, composed of a line of single sulfur vacancy sites, that has previously been shown to conglomerate together to form a local metallic MoS area within the MoS₂ monolayer. Second, the metallic Mo₆S₆ (MoS-NW) nanowire-type defect structure that forms along the edge of nanopores within the MoS₂ monolayer. Initial work has demonstrated that these MoS-NW form preferentially along the zig-zag sulfur terminated direction within the lattice. Through precise control over the electron beam irradiation of S sites along this direction, edge decorated nanopores can be fabricated. To increase the reliability of this fabrication method, Python-based codes have been developed that allow for <i>in situ </i>data acquisition, decoding and automated beam control in-line with the electron microscope workflow following the ensemble learning iterative training (ELIT) approach for deep convolutional neural networks (DCNNs). Using ELIT DCNNs, during fabrication, the image is decoded in real time into the atomic coordinates and identities allowing for precise targeting of atomic species and locations. In this regard, automated electron beam manipulation experiments have been developed that can form these beneficial defect structures that can lead to direct bandgap engineering.<br/> <br/>Microscopy research was performed at the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, which is a US Department of Energy (DOE), Office of Science User Facility.