In Situ Atomic-Scale Electron Beam Fabrication of 2D Materials with Automated Feedback-Control

Within the field of nanotechnology there is a desire to control the fabrication of nanostructures from the atomic-scale up. Scanning transmission electron microscopy (STEM) techniques have recently enabled precise manipulation of the atomic structure of materials which were previously not possible with traditional processing methods . This is done through the controlled positioning of a sub-Å sized electron (e)-beam to induce knock-on processes and thereby allowing precise atomic alteration of materials. Previous works have shown the ability to position dopant atoms in 2D and 3D materials and form specific atomic edge configurations or nanopores through controlled e-beam irradiation. These altered structures within the 2D material i.e. dopants, nanopores, nanowires, and their associated edge structures, have a large effect on the local electronic properties that, when controlled, are beneficial for nanoelectronic devices. However, the reaction pathways these manipulated atoms undertake are not well understood. In this study, a feedback-controlled e-beam system is used to demonstrate more precise control over the e-beam for nanostructure fabrication of 2D materials system while also allowing for studies of the e-beam interactions through <i>in situ </i>visualization of the atomic fabrication process. This system moves the beam in a predetermined path with a given dwell time and electron dose, which allows for highly accurate control over the location, size and shape of the desired architectures through automated feedback control. This direct control over the milling parameters combined with automated image-based feedback allow for in-depth studies of the fabrication process of different nanostructures and can reveal new insights into the atomic transformation pathways within different 2D material systems.<br/>For this study the <i>in situ </i>fabrication of both 2D Ti₃C₂T_x MXene and MoS₂ was conducted on a Nion UltraSTEM with the external feedback-controlled e-beam system interfaced to the microscope. The milling process of MXene was observed as a function of temperature and it was found that, as temperature increased, the milling behavior followed a much more ordered process to form a metastable Ti₂C phase during drilling that persisted after halting the milling process to form defective structure within the MXene monolayer. Atomic fabrication studies conducted on MoS₂ were also conducted and focused on controlling the formation of desired nanopore edge reconstructions within a monolayer to control the local electronic properties by aligning different shaped beam paths along crystallographic directions. From these studies it has been shown that this e-beam control system allows for in-depth <i>in situ </i>studies of transformations that high-energy e-beam irradiation induces on 2D materials while also increasing the degree of control available to fabricate nanoscale devices using automated STEM techniques.