Atomic engineering on 2D materials using electron irradiation and chemical protection

Abstract

Controlling the exact atomic structure is an ultimate form of engineering. Atomic manipulation and atom-by-atom assembly can create functional structures that are hard to synthesize chemically. Defects with one- or few-atom-scale pertain intriguing properties that can be applicable to fields like Quantum Engineering (e.g. nitrogen vacancy center, single photon emitter, etc.), or Single-Atom Catalysis. Historically, scanning tunneling microscopy (STM) has demonstrated good stepwise control of single atoms, leading to physicochemical insights and technological advances. However, their scalability and throughput are severely limited by the mechanical probe movements, and its applicability is constrained by the low-temperature environment (usually lower than 77K) needed for stabilize the structure. Therefore, a method of controlling atoms at room-temperature without mechanical movement is essential for a broader interest and unleashing the constraints.

The advancement of aberration corrector makes it possible to focus high-energy (usually ranging from 30 keV to 300 keV) electron beams to a single-atom scale inside scanning transmission electron microscope (STEM). Despite being a versatile tool for characterizing the precise atomic structures of materials, STEM has also demonstrated the capability of controlling atoms on two-dimensional (2D) materials, like a substitutional dopant in graphene or molybdenum disulfides (MoS2). This turns the irradiation damage of electron beam (which is not what we want) to a powerful tool with a positive value (what we want). While controlling atoms using STEM is promising, it is still haunted by the fact that most of the dynamic processes are random. The core of this thesis, a theoretical framework called Primary Knock-on Space (PKS), will be introduced for optimizing the control process by biasing the possibilities of different atomic dynamics.

This framework predicts how various external factors tunable in experiment, such as temperature, electron beam incident angle, electron beam voltage, and dopant species, can influence the atom dynamics. It is proved to be useful in guiding the control process towards a more deterministic route. Following the introduction of the framework, several proof-of-concept experiments are demonstrated for validating the PKS framework. The future of Atomic Engineering will also be envisioned at the end. An additional corrosion inhibition of 2D materials will also be discussed, which is found to be critical during the materials transfer process.