Atomic and near-atomic scale manufacturing (ACSM) represents the processing techniques for high-end products that require not only fabrication precision and feature size at the atomic level, but also material removal, migration, or addition at the atomic level or near atomic scale. ACSM benefits from the special quantum, electromagnetic and thermal effects at the atomic or near-atomic level and shows great potential for the fabrication of next-generation chips, single-electron transistors, quantum bits, spin-based logic devices, atomic binary gates and single-atom memories. Despite the significant benefits ACSM can offer, the challenges it presents are enormous, especially when using traditional manufacturing tools. Because the challenges in implementing ACSM lie not only in the extremely small scale at which it can be worked on, but also in the fundamental understanding of atomic interactions, which is based on quantum theory rather than classical theory.
Prof Xichun Luo and his PhD student Jian Gao from the Center for Precision Manufacturing at the University of Strathclyde, Prof Fengzhou Fang from Tianjin University and University College Dublin and Prof Jining Sun from Dalian University of Technology have a paper entitled “Fundamentals of atomic and near-atomic scale manufacturing: A review” in International Journal of Extreme Manufacturing. This paper discusses and summarizes the basics of ACSM processes with the aim of identifying the intrinsic problems that prevent its realization. This review paper begins with a discussion of quantum mechanics in manufacturing and then builds on it to explain the nature of atom-atom and energy beam-matter interactions. It then summarized the mechanisms of several ACSM processes and reviewed their modeling techniques to introduce the development into simulation research. After a discussion of the current studies, future fundamental research by ACSM related to process modeling, material selection or preparation, and control of manufacturing tools and environments is proposed.
Despite the achievements in experimental and theoretical research, ACSM is still in its infancy and challenges remain in several aspects, including achieving deterministic manufacturing and product stability. First, atomic-scale resolution requires fabrication tools to achieve effective control over atoms or atom clusters. The interactions that dominate this process are quantum mechanics. The phenomena of interaction are of an uncertain nature; As a result, ACSM can be difficult to perform and subject to uncertainty. Second, even when atomic-scale structures are successfully fabricated, maintaining their stability is a formidable challenge. Atoms that build atomic-scale patterns are usually accompanied by a very low atomic diffusion barrier. The self-diffusion processes can easily damage structural integrity and compromise functions. When making single-atom transistors, atomic patterns on semiconductors could decompose and migrate on the surface like water droplets on a hot plate.
Manufacturing determinism can be improved by increasing the patterning resolution, as this allows control of a small number of atoms without disturbing other surrounding atoms. Manufacturing tools and processed substrate materials can interact in different ways, but the achievable resolution in a manufacturing zone depends on the feature size of the interaction region where the physical or chemical reaction that dominates manufacturing takes place. Therefore, minimizing the interaction domain is key to improving the resolution and determinism of ACSM processes.
When atomic or near-atomic scale patterns are fabricated, some measures are required to maintain their stability in order for the fabricated structures to retain their functionality. The stability of the structures could be related to the physical properties of the material, surface lattice structure, processing history and environmental influences. Basically, however, the two important determinants of stability are the chemical reactivity of the surface and the structural properties related to the lattice structure and atomic interactions. To provide long-term cyclic stability, atomic or near-atomic scale structures must be specially designed or modified, and rational choice of substrate material is required.
Professor Xichun Luo, Mr. Jian Gao, Professor Fengzhou Fang and Professor Jining Sun have identified some challenges in fundamentally studying ACSM processes:
“Apparently, quantum mechanics governs the interactions in ACSM. How can you use this theory to efficiently model the manufacturing process?”
“The first principles calculation is the most direct and accurate method to calculate the quantum mechanical effect, but the calculation requires a lot of computing power. To provide effective and reliable simulation for larger systems, several advanced simulation approaches could be used, including Reaxff molecular dynamics simulation, machine learning-based multiscale simulation, hybrid classical and quantum mechanical simulation, and molecular dynamics simulation using potential-from-principle calculations.”
“To achieve ACSM, is it necessary to use tools of atomic or near-atomic size? Like using atomically sharp tips, atomic ion or electron beams?”
“The atomic tool and beam size will certainly improve manufacturing determinism as they will interact with fewer atoms. In general, manufacturing resolution is more directly related to the size of the interaction area in which physical or chemical reactions that dominate manufacturing take place. In some manufacturing processes, the size of the interaction area is smaller than the tool size, which allows the process to have a much smaller structure than the manufacturing tool.”
“Material selection seems to be a key issue at ACSM. What are the basic requirements for materials?”
“The selection or preparation of appropriate working materials will determine the interatomic ‘force’ and thus improve the likelihood of expected pattern formation and stabilize atomic-scale patterns. In order to generate atomic-scale patterns, materials must meet two conditions: i) materials should respond to the interaction with good sensitivity, since ACSM usually yields a small force or energy; ii) Materials should be associated with relatively stable structures to maintain atomic-scale patterns, usually with high defect diffusion barriers.”
International Journal of Extreme Manufacturing (IF: 10,036) is a new multidisciplinary, doubly anonymous, peer-reviewed and fully open access journal that uniquely covers the fields of extreme manufacturing. The journal is dedicated to publishing original articles and reviews of the highest quality and impact in the fields of extreme manufacturing, from fundamentals through processes, measurements and systems to materials, structures and devices with extreme functionalities.
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