Laser machining, as one of the most significant micro/nano-manufacturing technologies, shows the capability of achieving ultimate accuracy, feature size and surface integrity at atomic scale. This has the potential to revolutionize the production of critical components and devices across various fields, which represents the frontier of manufacturing technology.
Publishing in the International Journal of Extreme Manufacturing, the team based at the State Key Laboratory of Precision Measuring Technology & Instruments, Laboratory of Micro/Nano Manufacturing Technology (MNMT) at Tianjin University reviewed how materials can be directly removed by laser in a highly deterministic manner, which is the foundation of advanced manufacturing technology.
It is clarified that laser-induced material removal at micro/nano scale can occur through thermal (ablation) and non-thermal (Coulomb explosion, photomechanical spallation) mechanisms. To improve the machined surface quality, thermal effect should be minimized, which can be achieved by reducing the wavelength and shaping the pulse train.
Furthermore, laser can remove a single atomic layer without disrupting the lattice structure below. This process is highly quantum mechanical and its controllability can be significantly enhanced by chemical adsorption and surface inter-diffusion of heteroatoms. It would enable the mass production of fascinating devices composed of atomic-scale structures.
Lead investigator Professor Fengzhou Fang remarked, "Manufacturing technology has evolved from the first paradigm, where precision was achieved at millimeter scale through handcraft (Manufacturing I), to the second paradigm based on machinery enabling a precision at micro/nano scale (Manufacturing II). We are now entering a new paradigm (Manufacturing III) where manufacturing objectives and processes directly focus on atoms. By precisely manipulating individual atoms or atomic layers in the modes of removal, migration and addition, we can realize atomic and close-to-atomic scale manufacturing (ACSM)."
Undoubtedly, the form accuracy and functional feature size will approach the limits of manufacturing technology in ACSM. However, ACSM is not a mere advancement of micro/nano manufacturing from a geometrical perspective. Due to the discrete nature of substances at atomic scale, quantum effects arise during manufacturing processes, and the material to be fabricated can no longer be considered as a continuum. For instance, "reducing the thickness of a material by 0.1 nm" might be nonsensical, while "removing a definite number of atomic layers" becomes critical. This immediately leads to the intriguing possibility of inducing no lattice damage on the machined surface/subsurface if the process is confined to only one atomic layer or even a single atom. Such extreme integrity is highly appealing in applications such as quantum devices and high-power laser optics.
Nowadays, it is still a great challenge to manipulate single atomic layer in a way balancing the ultimate accuracy and the mass production efficiency. Professor Fang said, "Laser machining is applicable to almost every kind of material, from conductors to dielectrics, and is highly suitable for achieving high throughput. This article demonstrates its potential in removing single atomic layer with minimal impact on the lattice structure."
It is a challenge to obtain good surface quality on materials that cannot be processed through photochemical reactions followed by chemical etching. In such cases, material is directly removed at micro/nano scale through thermal or non-thermal mechanisms. However, these do not allow for the removal of a few or a single atomic layer without damaging the underlying lattice structure, as indicated by Dr. Jinshi Wang.
Encouragingly, laser-induced atom emission and atomic layer desorption have been observed. In particular, experiments on bulk and 2D crystals have demonstrated the possibility of selectively removing only the topmost layer without disturbing the atoms in the second layer. The fundamentals of these atomic-scale processes must be understood using quantum theory. Additionally, the development of self-limiting and selective mechanisms, similar to atomic layer etching (ALE) technology, is required to improve efficiency and controllability. Laser direct writing has been employed to fabricate delicate structures in atomic layers of both 2D materials and bulk solids for optical and electronic applications.
Professor Fang said, "Laser machining proves to be a promising candidate for ACSM playing a critical role in Manufacturing III. Although there is still a long way to go, the new era of manufacturing is here. Armed with production engineering technologies ranging from macro to atomic scales, we anticipate a revolution in the products that will remarkably change our lives."
International Journal of Extreme Manufacturing (IF: 10.036) is a new multidisciplinary, double-anonymous peer-reviewed and diamond open-access without article processing charge journal uniquely covering the areas related to extreme manufacturing. The journal is devoted to publishing original articles and reviews of the highest quality and impact in the areas related to extreme manufacturing, ranging from fundamentals to process, measurement and systems, as well as materials, structures and devices with extreme functionalities.
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