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2019 Vol. 1, No. 1

Towards atomic and close-to-atomic scale manufacturing
Fengzhou Fang, Nan Zhang, Dongming Guo, Kornel Ehmann, Benny Cheung, Kui Liu, Kazuya Yamamura
2019, 1(1) doi: 10.1088/2631-7990/ab0dfc

Human beings have witnessed unprecedented developments since the 1760s using precision tools and manufacturing methods that have led to ever increasing precision, from millimeter to micrometer, to single nanometer, and to atomic levels. Researchers led by Prof. Fengzhou Fang from Tianjin University/University College Dublin have recently reviewed the development Atomic and Close to atomic Scale Manufacturing (ACSM) based on atomic level operation modes in subtractive, transformative, and additive manufacturing processes. Fang has formally proposed three phases of manufacturing advances:

• Manufacturing I: Craft based manufacturing by hand, as in the Stone, Bronze, and Iron Ages, in which manufacturing precision is at the millimeter scale.

• Manufacturing II: Precision controllable manufacturing using machinery where the material removal, transformation, and addition scales are reduced from millimeters to micrometers and nanometers. 

• Manufacturing III: Manufacturing objectives and processes directly focused on atoms, spanning the macro through the micro to the nanoscale where manufacturing is based on removal, transformation, and addition at the atomic scale, namely, atomic and close to atomic scale manufacturing.

In this review article, the authors systematically analysed literatures in area of subtractive manufacturing including ultra precision machining, high energy beam machining, atomic layer etching, atomic force microscope nanomachining, where atomic wide line was achieved by focused electron beam sculpture based on 2D materials, such as transition metal dichalcogenides. Sub nanometer finish can be achieved with ultra precision polishing and atomic layer etching, where defects free and single atomic layer removal are still not possible. Atomic scale additive manufacturing, featured with macromolecular assembly with feedstocks, such as DNAs, proteins and peptides, represents atomic precision manufacturing of biological machines. Atomic scale transformative manufacturing, such as using Scanning Tunnelling Microscopy, Atomic Force Microscopy and Scanning Transmission Microscopy, has demonstrated capability for operation of single atoms. They also summarized the metrology technologies for ACSM and current applications.

Today, the famous Moore’s law is approaching its physical limit. Computer microprocessors, such as the recently announced A12 Bionic chip and Kirlin 980, use a 7 nm manufacturing process with 6.9 billion transistors in a centimeter square chip. Such limits have been pushed to a 5 nm node and even a 3 nm node, which represents a few tens of atoms. Human beings are already stepping into the atomic era. Meanwhile, human society is facing unprecedented global challenges from depleting natural resources, pollution, climate change, clean water, and poverty.What shall we do? Such challenges are directly linked to the physical characteristics of our current technology base for producing energy and material products. According to the authors, it is the time to start changing both products and means of production via ACSM, which includes all of the steps necessary to convert raw materials, components, or parts into products designed to meet users' specifications. They believe research should focus on extensive study of fundamental mechanisms of ACSM, development of new functional devices, exploration of ACSM of extensive materials and amplifying throughput for future production.

Laser synthesis and functionalization of nanostructures
Costas P. Grigoropoulos
2019, 1(1) doi: 10.1088/2631-7990/ab0eca
The fundamental study of laser material interactions across length and time scales in the context of laser microprocessing and maskless nanomanufacturing has been the subject of intense research interest. Understanding of the associated energy transport phenomena has opened the way to applications on micro/nanofabrication, the synthesis of nanomaterials and their integration into electronic and energy devices. New methods have been introduced for the localized structural modification, growth and assembly of nanostructures. This article presents recent work on the nanoscale crystallization of semiconductor materials applied to structural color metasurfaces, the directed growth of semiconductor materials with high spatial and temporal resolution, and the laser modification of two-dimensional layered semiconductors, including the demonstration of spatially selective and stable doping.
Hybrid femtosecond laser three-dimensional micro-and nanoprocessing: a review
Koji Sugioka
2019, 1(1) doi: 10.1088/2631-7990/ab0eda
Currently, laser is an essential tool for processing and synthesis of diverse materials and thereby is widely employed for practical use. Prof. Sugioka’s team aims at research and development of advanced laser processing which realizes low environmental load, high quality, high efficiency fabrication of materials by using ultrafast lasers such as femtosecond and picosecond lasers. The developed techniques include three-dimensional (3D) micro/nanofabrication, high aspect ratio machining, and synthesis of new materials, which are applied for fabrication of biochips and high function photonic and electronic micro/nanodevices. Among them, 3D micro/nanofabrication is reviewed in this paper. The extremely high peak intensity associated with ultrashort pulse width of femtosecond lasers enabled inducing nonlinear multiphoton absorption in materials that are transparent to the laser wavelength. More importantly, focusing the fs laser beam inside the transparent materials confined the nonlinear interaction to within the focal volume only, realizing 3D micro/nanofabrication. This 3D capability offers three different processing schemes for use in fabrication: undeformative, subtractive, and additive. Furthermore, a hybrid approach of different schemes can create much more complex 3D structures and thereby promises to enhance the functionality of the structures created. Thus, hybrid fs laser 3D microprocessing opens a new door for material processing.
Micromanufacturing of composite materials: a review
Mahadi Hasan, Jingwei Zhao , Zhengyi Jiang
2019, 1(1) doi: 10.1088/2631-7990/ab0f74
Recently, the use of composite materials in miniaturized scale is receiving much attention in the fields of medicine, electronics, aerospace, and microtooling. A common trend for producing miniaturized composite parts is micromanufacturing. This trend to miniaturization has, in fact, moved very quickly during the last two decades, driven primarily by electronics and silicon (Si)-based products. Nevertheless, Si-based products have some intrinsic limitations in respect to geometry (2D and 2.5D), material (only Si), mechanical performance and cost. These issues have led researchers to find alternative bulk materials. Consequently, the possibilities of using bulk materials, such as metals, ceramics, polymers, and their alloys, are also so saturated that it may be difficult to achieve the highest material properties by a monolithic material. Composite materials, on the other hand, exhibit endless possibilities for meeting many of the emerging industrial requirements, in terms of extreme mechanical, electrical, magnetic, optical, and thermal properties. By choosing an appropriate combination, it is also possible to attain specific properties, and thus composite materials are indispensable in a variety of applications today from micro- to nanoscale. There has been, however, no comprehensive literature published that reviews, compares, and discusses the ongoing micromanufacturing methods for producing miniaturized composite components. This study identifies the major micromanufacturing methods used with composite materials, categorizes their subclasses, and highlights the latest developments, new trends, and effects of key factors on the productivity, quality, and cost of manufacturing composite materials. A comparative study is presented that shows the potential and versatility associated with producing composite materials along with possible future applications. This review will be helpful in promoting micromanufacturing technology for fabricating miniaturized products made of composite materials to meet the growing industrial demand worldwide.
Additive manufacturing of precision optics at micro and nanoscale
Abolfazl Zolfaghari, Tiantong Chen, Allen Y. Yi
2019, 1(1) doi: 10.1088/2631-7990/ab0fa5

In optical manufacturing, as an alternative, additive manufacturing processes have been gaining a lot of interest because of their unique capabilities in the fabrication of extremely complex shapes that was quite difficult or impossible in the past using traditional fabrication methods, such as precision machining, compression or injection molding processes. Additive manufacturing also provides extreme flexibility to the design and manufacturing of optical components compared to more traditional processes. Additive manufacturing can be utilized to fabricate single optical elementss or systems at both microscale or nanoscale level. Other advantages over conventional methods are less material waste and less time between design and manufacturing. Moreover, its capability in the manufacturing of multiple parts without assembly, although has not yet been completely developed, can be considered another advantage. 

Additive manufacturing of precision optics offers a solution to extremely high level of customization. At present stage, additive manufacturing of precision optical components excels at both microscale (microlens or micromirror) and nanoscale optical fabrication with most work conducted on the processes for microoptical components. Thus this review is mainly focused on discussions about optical fabrication at micro and nanoscale since the additive manufacturing processes available today are not easily scalable to large size optics. The limitations and achievements of these additive manufacturing methods for micro and nanoscale optical fabrication are discussed in details in the review as well. For applications of additive manufacturing of optics with nanoscale features, the processes reviewed include dip pen nanolithography, electrohydrodynamic jet printing, and direct laser writing. 

Additive manufacturing of precision optical devices has shown promising results in fabricating high performance optical components. The devices and systems consisting of these components have also demonstrated unique features and performance. Although the exact capability of this exciting technology is difficult to determine based on the existing information, the information available today clearly described a promising group of processes that could potentially revolutionize optical fabrication in the near future. However, before additive manufacturing can be further implemented, there are many unanswered questions and issues need to be resolved. These issues include, but are certainly not limited to, things such as index distribution, geometry, and volume shrinkage of the optical elements. The aim of this review is to provide a platform for researchers and industrial communities to engage and eventually implement this cutting edge manufacturing process and its associated products.

A review on the erosion mechanisms in abrasive waterjet micromachining of brittle materials
J Wang, T Nguyen
2019, 1(1) doi: 10.1088/2631-7990/ab1028
As an advanced manufacturing technology with distinct advantages over the other technologies on various aspects, ultrahigh pressure abrasive waterjet (AWJ) has been increasingly used by industry for processing various materials. The research group at the University of New South Wales (UNSW) in Australia has been developing this technology and explore the associated sciences for over 20 years. A recently published bibliometric analysis of abrasive water jet machining research has identified the UNSW group as the most influential and active group in the world in this subject area. Since 2000, this group has been taking a new avenue to develop micro AWJ technologies to meet the need of industry in the fabrication of miniature structures with high-integrity surface quality. This effort is motivated by the fact that the materials used to construct miniature structures are often difficult-to-machine and many readily available technologies either cannot realise the necessary precision or are costly. As a result, damage-free fabrication of micro structures at commercially viable cost has been claimed as one of the most cutting-edge technologies in the 21st Century. This review summarises some of the work that has been undertaken at UNSW on the development of an AWJ micro-machining technology, focusing on the system design currently employed to generate a micro abrasive jet, the erosion mechanisms associated with the processing of some typical brittle materials of both single- and two-phases, and the processing models developed for mathematically and quantitatively estimating the process performance measures. The review concludes on the viability of the technology and the prevailing trend in its development.
The ‘skin effect’ of subsurface damage distribution in materials subjected to high-speed machining
Bi Zhang, Jingfei Yin
2019, 1(1) doi: 10.1088/2631-7990/ab103b
The machining of difficult-to-machine materials, such as titanium alloys, hard and brittle materials and silicon carbide reinforced aluminum composite, has been suffering from the machining-induced damage (MID). Currently, various theories and techniques are available for machining of these materials but with their respective limitations. High-speed machining (HSM) is featured with high efficiency and high quality of a machined workpiece with no limitations to the workpiece materials. However, the fundamental mechanisms of HSM remain unknown, which obstructs its applications. This paper proposed the “skin effect” of MID in HSM. Based on the published work on MID, the paper identifies strain rate as the dominant factor for the “skin effect” although many other factors may also come to play. The paper elucidates that material deformation at high strain rates (> 103 s-1) leads to material embrittlement which in turn contributes to the “skin effect” of MID. The paper then discusses the “skin effect” in terms of dislocation kinetics and crack initiation and propagation. It provides guidance to predicting the material deformation and damage at a high strain-rate for applications ranging from the armor protection, quarrying, petroleum drilling, and high-speed machining of engineering materials.
Self-limiting laser crystallization and direct writing of 2D materials
Zabihollah Ahmadi, Baha Yakupoglu, Nurul Azam, Salah Elafandi , Masoud Mahjouri-Samani
2019, 1(1) doi: 10.1088/2631-7990/ab0edc
The recent discovery of atomically thin two-dimensional (2D) quantum materials including transition metal dichalcogenides (TMDCs) has revealed a promising potential for advancing the future of optoelectronics, photonics, sensing, and energy applications. Direct growth, patterning, and integration of 2D materials on various substrates are essential steps toward enabling their potential for use in the next generation of devices. The conventional gas-phase growth techniques, however, are not compatible with direct patterning processes. In this work, a laser-based synthesis and processing method is reported that relies on self-limiting laser crystallization (SLLC) of the stoichiometric amorphous thin layer (~3-5 nm) of 2D materials. This technique mainly takes advantage of significant contrasts between the optical properties of the amorphous and crystalline MoS2 phases allowing the deliberate design of laser 2D material interactions for the self-limiting crystallization phenomena with increased quality and a broad processing window. This unique laser processing approach allows high-quality crystallization, direct writing, patterning, and the integration of various 2D materials into future functional devices.