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.

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.

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.