1 Introduction

In 1959, in his famous talk “There’s Plenty of Room at the Bottom”, Feynman [1] proposed the idea to “arrange the atoms the way we want” to manufacture devices “on a small scale” to “get an enormously greater range of possible properties that substances can have, and of different things that we can do”. He clearly indicated the “possibility of manoeuvring things atom by atom”. This inspired global scientists and researchers to devote significant efforts toward this attractive opportunity. Since then, the importance and necessity of promoting manufacturing to a finer scale approaching “atoms” is widely acknowledged, and consequently, nanotechnology has been greatly advanced.

However, by now, we have not achieved that “if we go down far enough, all of our devices can be mass produced so that they are absolutely perfect copies of one another”, as Feynman anticipated. The most precise mass production technologies today are still limited at the nanoscale, such as the 2-nm chips which have already been demonstrated. The success in nanomanufacturing does not mean that we could just miniaturise along the existing path, as a number of problems arise; the most disruptive one is the fundamental changes when the laws of quantum mechanics become dominant. The behaviour of objects at the atomic and molecular scale cannot be described by classical physics anymore, and follow the often counterintuitive rules of quantum mechanics.

Hence, simply driving the precision of manufacturing down to the atomic regime without factoring in that the technology would enter a new realm does not provide a sustainable way for development and innovation. The proposal of Manufacturing III, which is the new paradigm of manufacturing advancement, clarifies the laws of manufacturing development, and formally indicates atomic and close-to-atomic scale manufacturing (ACSM) is the fundamental technology of Manufacturing III [2]. For Manufacturing III and ACSM, manufacturing precision at or approaching atomic scale is only one of the key features, wherein the more important contribution is ACSM, which emphasises that quantum effects play the dominant role in the molecular/atomic interaction process. This is the essential criterion to discriminate ACSM from the contemporary manufacturing processes which might also be able to achieve atomic precision but are mainly dominated by the classical mechanics based on the continuity of materials.

Table 1 Important events during ACSM development in the last 10 years
Full size table

As ACSM is still in the fledging stage, this article intends to elaborate its concept and core proposition. It is expected that it could benefit the convergence of relevant efforts toward the more effective research and development in ACSM.

2 Development of ACSM conception

ACSM came up from a background centred at manufacturing precision, and the manufacturing advancement could be divided into three paradigms [2, 3].

  1. (i)

    Manufacturing I, basically handcrafting, achieves millimetre and sub-millimetre scale precision significantly depending on human skills and experience.

  2. (ii)

    Manufacturing II, machine-based scalable manufacturing, successfully brings the mass production to micrometre and nanometre scale precision with good repeatability as a basic prerequisite of modern industrialisation.

  3. (iii)

    Manufacturing III, with distinct fundamental theory (quantum theory) from Manufacturing I (experience and know-how) and II (classical theory), enters the atomic and close-to-atomic scale material processing (removal, migration and addition), and potentially enables extraordinary properties and applications.

It is important to emphasise that Manufacturing I, II and III are coexisting in the contemporary industries, and will, on the long run.

The three paradigms of manufacturing development were proposed by Fang in 2012 when he investigated the principles inherent to manufacturing advancement, inspired by the emerging concept of Industry 4.0. At that time, Industry 4.0 was a new conception, and it was intensively discussed how to fulfil and enrich the framework. Fang considered Industry 4.0 as a higher stage of modern industrialisation would provide plenty of benefits to mass production through emerging technologies like artificial intelligence (AI) and internet of things (IoT). However, he found that Industry 4.0 still maintained the same fundamentals as conventional manufacturing. For instance, no matter how automatic or intelligent the manufacturing process can become, the materials are still processed following classical mechanics, and the precision of manufacturing would still be largely limited by the machine precision at the micro and even nano scale. Faithful to the technical nature of manufacturing, he tried to figure out if it was possible to sort out another thread of advancement of manufacturing.

Here, a key question to ask is: what is manufacturing? Manufacturing is defined as the entire process of converting raw materials into finished products that satisfy user demands, whereby the objective is to obtain the required functionality and performance, thereby meeting the usage requirement of the products. Based on the development history of manufacturing technologies, it needs to be stipulated that manufacturing precision and functional feature size are paramount to the advancement of manufacturing, as evidenced by the continuous decrease of line width of IC chips and many other examples. The final performance of products is directly determined by the manufacturing precision and functional feature size. Therefore, the definition of manufacturing reminds us of tracing back to the primary remit of manufacturing—the precision and functional feature size.

Nowadays, there are various manufacturing technologies, such as digital manufacturing, agile manufacturing, green manufacturing, and smart manufacturing, for which we acknowledge their significant and indispensable contributions to the development of manufacturing. However, if the manufacturing precision and required functional feature size cannot be achieved, loss of the expected functionality and performance would make all the above adjectives meaningless. We draw an analogy here: if we had a “1” in the first digit, surely the more “0s” behind it, the larger the formed number is. But without the “1”, no matter how many “0s”, the final value will remain at zero. Manufacturing precision and the target size of functional features are the “1”, and all the other properties we add to the manufacturing process as mentioned above are the “0”.

Rooted in the improving feature size and precision, mass manufacturing has progressed from millimetre precision to micrometre precision, and even to nanometre precision by now. It is easy to predict that we will enter the sub-nanometre precision era next. However, is such a prediction so simple? The diameters of the atoms are at the sub-nanometre or Ångstrom level. When approaching below 1 nm, the quantum mechanical interactions between atoms dominate course of manufacturing. Thus, traversing from nano scale to the atomic scale implies that the basis of manufacturing would be governed by other, vastly different principles—those of quantum mechanics.

We could imagine addition, removal or migration of atoms, like we do 3D printing, cutting and forming at the macroscopic scale. There is also a need for digital manufacturing, agile manufacturing, green manufacturing, and smart manufacturing at atomic scale afterwards, ACSM, however represents the underlying technology. Based on such a philosophy, the three paradigms of manufacturing advancement were developed, and ACSM was recognised as the core competence of Manufacturing III. Consequently, the term “Atomic and Close-to-atomic Scale Manufacturing” was coined.

Like many other ideas when initially formed, no paper was published immediately on ACSM due to lack of supporting evidence in relevant research as an emerging concept. Although this proposal was circulated orally in scientific discussions, it did not spread widely at that time. Until 2014, when Fang delivered two speeches on the three paradigms of manufacturing in a workshop and a university seminar, respectively, the concept of ACSM began to be accepted across wider circles. One year later, People’s Daily published an article on Manufacturing III, which was the first official written record of ACSM [4]. Then a technical publication on ACSM was made in 2016 [5]. Afterwards, a series of talks and journal papers were published on ACSM at various international conferences and academic journals.

These efforts further inspired more researchers to participate in ACSM, which was evidenced by the sharply increased publications titled by ACSM since 2020. At the end of 2022, the Chinese Academy of Engineering, Clarivate and the Higher Education Press of China jointly released the “Global Engineering Frontiers 2022” which listed ACSM as the next-generation core technology for fabricating the extreme optical components [6].

Table 1 constitutes a brief review on how the ACSM conception continues to unfold. For ACSM, the foundation of the skyscraper is currently laid, precision and functional feature size would be the major focus at this fledging stage.

3 Core proposition of ACSM

Three key features that ACSM involves: (i) the atomic and close-to-atomic “scale”, (ii) the nature of manufacturing, and (iii) the basis formed by quantum theory.

3.1 Interpretation of the “scale”

How to understand the “scale” in ACSM? The emergence of relevant conceptions/terms, such as ACSM and atomically precise manufacturing (APM), are basically driven by the advancement of nanomanufacturing, when researchers pursued for the limit of nanomanufacturing. Hence, naturally and reasonably, ACSM aims at the sub-nanometre (Ångstrom) metrics. Francium is considered as the largest atom with a non-bonded atomic radius of 0.348 nm [7]. When the manufacturing enters the Ångstrom range, we are approaching the atomic scale.

When the “scale” is mentioned, instead of “level”, or “precision”, it indeed implies substantial difference.

  1. (i)

    “Atomic level” is basically a descriptive phrase which reflects the interactions or phenomena occurring at such a level, and it has been widely used in various situations. This term has not been particularly well defined for targeting the manufacturing at such a tiny scale, although “atomic level manufacturing” is used.

  2. (ii)

    “Atomic” is similar with the above, which is a fundamental concept of 20th-century physics. “Atomic manufacturing” first emerged in physics or materials areas, which referred to the exploration of physical mechanisms or material synthesis from the atomic perspective. It is not a well-defined terminology related to manufacturing. “Atomic manufacturing” and “atomic level manufacturing” are sometimes interchanged due to their vague definition.

  3. (iii)

    APM is a formally defined terminology presented in 2007 as part of the “Productive Nanosystems—A Technology Roadmap” [8]. As the embodiment of collective intelligence from multiple scholars, that document made an impressive summary on the state-of-the-art, and elucidated future directions. It mainly focused on the manufacturing precision, which is only one important indicator of manufacturing, therefore APM did not embrace all the key features relevant to the atomic scale.

    For example, both, quantum and molecular dynamics models were mentioned in the document for the simulation and study of the systems. Deep down into the atomic scale, the behaviour of atoms/molecules should be described based on the discrete particles. Thus, manufacturing at such small scale should be largely captured by quantum theory. Such a difference in fundamental theory would cause enormous discrepancy on the results. Moreover, it is also not reliable to use a single index (“precise”) to evaluate and classify the manufacturing technologies. An example is that polishing has been reported to achieve the atomic precision successfully, however, it may not need a substantial understanding of quantum mechanics.

  4. (iv)

    The “scale” used in the ACSM can be reflected at least through the following aspects: the scale of manufacturing precision; the scale of minimum functional features; the scale of material manipulation (removal, migration or addition). Based on the above discussion, it can be seen that the “scale” of ACSM is a multi-dimensional definition with rich meaning. Only focusing on the precision is a one-dimensional criterion which is not sufficient, as explained above (The “one-dimensionality” here does not only mean spatial 1D, but also a single index). Some functional materials or structures, such as graphene, are generally two-dimensional (2D in space) conceptions which can offer some basic functionality but are not sufficient for independently realising the eventually expected performance. When fabricating the device, it refers to three-dimensional objects that integrate the 1D/2D materials and structures, multiple one-dimensional indices (like precision), and 3D components, to form a more complex architecture. In addition, the “scale” of ACSM also includes atomic surface integrity. It not only reflects the atomic-scale geometrical and structural features of the surface, and physical/chemical properties of the formed functional surfaces, but also covers the sub-surface properties, which may impact the final performance of the products during service. Hence, the “scale” of ACSM should be understood from the multi-dimensional perspective relating manufacturing processes, processed objects, and final products.

  1. (v)

    ACSM also includes the “close-to-atomic” scale which is different from all the other terms that only emphasize the atomic precision/level/scale. The basic consideration is originated from the facts that there are many more diversified molecules in the world than atoms. The implementation of atomic scale manufacturing and formation of stable products may be achieved through the molecular interactions or some production systems at the close-to-atomic scale.

3.2 Nature of manufacturing

Conventionally, manufacturing is defined as the entire process of converting raw materials into finished products that satisfy user demands. Covering the atomic scale processing, manufacturing could be redefined as the entire process of organising atoms/molecules in certain ways to form materials (and then to components) or directly build components, and then to finished products that satisfy user demands.

Although some processes indeed achieved atomic or close-to-atomic scale operation, such as the synthesis of inorganic materials or proteins, as long as these structures do not provide the final expected functionality or performance, such processes cannot be defined as “manufacturing”. As a typical example, years ago molecular wires and switches were demonstrated, however no comparably precise frameworks were available to hold and organize them. Basically, they may not be a functional system, or even a component for satisfying users’ expectation. Another example is the relocation of atoms through scanning tunnelling microscope (STM); few reports have been revealed on the usability of such artificial atomic / molecular structures to provide direct functionalities to human use. Thus, such atomic scale operation itself cannot be defined as manufacturing, which may be considered as a key technology for establishing the manufacturing process of finished products.

There are also many successful cases from material synthesis that exact atomic/molecular structures formed in the functional materials. However, as long as the functionality of these materials are not directly used by the users or do not form the final products, strictly it can be technically described as material fabrication, instead of manufacturing. From these instances, based on the nature of manufacturing, it is clear that manufacturing is different from operation or fabrication in physics, biology and materials.

3.3 Dominant role of quantum mechanics

Another important feature implied by ACSM is, although not so explicit from the terminology itself, ACSM is built on quantum mechanics. ACSM accounts for the dominance of quantum effects through electron clouds, intermolecular (nonbonding) interactions (such as Van der Waals forces), intramolecular (bonding) interactions (such as ionic, covalent, metallic bonding), etc. The uncertainty feature and discretization of particles in quantum mechanics have caused major challenges such as deterministic manufacturing and product stability [9].

In contrast, conventional manufacturing processes are usually described by classical mechanics. While even some ultra-precision machining technologies have achieved atomic scale precision, the material removal mechanisms still rely on the continuity of materials based on classical mechanics.

This is the key feature distinguishing ACSM from the other conceptions at atomic scale. It is easy to find that, without the unambiguous definition, “precision” tended to become the primary, or even the sole criterion to identify or define the ACSM, which became quite common in the recent decade. Plenty of publications declared the atomic scale/level/precision manufacturing due to the achievement of atomic precision, which might obscure the boundary between nanomanufacturing and ACSM. Based on the three paradigms of manufacturing advancement, this washed out the border between Manufacturing II and III. But by virtue of the theory (quantum mechanics or classical mechanics), it is more direct and accurate to make the discrimination. ACSM is proposed to drive the understanding and overcoming of quantum uncertainty for direction or control of atomic/molecular behaviour. This is a major contribution from ACSM to establish a clearer and more applicable definition for converging the efforts toward this promising area.

Based on the above discussion, a brief definition of ACSM can be given: ACSM is the quantum theory dominated manufacturing that is characterised by the atomic or close-to-atomic scale in material manipulation, manufacturing precision or minimum functional features.

4 Conclusions

ACSM is the quantum theory dominated manufacturing that is characterised by the atomic or close-to-atomic scale in material manipulation, manufacturing precision or minimum functional feature sizes. This article elaborates the core proposition of ACSM around the multi-dimensional meaning of “scale”, the nature of manufacturing and the dominant role of quantum mechanics. Instead of only focusing on the precision, ACSM systematically defines a new paradigm of manufacturing, namely Manufacturing III, with a distinct theoretical basis from the contemporary manufacturing technologies (Manufacturing II) although some of which have realised atomic level precision.

ACSM represents a new era of manufacturing. When it was first proposed, it was generally thought that there was still a long way to realise such a fancy idea. However, the dramatically increased activities in recent years evidenced that new era dawned. The roadmap of deploying ACSM is in preparation, which will be a beneficial supplement to make the ACSM system more complete. It is expected that more scientists and researchers will join the ACSM community and benefit from this significantly important domain of the new technology.