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The Way to Nanoarchitectonics and the Way of Nanoarchitectonics

Masakazu Aono * and Katsuhiko Ariga

M. Aono, K. Ariga World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1–1 Namiki , Tsukuba 305–0044 , Japan E-mail: AONO.Masakazu@nims.go.jp

DOI: 10.1002/adma.201502868

materials, we may think that they are new materials. However, there is a possibility that these materials already exist within the laws of nature. Nature is waiting for our fi ndings and we come to reach this desirable answer.

The second methodology is fabricating artifi cial heterostructures, such as hetero-junctions and heteroassemblies, especially with combinations that do not naturally occur. Forming interfacial environments upon contacting and fusing two kinds of materials often results in unexpected functions, such as the quantum Hall effect and interfacial superconductivity. Expan-sion of this concept also leads to the fab-

rication of functional device elements, including semiconduc-tive integrated circuits and organic electroluminescence units. They rely on microfabrication technology, with which we can construct structures of artifi cial materials.

Interestingly, attention to the creation of novel materials sys-tems upon the coupling and joining of separate components historically happened in the fi elds of chemistry and biology at a similar time to the microfabrication technology. A repre-sentative example is the concept of supramolecular chemistry. Supramolecular chemistry is defi ned as a chemistry beyond the molecule, bearing on the organized entities of higher com-plexity that result from the association of two or more chemical species held together by intermolecular forces. Supramolecular complexes and assemblies are supposed to have properties far beyond summation of the individual components. Although there are certain differences in system size, the concepts and effects of both heterojunction technology and supramolecular chemistry share the same features. In addition, the creation of novel materials and systems can be found in biological sciences, as seen in chimera proteins and DNA origamis. All these mate-rials can be assembled into artifi cial lattice structures by appro-priate techniques, such as layer-by-layer assembly. This progress in chemistry and biology has been fused with microtechnolog-ical developments.

The emerging third methodology could be recently found in the fi nal chamber of materials secrets: the topological control of electronic statuses. The importance of topology on the electronic status of materials was theoretically discovered and has been experimentally demonstrated, as seen in topological insulators and topological superconductors. Signifi cant progress on mate-rials innovation with this third methodology is highly expected.

The requirements for further progress in these three meth-odologies are briefl y summarized below. For the fi rst method-ology, the tools and methods are already well developed. Even

1. How Can We Create New Materials?

Necessity is the mother of invention. Innovation is often driven by necessity in minds. Similarly, the creation of novel mate-rials is the mother of science and technology, i.e., fi nding and preparing new materials strongly stimulates the progress and development of science and technology. For example, a tele-scope can be invented only with transparent glass, and the innovation of the light bulb was made with bamboo fi bers. A simple material, silicon, opens huge technological success in integrated electric circuits, which is accompanied by a social reform with advanced computers. Certain semiconductive materials create lots of technological innovations, such as blue light light-emitting diodes (LEDs).

Methodologies on developing functional materials and/or function developments of materials can be roughly categorized as follows: i) traditional materials syntheses; ii) fabrication of artifi cial structures; and iii) emerging science and technology such as topological control. The fi rst methodology is based on material creation through control of sequences, arrangements, and confi gurations of atoms. The preparation of new inorganic materials through the concept of condensed matter physics and the synthesis of novel organic compounds by organic chemistry are typical examples. This methodology can be regarded as a typical way of traditional materials science. When we fi nd such

The critical differences between microtechnology and nanotechnology are discussed, and the necessity of a new paradigm, nanoarchitectonics, is proposed for the future development of nanotechnology. An important task in material fabrication is to harmonize various factors and effects, and to com-bine them into functional nanomaterials and nanosystems. It is the way of architectonics rather than that of an individual technology. Therefore, a novel terminology, nanoarchitectonics (nano + architecto +nics) has been proposed as a new paradigm of materials science and technology on the nanoscale. The statement by Feynman that “there’s plenty of room at the bottom” is really true. With nanoarchitectonics in our hands, we can re-open the door to Feynman’s huge room.

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ESSAY though new techniques are required in materials synthesis, fun-

damental ways of thinking in the corresponding fi elds are well matured and provide good solutions. Although we do not have to worry about further progress in the fi rst methodology, the addition of new techniques from nanotechnology would give new spice to this methodology. The second methodology has so far been developing with heavy contributions from micro-technology. Further development of this methodology requires a transition from microtechnology to nanotechnology. It is also a key to fuse both top-down-type materials creation and bottom-up-type materials preparation, mainly for organic biological materials. The third methodology has to be carried out with scientifi c and technological considerations of nano meter-sized dimensions. Nanotechnology is a crucial factor for the third methodology. According to these considerations, we can rec-ognize nanotechnology as the most important key concept for future materials science.

2. We Cannot Find NANO on the Road Extrapolated From MICRO

Can we fully proceed nanotechnology with the current level of knowledge and skill? Probably, many of us want to say “yes”, but the true answer is “no”. Even scientists in nanotechnology seem to think that nanotechnology is just an extension of microtech-nology, that nanotechnology is only a precise version of micro-technology, and that there are no conceptual and fundamental differences between nanotechnology and microtechnology. Sticking to such misunderstanding thoughts underestimates the power and ability of nanotechnology. We need to realize the fundamental and qualitative differences between microtech-nology and nanotechnology.

Figure 1 summarizes materials science and technology in all dimensions. Macroscopic (visible-size) materials/system construction, including the construction of buildings,

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Figure 1. Fabrication paradigm of materials in all scales.

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carpentry work, D.I.Y. (do-it-yourself) jobs, and the hobby of plastic modeling all rely on known mechanics. Even large complicated structures and fi nger-size fi ne structures can be constructed exactly according to their design drawings and blueprints. If we have materials, tools, and skills, we can make what we want.

Similar concepts and strategies are indeed applicable to material construction on the microscopic invisible scale, using advanced techniques, so called microfabrication, based on var-ious techniques such as photolithography. Even though objects and systems are not directly visible by the naked eye, fi ne structures can be fabricated with microscopic structural preci-sion using fi nely designed tools and sophisticated processes. Ultimate improvements of known construction methodologies have made microfabrication a great success. With microfabri-cation techniques, we are supposed to construct microscale-objects that exactly refl ect their design drawings. On the micro-scopic scale, we can basically expect structures and properties from their designs.

Next, very small objects, such as atoms and molecules, are considered. The synthesis of organic molecules is often accomplished according to reaction schemes from textbooks and the literature if skill and experience are enough. New routes for molecular contraction are possibly proposed by applying a knowledge of organic chemistry and even by theo-retical calculations. The correctness of the proposed schemes is actually demonstrated by experimental efforts. Building of mole cules through connecting and breaking bonding can be done exactly according to reaction schemes drawn on paper. The creation of molecules through connecting atoms is also done through logical designs. The preparation of inorganic materials is conducted though rules of lattice structures and other known natural laws.

Unlike for macroscale, microscale, and atomic-/mole-cular-scale phenomena, the fabrication of materials and con-structing systems on the nanoscale or mesoscale regions are not always done decisively according to their design drawings, because uncontrollable and unexpected disturbances and fl uc-tuations have signifi cant effects. The physical phenomena and behavior of materials in these scale regions cannot avoid the infl uence of thermal/statistical fl uctuations and mutual interactions that inevitably occur between components atoms, mole cules, and materials. Outputs such as materials structures and properties are not simply determined by known inputs. A design drawing that we make is not an omnipotent guide, and could be a low-valued reference or even a useless piece of paper.

In the nanoscale region, an input signal to a particular target may also provide perturbations to surrounding moie-ties or components that cause additional mutual interactions. Therefore, in the nanoscale region, the synthesis and fabri-cation of materials and/or using nanoscale components are signifi cantly different from the decisive and plannable fabri-cation in the microscale region. For materials fabrication on the nanoscale, concerted harmonization of various interac-tions and effects are necessary, together with many kinds of techniques and tricks to control materials organization, and stimulating spontaneous processes such as self-assembly/organization. Techniques have to include control during

atomic/molecular manipulation, organic chemistry and physico-chemical reactions, and the application of external physical stimuli. These combined efforts correspond to archi-tecting work rather than to a simple assembly of techniques (technology).

The essence of nano is different from that of micro. We may have misinterpreted the true meaning of nanotechnology. It is not a superior version of microtechnology.

3. Nanoarchitectonics Has Been Invented

As mentioned above, nanotechnology is not a methodology based on a simple advancement of microtechnology. The quality, meaning, and signifi cance of nanotechnology are different from those of microtechnology. However, these two technologies are unfortunately mixed in many cases. In order to fi x this point and correct a paradigm shift, a proposal with novel terminology must be done. An important task in material fabrication is to harmonize various factors and effects, and to combine them into functional nanomaterials and nanosystems. It is the way of archi-tectonics rather than that of an individual technology. Therefore, a novel terminology, nanoarchitectonics (nano + architecto + nics) has been proposed as a new paradigm of materials science and technology on the nanoscale. [ 1 ] This terminology with this meaning was fi rst used by Masakazu Aono in the year 2000 at the 1st International Symposium on Nanoarchitectonics Using Suprainteractions in Tsukuba, Japan. In scientifi c literature, Hecht fi rst used this terminology in a title in 2003. [ 2 ]

Nanoarchitectonics aims at opening a new paradigm of nanotechnology with the following key concepts. They are also tools for the way of nanoarchitectonics.

i) To create reliable nanomaterials or nanosystems by organ-izing nanoscale structures (nanoparts) even with some una-voidable unreliability.

ii) To note that the main players are not the individual nano-parts but their interactions, which cause a new functionality to emerge.

iii) To recognize unexpected emergent functionalities that can result from assembling or organizing a huge number of na-noparts.

iv) To explore a new theoretical fi eld where conventional fi rst-principles computations are combined with novel bold approximations.

In recent years, nanoarchitectonics has begun to spread into many fi elds and became a common and basic concept, as seen in nanostructured materials, [ 3 ] supramolecular assemblies, [ 4 ] hybrid materials, [ 5 ] fabrication methodologies, [ 6 ] energy and environmental sciences, [ 7 ] device and physical application, [ 8 ] and bio and medical applications. [ 9 ] As seen in these devel-opments, it is clear that nanoarchitectonics is not limited to simple atomic and molecular manipulations and can be widely applicable for materials science. The latter concept is especially called materials nanoarchitectonics.

On the other hand, creation of nanoscale materials and sys-tems often leads to fi nding unexpected properties. The latter are based on mutual interactions between components where

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Adv. Mater. 2015, DOI: 10.1002/adma.201502868

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unusual effects based on specifi c structures, environments, orientations, and organization can be found with a high prob-ability. We might not know most of these possible fi ndings. The statement by Feynman that “there’s plenty of room at the bottom” is really true. At the nanoscale, there are still many things awaiting discovery. Unfortunately, so far, we have misun-derstood the true meaning of Feynman’s word because of con-ceptual mixing between microtechnology and nanotechnology. However, with nanoarchitectonics in our hands we can re-open the door to Feynman’s huge room.

Acknowledgements This work was partly supported by the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.

Received: June 14, 2015 Revised: June 30, 2015

Published online:

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