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Applied Nanotechnology: The Conversion of Research Results to Products
By Jeremy J. Ramsden
William Andrew
Copyright © 2009 Jeremy R. Ramsden
All right reserved.
ISBN: 978-0-8155-2024-5
Chapter One
What is Nanotechnology?
CHAPTER CONTENTS
1.1 Nanotechnology as Process 4 1.2 Nanotechnology as Materials 7 1.3 Nanotechnology as Materials, Devices and Systems 8 1.4 Direct, Indirect and Conceptual Nanotechnology 9 1.5 Nanobiotechnology and Bionanotechnology 10 1.6 Nanotechnology—Toward a Definition 10 1.7 The Nanoscale 11 1.8 Nanoscience 11 Further Reading 12
In the heady days of any new, emerging technology, definitions tend to abound and are first documented in reports and journal publications, then slowly get into books and are finally taken up by dictionaries, which do not prescribe, however, but merely record usage. Ultimately the technology will attract the attention of the International Standards Organization (ISO), which may in due course issue a technical specification (TS) prescribing in an unambiguous manner the terminology of the field, which is clearly an essential prerequisite for the formulation of manufacturing standards.
In this regard, nanotechnology is no different, except that nanotechnology seems to be arriving rather faster than the technologies we might be familiar with from the past, such as steam engines and digital computers. As a reflection of the rapidity of this arrival, the ISO has already set up a Technical Committee (TC 229) devoted to nanotechnologies. Thus, unprecedentedly in the history of the ISO, we shall have technical specifications in advance of a significant industrial sector.
The work of TC 229 is not yet complete, however, hence we shall have to make our own attempt to find a consensus definition. As a start, let us look at the roots of the technology. They are widely attributed to Richard Feynman, who in a now famous lecture at Caltech in 1959 advocated manufacturing things at the smallest possible scale, namely atom by atom—hence the prefix "nano", atoms typically being a few tenths of a nanometre (10-9 m) in size. He was clearly envisaging a manufacturing technology, but from the lecture we also have glimpses of a novel viewpoint, namely that of looking at things at the atomic scale—not only artefacts fashioned by human ingenuity, but also the minute molecular machines grown inside living cells.
1.1 NANOTECHNOLOGY AS PROCESS
We see nanotechnology as looking at things—measuring, describing, characterizing and quantifying them, and ultimately reaching a deeper assessment of their place in the universe. It is also making things. Manufacturing was evidently very much in the mind of the actual inventor of the term "nanotechnology", Norio Taniguchi from the University of Tokyo, who considered it as the inevitable consequence of steadily improving engineering precision (Figure 1.1). Clearly, the surface finish of a workpiece achieved by grinding cannot be less rough than atomic roughness, hence nanotechnology must be the endpoint of ultraprecision engineering.
At the same time, improvements in metrology had reached the point where individual atoms at the surface of a piece of material could be imaged, hence visualized on a screen. The possibility was of course already inherent in electron microscopy, which was invented in the 1930s, but numerous incremental technical improvements were needed before atomic resolution became attainable. Another development was the invention of the "Topografiner" by scientists at the US National Standards Institute. This instrument produced a map of topography at the nanoscale by raster scanning a needle over the surface of the sample. A few years later, it was developed into the scanning tunneling microscope (STM), and in turn the atomic force microscope (AFM) that is now seen as the epitome of nanometrology (collectively, these instruments are known as scanning probe microscopes, SPMs). Hence a little more than 10 years after Feynman's lecture, advances in instrumentation already allowed one to view the hitherto invisible world of the nanoscale in a very graphic fashion. There is a strong appeal in having a small, desktop instrument (such as the AFM) able to probe matter at the atomic scale, which contrasts strongly with the bulk of traditional high-resolution instruments such as the electron microscope, which needs at least a room and perhaps a whole building to house it and its attendant services. Every nanotechnologist should have an SPM in his or her study!
In parallel, people were also thinking about how atom-by-atom assembly might be possible. Erstwhile Caltech colleagues recall Richard Feynman's dismay when William McLellan constructed a minute electric motor by hand-assembling the parts in the manner of a watchmaker, thereby winning the prize Feynman had offered for the first person to create an electrical motor smaller than 1/64th of an inch. Although this is still how nanoscale artefacts are made (but perhaps for not much longer), Feynman's concept was of machines making progressively smaller machines ultimately small enough to manipulate atoms and assemble things at that scale. The most indefatigable champion of that concept was Eric Drexler, who developed the concept of the assembler, a tiny machine programed to build objects atom by atom. It was an obvious corollary of the minute size of an assembler that in order to make anything of a size useful for humans, or in useful numbers, there would have to be a great many assemblers working in parallel. Hence, the first task of the assembler would be to build copies of itself, after which they would be set to perform more general assembly tasks.
This program received a significant boost when it was realized that the scanning probe microscope (SPM) could be used not only to determine nanoscale topography, but also as an assembler. IBM researchers iconically demonstrated this application of the SPM by creating the logo of the company in xenon atoms on a nickel surface at 4 K: The tip of the SPM was used to laboriously push 18 individual atoms into location. Given that the assembly of the atoms in two dimensions took almost 24 hours of laborious manual manipulation, few people associated the feat with steps on the road to molecular manufacturing. Indeed, since then further progress in realizing an assembler has been painstakingly slow; the next milestone was Oyabu's demonstration of picking up (abstracting) a silicon atom from a silicon surface and placing it at somewhere else on the same surface, and then carrying out the reverse operation. Following on in the spirit of Taniguchi, semiconductor processing—the sequences of material deposition and etching through special masks used to create electronic components—integrated circuits—has now achieved feature sizes below the threshold of 100 nm that is usually considered to constitute the upper boundary of the nano realm (the lower boundary being about 0.1 nm, the size of atoms).
Frustration at being unable to apply "top-down" processing methods to achieve feature sizes in the nanometer, or even the tens of nanometers range stimulated the development of "bottom-up" or self-assembly methods. These were inspired by the ability of randomly ordered structures, or mixtures of components, to form definite structures in biology. Well-known examples are proteins (merely upon cooling, a random polypeptide coil of a certain sequence of amino acids will adopt a definite structure), the ribosome, and bacteriophage viruses—a stirred mixture of the constituent components will spontaneously assemble into a functional final structure.
At present, a plethora of ingeniously synthesized organic and organometallic compounds capable of spontaneously connecting themselves to form definite structures are available. Very often these follow the hierarchical sequence delineated by A.I. Kitaigorodskii as a guide to the crystallization of organic molecules (the Kitaigorodskii Aufbau Principle, KAP)—the individual molecules first form rods, the rods bundle to form plates, and the plates stack to form a three-dimensional space-filling object. Exemplars in nature include glucose polymerizing to form cellulose molecules, which are bundled to form fibrils, which in turn are stacked and glued with lignin to create wood. Incidentally, this field already had a life of its own, as supramolecular chemistry, before nanotechnology focused interest on self-assembly processes.
Molecular manufacturing, the sequences of pick and place operations carried out by assemblers, fits in somewhere between these two extremes. Insofar as a minute object is assembled from individual atoms, it might be called "bottom-up". On the other hand, insofar as atoms are selected and positioned by a much larger tool, it could well be called "top-down". Hence it is sometimes called "bottom-to-bottom". Figure 1.2 summarizes the different approaches to nanofacture (nanomanufacture).
1.2 NANOTECHNOLOGY AS MATERIALS
The above illustrates an early preoccupation with nanotechnology as process—a way of making things. Before the semiconductor processing industry reduced the feature sizes of integrated circuit components to less than 100 nanometers, this however, was no real industrial example of nanotechnology at work. On the other hand, while process—top-down and bottom-up, and we include metrology here—is clearly one way of thinking about nanotechnology, there is already a sizable industry involved in making very fine particles, which, because their size is less than 100 nm, might be called nanoparticles. Generalizing, a nano-object is something with at least one spatial (Euclidean) dimension less than 100 nm; from this definition are derived those for nanoplates (one dimension less than 100 nm), nanofibers (two dimensions less than 100 nm), and nanoparticles (all three dimensions less than 100 nm); nanofibers are in turn subdivided into nanotubes (hollow fibers), nanorods (rigid fibers), and nanowires (conducting fibers).
Although nanoparticles of many different kinds of materials have been made for hundreds of years, one nanomaterial stands out as being rightfully so named, because it was discovered and nanoscopically characterized in the nanotechnology era: graphene and its compactified forms, namely carbon nanotubes (Figure 1.3) and fullerenes (nanoparticles).
A very important application of nanofibers and nanoparticles is in nanocomposites, as described in more detail in Chapter 6.
1.3 NANOTECHNOLOGY AS MATERIALS, DEVICES AND SYSTEMS
One problem with associating nanotechnology exclusively with materials is that nanoparticles were deliberately made for various aesthetic, technological and medical applications at least 500 years ago, and one would therefore be compelled to say that nanotechnology began then. To avoid that problem, materials are generally grouped with other entities along an axis of increasing complexity, encompassing devices and systems. A nanodevice, or nanomachine, is defined as a nanoscale automaton (i.e., an information processor), or at least as one containing nanosized components. Responsive or "smart" materials could of course also be classified as devices. A device might well be a system (of components) in a formal sense; it is not generally clear what use is intended by specifying "nanosystem", as distinct from a device. At any rate, materials may be considered as the most basic category, since devices are obviously made from materials, even though the functional equivalent of a particular device could be realized in different ways, using different materials.
1.4 DIRECT, INDIRECT AND CONCEPTUAL NANOTECHNOLOGY
Another axis for displaying nanotechnology, which might be considered as orthogonal to the materials, devices and systems axis, considers direct, indirect and conceptual aspects. Direct nanotechnology refers to nanosized objects used directly in an application—a responsive nanoparticle used to deliver drugs to an internal target in the human body is an example. Indirect nanotechnology refers to a (probably miniature) device that contains a nanodevice, possibly along with other micro or macro components and systems. An example is a cellphone. The internal nanodevice is the "chip"—the integrated electronic information processor circuits with feature sizes less than 100 nm. All the uses to which the cellphone might be put would then rank as indirect nanotechnology. Given the ubiquity of contemporary society's dependency on information processing, nanotechnology is truly pervasive from this viewpoint alone. It is, of course, the very great processing power, enabled by the vast number of components on a small chip, and the relatively low cost (arising from the same reason), both of which increasingly rely on nanotechnology for their realization, that makes the "micro" processor ubiquitous.
(Continues...)
Excerpted from Applied Nanotechnology: The Conversion of Research Results to Products by Jeremy J. Ramsden Copyright © 2009 by Jeremy R. Ramsden. Excerpted by permission of William Andrew. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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