Read an Excerpt
Emerging Nanotechnologies for Manufacturing
By Waqar Ahmed, Mark J. Jackson
ElsevierCopyright © 2009 Elsevier Inc.
All rights reserved.
Nanotechnology to Nanomanufacturing
W. Ahmed, M.J. Jackson and I.Ul Hassan
1.1 Introduction 2
1.2 Approaches to Nanotechnology 3
1.3 Transition from Nanotechnology to Nanomanufacturing 4
1.3.1 Top-down approach 5
1.3.2 Bottom-up approach 8
1.4 Conclusions 13
Nanotechnology is a term that is used to describe the science and technology related to the control and manipulation of matter and devices on a scale less than 100 nm in dimension. It involves a multidisciplinary approach involving fields such as applied physics, materials science, chemistry, biology, surface science, robotics, engineering, electrical engineering and biomedical engineering. At this scale the properties of matter is dictated and there are few boundaries between scientific disciplines. Generally, two main approaches have been used in nanotechnology. These are known as the 'bottom-up' and 'top-down' approaches. The former involves building up from atoms into molecules to assemble nanostructures, materials and devices. The latter involves making structures and devices from larger entities without specific control at the atomic level. Progress in both approaches has been accelerated in recent years with the development and application of highly sensitive equipment. For example, instruments such as atomic force microscope (AFM), scanning tunnelling microscope (STM), electron beam lithography, molecular beam epitaxy, etc., have become available to push forward development in this exciting new field. These instruments allow observation and manipulation of novel nanostructures. Considerable research is being carried throughout the world in developing nanotechnology, and many new applications have emerged. However, a related term is nanomanufacturing, used to describe industrial scale manufacture of nanotechnology-based objects at high rate, low cost and reliability. In this paper we discuss the opportunities and challenges facing the transition from nanotechnology to nanomanufacturing. Tools, templates and processes are currently being developed that will enable high volume manufacturing of components and structures on a nanoscale and these are reviewed. These advancements will accelerate the development of commercial products and enable the creations of a new generation of applications in various different commercial sectors including drug delivery, cosmetics, biomedical implants, electronics, optical components, automotive and aerospace parts.
Although nanotechnology has been around since the beginning of time, the discovery of nanotechnology has been attributed to Richard Feynman 1 who presented a paper called 'There is Plenty of Room at the Bottom' on 29 December 1959 at the annual meeting of the American Physical Society. Feynman talked about the storage of information on a very small scale, writing and reading in atoms, about miniaturization of the computer, building tiny machines, tiny factories and electronic circuits with atoms. He stated that 'In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anybody began seriously to move in this direction'. However, he did not specifically use the term 'nanotechnology'. The first use of the term 'nanotechnology' has been attributed to Norio Taniguchi in a paper published in 1974 'On the Basic Concept of "NanoTechnology"'.
Since then several definitions of nanotechnology have evolved. For example, the dictionary definition states that nanotechnology is 'the art of manipulating materials on an atomic or molecular scale especially to build microscopic devices'. Other definitions include the US government which state that 'Nanotechnology is research and technology development at the atomic, molecular or macromolecular level in the length scale of approximately 1–100 nm range, to provide a fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices and systems that have novel properties and functions because of their small and/or intermediate size'. The Japanese have come up with a more focused and succinct definition for 'True Nano' as nanotechnology which is expected to cause scientific or technological quantum jumps, or to provide great industrial applications by using phenomena and characteristics peculiar in nano-level.
Regardless of the definition that is used, it is evident that the properties of matter are controlled at a scale between 1 and 100 nm. For example, chemical properties take advantage of large surface to volume ratio for catalysis and interfacial and surface chemistry is important in many applications. Mechanical properties involve improved strength hardness in light-weight nanocomposites and nanomaterials, altered bending, compression properties, nanomechanics of molecular structures. Optical properties involve absorption and fluorescence of nanocrystals, single photon phenomena, photonic bandgap engineering. Fluidic properties give rise to enhanced flow using nanoparticles, and nanoscale adsorbed films are also important. Thermal properties give increased thermoelectric performance of nanoscale materials and interfacial thermal resistance is important.
1.2 APPROACHES TO NANOTECHNOLOGY
Numerous approaches have been utilized successfully in nanotechnology, and as the technology develops further approaches may emerge. The approaches employed thus far have generally been dictated by the technology available and the background experience of the researchers involved. Nanotechnology is a truly multidisciplinary field involving chemistry, physics, biology, engineering, electronics, social sciences, etc., which need to be integrated together in order to generate the next level of development (Figure 1.1). Fuel cells, mechanically stronger materials, nanobiological devices, molecular electronics, quantum devices, carbon nanotubes, etc. have been made using nanotechnology. Even social scientists are debating ethical use of nanotechnology.
The two main approaches to explaining nanotechnology to the general public have been oversimplified and have become known as the 'top-down' approach and the 'bottom-up' approach. The top-down approach involves fabrication of device structures via monolithic processing on the nanoscale. This approach has been used with spectacular success in the semiconductor devices used in consumer electronics. The bottom-up approach involves the fabrication of device structures via systematic assembly of atoms, molecules or other basic units of matter. This is the approach nature uses to repair cells, tissues, organs of living and organ systems in living things, and indeed for life processes such as protein synthesis. Tools are evolving which will give scientists more control over the synthesis and characterization of novel nanostructures and yield a range of new products in the near future.
1.3 TRANSITION FROM NANOTECHNOLOGY TO NANOMANUFACTURING
Throughout the world a huge amount of research is being carried out, and governments and research organizations are spending large amounts of money and human resources into nanotechnology. This has generated interested scientific output and potential commercial applications, some of which have been translated into products produced on a large scale. However, in order to realize commercial benefits far more lab-scale applications need to be commercialized, and for that to happen nanotechnology needs to enter the realm of nanomanufacturing. This involves using the technologies available to produce products on a large scale which is economically viable. Regardless of whether a top-down or bottom-up approach is used, a nanomanufacturing/ nanofabrication technology should be:
* capable of producing components with nanometre precision;
* able to create systems from these components;
* able to produce many systems simultaneously;
* able to structure in three dimensions;
1.3.1 Top-down approach
The most successful industry utilizing the top-down approach is the electronics industry (Figure 1.2).
This industry is utilizing techniques involving a range of technologies such as chemical vapour deposition (CVD), physical vapour deposition (PVD), lithography (photolithography, electron beam and X-ray lithography), wet and plasma etching, etc. to generate functional structures at the micro- and nanoscale (Figure 1.3). Evolution and development of these technologies have allowed emergence of the numerous electronic products and devices that have enhanced the quality of life throughout the world. The feature sizes have been shrinking continuously from about 75 µm to below 100 nm. This has been achieved by improvements in deposition technology and more importantly due to the development of lithographic techniques and equipment such as X-ray lithography and electron beam lithography.
Techniques such as electron beam lithography, X-ray lithography and ion beam lithography, all have advantages in terms of resolution achieved; however, there are disadvantages associated with cost, optics and detrimental effects on the substrate. These methods are currently under investigation to improve upon current lithographic process used in the IC industry. With continuous developments in these technologies, it is highly likely that the transition from microtechnology to nanotechnology will generate a whole new generation of exciting products and features.
Let us take an example of a demonstration of how several techniques can be combined together to form a 'nano' wine glass (Figure 1.4). In this example, a focused ion beam and CVD have been employed to produce this striking nanostructure.
The top-down approach is being used to coat various coatings to give improved functionality. For example, vascular stents are being coated using CVD technology with ultra-thin diamond-like carbon coatings in order to improve biocompatibility and blood flow (Figure 1.5). Graded a-SixCy:H interfacial layers results in greatly reduced cracking and enhanced adhesion.
1.3.2 Bottom-up approach
The bottom-up approach involves making nanostructures and devices by arranging atom by atom. The scanning tunnelling microscope (STM) has been used to build nano-sized atomic features such as the letters IBM written using xenon atoms on nickel (Figure 1.6). While this is beautiful and exciting, it remains that the experiment was carried out under carefully controlled conditions, that is liquid helium cooling and high vacuum, and it took approximately 24 hours to get the letters right. Also the atoms are not bonded to the surface just adsorbed and a small change in temperature or pressure will dislodge them. Since this demonstration significant advances have been made in nanomanufacturing.
The discovery of the STM's ability to image variations in the density distribution of surface-state electrons created in the artists a compulsion to have complete control of not only the atomic landscape, but also the electronic landscape. Figure 1.7 shows 48 iron atoms positioned into a circular ring in order to 'corral' some surface-state electrons and force them into 'quantum ' states of the circular structure. The ripples in the ring of atoms are the density distribution of a particular set of quantum states of the corral. The artists were delighted to discover that they could predict what goes on in the corral by solving the classic eigenvalue problem in quantum mechanics – a particle in a hard-wall box.
Excerpted from Emerging Nanotechnologies for Manufacturing by Waqar Ahmed, Mark J. Jackson. Copyright © 2009 Elsevier Inc.. Excerpted by permission of Elsevier.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.