Editorial Feature

Tools and Fabrication in Bottom-up Manufacturing for Nanotechnology

The tools here support rather more futuristic approaches to large-scale production and nanofabrication based on bottom-up approaches, such as nanomachine production lines. This approach is equivalent to building a car engine up from individual components, rather than the less intuitive method of machining a system down from large blocks of material. Indeed, although such techniques are still in their infancy, the DTI (Department of Trade and Industry, UK) report a recent movement away from top-down techniques towards self-assembly within the international research community. Scientists and engineers are becoming increasingly able to understand, intervene and rearrange the atomic and molecular structure of matter, and control its form in order to achieve specific aims.

Self-Assembly and Self-Organisation

Self-assembly refers to the tendency of some materials to organise themselves into ordered arrays. This technique potentially offers huge economies, and is considered to have great potential in nanoelectronics. In particular, the study of the self-assembly nature of molecules is proving to be the foundation of rapid growth in applications in science and technology. For example, Ottilia Saxl reports that the Stranski–Krastonov methods for growing self-assembly quantum dots has rendered the lithographic approach to semiconductor quantum dot fabrication virtually obsolete.

Creating New Nanocomposites with Organic Molecules

In addition, self-assembly is leading to the fabrication of new materials and devices. The former area of materials consists of new types of nanocomposites or organic/inorganic hybrid structures that are created by depositing or attaching organic molecules to ultra-small particles or ultra-thin man-made layered structures.

Organic Films and Solid-state Chips

Similarly, the latter area of devices range from the production of new chemical and gas sensors, optical sensors, solar panels and other energy conversion devices, to bioimplants and in vivo monitoring. The basis of these technologies is an organic film (the responsive layer) which can be deposited on a hard, active electronic chip substrate. The solid-state chip receives signals from the organic over-layer as it reacts to changes in its environment, and processes them. The applications for these new materials and devices are summarised in Table 1.

Table 1. Applications for new materials and devices resulting from self-assembly and self-organisation.

Name

Technique

Application

New Materials

Sol-gel technology

Inorganic and organic component combination.

The design of different types of materials; functional coatings.

Intercalation of polymers

Intercalation of polymers with other materials (DNA, drugs).

Toxicity testing, drug delivery and drug performance analysis.

Nano-emulsions

Nano-particle size and composition selected.

Production of required viscosity and absorption characteristics.

Biometrics

Design of systems, materials and their functionality to mimic nature.

Biosensing and optical switching.

New Devices

Field-sensing devices

Combination of molecular films with optical waveguides and resonators.

Biosensing and optical switching.

Material-sensing devices

Surfaces of liquid crystals or thin membranes and other organic compounds can be used to detect molecules via structural or conductive changes.

Gas and chemical sensing.

Software Modelling to Simulate Molecular Structures

Molecular modelling software is another fabrication technique of wide-ranging applicability as it permits the efficient analysis of large molecular structures and substrates. Hence, it is much used by molecular nanotechnologists, where computers can simulate the behaviour of matter at the atomic and molecular level. In addition, computer modelling is anticipated to prove essential in understanding and predicting the behaviour of nanoscale structures because they operate at what is sometimes referred to as the mesoscale, an area where both classical and quantum physics influence behaviour.

Nanometrology

Fundamental to commercial nanotechnology is repeatability, and fundamental to repeatability is measurement. Nanometrology, then, allows the perfection of the texture at the nanometre and subnanometre level to be examined and controlled. This is essential if highly specialised applications of nanotechnology are to operate correctly, for example X-ray optical components and mirrors used in laser technologies.

Note: A complete list of references can be found by referring to the original text.

Primary author: Alexander Huw Arnall.

Source: Greenpeace report, ‘Future Technologies, Today’s Choices Nanotechnology, Artificial Intelligence and Robotics; A technical, political and institutional map of emerging technologies’, July 2003.

For more information on this source please visit Greenpeace.

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