Page 115 - Nanotechnology an introduction

Chapter Contents

10.1 Systems 199
10.2 Materials Selection 200
10.3 Defects in Nanograins 202
10.4 Spacial Distribution of Defects 203
10.5 Strategies to Overcome Component Failure 204
10.6 Computational Modeling 205
10.7 “Evolutionary” Design 206
10.8 Performance Criteria 208
10.9 Scaleout 209
10.10 Standardization 209
10.11 Creative Design 210
10.12 Produceability 210
10.13 Summary 211
10.14 Further Reading 211
Systems and nanosystems are defined. Nanotechnology implies many departures from traditional engineering practice. For example, one is ultimately no longer constrained to merely select suitable materials; rather materials with exactly
the required properties can be specified and produced. Computation is much more intimately connected with nanotechnology than with larger-scale technologies, because explicit and reliable simulation of complete systems is often possible.
To cope with vastification, evolutionary computation offers a solution, vastly amplifying human capabilities. With any nanosystem, it needs to be considered how its function can be made useful for human beings. Scaleout – massive
parallelization – eliminates the barriers associated with traditional scaleup. Any viable, integrated technological system requires standardization, first of vocabulary, then of the components used in constructing the artifacts of the technology.
Nanotechnology offers magnificent opportunities for creative design, possibly allowing a new era of innovation to nucleate and grow. Such growth will be driven not only by the possibilities inherent in the technology, but also by the fact that
a far greater proportion of the population should be able to contribute than hitherto to conventional design and realization. Manufacturing variability is a considerable challenge at the nanoscale and feasible, high-volume production routes have
yet to be achieved.
Keywords: materials selection, defects, reliability, manufacturability, modeling, evolutionary design, scaleout, standardization
This chapter comprises rather a miscellany of topics, because nanotechnology is not yet so far advanced as to comprise systems to any
meaningful extent. Key elements in developing a viable industrial system are explored.

10.1. Systems
The essence of a system is that it cannot be usefully (for the purposes of analyzing its function or optimizing its design) decomposed into its
constituent parts. Two or more entities (or activities) constitute a system if the following four conditions, enumerated by R.L. Ackoff, are satisfied:

1. We can talk meaningfully of the behavior of the whole of which they are the only parts.
2. The behavior of each part can affect the behavior of the whole.
3. The way each part behaves and the way its behavior affects the whole depends on the behavior of at least one other part.
4. No matter how we subgroup the parts, the behavior of each subgroup will affect the whole and depends on the behavior of at least one other
subgroup.
The word “nanosystem” can be defined as a system whose components are in the nanoscale.
An example of a system that might justifiably be called “nano” is the foot of the reptile called the gecko, many species of which can run up vertical
walls and upside down across ceilings. Their feet are hierarchically divided into tens of thousands of minute pads that allow a large area of
conformal contact with irregular surfaces. The adhesive force is provided by the Lifshitz–van der Waals interaction (see Section 3.2), normally
considered to be weak and short range, but additive and hence sufficiently strong in this embodiment if there are enough points of contact.
Attempts to mimic the foot with a synthetic nanostructure have only had very limited success, because the real foot is living and constantly adjusted
to maintain the close range conformal contact needed for the interaction to be sufficiently strong to bear the weight of the creature, whereas the
synthetic foot is static, and typically irreversibly damaged merely upon detachment. Each nanoscale footlet (the smallest subdivision, the part that is
actually in contact with the surface) is only part of a system in the living creature, whose brain is involved in maintaining adhesion.

10.2. Materials Selection
When confronted with a macroscale design problem, one may use charts of the type shown in Figure 10.1 to select a suitable material fulfilling the
functional requirements. Complex problems may impose more than two constraints on properties, hence many such diagrams may be required,
since it is visually problematical to construct them in more than two dimensions. However, this procedure imposes some decomposability on the
problem, which is contrary to the spirit of it being a system (Section 10.1). Furthermore, the decomposition is arbitrary, there being numerous
possible binary combinations of properties, which may influence the design choices in different ways. Finally, we notice that the entire property
space is by no means comprehensively covered. Light and strong, or heavy and weak materials remain elusive, for example.