Thesis-PDF - IAP/TU Wien

2.4.1 Self-Assembly and Emergent Structures
Many of the nanoscale systems are produced in large quantities. The processing
steps required (e.g. chemical additives, light, heat, altered solvent conditions) are
often completed by and interact with behavior intrinsic to the building blocks
themselves. This behavior emerges out of the interaction within the collection
of atoms and molecules. Every day life examples are the alignment of the polar
molecules to form the skin of soap bubbles or the growing of ice crystals when water
is sufficiently cooled down. Similar processes happen at the nanoscale, when e.g.
nanotubes start to grow at crystalline nucleation sites, when nanopores distribute
themselves evenly in a material ([27]) or when proteins fold and self-assemble to
attain their conformational structure required to perform their function.
2.4.2 Reliability
Functional nanostructures should work reliably. That implies a reliable manufacturing
method and means to test a finished device or material. Problems are
adhesion, friction, wear, fracture, fatigue and contamination. Due to the high
surface/volume ratio, devices with moving parts are particularly prone to stiction
(high static friction). Furthermore not all material properties, e.g. for thin films,
may be well known, making it difficult to predict their behavior and are possibly
error prone.
The tools from macroscopic domains may not longer work, classical mechanics
(Young’s modulus of elasticity, hardness, bending strength, fracture toughness and
fatigue life) must be partly replaced by molecular mechanics and finite element
modeling to simulate the behavior nanosystems.
As of today, there exist no fabrication standards for nanoscale devices and
materials, making comparison difficult. Main techniques are rather experimental
than state of the art.
Storage issues, especially of MEMS and NEMS, as e.g. dust or debris can
provoke failure. E.g. mechanical parts can be blocked or damaged or short-circuits
provoked. ([8])
2.4.3 Environmental Implications
Because of their small size, nanoparticles can in certain cases penetrate cell membranes
and integrate themselves into larger molecules. They can resist cellular
defense systems but are large enough to interfere with cell processes. For example,
in an inhalation experiments with rats, using 13 C-labeled particles, it was found
that nanosized particles (∼ 25 nm) were taken up by the nerve cells and deposited
in the central nervous system (CNS). Investigation also showed that these particles
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