Thesis-PDF - IAP/TU Wien

have to be taken into account. Complexity 4 is a property of a system in its own
right. It is even an essential ingredient of real systems, containing more than just
a hand full of atoms.
The philosopher Aristotle (384-322 b.C.) already knew that "The whole is
more than the sum of its parts", intuitively pointing at the possible emergence of
new phenomena when systems increase in size and in number of parts.
It is for example well understood what happens when two atoms collide, but
a very different matter trying to understand what happens when an atom collides
with a whole cluster of atoms or even a surface of a solid. There can e.g. be atoms
of different kinds, having different energy states, chemical bonds and the like. As
one can imagine, the complications steeply rise in number and difficulty. The laws
of particle interaction can only provide a first basis of an explanation how these
things behave.
How electrically charged atoms (ions) impact surfaces is for instance a very
interesting but difficult question. There exists a variety of models trying to explain
the mechanisms of energy transfer between ion and surface or the formation of ioninduced
defects at the surface, but none can be easily applied to a specific problem.
Possible applications include nanopatterning, surface alteration or doping, surface
analytics, surface cleaning, surface sputtering and more ([3], [4]).
In the world of nanoscale objects, new systems with only nuclei, electrons
and photons can be devised endlessly. The newly acquired freedom and ability
to manipulate the small also comes at a price - the need to understand at least
in part the complexity that these real systems exhibit. Additionally, other effects
such as quantum mechanical ones become important at this small scale, or the
high surface to volume ratio of small objects assigning new importance to many
of the common physical effects 5 otherwise too tiny to make a difference.
As bottomline, citing Peter Wolynes, a biophysicist at the University of Illinois,
"The new frontier about which we know nothing is how to describe complex
systems far from equilibrium in a unified way. [...] Such systems range from
sand piles to biological cells to computers, but it is not clear whether or how the
principles of statistical mechanics apply to them.". The more sophisticated our
nanotechnological creations become, the more thorough understanding of complex
systems is needed. Every bit of acquired knowledge potentially unlocks new ways
to look at things, new possibilities to interact and experiment, new challenges to
4 There is some difficulty (and complexity) in the definition of the term "Complexity" itself.
An attempt to classify and define its different facets can e.g. be found in [5].
5 For example combustion engines do not work anymore at this scale, chemical energy must
be turned directly into mechanical energy without using intermediary heat. Gold turns red when
present in form of very small particles. Particles under a certain size are able to pass unhindered
through cell membranes, e.g. to target disease sites. Defectless nanostructured materials can be
built orders of magnitude stronger than what is available today (e.g. carbon-nanotube enforced
matrix materials)
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