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Colloids can indeed do much more: they are also
interesting model systems for solid-state physics, because the bonding
behaviour of the relatively large particle can be compared with that
of much smaller atoms. Since they react more slowly than atoms, we can
use them to observe and study processes in solid-state physics. But
there is a problem: most atoms, unlike most other particles, are not
by rule spherically symmetric, but rather have deformed "orbitals"
which project into space like dumbbells or ovals.
The team of researchers from the Max Planck
Institute of Colloids and Interfaces, led by Dr Wang, has now produced
particles that do not interact with their neighbours in spherically
symmetric ways. So they placed a colloidal crystal on a surface (image
2) and bombarded it with reactive ions, reducing the particles in the
upper layer to the desired size and expanding the free surfaces
between the colloids.
They also metallised the crystal with gold. Part of
the gold passed through the gaps in the upper layer as if through a
stencil, all the way to the lower layers. In this way, patterns of
metallisation of various symmetries and at nanoscale sizes are
produced (see image 1). Gold surprisingly also lodged itself in the
deep layers on the underside of the particles. (image 1, right)
For years, chemistry has had a number of methods to
intentionally use gold in reactions, for example, in joining
particular molecules. Thus the particles partially overlaid with gold
expand the tool kit of "colloid atoms". The chemists hope that in the
future they will be able to build "colloid molecules" or new kinds of
colloid crystals. For the chemistry of colours, too, there are more
possibilities: new, shimmering colours, that, for example, change with
the surrounding temperature or humidity. In the long-term, however,
the most attractive applications appear to be in optical data
processing. |
