Thin films and nanostructured coatings for eco-efficient buildings - Nanotechnology in Eco-efficient Construction - page 159

sea-level rise, to take one particularly well recorded property, is 3.3 0.4 mm

per year, almost half of which is due to melting glaciers and ice caps (Nerem
et al. , 2010; Jacob et al. , 2012). Furthermore, the geographically uneven
distribution of most of the natural resources has huge macroeconomic
effects and is also prone to yield political unrest and human disasters. The
only sustainable way forward is through changes in life-style and the adop-
tion of more eco-effi cient technologies - also known as 'green' technologies
or 'cleantec' - which are affordable and operate in harmony with nature's
energy fl ows rather than in opposition to them, as discussed in some depth
in a recent topic by Smith and Granqvist (2010).
Thin fi lms and nanostructured coatings are at the heart of the eco-
effi cient technologies because they allow one to do a lot with a little. We
consider two cases, and as a fi rst example we imagine a block of aluminium
that is small enough that it can easily be carried by hand. By use of a thin
fi lm technology, such as vacuum evaporation or sputtering, one can deposit
this material so that it produces a refl ecting surface over a square kilometer.
In full sunlight, this surface refl ects of the order of a Gigawatt that other-
wise might have been absorbed by the earth. Then, as a second example,
imagine that this aluminium surface is covered with an equally thin nano-
structured coating with tiny metallic particles embedded in an oxide host.
Now the surface is no longer visibly refl ecting but is dark and can serve as
an excellent 'selective' solar absorber that not only picks up the energy but
retains it and avoids strong thermal re-emission.
There are a great many analogous examples of thin fi lms and nanostruc-
tured coatings that can be used to obtain not only energy effi ciency, as in
the two examples above, but also human comfort and security. In many
cases, these fi lms and coatings must be used in conjunction with other,
perhaps bulk, materials to achieve a certain desired function. A full discus-
sion of these options is neither possible nor desirable here, and many more
examples are given elsewhere (Smith and Granqvist, 2010). However, we
note that thin fi lms and nanostructured coatings are of much interest for
many of the eco-effi cient technologies discussed in other chapters in this
topic. Thus photocatalytic oxide fi lms require well-defi ned nanostructures
in order to have maximum effi ciency (Fujishima et al. , 2008; Henderson,
2011), windows with high thermal insulation must incorporate a transparent
thin fi lm with low thermal emittance to avoid radiative heat transfer, and
photovoltaic cells - irrespectively of their being of fi rst, second or third
generation - normally contain thin fi lms serving as current collectors. In
particular, switchable glazing technology relying on thin fi lms and nano-
structured coatings is discussed elsewhere in this topic.
The fi lms that are of concern in this chapter have thicknesses that typi-
cally lie between 10 nm and 10

±

￿ ￿ ￿ ￿ ￿ ￿

m; they may be metallic, semiconducting
or dielectric and deposited onto rigid substrates of metal, plastic or glass

μ