A method of forming a nanostructure having the form of a tree, comprises a
first stage and a second stage. The first stage includes providing one or
more catalytic particles on a substrate surface, and growing a first
nanowhisker via each catalytic particle. The second stage includes
providing, on the periphery of each first nanowhisker, one or more second
catalytic particles, and growing, from each second catalytic particle, a
second nanowhisker extending transversely from the periphery of the
respective first nanowhisker. Further stages may be included to grow one
or more further nanowhiskers extending from the nanowhisker(s) of the
preceding stage. Heterostructures may be created within the nanowhiskers.
Such nanostructures may form the components of a solar cell array or a
light emitting flat panel, where the nanowhiskers are formed of a
photosensitive material. A neural network may be formed by positioning
the first nanowhiskers close together so that adjacent trees contact one
another through nanowhiskers grown in a subsequent stage, and
heterojunctions within the nanowhiskers create tunnel barriers to current
flow.