Scientists have studied crystallisation for a very lng time, but there is still much that is not understood.
I work on making it better understood. For example,
for centuries chemists have known that scratching
the side of a flask containing a solution facilitates
crystallisation; the crystals form along the scratch.
A PhD student of mine, Amanda Page, and
I have for the first time undertaken
computer simulations
of crystallisation in grooves
to try and understand
this. We
found
that crystallisation in grooves is indeed fast.
Computer simulation is perhaps the most powerful tool we have
for studying nucleation, it is the only one that allows us
to see the nucleus of the crystal growing when it is still
microscopic. See the simulation snapshot on the left which shows
a nucleating crystal in a groove. The groove itself is not shown
but you see that the crystal conforms to the two surfaces of
groove: the bottom one which is horizontal and the top one which is
at angle of 70 degreees to the horizontal.
The simulations of Amanda were very succesful but, like a
lot of good science, they raised as many questions as they answered.
I am interested in recruiting a PhD student to answer some of these
questions. For example, Amanda used grooves with surfaces
that are completely smooth. When a molecular crystal forms on a surface
the molecules forming the new crystal feel the molecules of
the surface they are forming in. Often this surface is itself
a crystal, so we have one crystal forming on another. This is called
epitaxy and it is widely used, e.g., in semiconductors, but again
it is poorly understood. I would like to create crystal surfaces
and study nucleation of another crystal on these surfaces.
Crystallisation would be studied when the two crystals match,
i.e., have the same spacing between the molecules in the crystal
lattice, and have different spacings. We would compare the
results in the two cases.
One of the interesting open questions in crystallisation
concerns defects. To the right is a defected crystal
that has formed in a groove. The stripes of different
colours indicate alternating domains of two different
but similar crystal lattices - denoted by yellow and blue.
Where blue meets yellow there is a crystal defect called
a stacking fault. These defects tend to freeze in, i.e.,
once they form it is very diffiult to remove them.
I am interested in quantifying how difficult they are to
remove and what strategies could be developed to either
prevent them forming or to anneal them out.
In nature, huge highly ordered crystals can be formed by
living organisms, e.g., sea urchins, but we do not know how
they do it. I think this is an intriguing problem to study:
Sea urchins show that it can be done, but we have to work out how!
The project will involve state-of-the art computer simulation techniques (as are already being used in my group) to study the nucleation of crystalline phases. I have written a review (pdf) which gives more details of nucleation.
If you are interested and have or will soon get a first or upper second class degree in Physics or a related subject, please email me at r.sear@surrey.ac.uk. Funding is available for UK students.
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