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EP/J006106/1 - Computer Simulation of the Thermal Epitaxial Nucleation of Crystals

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Dr R Sear EP/J006106/1 - Computer Simulation of the Thermal Epitaxial Nucleation of Crystals

Principal Investigator - Surrey Materials Institute Physics, University of Surrey

Scheme

Standard Research

Research Areas

Computational & Theoretical Chemistry Computational & Theoretical Chemistry

Surface Science Surface Science

Start Date

06/2012

End Date

06/2015

Value

£281,225

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Grant Description

Summary and Description of the grant

Crystallisation lies at the heart of a vast array of natural phenomena and technological processes, including scale-formation, the production of new drugs, and the formation of ice in the atmosphere. The earliest stage of the formation of a crystal is called nucleation. Nucleation can control crucial features of a crystal, such as its structure, its orientation, and its size. Despite this, our understanding of these crucial nucleation events is poor.

Crystals almost always nucleate on solid surfaces, usually the surfaces of the microscopic impurities that are always present - no real system is 100% free of all impurities. The process of nucleation on a surface is known as heterogeneous nucleation. Most solid impurity particles will be crystalline. Thus we have one crystalline substance with one crystal lattice nucleating on another with its own crystal lattice. If the two crystal lattices are sufficiently similar the two lattices can be in step with each other, this is called epitaxial nucleation. This is believed to be why silver iodide is so good at inducing at the crystallisation of water. However, epitaxial nucleation is not well understood. In experiment the nucleus is perhaps only a few billionths of a metre across and exists for a fraction of a second, and therefore has never been observed.

We will get round the problem of not being able to see the nucleus in an experiment by studying nucleation in a computer. A computer simulation of nucleation can observe the nucleus forming in molecular detail. The proposed research will try and answer basic but so-far unanswered questions about epitaxial nucleation, with the aim of understanding which crystal surfaces are good at inducing crystallisation, and which are bad, and why this is. The proposed research is to undertake the first quantitative computer simulation study of the nucleation rates and microscopic behaviour of the thermal nucleation of a crystal on a crystalline substrate.

We hope that by increasing our understanding of epitaxial nucleation, in the future we will be able to better control the nucleation of crystals. Crystallisation is important to us for many reasons. Through the formation of snow it affects our climate. Also, many of the materials we rely on are crystalline and crystallisation is at the hear of many industrial processes. Crystallisation control is important even in places where you might not expect it, for example in making both pharmaceuticals and chocolate.

Some of the questions we hope to answer are as follows. How does the speed of nucleation vary if we vary the difference between the crystal lattice of the surface and that of the nucleating crystal? It is known that if the two lattices are very similar then nucleation is fast. Also, crystal surfaces have steps and terraces. We want to know: Does a new crystal start on a flat part of the surface or at a step? Finally, all solids have defects in their crystalline lattices, places where the lattice is not perfect. We will see if nucleation is faster or slower at these defects.

Structured Data / Microdata


Grant Event Details:
Name: Computer Simulation of the Thermal Epitaxial Nucleation of Crystals - EP/J006106/1
Start Date: 2012-06-06T00:00:00+00:00
End Date: 2015-06-05T00:00:00+00:00

Organization: University of Surrey

Description: Crystallisation lies at the heart of a vast array of natural phenomena and technological processes, including scale-formation, the production of new drugs, and the formation of ice in the atmosphere. The earliest stage of the formation of a crystal is cal ...