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Computer Simulation of the Thermal Epitaxial Nucleation of Crystals

晶体热外延成核的计算机模拟

基本信息

批准号：
EP/J006106/1
负责人：
Richard Sear
金额：
$ 35.83万
依托单位：
University of Surrey
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ006106%2F1
关键词：
Computer Simulation Thermal Epitaxial Nucleation

项目摘要

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.

结晶是一系列自然现象和技术过程的核心，包括结垢、新药生产和大气中冰的形成。晶体形成的最早阶段称为成核。成核可以控制晶体的关键特征，如结构、取向和大小。尽管如此，我们对这些关键的成核事件的理解很差。晶体几乎总是在固体表面上成核，通常是一直存在的微观杂质的表面--没有一个真正的系统是100%没有所有杂质的。表面成核的过程称为非均相成核。大多数固体杂质颗粒将是结晶的。因此，我们有一个晶体物质，一个晶格在另一个晶格上成核，而另一个晶格又有自己的晶格。如果两个晶格足够相似，两个晶格可以彼此步调一致，这称为外延成核。这被认为是为什么碘化银在诱导水结晶方面如此出色的原因。然而，外延成核还没有被很好地理解。在实验中，原子核可能只有几十亿分之一米宽，只存在几分之一秒，因此从未被观测到。我们将通过在计算机中研究成核来解决在实验中看不到原子核的问题。核化的计算机模拟可以观察到分子细节上的核形成。这项拟议的研究将试图回答有关外延成核的基本问题，但到目前为止尚未得到回答，目的是了解哪些晶体表面有利于诱导结晶，哪些晶体表面不好，以及为什么会这样。拟议的研究将首次对晶体在晶体衬底上热成核的成核率和微观行为进行定量的计算机模拟研究。我们希望通过增加对外延成核的认识，在未来能够更好地控制晶体的成核。结晶对我们来说很重要，原因有很多。雪的形成影响了我们的气候。此外，我们所依赖的许多材料都是结晶的，许多工业过程都在进行结晶。结晶控制即使在你可能意想不到的地方也很重要，例如在制药和巧克力制造中。我们希望回答以下一些问题。如果我们改变表面的晶格和成核晶体的晶格之间的差异，成核速度是如何变化的？已知，如果两个晶格非常相似，则成核速度较快。此外，水晶表面也有台阶和露台。我们想知道：新的晶体是从表面的平坦部分开始的，还是从一个台阶开始的？最后，所有固体的晶格都有缺陷，也就是晶格不完美的地方。我们将看看这些缺陷的成核速度是快还是慢。