Physical properties of materials at the nanoscale

该研究计划旨在了解材料的原子尺度结构如何影响其在更大尺度上的性质，重点是纳米尺度系统，即纳米颗粒，纳米结等。为此，我们采用各种计算方案，提供系统的相关物理，特别是分子动力学模拟，同时也允许我们单独检查不同参数的影响。我们的研究计划将集中在三个不同的主题：*（i）激光-物质相互作用，特别是超短（几fs到几百ps），强激光脉冲对固体材料的烧蚀，这是我们过去在很大程度上贡献的问题。我们将特别研究消融的问题和随后在浸没在液体（通常是水）中的靶中产生纳米颗粒的问题，这是一种常规用于产生纳米颗粒的方法，其本身用于例如医疗应用。我们将研究激光脉冲的“操纵”，以优化喷射物质的结构，并实现量身定制的特性-一种称为脉冲成形的方法。最后，我们将研究热密度物质和“等离子体”制度，其中物理学主要是由非热过程，特别是库仑效应（排斥，爆炸，电荷效应）。* （二）纳米热疗：我们感兴趣的是确定热量如何在纳米材料中传输和消散，特别是半导体和碳基材料。为此目的，我们研究声子的贡献，热传输，即各种模式如何贡献个人的热流，以及它们如何相互关联。我们已经发现，这些相关性对热流衰减起作用，这解释了为什么一维材料是如此好的热导体。我们将把这项工作扩展到更大规模的结构，更现实的模型和更高的维度。* （iii）无序材料：我们的目标是在基本层面上了解原型非晶半导体a-Si的结构，特别是缺陷的性质及其对局部有序和弛豫的影响。我们预计，答案将来自详细比较的结构数据的a-Si与那些最近已成为可从高能X射线衍射实验的a-Ge。这种比较提供了数据的“对比”，并将对订单的各种贡献有所了解。我们将首先开发/优化a-Ge的模型，将其与a-Si的模型进行比较。使用这两个模型，我们将详细说明一种方法，用于更紧密地模拟制造和退火样品之间的差异，这是一个尚未得到妥善解决的问题。**

This research program aims at understanding how the atomic-scale structure of materials affects their properties on the larger scale, focusing on nanoscale systems, viz. nanoparticles, nanojunctions, etc. For this purpose, we resort to a variety of computational schemes that provide the relevant physics of the systems, in particular molecular dynamics simulations, and at the same time allow us to examine the effect of different parameters individually. Our research program will focus on three different themes: ***(i) Laser-matter interactions, in particular ablation of solid materials by ultrashort (several fs to hundreds of ps), intense laser pulses, a problem to which we have largely contributed in the past. We will in particular examine the problem of ablation and the subsequent production of nanoparticles in targets immersed in a liquid (typically water), a method routinely used for the production of nanoparticles, which are themselves used e.g. in medical applications. We will investigate the "manipulation" of the laser pulse so as to optimize the structure of the ejected matter and achieve tailor-made properties - a method referred to as pulse-shaping. Finally, we will examine the warm-dense matter and "plasma" regimes, where the physics is dominated by non-thermal processes, and in particular Coulomb effects (repulsion, explosion, charge effects). ***(ii) Nanothermics: We are interested in determining how heat is transported and dissipated in nanoscale materials, in particular semiconductors and carbon-based materials. For this purpose, we examine the phonon contributions to heat transport, i.e. how the various modes contribute individual heat currents and how they cross-correlate. We have found that these correlations act against heat current decay, which explains why one-dimensional materials are such good heat conductors. We will extend this work to larger scale structures, more realistic models, and higher dimensionalities. ***(iii) Disordered materials: Our aim here is to understand at the fundamental level the structure of the prototypical amorphous semiconductor a-Si, in particular the nature of defects and their influence on local order and relaxation. We expect that answers will come from a detailed comparison of structural data for a-Si with those for a-Ge which have recently become available from high energy x-ray diffraction experiments. Such a comparison provides "contrast" in the data and will give some understanding of the various contributions to order. We will first develop/optimize a model for a-Ge, which will be compared to our model for a-Si. Using these two models, we will elaborate a method for simulating more closely the difference between as-made and annealed samples, a problem that has not yet been properly addressed. **