Polycrystalline materials - comparison between theory and experiment

本项目的主题将是研究不同的理论(如EMA，ARTT和ARIT)，这些理论都描述了多晶材料的(IR)反射或透射谱，以及详细的适用范围。有些理论只适用于大或小的微晶、孤立的颗粒或致密的样品，无论是否考虑颗粒的形状。我们还通过自己的研究发现，从计算光谱中获得的结果并不一致。天文学家对这种情况也很感兴趣，因为从拟合的光谱中获得的关于粒子大小和形状的信息决定了这些粒子的形成过程。因此，从测量光谱中尽可能精确地获取信息是非常重要的。由于缺乏合适的样品来定义粒子形状、大小和相互之间的距离，因此我们打算用时域有限差分计算来创建“实验”参考光谱，并将不同理论计算的光谱与这些光谱进行比较。不同的理论在必要的计算时间和精力上也有很大的不同。我们还打算研究与粒子形状有关的能带分裂，这是由其中一个理论预测的。对于在无尘室中产生的样品，我们也可以研究粒子尺寸效应和简单材料在一定程度上的能带分裂。例如，有必要确定“大”和“小”粒子、“孤立”和“不那么孤立”的粒子之间的界限。极限值取决于相应跃迁偶极矩的振子强度。有了这样的知识计划，我们就可以重现实际测量的光谱，这意味着不是用有限差分时间域计算气溶胶测量的谱。气溶胶测量已经完成，并将由天文研究所提供。

The subject of this project will be the investigation of different theories (e.g. EMA, ARTT and ARIT) that all describe the (IR) reflection or transmission spectra of polycrystalline materials, and the ranges of applicability in detail. Some theories are only valid for large or small crystallites, isolated particles or compact samples, with or without taking into account the particle shape. We found, also with own investigations, that the results gained from the calculated spectra are not consistent with each other.The astronomer's interest in this situation is also very high since the information gained from the fitted spectra about particle size and shape determine the formation process of those particles. Therefore it is very important to gain information out of the measured spectra as precise as possible.Due to the lack of suitable samples with defined particle shape, size and distance to each other is it our intention to create "experimental" reference spectra with Finite Difference Time Domain calculations and compare spectra calculated with different theories to these spectra. The different theories also differ very strongly in the necessary calculation time and effort. We also intend to investigate the band splitting in dependency of the particle shape, which is predicted by one of the theories.With samples, that are produced in a clean room can we also investigate particle size effects and the band splitting for simple materials to a certain extend.It is e.g. necessary to determine the limits between "large" and "small" particles, "isolated" and "not so isolated" particles. The limits depend on the oscillator strengths of the corresponding transition dipole moment.With the so gained knowledge plan we to reproduce real measured, that means not by Finite Difference Time Domaine calculated spectra of aerosol measurements. The aerosol measurements are already performed and will be provided by the Institute of Astronomy.