Silicon-based nanocomposites for thermoelectric applications

该项目的主要目标是实现高效和可持续的硅基热电材料。在第二个资助期，文献中理论上提出的所谓的“合金中的纳米颗粒”方法形成了一个指导方针。它结合了短波长声子在普通合金中不规则位置原子上的有效散射和长波长声子在较大结构(如纳米颗粒)上的有效散射。金属硅化物纳米颗粒被考虑用于这一目的。在第一个供资期间开发的两个耦合粒子反应堆使这一概念得以实现。这一概念还包括调制掺杂的方法，即具有非常高掺杂浓度的小区域与低掺杂浓度区域交替。这使得电子传输路径不会在带电的掺杂剂上发生库仑散射，而掺杂剂团簇则充当声子散射的有效中心。对于块体样品，必须开发一种电流辅助烧结工艺，以保持所需的“纳米颗粒在合金中”的结构，并防止在烧结过程中所有组分的普遍合金化或相分离。对于薄膜，将使用多层方法，其中激光退火法将与直流等离子体中的氢化或微波加热相结合。薄膜的导热系数将使用由Völklein教授小组在这一优先计划范围内开发的方法以及基于海市蜃楼效应的光学非接触方法来测量。为了更深入地了解热电性能和结构形成过程，将开发一个3D-Onsager网络模型，其中的输入来自压实过程中微观过程的分子动力学模拟。

The main goal of this project is the realization of efficient and sustainable silicon based thermoelectric materials. In this second funding period, the so called “nanoparticle in alloy” approach, theoretically proposed in the literature, forms a guide line. It combines the efficient scattering of phonons with short wavelengths on irregularly positioned atoms in common alloys with the efficient scattering of phonons with long wavelengths on larger structures, like nanoparticles. Metal silicide nanoparticles are considered for this purpose. Two coupled particle reactors, developed during the first funding period, allow for the realization of this concept. The concept includes also the approach of modulation doping, were small areas with very high doping concentrations alternate with areas of low doping concentration. This allows for electronic transport pathways without Coulomb scattering on charged dopants, while the clusters of dopants act as efficient centers for phonon scattering. For bulk samples, a current assisted sintering process has to be developed, in order to maintain the desired “nanoparticle in alloy”-structure and to prevent a general alloying of all components or a phase separation during sintering. For thin films, a multilayer approach will be used, where the laser annealing process will be combined with hydrogenation in DC plasmas or microwave heating. The thermal conductivity of the thin films will be measured with methods developed within this priority program by the Group of Prof. Völklein as well as with an optical non-contact method based on the mirage effect. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D-Onsager network model will be developed, where input is taken from the molecular dynamic modelling of the microscopic processes during compaction.