García-Suárez Víctor Manuel
Department of Physics, University of Oviedo & CINN, 33007 Oviedo, Spain.
Materials (Basel). 2023 Jan 10;16(2):660. doi: 10.3390/ma16020660.
Current solid-state thermoelectric converters have poor performance, which typically renders them useless for practical applications. This problem is evidenced by the small figures of merit of typical thermoelectric materials, which tend to be much smaller than 1. Increasing this parameter is then key for the development of functional devices in technologically viable applications that can work optimally. We propose here a feasible and effective design of new thermoelectric systems based on physical gaps in nanoscale junctions. We show that, depending on the type of features, i.e., the character of surface/edge states, on both sides of the gap, it is possible to achieve high figures of merit. In particular, we show that, for configurations that have localized states at the surfaces/edges, which translate into sharp resonances in the transmission, it is possible to achieve large Seebeck coefficients and figures of merit by carefully tuning their energy and their coupling to other states. We calculate the thermoelectric coefficients as a function of different parameters and find non-obvious behaviors, such as the existence of a certain coupling between the localized and bulk states for which these quantities have a maximum. The highest Seebeck coefficients and figures of merit are achieved for symmetric junctions, which have the same coupling between the localized state and the bulk states on both sides of the gap. The features and trends of the thermoelectric properties and their changes with various parameters that we find here can be applied not only to systems with nanogaps but also to many other nanoscale junctions, such as those that have surface states or states localized near the contacts between the nanoscale object and the electrodes. The model presented here can, therefore, be used to characterize and predict the thermoelectric properties of many different nanoscale junctions and can also serve as a guide for studying other systems. These results pave the way for the design and fabrication of stable next-generation thermoelectric devices with robust features and improved performance.
当前的固态热电转换器性能不佳，这通常使其在实际应用中毫无用处。典型热电材料的优值较小，往往远小于1，这一问题就证明了这一点。因此，提高这个参数是开发在技术上可行且能最佳运行的功能器件的关键。我们在此提出一种基于纳米级结中的物理间隙的新型热电系统的可行且有效的设计。我们表明，根据间隙两侧特征的类型，即表面/边缘态的特性，可以实现高优值。特别是，我们表明，对于在表面/边缘具有局域态的构型，这会转化为传输中的尖锐共振，通过仔细调整它们的能量以及它们与其他态的耦合，可以实现大的塞贝克系数和优值。我们计算了作为不同参数函数的热电系数，发现了一些不明显的行为，例如局域态和体态之间存在某种耦合，在此耦合下这些量达到最大值。对于对称结，即间隙两侧的局域态和体态之间具有相同耦合的结，能实现最高的塞贝克系数和优值。我们在此发现的热电性质的特征、趋势及其随各种参数的变化不仅可以应用于具有纳米间隙的系统，还可以应用于许多其他纳米级结，例如那些具有表面态或在纳米级物体与电极之间的接触附近局域化的态的结。因此，这里提出的模型可用于表征和预测许多不同纳米级结的热电性质，也可作为研究其他系统的指南。这些结果为设计和制造具有稳健特性和改进性能的稳定下一代热电器件铺平了道路。
