Superlattices with scattering mechanisms at multiple length scales efficiently scatter phonons at all relevant wavelengths and provide a convenient route to reduce thermal transport. Here, we show, both experimentally and by atomistic simulations, that SiGe superlattices with well-established compositional gradients and a sufficient number of interfaces exhibit extremely low thermal conductivity.
Our results reveal that the thermal conductivity of long-period (30–50 nm) superlattices with thicknesses below 200 nm is still thickness-dependent and higher than that of the corresponding alloy thin film. Increasing the number of periods up to 16 has a strong impact on heat propagation, leading to thermal conductivity values below the thin-film alloy limit. Lattice dynamics calculations confirm that the reduced thermal conductivity stems from the simultaneous effects of mass scattering, graded interface scattering, and coherent interference from the lattice periodicity. This study provides a significant step forward in understanding the role of compositional gradients in heat transport across nanostructures. The strategy of employing long-period graded superlattices with extremely low thermal conductivities has great potential for micro- and nano-thermoelectric generation and cooling of Si-based devices.
Sustainable energy conversion & storage systems
Beating the Thermal Conductivity Alloy Limit Using Long-Period Compositionally Graded Si1–xGex Superlattices
P. Ferrando-Villalba, Shunda Chen, A. F. Lopeandía, F. X. Alvarez, M. I. Alonso, M. Garriga, J. Santiso, G. Garcia, A. R. Goñi, D. Donadio*, and J. Rodríguez-Viejo*
Optimization of a new system for organic solar cells is a multiparametric analysis problem which requires substantial efforts in terms of time and resources. The strong microstructure dependent performance of polymer:olymer cells makes them particularly difficult to optimize, or to translate previous knowledge from spin coating into more scalable techniques.
The development of high energy density battery technologies based on divalent metals as the negative electrode is very appealing. Ca and Mg are especially interesting choices due to their combination of low standard reduction potential and natural abundance.
Interfacial thermal transport plays a prominent role in the thermal management of nanoscale objects and is of fundamental importance for basic research and nanodevices. At metal/insulator interfaces, a configuration commonly found in electronic devices, heat transport strongly depends upon the effective energy transfer from thermalized electrons in the metal to the phonons in the insulator.
The global energy demand continues to grow both due to the increasing population and wealth. As one of the potential solutions, renewable energy resources can relieve the pressure on conventional energy sources. However, due to fluctuations in both supply and demand, they need to be complemented with load-leveling technologies.
We present a method to dissolve carbon nanotubes that simultaneously allows to prepare n-doped films. These films are composed of thinner bundles of longer tubes when compared to films prepared using surfactants and sonication.