Seminars Archive

Seebeck effect at graphite-diamond interfaces in buried conductive channels

Sana Salami - sana.salami@univ-lyon1.fr
CNRS, University of Lyon, Université Claude Bernard Lyon 1, Institut Lumière Matière, F-69622, Villeurbanne, France

Abstract
An important parameter in thermoelectricity is the Seebeck coefficient, which plays a significant role in the figure of merit and must be enhanced to improve thermoelectric efficiency (zT=Seebeck²·electrical conductivity/thermal conductivity). Known effects that enhance the Seebeck coefficient include drag interactions between electrons and phonons, known as the "phonon-drag" effect, under the influence of an electric current (Peltier effect) or a temperature gradient (Seebeck effect). However, the enhancement of the Seebeck coefficient due to the phonon-drag effect typically occurs within the temperature range where lattice thermal conductivity is at its maximum. As a result, the use of the phonon-drag effect to increase the Seebeck coefficient in thermoelectric applications is limited because it contradicts with the optimization of the figure of merit. However, recent experimental and theoretical work has shown that, in some cases, the phonons primarily responsible for the phonon-drag effect may differ in phase space, momentum and energy from those that primarily dominate the lattice thermal conductivity, allowing both effects to be optimised independently.
In our work, we investigate the phonon-drag effect at an interface where the electron and phonon gases belong to different media. The model system under study consists of an implanted diamond structure, where a conductive channel is buried beneath the diamond surface through ion implantation. We examined the temperature dependent electrical conductivity and Seebeck coefficient in samples implanted under varying conditions and subjected to different annealing temperatures. The results revealed different conduction mechanisms influenced by implantation and annealing conditions, which directly impact the microstructure of the conductive channel. In a recent publication (Salami et al.,2024), we demonstrated that the low temperature electronic transport properties of the conductive channel,graphitized through high temperature annealing, exhibit behavior very similar to bulk graphite. In this presentation, after introducing the system and recalling our initial findings, I will present our latest measurements obtained as a function of annealing temperature, which highlight an original electronic transition followed by an intriguing behavior of the Seebeck coefficient.



References
[1] S. Salami, R. Debord, V.M. Giordano, R. Fulcrand, N. Mahonisi, Z. Mthwesi, N. Blanchard, A. Every, S. Vignoli, C. Adessi, S.R. Naidoo, S. Pailhès, Phonon-drag in a graphite channel buried in diamond, Solid State Sciences, Volume 151, 2024