Periodic Reporting for period 1 - Phonon-ART (Uncovering Phonon Dynamics by Advanced Raman Techniques)
Reporting period: 2020-11-01 to 2022-10-31
Technologies based on electrons and photons have changed many aspects of our daily lives. Controlling electrons in semiconductor materials has allowed for mainstream technologies such as laptops and mobile phones, while the control of photons is critical for wireless communication or the use of optical fibers. Meanwhile, in many technologies such as nanoelectronics, heat management becomes the bottleneck for the next generation development. In many materials heat is carried mostly by phonons, mechanical vibrations of the atomic lattice and are responsible for the transmission of both sound and heat. Therefore, controlling phonons analogously to photons and electrons becomes indispensable to develop analogous technologies based on sonic and thermal materials and devices. However, this is an extremely complicated task, and many efforts are devoted towards developing new materials and experimental techniques capable of measuring reliably phonons. This is particularly difficult to achieve in nanomaterials, field that is experiencing deep research since advances in nanofabrication now make it possible to scale the characteristic dimensions of nanostructures to under 10nm. Understanding thermal transport in such nanoscale systems is crucial not only to advanced fundamental science but also to push energy-efficient technological applications that are on high demand. This project sought to enlighten the fundamental mechanism responsible for thermal transport away from nanoscale heat sources and diamond, both material systems very relevant for the semiconductor industry. In particular, this project aimed at advancing this understanding by implementing new techniques based on ultrafast lasers in order to characterize thermal transport at the nanoscale. We proposed to develop ultrafast conventional and stimulated Raman spectroscopy techniques to study how these materials cool down over time after impulsive heating, and therefore, identify the most promising avenues to effectively dissipate heat in nanoelectronics devices. The Phonon-ART project concluded that time-resolved Raman spectroscopy techniques in combination with transient reflectivity measurements is a extremely powerful approach to study electron and phonon dynamics in a range of materials from bulk semiconductors to graphite to graphene.
In this project we have developed a versatile experimental setup capable of performing time-resolved spontaneous, and stimulated Raman spectroscopy measurements. In addition, we have developed another complementary technique, called transient reflectivity which is able to access information related to both electron and phonon dynamics in our materials. With these techniques we were able to characterize thermal and electron dynamics of a range of materials: from bulk semiconductors, to supported graphite, to suspended graphite of different thicknesses.
Firstly, we performed spontaneous time-resolved Raman measurements on bulk materials. Since spontaneous Raman scattering efficiency is extremely weak, we also implemented time-resolved stimulated Raman spectroscopy measurements that allow us to critially increase the Raman signal from these materials. These techniques enable us to extract the phonon lifetime of materials after excitation, which is key to better understand thermal transport at the nanoscale, as well as to extract the temperature evolution of the phonons, key to observe also exotic thermal behaviors.
Finally, we implemented and used our transient reflectivity setup to study the ultrafast dynamics of graphite of different layer thicknesses at room temperature. Graphene is a material extremely relevant to push the limits of heat transfer as it has shown clear deviation from the conventional diffusive thermal transport. This technique helped us to understand the influence of a silicon substrate on the dynamics of heat carriers at different time-scales, such as electrons at short times (~fs, few ps), and phonons at longer times (~100ps). It also provided information about the electron-phonon coupling which is key to understand the energy relaxation mechanisms.
The following actions were taken during the duration of the fellowship for its dissemination:
- Link to the MSCA website for the project, linked to the existing Zardo group homepage.
- Publication of articles in peer-reviewed journals in which the MSCA:
o B. Abad et al. “The 2022 Applied Physics by Pioneering Women: a Roadmap” Journal of Physics D: Applied Physics. (Accepted) 2022. We were invited to write section 15: “Nanophotonics and Nanophononics”.
o Articles in preparation.
- Oral presentations at international conferences:
o Swiss NanoConvention 2022, invited by Prof. Barbara Rothen-Rutishauser, Fribourg (Switzerland), July 2022 (Invited talk)
o “Phonon engineering in semiconductor superlattice nanowires: phonons and thermal transport”. Nanowire Week 2022, Chamonix, France, 2022.
o “Extreme ultraviolet beams probe mechanical and structural properties of nanostructured metalattices”. E-MRS Spring 2021, Online, France, 2021.
o “Mechanical and structural properties of nanostructured metalattices probed by coherent EUV beams”. MRS Spring 2021, Online, USA, 2021.
- Other outreach activities:
o NCCR video campaign celebrated the 50th anniversary of women obtaining the right to vote in Switzerland, showing the implemented setup - https://www.youtube.com/watch?v=Wv9e85QpLik(opens in new window)
Firstly, we performed spontaneous time-resolved Raman measurements on bulk materials. Since spontaneous Raman scattering efficiency is extremely weak, we also implemented time-resolved stimulated Raman spectroscopy measurements that allow us to critially increase the Raman signal from these materials. These techniques enable us to extract the phonon lifetime of materials after excitation, which is key to better understand thermal transport at the nanoscale, as well as to extract the temperature evolution of the phonons, key to observe also exotic thermal behaviors.
Finally, we implemented and used our transient reflectivity setup to study the ultrafast dynamics of graphite of different layer thicknesses at room temperature. Graphene is a material extremely relevant to push the limits of heat transfer as it has shown clear deviation from the conventional diffusive thermal transport. This technique helped us to understand the influence of a silicon substrate on the dynamics of heat carriers at different time-scales, such as electrons at short times (~fs, few ps), and phonons at longer times (~100ps). It also provided information about the electron-phonon coupling which is key to understand the energy relaxation mechanisms.
The following actions were taken during the duration of the fellowship for its dissemination:
- Link to the MSCA website for the project, linked to the existing Zardo group homepage.
- Publication of articles in peer-reviewed journals in which the MSCA:
o B. Abad et al. “The 2022 Applied Physics by Pioneering Women: a Roadmap” Journal of Physics D: Applied Physics. (Accepted) 2022. We were invited to write section 15: “Nanophotonics and Nanophononics”.
o Articles in preparation.
- Oral presentations at international conferences:
o Swiss NanoConvention 2022, invited by Prof. Barbara Rothen-Rutishauser, Fribourg (Switzerland), July 2022 (Invited talk)
o “Phonon engineering in semiconductor superlattice nanowires: phonons and thermal transport”. Nanowire Week 2022, Chamonix, France, 2022.
o “Extreme ultraviolet beams probe mechanical and structural properties of nanostructured metalattices”. E-MRS Spring 2021, Online, France, 2021.
o “Mechanical and structural properties of nanostructured metalattices probed by coherent EUV beams”. MRS Spring 2021, Online, USA, 2021.
- Other outreach activities:
o NCCR video campaign celebrated the 50th anniversary of women obtaining the right to vote in Switzerland, showing the implemented setup - https://www.youtube.com/watch?v=Wv9e85QpLik(opens in new window)
During the duration of the Phonon-ART project, we were able to implement a powerful experimental setup that is capable of measuring not only phonon dynamics but also electron dynamics of a wide range of materials of critical importance for the semiconductor industry. Moreover, the versatility of this setup enabled to further the understanding of the electron-phonon coupling, critical to improve both electronic and thermal devices. The results coming out from this project will impact new technologies, as they allow to identify the fundamental mechanisms to improve heat dissipation efficiency in modern devices, that are ubiquitous in our daily lives.