TITLE: Thermal transport engineering in low-dimensional materials and devices
AUTHOR: Alexandros El Sachat, researcher at Institute of Nanoscience and Nanotechnology, National Center for Scientific Research "Demokritos" (Athens, Greece)
WHEN: November, 5th - 12PM
WHERE: Salón de Actos, ICMM-CSIC
ABSTRACT: We present a comprehensive overview of several interrelated scientific studies that address the engineering of thermal and thermoelectric transport in low-dimensional materials and devices. The first study demonstrates the successful realization of large area cross-plane thermal insulation by engineering ultra-thin lattice mismatched epitaxial van der Waals heterostructures[1].
In the second study, we investigate the temperature-dependent in-plane and cross-plane thermal conductivity in nanopatterned suspended MoS2 and supported WS2 films with varying thickness in a wide temperature range (80-460 K). The research uncovers that nanopatterning is an efficiency approach to create 2D heat-routing structures that effectively confine and guide heat flow in prespecified directions [2]. Additionally, we find that WS2 exhibits an exceptionally high in-plane thermal conductivity, ~1000 Wm-1K-1 at 80 K and tunable thermal anisotropy, i.e. increases from 30 (460 K) to 78 (80 K), which is observed to originate from the strong reduction of the out-of-plane component triggered by the onset of the quasi-ballistic transport regime [3].
Last, we investigate local thermal and thermoelectric transport in devices based on nanopatterned SnSe2. We found that while thermal transport varies on distances of a few tens of nanometres, the modification of Seebeck coefficient expands on much larger distance with the characteristic Seebeck exponential “decay length” being on the order of 1 μm. By selecting appropriate density and diameter of the nanofabricated patterns, we demonstrate the possibility to create large areas of Seebeck coefficient modification. Collectively, these works advance thermal management technologies and foster the design of customized thermoelectric devices.
BIO: Dr Alexandros El Sachat studied physics at National and Kapodistrian University of Athens in Greece. In 2012 he received his master degree in "Microsystems and Nanodevices" from the National Technical University of Athens (NTUA), where he specialized in solid-state physics, optical spectroscopy and elastic light scattering in soft matter. Between 2013-2017 he obtained his PhD degree from the Autonomous University of Barcelona, where he was involved in different projects focused on the thermal characterization of nanostructured and 2D materials using Scanning Thermal Microscopy and Raman thermometry for applications in nanoelectronics and energy conversion. During the time of his Ph.D. studies, he established collaboration with several European partners, e.g., ULANC, IBM, VTT, ICMAB and CNRS and started research dedicated to nanoscale thermal transport. Between 2017-2019, during his research internship at IBM-Zurich and postdoc at UAM, he studied local thermal and thermoelectric transport phenomena in 2D based devices using state-of-the-art scanning probe techniques, such as Scanning Tunnelling Microscopy and Scanning Thermal Microscopy. In 2019 he joined the group of Prof. C. Sotomayor and focused on developing a frequency-domain thermo-reflectance system to study thermal transport in 2D materials.
In 2021 he got a Marie Skłodowska-Curie postdoctoral fellowship to study thermoelectric devices based on epitaxial semiconductors and in 2023 he received an ERC grant to understand transport phenomena in 2D materials and nano-constrictions for developing energy-efficient nanoelectronics. His work has led to 30 scientific peer-reviewed articles (h-index: 15), 1 book chapter, 10 invited talks and more than 30 oral talks at international conferences. Currently, his is a tenure-track Researcher at National Centre for Scientific Research "Demokritos" in Greece, leading the research work on nanoscale transport phenomena in low-dimensional materials.
