Ultrafast coherent beams illuminate understanding of phonon transport

Nanofabrication techniques now make it possible to synthesize materials with atomic-scale characteristics. At these sizes, traditional models fail to predict the fundamental properties of materials, thus new experimental and theoretical tools are needed in order to discover new physics. Phonons—vibrations of the atomic lattice—are responsible for sound and heat propagation, and behave radically differently in nanostructured systems. Controlling phonons is key for engineering both mechanical and thermal properties, critical to lightweight and energy-efficient nano-electronics, thermoelectric devices, photovoltaics, and sensors. However, measuring thermal transport at the nanoscale is especially difficult due to small, localized temperature gradients as well as significant thermal contact resistances. Measuring nondestructively mechanical properties at the nanoscale is also challenging due to substrate influence and difficult control over the applied tensile stress, yet it is needed for designing compliant devices. To overcome these challenges, non-contact laser-based metrology techniques are used nondestructively to access these properties. Here, I will present advances in the understanding of non-diffusive heat flow away from nanoscale heat sources probed by extreme ultraviolet coherent beams [1]. Additionally, I will show how we extended these measurements to probe the thermal, mechanical and structural properties of complex metalattices with sub-100nm periodicity [2, 3, 4]. Finally, I will present recent efforts in the development of a multi-measurement versatile technique based on transient reflectivity and time-resolved Raman spectroscopy to characterize carrier and lattice dynamics.

[1] Beardo, J. L. Knobloch, L. Sendra, J. Bafaluy, T. D. Frazer, W. Chao, J. N. Hernandez-Charpak, H. C. Kapteyn, B. Abad, M. M. Murnane, F. X. Alvarez, and J. Camacho. “A General and Predictive Understanding of Thermal Transport from 1D- and 2D-Confined Nanostructures: Theory and Experiment”. ACS Nano, 2021, 15 (8), 13019-13030.

[2] B. McBennett, A. Beardo. E.E. Nelson. B. Abad, T.D. Frazer, A. Adak, Y. Esashi, B. Li, H.C. Kapteyn, M.M. Murnane, J. L. Knobloch. “Universal Behavior of Highly Confined Heat Flow in Semiconductor Nanosystems: From Nanomeshes to Metalattices”. Nano Letters, 2023, 23, 6, 2129-2136.

[3] B. Abad, J. Knobloch, T. Frazer, J. Hernández-Charpak, H. Cheng, A. Grede, N. Giebink, T. Mallouk, P. Mahale, W. Chen, Y. Xiong, I. Dabo, V. Crespi, D. Talreja, V. Gopalan, J. Badding, H. Kapteyn, M. Murnane. “Nondestructive measurements of the mechanical and structural properties of nanostructured metalattices” Nano Letters, 20, 5, 3306-331 (2020)

[4] J. L. Knobloch, B. McBennett, T. D. Frazer, C. Bevis, S. Yazdi, A. Adak, E. E. Nelson, Jorge. N. Hernández-Charpak, H. Y. Cheng, A. J. Grede, P. Mahale, N. N. Nova, N. C. Giebink, T. E. Mallouk, J. V. Badding, H. C. Kapteyn, B. Abad, and M. M. Murnane. “Structural and elastic properties of empty-pore metalattices extracted via nondestructive coherent extreme UV scatterometry and electron tomography.” ACS Nano, 2022, 14 (36), 41316-41327.