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Friday 12 Oct 2018Thermal energy propagation in Si membranes and phononic crystals

Clivia M. Sotomayor Torres - Catalan Institute of Nanoscience and Nanotechnology

Newman Red 14:30-15:30

Thermal transport in free-standing silicon membranes has attracted increasing attention to advance the understanding of how the volume-to-surface ratio [1], phononic crystal periodicity, disorder [2] and air convection [1] impact on thermal phonon propagation. We will discuss the physical regimes under which the dominance of each and all of the above takes place.

Our experiments were performed over a range of 300 to 1000 K [1] in purpose-designed 2D phononic crystals in the form of free-standing membranes patterned by electron beam lithography and dry etching [3]. The band structure of 2D phononic crystals was calculated using FEM [4], the experimental methods include Brillouin scattering, pump-and-probe picosecond acoustics [2] and laser Raman thermometry [5].

Comparing holey phononic structures with a periodic solid perturbation on the membranes and solid-solid phononic crystals made out metallic cones periodically positioned on a membranes leads to a better understanding of the role of symmetry.

One of the main parameter is found to be the surface to volume ratio, which is affected by air convection losses and by the shape of the necks of the phononic crystal design. Furthermore, the realisation of solid-solid phononic crystals points to the possibility to tailor multiple ways of storing and retrieving energy in these periodic oscillators when coupled to Lamb waves.

[1] B. Graczykowski et al, accepted Nature Communications

[2] M. R. Wagner et al, Nano Letters 16 5661 (2016)

[3] M. Sledzinska et al., Microelectronic Eng, 149, 41 (2016)

[4] B. Graczykowski et al., Phys. Rev. B 91 075414 (2015)

[5] ] E. Chavez Angel et al., Appl. Phys. Lett. Materials 2 012113 (2014); J. S. Reparaz et al., Rev. Sci. Instruments 85 034901 (2014).

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