posted on 2022-09-02, 18:36authored byJoshua L. Knobloch, Brendan McBennett, Charles S. Bevis, Sadegh Yazdi, Travis D. Frazer, Amitava Adak, Emma E. Nelson, Jorge N. Hernández-Charpak, Hiu Y. Cheng, Alex J. Grede, Pratibha Mahale, Nabila Nabi Nova, Noel C. Giebink, Thomas E. Mallouk, John V. Badding, Henry C. Kapteyn, Begoña Abad, Margaret M. Murnane
Semiconductor
metalattices consisting of a linked network of three-dimensional
nanostructures with periodicities on a length scale <100 nm can
enable tailored functional properties due to their complex nanostructuring.
For example, by controlling both the porosity and pore size, thermal
transport in these phononic metalattices can be tuned, making them
promising candidates for efficient thermoelectrics or thermal rectifiers.
Thus, the ability to characterize the porosity, and other physical
properties, of metalattices is critical but challenging, due to their
nanoscale structure and thickness. To date, only metalattices with
high porosities, close to the close-packing fraction of hard spheres,
have been studied experimentally. Here, we characterize the porosity,
thickness, and elastic properties of a low-porosity, empty-pore silicon
metalattice film (∼500 nm thickness) with periodic spherical
pores (∼tens of nanometers), for the first time. We use laser-driven
nanoscale surface acoustic waves probed by extreme ultraviolet scatterometry
to nondestructively measure the acoustic dispersion in these thin
silicon metalattice layers. By comparing the data to finite element
models of the metalattice sample, we can extract Young’s modulus
and porosity. Moreover, by controlling the acoustic wave penetration
depth, we can also determine the metalattice layer thickness and verify
the substrate properties. Additionally, we utilize electron tomography
images of the metalattice to verify the geometry and validate the
porosity extracted from scatterometry. These advanced characterization
techniques are critical for informed and iterative fabrication of
energy-efficient devices based on nanostructured metamaterials.