posted on 2021-09-24, 21:03authored byAlessandra Milloch, Riccardo Mincigrucci, Flavio Capotondi, Dario De Angelis, Laura Foglia, Gabor Kurdi, Denys Naumenko, Emanuele Pedersoli, Jacopo S. Pelli-Cresi, Alberto Simoncig, Björn Wehinger, Claudio Masciovecchio, Filippo Bencivenga
The
characterization of thermal and elastic properties at the nanometer
length scale is fundamental for the implementation of materials in
nanotechnology. Here, we show how four-wave mixing of extreme ultraviolet
ultrashort pulses allows for high-precision measurements of nanoscale
elasticity in thin suspended silicon nitride membranes through the
generation and detection of Lamb waves at 10’s of nm wavelengths.
Our approach is contact-free and nondestructive, and it provides an
estimate of both shear and longitudinal elastic moduli, without the
need of nanopatterning. The data provide important information on
nanoscale thermal transport and reveal a heat carrier behavior compatible
with the diffusive regime. By controlling the fluence of the free-electron
laser excitation pulses, we study the dependence of elastic moduli
and the thermal relaxation rate on the sample temperature, which increases
by hundreds of kelvins due to radiation absorption. At the same time,
the experimental data allow us to estimate the characteristic time
of phonon attenuation. The capability of determining this parameter,
as well as the elastic moduli, at nanoscale wavelengths is a key aspect
for the fundamental understanding of solids without translational
invariance.