posted on 2023-11-20, 17:34authored byCameron Wright, Gregory V. Hartland
The fundamental and n = 3 overtones of Au nanoplate
thickness vibrations have been studied by transient absorption microscopy.
The frequencies of the n = 3 overtone are less than
3× the frequency of the fundamental. This anharmonicity is explained
through a continuum mechanics model that includes organic layers on
top of the nanoplate and between the nanoplate and the glass substrate.
In this model, anharmonicity arises from coupling between the vibrations
of the nanoplate and the organic layers, which creates avoided crossings
that reduce the overtone frequencies compared to the fundamental.
Comparison of the experimental and calculated quality factors shows
that coupling occurs to the top organic layer. Good agreement between
the measured and calculated quality factors is obtained by introducing
internal damping for the nanoplate. These results show that engineering
layers of soft material around metal nanostructures can be used to
control the vibrational lifetimes.