Substrate influence on the vibrational response of gold nanoresonators: Towards tunable acoustic nanosources

Abstract

The development of applications based on metallic nano-objects requires an extensive knowledge of their vibrational properties. Its size, shape, materials or even crystallinity have a strong influence on the vibrational frequencies of a nano-object. It is also known that the coupling with environment has a strong effect on the lifetime of its resonating modes. However, the impact of the contact between a nano-object and its substrate still requires further investigation. Here we report on the vibrational response of gold disks for different contact area with a silicon substrate. The investigation of the quality factor of the first thickness mode of the disks highlights an important energy transfer from the disks to the substrate. The impact of the size of the contact area on the frequencies of the radial eigenmodes is also reported both experimentally and numerically.Finally, it is shown that such objects can be excited by acoustic waves propagating from the substrate. These findings display the possibility to use nanodisks to develop acoustic microscopy at the nanoscale.

Strong Substrate Binding Modulates the Acoustic Quality Factors in Gold Nanodisks

“…39 Q-factors approaching 70 were also accomplished for AuNDs on glass pillars. 40 These results indicate that lithographically prepared particles could indeed support increased Q-factors and compete with colloidal nanostructures. Still, in order to reliably achieve large Qfactors with lithographically prepared nanostructures and utilize them in applications, a comprehensive understanding of their damping behavior is required.…”

“…Previous studies have reported Q-factors of ∼10 for Au nanorings and weakly bound AuNDs, 28,37 ∼50 for Au nanorods, 38 and ∼70 for strongly bound AuNDs and AuNDs on pillars. 39,40 The wide range of Q-factors, therefore, indicates that intrinsic damping can be reduced. We suggest that polycrystallinity can be minimized through control of the lithographic process, especially the use of slow evaporation rates for crystal growth and a high vacuum for minimized contamination.…”

“…On glass, acoustic behavior was previously reported to be strongly affected by intrinsic damping due to polycrystallinity, leading to constant small Q -factors independent of the substrate . On the contrary, larger Q -factors were achieved by placing AuNDs on glass pillars for reduced extrinsic damping into the substrate . Despite experiencing intrinsic damping, AuNDs on sapphire substrates exhibited aspect ratio-dependent Q -factor enhancements, which, under the assumption of strong particle-substrate binding, were theoretically attributed to reduced extrinsic damping due to mode hybridization effects .…”

“…28 On the contrary, larger Q-factors were achieved by placing AuNDs on glass pillars for reduced extrinsic damping into the substrate. 40 Despite experiencing intrinsic damping, AuNDs on sapphire substrates exhibited aspect ratio-dependent Q-factor enhancements, which, under the assumption of strong particlesubstrate binding, were theoretically attributed to reduced extrinsic damping due to mode hybridization effects. 39 Similar hybridization between acoustic modes of the particle and the substrate in the strong-binding regime was previously found for AuNDs on glass and Au nanocrosses on quartz substrates, but no Q-factors were investigated.…”

Towards acoustic microscopy at the nanoscale by coupling atomic force microscopy with picosecond ultrasonics

“…The study of vibrations of nanoparticles, notably by time-resolved spectroscopy [24][25][26], have highlighted a strong coupling between a nanoparticle and its environment, especially with its substrate [27][28][29]. Several studies have taken advantage of this coupling in order to probe properties at the nanoscale [30] and to use nanoparticles as acoustic nanosources [31][32][33][34][35]. Although the emission of a controlled frequency acoustic field in the GHz range has been proven for several shapes and materials, these sources are not adapted to the development of acoustic microscopy at the nanometric scale.…”