Signatures of Small Morphological Anisotropies in the Plasmonic and Vibrational Responses of Individual Nano-objects

Abstract

The plasmonic and vibrational properties of single gold nanodisks patterned on a sapphire substrate are investigated via spatial modulation and pump-probe optical spectroscopies. The features of the measured extinction spectra and time-resolved signals are highly sensitive to minute deviations of the nanodisk morphology from a perfectly cylindrical one. An elliptical nanodisk section, as compared to a circular one, lifts the degeneracy of the two nanodisk in-plane dipolar surface plasmon resonances, which can be selectively excited by controlling the polarization of the incident light. This splitting effect, whose amplitude increases with nanodisk ellipticity, correlates with the detection of additional vibrational modes in the context of time-resolved spectroscopy. Analysis of the measurements is performed through the combination of optical and acoustic numerical models. This allows us first to estimate the dimensions of the investigated nanodisks from their plasmonic response, and then to compare the measured and computed frequencies of their detectable vibrational modes, which are found in excellent agreement. This study demonstrates that single-particle optical spectroscopies are able to provide access to fine morphological characteristics, representing in this case a valuable alternative to traditional techniques aimed at post-fabrication inspection of subwavelength nanodevice morphology.

Ultrafast Thermo-Optical Dynamics of a Single Metal Nano-Object

“…1c) and have been the scope of recent studies. 36,37 This feature partly overlaps with a monotonic decay of the signal associated to ND cooling (i.e., dissipation of the thermal energy injected by the pump pulse, also occurring on a nanosecond timescale, process 3 in Fig. 1c).…”

“…ε was written as ε(ω)=ε JC (ω)+ωp 2 /(ω(ω+iγ0))-ωp 2 /(ω(ω+iγ)), which corresponds to describing the dielectric response of gold conduction electrons by a Drude term 30 involving the bulk gold plasma frequency ωP (ℏωP = 9.01 eV) and an optical scattering rate γ of the conduction electrons larger than that of bulk gold (ℏγ0 ≈ 50 meV). 37 ND illumination by a linearly polarized plane wave was considered. Absorption and scattering cross-sections were deduced from the computed electric field and summed to yield the extinction one.…”

In-Plane Thermal Diffusivity Measurements of Polyethersulfone Woven Textiles by Infrared Thermography

“…More generally, it was shown how lock-in thermography allows the detection of the thermal anisotropy in textiles at a mesoscopic scale [ 32 ], and a new theoretical approach was introduced to predict the conditions required to observe in-plane thermal anisotropy. The resulting theoretical model is a useful tool for designing textiles with tailored thermal properties, while machine-learning-based algorithms (neural networks [ 33 ], genetic algorithms [ 34 , 35 ] and other optimization search methods [ 36 , 37 , 38 , 39 , 40 ]) can be introduced to further optimize the thermal performance of the designed textile.…”

Titanium and Silicon Dioxide-Coated Fabrics for Management and Tuning of Infrared Radiation

“…Local correlations among the content of bioceramic nanopartcicles, the IR emissivity, and the acoustic and mechanical properties of the textiles can be found by using other spatially and time resolved experimental techniques [ 46 , 47 , 48 ].…”