Calculations performed based on Mie theory to determine the squared near-field amplification N2 at 800 nm (at the surface of the particle, where it becomes maximum, and at a radial distance r = 1.5 nm away from it), the characteristic diffusion length Λ for the examined nanostructures, (taken as the distance at which N is reduced by one half of its maximum value), the absorption cross-section σabs and the volumetric absorption σabs/Vnp.
| Sample | N 2 (r = 0 nm), (λ = 800 nm) | N 2 (r = 1.5 nm), (λ = 800 nm) | Λ [nm] | σ abs [nm2], (λ = 800 nm) | σ abs/Vnp [10−4 nm−1], (λ = 800 nm) |
|---|---|---|---|---|---|
| AuNP 40 nm | 13.47 | 10.04 | 9.7 | 22.8 | 6.8 |
| AuNP 60 nm | 14.98 | 12.18 | 14 | 89 | 7.8 |
| AuNP 80 nm | 17.22 | 14.75 | 19 | 248 | 9.3 |
| AuNP 100 nm | 20.25 | 17.81 | 22.6 | 577 | 11 |
| AuNP 150 nma | 26.73 | 24.2 | 32 | 2560 | 15 |
| AuNP 200 nma | 19.54 | 18.15 | 43 | 3980 | 9.5 |
| AuNSb | 34.81 | 31.02 | 26.3 | 3470 | 38 |
a
Because of pronounced electromagnetic retardation, the N was calculated axially from the center of the particle at an angle (instead of parallel) to the laser polarization.
b
The influence of PEG was considered by setting a medium layer refractive index of 1.4, which brings the theoretical plasmon resonance peak to one of the samples.