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SEM micrographs of nanodisk arrays fabricated by hole-mask colloidal lithography from [(a) and (b)] Au, [(c) and (d)] Pt, and [(e) and (f)] Pd. Note the absence of long-range order and the increasing importance of polydispersity in the particle size distribution for small disks . The nominal particle diameters correspond to (a) , (b) , (c) , (d) , (e) , and (f) .
(a) Schematic drawings of the measurement geometry for an extinction measurement and [(c) and (d)] the different configurations used in the integrating sphere experiments. In the configuration shown in (b), where the sample is placed on the back port of the integrating sphere detector with a 3° tilt from the normal, backward scattering in one half-space is collected, including the specular contribution (referred to as configuration S1 in the text). With configuration (c), where the sample is placed on the front port of the integrating sphere, forward scattering is collected in one half-space (referred to as configuration in the text), however, the contribution in normal forward direction (corresponding to what is measured in an extinction experiment) is excluded. The situation (d) measures again the backward scattered light in one half-space, though this time the specular component is not entering the detector so that only diffuse scattering is detected (referred to as configuration in the text).
Measured extinction (red), absorption (blue), and scattering (green) efficiencies for Ag nanodisks with nominal diameters varying from (a) , (b) , (c) , (d) , (e) , (f) , (g) , and (h) . The arrows indicate higher plasmonic modes.
Measured extinction, absorption, and scattering efficiencies for Au nanodisks with diameters varying from (a) , (b) , (c) , (d) , (e) , (f) , (g) , and (h) . The arrows indicate higher plasmonic modes.
Measured extinction, absorption, and scattering efficiencies for Pt nanodisks with diameters varying from (a) , (b) , (c) , (d) , (e) , (f) , (g) , and (h) . The arrows indicate higher plasmonic modes.
Measured extinction, absorption, and scattering efficiencies for Pd nanodisks with diameters varying from (a) , (b) , (c) , (d) , (e) , (f) , (g) , and (h) . The arrows indicate higher plasmonic modes.
The intensities of backward scattered light, as a function of wavelength of the incident light, with (configuration , full line) and without specular contribution (configuration , dotted line) are shown for disks of (a) Ag, (b) Au, (c) Pt, and (d) Pd. Observe the different relative strengths of dipolar and quadrupolar plasmon peaks for the different materials in configuration as well as the almost total absence of a dipolar contribution to the scattering spectrum of Pt and Pd nanodisks measured in configuration . Note that the data presented in this figure are not normalized for particle coverage.
The experimental scattering cross sections as a function of disk diameter are shown for Ag (red squares), Au (blue triangles), Pt (green inverted triangles), and Pd (black right triangles). Calculated results using the spheroid theory are shown by full or dashed lines, marked metal-X theory. Good agreement is found between theory and experiment, but the theoretical cross sections are generally larger than the experimental ones. (b) The absorption cross sections for all four metals. Good agreement between experiment and theory is found for Pt and Pd, while the model fails to account for the experimental absorption cross sections for Ag and Au nanodisks with . (c) Branching ratios between the scattering and absorption decay channels for the four metals. The absorption channel is found to be dominant for all diameters of Pt and Pd nanodisks, while the crossover diameters (between a regime of dominant absorption and a regime of dominant scattering) of 110 and are found for Ag and Au, respectively. The model is found to well reproduce the trends and absolute numbers for Pt and Pd, while the agreement for Ag and Au nanodisks with is poor. Note the logarithmic scale for all figures.
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