Rounded, regular and marks decahedral nanoparticles

In experiments, the most common shapes have truncated vertices and correspond to particles named Marks decahedron and the round decahedron. 

The first structure [54] contains extra 111 facets and turns out to be quite stable. In particularly clean growth conditions (weak interactions with substrates), it results one of the predominant shapes for the size interval taken into account. An alternative way to describe the Marks decahedron is as a regular decahedron, which has truncations on its facets, as shown in Fig. 3.11 (3y, 3x and 3z). 

The other type of decahedral particle, which is often observed, corresponds to the round pentagonal particle. An example of these 

In Fig. 3.11 we can note a large anisotropy of the spectra when the light incidence is such that the electric field is parallel and perpendicular to the pentagonal motif. When the electric field is parallel to the pentagon, the corresponding spectra are very wide with a FWHM (full width at half maximum) of about 90 nm, and a maximum at about 425 nm. Except near the maxima, where small differences are observed, the spectra for both parallel polarizations are almost identical. On the other hand, when the electric field is perpendicular to the pentagon, the spectrum shows a maximum at about 350 nm which is more than two times less intense and presents a FWHM of about 45 nm. 

In Fig. 3.11 we observe for the perpendicular polarization, that the optical response of the regular decahedron does not change for small truncations, in both cases, the Marks and rounded decahedra. For both parallel polarizations, the spectra of the truncated decahedra show differences with respect to the regular ones. The observed effects are similar to those already seen in the case of truncated cubes (Fig. 3.10) as a result of the increment of the faces, the main resonance is blue-shifted and its FWHM decreases. Finally, as for more regularly shaped nanoparticles, also for such kind of NPs the spectra show a red-shift with increasing size as a consequence of the radiation effects. 

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