Figure 1
From: Octahedral faceted Si nanoparticles as optical traps with enormous yield amplification
(a) Schematic view of the inductively coupled plasma chemical vapour deposition system with its typical vertical geometry; the RF applied to a solenoid produces a magnetic field perpendicular to the sample and induces a tangential electric field. This scheme, contrary to parallel plate configurations, ensures the plasma is highly ionised (≈5 × 1011 ions/cm3) and able to form large crystalline Si-NP competitively to Si amorphous deposition, which is very limited; (b) Transmission Electron Microscopy analyses with the indicated planes forming the facets of the Si-NP surfaces. This Si-NP has the (220) zone axis orthogonal to the sample surface to enhance the visibility of the facets. The frame on the right shows a snapshot of a 360° view of a single Si-NP obtained by 3D Transmission Electron Tomography and software reconstruction that shows all the facets of an octahedral Si-NP. (c) X-Ray polar figure, collected at the (111)-Si pole, showing a large signal at χ = 0 and a ring at χ = 70.5°. Those features are related to each other by a crystallographic relationship (i.e., they belong to the same domains) and indicate the presence of a unique zone axis with (111) planes parallel to the substrate. Note, in fact, that the planes at the polar figure centre and those at the ring position form an angle as large as expected in the perfect silicon lattice structure. Those findings attest that most of the particles (86% on the basis of the relative peak intensity, see ref. 33) landed on the substrate with the (111) plane faces exposed upwards, as indicated in the sketch of the octahedral Si-NPs and touched the substrate with the opposite (111) face. The (111) rocking curve related to those planes is very narrow, which indicates a minimal angular dispersion with respect to the [111] landing axis. The presence of the ring in the polar figure indicates a rotational degree of freedom around the landing axis, as expected, because there is no preferentiality in the x–y directions.
