Effect of surface reconstruction on the structural prototypes of ultrasmall ultrabright Si29 nanoparticles

Abstract

We propose, using density functional, configuration interaction, and quantum Monte Carlo calculations, structural prototypes of ultrasmall ultrabright particles prepared by dispersion from bulk. We constructed near spherical structures (Td point group symmetry) that contain 29 Si atoms, five of which constitute a tetrahedral core and the remaining 24 constitute a hydrogen terminated reconstructed Si surface. The surface is a highly wrinkled or puckered system of hexagons and pentagons (as in a filled fullerene). We calculated, for several surface reconstruction models, the coordinates of atoms, the absorption spectrum, the absorption edge, polarizability, and the electron diffraction pattern. The Si29H24 (six reconstructed surface dimers) gives a size of 0.9 nm, an absorption spectrum and bandgap (3.5±0.3 eV), in fair agreement with measurement. The structure yields a polarizability of 830 a.u. with an effective “dielectric” constant of ∼6.0. The calculated electron diffraction of single particles shows residual crystalline coherent scattering for large but not small scattering angles.

Optical Characterization of Ultrasmall Si Nanoparticles Prepared through Electrochemical Dispersion of Bulk Si

“…[10][11]57 Previous analysis including high-resolution TEM imaging, size exclusion chromatography, and computational modeling shows that a discrete set of particle sizes is favored for the Si clusters etched from the wafer, the smallest of which is ∼1 nm in diameter. [10][11]21 For the conditions used here, the analysis suggests (see also IV-D) structures similar to the Si 29 H 24 cluster (monohydride, ∼1 nm, Figure 11) as the dominant source of PL in the starting material. The absorption and PL spectra for the Si-np, freshly prepared in 2-propanol (sample a), are shown in Figure 1 and outlined in Tables 1a and 2a. C. NaOH/HCl Dilutions.…”

“…[47][48][49][50][51][52][53][54][55][56] For Si and Ge nanoparticles prepared through various routes such as solution-phase synthesis, [1][2][3][4][8][9] electrochemical etching, 10-13 laser ablation, 14,15 and using supercritical fluids, [16][17][18] the suggested PL sources have ranged from delocalized quantum confinement states 15 to localized SiSi surface dimer states. [19][20][21] This apparent range of available mechanisms is seen more clearly in recent computational modeling of nanoscale Si and Ge clusters, which has shown transitions ranging from delocalized core states in H-passivated Si-np to localized surface states for particles containing a silanone (SidO) group. [22][23][24][25] These prospects raise the exciting potential for controlling the PL properties of Si and Ge nanoparticles by using different treatments to create the desired surface chemistry.…”

Wideband luminescence from bandgap-matched Mg-based Si core-shell geometry nanocomposite

“…We used ultra-small Si nanoparticles [27][28][29][30][31] with Si-H termination. The nanoparticles are prepared from Si wafers by chemical etching in HF and H 2 O 2 using electrical or hexachloroplatinic acid catalyst.…”

Optics in Nanotechnology

“…Fig. 10.16 (right) [33][34][35][36][37]. One important characteristic of these particles is that the energy and momentum conservation rules governing light interaction get modified.…”