Optical properties of amorphous and crystalline silicon surfaces functionalized with Ag_n adsorbates

Abstract

Light absorption by nanostructured surfaces of silicon, relevant to the capture of solar radiation, has been modeled starting from their atomic structure and calculating electronically excited states. Thin, two-layer silicon slabs were cut from a model optimized amorphous supercell and studied to elucidate the effect of adsorbate geometry and size for small silver clusters chemisorbed onto the hydrogen-passivated semiconductor surface. Density functional (DFT) and time-dependent DFT (TD-DFT) methods were performed to calculate optical properties of the amorphous Ag n /a-Si surface. Optimized geometries, density of states, band gap and binding energies, and excited-stated spectra and oscillator strengths have been calculated within the DFT and TD-DFT approaches. The results demonstrate the correlation between these properties and the size of the systems, and are compared with those we previously obtained for the corresponding crystalline Ag n /Si(111) surfaces. Similar trends are observed for the amorphous and crystalline silicon slabs as the number of silver atoms included in the clusters were increased. Our results demonstrate that Ag n clusters adsorbed on amorphous slabs are significant contributors to increased light absorption of lower energy photons.

Ultrafast Photoluminescence in Quantum-Confined Silicon Nanocrystals Arises from an Amorphous Surface Layer

“…The rapid decay process we observe in completely amorphous (8 W) Si NPs is likely hole trapping in the strained regions of the amorphous network. This type of trapping was suggested in recent theoretical works by Lajoie et al and Wagner et al Given that a multitude of characterization methods (TEM, FTIR, Raman) indicate that highly crystalline particles still present an amorphous surface layer, we suggest that hole trapping processes occur in this thin amorphous shell.…”

Size Effect in Mechanical Properties of Nanostructured Coatings

“…Also, empirical observations show that this type of coatings makes bonds with aluminum, while conventional Fe-Al coating is not easily performed. It is expected this method be of frequent applications [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101].…”

Photoexcited Electron Lifetimes Influenced by Momentum Dispersion in Silicon Nanowires

“…A number of first-principles techniques beyond the Born–Oppenheimer approximation have been developed to describe hot carrier relaxation dynamics in different solids − and nanostructures, − including surface-hopping techniques combined with methods ranging from density functional theory (DFT) − to the multilevel Redfield theory. − Our group has been focusing on the computational modeling of various Si derived materials, ranging from molecules to nanostructures, using first-principles approaches. The electronic structure and excited-state dynamics calculations allow for a detailed analysis of optical properties and charge carrier relaxation based on Redfield theory. − Han et al performed time-dependent excited-state molecular dynamics (TDESMD) − calculations to describe the photoinduced ring-opening reactions during the preparation of Si containing materials from cyclohexasilane molecules . Chen et al modeled relaxation rates of photoexcited electrons and holes in Si QDs with Al and P dopants by applying an ab initio treatment, which is useful in the analysis of pump–probe spectroscopy measurements .…”