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Your search keyword '"Marri, Ivan"' showing total 2 results
Start Over Author "Marri, Ivan" Topic optoelectronic properties
2 results on '"Marri, Ivan"'

1. First Principle Studies of B and P Doped Si Nanocrystals.

Author

Marri, Ivan, Degoli, Elena, and Ossicini, Stefano

Subjects
*NANOSILICON, *PHOSPHORUS, *BORON, *DOPING agents (Chemistry), *OPTICAL properties, *ACTIVATION energy
Abstract

The properties of n- and p-doped silicon nanocrystals obtained through ab initio calculations are reviewed here. The aim is the understanding of the effects induced by substitutional doping on the structural, electronic and optical properties of free-standing and matrix-embedded Si nanocrystals. The preferential positioning of the dopants and their effects on the structural properties with respect to the undoped case, as a function of the nanocrystals diameter and termination, are identified through total-energy considerations. The localization of the acceptor and donor related levels in the band gap of the Si nanocrystals, together with the impurity activation energy, are discussed as a function of the nanocrystals size. The dopant induced differences in the optical properties with respect to the undoped case are presented. Finally, the case of B and P co-doped nanocrystals is discussed showing that if carriers are perfectly compensated, the Si nanocrystals undergo a minor structural distortion around the impurities inducing a significant decrease of the impurities formation energies with respect to the single doped case. Due to co-doping, additional peaks are introduced in the absorption spectra, giving rise to a size-dependent red shift of the absorption spectra. [ABSTRACT FROM AUTHOR]

Published
2018
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2. Structural, electronic, and surface properties of anatase TiO2 nanocrystals from first principles

Author

Iacomino, A., Cantele, G., Ninno, D., Marri, Ivan, Ossicini, Stefano, A., Iacomino, G., Cantele, Ninno, Domenico, I., Marri, and S., Ossicini

Subjects
ABSORPTION-SPECTROSCOPY, TITANIUM-DIOXIDE NANOPARTICLES, PHOTOACOUSTIC-SPECTROSCOPY, CONDUCTION-BAND ELECTRONS, Titanium dioxide, nanoparticles, optoelectronic properties, photovoltaics, NANOSTRUCTURED TIO2
Abstract

The structural and electronic properties of anatase TiO2 nanocrystals (NCs) are investigated through first-principles calculations. The dependence of the structural properties (e.g., NC volume variations) on the surface chemistry is discussed by considering two different surface coverages (dissociated water and hydrogens). Both prevent a pronounced reconstruction of the surface, thus ensuring a better crystalline organization of the atoms with respect to the bare NC. In particular, the results for the hydrated NC do show the largest overlap with the experimental findings. The band-gap blueshift with respect to the bulk shows up for both the bare and the hydrated NC, whereas hydrogen coverage or oxygen desorption from the bare NCs induce occupied electronic states below the conduction levels thus hindering the gap opening due to quantum confinement. These states are spatially localized in a restricted region and can be progressively annihilated by oxygen adsorption on undercoordinated surface titanium atoms. Formation energy calculations reveal that surface hydration leads to the most stable NC, in agreement with the experimental finding that the truncated bipyramidal morphology is typical of the moderate acidic environment. Oxygen desorption from the bare NC is unfavorable, thus highlighting the stabilizing role of surface oxygen stoichiometry for TiO2. Available experimental data on the electronic and structural properties of TiO2 NCs are summarized and compared with our results.

Published
2008
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