Effect of passivants in energy gap of Si 47X 24Y 36 nano-clusters: A theoretical investigation

Abstract

Passivation on the surface of the nano-cluster Si 47 core cluster can lead to the formation of Si 47X 24Y 36, where X and Y represent the inner and outer layer passivated positions, respectively. Accordingly, X and Y positions can accommodate one and three passivants, respectively. Herein, the density functional theory (DFT) and B3LYP method with the 6-31G(d) basis set were used to generate the electronic structures (HOMO, LUMO and energy gap between HOMO and LUMO) for two different fully passivated Si nano-clusters of Si 47X 60 and Si 47X 24Y 36, both with a T d symmetry. The optimized structures were obtained with the local density approximation (LDA) implemented in SIESTA package. For fully passivated Si 47X 60 nano-clusters (X=–H, –CH 3, –OH, –NH 2, –F, –SiH 3, –SH, –Cl, –C 2H 5 and –OCH 3) alkyl passivants (–CH 3 and –C 2H 5) affect insignificantly the calculated energy gaps while electron-withdrawing passivants give red-shifted electronic spectra. Same investigations were also conducted for the partially hydrogenated Si nano-clusters, inner layer passivated Si 47X 24H 36 and outer layer passivated Si 47H 24Y 36. The calculated energy gaps of Si nano-clusters with inner layer passivation (Si 47X 24H 36) are close to that of Si 47X 60, both inner and outer layers passivated. Hence, the outer layer passivant effect is insignificant, which is also demonstrated by insignificant changes in energy gaps ( ≤ 0.5 eV ) for the Si nano-clusters with outer layer passivation since the difference of the Mülliken charge is ≤ 0.1 eV .