Bridge- and Double-Bonded O and NH on Fully OH- and NH 2 -Terminated Silicon Nanocrystals: Ground and Excited State Properties

The authors model fully hydroxyl‐ (OH‐) and amino‐ (NH2‐) terminated silicon nanocrystals (Si‐NCs) by time‐dependent density functional theory (TD‐DFT), and replace OH or NH2 groups by respective double‐ (=) or bridge‐bonded (>) groups >/ = O or >/ = NH. Investigating ground state (GS) gaps and interface charge transfers (ICTs) from Si‐NCs to anion groups, the authors show the impact of >/ = O and >/ = NH. Excited state (ES) calculations yielded transition energies Etrans, oscillator strengths fosc and transition rates Abs . The exciton binding energy R* increases with ICT modulation in particular for >/ = O. Increase of Abs is high for =O and comparatively low for >O which correlates with increased (decreased) ionisation of =O (>O), as compared to nominal OH termination. Findings are also met by >/=NH on Si‐NCs, though the authors find the results there to be less apparent which is arguably originating from the specific anionic nature of N. As a result, Si‐NCs with >O and in particular =O bonds show significantly increased optical activity, but also higher R* values. The latter hampers exciton dissociation, hence carrier transport, and results in an increased redshift in photoluminescence (PL). These statements apply also to Si3N4‐embedded Si‐NCs, though the differences there are less articulate.D.K. acknowledges funding by the 2015 UNSW Blue Sky Research Grant, funding by 2012, 2014, and 2016 DAAD-Go8 joint research cooperation schemes and the 2018 Theodore-von-Kàrmàn Fellowship of RWTH Aachen University, Germany. Y.Y. acknowledges funding by the 2016 DAAD-UA joint research cooperation schem