Energy, Environment and Water Research Center

Energy, Environment and Water Research Center

Abstract

Silicon nanocrystals (NCs) embedded in amorphous dielectric matrices (a-SiO2) have attracted considerable attention both for their fundamental properties and potential applications in photonics and nanoelectronics. These nanocomposite systems exhibit strong optical activity (efficient light emission, optical gain) which makes them suitable for optical devices. The embedded NCs can also be efficiently charged which makes them suitable for charge storage elements in non-volatile memory devices. It is universally accepted that these properties strongly depend on the nature of the interface between the NCs and the embedding medium, but exactly this parameter is the least well understood issue of the whole problem.


                    

Si Nanocrystal embedded in a-SiO2                          HOMO electronic charge density                                            

Prof. Kelires will review in his talk their extensive studies [1-4] which shed light on several issues regarding the stability of the interface as a function of the NC size, its structure, both topological and chemical, and the effects produced by variations of these parameters on the electronic and optical response of the system. We discuss the interplay between quantum confinement (QC) effects, oxygen interfacial states, and topological deformations in controlling the photoluminescence (PL) energies. This is achieved by studying the electronic structure, the dielectric function and the absorption coefficient of the composite system. We identify two distinctly different regimes. For NCs larger than 3-4 nm, the QC effects (free excitonic recombination) are shown to be the dominant factor in agreement with experimental studies [5,6]. For smaller sizes, he proposes that the observed pinning of the gap and the associated redshift of the PL energies is heavily influenced by the topological distortions, overwhelming the effect from the localized states due to interface oxygen bonds. He will also discuss the issues of faceting of the embedded NCs [2] and of possible ordering in the amorphous matrix [4]. Comparison with other theoretical and experimental studies on the above subjects will be done in order to assess the state-of-the-art in this important field.

[1] G. Hadjisavvas and P. C. Kelires, Phys. Rev. Lett. 93, 226104 (2004).
[2] G. Hadjisavvas, I. Remediakis, and P. C. Kelires, Phys. Rev. B 74, 165419 (2006).
[3] G. Hadjisavvas and P. C. Kelires, Physica E 38, 99 (2007).
[4] K. Kleovoulou and P. C. Kelires (unpublished).
[5] E. Lioudakis et al., Physica E 38, 128 (2007).
[6] M. Volkin et al., Phys. Rev. Lett. 82, 197 (1999).

For more information contact Dr. Emmanouil Lioudakis +357 22208600 or email m [dot] lioudakis [at] ucy [dot] ac [dot] cy.