Interacting si nanocrystals in a-SiO2 : a Monte Carlo study
Εμβυθισμένοι νανοκρύσταλλοι si σε a-SiO2 : μαι μελέτη Monte Carlo
Silicon nanocrystals (Si-nc) embedded in amorphous dielectric matrices (a-SiO2) have attracted considerable attention both for their fundamental properties and potential applications in Si-based optoelectronic and quantum computing devices. It is
particularly a very interesting subject to realize ordered Si-nc assemblies (quantum dot photonic crystals or two-dimensional superlattices). For such an aim, it is necessary to control both the size of Si-nc and their inter-particle distances and positioning/ordering. Despite its importance, a lot of issues concerning the interparticle
interaction of Si-nc still remain unclear.
We present here results of Monte Carlo simulations which shed light onto these
issues. In our approach, the generation of the embedding a-SiO2 structure is achieved via a modified Wooten-Winer-Weaire method. Starting from crystalline betacristobalite,
the network is amorphized through bond-breaking and switching moves.
The Si-nc is positioned at the center of the cell. The energies are calculated using the Keating-like potential. Bond-conversion moves of the type Si-Si to Si-O-Si, and vice versa, allows us to study interdiffusion in the system. A 3.0 nm Si-nc is chosen for our simulations. Through the periodic boundary conditions the inter-particle distance of
the nc vary from 0.5 to 4.0 nm.
The energetics, stability and mechanical properties of embedded Si-nc in a-SiO2 and their variations versus the inter-particle distances are examined. We have shown that
the interface properties of Si-nc are strongly influenced by the embedding amorphous oxide matrix. We especially find that the interfacial energy decreases with the variation of the interparticle distance, indicating higher stability of the entire nanocomposite system. There is also indication for preferential ordered arrangements
of Si nanocrystals at optimum distances. Large deformations were observed, with the deviations in bond angles to be the dominant contributor to the strain energy. Our findings might play a crucial role in understanding and optimizing the PL properties of ordered Si-nc assemblies.