Mechanism and crucial parameters on GaN nanocluster formation in a silica matrix

Abstract

The formation of wurtzite GaN nanoclusters in an amorphous silica matrix, via gallium and nitrogen ion implantation and rapid thermal annealing, is identified using Extended X Ray Absorption Fine Structure analysis. The mechanism and the crucial parameters that rule the formation of the nanoclusters are established by the use of molecular dynamics simulations. The dominant structural parameters are found to be the concentration of the silicon and oxygen vacancies that are formed during the implantation and the annealing temperature. It is concluded that annealing at 1400 K and 8% Ga/Si and 12% N/O ratios are needed for the formation of GaN nanoclusters. In addition to that, the GaN nanocluster formation is accomplished only when the vacancy concentrations of silicon and oxygen atoms are equal to 10% and 20%, respectively. Finally, the observation of various snapshots upon an increase of the annealing duration indicates the coalescence of smaller GaN nuclei towards larger ones, designating that the Ostwald ripening is a dominant mechanism.

Enhanced thermal conductivity in percolating nanocomposites: a molecular dynamics investigation

“…This was counter-checked at room temperature on a couple of composite structures, with long runs. We expect movement and eventual merge of the nanoinclusions for temperatures higher than 1000 K as it has been observed in a previous work [24].…”

“…(a) an initial amorphous SiO 2 bulk was prepared with the desired structural characteristics (radial distribution function, density) [24]. The size of the SiO 2 box was 10.164 nm by 13.203 nm by 13.819 nm, with a total volume of 1854.44 nm 3 .…”

“…The thermal conductivity of bulk amorphous SiO 2 has been calculated with the EMD method and was found to be 1.14 W/mK, in good agreement with experimental findings (1.37 W/mK) [27], theoretical calculations [28,29] by GKMA (Green-Kubo Modal Analysis) method (1.32 W/mK) and MD (1.17 W/mK), taking into account that with classical dynamics, quantum corrections are not considered. As a first step, we have investigated thermal transport in two composites of 16 nanoinclusions, with a volume fraction of 12.2%, one obtained during the formation of crystalline GaN nanocluster inside silica [24], and characterized by polydisperse elliptical particles, and one with monodisperse spherical particles with the same average radius and with uniform spatial distribution. In the first case, the thermal conductivity has been found to be 1.97 ± 0.2 W/mK, while for the second composite system it was found equal to 2.18 ± 0.2 W/mK.…”

“…Changing the inclusion radius, while keeping the simulation box size constant, corresponds to changing the crystalline volume fraction. In order to [24]. The cut-plane is made for a given depth of the simulation box and only a couple of nanoinclusions with different sizes can be seen.…”

“…More specifically, we present a molecular dynamics investigation on a system which has recently been experimentally realized, made of GaN nanoclusters in an amorphous silica matrix [23]. Some of us, using the right concentration ratios and annealing temperatures, could already model such composites, observing the cluster formation by means of Molecular Dynamics (MD) simulations [24].…”