Abstract
We performed nanosecond timescale computer simulations of clusterization and agglomeration processes of boron nitride (BN) nanostructures in hot, high pressure gas, starting from eleven different atomic and molecular precursor systems containing boron, nitrogen and hydrogen at various temperatures from 1500 to 6000 K. The synthesized BN nanostructures self-assemble in the form of cages, flakes, and tubes as well as amorphous structures. The simulations facilitate the analysis of chemical dynamics and we are able to predict the optimal conditions concerning temperature and chemical precursor composition for controlling the synthesis process in a high temperature gas volume, at high pressure. We identify the optimal precursor/temperature choices that lead to the nanostructures of highest quality with the highest rate of synthesis, using a novel parameter of the quality of the synthesis (PQS). Two distinct mechanisms of BN nanotube growth were found, neither of them based on the root-growth process. The simulations were performed using quantum-classical molecular dynamics (QCMD) based on the density-functional tight-binding (DFTB) quantum mechanics in conjunction with a divide-and-conquer (DC) linear scaling algorithm, as implemented in the DC-DFTB-K code, enabling the study of systems as large as 1300 atoms in canonical NVT ensembles for 1 ns time.
Highlights
Boron nitride, boron nitride (BN), is a compound isoelectronic with elemental carbon and can appear in rich crystalline phases, including fullerene-like (0D), nanotubes (1D, BNNTs), hexagonal graphene-like (2D, h-BN) and diamond-like (3D, cubic c-BN).[1]
We have computationally studied the transformation and boron nitride nanostructure (BNNS) synthesis processes from a hot, high pressure gas containing various combinations of precursors B, N, and H, typically expected in plasma synthesis, to elucidate the detailed dynamics of self-assembly mechanisms into clusters and aggregates at various temperatures
We have used quantumclassical molecular dynamics (QCMD) simulations based on density-functional tight-binding (DFTB) quantum chemical potential, as implemented in the DC-DFTB-K code, to study large systems containing about 1300 atomic particles in canonical NVT ensembles for 1 ns, in a temperature range from 1500 to 6000 K
Summary
BN, is a compound isoelectronic with elemental carbon and can appear in rich crystalline phases, including fullerene-like (0D), nanotubes (1D, BNNTs), hexagonal graphene-like (2D, h-BN) and diamond-like (3D, cubic c-BN).[1]. Edge Article containing molecules without the presence of a pre-existing catalyst nanoparticle,[24] as well as by exposure of boron clusters to a nitrogen atmosphere.[24,25,26] In both cases, high temperature conditions of around 2000 K are shown to be crucial in the process, enabling fast diffusion of N, B or BN species to an adequate lowest energy position in the nanolattice, usually towards structural defects and the open or closed ends of the tubes. It is hypothesized in the literature that hydrogen in nitrogen plasma is necessary to prevent the recombination of nitrogen atoms to non-reactive dinitrogen molecules.[8,23]
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