Molecular Dynamics Simulation of Nanoparticle Chain Aggregate Sintering
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Molecular Dynamics Simulation of Nanoparticle Chain Aggregate Sintering Takumi Hawa1,2 and Michael R Zachariah1,2 1 University of Maryland, College Park, MD, 20742 2 National Institute of Standards and Technology, Gaithersburg, MD, 20899 ABSTRACT Sintering of silicon nanoparticle chain aggregates are investigated using molecular dynamics (MD) simulations at 1500 K, which is about melting temperature at the size range we tested. The straight chain aggregates consist of upto 40 particles and the primary particles of 2.5 to 5 nm sizes are considered. The sintering time increases with increase the total volume of the chain aggregate or with increase the exposed initial surface area of the chain. A mathematical model was developed to describe the dynamics of sintering of chain aggregates. The model was able to predict the sintering time with excellent agreement with the results obtained from MD simulations. We also studied the chain aggregate that has a secondary branch coming out from the edge of the primary branch (L-shape) and from the middle of the primary branch (T-shape). In general, sintering time changes as much as 30% of that of a straight chain which contains the same volume of particles. INTRODUCTION Fabrication of the desired size with a narrow size distribution, and desired structure, is seen as one of the major challenge in robust implementation of nanoscience to a nanotechnology. The two most obvious ways to control the size of primary particles grown from the vapor are to either change the characteristic collision time by dilution or change the coalescence time by changing particle temperature. For large scale production or for ultraclean materials, a gas phase production method is generally the method of choice [1-4]. Aerosol synthesis however, typically results in highly aggregated structures. The size of the spherical primary particles and the growth of agglomerates are determined by the rate of collision and subsequent sintering of particles. To understand the dynamics it would be useful to understand how aggregates sinter. Several researchers have approached the problem of aggregate sintering using Monte-Carlo [5, 6] or other Brownian dynamics approaches [7]. However, all previous approaches were simulated by making assumptions as to how sintering would occur in an aggregate, and then applying a standard sintering approach to map the evolution of the morphology. Our approach is to investigate how this aggregate sintering is actually taking place by use of atomistic simulation, and probe how it might differ from the simplest case of binary particles. We use the results to obtain both insight, and a better approach to phenomenologically modeling aggregate particle sintering. To the best of our knowledge, there is no MD work that has investigated the sintering of nanoparticle aggregate chains. In this paper we focus on the simplest geometric representation of an aggregate, that of a chain of particles of equal primary particle size. We will use MD simulation to track
the evolution of a s
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