Nano-scale materials possess many unique physical and chemical properties which are not found in bulk materials. The ability to synthesize these materials by design is one of the greatest challenges in materials science. Advances towards meeting this challenge will lead to discoveries in fields such as plasmonics, photonics, catalysis, and energy sciences. DNA-directed self assembly has emerged as a novel approach for generating nanoparticle superlattices, where nanoparticle "atoms" functionalized with a dense shell of DNA linkers, termed programmable atom equivalents (PAEs), are assembled into crystalline superlattices with tunable compositions, crystal symmetries, and lattice parameters. To bring the potential of this technique into real applications requires a deep understanding of the precise control of the spatial distribution and orientation of the nano-scale building blocks. Theoretical models and computer simulations can play an important role in the understanding of the assembly process over multiple length scales, and eventually predict various phase behaviours. This thesis studies DNA-directed nanoparticle assembly via multi-scale modeling and simulation. The original work can be divided into three parts: (i) DNA-directed assembly is a well developed approach in constructing desired nano-scale architectures, while E-beam lithography is widely utilized for high resolution nano-scale patterning. Recently, a new technique combining these two methods was developed to epitaxially grow DNA-mediated nanoparticle superlattices on patterned substrates with specific orientation and controllable sizes. However, defects were observed which restricted this technique from building large-scale superlattices for real applications. In order to optimize the epitaxial growth, we used molecular dynamics simulations to study the nature of the formation of these defects and further developed design rules to dramatically reduce defects. \t (ii) efects play an important role in materials science. Like any solid in nature, superlattices can contain different kinds of structural defects, which significantly alter their physical properties. They may provide material advantages or disadvantages. Further development of these materials requires a deeper understanding and good control over structural defect formation. We used Monte Carlo simulations to conduct a systematic study of defect formation in epitaxial growth of nanoparticle superlattices at a much larger length scale. The simulations show two main results. First, structural defects have long range correlations and form one-dimensional clusters with an exponential length distribution. Second, these linear defects exhibit spontaneous symmetry breaking and undergo a liquid crystal phase transition. Furthermore, we introduced a mean-field theoretical approach, which is in strong agreement with the simulation results. (iii) In previous studies, we focused on spherical nanoparticle building blocks. However, non-spherical nanoparticles are ideal building blocks for self assembly into various functional nanomaterials due to their unique and anisotropic physical properties. With the advent of methods for preparing non-spherical building blocks, DNA-directed assembly of anisotropic nanoparticles has attracted the interest of both experimental and computational research. The challenge is how to assemble these anisotropic nanoparticles into required target structures to obtain desired properties. Here we conducted multi-scale molecular dynamics simulations and Monte Carlo simulations to study the DNA-directed assembly of tetrahedron nanoparticles. We observed quasicrystalline structures with five fold symmetry in the assemblies. Further, we demonstrated that icosahedral nanocages can be formed by truncated tetrahedron building blocks with specific preconfiguration.

Last modified

• 11/24/2019

Creator

• Saijie Pan

DOI

• https://doi.org/10.21985/n2-bery-8a12

Keyword

• self-assembly
• nanoparticle
• DNA
• Molecular Dynamics
• Monte Carlo

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright