title: Controllable two-stage droplet evaporation method and its nanoparticle self-assembly mechanism.
abstract: Bottom-up self-assembly is able to constitute a variety of structures and has been thought to be a promising way for advanced nanofabrication. Droplet evaporation, as the simplest method, has been used in various self-assemblies. However, the assembled area is not large enough and the order is still not well controlled. Here we show a facile and controllable two-stage droplet evaporation method by adjusting the humidity and temperature of the evaporating droplet. Taking the highly monodispersed gold nanorods (GNRs) as an example, large-area, self-assembly monolayer arrays are reproducibly achieved. To understand the self-assembly mechanism, we adopted simplified models to analyze the interactions between the nanorods. The results show that a metastable state of secondary-energy-minimum exists, especially in the latter stage of the assembly process, leading to the ordered arrays. A large electrostatic barrier between the assembled arrays prevents the formation of the multilayer structures and thereby leads to the preferential monolayers. Moreover, we predict possibilities of different types of assemblies of the nanorods, and a schematic phase diagram is finally given. The results here may offer a way toward high-quality self-assembled nanoparticles superlattices for use in enhanced spectroscopy, sensors, or nanodevices.
authors.affiliation: Laboratory for Nanodevices, National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Xie
authors.forename: Shengming
authors.initials: S
authors.lastname: Guo
authors.forename: Chuanfei
authors.initials: C
authors.lastname: Guo
authors.forename: Meng
authors.initials: M
authors.lastname: He
authors.forename: Dongxue
authors.initials: D
authors.lastname: Chen
authors.forename: Yinglu
authors.initials: Y
authors.lastname: Ji
authors.forename: Ziyu
authors.initials: Z
authors.lastname: Chen
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Wu
authors.forename: Qian
authors.initials: Q
authors.lastname: Liu
authors.forename: Sishen
authors.initials: S
authors.lastname: Xie
mesh_terms: D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D014835:Volatilization
chemical_list: D006046:Gold