Directed self-assembly of ordered structures as a simple nanotechnology tool
(Nanowerk Spotlight) The use of spontaneous self-assembly as a lithography- and external field-free means to construct well-ordered, often intriguing structures has received much attention for its ease of organizing materials on the nanoscale into ordered structures and producing complex, large-scale structures with small feature sizes. These self-organized structures promise new opportunities for developing miniaturized optical, electronic, optoelectronic, and magnetic devices.
An extremely simple route to intriguing structures is the evaporation-induced self-assembly of polymers and nanoparticles from a droplet on a solid substrate. However, flow instabilities within the evaporating droplet often result in non-equilibrium and irregular dissipative structures, e.g., randomly organized convection patterns, stochastically distributed multi-rings, etc. Therefore, fully utilizing evaporation as a simple tool for creating well-ordered structures with numerous technological applications requires precise control over several factors, including evaporative flux, solution concentration, and the interfacial interaction between solute and substrate.
To this end, a group of scientists has developed a simple and straightforward method to create gradient concentric rings of multi-walled carbon nanotubes (MWCNTs) over large surface areas with controlled density by combining two consecutive self-assembly processes, namely, evaporation-induced self-assembly of polymers in a sphere-on-flat geometry, followed by subsequent directed self-assembly of MWCNTs on the polymer-templated surfaces.