High-rate Electro-fluidic Directed Assembly of Nanoelements on Insulating Substrates

Abstract

Directed assembly of nanoelements has been used to fabricate devices for diverse applications. The challenge of using such techniques consists of developing highly scalable, high-rate (fast) assembly techniques for placing nanoelements precisely on either conductive or insulating surfaces. In fluidic assembly, nanoelement migration toward the substrate is only driven by the concentration gradient between the assembly region and bulk solution therefore it is a slow process. On the other hand, electric field induced assembly techniques (such as electrophoresis) are very fast, however, they need a conductive surface and the assembly has to occur on a conductive substrate. This is not desirable for many electronics applications. Here, we introduce a new, high-rate electro-fluidic assembly technique that enables directed assembly on any type of insulating surfaces. The significance of this technique is that the assembly process is 100 times faster than fluidic assembly (the only technique used today on insulating surfaces). Polystyrene Latex nanoparticles (50nm) and gold nanoparticles (50nm) have been successfully assembled. We have shown that the assembly is a function of pulling speed, pH of the solution and it is highly dependent on the applied voltage. We are able to achieve full particle coverage with trenches having different orientations and structures that exhibits the robustness of the assembly method for any two dimensional configuration. The process is being applied to SWNTs assembly to increase the assembly speed by two orders of magnitude. The assembled SWNT structures size range from 100nm to 3microns.