Simultaneous templated assembly of different-sized nanocomponents by selective removal

Abstract

This work presents an application where Templated Assembly by Selective Removal (TASR) was used to assemble spherical components of two different sizes onto a common substrate according to a specific layout. TASR is a potential rapid, cost effective, and large scale parallel nanomanufacturing method. It consists of patterning a template into shapes complementary to the components to be assembled, and then using adhesion and fluid flow to selectively keep the components in certain locations on the substrate and remove them from all other locations. Adhesion is induced by growing self assembled monolayers (SAMs) on the components and template which are then placed in an assembly mixture of water and acetone. Fluid flow is induced by subjecting the assembly mixture to an acoustic wave generated by an ultrasonic transducer. Assembly is achieved only in the sites which match the shapes of the components, where retention due to adhesion dominates over removal due to fluid flow. The thesis presents an experiment in which TASR is used to assemble 636 nm and 2 glm diameter silica spheres on a silicon oxide layer grown and patterned on a silicon substrate. The SAM precursor used is OTC.

(cont.) The experiment is conducted using varying water concentrations in the assembly mixture and varying input voltages to the acoustic transducer. The results show that the yield, or the degree to which assembly takes place, can be selectively high, on the order of 90% for components in matching sites, and not more than 10% for components in non-matching sites. A first order theoretical model developed by Jung [21] is adjusted and used to explain the experimental results. Yield is found to be mostly a function of the ratio of the adhesive retention moment to the fluidic removal moment attempting to roll the components along the substrate. The correlation also predicts that when sufficiently high values of this ratio are reached (about 8 nominally), while simultaneously assuring appropriate stirring of the assembly mixture, full, selective yield can be achieved. The success of the experiment demonstrates the feasibility of using TASR in practical applications for building functional nanodevices having different component shapes and sizes. The verification of the model enhances the understanding of the process and facilitates the building of such devices.