INTRODUCTION TO NANOFABRICATION

The animation here explains what the terms "periodic array" and "nano-scale" stand for. Periodic nano structures can be used for many applications in electronics, magnetic devices, sensors and filters. For these applications, ordered features such as regular patterns of magnetic particles that can be used to store data, or of holes for small particle filters are essential.

Self assembly is the self organization of particles in order to minimize the overall energy of a system. We have all witnessed how oil separates from water if the two are mixed together in a salad dressing. The preferred interactions of fat molecules with each other and of water molecules with each other drive this kind of organization. The animation on self assembly describes how more complex systems can order.

The molecules commonly used in self assembly research, especially for the applications that our laboratory is interested in, are block copolymers. A polymers is a large molecules composed of a repeating smaller molecule units linked in a chain. Block copolymers contain different kinds of chains linked together. The different chains, called blocks, are selected to repel each other. The ratio of the sizes of the different blocks controls the kind of a structure that can form ranging from parallel planes or cylinders to an interconnected network to spherical structures. The animation here should help you visualize these self assembly concepts for block copolymers.

The overall length of the polymer allows us to control the size of features (the larger each block the larger the features). The chemistry of the different blocks can be selected such that one of the blocks is more sensitive to certain processing (such as etching) and can be removed, while the other block remains on a surface that was coated with the block copolymer, leaving a periodic array.
The array structure that our laboratory is interested is spheres of poly(ferrocenyldimethylsilane) or PFS in a polystyrene or PS matrix that is removed by etching.

Another important factor in making our patterns is the perfection of the ordering of the features. When we look at spheres formed on a flat substrate locally, they seem to form ordered hexagonal arrangements. The ordering of these spheres is lost over long distances of the pattern.
One technique to improve the ordering of the pattern is place polymers in a template that will help them organize by interacting with the walls of the template. The animation explains one type of a "grooved" template, and shows how it can produce larger ordred regions of the polymer spheres we are researching.

Prepared by Marianna Shnayderman