Templated Colloidal Self Assembly
A colloidal crystal (CC) is a material composed of discrete nanoparticles (NP), either in 2D or 3D, with properties which are determined not only by the chemical identity of the NP but also by their physical shape, size, and distribution or symmetry. This latter physical component confers to CC material properties which are not present in their chemical bulk and provides a lever through which properties can be manipulated through the arrangement of NP in space. This project achieves this spatial arrangement of NP using principles of colloidal interactive forces, such that NP self-assemble automatically into symmetries we desire. This project achieves this at the contact meniscus between the colloidal suspension and a piece of substrate. This is actually much simpler than it sounds – equivalent to letting a drop of coffee dry on a porcelain surface and then collecting the coffee stains afterwards. 3D CC materials can be used in photonic devices when the NP have sizes in the range of visible wavelengths (300-600 nm) and 2D CC materials can be used as lithographic masks and membranes. Both of these application aspects have been investigated, culminating in new designs for solar cells making use of CC materials as well as new lighographic methods for patterning. When templates are designed into the substrate, we achieve two additional degrees of control – determining the in-plane orientation of the CC, and the ability to produce non-close packed NP arrangements, both of which are pioneering new beginnings for the continued development of this class of advanced material.
Examples of colloidal crystals formed using surface templates
Colloidal crystals grown on gratings of Si valleys defined by resist edges