Chemical Physics Seminar: Understanding and Controlling 3D Assembly at the Nanoscale: Directed Assembly of Block Copolymers

Abstract:

Nanostructures are the building blocks for many technological applications such as photovoltaic, energy storage, and semiconductor devices. To meet the demands of these applications, precise control over the nanoscale dimensions and tailored functionality of the nanostructure is needed. Self-assembly of polymers, nanoparticles, and DNA can reach the desired nanometric dimension with scalable manufacturing processes, and is therefore considered a promising pathway for nanostructure formation. Among the challenges to realize this promise are: (1) the ability to control the assembly in three dimensions, and (2) engineering the nanostructure functionality and improving its performance.

In this talk, I will discuss methods for controlling the three-dimensional assembly of block-copolymers (BCP) using guiding chemical pre-patterns and will demonstrate how better understanding of the 3D structure can be achieved through transmission electron microscopy (TEM) tomography. Functionalization of the BCP nanostructure was performed by selectively growing metal oxide in one microdomain of the BCP. This selective growth was also utilized as a new staining technique for angular dark field (ADF) scanning TEM (STEM) imaging of BCPs. 3D characterization, using ADF-STEM tomography, enabled us to probe hidden structures and to analyze the through-film morphology, changes in feature’s roughness with depth, and the formation of defects in directed self-assembled lamellae for nanofabrication, and cylindrical structure for membrane application. The fundamental relationship between 2D patterns and 3D assembly was probed in directed self-assembly of sphere-forming BCP films. With these examples I hope to show you the prospects of understanding and designing 3D assembly.