Directed Assembly of Nanoparticles in Block Copolymer Thin Films: Role of Defects.

The structure of A-b-B diblock copolymer (BCP) thin films is often exploited for “tailoring” the self-assembly of nanoparticles into various geometries, characterized by long-range order. Mechanistically, the nanoparticles are sequestered within the A or B domains of the copolymer, and the domains act as scaffolds to direct the assembly of the nanoparticles. We show that in BCP thin films, which order at suboptimal thicknesses, dislocations play a dominant role in determining the spatial organization of sufficiently large nanoparticles. The nanoparticles preferentially segregate to the core of edge dislocations, which are ubiquitous in these materials. To this end, the two-dimensional planar shape of the islands and holes determine the self-assembled geometry of the nanoparticles. We also show that the so-called “healing length”, λ, increases with film thickness, h, in a manner consistent with λ ∝ h1/2, in accordance with theory. In films of thickness between L< h< 3L, where Lis the domain spacing, λ largely determines the average size of the region within which the nanoparticles are sequestered. [ABSTRACT FROM AUTHOR]