Directed Self-assembly of Block Copolymer Thin Films by Electrospray Deposition

Block copolymers (BCPs) have been explored extensively as a "bottom-up" platform for nanofabrication due to their self-assembly on pertinent length scales (3-100 nm), and the versatility of available means for controlling the length scale and chemical functionality through molecular design. To fully realize their potential in nanotechnological applications, it is crucial to simultaneously develop long-range order and exert orientational control over microphase separated structures produced by BCP self-assembly. Although a variety of methods have been extensively explored to effect directed self-assembly of BCPs, exerting structural control in thin films beyond the near surface regime (ca. 100nm) remains a difficult challenge. This is particularly the case for the generation of vertically aligned structures in thin films. In the present work, we introduce electrospray as an effective means of depositing well-ordered BCP thin films of arbitrary thickness in a continuous or uninterrupted fashion as an analogue to physical vapor deposition.;Detailed examination of process parameters are performed to optimize the ordering of the BCP thin film as well as unveil the equilibration kinetics that underpins morphology development in the process. We demonstrate that continuously equilibrated growth of BCP thin films can be achieved to realize epitaxial growth of BCP films on neutralizes substrates well above 500 nm. Two regimes of deposition - "wet" and "dry" spray modes, are explored and compared, where either solvent or thermal annealing is the dominant equilibration force. Perpendicular morphology can be dictated on preferential substrates by the solvent evaporation field and vitrification of non-equilibrated morphology through in-situ crosslinking permits persistence of the pattern beyond the 1 micron scale where conventional surface directed morphologies degenerate. Finally, multi-dimensional directed self-assembly in ESD is discussed where complex morphologies with controllable size and orientations can be fabricated through sequentially deposited BCP multi-layers. The fact that deposition is carried through charged droplets allows spatial control of the deposition for patterning of BCP thin films. These findings substantiate that electrospray offers a new and potentially exciting route for controlled, continuous growth of BCP thin films and manipulation of their microstructure.