Templated Self‐Assembly of Block Copolymers: Top‐Down Helps Bottom‐Up

One of the key challenges in nanotechnology is to control a self‐assembling system to create a specific structure. Self‐organizing block copolymers offer a rich variety of periodic nanoscale patterns, and researchers have succeeded in finding conditions that lead to very long range order of the domains. However, the array of microdomains typically still contains some uncontrolled defects and lacks global registration and orientation. Recent efforts in templated self‐assembly of block copolymers have demonstrated a promising route to control bottom‐up self‐organization processes through top‐down lithographic templates. The orientation and placement of block‐copolymer domains can be directed by topographically or chemically patterned templates. This templated self‐assembly method provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales.     

Directed Self‐Assembly of Templatable Block Copolymers by Easily Accessible Magnetic Control

Magnetic control has been a prosperous and powerful contactless approach in arraying materials into high‐order nanostructures. However, it is tremendously difficult to control organic polymers in this way on account of the weak magnetic response. The preparation of block copolymers (BCPs) with high magnetostatic energy is reported here, relying on an effective electrostatic coupling between paramagnetic ions and polymer side chains. As a result, the BCPs undergo a magnetically directed self‐assembly to form microphase‐segregated nanostructures with long‐range order. It is emphasized that such a precisely controlled alignment of the BCPs is performed upon a single commercial magnet with low‐intensity field (0.35 Tesla). This strategy is profoundly easy‐to‐handle in contrast to routine electromagnetic methods with high‐intensity field (5–10 Tesla). More significantly, the paramagnetic metal component in the BCP samples can be smartly removed, providing a template effect with a preservation of the directed self‐assembled nanofeatures for patterning follow‐up functionalized species through the original binding site.     

Directed Self‐Assembly of Star‐Block Copolymers by Topographic Nanopatterns through Nucleation and Growth Mechanism

Exploring the ordering mechanism and dynamics of self‐assembled block copolymer (BCP) thin films under confined conditions are highly essential in the application of BCP lithography. In this study, it is aimed to examine the self‐assembling mechanism and kinetics of silicon‐containing 3‐arm star‐block copolymer composed of polystyrene (PS) and poly(dimethylsiloxane) blocks as nanostructured thin films with perpendicular cylinders and controlled lateral ordering by directed self‐assembly using topographically patterned substrates. The ordering process of the star‐block copolymer within fabricated topographic patterns with PS‐functionalized sidewall can be carried out through the type of secondary (i.e., heterogeneous) nucleation for microphase separation initiated from the edge and/or corner of the topographic patterns, and directed to grow as well‐ordered hexagonally packed perpendicular cylinders. The growth rate for the confined microphase separation is highly dependent upon the dimension and also the geometric texture of the preformed pattern. Fast self‐assembly for ordering of BCP thin film can be achieved by lowering the confinement dimension and also increasing the concern number of the preformed pattern, providing a new strategy for the design of BCP lithography from the integration of top‐down and bottom‐up approaches.