(498a) Sequential Infiltration Synthesis On Polymers for Nanofabrication

Intensive research has focused on generating patterned nanomaterials by selective, localized synthesis in the microdomains of self-assembled block copolymers (BCPs) template. For sophisticated control of the final nanomaterials, it is critical to understand the behavior of the complex processes involved in the localized synthesis within BCP films. However, limited research has been done to understand these phenomena. 

Sequential infiltration synthesis (SIS) method with BCPs template represents a hybrid soft and hard lithographic process and has been demonstrated as a promising solution to controllably synthesize patterned 2D and 3D nanofeatures of different materials with well-defined dimensions (down to sub-10 nm). Owing to its step-wise, substrate reactive site-limited heterogeneous reaction mode, SIS offers a great opportunity to investigate the complex diffusion and localized chemical reactions during the synthesis through the step-by-step mode.

In this work, we utilized sequential infiltration synthesis (SIS) of TiO₂ as the platform to investigate the behavior of reactant infiltration and localized reaction within polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA). Similar studies were also performed onto two pure homopolymer (PS and PMMA) films. The in-situ quartz crystal microbalance (QCM) analysis and ex-situ SEM and XPS showed that the step-wise, substrate reactive site-limited heterogeneous growth mode in SIS is critical to eliminate undesired homogeneous reactions, and enable unprecedented control over the localized synthesis over previous methods. Furthermore, the experimental result illustrated that the unique segregated nanodomains in the self-assembled PS-b-PMMA thin film function as active channels to deliver reactants for the selective localized reaction in the PMMA domains during the SIS. Such mechanistic understandings shed lights on the mechanisms and potential problems in other localized synthesis methods involving BCPs as the substrate.