Sequential infiltration synthesis (SIS) is becoming an important tool for resist hardening and formation of unique nanostructures. SIS is a variant of atomic layer deposition (ALD), in which the organometallic precursors are allowed to diffuse into the polymeric substrate before condensation. In contrast to ALD, the extended diffusion time in SIS potentially allows for extensive penetration into the substrate. An important parameter in SIS is the affinity of the precursor with the polymer substrate. Differences in affinity can be exploited, for e.g., for generation of patterned structures within block copolymers. To date, the interactions between the precursor molecules, for example trimethyl aluminium (TMA) have been inferred from in situ or ex situ vibrational spectroscopy. Potentially much richer information can be gained from NMR and transmission FTIR spectroscopy of solutions of precursor and polymer. Fundamental studies of PMMA and TMA allow identification and screening of novel polymer substrates for SIS. Previous studies have provided broad design rules for SIS; e.g., highly-polar and strongly basic structures enhance uptake of precursors. The precursor molecules such as TMA are Lewis acids and hence will associate with functional groups having base character. We have investigated SIS polymers that incorporate a stronger Lewis base group, sulfinyl, in poly((2-methylsulfinyl) ethyl methacrylate) (PMSEMA). Details of the interactions between TMA and PMSEMA in solution, and as films, and comparison with a range of other materials, provide information on potential of these materials for SIS.
Photo-directed orientation control of block copolymer (BCP) domains is a powerful method for generating distinct regions of perpendicular and parallel-aligned lamella in a single film layer. In this study we demonstrate the versatility of Poly(aryl methacrylate) films for controlling the wetting behaviour of PS-b-PMMA films after UV irradiation. Upon exposure to UV light (254 nm), the surface polarity of Poly(aryl methacrylate) films changed due to the photo-Fries rearrangement of the aromatic ester groups. The switch of PS-b-PMMA alignment from parallel to perpendicular lamellar structures was demonstrated after UV exposure to appropriate doses of poly(aryl methacrylate) films. The UV dose required to switch alignment and orientation in a wide range of BCP films can be tailored by rational structural design of the poly(aryl methacrylate). This simple, rapid, cost-effective and flexible approach to controlling BCP orientation makes this photo-directing chemoepitaxy approach promising for block copolymer self-assembly applications.
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