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Mussel-Inspired Strategy for Stabilizing Ultrathin Polymer Films and Its Application to Spin-On Doping of Semiconductors

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journal contribution
posted on 19.07.2018, 17:56 by Reika Katsumata, Ratchana Limary, Yuanyi Zhang, Bhooshan C. Popere, Andrew T. Heitsch, Mingqi Li, Peter Trefonas, Rachel A. Segalman
Stabilizing ultrathin films, in particular avoiding dewetting, is critical to the application of polymer thin films from biology to electronics. To address this issue, a wide range of approaches have been developed, including self-assembled monolayers to modify surface energy, and covalent attachment methods, such as surface-initiated polymerization and grafting of end-functionalized polymers. However, most of these approaches either require postprocessing of the substrates or are applicable only to the specific combination of polymers and substrates. Herein, we introduce a mussel-inspired universal adhesive moiety, dopamine, as an end group for any polymer to promote film stability, and demonstrate its application to spin-on doping on silicon, in particular. Leveraging the versatility of reversible addition–fragmentation chain transfer (RAFT) polymerization, the dopamine moiety is incorporated as an end group. Dopamine functionalized 15 nm thick films are more thermally stable at 230 °C on a variety of semiconductor-relevant surfaces (Si–OH, SiOx, TiN, and Si3N4), while control polymer films with a carboxyl end group severely dewet. The dopamine end group also ensures successful sub-10 nm thick conformal coatings on three-dimensional surfaces, confirmed by cross-sectional scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS). Furthermore, as a polymeric spin-on doping material, dosage of dopant with the dopamine-functionalized polymer is comparable or higher than that with the control end group, demonstrating one of the promising applications of such conformal coatings.