title: Ultrathin random copolymer-grafted layers for block copolymer self-assembly.
abstract: Hydroxyl-terminated P(S-r-MMA) random copolymers (RCPs) with molecular weights (Mn) from 1700 to 69000 and a styrene unit fraction of approximately 61% were grafted onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder-forming PS-b-PMMA block copolymer (BCP) thin films. When the thickness (H) of the grafted layer is greater than 5-6 nm, a perpendicular orientation is always observed because of the efficient decoupling of the BCP film from the polar SiO2 surface. Conversely, if H is less than 5 nm, the critical thickness of the grafted layer, which allows the neutralization of the substrate and promotion of the perpendicular orientation of the nanodomains in the BCP film, is found to depend on the Mn of the RCP. In particular, when Mn = 1700, a 2.0 nm thick grafted layer is sufficient to promote the perpendicular orientation of the PMMA cylinders in the PS-b-PMMA BCP film. A proximity shielding mechanism of the BCP molecules from the polar substrate surface, driven by chain stretching of the grafted RCP molecules, is proposed.
authors.affiliation: †Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Universitá del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy.|‡INSTM, UdR, Alessandria, Italy.
authors.forename: Katia
authors.initials: K
authors.lastname: Sparnacci
authors.affiliation: †Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Universitá del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy.|‡INSTM, UdR, Alessandria, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Antonioli
authors.affiliation: †Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Universitá del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy.|‡INSTM, UdR, Alessandria, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Gianotti
authors.affiliation: †Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Universitá del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy.|‡INSTM, UdR, Alessandria, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Laus
authors.affiliation: §Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza, Italy.
authors.forename: Federico Ferrarese
authors.initials: FF
authors.lastname: Lupi
authors.affiliation: §Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza, Italy.
authors.forename: Tommaso Jacopo
authors.initials: TJ
authors.lastname: Giammaria
authors.affiliation: §Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Seguini
authors.affiliation: §Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Perego
keywords: P(S-r-MMA); PS-b-PMMA; molecular weight; rapid thermal processing (RTP); self-assembly