Polymer Communication Fabrication of patterned high-density polymer graft surfaces. II. Ampli®cation of EB-patterned initiator monolayer by surface-initiated atom transfer radical polymerization Yoshinobu Tsujii, Muhammad Ejaz, Shinpei Yamamoto, Takeshi Fukuda * , Kunji Shigeto, Ko Mibu, Teruya Shinjo Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan Received 17 January 2002; received in revised form 7 February 2002; accepted 7 February 2002 Abstract Patterned ®lms of a low-polydispersity polymer densely end-grafted on a silicon substrate were fabricated for the ®rst time by the combined use of electron beam EB) lithography and living radical polymerization; a focused EB was scanned on an initiator-immobilized substrate to selectively bombard and decompose the initiator, and then the EB-induced pattern was ampli®ed by the atom transfer radical polymerization ATRP) technique using Cu/ligand complexes. Ellipsometric and atomic force microscopic studies indicated that doses suf®ciently larger than 2000 mC/cm 2 would completely decompose the monolayer of the initiator, 2-4-chlorosulfonylphenyl)ethyltrichlor- osilane,andthatthesurface-initiatedATRPcouldamplifytheEB-produced®nepatternoftheinitiatormonolayer. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Atom transfer radical polymerization; Electron beam lithography; Polymer brush 1. Introduction Arti®cially designed ®ne patterning of polymer ®lms is often demanded in various ®elds of science and technology such as those related with microelectronics and functional sensor devices. For this purpose, a polymer resist layer is usually spin-coated on a substrate and patterned by lithographic techniques. However, such a polymer ®lm has a limited applicability as a functional surface because of its insuf®cient stability against temperature, solvents, and mechanical forces. Thus, a number of different approaches have been made to fabricate a patterned polymer layer that isstable,e.g.eveninawetsystem.Forexample,Ru Èheetal. [1] prepared a patterned graft layer by selectively photoini- tiating polymerization from an azo-compound chemically immobilized on a surface. In this case, the grafting proceeded in a conventional free radical polymerization process, so that the chain length and chain length distribu- tion of graft polymers were poorly controlled, resulting in a poor resolution of the graft pattern. Recently, living radical polymerization LRP) techniques have been successfully applied to surface-initiated graft polymerization to densely end-graft low-polydispersity polymers on a surface [2±19]. In our previous paper [17], we demonstrated that a surface- initiated LRP technique could amplify the two-phase morphology of the initiator monolayer ®xed on a substrate with a spatial resolution as high as ca. 100 nm. Hawker and co-workers [20] also applied the surface-initiated LRP to a self-assembled initiator monolayer patterned with a mm-resolution by the microcontact printing method. This paper describes the ®rst attempt to fabricate a ®nely patterned graft layer with a nano-scale resolution by the combined use of surface-initiated LRP and electron beam EB)lithography.Thefabricationprocess,whichconsistsof two steps, is schematically shown in Fig. 1. The ®rst step is the EB-lithographic patterning of the initiator monolayer ®xed on a substrate; a focused EB is scanned on the substrate to selectively bombard and decompose the initiator.EBlithographyisapromisingtechniquetoachieve a spatial resolution as high as 10 nm [21,22]. However, insuf®cient permeability of EB can provide undesirable results especially for thick resist layers. This drawback is absent in the present system where the monolayer of the initiatorispatterned.Infact,anultra®nepatternwascreated by EB-patterning a self-assembled monolayer SAM) [23,24]. The second step is the ampli®cation of the EB- induced pattern by surface-initiated LRP. The controlled Polymer 43 2002) 3837±3841 0032-3861/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII:S0032-386102)00124-6 www.elsevier.com/locate/polymer * Corresponding author. Tel.: 181-774-38-3161; fax: 181-774-38-3170. E-mail address: fukuda@scl.kyoto-u.ac.jp T. Fukuda).