Scanning Thermal Lithography as a Tool for Highly Localized Nanoscale Chemical Surface Functionalization
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Scanning Thermal Lithography as a Tool for Highly Localized Nanoscale Chemical Surface Functionalization. Joost Duvigneau,1 Holger Schönherr2 and G. Julius Vancso1 1 Department of Materials Science and Technology of Polymers, University of Twente, MESA+ Institute for Nanotechnology, Postbus 217, 7500 AE, Enschede, The Netherlands. 2 Department of Physical Chemistry I, University of Siegen, Adolf-Reichwein-Str. 2, 57076, Siegen, Germany. ABSTRACT We report on Scanning Thermal Lithography (SThL), a recently introduced lithographic tool, for local thermochemistry on tert-butyl acrylate based polymer films featuring chemical cross links. The tailored polymer films afford platforms for controlled high molecular density coupling and surface immobilization of biologically relevant molecules, such as proteins. The thermally labile tert-butyl ester groups in tert-butyl acrylate based polymer films can be cleaved in air at temperatures above 150 °C to yield carboxylic acid functional groups for further (bio)conjugation. The films were optimized to avoid plastic deformation at the elevated temperatures used during SThL. Exploiting these properties patterns with length scales as small as 35 ± 6 nm have been successfully thermally activated with SThL. Hence SThL comprises an attractive approach for the development of e.g. (bio)sensors and platforms for cell surface interaction studies with nanoscale patterns. INTRODUCTION Recently two exciting, novel approaches, i.e. Scanning Thermal Lithography (SThL) and Reactive Imprint Lithography (RIL), have been introduced for the thermochemical surface functionalization of soft condensed matter. RIL has been introduced by us in an effort to exploit heat for combined imprinting (i.e. topographical shaping) and chemical functionalization of polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBA) polymer films on microscopic and macroscopic length scales. SThL has been introduced by King and coworkers[1] and by us[2] as an alternative approach for highly localized thermochemical surface functionalization. In SThL heatable cantilevers which comprise resistive heater elements embedded at the cantilever end are utilized for the confined delivery of heat at the probe tip-sample interface (Figure 1). Compared to the well known limitations of conventional lithography or various drawbacks of other scanning probe lithographies (SPLs) heat transport at small length scales is expected to be much less restricted. Since its introduction SThL has proven to be a promising nanotechnology tool for nanoscale chemical surface functionalization. The reaction mechanism for the thermal deprotection reaction of the tert-butyl ester was described elsewhere for PS-b-PtBA block copolymer film platforms (Figure 1).[2, 3] Upon heating PtBA containing films above the thermal deprotection temperature of the tert-butyl ester the ester bond is thermally cleaved resulting in the formation of carboxylic acid groups and the liberation of gaseous isobutylene. Upon further heating, anhydride groups are formed through an
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