Towards Nanoscale Thermal Scanning Probe Lithography
Many applications of nanoscience and technology require methods to reliably write and erase tiny structures on surfaces. Approaches on the basis of Atomic Force Microscopy (AFM) include shaving, grafting, molecular transport, and electric fields. Thermal Scanning Probe Lithography (TSPL) was introduced as a new lithographic tool for nanoscale thermal chemical lithography on polystyrene-block-poly(tertbutyl acrylate) (PS-b-PtBA) polymer thin films. TSPL utilises the highly localised resistive Joule heating at the cantilever end of self-heating silicon AFM cantilevers to locally thermally chemically modify small domains on PS-b-PtBA films. The thermally labile tert-butyl ester groups can be thermolysed at temperatures above 150 C to yield carboxylic acid and anhydride functionalities We have successfully demonstrated the local thermal functionalisation via TSPL and subsequent wet chemical grafting reactions with fluoresceinamine or PEG on PS644-b-PtBA938 films for domains as small as 370 by 580 nm. The resolution limits of this new scanning probe lithography approach have not been established as yet, but temperature, duration of tip-samples contact and feedback settings, among other things are expected to contribute to attainable minimum feature size and separation. Future work will systematically explore the nanoscale thermal activation of polymer films as well as the characterization of these thermal chemical modified polymer films surfaces at nanometer length scales.
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