Report

Subtractive Patterning via Chemical Lift-Off Lithography

Science  21 Sep 2012:
Vol. 337, Issue 6101, pp. 1517-1521
DOI: 10.1126/science.1221774

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Patterning by Subtraction

Soft lithographic patterning is usually a “positive” inking process. A polymer stamp is cured on a hard master substrate and then inked with molecules such as alkane thiols, which can then be transferred to a second substrate (such as gold). However, the resolution of the transferred pattern is often degraded by surface diffusion. Liao et al. (p. 1517; see the Perspective by Rogers) obtained higher resolution in a subtractive approach, in which oxygen-plasma–activated silicone stamps removed hydroxyl-terminated alkane thiols from gold surfaces. This lift-off process also removed the terminal gold atom bound to the alkane thiol. The bare regions could be backfilled with protein molecules, and multiple lift-off steps could create patterns with features as small as 40 nanometers.

Abstract

Conventional soft-lithography methods involving the transfer of molecular “inks” from polymeric stamps to substrates often encounter micrometer-scale resolution limits due to diffusion of the transferred molecules during printing. We report a “subtractive” stamping process in which silicone rubber stamps, activated by oxygen plasma, selectively remove hydroxyl-terminated alkanethiols from self-assembled monolayers (SAMs) on gold surfaces with high pattern fidelity. The covalent interactions formed at the stamp-substrate interface are sufficiently strong to remove not only alkanethiol molecules but also gold atoms from the substrate. A variety of high-resolution patterned features were fabricated, and stamps were cleaned and reused many times without feature deterioration. The remaining SAM acted as a resist for etching exposed gold features. Monolayer backfilling into the lift-off areas enabled patterned protein capture, and 40-nanometer chemical patterns were achieved.

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