Highly compliant static microcantilevers fabricated in gold nanocomposite materials

Abstract

Static microcantilevers with superior stress sensitivity were produced out of a novel Au–Ta metal nanocomposite, and successfully employed for the detection of chemisorbed dodecanethiol. Au–Ta nanocomposite films of various compositions were first synthesized by co-sputtering in order to assess the chemisorption of alkanethiol molecules on their surfaces. Previous x-ray diffraction analysis showed that from 0–50% at. Ta, the films retain gold's FCC structure and ⟨1 1 1⟩ texture necessary for the formation of an alkanethiol self-assembled monolayer. Attachment of dodecanethiol molecules from vapor phase onto the surface of our Au–Ta films was then quantified using contact angle measurements and x-ray photoelectron spectroscopy. As suggested by the x-ray diffraction results, the incorporation of small amounts of tantalum (5% and 10% at. Ta films) had little adverse effect on the attachment of dodecanethiol. However, this ceased to be the case at 20% at. Ta and above. Static microcantilevers were then fabricated directly out of a 5% Au–Ta nanocomposite alloy by patterning the sputtered Au–Ta layer onto a silicon wafer using contact photolithography and releasing the cantilever with an SF6 reactive ion etch. Cantilevers 140 µm long, 20 µm wide, and 369 nm thick showed a spring constant of 10.5 mN m−1. The detection of chemisorbed dodecanethiol molecules was successfully demonstrated with these structures through the monitoring of static deflections.