Fabrication and characterization of e-beam photoresist array for biomimetic self-cleaning dry adhesives

Abstract

Inspired from gecko foot-hairs, this paper presents the fabrication and characterization of e-beam photoresist nano-pillar array as biomimetic self-cleaning dry adhesives. Resist pillars of different widths and pitches were designed and fabricated using e-beam lithography. The pillar array of the negative e-beam resist (SAL 601) laterally collapsed after development, resulting from larger surface energy. The positive e-beam resist (ZEP 520A) is suitable for fabricating nano-pillar array. An AFM plateau tip was used to measure and characterize the adhesion force of the resist pillar array. The adhesion strengths significantly increase with the decreasing pillar width at the same pillar pitch and height. The contact angle measurement was used to evaluate the self-cleaning effect. Air trapped in the nano-gap between the pillars made the surface approach to the Cassie’s state of hydrophobicity. Since the contact angle and the adhesion strength have opposite trends with the contact area ratio, the result indicates that the dry adhesive needs to decrease to nanometer scale for obtaining the self-cleaning effect.