Batch Fabrication at Room Temperature of Arrays of Freestanding Nanoneedles

S. Arva, M.M. Yazdanpanah, R.W. Cohn
University of Louisville, US

Keywords: self-assembly, array, freestanding, nanoneedles, high aspect ratio, AFM probes

Abstract:

As melted gallium reacts with metal films (e.g. Ag, Au, Pt) alloy nanostructures self-assemble through crystallization. Of particular interest are the needle structures that self-assemble when Ga reacts with Ag to form Ag2Ga. Previously we demonstrated the selective growth and orientation of individual nanoneedles. Nanoneedles between 25 and 1000 nm in diameter and 1 to 100 micrometer in length have been grown onto various devices including AFM probes, quartz tuning forks and scanning tunneling microscope tips. Herein we report on efforts to develop a wafer-level method of batch fabrication of arrays of freestanding nanoneedles. Experiments are performed with a silver-coated array of silicon micromachined pillars. The pillar array is immersed in a film of gallium (typically for 30 s.) The array is then retracted forming a meniscus between the Ga and the end of the pillars. After 2 min, the array is retracted at a constant velocity to form array of freestanding nanoneedles. Based on their high aspect ratio, constant diameter and flexibility nanoneedle-tipped devices have potential applications to nanoprobing and nanomanipulation of liquids and soft complex materials, including individual live cells. Also, these nanoneedles are used as ultra sensitive nano-cantilever capable of detecting sub Pico-Newton forces.