Fabrication of mesoscale topographical gradients in bulk titanium and their use in injection moulding

Abstract

Fabrication methods for titanium substrates exhibiting continuous micro and nano scale arrays, with increasing feature heights over the length of the array are reported. The resultant feature heights spanned 0–2μm. Patterned gradient arrays of circular features with diameters of: 500nm, 1μm and 2μm, spaced by twice the diameter were manufactured by the process using specially prepared titanium substrates. Patterns were exposed by electron beam lithography and the length of the patterned arrays was 15mm or 20mm. This work presents two selectivity amplification processes to achieve a gradient of feature heights ranging over the titanium array after consecutive reactive ion etching processes. The first, route A: a HSQ on Ti, gradient amplification process. The second, route B, a SiO2 layer amplification transfer into Ti. The crucial initial gradient component deposited for the amplification process for both routes was a diffusion limited plasma polymerised hexane gradient. Etching using respective reactive ion etch chemistries for each gradient transfer through the various selectivity amplification layers (employing consecutive etch steps, in this way) enables a dual amplification for each route to manufacture. The original gradient is transferred into titanium as a function of the sum of the respective selectivities between the materials, using the appropriate dry etch plasma conditions. The substrates henceforth are referred to as inlays, and were tested for use as a high throughput platform for polymer replication by injection moulding. It is envisaged that the fabrication methodology and resultant topographies have use in a range of engineering applications. The overall selectivity to Ti for polymerised hexane is increased by more than 20 times using each dual amplification process.