Maskless, High‐Precision, Persistent, and Extreme Wetting‐Contrast Patterning in an Environmental Scanning Electron Microscope

Abstract

1 This is the pre-peer reviewed version of the following article:Liimatainen, V., Shah, A., Johansson, L.-S., Houbenov, N. and Zhou, Q. (2016), Maskless, High-Precision, Persistent, and Extreme Wetting-Contrast Patterning in an Environmental Scanning Electron Microscope. Small. doi:10.1002/smll.201503127, which Since the past decade, micro-and nanopatterns with high wetting contrast for water have been reported on natural [1,2] and man-made [3,4] surfaces. Such patterns have found uses in a diverse set of applications, including water collection from humid air mimicking desert beetles; [5] enhancing boiling heat transfer; [6] microelectromechanical systems (MEMS) assembly using surface tension-driven self-alignment; [7] arranging nanostructures in ordered arrays [8] for 2 nanophotonic devices e.g. antennas, filters and optical processing circuits; [9] transport of both droplets [10] and liquid flows [11] for lab-on-a-chip devices; and solving cross-contamination and cell migration problems in ultrahigh-density living cell microarrays. [12] Many highly successful methods utilizing well-developed technologies have been employed to produce those micro and nanoscale wetting features, from conventional photolithographic methods, laser interference lithography, [13,14] electron beam lithography (EBL), [15,16] to near-field scanning optical microscopy (NSOM), [17,18] microcontact printing (µCP) [19,20] and pulsed laser beams; [21,22] however, these techniques also have their limitations. For example, in conventional photolithography, sub-µm resolution requires expensive equipment and the wet processing steps may damage the often delicate surface structure of superhydrophobic substrates; laser interference lithography can only produce features in the shape of a few types of interference patterns; microcontact printing techniques use a stamping process that is challenging to apply on rough surfaces; [23] focused, pulsed laser beams have a resolution of few µm, limited by the beam spot size; and specific, photo-or electron sensitive materials are required for NSOM and EBL. The pursuit for an effective method of fabricating highresolution wetting patterns with extreme wetting contrast is still ongoing.One potential solution is direct electron beam writing, where the beam modifies the surface directly without any pattern-transferring layer or further processing steps. In previous works, the effect of electron beams on surface wetting properties has been studied; e.g. high-energy electron beams (> 500 keV) can tune the wettability of poly(ethylene terephthalate) (PET) films, [24] poly-l-lactic acid (PLLA), [25] rubber [26] and textile fabrics, [27] where the maximum changes in water contact angles varied from 15° to 32°; and low-energy electron beams (< 0.5 keV) [28,29] can increase the water contact angle by 71° on a silicon dioxide surface, and by 25° on a zinc oxide nanomaterial. In the aforementioned works, electron beam has not been controlled to produce wetting patterns in specific shapes on the surface. 3In this p...

Surface tension-driven self-alignment

“…Recently, electron beam was employed to achieve patterned wetting and create mm-sized superhydrophilic patterns on superhydrophobic substrates. 52 Hydrophobic sidewalls surrounding hydrophilic mesa-type receptors were also shown to improve liquid confinement and benefit the capillary self-alignment performance. 26,41 Similar observations were shown to apply to the surface conditioning of components.…”

Wetting Properties of Black Silicon Layers Fabricated by Different Techniques

“…Various patterning approaches are used to texture the silicon substrates, including conventional photolithography, electron-beam and colloidal lithography, sandblasting, templated deposition, and maskless electrochemical etching. [7][8][9] As a result, surface textures of various shapes are formed, including holes, columns, pillars, wires, needles, etc. The pursuit of an effective patterning approach is still ongoing.…”

Simple and Scalable Chemical Surface Patterning via Direct Deposition from Immobilized Plasma Filaments in a Dielectric Barrier Discharge

“…[ 13 , 14 , 15 , 16 ] Direct deposition/surface modification with energy beams is also common, but can be time‐consuming as they generally require low pressure environments and/or can only treat small areas. [ 17 , 18 ] In this realm, plasma technologies have been the tools of choice because they allow thin‐film etching and deposition. [ 19 , 20 ] In particular, dielectric barrier discharges (DBD) at atmospheric pressure are an attractive choice for industrial scale surface processing because they are scalable to large areas and can be easily implemented on process lines without the need for complex vacuum systems.…”