Engineering of Micro‐ and Nanostructured Surfaces with Anisotropic Geometries and Properties

Abstract

Widespread approaches to fabricate surfaces with robust micro- and nanostructured topographies have been stimulated by opportunities to enhance interface performance by combining physical and chemical effects. In particular, arrays of asymmetric surface features, such as arrays of grooves, inclined pillars, and helical protrusions, have been shown to impart unique anisotropy in properties including wetting, adhesion, thermal and/or electrical conductivity, optical activity, and capability to direct cell growth. These properties are of wide interest for applications including energy conversion, microelectronics, chemical and biological sensing, and bioengineering. However, fabrication of asymmetric surface features often pushes the limits of traditional etching and deposition techniques, making it challenging to produce the desired surfaces in a scalable and cost-effective manner. We review and classify approaches to fabricate arrays of asymmetric 2D and 3D surface features, in polymers, metals, and ceramics. Analytical and empirical relationships among geometries, materials, and surface properties are discussed, especially in the context of the applications mentioned above. Further, opportunities for new fabrication methods that combine lithography with principles of self-assembly are identified, aiming to establish design principles for fabrication of arbitrary 3D surface textures over large areas.

Strain-engineered manufacturing of freeform carbon nanotube microstructures

“…While symbiotic growth of the integrated circuit and microelectromechanical systems (MEMS) industries has enabled innovations in three-dimensional (3D) fabrication that leverage semiconductor processing tools, these methods, such as interference or inclined exposure lithography, are typically limited to arrays of identical structures [6][7][8] . Rapid prototyping methods such as direct laser writing, multiphoton lithography and focused ion beam milling can create arbitrary forms but are serial, and therefore have lower areal throughput 9,10 .…”

Self-assembly of micro/nanosystems across scales and interfaces

“…Though several implementations may be possible at each specific scale, across scales the embodiments tends to differ, even to a significant extent, due to force scaling effects and the consequent hierarchy among force magnitudes and ranges uniquely pertaining to each scale. In this regard, SA is foremostly suitable at (sub-)millimetric scales because of the variety and tuneability of interactions available -including gravitational, capillary, fluidic, electric, magnetic, hydrophobic, entropic -and the increasing freedom in design, fabrication and functionalization of components and substrates [5,[21][22][23]. In the next section, the SA of microand nanosystems is exemplified through three fluidic embodiments pertaining to three different physical scales.…”

External‐Field‐Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface

“…[1][2][3][4][5][6][7][8] The liquid-wetting behavior on a solid or liquid surface is mainly dependent on the chemical composition and surface roughness, which play important roles in liquid transport. [9][10][11][12][13][14][15][16] The wettability gradient of a surface for a liquid droplet with an asymmetrical contact angle (CA) can produce a driving force for liquid motion, which is generally generated by introducing a chemical or structure gradient. [17][18][19][20][21][22][23][24][25][26][27][28] External-field-responsive liquid transport has received extensive research interest owing to its important applications in microfluidic devices, biological medical, liquid printing, separation, and so forth.…”