3D lithography by rapid curing of the liquid instabilities at nanoscale

Abstract

In liquids realm, surface tension and capillarity are the key forces driving the formation of the shapes pervading the nature. The steady dew drops appearing on plant leaves and spider webs result from the minimization of the overall surface energy [Zheng Y, et al. (2010) Nature 463:640-643]. Thanks to the surface tension, the interfaces of such spontaneous structures exhibit extremely good spherical shape and consequently worthy optical quality. Also nanofluidic instabilities generate a variety of fascinating liquid silhouettes, but they are however intrinsically short-lived. Here we show that such unsteady liquid structures, shaped in polymeric liquids by an electrohydrodynamic pressure, can be rapidly cured by appropriate thermal treatments. The fabrication of many solid microstructures exploitable in photonics is demonstrated, thus leading to a new concept in 3D lithography. The applicability of specific structures as optical tweezers and as novel remotely excitable quantum dots-embedded microresonators is presented.A wide variety of lithographic techniques have been developed for fabricating 3D structures (1-5), such as soft lithography (6) that allows one to develop lab-on-chip devices with applications ranging from organic light emitting diode to biology and biochemistry (7). Among others, "capillary-force lithography" is able to nicely pattern polymers at nano-/microscale, but with a very low aspect ratio, in a single step and avoiding the use of external forces (8). Other approaches generate self-patterned structures by using destabilizing forces produced by electric fields, namely electrohydrodynamic (EHD) lithography (9). In EHD lithography, amazing polymeric patterns have been reported, demonstrating the possibility of controlling the process with high accuracy. This method appears suitable only for a few types of periodic patterns having a relatively low aspect ratio (i.e., pillars, dots, and lines). In fact, the control of liquid film instabilities is a demanding task as very little perturbations could drag the nanofluidic system toward nonfully predictable configurations. Such occurrence, for high aspect-ratio features, would prevent the achievement of the expected final steady state. The EHD lithography is usually performed at temperatures above the glass transition of the polymer film [typically polystyrene or poly (methyl methacrylate)], obtaining permanent microstructures by slow annealing and successive cooling, taking hours (10-13).In general, the hydrodynamic techniques produce steadystate structures resulting from the equilibrium state of a specific fluidic effect. Conversely, the core of our approach consists in "rapid-curing" temporary structures, which evolve continuously under specific fluidic instabilities, by a fast heating procedure. The interesting aspect of this approach is that it gives access to very intriguing fluid shapes, occurring in unsteady fluid physics at nanoscale, which could be very useful in modern science. As investigated recently, breakup of viscoelastic filaments...

3D Printing of Transparent and Conductive Heterogeneous Hydrogel–Elastomer Systems

“…For applications where a higher resolution is required, many techniques and products are available to adjust the rheological behavior of the PDMS precursor. [5,24,[43][44][45][46][47] The development of the hydrogel precursor for our extrusion printing was more demanding and required a balance between conductivity, stability, and rheological characteristics.…”

Modulating patterns of two-phase flow with electric fields

“…BOAS flow, owing to its special flow structures, may be particularly useful in some applications, such as optical-sensor fabrication. 21 In BOAS flow, queues of droplets are connected by a series of liquid threads, which makes them look like a fluid necklace with regular periods. [21][22][23][24][25] The BOAS pattern is easily found in nature, such as silk beads and cellular protoplasm, and is often encountered in industrial processes as well, such as in electrospinning and anti-misting.…”

“…21 In BOAS flow, queues of droplets are connected by a series of liquid threads, which makes them look like a fluid necklace with regular periods. [21][22][23][24][25] The BOAS pattern is easily found in nature, such as silk beads and cellular protoplasm, and is often encountered in industrial processes as well, such as in electrospinning and anti-misting. 21,22 In general, it is thought that BOAS structure occurs mostly in viscoelastic fluids 22 and is an unstable structure, which evolves continually and breaks eventually.…”

Meniscus confined fabrication of multidimensional conducting polymer nanostructures with scanning electrochemical cell microscopy (SECCM)

“…4,5 While many fabrication methods abound, 6 probebased techniques, such as dip pen 7 and fountain pen 8 lithography, electrospinning, 9 scanning electrochemical microscopy 10,11 and meniscus-based methods [12][13][14][15][16][17][18][19][20] offer exciting new ways to fabricate novel structures. Previous meniscus-based fabrication techniques 20 have made structures that have tended to make contact with a substrate at a limited number of points.…”

“…Previous meniscus-based fabrication techniques 20 have made structures that have tended to make contact with a substrate at a limited number of points. [12][13][14][15][16][17][18][19][20] Here, we show how a dual barrel (theta) pipet, used in scanning electrochemical cell microscopy (SECCM) mode, [21][22] provides a positional feedback mechanism to control the distance between the end of the pipet 25 and the surface. This allows extended multidimensional nanostructures to be formed and prevents pipet crash, or the meniscus becoming detached from, the surface (vide infra) during patterning.…”