Hierarchical structure formation and pattern replication induced by an electric field

Morariu, M.; Voicu, Nicoleta E.; Schäffer, Erik; Lin, Zhiqun; Russell, Thomas P.; Steiner, Ullrich

doi:10.1038/nmat789

Cited by 265 publications

(264 citation statements)

References 14 publications

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“…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)(11)(12)(13).…”

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confidence: 99%

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

Grilli

Coppola

Vespini

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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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...

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confidence: 99%

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

Grilli

Coppola

Vespini

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…[ 16 ] Here, we have applied this principle to polymer trilayers in our HEHD approach. The structure formation in a multilayer fi lm can be controlled by carefully designing the layer sequence.…”

Section: Resultsmentioning

confidence: 99%

Hierarchical Electrohydrodynamic Structures for Surface‐Enhanced Raman Scattering

2012

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Surface enhanced Raman scattering (SERS) is a well‐established spectroscopic technique that requires nanoscale metal structures to achieve high signal sensitivity. While most SERS substrates are manufactured by conventional lithographic methods, the development of a cost‐effective approach to create nanostructured surfaces is a much sought‐after goal in the SERS community. Here, a method is established to create controlled, self‐organized, hierarchical nanostructures using electrohydrodynamic (HEHD) instabilities. The created structures are readily fine‐tuned, which is an important requirement for optimizing SERS to obtain the highest enhancements. HEHD pattern formation enables the fabrication of multiscale 3D structured arrays as SERS‐active platforms. Importantly, each of the HEHD‐patterned individual structural units yield a considerable SERS enhancement. This enables each single unit to function as an isolated sensor. Each of the formed structures can be effectively tuned and tailored to provide high SERS enhancement, while arising from different HEHD morphologies. The HEHD fabrication of sub‐micrometer architectures is straightforward and robust, providing an elegant route for high‐throughput biological and chemical sensing.

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“…To define the number, position, and distances of the objects on a surface, it is often necessary to direct their assembly by means of suitable prepatterned substrates or stamps. Nanopatterned surfaces have been fabricated by nanoimprinting (Wang et al, 1999), contact printing (Kumar & Whitesides, 1993;Xu et al, 2007), microtransfer molding (Zhao et al, 1996), pattern replication induced by an electric field (Morariu et al, 2003), lithographically induced self-construction , grid-assisted self-organization (Cavallini et al, 2002), and self-assembly among others. Most of these techniques rely on a soft mould or stamp (Quake & Sherer, 2000).…”

Section: Introductionmentioning

confidence: 99%