A versatile approach to fabricate ordered heterogeneous bull's-eye-like microstructure arrays

A simple method for fabricating patterned curvilinear microstructures in poly(dimethylsiloxane) by selective wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three-stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first-generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip-coating process, an ordered polyethylene glycol (PEG) polymer-dot array forms on the HDT-patterned gold substrate. Finally, based on a REM process, the PEG-dot array on gold substrate is used to fabricate a second-generation PDMS stamp with microcavity array, and the second-generation PDMS stamp is used to generate third-generation PDMS stamp with microbump array. These fabricated new-generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new-generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.

Fabrication of heterogeneous double-ring-like structure arrays by combination of colloidal lithography and controllable dewetting

We report a novel technique for fabricating the heterogeneous double-ring-like structural array by colloidal lithography and two-step dewetting process. First, the 2D non-closed-packed (ncp) silica sphere arrays were obtained by lift-up lithography. Then, the ncp sphere array transferred onto the Rhodamine B (RB)@poly(vinyl alcohol) (PVA) film was used for the mask during reactive ion etching (RIE) process. Sequentially, the substrate with RB@PVA ring-like structure arrays under the silica sphere was dip-coated from poly(N-vinylcarbazole) (PVK) chloroform solution with certain concentration. Due to the presence of ordered 2D sphere arrays, the two-step dewetting behavior happened on top of the sphere and the silicon wafer between adjacent spheres, respectively. After removing the silica sphere arrays by hydrofluoric acid, the RB@PVA/PVK heterogeneous double-ring-like structure array was exhibited on the substrate. We characterized this particular structure by SEM, AFM, and fluorescence spectrum, which prove that both the inner RB@PVA ring and outer PVK ring are independent without any reaction. Accordingly, this method could be extended to other materials owing to its universality. These unique structural arrays have potential application in optoelectronic devices, surface photocatalysis, and surface enhanced Raman scattering (SERS).

Ordered polymeric microhole array made by selective wetting and applications for electrochemical microelectrode array

In this paper, we report the microelectrode array fabrication using selective wetting/dewetting of polymers on a chemical pattern which is a simple and convenient method capable of creating negative polymeric replicas using polyethylene glycol (PEG) as a clean and nontoxic sacrificial layer. The fabricated hole-patterned polypropylene film on gold demonstrated enhanced electrochemical properties. The chemical pattern is fabricated by microcontact printing using octadecanethiol (ODT) as an ink on gold substrate. When PEG is spin-cast on the chemical pattern, PEG solution selectively dewets the ODT patterned areas and wets the remaining bare gold areas, leading to the formation of arrayed PEG dots. A negative replicas of the PEG dot array is obtained by spin-coating of polypropylene (PP) solution in hexane which preferentially interacts with the hydrophobic ODT region on the patterned gold surface. The arrayed PEG dots are not affected the during PP spin-coating step because of their intrinsic immiscibility. Consequently, the hole-patterned PP film is obtained after PEG removal. The electrochemical signal of the PP film demonstrates the negligible leakage current by high dielectric and self-healing of defects on the chemical pattern by the polymer. This method is applicable to fabrication of microelectrode arrays and possibly can be employed to fabricate a variety of functional polymeric structures, such as photomasks, arrays of biomolecules, cell arrays, and arrays of nanomaterials.

Thin-film-based nanoarchitectures for soft matter: controlled assemblies into two-dimensional worlds

Controlling the organization of molecular building blocks at the nanometer level is of utmost importance, not only from the viewpoint of scientific curiosity, but also for the development of next-generation organic devices with electrical, optical, chemical, or biological functions. Self-assembly offers great potential for the manufacture of nanoarchitectures (nanostructures and nanopatterns) over large areas by using low-energy and inexpensive spontaneous processes. However, self-assembled structures in 3D media, such as solutions or solids, are not easily incorporated into current device-oriented nanotechnology. The scope of this review is therefore to introduce the expanding methodology for the construction of thin-film-based nanoarchitectures on solid surfaces and to try to address a general concept with emphasis on the availability of dynamic interfaces for the creation and manipulation of nanoarchitectures. In this review, the strategies for the construction of nanostructures, the control and manipulation of nanopatterns, and the application of nanoarchitectures are described; the construction strategies are categorized into three classes: i) π-conjugated molecular assembly in two dimensions, ii) bio-directed molecular assembly on surfaces, and iii) recent thin-film preparation technologies.