Showing papers by "Younan Xia published in 1998"

Macroporous Membranes with Highly Ordered and Three‐Dimensionally Interconnected Spherical Pores

Abstract: We have demonstrated the fabrication of highly ordered three-dimensional macroporous membranes with crystalline assemblies of monodispersed mesoscale particles (∼200 nm to ∼10 μm in diameter) as templates We filled the void spaces among the particles with a UV-curable liquid prepolymer by capillary action Subsequent solidification of the prepolymer and dissolution of the particles yielded a membrane film consisting of a highly organized and three-dimensionally interconnected framework of spherical pores The pores are uniform in size, with dimensions defined by the diameter of the particles The pores are completely exposed on both top and bottom surfaces of the membrane film In addition to those applications associated with conventional macroporous materials, the macroporous membranes fabricated here are potentially useful as photonic bandgap structures or as supports for the fabrication of diffractive optical sensors due to their specified and highly ordered structures

Fabrication of Three-Dimensional Macroporous Membranes with Assemblies of Microspheres as Templates

Abstract: Assemblies of polymer beads were used as templates to produce macroporous membranes of polymers and ceramics. These membranes consist of spherical pores whose sizes could be precisely controlled in...

Microfabrication, Microstructures and Microsystems

Abstract: This review gives a brief introduction to materials and techniques used for microfabrication. Rigid materials have typically been used to fabricate microstructures and systems. Elastomeric materials are becoming attractive, and may have advantages for certain types of applications. Photolithography is the most commonly used technique for the fabrication of structures for microelectronic circuits, microelectromechanical systems, microanalytical devices and micro-optics. Soft lithography represents a set of non-photolithographic techniques: it forms micropatterns of self-assembled monolayers (SAMs) by contact printing and generates microstructures of polymers by contact molding. The aim of this paper is to illustrate how non-traditional materials and methods for fabrication can yield simple, cost-effective routes to microsystems, and now they can expand the capabilities of these systems.

Use of Electroless Silver as the Substrate in Microcontact Printing of Alkanethiols and Its Application in Microfabrication

Abstract: We have employed electroless deposition to prepare smooth films (mirrors) of silver that could be used as substrates in microcontact printing (μCP) of alkanethiols. Good-quality SAMs of hexadecanethiolate were formed on thin films of electroless silver by printing with an elastomeric stamp; these SAMs were effective resists in protecting the underlying silver from etching in an aqueous ferricyanide solution. Thin films of silver prepared by electroless deposition show a granular morphology (the grain sizes are ∼30−60 nm) and have a rougher surface than those prepared using e-beam or thermal evaporation. As a result, hexadecanethiol liquid spreads more rapidly on electroless silver than on evaporated silver when μCP is carried out in air. This process of reactive spreading limits the resolution and fidelity of pattern transfer to electroless silver films by μCP, but could also be used as a convenient method for reducing the sizes of features of SAMs generated using μCP. The smallest features that we have f...

Photolithography with transparent reflective photomasks

Abstract: A new type of photomask was fabricated by casting a prepolymer of a transparent, elastomeric polymer (polydimethylsiloxane, PDMS) against a Si(100) master whose surface has been patterned with V-shaped trenches or pyramidal pits using anisotropic etching. The PDMS replica, when placed in contact with a film of photoresist and illuminated, acts as a photomask. The sidewalls of the trenches and pits in the silicon master meet with the plateaus in dihedral angles of 54°; as a result, the PDMS replica selectively blocks the incident light in regions where it has sloping features by total internal reflection, and acts as a reflective contact mask for photolithography. The feasibility of this new type of photomask has been demonstrated by the fabrication of micropatterns in photoresist (and in an underlying silicon substrate) with smaller feature sizes and higher complexities than those present on the original chrome mask used in patterning the silicon master. The patterns produced using these elastomeric photo...

Fabrication of microstructures using shrinkable polystyrene films

Abstract: This paper demonstrates the combination of reactive ion etching (RIE) and shrinkable polystyrene (PS) films to reduce the feature size of microstructures and to generate microstructures with high aspect ratios on both planar and curved surfaces. A shrinkable PS film is patterned with relief structures using RIE through a physical mask. The patterned surface is heated and shrinks. After shrinking, the size of microstructures decreases by a factor of four to five, and their height increases by a factor of ∼ 20. Thermal shrinkage results in a 100-fold increase in the aspect ratio of the patterned microstructures in the PS film. Microstructures as high as ∼ 126 μm with aspect ratio of ∼9.5 have been generated. The smallest structures fabricated using this strategy are rectangular pits ∼ 1.4 μm × 1.7 μm in size. Fabrication of microstructures on curved surfaces has been demonstrated by folding a patterned PS film and allowing it to shrink in place.