Enoch Kim

Complex Optical Surfaces Formed by Replica Molding Against Elastomeric Masters

Complex, optically functional surfaces in organic polymers can be fabricated by replicating relief structures present on the surface of an elastomeric master with an ultraviolet or thermally curable organic polymer, while the master is deformed by compression, bending, or stretching. The versatility of this procedure for fabricating surfaces with complex, micrometer- and submicrometer-scale patterns was demonstrated by the production of (i) diffraction gratings with periods smaller than the original grating; (ii) chirped, blazed diffraction gratings (where the period of a chirped grating changes continuously with position) on planar and curved surfaces; (iii) patterned microfeatures on the surfaces of approximately hemispherical objects (for example, an optical surface similar to a flys eye); and (iv) arrays of rhombic microlenses. These topologically complex, micropatterned surfaces are difficult to fabricate with other techniques.

Microscopic patterning of orientated mesoscopic silica through guided growth

The supramolecular assembly of surfactant molecules at a solid–liquid interface can produce tubular structures with diameters of around 10 nm (refs 1,2,3,4), which can be used for the templated polymerization of mesoporous silica thin films. The orientation of the tubules depends primarily on the nature of the substrate–surfactant interaction. These nanostructured films hold much promise for applications such as their use as orientated nanowires, sensor/actuator arrays and optoelectronic devices. But a method of patterning the tubules and orientating them into designed arrangements is required for many of these possibilities to be realized. Here we describe a method that allows the direction of growth of these tubules to be guided by infiltrating a reaction fluid into the microcapillaries of a mould in contact with a substrate. An electric field applied tangentially to the surface within the capillaries induces electro-osmotic flow, and also enhances the rates of silica polymerization around the tubules by localized Joule heating. After removal of the mould, patterned bundles of orientated nanotubules remain on the surface. This method permits the formation of orientated mesoporous channels on a non-conducting substrate with an arbitrary microscopic pattern.

Microcontact Printing of Alkanethiols on Silver and Its Application in Microfabrication

Microcontact printing was used to generate patterned self-assembled monolayers of alkanethiolates on the surfaces of evaporated films of copper. These patterned SAMs could be directly used as ultrathin resists that protected the underlying copper from etching in aqueous solutions of FeCl3/HCl or FeCl3/NH4Cl. Arrays of junctions of Ag/Ag2O/Cu were fabricated using a multistep procedure that combines metal evaporation, microcontact printing, and selective etching.

Pattern transfer to silicon by microcontact printing and RIE

Microcontact printing techniques employing self-assembled alkanethiol monolayers in the production of metal masks have been combined with reactive ion etch for subsequent pattern transfer to silicon. Silicon feature sizes of about 300 nm have been demonstrated. Some inadequacies in the self-assembled monolayers (SAMs)-formed metal masks have been characterized by electron microscopy. Particularly, nickel etch control and metal feature edge definition remain problems to be solved if the process is to be employed in submicron feature production. Nickel patterns produced in the process and used as masks without the gold overlayer were successful as masks in the reactive ion etching (RIE) process. They also appear to give a somewhat improved edge definition over processes in which the gold layer remains.

Fabrication of micrometer-scale structures on GaAs and GaAs/AlGaAs quantum well material using microcontact printing

Microcontact printing (CP) was used in conjunction with self-assembled monolayers (SAMs) of hexadecanethiolates to fabricate gold etch masks on GaAs and GaAs/AlGaAs quantum-well substrates; patterns in the mask were transferred into the semiconductor with an anisotropic dry chemical-etch process. The measured luminescence efficiency of the etched features in GaAs/AlGaAs was similar to that of samples patterned using conventional lithography; this observation indicates that no mechanical or chemical damage is incurred in the CP process.

Soft lithography and surface chemistry: enabling tools for new bioassays

The process of drug discovery can be accelerated by increasing the information content of bioassays and by employing assay platforms that are amenable to high throughput screening techniques. In this paper, we demonstrate how the combination of soft lithography with controlled surface chemistry achieves these goals in a wide spectrum of bioassays. A number of soft lithographic methods can be used to generate micro-structures for the purposes of increasing assay density, diversity of test conditions and improving assay detection qualities. In addition, soft lithography, combined with specific surface chemistry modification procedures and protein engineering, may be used to control the localized molecular and biological properties of substrates, thereby enabling the development of new types of bioassays. The developed methodologies are simple, easily implemented, and lend themselves well to automation. Experimental results and prototypes are presented to illustrate the capabilities of these new techniques. For example, soft lithography and surface chemistry are employed for chemically patterning substrates, stenciling biological entities onto substrates and confining solutions. As a result, information-rich, highdensity bioassays can be obtained where biological targets, surface properties and medium solutions are carefully determined and controlled.