Room-temperature Imprinting Research Articles

Room temperature imprinting of water-based microparticulate inks for realizing glass microfluidic channels

The combination of imprinting and extrusion overprinting of composite glass materials offers a pathway for the fabrication of fully integrated functional microfluidic devices. Utilizing novel low-temperature phosphate glasses, originally developed for 3D extrusion printing, imprinting now has been achieved with soft stamps. The current hybrid process demonstrates superior resolution compared to previously reported extrusion techniques, presenting possibilities for applications such as open microfluidic channels that can subsequently be sealed by extrusion printing. The water-based microparticle glass-ink enables patterning at room temperature and its solidification occurring through water evaporation within the glass particle scaffold. Following the demolding, sintering is conducted at a temperature of 485 °C, resulting in dense glass elements with porosity levels below 1 %. For straightforward microfluidic channel structures featuring channels ranging from 100-200 µm in width, the shape is fully preserved during demolding and sequential annealing. The shrinkage observed is almost isotropic. The channels were successfully tested in an open microfluidic setup and initial tests were performed with the closed channels.

Micro-Nano Machining TiO2 Patterns without Residual Layer by Unconventional Imprinting

Usually, the residual layer remains after patterning TiO2 sol. The existence of the TiO2 residual layer in the non-pattern region affects its application in microelectronic devices. Here, a simple method, based on room-temperature imprinting, to fabricate a residual-free TiO2 pattern is proposed. The thermoplastic polymer with Ti4+ salt was fast patterned at room temperature by imprinting, based on the different interfacial force. Then, the patterned thermoplastic polymer with Ti4+ salt was induced into the TiO2 lines without residual layer under the hydrothermal condition. This method provides a new idea to pattern metal oxide without residual layer, which is potentially applied to the gas sensor, the optical detector and the light emitting diode.

Fluorescence enhancement of strip patterned silver nanoparticle platforms prepared by room-temperature imprinting technique

Fluorescence enhancement of strip patterned silver nanoparticle platforms prepared by room-temperature imprinting technique

Patterning thermoplastic polymers by fast room-temperature imprinting

To avoid the high-temperature process of thermal imprinting, the room-temperature imprint lithography was proposed to pattern thermoplastic polymers. However, the room-temperature imprint lithography is still limited by rigorous condition of high pressure and wasting time. In order to overcome the above-mentioned disadvantages, we have introduced a fast (5 s) imprint method, which is based on the difference of two interfacial forces, to pattern thermoplastic polymers under room-temperature without additional pressure. This method is appropriate for the flat substrate, the curved substrate and the flexible substrate. Furthermore, we also have successfully fabricated 3D hierarchical patterns with antireflection by this method.

Room temperature direct imprinting of porous glass prepared from phase-separated glass

This work describes a room-temperature imprinting of nanoporous glass prepared by selective chemical etching of phase-separated glass. A highly porous (58%) and highly transparent (>90%) porous glass layer can be formed on a transparent phase-separated glass substrate. It is shown that the lateral resolution of the imprinting is a few tens of nanometers. As the porosity increases, the imprint depth increases and reaches up to 90% of the height of the mold pattern. The porous glass has a wider transmittance window (300–2700 nm) and a higher thermal durability (∼500 °C) than other materials used for imprinting. The technique has various potential applications such as diffraction optical elements, waveguides, biosensors, and microfluidic devices.

Fabrication of Micropatterns on Silica Glass by a Room-Temperature Imprinting Method

A nanocomposite was prepared from fumed silica and PVA. Investigation of the morphology of the composite by TEM and electron energy-loss spectroscopy reveals that the nanocomposite consists of homogeneously dispersed SiO2 nanoparticles and PVA. Micropatterns on the nanocomposite were fabricated by room-temperature imprinting. Micropatterned silica glass was obtained by sintering the nanocomposite at 1100°C in air.

Room-Temperature Nanoimprinting Using Liquid-Phase Hydrogen Silsesquioxane with Hard Poly(dimethylsiloxane) Mold

A new room-temperature imprinting method was developed using liquid-phase hydrogen silsesquioxane (HSQ) with a hard poly(dimethylsiloxane) (h-PDMS) mold. The simultaneous imprinting of arbitrary patterns including both submicron and greater than 100 µm patterns on a 4-in. wafer were replicated at room-temperature and a low pressure with high throughput, because the solvent in HSQ gradually evaporated through the pores of the h-PDMS mold. A bilayer structure was successfully fabricated using as HSQ pattern as an etching mask without removing the residual layer.

Patterning of Layer-by-Layer Assembled Organic−Inorganic Hybrid Films: Imprinting versus Lift-Off

Layer-by-layer (LbL) assembled organic-inorganic poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH)/ Au nanoparticle hybrid films are patterned by using Norland Optical Adhesive 63 (NOA 63) polymer molds. Depending on the rigidity of the hybrid films, their patterning can be realized by a room-temperature imprinting or lift-off process. For [(PAA/PAH)1-(Au nanoparticle/PAH)3]*10 and [(PAA/PAH)3-(Au nanoparticle/PAH)3]*5 films which have a low content of Au nanoparticles, the films can be imprinted at room temperature to form patterned films with large areas because of the compressibility and fluidity of the films under high pressure. The Au nanoparticle/PAH films, which have an extremely high content of Au nanoparticles and are fragile, can be patterned by a lift-off process during which the film contacted with the NOA 63 mold was peeled off because of the strong adhesion between the film and the mold and the fragility of the film. The complementary room-temperature imprinting and lift-off methods with polymer NOA 63 molds provide facile and general ways to pattern LbL assembled organic-inorganic films with various film compositions.

Adhesive Force Assisted Imprinting of Soft Solid Polymer Films by Flexible Foils

We report a simple, rapid, room temperature, pressure-less and large area (approximately cm2) imprinting technique for high fidelity patterning of soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, both on planar and curved surfaces. The key element of the method is the use of patterned thin flexible foils that readily and rapidly attain a conformal contact with soft (shear modulus < 0.1 MPa) solid surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous elastic deformations of the surface on the scale of the features. For example, we used the protective aluminum foils of commercial data storage discs, both with or without data stored, for micron and sub-micron pattern transfer. The patterns are made permanent by UV-ozone treatment (for PDMS) or by controlled drying (for hydrogels). Interestingly, elastic contact imprinting of very thin (< 300 nm) films results in about 50% miniaturization of the original foil feature sizes. Complex two dimensional patterns could also be formed even by using a simple one dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

Cell Adhesion Properties of Patterned Poly(acrylic acid)/Poly(allylamine hydrochloride) Multilayer Films Created by Room-Temperature Imprinting Technique

Patterned poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) multilayer films with line structures of different lateral size and vertical height were fabricated by a room-temperature imprinting technique, and their cell adhesion properties were investigated. The nonimprinted PAA/PAH multilayer films are cytophilic toward NIH/3T3 fibroblasts and HeLa cells whether PAA or PAH is the outer most layer. In contrast, the PAA/PAH multilayer films with a 6.5-microm-line/3.5-microm-space pattern structure are cytophobic toward NIH/3T3 fibroblasts and HeLa cells when the height of the lines is 1.29 microm. By either increasing the lateral size of the patters to 69-microm-line/43-mum-space or decreasing the height of the imprinted lines to approximately 107 nm, imprinted PAA/PAH multilayer films become cytophilic. This kind of transition of cell adhesion behavior derives from the change of the physical pattern size of the PAA/PAH multilayer films and is independent of the chemical composition of the films. The easy patterning of layer-by-layer assembled polymeric multilayer films with the room-temperature imprinting technique provides a facile way to tailor the cellular behavior of the layered polymeric films by simply changing the pattern dimensions.

Soft lithography meets self-organization: Some new developments in meso-patterning

This is a brief review of our recent and ongoing work on simple, rapid, room temperature, pressure-less and large area (∼ cm2) imprinting techniques for high fidelity meso-patterning of different types of polymer films. Examples include soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, thermoplastics like polystyrene (PS), polymethylmethacrylate (PMMA) etc both on planar and curved surfaces. These techniques address two key issues in imprinting: (i) attainment of large area conformal contact with the stamp, especially on curved surfaces, and (ii) ease of stamp detachment without damage to the imprinted structures. The key element of the method is the use of thin and flexible patterned foils that readily and rapidly come into complete conformal contact with soft polymer surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous deformations of the film surface on the scale of the features. Complex two-dimensional patterns could also be formed even by using a simple one-dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

Room-Temperature Imprinting Poly(acrylic acid)/Poly(allylamine hydrochloride) Multilayer Films by Using Polymer Molds

Layer-by-layer assembled polyelectrolyte multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) have been successfully patterned by room-temperature imprinting using a Norland Optical Adhesives (NOA 63) polymer mold. The proper amount of water in the PAA/PAH multilayer film can decrease the viscosity of the film and facilitate the imprinting. Many factors, such as imprinting pressure, length of imprinting time, and the structure and size of the patterns in the polymer mold, can produce an influence on the final imprinted pattern structures on multilayer films. A high imprinting pressure of 100 bar and elongated imprinting time of several hours is needed to achieve a patterned PAA/PAH multilayer film with a feature size of several tens of micrometers. With a twice imprinting, grid structures can be successfully produced when a NOA 63 mold having line structures is used. Room-temperature imprinting by using polymer NOA 63 mold provides a facile way to fabricate layered polymeric films with various kinds of pattern structures.

Room Temperature Mechanical Thinning and Imprinting of Solid Films

The mechanical patterning of thin films has received recent attention due to significant potential for efficient nanostructure fabrication. For solid films, mechanically thinning wide areas remains particularly challenging. In this work, we introduce a new plastic ratchet mechanism involving small amplitude (<10 nm), oscillatory shear motion of the forging die. This isothermal mechanism significantly extends mass transport across surfaces, broadening the scope of nanoscale processing for a potentially wide class of solid ductile materials.

Contrast modified room-temperature imprint lithography

Contrast modified room-temperature imprinting that can enhance the penetration depth of pattern, lower the applied pressure, and enable complete removal of the residual layer in the pattern window is developed. It is based on the contrast modification of the intensity of the light illuminated on the imprinted pattern. The contrast modification is made possible by the induction of intensity contrast that is caused by the total internal reflection of the light impinging on the slightly imprinted pattern structure. A condition for successful pattern formation is established through a simple geometric model and experimental results.

Room-temperature imprint lithography by solvent vapor treatment

We demonstrate room-temperature nanoimprint lithography using solvent vapor treatment of the polymer film on a substrate. In this method, the film treated with the solvent vapor is pressed with a mold at room temperature, requiring no heating that has been needed for the lithography. We show that the mold or mask patterns down to 60 nm can well be transferred onto the polymer film without any problem of the polymer adhering to the mold. The vapor treatment of the dried polymer film results in lowering both the viscosity and the glass transition temperature, thereby allowing for the room-temperature lithography. This room-temperature imprinting should make the imprint lithography more valuable for practical applications.