Liguo Gao

Simple approach to wafer-scale self-cleaning antireflective silicon surfaces.

A simple approach to wafer-scale self-cleaning antireflective hierarchical silicon structures is demonstrated. By employing the KOH etching and silver catalytic etching, pyramidal hierarchical structures were generated on the crystalline silicon wafer, which exhibit strong antireflection and superhydrophobic properties after fluorination. Furthermore, a flexible superhydrophobic substrate was fabricated by transferring the hierarchical Si structure to the NOA 63 film with UV-assisted imprint lithography. This method is of potential application in optical, optoelectronic, and wettability control devices.

Biomimetic Antireflective Si Nanopillar Arrays

The Fresnel reflection of incident light comes from the large refractive index discontinuity at the interface of two media. The high reflective index of Si results in the reflection of up to 40% of the incident light, which severely limits the performance of Si based optical and optoelectronic devices, such as solar cells, displays, and light sensors. Thin film coatings with intermediate or gradient refractive indices are commonly utilized to suppress undesired Fresnel reflection. However, the stability problems induced by adhesiveness and thermal mismatch are often associated with such approaches. Since the corneas of nocturnal-moth eyes were found to have antireflective properties, surface-relief arrays with dimension smaller than the wavelength of incident light have been considered an alternative to thin-film coatings, which are more stable and durable than surface coatings since only one material is involved. In the last decade, increasing effort has been devoted to the fabrication of such surface antireflection structures. Many different structures, such as nanorods and nanopillars, gratings, porous structures, and nanotubes have been created in order to suppress surface reflection. The basic purpose of this technique is to introduce a refractive index gradient between air and a substrate material by creating a structured layer. Reflection can be substantially suppressed for a wide spectral bandwidth and over a large field of view. Due to the applications of Si in modern optical and optoelectronic industry, a variety of techniques for producing subwavelength ‘‘moth eye’’ structures on Si have been proposed, such as electron-beam lithography, laser interference lithography, and nanoimprint lithography. However, these

A Strategy for Patterning Conducting Polymers Using Nanoimprint Lithography and Isotropic Plasma Etching

Conducting polymer (CP) patterns with feature sizes of submicrometer to nanometer dimensions have attracted considerable attention due to their applications in light-emitting diodes (OLEDs), organic field effect transistors (OFETs), polymeric electrochromic devices, sensors, and biotechnology. In the last decade, the integration of two or more functional materials together is of increasing interest because materials with multiple components may exhibit integrative properties that single component materials do not possess. For example, CPs have been integrated with doping agent molecules or nanoparticles in order to improve properties or achieve multiplex character. Efforts to prepare conducting polymer patterns have mainly focused on photochemical patterning, microcontact printing (mCP), scanning probe lithography (SPL), electron-beam lithography (EBL), and dip-pen nanolithography. However, most of the techniques are incapable of integrating high resolution with high throughput. Nanoimprint lithography (NIL), which has gained significant attention due to its low cost and high throughput, is based on the mechanical deformation of the resist polymer by heating above the glass transition temperature (Tg) or by UVcrosslinking. By taking the CP or its mixture as resist layers and a subsequent reactive ion etching process, CPs have been patterned using NIL. However, NIL can only be applied on polymers that have a Tg or are UV-crosslinkable.

Fabrication of TiO2 Arrays Using Solvent-Assisted Soft Lithography

We present a simple solvent-assisted soft lithography method to fabricate titania (TiO(2)) patterns. The dimensions of the TiO(2) features can be controlled by adjusting the concentration of the solution, the solvent evaporation duration, and temperature. This method may provide a facile route for fabricating large area patterns of metal oxide.

Creating bicolor patterns via selective photobleaching with a single dye species.

Bicolor fluorescent pattern in thin polymer film is fabricated via a photobleaching process. Dye molecules exhibit monomer emission when they are dispersed inside the polymer and aggregate emission when they are on the surface of the polymer. Thus, a mixed emission of monomer and aggregate can be obtained by evaporating a single dye species on the polymer film. Bicolor pattern in thin polymer film is readily formed by selective photobleaching. This process is particularly attractive for the fabrication of bicolor patterns on flat substrates using a single dye species, which is of potential applications in photonic/electronic devices.

Anisotropic growth of organic semiconductor based on mechanical contrast of pre-patterned monolayer

Site-selective anisotropic growth of perylene film is achieved by using a striped Langmuir–Blodgett (LB) monolayer as an alignment layer. The stripes significantly increase the grain size along the stripe direction due to increased diffusion length. By controlling the grain boundaries and the molecular alignment, a mobility anisotropic ratio of ∼10 for the current flow parallel and perpendicular to the stripes has been observed.

Fabrication of split-ring resonators by tilted nanoimprint lithography

An efficient fabrication technique for large area periodic metallic split-ring arrays has been demonstrated by the combination of tilted nanoimprint lithography and nanotransfer imprinting. The feature size of the split-rings can be adjusted by varying the key geometry parameters of the original imprinting mold. Due to the flexible nature of PDMS molds, these arrays can be patterned on curved surfaces. The molds for nanoimprint lithography and nanotransfer imprinting can be used multiple times without a loss of fidelity.

Fabrication of multicolor patterns with a single dye species on a polymer surface.

Multicolored patterns can be fabricated by evaporating a single dye species on a prepatterned polymer substrate. The ratios of dye to polymer are different on protrusion and recess areas of the prepatterned surface, which can result in different aggregates and emissions. The polymer substrate was prepatterned using nanoimprint lithography (NIL) without any further process. This method may provide a facile route for fabricating large-area multicolored patterns.