Sen-Yeu Yang

Enhancing Surface Plasmon Detection Using Template-Stripped Gold Nanoslit Arrays on Plastic Films

Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, high-throughput and low-cost fabrication techniques are the main issues which should be addressed. In this study, chip-based nanostructures for intensity-sensitive detection were fabricated and tested using a thermal-annealing-assisted template-stripping method. Large-area uniform nanoslit arrays with a 500 nm period and various slit widths, from 30 to 165 nm, were made on plastic films. A transverse magnetic-polarized wave in these gold nanostructures generated sharp and asymmetric Fano resonances in transmission spectra. The full width at half-maximum bandwidth decreased with the decrease of the slit width. The narrowest bandwidth was smaller than 10 nm. Compared to nanoslit arrays on glass substrates using electron-beam lithography, the proposed chip has a higher intensity sensitivity up to 10367%/RIU (refractive index unit) and reaches a figure of merit up to 55. The higher intensity sensitivity for the template-stripped nanostructure is attributed to a smoother gold surface and larger grain sizes on the plastic film, which reduces the surface plasmon propagation loss.

Fabrication of a nano/micro hybrid lens using gas-assisted hot embossing with an anodic aluminum oxide (AAO) template

This paper reports a novel and effective method for the fabrication of a polymeric nano/micro hybrid lens array. The nanostructure and microlens arrays are fabricated on the same polycarbonate (PC) substrate by hot embossing in sequence. First, an anti-reflection PC film with sub-wavelength nanostructures is fabricated using an anodic aluminum oxide (AAO) template. The anti-reflection characteristic of nanostructures on the PC film is evaluated. Then an array of convex microlenses is formed from the nanostructured PC film using a stainless steel mold with a microhole array. Both processes employ gas-assisted hot embossing to perform the partial protrusion of the film into nano-sized or micro-sized holes in the AAO template and steel mold. The optical property of the microlens has been verified. This proposed technique has proven its potential for effectively fabricating a nano/micro hybrid lens array on a polymeric substrate.

A novel method for rapid fabrication of microlens arrays using micro-transfer molding with soft mold

This paper reports a novel technique for fabricating polymeric microlens arrays based on micro-transfer molding with soft mold. The soft mold with a micro-holes array is made by casting a pre-polymer of PDMS against a silicon master. The silicon master of the micro-cylinders array is prepared using photolithography and deep reactive ion etching. During the micro-transfer molding operation, the surface of the soft mold of the micro-holes array is filled with liquid UV curable photopolymer, and the soft mold is then pressed against the flat substrate with a slight pressure for a period of time. After the soft mold is removed from the substrate, surface tension causes the liquid photopolymer cylinders to assume a spherical shape. Finally, the liquid photopolymer is cured by UV irradiation at room temperature. A substrate with a microlens array pattern can be successfully fabricated. In this study, a micro-transfer molding facility with UV exposure capacity has been designed, constructed and tested. The 100 × 100 arrays of a polymeric microlens have been successfully produced. Under the condition of 50 kPa stamping pressure, 6 s duration and 500 mJ cm−2 UV curing dose, the microlenses were successfully formed on the plastic substrate. Their optical properties were verified with a beam profiler. In addition, microlenses of different curvatures and focal lengths can be obtained by using substrates with different surface wettabilities. This study shows that micro-transfer molding can be used for the fabrication of polymeric microlens arrays with high productivity and low cost.

A gasbag-roller-assisted UV imprinting technique for fabrication of a microlens array on a PMMA substrate

Roller imprinting has been one of the most effective replication techniques due to its continuous nature and mass productivity. To improve the pressure uniformity and enhance the replication precision, a novel gasbag-roller-assisted UV imprinting process is designed and developed in this study. A belt-type polydimethylsiloxane (PDMS) mold with cavities for forming a microlens array is prepared. A gasbag roller is employed to exert pressure on the contact area between the PDMS mold and a PMMA substrate. Due to the isotropic pressure provided by the gasbag roller, the contact area between the mold and the substrate is increased and the uniformity of the imprinting pressure is enhanced. Precise replication and complete UV curing are thus achieved. A gasbag-roller-assisted UV-based imprinting facility is constructed, and the experiments are conducted. The results prove that a microlens array can be successfully fabricated on a 2 mm thick PMMA substrate. The shape profile and optical property of the microlens are also evaluated.

Fabricating Nanostructures by Atomic Force Microscopy

In this study, we used a conductive Atomic Force Microscopy (AFM) probe to fabricate nanostructures and nanopatterns on a silicon chip using nano-oxidation technology. The height of grown oxidized nanodots tends to increase as the piezoelectric loading in nano-oxidation increases, while the number of oxidized nanodots affects the height of oxidation. In terms of patterning, the height and width of nanodots tend to decrease as the probe scanning speed increases. Moreover, in this study, we used nano-oxidation to perform complex nanopatterning, and found that complex and well-defined nanopatterns could be fabricated on a scale of 1000 ×1000 nm2. The technology proposed in this study can directly define nanostructures without limitations of the wavelength of the light source and light diffraction. The technology has the advantages of low cost and great potential for development.

Novel fabrication of an Au nanocone array on polycarbonate for high performance surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) with enormous enhancements has been applied for ultra-sensitive detection in various fields, but the fabrication of large-scale, controllable and cost-effective substrates is a major challenge. We propose a novel fabrication process with a gas-assisted hot embossing process and an anodic aluminum oxide template to obtain the SERS substrate on a 1 × 1 cm polycarbonate film. The SERS spectra of 4-mercaptobenzoic acid (PMBA) on the gold substrate have been measured. The enhancement factors are between 3.99 × 107 and 4.92 × 107, depending on the heights of nanocones, which can be controlled by the embossing temperature and pressure. The simple and inexpensive SERS substrate has potential for wide application in SERS-based sensors.

Fabrication of microlens arrays using a CO2-assisted embossing technique

This paper reports a method to fabricate microlens arrays with a low processing temperature and a low pressure. The method is based on embossing a softened polymeric substrate over a mold with micro-hole arrays. Due to the effect of capillary and surface tension, microlens arrays can be formed. The embossing medium is CO2 gas, which supplies a uniform pressing pressure so that large-area microlens arrays can be fabricated. CO2 gas also acts as a solvent to plasticize the polymer substrates. With the special dissolving ability and isotropic pressing capacity of CO2 gas, microlens arrays can be fabricated at a low temperature (lower than Tg) and free of thermal-induced residual stress. Such a combined mechanism of dissolving and embossing with CO2 gas makes the fabrication of microlens arrays direct with complex processes, and is more compatible for optical usage. In the study, it is also found that the sag height of microlens changes when different CO2 dissolving pressure and time are used. This makes it easy to fabricate microlens arrays of different geometries without using different molds. The quality, uniformity and optical property of the fabricated microlens arrays have been verified with measurements of the dimensions, surface smoothness, focal length, transmittance and light intensity through the fabricated microlens arrays.

Application of Vacuum-Assisted Filling System with Ultraviolet-Light-Emitting Diode Array to Fabrication of Waveguide Microstructures

In this study, we proposed a novel technology for developing a nanoscale, high-resolution, and cost-efficient next-generation semiconductor process that uses exposure technology with ultraviolet-light-emitting diode (UV-LED) arrays and poly(dimethylsiloxane) (PDMS) flexible soft mold imprint technology in order to develop a vacuum-assisted photoresist filling technology for microstructures. By integrating the characteristics of the PDMS soft mold, photocure resist, and vacuum-assisted filling system to fabricate waveguide components, conformal contact was obtained between a PDMS soft mold and a substrate surface, at a low surface free energy. The vacuum-assisted filling system was used to achieve compact and complete photoresist filling. There is no residual layer left after filling and a subsequent process is no longer necessary; thus, cost and process time can be effectively reduced. Recently, nanometer component manufacturing technology and its applications have become more sophisticated.

A high-brightness light guide plate with high precise double-sided microstructures fabricated using the fixed boundary hot embossing technique

In recent years, microstructures have been widely applied in many key optical elements and bio-elements. The effective and efficient fabrication of optical elements and bio-elements with superior performance has become an essential challenge. This requires very accurate shape replication of microstructures. The plate-to-plate hot embossing process is the most likely method of mass production for the replication of double-sided micro/nano structures with high precision and quality. However, the traditional uniform heating hot embossing process as the free boundary of open die forging leads to variation. In this research, three techniques are implemented; the conventional uniform heating technique, the non-uniform pressure compensating technique and the fixed boundary hot embossing technique. The temperature distribution of the hot-plates of the fixed boundary hot embossing technique are designed to keep the temperature in the center part higher than the outer part on the surface of the substrates. This phenomenon changes free boundary in conventional uniform heating into fixed boundary. The results demonstrate the potential of the fixed boundary hot embossing technique for the fabrication of large-area high brightness LGPs with double-sided microstructures. The results are also helpful for enhancing the performance of optical elements and bio-elements fabricated using the fixed boundary hot embossing technique.

Low-Cost and Rapid Fabrication of Metallic Nanostructures for Sensitive Biosensors Using Hot-Embossing and Dielectric-Heating Nanoimprint Methods

We propose two approaches—hot-embossing and dielectric-heating nanoimprinting methods—for low-cost and rapid fabrication of periodic nanostructures. Each nanofabrication process for the imprinted plastic nanostructures is completed within several seconds without the use of release agents and epoxy. Low-cost, large-area, and highly sensitive aluminum nanostructures on A4 size plastic films are fabricated by evaporating aluminum film on hot-embossing nanostructures. The narrowest bandwidth of the Fano resonance is only 2.7 nm in the visible light region. The periodic aluminum nanostructure achieves a figure of merit of 150, and an intensity sensitivity of 29,345%/RIU (refractive index unit). The rapid fabrication is also achieved by using radio-frequency (RF) sensitive plastic films and a commercial RF welding machine. The dielectric-heating, using RF power, takes advantage of the rapid heating/cooling process and lower electric power consumption. The fabricated capped aluminum nanoslit array has a 5 nm Fano linewidth and 490.46 nm/RIU wavelength sensitivity. The biosensing capabilities of the metallic nanostructures are further verified by measuring antigen–antibody interactions using bovine serum albumin (BSA) and anti-BSA. These rapid and high-throughput fabrication methods can benefit low-cost, highly sensitive biosensors and other sensing applications.