Shinill Kang

Fabrication of a microlens array using micro-compression molding with an electroformed mold insert

Polymeric microlens arrays, with a diameter of 36–96 μm, a radius of curvature of 20–60 μm and a pitch of 250 μm, were fabricated using micro-compression molding with electroformed mold inserts. We used the reflow method and the electroforming process to make the mother and the metallic mold inserts, respectively. Micro-compression molding with powder polymer was developed to replicate microlenses. The surface profiles, imaging qualities, and surface roughness of the microlenses were measured and analyzed.

Continuous ultraviolet roll nanoimprinting process for replicating large-scale nano- and micropatterns

With the increasing demand for large-scale nano- and micropatterns in the field of digital displays, nano- and micropattern replication technology has become a research priority. In this study, a continuous ultraviolet (UV) roll nanoimprinting process using a pattern roll stamper for the replication of large-scale nano- and micropatterns was designed and constructed. Several flexible nano- and micropatterns with large areas were fabricated and analyzed as tests of this continuous UV imprinting process.

Hierarchical MnCo-layered double hydroxides@Ni(OH)2 core–shell heterostructures as advanced electrodes for supercapacitors

Rational assembly and hetero-growth of hybrid structures consisting of multiple components with distinctive features are a promising and challenging strategy to develop materials for energy storage applications. Herein, we propose a supercapacitor electrode comprising a three-dimensional self-supported hierarchical MnCo-layered double hydroxides@Ni(OH)2 [MnCo-LDH@Ni(OH)2] core–shell heterostructure on conductive nickel foam. The resultant MnCo-LDH@Ni(OH)2 structure exhibited a high specific capacitance of 2320 F g−1 at a current density of 3 A g−1, and a capacitance of 1308 F g−1 was maintained at a high current density of 30 A g−1 with a superior long cycle lifetime. Moreover, an asymmetric supercapacitor was successfully assembled using MnCo-LDH@Ni(OH)2 as the positive electrode and activated carbon (AC) as the negative electrode. The optimized MnCo-LDH@Ni(OH)2//AC device with a voltage of 1.5 V delivered a maximum energy density of 47.9 W h kg−1 at a power density of 750.7 W kg−1. The energy density remained at 9.8 W h kg−1 at a power density of 5020.5 W kg−1 with excellent cycle stability.

Replication qualities and optical properties of UV-moulded microlens arrays

UV-moulded microlens arrays with high replication quality were fabricated using a parametric design method. It is important to maximize replication quality because one can obtain replicated micro-optical components with desired properties by accurate control of the shape. In this study, nickel mould inserts for microlens arrays with lenses having diameters between 3 and 230??m were fabricated by an electroforming process. The reflow method was used to make the master for the metallic mould insert. A UV-moulding system was designed and constructed, and the effects of compression pressure and UV-curing dose on the replication quality of UV-moulded microlens arrays with a diameter of 14??m were examined experimentally. Finally, geometrical and optical properties of the replicated microlens arrays were measured and analysed.

Controlled electrochemical growth of Co(OH)2 flakes on 3D multilayered graphene foam for high performance supercapacitors

The present research describes successful enchase of Co(OH)2 microflakes by the potentiodynamic mode of electro-deposition (PED) on porous, light weight, conducting 3D multilayered graphene foam (MGF) and their synergistic effect on improving the supercapacitive performance. Structural and morphological analyses reveal uniform growth of Co(OH)2 microflakes with an average flake width of ∼30 nm on the MGF surface. Moreover, electrochemical capacitive measurements of the Co(OH)2/MGF electrode exhibit a high specific capacitance of ∼1030 F g−1 with ∼37 W h kg−1 energy and ∼18 kW kg−1 power density at 9.09 A g−1 current density. The superior pseudoelectrochemical properties of cobalt hydroxide are synergistically decorated with high surface area offered by a conducting, porous 3D graphene framework, which stimulates the effective utilization of redox characteristics and mutually improves electrochemical capacitive performance with charge transport and storage. This work evokes scalable electrochemical synthesis with the enhanced supercapacitive performance of the Co(OH)2/MGF electrode in energy storage devices.

Fabrication of polymeric microlens of hemispherical shape using micromolding

Polymeric microlenses play an important role in reducing the size, weight, and cost of optical data storage and optical communication systems. We fabricate polymeric microlenses using the microcompression molding process.The design and fabrication procedures for mold insertion is simplified using silicon instead of metal. PMMA powder is used as the molding material. Governed by process parameters such as temperature and pressure histories, the micromolding process is controlled to minimize various defects that develop during the molding process. The radius of curvature and magnification ratio of fabricated microlens are measured as 150 μm and over 3.0, respectively.

Replication Technology for Micro/Nano Optical Components

Micro/nano replication processes, including micro/nano thermal forming (compression molding and hot embossing), UV-molding, micro injection molding, and glass micro molding are regarded as the most promising mass-production methods for micro/nano optical components because they offer high repeatability, mass producibility with low-cost and versatility in terms of molding material selection. To replicate micro/nano optical components, it is required to prepare the mold inserts that have the cavities of the same shape as the components. One can use any established methods to make mold, such as direct machining, wet etching, dry etching, electroforming, compaction and sintering, and so on. This paper reviews the general issues on mold fabrication and replication technologies for micro/nano optical components with our recent work and results in these areas.

Controllable sulfuration engineered NiO nanosheets with enhanced capacitance for high rate supercapacitors

NiO has been intensively studied as a promising electrode material for supercapacitors because of its high theoretical specific capacitance, well-defined redox behavior, and good chemical compatibility with nickel foam. However, it still suffers from inferior rate capability and cycling stability because of the simple component and random structural integration. Herein, we report a tunable sulfuration process of NiO nanosheets constructed on porous nickel foam for supercapacitor applications. The resulting NiO/Ni3S2 with distinct structural features exhibits an ultra-high specific capacitance of 2153 F g−1 at a current density of 1 A g−1, and the capacitance is retained at 1169 F g−1 even at a current density as high as 30 A g−1. An asymmetric supercapacitor device fabricated with NiO/Ni3S2 as the positive electrode and activated carbon as the negative electrode delivers high energy and power densities (52.9 W h kg−1 at 1.6 kW kg−1; 26.3 W h kg−1 at 6.4 kW kg−1), and good cycling stability (a capacitance retention of 92.9% over 5000 cycles).

Fabrication of transparent conductive tracks and patterns on flexible substrate using a continuous UV roll imprint lithography

A method is proposed to fabricate conductive patterns and tracks on large area flexible substrates using a UV roll imprinting lithography process. A durable metal roll stamp, which is extendable to mass production, was fabricated by using a series of photolithography, electroforming and anti-adhesion coating processes. Indium tin oxide (ITO) conductive patterns and tracks with line widths of 2–20 µm were formed by using the UV roll imprinting process and a subsequent etching process. The geometrical properties and electrical conductivity of fabricated ITO patterns and tracks were measured and analysed.

Nanoscale patterning of complex magnetic nanostructures by reduction with low-energy protons

Techniques that can produce patterns with nanoscale details on surfaces have a central role in the development of new electronic, optical and magnetic devices and systems. High-energy ion irradiation can produce nanoscale patterns on ferromagnetic films by destroying the structure of layers or interfaces, but this approach can damage the film and introduce unwanted defects. Moreover, ferromagnetic nanostructures that have been patterned by ion irradiation often interfere with unpatterned regions through exchange interactions, which results in a loss of control over magnetization switching. Here, we demonstrate that low-energy proton irradiation can pattern an array of 100-nm-wide single ferromagnetic domains by reducing [Co(3)O(4)/Pd](10) (a paramagnetic oxide) to produce [Co/Pd](10) (a ferromagnetic metal). Moreover, there are no exchange interactions in the final superlattice, and the ions have a minimal impact on the overall structure, so the interfaces between alternate layers of cobalt (which are 0.6 nm thick) and palladium (1.0 nm) remain intact. This allows the reduced [Co/Pd](10) superlattice to produce a perpendicular magnetic anisotropy that is stronger than that observed in the metallic [Co/Pd](10) superlattices we prepared for reference. We also demonstrate that our non-destructive approach can reduce CoFe(2)O(4) to metallic CoFe.