Yen-Ling Tsai

Improved output power of GaN-based light-emitting diodes grown on a nanopatterned sapphire substrate

This letter describes the improved output power of GaN-based light-emitting diodes (LEDs) formed on a nanopatterned sapphire substrate (NPSS) prepared through etching with a self-assembled monolayer of 750-nm-diameter SiO2 nanospheres used as the mask. The output power of NPSS LEDs was 76% greater than that of LEDs on a flat sapphire substrate. Three-dimensional finite-difference time-domain calculation predicted a 40% enhancement in light extraction efficiency of NPSS LEDs. In addition, the reduction of full widths at half maximum in the ω-scan rocking curves for the (0 0 2) and (1 0 2) planes of GaN on NPSS suggested improved crystal quality.

Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres

The output power enhancement of the GaN-based light-emitting diodes (LEDs) featuring two-dimensional (2D) hole arrays is demonstrated. The 2D air hole arrays were first generated in the photoresist by utilizing the focusing nature of microspheres, and then transferred onto the GaN surface through dry etching. The maximum output power of the surface-textured LEDs was enhanced by 45% compared with the LEDs without surface texturing. The finite-difference time-domain calculation was performed and revealed that the light extraction efficiency of the textured LEDs increased with increasing etching depth.

Patterning Periodical Motif on Substrates Using Monolayer of Microspheres: Application in GaN Light-Emitting Diodes

In this article, we present a method of patterning a GaN substrate using polystyrene spheres and its inversed structure as the mask. By dry etching, different surface morphologies and depths of the GaN substrate can be obtained by changing the etching time. We used such a sphere-patterned GaN substrate to fabricate GaN-based light-emitting diodes (LED). It was found that the total lighting output of the sphere-patterned GaN LED was increased by 37%.

Rapid fabrication of 2D and 3D photonic crystals and their inversed structures.

In this paper a new technique is proposed for the fabrication of two-dimensional (2D) and three-dimensional (3D) photonic crystals using monodisperse polystyrene microspheres as the templates. In addition, the approaches toward the creation of their corresponding inversed structures are described. The inversed structures were prepared by subjecting an introduced silica source to a sol-gel process; programmed heating was then performed to remove the template without spoiling the inversed structures. Utilizing these approaches, 2D and 3D photonic crystals and their highly ordered inversed hexagonal multilayer or monolayer structures were obtained on the substrate.

Synthesis, characterization, and highly acid-resistant properties of crosslinking β-chitosan with polyamines for heavy metal ion adsorption

This study primarily used β-chitosan as the main reactant and benzaldehyde as the protecting group to convert the amine groups on location C2 of chitosan into Schiff bases. Grafting and crosslinking of epichlorohydrin and triethylenetetramine with chitosan was conducted and the structural changes were analyzed with Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), elemental analyses (EA), differential scanning calorimeter (DSC), X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) to prove the successful modification to form crosslinked β-chitosan. Lastly, this study compared the heavy metal ion (such as Cu2+ and Ag+) adsorption capacities of chitosan before and after the graft modification. The capacity of modified chitosan for adsorbing copper ions improved in acid environments with pH of 2 to 6. The capacity increased from 67.76 mg g−1 to 117.60 mg g−1 when the pH value was 6. In addition, the capacity of adsorbing silver ions was higher than that of adsorbing copper ions and it enhanced from 116.80 mg g−1 to 151.20 mg g−1 when the pH level was 6. Furthermore, the modified crosslinked β-chitosan had an excellent acid-resistant property.