Chaemin Chun

Well-ordered TiO2 nanostructures fabricated using surface relief gratings on polymer films

Well-ordered TiO2 nanostructures such as 1-dimensional nanowire arrays, 2-dimensional square and hexagonal hole arrays, and 3-dimensional wire junction arrays were fabricated by a simple, controllable, economical, and reproducible method using surface relief gratings on azobenzene-functionalized polymer films as a template in the sol–gel reaction of a Ti precusor. In addition, as an application of TiO2 nanostructure, transparent electrodes were patterned by selective dry etching with the TiO2 nanowire array etch mask. Scanning electron microscope and atomic force microscope images confirmed the successful formation of a variety of well-ordered TiO2 nanostructures and nanopatterning of transparent electrodes.

A novel azobenzene-based amorphous molecular material with a spiro linked bifluorene

A novel, high Tg azobenzene-based amorphous molecular material, spiro-ADA, was designed and synthesized via a palladium catalyzed amination reaction. The introduction of bulky spiro linked bifluorene with the non-planar structure of triphenylamine of spiro-ADA prevented crystallization of the molecules and led to good amorphous film formation and thermal stability with a high glass transition temperature of 147 °C. Photoinduced behavior such as optically induced birefringence, diffraction efficiency, and surface relief gratings (SRGs) were investigated in relation to their unique molecular structures. Because of the high concentration of azobenzene groups and a low molecular mass, the films showed a very rapid response to linearly polarized light, a high diffraction efficiency of 38.7%, and a large modulation depth of around 320 nm. In addition, the thermal stability of SRGs inscribed on the spiro-ADA film was measured and found to be very stable below Tg despite its low molar mass and the absence of any chain entanglement.

Interferometric inscription of surface relief gratings on optical fiber using azo polymer film

We report the fabrication and characteristics of surface relief grating on the end surface of silica optical fiber with a diameter of 125 μm. One- and two-dimensional gratings were inscribed on the fiber surface covered with azo polymer thin-film layer using interferometric methods. Diffraction beam patterns of the zeroth and the first order due to surface relief gratings were observed using a 635 nm laser, and the relation between the measured diffraction beam pattern and the grating period was also investigated.

Absorption Wavelength Dependent Photodynamic Motions in Donor-Acceptor Type of Azobenzene Polymer Films

The dynamic properties of photoinduced molecular alignment and holographic inscription of surface relief gratings (SRG) were investigated depending on absorption wavelength of ππ* and nπ* transition in donor–acceptor type of azopolymers, which contain different electron-withdrawing substituents [CF3, CN, CNCl, NO2, (CN)2] on the azobenzene. As the cis–nπ* absorption band approaches the excitation wavelength (488 nm), the photoinduced molecular alignment rapidly occurs. The rate of SRG formation was proportional to the rate of the photoinduced molecular alignment when the ππ* absorption wavelength of the trans is higher than 440 nm.