Jeeyoung Lee

Nanostructured TiO2 diffraction grating fabricated via imprinting and TiCl4 treatment

We show here that a highly effective diffraction grating can be embedded into a nanoparticulate TiO2 film via imprinting combined with TiCl4 treatment. A thin TiO2 film spin-coated on a glass substrate was patterned by imprinting and this patterned layer was TiCl4-treated with a higher concentration than for a thicker over-coated TiO2 film. Due to the refractive index difference between the two layers, the incident light could be strongly diffracted. Different types of gratings have been incorporated into the films. A line grating with a 2 μm period and 1.2 μm thickness generated diffracted beams up to 3rd-order, with total diffraction efficiencies over 90% at 633 nm. This method has potential applications in TiO2-based photovoltaic and photocatalytic devices.

Grating-coupled surface plasmon resonance on bulk stainless steel

Grating-coupled surface plasmon resonance (SPR) is demonstrated with one-dimensional gratings fabricated on the surface of bulk stainless steel using imprinting combined with electrochemical etching. The extent of light coupling and the wavelengths of SPR peaks were characterized with respect to the incident angle and polarization states of the light. When the plane of incidence was orthogonal to the grating grooves, only TM polarization was absorbed at two different wavelengths. In the plane of incidence parallel to the grooves, a single resonance peak was observed only when the incident light was TE-polarized. The dependence of SPR wavelengths on the incident angle was in good agreement with theoretical consideration.

Laser-Induced Dewetting of Metal Thin Films for Template-Free Plasmonic Color Printing

Plasmonic color laser printing has several advantages over pigment-based technology, including the absence of ink and toner and the production of nonfading colors. However, the current printing method requires a template that should be prepared via nanofabrication processes, making it impractical for large-area color images. In this study, we show that laser-induced dewetting of metal thin films by a nanosecond pulsed laser can be effectively utilized for plasmonic color printing. Ag, Au, and their complex films deposited on a glass substrate were dewetted into different surface structures such as droplets, rods, and ripples, depending on the incident laser energy. The resulting morphological evolutions could be explained by Rayleigh and capillary instabilities. For a bimetallic film comprising Ag nanowires coated on a Au layer, a few different plasmonic colors were generated from a single sample simply by changing the laser fluence. This provides a possible method for implementing plasmonic color laser printing without using a prepatterned template.