Square spiral photonic crystal with visible bandgap

Abstract

Nanoimprint lithography was combined with glancing angle deposition (GLAD) of titanium dioxide to fabricate a square spiral columnar film with a bandgap in the visible spectral range. Nanoimprint stamps were fabricated with seed spacing ranging from 80 to 400 nm, and four periods of square spiral film were deposited on top of the 320 nm array of seeds. The ratio of lattice spacing, vertical pitch and spiral arm swing was chosen as a : P : A = 1 : 1.35 : 0.7 and the deposition angle was fixed at 86° to maximize the square spiral film’s bandgap. Reflectivity measurements show that the fabricated structure exhibit a pseudo-gap centered at around 600 nm wavelength, in good agreement with finite difference electromagnetic simulations. The absence of a full 3D bandgap is due the deviation of GLAD columns’ cross-section from the optimal one, which has to be highly elongated in the deposition plane. However, simulations show that a geometry close to the fabricated one will produce a full 3D bandgap, if the structure is inverted. The material refractive index in such an inverted photonic crystal can be as low as n = 2.15.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…Meanwhile, with swing tilting rotation, the substrate is smoothly rotated back-and-forth along its azimuth within an angular range of D/, which is called the swing angle. These methods have also been used to obtain 3D nanostructures on substrates with previously deposited seed patterns [94,95] (see Section 2.5).…”

Wafer-scale, three-dimensional helical porous thin films deposited at a glancing angle

“…45 At a of 86 , TiO 2 anatase SHPTFs were deposited onto a seeding array with a lattice space of 320 nm. 47 There are 8 sweeps per square spiral arm, and the ratio of lattice spacing, vertical pitch and spiral arm swing is a : P : A ¼ 1 : 1.35 : 0.7. The reectivity measurement showed that the anatase SHPTFs have a pseudo-bandgap centered at l $600 nm, in good agreement with the nite difference electromagnetic simulation.…”

Optical properties of nanostructured WO3 thin films by GLancing Angle Deposition: Comparison between experiment and simulation

“…They showed that it was possible to tune selective transmission of linearly polarized light for thin films with S-shape structures nano-designed by GLAD. In 2012, this method was used to simulate optical reflection of thin films composed of columns grown with a squared spiral shape [27] in order to model interference mirrors [28]. Among the panel of metal oxides deposited by GLAD, some studies have been focused on stoichiometric tungsten oxide WO 3 thin films [29][30][31] because this dielectric material has a high refractive index (n WO3 = 2.5 [32]).…”