Zeolite films as building blocks for antireflective coatings and vapor responsive Bragg stacks

Abstract

Zeolite films (LTL, BEA and MFI) are prepared with a thickness in the range 50-170 nm through a multistep spin-on deposition method. The optical properties of the zeolite films including refractive index, extinction coefficient and thickness are determined from the reflectance spectra using a nonlinear curve fitting method. The total free pore volume of the films using the Bruggeman effective medium theory is calculated. The potential of the zeolite films for broadband antireflection (AR) application is demonstrated. Five times reduction of the reflectance of a silicon substrate covered with the double AR films comprising of MFI type zeolite (120 nm) deposited on Nb2O5 (60 nm) is achieved. Additionally, the MFI zeolite film is used as a building block of vapor responsive Bragg stacks with a strong response towards acetone. The reversible response of the Bragg stacks towards acetone without additional annealing opens up the possibility of preparing sensors with optical read-out by incorporation of sensitive and transducer elements into a single device.

In-Situ Ellipsometric Study of the Optical Properties of LTL-Doped Thin Film Sensors for Copper(II) Ion Detection

“…It is seen from Figure 4 that the refractive index of the TEOS-LTL composites annealed at both temperatures was substantially lower compared to the TEOS-only layers. The reason is that the refractive index of the LTL zeolites (~1.37) [16] is less than the refractive index of the TEOS matrix, and thus LTL addition reduces the effective refractive index of the composite. Furthermore, the annealing at higher temperature also led to a reduction in the refractive index; this effect was most pronounced for doped samples.…”

Optical Properties of Sol-Gel Nb2O5Films with Tunable Porosity for Sensing Applications

“…Mesoporous materials (pore diameter in the range of 2-50 nm) have attracted the scientific interest due to their remarkable properties and potential applications in many advanced areas such as drug delivery systems, sensors, catalysis, photovoltaic cells, and fuel cells [9]. One attractive application of the mesoporous films can be realized when they are incorporated in one-dimensional stacks (Bragg stacks) as high refractive index building blocks [10,11]. In this case, an optical sensing could be realized on the basis of refractive index change due to the condensation of vapors in the pores [12][13][14].…”

Vapor Responsive One-Dimensional Photonic Crystals from Zeolite Nanoparticles and Metal Oxide Films for Optical Sensing

“…Nb 2 O 5 is a high refractive index material and could be assembled in thin film form by simple methods [14]. Besides, recently we have reported that Nb 2 O 5 could be successfully used as a high refractive index building block of a vapor responsive Bragg stack that comprises MFI zeolite as sensing element [15]. Zeolites are crystalline materials with framework-type structures built of regular and uniform pores of molecular dimensions [16].…”