*2.2. Preparation of TEOS-LTL Films*

As in [7], the ellipsometry measurements necessitated prolonged exposure of the zeolite films to water. In order to facilitate increased mechanical stability of the LTL-type zeolite films in solution, the LTL-type zeolites were mixed with a pre-hydrolyzed tetraethyl orthosilicate (TEOS).

The following composition was used: 24 mL TEOS, 17.5 mL ethanol, 3 mL of 0.04 M nitric acid and 12 mL of the 1.5 wt.% LTL zeolite suspension described in Section 2.1 [13]. This solution was magnetically stirred for 24 h, filtered (0.8 μm), and then spin-coated at 5000 rpm onto a Silicon wafer substrate. This procedure produced dry films with a thickness of approximately 220 nm. Reference TEOS-only

(i.e., no zeolites) samples were also fabricated in the same manner. Scanning electron microscopy studies were conducted to confirm the uniform distribution of LTL-type zeolites within the TEOS-LTL film.

All samples (both TEOS-LTL and TEOS-only) were initially annealed for 3 h to ensure that the zeolite nanoparticles contained no water prior to the ellipsometric measurements. For the single wavelength ellipsometric study, the samples were annealed at 170 ◦C under vacuum, whereas, for the spectroscopic ellipsometric study, the samples were annealed at 170 and 320 ◦C in air. The second annealing temperature, 320 ◦C, was added in order to compensate for the difference in the annealing conditions at 170 ◦C (i.e., vacuum vs. air), which arose due to the difference in available equipment across the multi-national laboratories contributing to the reported work. For the data presented for each study (single wavelength and spectroscopic) identical thermal treatment conditions were used, which facilitates meaningful analysis of the data.
