Thermal Conductivity of Cubic and Hexagonal Mesoporous Silica Thin Films

Abstract

This paper reports the cross-plane thermal conductivity of highly ordered cubic and hexagonal templated mesoporous amorphous silica thin films synthesized by evaporation-induced self-assembly process. Cubic and hexagonal films featured spherical and cylindrical pores and average porosity of 25% and 45%, respectively. The pore diameters ranged from 3 to 18 nm and film thickness from 80 to 540 nm while the average wall thickness varied from 3 to 12 nm. The thermal conductivity was measured at room temperature using the 3ω method. The experimental setup and the associated analysis were validated by comparing the thermal conductivity measurements with data reported in the literature for the silicon substrate and for high quality thermal oxide thin films with thicknesses ranging from 100 to 500 nm. The cross-plane thermal conductivity of the synthesized mesoporous silica thin films does not show strong dependence on pore size, wall thickness, or film thickness. This is due to the fact that heat is mainly carried by very localized non propagating vibrational modes. The average thermal conductivity for the cubic mesoporous silica films was 0.30 ± 0.02 W/m.K, while it was 0.20 ± 0.01 W/m.K for the hexagonal films. This corresponds to a reduction of 79% and 86% from bulk fused silica at room temperature.

Reflectance of surfactant-templated mesoporous silica thin films: Simulations versus experiments

“…Finally, Figure 2 shows SEM images of the cubic and hexagonal mesoporous silica thin films considered obtained with a JEM-2000 FX (JEOL, Ltd, Japan). More details on films' characterization can be found elsewhere [42].…”

Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

“…These films featured different crystallinity, porosity, and architecture. The results were compared with those previously reported for sol-gel templated mesoporous silica thin films [21]. Numerical simulations were not performed in the present study.…”

“…The thermal conductivity of at least three PSZ MEL thin film samples synthesized with the same second stage synthesis time was measured. Based on a previous study [21], the uncertainty on the thermal conductivity measurements associated with the 3ω method was estimated to be ± 15%. The later accounts for potential errors due to both the sample film preparation and the various steps involved in the 3ω method, i.e., sample dehydration, variation in PECVD nitride film thickness and inhomogeneity, pattern resolution during photolithography, metal deposition, thickness and width during evaporation and lift-off, and finally bias errors in the 3ω electrical measurements.…”

“…Principles, experimental apparatus and procedure as well as their validation have already been described elsewhere [21]. In brief, a conductive metallic wire, serving as both a thermometer and a line heat source, was patterned on top of the PSZ films.…”

Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy

“…16,17 In the synthesis, different structure-directing agents were used in order to predetermine the pore size of the titania matrix. BRIJ  S10 (Sigma-Aldrich, Steinheim, Germany) (polyoxyethylene (10) stearyl ether), 32 cetyltrimethylammonium bromide (CTAB, Sigma-Aldrich) (CH 3 (CH 2 ) 15 N + (CH 3 ) 3 Br -), 33 and Pluronic  P123 (P123, Sigma-Aldrich) (a triblock copolymer of EO 20 PO 70 EO 20 ) 34,35 were all used separately. Moreover, P123 was combined with poly(propylene glycol) (PPG, M n ∼4,000, Sigma-Aldrich) and used as a swelling agent to increase the pore size even further.…”