Thermal Conductivity of Highly-Ordered Mesoporous Titania Thin Films from 30 to 320 K

Abstract

ABSTRACT:11 This paper reports the cross-plane thermal conductivity of highly ordered amorphous and crystalline templated mesoporous titania 12 thin films measured by the 3ω method from 30 to 320 K. Both solÀgel and nanocrystal-based films were synthesized by evaporation-13 induced self-assembly, with average porosity of 30% and 35%, respectively. The pore diameter ranged from 14 to 25 nm. The size of 14 crystalline domains in polycrystalline mesoporous films were 12À13 nm, while the nanocrystals in the nanocrystal-based film were 15 9 nm in diameter. At high temperatures, the thermal conductivity of amorphous dense and mesoporous films showed similar trends 16 with respect to temperature. This was attributed to the fact that the presence of pores had a purely geometrical effect by reducing the 17 cross-sectional area through which heat can diffuse. By contrast, the thermal conductivity of polycrystalline dense and mesoporous 18 films behaves differently with temperature due to phonon scattering by pores and crystalline nanosize domains. In addition, at low 19 temperatures, the presence of pores caused the thermal conductivity of mesoporous films to be less temperature dependent than 20 their dense counterparts. Despite its crystallinity, the thermal conductivity of the nanocrystal-based film was about 40% less than that 21 of the polycrystalline mesoporous films. This was mainly attributed to its larger porosity, smaller crystal size, and strong phonon 22 scattering at the poorly interconnected nanocrystal boundaries. These results suggest various ways to control the thermal 23 conductivity of mesoporous materials for various applications.

Application of complex geometrical optics to determination of thermal, transport, and optical parameters of thin films by the photothermal beam deflection technique

“…The obtained values of thermal diffusivity and thermal conductivity for pure TiO 2 film are in good agreement with those from the literature, where values of 1.35-3.52 · 10 −6 m 2 s −1 and 1.38-6.01 Wm −1 K −1 were reported for thermal diffusivity and thermal conductivity of micrometer-sized TiO 2 films, respectively, [22]. It should be mentioned that their values strongly depend on the film structure, which, in turn, is determined by the process of its preparation [22,23]. Introducing particles to the TiO 2 material changes its thermal properties because of two effects.…”

Thermal Conductivity of Ordered Mesoporous Nanocrystalline Silicon Thin Films Made from Magnesium Reduction of Polymer-Templated Silica

“…The electrical resistance R e (T) was measured before each 3ω measurement and was fitted with the Bloch−Gruneisen model. 42,43 The amplitude of temperature oscillations in the mesoporous thin film ΔT f was then calculated by subtracting the amplitude of temperature oscillation of the deposited reference silicon nitride film ΔT ref (ω) from that of the mesoporous film with the protective silicon nitride film denoted by ΔT tot (ω) 44 ω ω…”

Thermal Conductivity Changes in Titanium-Graphene Composite upon Annealing

“…The thermal conductivity of bulk TiC (21 W/mK) [27,28] is two times higher than that of bulk TiO 2 (10 W/mK). [29] TiC film is expected to exhibit a better interface with Ti and graphene. [30] The thin films of TiC and TiO 2 are defective and the crystallinity is not good.…”