Thermal Conductivity Measurement of Tungsten Oxide Nanoscale Thin Films

Abstract

The out-of-plane thermal conductivity of sputtered tungsten oxide thin films with thickness of 100 to 300 nm was measured by two omega method based on a new analytical model with consideration of the interfacial thermal resistance between the films and the substrate. The influence of the tungsten oxide structure on the thermal conductivity was studied. The result reveals that the tungsten oxide thin films made with 10% reactive gas of oxygen had a mixed phase of WO 2 and WO 3 , while those made with 100% oxygen were WO 3 only. The thermal conductivity of WO 3 thin films is 1.63 Wm À1 K À1 , and that of WO 2 /WO 3 films is 1.28 Wm À1 K À1 . The difference is explained by a higher thermal resistance at the interface of WO 2 and WO 3 crystals caused by the mismatch of phonon state.

Anomalous Defect Dependence of Thermal Conductivity in Epitaxial WO3 Thin Films

“…Despite the small monoclinic distortion in the relaxed H δ WO 3 /LAO, it is still in line with the trend. The thermal conductivity of polycrystalline monoclinic WO 3 thin films is reported to be 1.63 W m −1 K −1 , lower than the trendline of our experimental data, which may be attributed to the fact that the grain boundaries make a major contribution to the scattering of phonons. We also show the volumetric strain as a horizontal axis, taking the bulk monoclinic structure as the unstrained reference, in Figure a, clearly indicating an increase of κ L upon compression and a reduction upon expansion, irrespective of substrate and stoichiometry.…”

Heat flux in metal cutting: Experiment, model, and comparative analysis

“…During the electro-discharge machining (EDM) process formation of a thin oxide layer, represented by WO 3 in case of cemented carbide, is commonly observed. Tungsten oxide has significantly lower thermal properties [30,31] than the bulk of cemented carbide, and therefore can act as a thermal barrier and may introduce potential computational errors, if ignored. Fig.…”

“…The chemical composition of the layer is identical to the bulk cemented carbide, yet it has much finer microstructure and a significant amount of porosity. Because the thermal properties of the recast layer are unknown, but expectedly lower than for the bulk, a worst-case scenario was considered where the properties of WO 3 [30,31] were assigned to the oxide and recast layers together. Computational model representing a solid tool was compared with a model of a tool having the 0.5 mm holes.…”

Microstructured Tungsten Oxide: A Generic Desorption/Ionization Substrate for Mass Spectrometry

“…WO 3 has many properties that make it an excellent substrate for SALDI MS. Its melting point is still very large (1473 °C); indeed, it is comparable to Si (1410 °C). Although its heat capacity is ∼3× higher than W15 and its thermal conductivity is an order of magnitude lower (1.63 Wm −1 K −1 16 compared to 173 Wm −1 K −1 ), at wavelengths shorter than its band gap (∼2.73 eV17) holes can be formed in the valence band of WO 3 that can react with trapped solvent (water or alcohols) to form protons, a reaction that is known to take place in solar cells based on this material 18, 19. Thus, SALDI experiments using WO 3 should readily work using the outputs of those lasers most typically found on MALDI instruments (N 2 , ∼3.68 eV; tripled Nd:YAG, ∼3.49 eV).…”