Transient thermoreflectance (TTR) techniques are ubiquitous methods for measuring thermal conductivity of bulk materials and thin-films. Both through-plane thermal conductivity k and in-plane thermal conductivity k should be independently measured in transversely anisotropic materials. When these properties are measured using conventional TTR techniques, the accuracy of the k measurement is dependent on the accuracy of measuring k and vice versa. This is especially problematic for thin-films measurements as uncertainty in k (∼5%) can propagate and grow for uncertainty in k. In this paper, we present a method for the simultaneous measurement of k and k using beam-offset frequency domain thermoreflectance (FDTR) with robust uncertainty estimation. The conventional diffusive heat transfer solution is analyzed to show that offset and heating frequency can independently control the sensitivity to directional thermal conductivity and extract values for k and k. Numerical uncertainty analyses demonstrate that sweeping both heating frequency and beam offset results in a reduction of measurement uncertainty. This modified measurement technique is demonstrated on crystalline alumina (c-AlO), amorphous alumina (a-AlO), quartz, fused silica, and highly oriented pyrolytic graphite.
Wood
is a universal building material. While highly versatile,
many of its critical properties vary with water content (e.g., dimensionality,
mechanical strength, and thermal insulation). Treatments to control
the water content in wood have many technological applications. This
study investigates the use of single-cycle atomic layer deposition
(1cy-ALD) to apply <1 nm Al2O3, ZnO, or TiO2 coatings to various bulk lumber species (pine, cedar, and
poplar) to alter their wettability, fungicidal, and thermal
transport properties. Because the 1cy-ALD process only requires a
single exposure to the precursors, it is potentially scalable for
commodity product manufacturing. While all ALD chemistries are found
to make the wood’s surface hydrophobic, wood treated with TiO2 (TiCl4 + H2O) shows the greatest bulk
water repellency upon full immersion in water. In situ monitoring
of the chamber reaction pressure suggests that the TiCl4 + H2O chemistry follows reaction-rate-limited processing
kinetics that enables deeper diffusion of the precursors into the
wood’s fibrous structure. Consequently, in humid or moist environments,
1cy-ALD (TiCl4 + H2O) treated lumber shows a
4 times smaller increase in thermal conductivity and improved resistance
to mold growth compared to untreated lumber.
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