Unlike many superlattice structures, Ruddlesden–Popper phases have atomically abrupt interfaces useful for interrogating how periodic atomic layers affect thermal properties. Here, we measure the thermal conductivity in thin films of the n = 1–5 and 10 members of the (SrTiO3)nSrO Ruddlesden–Popper superlattices grown by molecular-beam epitaxy and compare the results to a single crystal of the n = 1 Ruddlesden–Popper SrLaAlO4. The thermal conductivity cross-plane to the superlattice layering (k33) is measured using time-domain thermoreflectance as a function of temperature and the results are compared to first-principles calculations. The thermal conductivity of this homologous series decreases with increasing interface density. Characterization by x-ray diffraction and scanning transmission electron microscopy confirms that these samples have a Ruddlesden–Popper superlattice structure.
Silicon carbide/silicon carbide (SiC/SiC) composites are often used in oxidizing environments at high temperatures. Measurements of the thermal conductance of the oxide layer provide a way to better understand the oxidation process with high spatial resolution. We use time‐domain thermoreflectance (TDTR) to map the thermal conductance of the oxide layer and the thermal conductivity of the SiC/SiC composite with a spatial resolution of 3 μm. Heterodyne detection using a 50‐kHz‐modulated probe beam and a 10‐MHz‐modulated pump suppresses the coherent pick‐up and enables faster data acquisition than what has previously been possible using sequential demodulation. By analyzing the noise of the measured signals, we find that in the limit of small integration time constants or low laser powers, the dominant source of noise is the input noise of the preamplifier. The thermal conductance of the oxide that forms on the fiber region is lower than the oxide on the matrix due to small differences in thickness and thermal conductivity.
For heat-assisted magnetic recording (HAMR) heads, a major reliability limiter is the peak near-field transducer (NFT) temperature. Since the NFT is nanoscale, heat sinking is controlled by materials and interfaces within a few 100 nm of the NFT. Heat sinks can be metallic to take advantage of the 10x-100x higher thermal boundary conductance (TBC) of metal/metal interfaces, versus nonmetal interfaces. Oxide formation at these interfaces can greatly decrease the TBC and contribute to NFT failure. Likewise, the thermal resistance of material between the NFT and media recording layer greatly influences the NFT operating temperature. Here we use pump-probe thermoreflectance techniques (FDTR, TDTR) to study metal-metal interfaces and detect partial oxidation of a buried metallic thin film, as well as evaluate the interface thermal conductance of amorphous-amorphous interfaces in a film stack representative of a HAMR head-media interface.
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