TEM images of the GST–TiOx films. (a) Bright field and (b) HAADF images of a 50 nm thick amorphous GST–TiOx film with 9.1 mol. % TiOx content. (c–e) High resolution HAADF images of the amorphous GST–TiOx films with (c) 9.1 mol. %, (d) 23.1 mol. %, and (e) 28.6 mol. % TiOx content. Images in (a,b) were obtained with 300 kV acceleration, whereas (c–e) were obtained with 200 kV acceleration and aberration-correction.
The thermal conductivity Λ (upper) and electrical resistivity ρ (lower) of the GST–TiOx films measured upon annealing.
The room temperature thermal conductivity of the GST–TiOx films shown as a function of the volume fraction of TiOx. The dashed lines are calculated by an effective medium model. The model is obviously in disagreement with the data, especially for the crystalline films, indicating the failure of effective medium theory. The theoretical thermal conductivity indicating thermal transport by the random walk of thermal energy in crystalline GST, Λrand, is also shown for comparison.
(a) The relative contributions of electronic (open symbols, right axis) and phonon (filled symbols, left axis) transport to the thermal conductivity in GST–TiOx films estimated by means of the Wiedemann-Franz law. (b) The lattice thermal conductivity Λph of the GST–TiOx films obtained by subtracting the electronic thermal conductivity Λel from the Λ data plotted in Fig. 2.
The apparent interfacial thermal conductance G app of the crystalline GST/TiOx interfaces estimated for the GST–TiOx films, plotted against (a) temperature and (b) the content of TiOx. The interfacial thermal conductance G measured from the multi-stack structure is shown as a blue dashed line in (b). The estimated value from the diffuse mismatch model for the crystalline GST/TiO2(rutile) interface is shown together for comparison (orange dashed line).
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