In nano-device applications using two-dimensional (2D) van der Waals materials, a heat dissipation through nano-scale interfaces can be a critical issue for optimizing device performances. By using a time-domain thermoreflectance measurement technique, we examine a cross-plane thermal transport through mono-layered (n = 1) and bi-layered (n = 2) WSe 2 flakes which are sandwiched by top metal layers of Al, Au, and Ti and the bottom Al 2 O 3 substrate. In these nanoscale structures with hetero- and homo-junctions, we observe that the thermal boundary resistance (TBR) is significantly enhanced as the number of WSe 2 layers increases. In particular, as the metal is changed from Al, to Au, and to Ti, we find an interesting trend of TBR depending on the WSe 2 thickness; when referenced to TBR for a system without WSe 2 , TBR for n = 1 decreases, but that for n = 2 increases. This result clearly demonstrates that the stronger bonding for Ti leads to a better thermal conduction between the metal and the WSe 2 layer, but in return gives rise to a large mismatch in the phonon density of states between the first and second WSe 2 layers so that the WSe 2 -WSe 2 interface becomes a major thermal resistance for n = 2. By using photoemission spectroscopy and optical second harmonic generation technique, we confirm that the metallization induces a change in the valence state of W-ions, and also recovers a non-centrosymmetry for the bi-layered WSe 2 .
|Publication status||Published - 2019 Dec 1|
Bibliographical noteFunding Information:
This work was supported in part by the Science Research Center and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Nos 2015R1A5A1009962, 2018R1A2B2005331). This work was supported by the “GRI (GIST Research Institute)” Project through a grant provided by GIST in 2018.
© 2019, The Author(s).
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