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Ultralow Thermal Conductivity of Turbostratically Disordered MoSe2 Ultra-Thin Films and Implications for Heterostructures
摘要： Films containing 8, 16, 24, 32 and 64 MoSe2 layers were synthesized using the modulated elemental reactants (MER) method. X-ray reflectivity patterns showed that the annealed films were the targeted number of MoSe2 layers thick with atomically smooth interfaces. In-plane x-ray diffraction scans contained only hk0 reflections for crystalline MoSe2 monolayers. Specular x-ray diffraction patterns contained only 00l reflections, also indicating that the hk0 plane of the MoSe2 layers are parallel to the substrate. Both x-ray diffraction and electron microscopy techniques indicated that the hk0 planes are rotationally disordered with respect to one another, with all orientations equally probable for large areas. The rotational disorder between MoSe2 layers is present even when analyzed spots are within 10 nm of one another. Cross-plane thermal conductivities of 0.07 – 0.09 W m-1 K-1 were measured by time domain thermoreflectance, with the thinnest films exhibiting the lowest conductivity. The structural analysis suggests that the ultralow thermal conductivity is a consequence of rotational disorder, which increases the separation between MoSe2 layers. The bonding environment of the Se atoms also becomes significantly distorted from C3v symmetry due to the rotational disorder between layers. This structural disorder efficiently reduces the group velocity of the transverse phonon modes but not that of longitudinal modes. Since rotational disorder between adjacent layers in heterostructures is expected if the constituents have incommensurate lattices, this study indicates that these heterostructures will have very low cross-plane thermal conductivity.
关键词： rotational disorder,heterostructure,TMDs,turbostratic disorder,thermal conductivity,molybdenum diselenide
更新于2025-09-23 15:22:29
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Phenomena of Optical Metamaterials || Disorder in Metamaterials
摘要： Since the emergence of the metamaterial, the disorder within artificially structured materials has been a subject of extensive discussions. Metamaterial at optical frequency can be considered as a kind of man-made architecture material possessing unusual properties. One of its remarkable features is that the equivalent permittivities on different directions differ from each other and can be varied by designing its structure elaborately. It is worthwhile mentioning that this property is enhanced by the presence of the disorder promises that metamaterial may serve for surface plasmons (SPs) propagating with more flexible performances than conventional metal or ordered metamaterial. For instance, dealing with the photonic crystals, some disorder can dramatically degrade the reflection and transmission properties, which are based on constructive interferences. This chapter covers three different models of the disordered metamaterials: (i) rotational disorder, (ii) sliding disorder, and (iii) positional disorder.
关键词： sliding disorder,rotational disorder,positional disorder,surface plasmons,metamaterials,disorder
更新于2025-09-23 15:21:01