Nanoporous materials are widely explored as efficient adsorbents for the storage of gases and liquids as well as for effective low-dielectric materials in large-scale integrated circuits. These applications require fast heat transfer, while most nanoporous substances are thermal insulators. Here, the oriented growth of micrometer-sized single-crystal covalent organic frameworks (COFs) ribbons with nanoporous structures at an air−water interface is presented. The obtained COFs ribbons are interconnected into a continuous and purely crystalline thin film. Due to the robust connectivity among the COFs ribbons, the entire film can be easily transferred and reliably contacted with target supports. The measured thermal conductivity amounts to ∼5.31 ± 0.37 W m −1 K −1 at 305 K, which is so far the highest value for nanoporous materials. These findings provide a methodology to grow and assemble single-crystal COFs into large area ensembles for the exploration of functional properties and potentially lead to new devices with COFs thin films where both porosity and thermal conductivity are desired.

Thermal conductivity (κ) of the single-crystalline bilayer graphene (BLG) is investigated experimentally as a function of the interlayer twist angle (θ) and temperature using the optothermal Raman technique. The results show that a slight 2° twist angle leads to a κ decrease in 15% at ∼320 K. With the regulation of θ from 0° to 30°, the in-plane κ of the BLG decreases first and then increases showing an asymmetry V shape. The local maximum value of κ was reached when the twist angle is 30° and the highest value was found on the Bernal stacked BLG. The obtained κ is further found to be sensitive to the Moire periodicity but insensitive to the commensurate lattice constant of the twisted BLG. The non-equilibrium molecular dynamics simulation reveals that the twist angle in t-BLG affects the proportion of low-frequency phonons and finally changes the κ. The quantitative study validates the regulation of thermal conduction through the interlayer twist angle and favors the further understanding of thermal transport in the van der Waals bilayer systems.

The grain size effect on the thermal transport properties of hexagonal boron nitride (h-BN) thin films was experimentally investigated using the opto-thermal Raman technique. High-quality monolayer h-BN with mean grain sizes ranging from ~7 µm to ~19 nm were successfully synthesized on Pt foil by chemical vapor deposition (CVD). The thermal conductivity (κ) of the singlecrystalline h-BN was measured to be ~545 Wm −1 K −1 at 315K, well above the bulk value, and more than a factor of four higher than the value of poly-crystalline h-BN with mean grain size of ~19 nm. The very low thermal boundary conductance (deduced to be ~9.6 GW m −2 K −1 ) accounts for the significant reduction of κ for h-BN with small grain size. Molecular dynamics (MD) simulations reveal that due to the disordered vibrations of atoms along/near GB, the phonon scattering in polycrystalline h-BN is greatly enhanced compared to large-grained or single-crystalline samples. These results provide a deep understanding of the thermal transport in two-dimensional systems as well as the possible technological applications.

Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature. Clear spin accumulation signals are detected by the non-local measurement. By fitting the results to the one-dimensional diffusion equation, ∼ 8.6% spin polarization of the Co/Ag interface and ∼ 180 nm spin diffusion length in Ag are obtained. Thermal treatment results show that the spin accumulation signal drastically decreases after 100 • C annealing, and disappears under 200 • C annealing. Our results demonstrate that, compared to the spin diffusion length, the decrease and the disappearance of the spin accumulation signal are mainly dominated by the variation of the interfacial spin polarization of the Co/Ag interface.

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