We report on the investigation of thermal transport in noncured silicone composites with graphene fillers of different lateral dimensions. Graphene fillers are comprised of few-layer graphene flakes with lateral sizes in the range from 400 to 1200 nm and the number of atomic planes from 1 to ∼100. The distribution of the lateral dimensions and thicknesses of graphene fillers has been determined via atomic force microscopy statistics. It was found that in the examined range of the lateral dimensions, the thermal conductivity of the composites increases with increasing size of the graphene fillers. The observed difference in thermal properties can be related to the average gray phonon mean free path in graphene, which has been estimated to be around ∼800 nm at room temperature. The thermal contact resistance of composites with graphene fillers of 1200 nm lateral dimensions was also smaller than that of composites with graphene fillers of 400 nm lateral dimensions. The effects of the filler loading fraction and the filler size on the thermal conductivity of the composites were rationalized within the Kanari model. The obtained results are important for the optimization of graphene fillers for applications in thermal interface materials for heat removal from high-power-density electronics.

We report on experimental investigation of thermal contact resistance, RC, of the noncuring graphene thermal interface materials with the surfaces characterized by different degree of roughness, Sq. It is found that the thermal contact resistance depends on the graphene loading, ξ, non-monotonically, achieving its minimum at the loading fraction of ξ ~15 wt %. Decreasing the surface roughness by Sq~1 μm results in approximately the factor of ×2 decrease in the thermal contact resistance for this graphene loading. The obtained dependences of the thermal conductivity, KTIM, thermal contact resistance, RC, and the total thermal resistance of the thermal interface material layer on ξ and Sq can be utilized for optimization of the loading fraction of graphene for specific materials and roughness of the connecting surfaces. Our results are important for the thermal management of high-power-density electronics implemented with diamond and other wide-band-gap semiconductors.

We report on the fabrication and characterization of electronic devices printed with inks of quasi-one-dimensional (1D) van der Waals materials. The quasi-1D van der Waals materials are characterized by 1D motifs in their crystal structure, which allow for their exfoliation into bundles of atomic chains. The ink was prepared by the liquid-phase exfoliation of crystals of TiS3 into quasi-1D nanoribbons dispersed in a mixture of ethanol and ethylene glycol. The temperature-dependent electrical measurements indicate that the electron transport in the printed devices is dominated by the electron hopping mechanisms. The low-frequency electronic noise in the printed devices is of 1/f γ -type with γ ∼ 1 near-room temperature (f is the frequency). The abrupt changes in the temperature dependence of the noise spectral density and γ parameter can be indicative of the phase transition in individual TiS3 nanoribbons as well as modifications in the hopping transport regime. The obtained results attest to the potential of quasi-1D van der Waals materials for applications in printed electronics.

We report on the preparation of flexible polymer composite films with aligned metallic fillers composed of atomic chain bundles of quasi-one-dimensional (1D) van der Waals material, tantalum triselenide (TaSe3). The material functionality, embedded at the nanoscale level, is achieved by mimicking the design of an electromagnetic aperture grid antenna. The processed composites employ chemically exfoliated TaSe3 nanowires as the grid building blocks incorporated within the thin film. Filler alignment is achieved using the “blade coating” method. Measurements conducted in the X-band frequency range demonstrate that the electromagnetic transmission through such films can be varied significantly by changing the relative orientations of the quasi-1D fillers and the polarization of the electromagnetic wave. We argue that such polarization-sensitive polymer films with unique quasi-1D metallic fillers are applicable to advanced electromagnetic interference shielding in future communication systems.

Semiconductors have been studied as the most promising thermoelectric materials for the past decades due to their high Seebeck coefficient. Semimetals usually have a small Seebeck coefficient due to a small difference in the density of states between electrons and holes, compensating each other in the longitudinal direction. However, recent studies suggested that semimetals with large asymmetry between electrons and holes could be good thermoelectric candidates. Here, we report the crystal structure and thermoelectric properties of layered van der Waals semimetal ZrTiSe4. Micrometer-sized single crystals of ZrTiSe4 were obtained by the solid-state reaction. The single-crystal X-ray diffraction study suggests that this material exhibits a trigonal structure with space group P3̅m1 (no. 164), instead of a P2/m (no. 10) monoclinic phase reported in the previous work. ZrTiSe4 has the same crystal structure as ZrSe2 and TiSe2 with Zr and Ti atoms occupying the same site with equal occupancy. Polycrystalline ZrTiSe4 samples consolidated by cold pressing show a semi-metallic type of resistivity in the temperature range of 2–400 K and an n-type conducting behavior. The samples exhibit an unusually large Seebeck coefficient of −202 ± 11 μV K–1 at 300 K, notably higher than the parent phases of ZrSe2 and TiSe2 as well as other semimetals. Based on the first-principles calculations of the electronic band structure, the large Seebeck coefficient of ZrTiSe4 could arise from the conduction band convergence at the M point, resulting in a large density of states (DOS) effective mass for electrons and a highly asymmetric DOS about the chemical potential. Furthermore, owing to a low sound velocity and strong phonon scattering by boundaries and defects, the thermal conductivity exhibits weak temperature dependence and a low value of 2.2 ± 0.4 W m–1 K–1 at 300 K. This work provides useful insights into the crystal structure and thermoelectric properties of semimetal ZrTiSe4.