We report on the current-carrying capacity of the nanowires made from the quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by chemical and mechanical exfoliation were used to fabricate the mm-long TaSe3 wires with the lateral dimensions in the 20 to 70 nm range. Electrical measurements establish that the TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm(-2)-an order-of-magnitude higher than that for copper. Some devices exhibited an intriguing step-like breakdown, which can be explained by the atomic thread bundle structure of the nanowires. The quasi-1D single crystal nature of TaSe3 results in a low surface roughness and in the absence of the grain boundaries. These features can potentially enable the downscaling of the nanowires to lateral dimensions in a few-nm range. Our results suggest that quasi-1D van der Waals metals have potential for applications in the ultimately downscaled local interconnects.

We report on the results of the low-frequency (1/f, where f is frequency) noise measurements in MoS2 field-effect transistors revealing the relative contributions of the MoS2 channel and Ti/Au contacts to the overall noise level. The investigation of the 1/f noise was performed for both as fabricated and aged transistors. It was established that the McWhorter model of the carrier number fluctuations describes well the 1/f noise in MoS2 transistors, in contrast to what is observed in graphene devices. The trap densities extracted from the 1/f noise data for MoS2 transistors, are 2 × 1019 eV−1cm−3 and 2.5 × 1020 eV−1cm−3 for the as fabricated and aged devices, respectively. It was found that the increase in the noise level of the aged MoS2 transistors is due to the channel rather than the contact degradation. The obtained results are important for the proposed electronic applications of MoS2 and other van der Waals materials.

We demonstrated selective gas sensing with MoS 2 thin-film transistors using the change in the channel conductance, characteristic transient time and low-frequency current fluctuations as the sensing parameters. The back-gated MoS 2 thin-film field-effect transistors were fabricated on Si/SiO 2 substrates and intentionally aged for a month to verify reliability and achieve better current stability. The same devices with the channel covered by 10 nm of Al 2 O 3 were used as reference samples. The exposure to ethanol, acetonitrile, toluene, chloroform, and methanol vapors results in drastic changes in the source-drain current. The current can increase or decrease by more than two-orders of magnitude depending on the analyte. The reference devices with coated channel did not show any response. It was established that transient time of the current change and the normalized spectral density of the low-frequency current fluctuations can be used as additional sensing parameters for selective gas detection with thin-film MoS 2 transistors.

We report on the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe 2 ) obtained via the "graphene-like" mechanical exfoliation of crystals grown by chemical vapor transport. The ratio of the intensities of the Raman peak from the Si substrate and the E 2g peak of TaSe 2 presents a convenient metric for quantifying film thickness. The temperature coefficients for two main Raman peaks, A 1g and E 2g , are -0.013 and -0.0097 cm -1 / o C, respectively. The Raman optothermal measurements indicate that the room temperature thermal conductivity in these films decreases from its bulk value of ~16 W/mK to ~9 W/mK in 45-nm thick films. The measurement of electrical resistivity of the field-effect devices with TaSe 2 channels indicates that heat conduction is dominated by acoustic phonons in these van der Waals films. The scaling of thermal conductivity with the film thickness suggests that the phonon scattering from the film boundaries is substantial despite the sharp interfaces of the mechanically cleaved samples. These results are important for understanding the thermal properties of thin films exfoliated from TaSe 2 and other metal dichalcogenides, as well as for evaluating self-heating effects in devices made from such materials.KEYWORDS: van der Waals materials, tantalum diselenide, Raman spectroscopy, thermal conductivity, metal dichalcogenide, thin film *Corresponding authors: salguero@uga.edu (TTS) and balandin@ee.ucr.edu (AAB) 2 | P a g e

We report the fabrication and performance of all-metallic three-terminal devices with tantalum diselenide thin-film conducting channels. For this proof-of-concept demonstration, the layers of 2H-TaSe 2 were exfoliated mechanically from single crystals grown by the chemical vapor transport method. Devices with nanometer-scale thicknesses exhibit strongly non-linear currentvoltage characteristics, unusual optical response, and electrical gating at room temperature. We have found that the drain-source current in thin-film 2H-TaSe 2 -Ti/Au devices reproducibly shows an abrupt transition from a highly resistive to a conductive state, with the threshold tunable via the gate voltage. Such current-voltage characteristics can be used in principle for implementing radiation-hard all-metallic logic circuits. These results may open new application space for thin films of van der Waals materials.

Owing to their ultimate surface-to-volume ratio two-dimensional (2D) van der Waals materials are candidates for flexible gas sensor applications. However, all demonstrated devices had relied on direct exposure of the active 2D channel to gases, which presents problems for their reliability and stability. We demonstrated, for the first time, selective gas sensing with molybdenum disulfide (MoS 2 ) thin films transistors capped with a thin layer of hexagonal boron nitride (h-BN). The resistance change, R/R, was used as a sensing parameter to detect chemical vapors. It was found that h-BN dielectric passivation layer does not prevent gas detection via changes in the current in the MoS 2 channel. The detection was achieved without direct contact of the channel with analyte molecules R/R ratio as high 10 5 % in some cases. In addition, we show that the use of h-BN cap layers (thickness H~10 nm) improves sensor stability and prevents degradation due to environmental and chemical exposure.

We report on the transport and low-frequency noise measurements of MoS 2 thin-film transistors (TFTs) with thin (2-3 atomic layers) and thick (15-18 atomic layers) channels. The back-gated transistors made with the relatively thick MoS 2 channels have advantages of the higher electron mobility and lower noise level. The normalized noise spectral density of the low-frequency 1/ f noise in thick MoS 2 transistors is of the same level as that in graphene. The MoS 2 transistors with the atomically thin channels have substantially higher noise levels. It was established that, unlike in graphene devices, the noise characteristics of MoS 2 transistors with thick channels (15-18 atomic planes) could be described by the McWhorter model. Our results indicate that the channel thickness optimization is crucial for practical applications of MoS 2 TFTs.

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