Chemical vapor deposition allows the preparation of few-layer films of MoTe in three distinct structural phases depending on the growth quench temperature: 2H, 1T', and 1T. We present experimental and computed Raman spectra for each of the phases and utilize transport measurements to explore the properties of the 1T MoTe phase. Density functional theory modeling predicts a (semi-)metallic character. Our experimental 1T films affirm the former, show facile μA-scale source-drain currents, and increase in conductivity with temperature, different from the 1T' phase. Variation of the growth method allows the formation of hybrid films of mixed phases that exhibit susceptibility to gating and significantly increased conductivity.
Micron-scale single-crystal nanowires of metallic TaSe3, a material that forms -Ta-Se3-Ta-Se3-stacks separated from one another by a tubular van der Waals (vdW) gap, have been synthesized using chemical vapor deposition (CVD) on a SiO2/Si substrate, in a process compatible with semiconductor industry requirements. Their electrical resistivity was found unaffected by downscaling from the bulk to as little as 7 nm in width and height, in striking contrast to the resistivity of copper for the same dimensions. While the bulk resistivity of TaSe3 is substantially higher than that of bulk copper, at the nanometer scale the TaSe3 wires become competitive to similar-sized copper ones. Moreover, we find that the vdW TaSe3 nanowires sustain current densities in excess of 10 8 A/cm 2 and feature an electromigration energy barrier twice that of copper. The results highlight the promise of quasi-onedimensional transition metal trichalcogenides for electronic interconnect applications and the potential of van der Waals materials for downscaled electronics.
We report the fabrication of large-scale arrays of suspended molybdenum disulfide (MoS2) atomic layers, as two-dimensional (2D) MoS2 nanomechanical resonators. We employ a water-assisted lift-off process to release chemical vapor deposited (CVD) MoS2 atomic layers from a donor substrate, followed by an all-dry transfer onto microtrench arrays. The resultant large arrays of suspended single- and few-layer MoS2 drumhead resonators (0.5-2 μm in diameter) offer fundamental resonances (f0) in the very high frequency (VHF) band (up to ∼120 MHz) and excellent figures-of-merit up to f0 × Q ≈ 3 × 10(10) Hz. A stretched circular diaphragm model allows us to estimate low pre-tension levels of typically ∼15 mN m(-1) in these devices. Compared to previous approaches, our transfer process features high yield and uniformity with minimal liquid and chemical exposure (only involving DI water), resulting in high-quality MoS2 crystals and exceptional device performance and homogeneity; and our process is readily applicable to other 2D materials.
Wafer-scale MoS growth at arbitrary integer layer number is demonstrated by a technique based on the decomposition of carbon disulfide on a hot molybdenum filament, which yields volatile MoS precursors that precipitate onto a heated wafer substrate. Colorimetric control of the growth process allows precise targeting of any integer layer number. The method is inherently free of particulate contamination, uses inexpensive reactants without the pyrophoricity common to metal-organic precursors, and does not rely on particular gas-flow profiles. Raman mapping and photoluminescence mapping, as well as imaging by electron microscopy, confirm the layer homogeneity and crystalline quality of the resultant material. Electrical characterization revealed microampere output current, outstanding device-to-device consistency, and exceptionally low noise level unparalleled even by the exfoliated material, while other transport properties are obscured by high-resistance contacts typical to MoS devices.
We report on the chemical vapor deposition (CVD) growth of quasi-one-dimensional zirconium tritelluride (ZrTe 3 ) at temperatures below 600 °C and process times under an hour, which results in a material on a SiO 2 /Si wafer substrate that offers electrical conductivity comparable to the bulk. This study combines tailored CVD processing using a tube-in-a-tube technique with characterization by optical microscopy, Raman spectroscopy, and scanning electron microscopy. Transmission electron microscopy validates the composition and offers atomic contrast. Electrical transport measurements employ an yttriumgold stack to achieve good adhesion and low contact resistance. A positive temperature coefficient is observed, as expected for a metallic material. The obtained results are important for the proposed applications of quasi-one-dimensional van der Waals materials in the next-generation electronic devices.
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