Transition metal chalcogenides are a class of van der Waals materials displaying interesting electronic properties that depend on both the transition metal and the chalcogenide involved as well as the observed polymorph. Transition metal dichalcogenides, MX2, are quasi-2D materials that can vary electronically from semiconductors to metallic-like conductors, with some displaying superconductivity and charge density wave behaviors. MX2 materials consist of X-M-X layers where the metal centers are in an octahedral or trigonal prismatic configuration.1-2 Transition metal trichalcogenides, MX3, exhibit lower dimensionality structurally as quasi-1D materials consisting of MX6 trigonal prismatic chains. They do, however, show similar electronic properties including metallic-like conductivity, superconductivity, and charge density waves. These properties depend on orientation of the MX chains in the unit cell which changes depending on the metal and chalcogenide.3-4
For future electronics applications, it is important to understand the synthesis, characterization, manipulation and properties of MX2 and MX3 materials at the nanoscale. This talk focuses on the oxidative behavior of two important MX2’s, 1T-TiSe2 and 1T-TaSe2, as well as the synthesis and exfoliation behavior of a metallic MX3, TaSe3. The oxidation of 1T-TiSe2 and 1T-TaSe2 resulted in the onset of oxidation near 300 °C for both MX2’s. Under a critical temperature, 400 °C for 1T-TiSe2 and 700 °C for 1T-TaSe2, a self-limiting, surface oxidation was observed, analogous to previous studies with WSe2.5 TaSe3 was also successfully synthesized and characterized with special attention paid to the chemical exfoliation behavior and crystallinity. Partial exfoliation was achieved leading to highly crystalline belts6-7 up to several microns in length and reaching a minimum width of ~5 nm.
1. Lieth, R. M. A.; Terhell, J. C. J. M., Transition Metal Dichalcogenides. In Preparation and Crystal Growth of Materials with Layered Structures, Lieth, R. M. A., Ed. Springer Netherlands: Dordrecht, 1977; pp 141-223.
2. Samnakay, R.; Wickramaratne, D.; Pope, T. R.; Lake, R. K.; Salguero, T. T.; Balandin, A. A., Zone-Folded Phonons and the Commensurate–Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films. Nano Letters 2015, 15 (5), 2965-2973.
3. Furuseth, S.; Brattas, L.; Kjekshus, A., On the Crystal Structures of TiS3, ZrS3, ZrSe3, ZrTe3, HfS3 and HfSe3. Acta Chemica Scandinavica 1975, 29, 623.
4. Zybtsev, S. G.; Pokrovskii, V. Y.; Nasretdinova, V. F.; Zaitsev-Zotov, S. V., Growth, crystal structure and transport properties of quasi one-dimensional conductors NbS3. Physica B: Condensed Matter 2012, 407 (11), 1696-1699.
5. Liu, Y.; Tan, C.; Chou, H.; Nayak, A.; Wu, D.; Ghosh, R.; Chang, H.-Y.; Hao, Y.; Wang, X.; Kim, J.-S.; Piner, R.; Ruoff, R. S.; Akinwande, D.; Lai, K., Thermal Oxidation of WSe2 Nanosheets Adhered on SiO2/Si Substrates. Nano Letters 2015, 15 (8), 4979-4984.
6. Stolyarov, M. A.; Liu, G.; Bloodgood, M. A.; Aytan, E.; Jiang, C.; Samnakay, R.; Salguero, T. T.; Nika, D. L.; Rumyantsev, S. L.; Shur, M. S.; Bozhilov, K. N.; Balandin, A. A., Breakdown current density in h-BN-capped quasi-1D TaSe3 metallic nanowires: prospects of interconnect applications. Nanoscale 2016, 8 (34), 15774-15782.
7. Liu, G.; Rumyantsev, S.; Bloodgood, M. A.; Salguero, T. T.; Shur, M.; Balandin, A. A., Low-Frequency Electronic Noise in Quasi-1D TaSe3 van der Waals Nanowires. Nano Letters 2017, 17 (1), 377-383.