![]() The phase conversion using Argon plasma yields predominantly the 2H phase and the concentration of 1T phase is around 40% 34. The recent report on the solution phase synthesis of 1T MoS 2, in large concentrations, from the 2H phase yielded only nanosheets and, is not suitable for scalable device fabrication schemes 23. The 1T phase thus obtained is reported to be thermodynamically unstable and relaxes to 1T′ or 2H over time or above a temperature range of 150 ☌, which is in the range of standard sample processing temperatures for device applications 13, 26, 31, 35, 36. Intercalation gives a mixture of 1T, 1T′ and 2H phases 11, 13, 30. The transition has been achieved using alkali metal or hydrogen intercalation 11, 19, 25, 27, 28, 29, 30, substitutional doping by Re atom 31, annealing accompanied energetic electron-beam irradiation 12, 32, plasmonic hot electrons 33 and Argon plasma 34. The possibility of controllably and selectively engineering metallic 1T MoS 2 regions starting from the semiconducting 2H MoS 2 provides a new route for monolithic 2D circuits.ĢH to 1T phase transition happens via relative gliding of the Mo and S planes 12, 27. The 1T′ and 1T″ are distorted 1T phases 13. The 2H phase belongs to the space group P6 3 mmc with a trigonal prismatic coordination between Mo and S atoms and 1T belongs to \(P\barm\) space group with an octahedral coordination between the Mo and S atoms 26. The 1T phase has recently gained attention as a candidate for energy storage 19, 20, 21, hydrogen evolution 22, 23, 24 and as a low-resistance electrical contact for 2H MoS 2 devices 25. The 2H is the most widely explored phase for device applications 5, 14, 15, 16, 17, 18. The presence of polymorphic phases with distinct electrical properties while maintaining the layered nature makes MoS 2 a potential system 9, 10, 11, 12.Īmong the reported structural phases, 2H, 2H′ and 3R are semiconductors, 1T′ and 1T″ are narrow bandgap semiconductors and 1T is metallic 9, 10, 11, 12, 13. Rather than stacking, a lateral monolithic integration of regions with different electrical properties while preserving the two-dimensionality is an important ingredient for future microelectronics technology. Hybrid devices consisting of physically stacked layers of MoS 2 and other vW materials has also been explored for various device applications MoS 2/Graphene interfaces for improved electrical contacts 4, 5, MoS 2/h-BN hybrid systems for mobility engineering 3, 5 and electrostatic confinement 6, 7, 8, MoS 2/WSe 2 PN-junction devices 2 have been reported. In addition, our samples show negligible temperature dependence of resistance from 4 K to 300 K ruling out any hoping mediated or activated electrical transport.Īn all two-dimensional (2D) architecture involving vertical integration of van der Waals (vW) materials has been explored as a platform for the future semiconductor technology 1, 2, 3. The sheet resistance of our 1T MoS 2 sample is considerably lower and the carrier concentration is a few orders of magnitude higher than that of the 2H samples. The 1T samples exhibit Ohmic current-voltage characteristics in all temperature ranges without any dependence to the gate voltage, a signature of a metallic state. We conduct both two-probe and four-probe electrical transport measurements on devices with back-gated field effect transistor geometry in a temperature range of 4 K to 300 K. The 1T samples show excellent temporal and thermal stability making it suitable for standard device fabrication techniques. Our method allows lithographically defining 1T regions on a 2H sample. Here we demonstrate a controllable and scalable 2H to 1T phase engineering technique for MoS 2 using microwave plasma. A method for engineering a stable 1T phase from the 2H phase in a scalable manner and an in-depth electrical characterization of the 1T phase is wanting at large. Monolithic realization of metallic 1T and semiconducting 2H phases makes MoS 2 a potential candidate for future microelectronic circuits. ![]()
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