dc.description.abstract | Graphene has attracted much attention due to its unique two dimensional structure and physical properties, such as high carrier mobility. However, the gapless nature prohibits its application of logic circuits. Other two-dimensional layered nanomaterials, transition metal dichalcogenides(TMDs), such as MoS2, also show great potential in nanoelectronics and optical applications. MoS2 is superior than graphene to fabricate high-performance devices, because of its two-dimensional structure but also possesses thickness-dependent band gap.
Recently, several methods have been proposed to prepare MoS2 atomically thin layers, including exfoliation and chemical vapor deposition, etc. However, it is challenging for these methods to produce large area and continuous MoS2 thin films, and thus not suitable for large area electronics. In this thesis, we present a simple and scalable two-step method for MoS2 synthesis. First, we used UHV-sputter system to deposit MoS2 thin films on sapphire substrates by using a MoS2 target, followed by sulfurization in hot-wall furnace. This method produces large area and continuous MoS2 thin films, and provides excellent controllability on the number of layers of MoS2 by sputtering time. The 4×1 in2 MoS2 thin films, demonstrated in this study was limited by the quartz tube furnace with 1-inch diameter. If we increase the diameter of the quartz tube, MoS2 thin films with even larger areas can be expected. Various spectroscopic and microscopic methods, including Raman spectroscopy、photoluminescence spectroscopy、high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy confirmed that our films are high quality. We also fabricated bilayer and mutiple-layer top-gate MoS2 thin film transistors with reasonable electrical characterizations. By decreasing the temperature of sulfurization, we further improved the uniformity of our films. The bilayer MoS2 thin film transistors also show superior characteristics with on/off current ratio of 104、subthreshold swing 873 mV/decade and electron mobility of 0.0193 cm2/Vs. Although there are still various problems to be solved before realizing high-performance devices, this research serves as a starting point for future large-area MoS2 applications.
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