Single-layer MoS₂

This thesis explores the electronic properties of one layered transition-metal dichalcogenide – single-layer MoS2, and demonstrates the first transistors and integrated circuits with characteristics that outperform graphene electronics in many aspects and have comparable properties to nowadays silicon electronics. The first part describes the production methods of transition-metal dichalcogenides (TMDs) and optical detection of mechanically exfoliated TMDs. A simple optical model is used to calculate the contrast of nanolayers on SiO2 substrate. Atomic force microscopy is used for determination of the thickness of atomically flat layers. The optical contrast of thicker TMD layers is proposed for fast and ease differentiation among mono double and tri-layers. The second part is devoted to fabrication of filed-effect transistors based on single-layer MoS2. For the first time high current on/off ratio ∼ 108, subthreshold swing as low as 74 mV/dec and moderately high electron mobility ∼ 50 cm2/Vs are demonstrated. Subsequently, based on this platform we fabricated and demonstrated operation of the first logic gates, integrated circuits and small-signal analog amplifiers. The previous demonstrations in the first and the second part were based on the improved characteristics of filed-effect transistors with an HfO2 top gate dielectric that acts as a mobility booster in the same time. The physical mechanism of this improvement has been studied in the third section. The charge impurities and defects in SiO2 substrate are suggested to be the main reason of the mobility degradation in thin MoS2 layers. We performed Hall effect measurements in order to unambiguously determine the capacitance of the top gate dielectric and charge concentration in MoS2 channel. Magnetotransport measurements are presented as well demonstrating weak and strong localization in top-gated field-effect transistors based on single-layer MoS2.