Two-dimensional (2D) materials are a new class of materials with interesting physical properties and ranging from nanoelectronics to sensing and photonics. In addition to graphene, the most studied 2D material, monolayers of other layered materials such as semiconducting dichalcogenides MoS 2 or WSe 2 are gaining in importance as promising insulators and channel materials for field-effect transistors (FETs). The presence of a direct band gap in monolayer MoS 2 due to quantum mechanical confinement, allows room-temperature field-effect transistors with an on/off ratio exceeding 10 8 . The presence of high-k dielectrics in these devices enhanced their mobility, but the mechanisms are not well understood. Here, we report on electrical transport measurements on MoS 2 FETs in different dielectric configurations. Mobility dependence on temperature shows clear evidence of the strong suppression of charge impurity scattering in dual-gate devices with a topgate dielectric together with phonon scattering that shows a weaker than expected temperature dependence. High levels of doping achieved in dual-gate devices also
Logic circuits and the ability to amplify electrical signals form the functional backbone of electronics along with the possibility to integrate multiple elements on the same chip. The miniaturization of electronic circuits is expected to reach fundamental limits in the near future. Two-dimensional materials such as single-layer MoS2 represent the ultimate limit of miniaturization in the vertical dimension, are interesting as building blocks of low-power nanoelectronic devices, and are suitable for integration due to their planar geometry. Because they are less than 1 nm thin, 2D materials in transistors could also lead to reduced short channel effects and result in fabrication of smaller and more power-efficient transistors. Here, we report on the first integrated circuit based on a two-dimensional semiconductor MoS2. Our integrated circuits are capable of operating as inverters, converting logical “1” into logical “0”, with room-temperature voltage gain higher than 1, making them suitable for incorporation into digital circuits. We also show that electrical circuits composed of single-layer MoS2 transistors are capable of performing the NOR logic operation, the basis from which all logical operations and full digital functionality can be deduced.
Dichalcogenides with the common formula MX 2 are layered materials with electrical properties that range from semiconducting to superconducting. Here, we describe optimal imaging conditions for the optical detection of ultrathin, two-dimensional dichalcogenide nanocrystals containing single, double and triple layers of MoS 2 , WSe 2 and NbSe 2 . A simple optical model is used to calculate the contrast for nanolayers deposited on wafers with varying thicknesses of SiO 2 . The model is extended for imaging using the green channel of a video camera. Using AFM and optical imaging we confirm that single layers of MoS 2 and WSe 2 can be detected on 90 and 270 nm SiO 2 using optical means. By measuring contrast under broadband green illumination we are also able to distinguish between nanostructures containing single, double and triple layers of MoS 2 and WSe 2. We observe and discuss discrepancies in the case of NbSe 2 .(Some figures in this article are in colour only in the electronic version)The family of transition metal dichalcogenides with the common formula MX 2 , where M stands for transition metal (M = Mo, W, Nb, Ta, Ti) and X for Se, S or Te displays a rich variety of physical properties. Depending on the metal and the chalcogen involved, their electrical properties span the range from semiconducting to superconducting. Bulk dichalcogenide crystals are composed of vertically stacked layers bound together by weak van der Waals interaction. Just as in the case of graphene [1], single dichalcogenide layers can be extracted from bulk crystals [2,3] and deposited on substrates for further studies. Single MX 2 layers present a wide range of systems for studying mesoscopic transport in 2D and could find practical applications complementary to those of graphene. Bulk WSe 2 has, for example, been used in the past for fabrication of photovoltaic cells [4], whereas MoS 2 nanotubes [5] and nanowires [6] show confinement effects in their electronic and optical properties. Semiconducting dichalcogenides could also be interesting for fabrication of nanoscale field effect transistors [3, 7-9] while superconducting NbSe 2 could be a model for studying superconductivity in low-dimensional systems at mesoscopic scales [10,11].Locating and identifying single nanolayers of materials such as graphite [1] or semiconducting transition metal dichalcogenides [3] such as MoS 2 or WSe 2 is the first, enabling step in the study and practical applications of these materials. Atomic force microscopy (AFM) can be used to accurately determine both the vertical and lateral dimensions of nanolayers deposited on insulating substrates such as SiO 2 . AFM imaging is, however, time-consuming and the relatively slow throughput of the technique is a serious drawback. Scanning electron microscopy (SEM) or transmission electron microscopy (TEM) could also be used here, but contamination [12] due to electron-beam-induced deposition or knock-on damage in TEM due to electron-beam radiation-induced displacement of atoms could be a serious problem ...
In this Letter we demonstrate the operation of an analog small-signal amplifier based on single-layer MoS2, a semiconducting analogue of graphene. Our device consists of two transistors integrated on the same piece of single-layer MoS2. The high intrinsic band gap of 1.8 eV allows MoS2-based amplifiers to operate with a room temperature gain of 4. The amplifier operation is demonstrated for the frequencies of input signal up to 2 kHz preserving the gain higher than 1. Our work shows that MoS2 can effectively amplify signals and that it could be used for advanced analog circuits based on two-dimensional materials.Comment: Submitted version of the manuscrip
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