Electronic properties of transition-metal dichalcogenides
- PDF / 3,651,705 Bytes
- 8 Pages / 585 x 783 pts Page_size
- 81 Downloads / 254 Views
Introduction After quantum dots, nanowires, and nanotubes, two-dimensional (2D) materials in the form of sheets with atomic-scale thickness represent the most recent nanoscale material family under intense study. These materials appear in their bulk form as stacks of layers held together via van der Waals interaction in crystals. Single layers with atomic-scale thickness can be extracted from such crystals. The best-known example is graphite, composed of individual graphene layers. Twodimensional materials are attractive for use in electronic devices because, compared to nanowires and nanotubes, it is easier to fabricate complex structures from them. Their atomicscale thickness makes it possible to tune their properties using external electric fields, while control over the number of layers in mesoscopic structures gives an additional way to modify their electronic and optical properties.1,2 The first layered material to be thinned to a single monolayer (ML) was graphite, where the ML is referred to as graphene.3 It continues to be widely studied because of its rich physics and high mobility.4 However, pristine graphene does not have a bandgap, which is required for many applications in electronics and optoelectronics. Bandgaps can be engineered in graphene, but this increases complexity either reduces mobilities to the level of strained silicon films (∼100 cm2/Vs at room temperature) or requires voltages on the order of 100 V.5,6
One of the key advances that brought attention to 2D semiconductors was the demonstration of a field-effect transistor (FET) with a high ON/OFF ratio based on a single layer of MoS2,7 a semiconducting material from the transition-metal dichalcogenide (TMDC) family. This was the first demonstration of a high-quality device based on a 2D material other than graphene. MoS2 (Figure 1) is a member of a large family of materials known as TMDCs (please see the Introduction article in this issue of MRS Bulletin). They have the common chemical formula MX2, where M stands for a transition metal (M = Mo, W, Nb, Ta, Ti, Re) and X for Se, S, or Te. Bulk TMDC crystals are formed by vertical stacking of 2D layers that are ∼6.5 Å thick. Depending on the chemical composition, they can have different electrical properties ranging from semiconducting to superconducting. Single layers can be extracted using the micromechanical cleavage technique,9,10 commonly used for the production of graphene or liquid phase exfoliation, a mild solvent-based exfoliation technique.11 Large-area MoS2 can be grown using chemical-vapor-deposition-like growth techniques.12,13 The lack of dangling bonds also makes it possible to re-stack different 2D materials in the vertical direction and produce heterostructures14 without the requirement of lattice matching. Around 60 TMDC materials were known in the late 1960s, with around 40 of them having a layered structure15 (Table I).
Agnieszka Kuc, Jacobs University Bremen, Germany; [email protected] Thomas Heine, Jacobs University Bremen, Germany; [email protected] And
Data Loading...
