Molybdenum Disulfide

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A potential new wonder material for the electronics industry, both as an alternative to, and perfect partner for graphene.

Two-dimensional (2D) nanomaterials such as graphene, and molybdenum disulfide (MoS2) have been attracting increasing research interest in the past few years due to their unique material properties that promise a raft of new applications in sectors ranging from electronics to composites.

MoS2 is the inorganic compound with the formula MoS2. Single-layer MoS2 is 0.65 nm thick and is similar to graphene, except that it is a direct gap semiconductor, with a band gap of 1.8 eV. It has typically been used in industrial lubricant applications but it could potentially lead to new applications in high-speed logic circuits- on its own or in combination with graphene. It is a semiconductor with large band-gap which allows its use for logic devices, where a high Ion/Ioff ratio is required. Researchers at MIT, EPFL and the University of Manchester have been developing electronic circuits out of MoS2 where previously they sought to develop electronic applications for graphene.

Graphene has a major problem in alternative silicon electronics application as it lacks an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state,  and it therefore requires extensive modification in order to create one, whereas MoS2 naturally possesses one. Researchers at the Univeristy of Manchester have been developing graphene heterostructure devices with nanoscale  molybdenum disulfide acting as a vertical transport barrier.  MoS2 has also been  integrated with carbon nanotubes for application in high performance logic circuits.

The lack of a reliable large-scale production method is viewed as an inhibiting issue at present for their practical applications.  According to researchers however, the material is already widely produced as a lubricant and due to work in producing large sheets of the material in labs, scaling up production is likely to be easier than with other nanomaterials.     

 

Figure 1: Structure of 2D molybdenum disulfide (Image: Wang et al. / MIT)

MIT

Large sheets of MoS2 have been fabricated in the Jing Kong’s group in the Department of Electrical Engineering and Computer Science at MIT, via a chemical vapor deposition (CVD) process. Reserchers produced building blocks of electronic circuits on the sheets, as well as on MoS2 flakes produced by a mechanical method. They were able to fabricate a variety of basic electronic devices on the material: an inverter, which switches an input voltage to its opposite; a NAND gate, a basic logic element that can be combined to carry out almost any kind of logic operation; a memory device, one of the key components of all computational devices; and a more complex circuit called a ring oscillator, made up of 12 interconnected transistors, which can produce a precisely tuned wave output. Web: http://www.rle.mit.edu/rleonline/People/JingKong.html

 

Figure 2: Schematic of molybdenum disulfide incorporated into electronic circuit (MIT)

University of Manchester

Graphene pioneers at the University of Manchester have developed prototype devices based on graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temperature switching ratios of ≈50 and ≈10,000, respectively. Such devices have potential for high-frequency operation and large-scale integration. Web: http://www.condmat.physics.manchester.ac.uk/pdf/mesoscopic/publications/graphene/2012%20science%20tunnel%20FET.pdf

EPFL

The Laboratory of Nanoscale Electronics and Structures (LANES) at EPFL have developed a prototype microchip incorporating MoS2.  They have demonstrated that single-layer MoS2 can be used to fabricate transistors with extremely low leakage currents (25 fA/um).  The single-layer MoS2 was produced by scotch-tape peeling of naturally occuring molybdenite crystals. Web: http://lanes.epfl.ch/

 

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