MoS2

SEMINAR BY: RAHUL RAGHVENDRA

USN- 1MV11 EC076

WHAT IS MoS2?

WHY MoS2?

PROPERTIES OF MoS2

ENERGY BAND STRUCTURE

ENERGY BAND ENGINEERING

CARRIER MOBILITY

FABRICATION METHODS

DEVICE APPLICATIONS

CONCLUSIONS and OUTLOOK

Since the invention of the first transistor, silicon has been at the

heart of electronics but as the demands increases , we are asking way

too much out of silicon thus for all its drawbacks scientists began

searching for futuristic elements that can replace and even

outperform silicon.

This search led us to MoS2- single layer and few monolayer thick

2-dimensional semiconductor.

Its unique physical properties outperforms silicon and its closest

competitor graphene.

MoS2 is classified as a metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdenite, the principal ore for molybdenum.

In appearance and feel, molybdenum disulphide is similar to graphite.

It is widely used as a solid lubricant because of its low friction properties and robustness.

Excellent gate controlSaturation Scalability High current capabilityVery low noiseWide direct band gapIt exhibits good electrical and transport propertiesChemically and thermally stableTransparent and flexibleRelatively inexpensive

ATOMIC STRUCTURE:-

MoS2 belongs to the group of TMDs with the common formula MX2, wherein M represents a transition metal.

Within a single X-M-X layer, the M and X atoms form a 2D hexagonal sub-lattice

Fig.1 Arrangement of MoS2 Atoms

The Young’s modulus of MoS2 can be enhanced by a factor of five by sandwiching it between two Grapheme layers.

Fig.2. MoS2 sandwiched between Graphene layers

MoS2 also has the advantage that it is as stiff as stainless steelbut is also capable of being flexible.

It can be bent to large angles and can be stretched upto 10% of

its length.

It has a key advantage over graphene- it can amplify electronic signals at room temperature, while graphene must be cooled to 70 Kelvin- cold enough for nitrogen to turn into liquid.

Along with the other group-VI layered compounds, MoS2 exhibits semiconducting behavior.

The fundamental indirect band gap of bulk MoS2 is 1.22 to 1.23 eV, while the direct band gap ranges from 1.74 to 1.77 eV.

In 1973 Mattheiss used a non relativistic augmented-plane-wave (APW) method to calculate the electronic band structures of several TMDs, including MoS2.

Fig 3. DFT-GGA calculated band structures for (a) bulk MoS2, (b) 4-layer MoS2, (c) bi-layer

MoS2, and (d)monolayer MoS2 . The solid arrows indicate the lowest energy transitions.

MECHANICAL STRAIN:-

Mechanical strain can strongly affect the band structure, carrier effective masses, and transport, optical, and magnetic properties of MoS2 via changing the distance between the atoms and also the crystal symmetry.

Larger strain can be applied to low-dimensional MoS2 due to its mechanical flexibility, and its properties can be tuned by applied strain, which opens possibilities for developing new tunable electronic devices.

The energy band gap gradually decreases with increasing tensile strain, whereas it initially rises and then decreases linearly under applied compressive strain.

Fig.6 a) Top and side views of MoS2 monolayer lattice. b) Calculated band gap of monolayer MoS2 versus isotropic strain. c) – g) Electronic band structure of MoS2

monolayer under isotropic compressive strain of c) –8% and d) –2%,

e) Unstrained MoS2 monolayer, and under isotropic tensile strain of f) 2% and g) 8%. The red dashed line denotes the Fermi level.

The hole mobility (96.62 cm2 V−1 s−1) in monolayer sheets of MoS2 is about twice that of the electron mobility (43.96 cm2 V−1 s−1).

The highest mobility value of 700 cm2 V−1 s−1 was reported for a back-gated FET based on 10-nm-thick multilayer MoS2 flake.

The charge mobilities in MoS2 armchair nanoribbons can be regulated by edge modification owing to the changing electronic structures. In pristine armchair nanoribbons, the electron and hole mobilities are about 30 cm2 V−1 s−1 and 25 cm2 V−1 s−1, respectively.

[1]. MECHANICAL EXFOLIATION TECHNIQUE:-

Single and multilayer MoS2 films are deposited onto Si/SiO2 using the mechanical exfoliation technique.

The films were then used for the fabrication of field-effect transistors.

These FET devices can be used as gas sensors to detect nitrous oxide (NO).

Selective solution method to prepare Molybdenum Disulfide (MoS2) thin films for functional thin film transistors (TFTs).

The selective area solution-processed MoS2grows on top and around the gold (Au) source and drain electrodes and in the channel area of the TFT. MoS2 thicknesses in the channel area are in the order of 11 nm

Recent success in the growth of monolayer MoS2 via chemical vapor deposition (CVD) has opened up prospects for the implementation of these materials into thin film electronic and optoelectronic devices.

A schematic of the CVD process for growing single-layer MoS2

MoS2 has a wide range of applications.

This material is highly anisotropic with excellent nonlinear optical properties and also is a very good lubricant.

The layered material helps the membranes to have mechanical strengths some 30 times higher than that of steel.

It has stability at up to 1100 ◦C in an inert atmosphere.

It has a key advantage over graphene- it can amplify electronic signals at room temperature whereas graphenemust be cooled at 70 kelvin.

the mechanical strength and flexibility of these materials, we demonstrate integration onto a polymer substrate to create flexible and transparent FETs that show unchanged performance up to 1.5% strain.

Two-dimensional MoS2 may be used in sensors and memory and photovoltaic devices. Direct band gap and confinement effects in single-layer MoS2 makes this material attractive for optoelectronics.

Ultrasensitive monolayer-MoS2 phototransistors with improved device mobility and ON currents have been already demonstrated.

Molybdenite (MoS2) has a number of benefits over silicon (Si) when it comes to creating a micro chip. Future chips using MoS2 will be smaller than silicon chips. Reduced electricity consumption is another benefit, along with mechanical flexibility.

Two-dimensional materials, particularly the TMD mono layers, are emerging as a new class of materials.

Among them, semiconducting MoS2 is gaining increasing attention owing to an attractive combination of physical properties, which include band gap tunability and reasonably high electron mobility.

On the experimental front, researchers have focused on s practical applications of 2D MoS2, in particular the development of field-effect transistors,and negligible off current.

Ultrasensitive phototransistors, logic circuits, and amplifiers based on monolayer MoS2 have also been demonstrated, with good output current saturation and high currents.

The flexibility, stretchability, and optical transparency of monolayer MoS2 make it particularly attractive for transparent and flexible electronics.

Since the properties of MoS2 depend strongly on the number of monolayers, techniques providing control over the number of deposited monolayers are highly desirable.

For use in flexible electronics, the major challenge is to find approaches that would produce electronic-quality material at deposition temperatures below 400 ◦C necessitated by the need for growth directly on transparent plastic substrates.

Development of 2D MoS2-based devices, in particular FETs, for real applications also requires further studies of electrode and gate dielectric materials.