Graphene like 2D Materials
Graphene (an allotrope of carbon) was the first 2D material observed in 2004 by Prof. Andre Geim andProf. Kostya Novoselov at The University of Manchester. It has a 2D honeycomb structure.This material has gathered huge attention due to its fascinating properties. It has displayedhigh electron mobility, transparency, large Young's Modulus, high thermalconductivity and, tunable electronic and optoelectronic properties.Graphene gave birth to a varied class of crystals e.g MoS2, BN, Fluorographene,NdS2and MgBr. These type of materials have layered structure, with intralayer covalentbondingand interlayer Van derWaal forces. Hence, these are utilized as dry lubricant. The 2D materials are classified as graphene family (e.g silicene, germanene), 2D chalcogenides (e.g MoS2, WS2)and 2D oxides (e.g MoO3, WO3).
Graphene being zero band gap material, have restricted its application in semiconductor industry. Hence, in order to utilize it in devices or in solar cells weneed to introduce band gap. This can be achieved by different routes, such as (a) chemical modification of the surface of the sheet, (b) by application of mechanical strain into the system or (c) by forming nanoribbons of appropriate width and chirality.More recently, research in other 2D materials especiallyTransition Metal Dichalcogenides (TMDs) gained significant interest.TMD molecular unit is represented as MX2. Here M is the transition metal andX is the chalcogen. One layer of M atoms is in between two layers of X atoms. When the layers of different 2D materials are engineered together, they form vander Waals heterostructure. These are optimized as per the needs and usage indifferent devices.TMD monolayers have high carrier mobility and high on/off ratio that makes it attractive for the manufacture of devices. There is indirect to direct band gap transition from bulk to monolayer in TMDs. Hence, the emission efficiency is much higher for monolayer as comparedto the bulk. Monolayer in TMDs can sustain up to 10 percent strain. Band gap changes withthe amount of strain on the monolayer, hence changing the properties. Therefore,mechanical tuning of the electronic structure is significantly utitlized in electronics. Hence, these materials with interesting properties is a viable material for future research that will benefit the industries (specially photovoltaic) and hence the society.