Research Projects

Two-dimensional (2D) layered materials, also known as van der Waals (vdW) materials are defined as a class of crystals that can be peeled off layer by layer up to an extent of monoatomic layer. In these materials, the in-plane interatomic interactions are much stronger compared to those along the out of plane direction, in which layers are bonded by weak vdW force. Since the first exfoliation of single-layer graphene in 2004, the family of such vdW materials have garnered worldwide attention due to their unique structures, remarkable properties and having wide range of applications like field-effect transistors, flexible electronics, photodetectors, composite materials, energy storage devices, precise sensors, DNA sequencing and drug delivery. More than one thousand structures of vdW materials have been predicted to be easily exfoliated to monolayers or multilayers with fascinating physical properties, forming a large family of vdW materials including transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), silicene, stanene and so on. vdW materials offer a platform that allows creation of heterostructures (HSs) by integrating them into a monolayer or a multilayer stacking with a variety of properties. A plethora of opportunities appear when we start to combine two or more dissimilar vdW crystals in one vertical stack. Held together by vdW forces, such HSs allow a far greater number of combinations with diverse intriguing properties. When stacking different crystals together, the synergetic effects become very important. Charge redistribution might occur between the neighboring crystals in the stack that gives rise to different excitonic species such as bound exciton, trion, interlayer exciton, hybridized exciton, moiré excitons, biexcitons and so on. Furthermore, such changes can be tuned by adjusting the relative orientation between the individual layers such as twist angle thus generating a new area called twistronics. Lots of research and development is done in twistronics of Graphene, where much diverse electronic behaviour is observed stretching from non-conductive to superconductive, which depends sensitively on the angle between the layers. However, in contrast to the abundance of vdW materials, few twisted HSs have been studied until now nonetheless in atomically thin 2D TMDs. Although few groups have reported the synthesis of several twisted heterostructures (t-HSs) using chemical vapor deposition (CVD) followed by wet transfer method, but there are many drawbacks in the processes such as deficiency of clean interface, limited size and lack of control over the angle, which limits its device applications as well as exploring angle specific fundamental science. Hence, there is an urgent need for angle controlled in-situ growth of vdW HSs. In this proposal, we aim to fabricate in-situ growth of large area vdW HSs for selected twist angles by optimizing the CVD process parameters.