Strain Engineering of two dimensional materials by Scanning Tunneling Microscopy
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Strain Engineering of two dimensional materials by Scanning Tunneling Microscopy


Strain engineering on layered two dimensional materials has gained some interest for mod- ulating device electronics. This is done by twisting layered materials, stretching flexible substrates or applying hydro-static pressures. Our work offers to the straintronics and twistronics commu- nity, a new pathway of deforming individual atoms on surface controllably by tip-induced forces and probe in-situ the mechanical and electronic properties on surface under strain which can be exploited for innumerable applications.Tunneling gaps of interatomic distances can induce strain by individual atomic deformation controllably and elastically with an STM tip and while under strain probe in-situ their mechanical VDW strength or elasticity and electronic band structure. Such capabilities can be exploited in force microscopy studies of soft matter, biological, chemical and physical sensors or 2D materials based semiconductor nanoelectronics. We demonstrate that various weak forces only at small tip- surface gaps become strong enough to deform surfaces of graphite, monolayer graphene, Niobium diselenide and their step heights that reveals their dependence on their structural anisotropy. Addi- tionally we provide an application to our tip-induced deformative approach by locally deforming moiré patterns (partly shown in following figure) which not only reveals their mechanical prop- erties like interlayer VDWs strength of different moiré domains (including the domain walls) but also exhibits flattening of moire flat bands under strain. The flat bands aspect have helped understand the imaging issues of topologically protected grain boundaries. We reveal various experimental challenges and solutions to probing grain bound- aries that have distinct spectroscopic states on their surfaces. They play a role in charging or discharging effects on the grain boundary sensed by the STM. The origin of the flat band states around zero bias has been shown to be caused by the zigzag edges and the other VHS states could be caused the distinct topological arrangement of non-hexagons. Flat bands or VHS peaks also can be observed on moire patterns. We observe how mechan- ically the moire domains can be deformed and in-situ observe the deformation of electronic bands. Such band modulating approach by tip-induced forces have not been explored. We approach the strained moire patterns from the point of view of domain walls. Domain walls are confined 1D structures on 2D moire surfaces.

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