  Atomic modulations of two-dimensional materials using scanning tunneling
microscope (STM) tip-induced forces modifies their mechanical and electrical
properties. In situ topographic and spectroscopic probing through electrical
tunneling has been used for straining sheets of graphite, monolayer graphene
and NbSe2. The findings also resolve a thirty-five-year-old controversy
involving numerous proposed models to explain the source of anomalously high
measured atomic amplitudes (of up to 24 Angstroms, expected 0.2 Angstroms) from
atomic corrugation on graphite surfaces. Our findings attributes the anomaly to
surface elastic deformation characteristics of soft 2D monatomic sheets of
graphene and graphite in contrast to NbSe2 which is associated with their local
bonding configurations. The tip-induced deformations are shown to induce
controlled strain on the material surface atomically and it offers a new way
for strain engineering. Topographic deformation of formed graphitic Moire
patterns reveals the inter-layer van der Waals (vdW) strength varying across
its domains. In-situ tunneling spectroscopy associated with straining of the
Moire domains reveals electronic flat band formation controllably thereby
creating a platform for many-body correlations. The paper cautions anomalous
observations when probing 2D materials at small gap distances with their strain
induced effects and provides guidelines to exploit or avoid this effect.
