  Non-invasive imaging of the atomic arrangement in two-dimensional (2D)
Ruddlesden-Popper hybrid Perovskites (RPPs), as well as understanding the
related effects is challenging, due to the insulating nature and softness of
the organic layers which also obscure the underlying inorganic lattice. Here,
we demonstrate a sub-angstrom resolution imaging of both soft organic layers
and inorganic framework in a prototypical 2D lead-halide RPP crystal via
combined tip-functionalized Scanning Tunneling Microscopy (STM) and non-contact
Atomic Force Microscope (ncAFM) corroborated by theoretical simulations. STM
measurements unveil the atomic reconstruction of the inorganic lead-halide
lattice and overall twin-domain composition of the RPP crystal, while ncAFM
measurements with a CO-tip enable non-perturbative visualization of the
cooperative reordering of surface organic cations driven by their hydrogen
bonding interactions with the inorganic lattice. Moreover, such a joint
technique also allows for the atomic-scale imaging of the electrostatic
potential variation across the twin-domain walls, revealing alternating
quasi-one-dimensional (1D) electron and hole-channels at neighboring
twin-boundaries, which may influence in-plane exciton transport and
dissociation.
