Sub-angstrom Non-invasive Imaging of Atomic Arrangement in 2D Hybrid Perovskites

TL;DR

This paper presents a novel sub-angstrom resolution imaging technique combining STM and ncAFM to visualize the atomic structure and electrostatic variations in 2D hybrid perovskites non-invasively.

Contribution

The study introduces a combined STM and ncAFM approach with theoretical simulations for detailed atomic and electrostatic imaging of 2D RPPs, revealing surface reordering and domain wall properties.

Findings

Atomic reconstruction of inorganic lattice observed

Organic cation reordering driven by hydrogen bonds visualized

Electrostatic potential variation across twin-domain walls mapped

Abstract

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.