# Nonuniform quantum-confined states and visualization of hidden defects in thin Pb(111) films

## TL;DR

This study investigates quantum-confined states and hidden defects in ultrathin Pb(111) films using low-temperature STM, revealing spatial nonuniformities and large-scale inhomogeneities linked to internal defects and local potentials.

## Contribution

It demonstrates the spatial variation of quantum-confined states and visualizes hidden defects in Pb films, connecting conductance inhomogeneities to internal structural defects.

## Key findings

- Quantum-confined states are mainly determined by local film thickness.
- Tunneling conductance shows spatial nonuniformity matching Si(111)7x7 reconstruction.
- Large-scale inhomogeneities correlate with internal defects and local stresses.

## Abstract

The spatial distribution of the differential conductance for ultrathin Pb films grown on Si(111)7x7 substrate is studied by means of low-temperature scanning tunneling microscopy and spectroscopy. The formation of the quantum--confined states for conduction electrons and, correspondingly, the appearance of local maxima of the differential tunneling conductance are typical for Pb films; the energy of such states is determined mainly by the local thickness of Pb film. We demonstrate that the magnitude of the tunneling conductivity within atomically flat terraces can be spatially nonuniform and the period of the small-scale modulation coincides with the period of Si(111)7x7 reconstruction. For relatively thick Pb films we observe large-scale inhomogeneities of the tunneling conductance, which reveal itself as a gradual shift of the quantized levels at a value of the order of 50 meV at distances of the order of 100 nm. We believe that such large-scale variations of the tunneling conductance and, respectively, local density of states in Pb films can be related to presence of internal defects of crystalline structure, for instance, local electrical potentials and stresses.