Simultaneous imaging of dopants and free charge carriers by STEM-EELS

TL;DR

This paper demonstrates nanoscale imaging of dopants and free charge carriers in La-doped BaSnO3 using high-resolution STEM-EELS, revealing inhomogeneities and localized plasmons, and quantifying electronic properties.

Contribution

It introduces a novel method combining STEM-EELS to simultaneously image dopants and charge carriers at the nanoscale in a bulk material.

Findings

Revealed chemical and electronic inhomogeneities within a single nanocrystal.

Identified localized infrared surface plasmons, including a new highly confined mode.

Quantified carrier density, effective mass, and dopant activation percentage.

Abstract

Doping inhomogeneities in solids are not uncommon, but their microscopic observation and understanding are limited due to the lack of bulk-sensitive experimental techniques with high-enough spatial and spectral resolution. Here, we demonstrate nanoscale imaging of both dopants and free charge carriers in La-doped BaSnO3 (BLSO) using high-resolution electron energy-loss spectroscopy (EELS). By analyzing both high- and low-energy excitations in EELS, we reveal chemical and electronic inhomogeneities within a single BLSO nanocrystal. The inhomogeneous doping leads to distinctive localized infrared surface plasmons, including a novel plasmon mode that is highly confined between high- and low-doping regions. We further quantify the carrier density, effective mass, and dopant activation percentage from EELS data and transport measurements on the bulk single crystals of BLSO. These results represent a unique way of studying heterogeneities in solids, understanding structure-property relationships at the nanoscale, and opening the way to leveraging nanoscale doping texture in the design of nanophotonic devices.