Nanodiamond grain boundaries and lattice expansion drive Silicon vacancy emission heterogeneity

TL;DR

This study uses advanced electron microscopy to link nanodiamond structural features, like grain boundaries and lattice expansion, to variations in silicon-vacancy emission, advancing understanding of quantum emitter heterogeneity.

Contribution

It provides the first atomic-scale correlation between nanodiamond structure and SiV$^-$ emission heterogeneity using cathodoluminescence and STEM techniques.

Findings

Different crystalline domains show distinct emission energies and brightness.

Near-surface SiV$^-$ emitters remain bright despite heterogeneity.

Lattice expansion and distortions cause shifts in emission wavelengths.

Abstract

Silicon-vacancy (SiV$^-$) centers in diamond are promising candidates as sources of single-photons in quantum networks due to their minimal phonon coupling and narrow optical linewidths. Correlating SiV$^-$ emission with the defect's atomic-scale structure is important for controlling and optimizing quantum emission, but remains an outstanding challenge. Here, we use cathodoluminescence imaging in a scanning transmission electron microscope (STEM) to elucidate the structural sources of non-ideality in the SiV$^-$ emission from nanodiamonds with sub-nanometer-scale resolution. We show that different crystalline domains of a nanodiamond exhibit distinct zero-phonon line (ZPL) energies and differences in brightness, while near-surface SiV$^-$ emitters remain bright. We correlate these changes with local lattice expansion using 4D STEM and diffraction, and show that associated blue shifts from the ZPL are due to defect density heterogeneity, while red shifts are due to lattice distortions.