Detection of Photons Emitted from Single Er Atoms in Energy Dispersive X-ray Spectroscopy

Detecting the photons emitted from single quantum objects is highly desired to diagnose nano-scale devices. It has been, however, believed very difficult to sense single atoms in optical spectroscopy due to the inferior detection efficiency. We demonstrate here the successful detection of the characteristic x-ray signals from single Er atoms in energy dispersive x-ray spectroscopy (EDX). Highly focused electron probe in an aberration-corrected scanning transmission electron microscope (STEM) was used to excite the single Er atoms aligned in carbon cages, namely the peapod. The intensities of Er L and M lines from single Er atom were found to be 104 ~ 105 times less than that of the N-edge of electron energy-loss spectroscopy (EELS), suggesting the intrinsic difficulty to sense single atoms in X-ray spectroscopy. Nevertheless, this work will certainly ensure the possibilities to obtain X-ray spectra from single atoms and to evaluate the fluorescence yield at single atom basis, therefore the technique will likely find wide fields of applications in nano-physics research.