Prospects for detecting individual defect centers using spatially resolved electron energy loss spectroscopy

We consider the prospects of locating and characterizing individual defect centers in bulk materials using electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). We simulate STEM-EELS maps for two important defect centers in diamond, namely, the negatively charged nitrogen-vacancy defect and the neutral silicon-vacancy defect. We use density-functional theory to compute the defect electronic structure and a Møller potential formalism to compute the inelastic electron scattering. Our results indicate that it should be possible to use STEM-EELS to obtain the transverse locations of these defects to within about 1 nm. We calculate the plane-wave scattering cross sections for these individual defects to be of the order of 10-4 Å2, which indicates that the EELS signals should be within detectable limits. Calculated spectral maps and scattering cross sections are given as a function of the defect orientation, and we show that the results can be interpreted using a tight-binding description of the defect electronic structure.