Single Atomic Defect Conductivity for Selective Dilute Impurity Imaging in 2D Semiconductors

Precisely controlled impurity doping is of fundamentalsignificancein modern semiconductor technologies. Desired physical propertiesare often achieved at impurity concentrations well below parts permillion level. For emergent two-dimensional semiconductors, developmentof reliable doping strategies is hindered by the inherent difficultyin identifying and quantifying impurities in such a dilute limit wherethe absolute number of atoms to be detected is insufficient for commonanalytical techniques. Here we report rapid high-contrast imagingof dilute single atomic impurities by using conductive atomic forcemicroscopy. We show that the local conductivity is enhanced by morethan 100-fold by a single impurity atom due to resonance-assistedtunneling. Unlike the closely related scanning tunneling microscopy,the local conductivity sensitively depends on the impurity energylevel, allowing minority defects to be selectively imaged. We furtherdemonstrate subsurface impurity detection with single monolayer depthresolution in multilayer materials.