Bond inversion dynamics and spectroscopy of single atom dopants in 2D materials

Orateur : Quentin RAMASSE (SuperSTEM Laboratory (University of Liverpool and University of Leeds))

Graphene’s and other 2D materials novel properties can be controlled and tuned through defects such as single atom dopants, step edges, interfaces, and grain boundaries. This defect engineering takes place quite literally at the atomic level, where one of most powerful means of characterization arguably lies within a combination low voltage scanning transmission electron microscopy, energy loss spectroscopy (STEM-EELS) and ab initio calculations. With these instruments, single atom defects can be imaged directly at atomic resolution, revealing for instance the successful low-energy ion implantation of single N or B dopants in graphene, a technique widely used by the semiconductor industry and with the potential to revolutionize graphene technology [1]. These ’gentle’ STEM observation conditions can nevertheless be used to drive the diffusion of substitutional dopants such as Si through single layer graphene, one atomic jump at time [2]. A combined experimental and theoretical study, making use of ab initio molecular dynamic calculations, revealed that for Si dopants these jumps are not due to impact on the Si atom, but to sub-thresold impact events on the surrounding C atoms. But these events happen rarely enough, however, to enable careful electronic structure studies : the sensitivity of EELS of is such that is possible to study how these atoms bond to one another, with subtle differences in spectral fine structure used to distinguish between bonding configurations of single Si, B or N dopants in graphene and their impact on the electronic structure of neighbouring carbon atoms [3].

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