Imaging the potential distribution of individual charged impurities on   graphene by low-energy electron holography
  While imaging individual atoms can routinely be achieved in high resolution transmission electron microscopy, visualizing the potential distribution of individually charged adsorbates leading to a phase shift of the probing electron wave is still a challenging task. Low-energy electrons (30 - 250 eV) are sensitive to localized potential gradients. We employed low-energy electron holography to acquire in-line holograms of individual charged impurities on free-standing graphene. By applying an iterative phase retrieval reconstruction routine we recover the potential distribution of the localized charged impurities present on free-standing graphene. 
Tatiana Latychevskaia, Flavio Wicki, Conrad Escher, Hans-Werner Fink
cond-mat.mes-hall cond-mat.mtrl-sci physics.ins-det