1. Spatially Resolved Mapping of Electrical Conductivity Across Domain and Grain Boundaries in Graphene CNMS Staff Science Highlight Scientific Achievement Significance and Impact Research Details K. W. Clark, X.-G. Zhang, I. V. Vlassiouk, G. He, R. M. Feenstra, and A.-P. Li, ACS Nano, DOI: 10.1021/nn403056k A two-dimensional profile of electronic conductivity was quantitatively resolved on graphene with scanning tunneling potentiometry (STP). Both grain and domain boundaries exhibit a potential barrier for electron transport, showing an electronic transition region with direct correlation to charge density variations and boundary atomic structures. This work presents a new atomic level approach to the study of the spatial profile of conductivity in a 2D material with a one-to-one correspondence to the structure. The study reveals the roles of different types of defects in both epitaxial and CVD grown graphene, providing information on the electron scattering process at an unprecedented atomic level. Electrical transport properties are studied with a 4-probe STM by measuring the electrochemical potential variation across individual defects with a current flowing in the graphene. Transport properties are analyzed and correlated to the defect structures and electronic properties. (b) Work was performed at ORNL and at the Carnegie Mellon University (a)Schematic diagram of simultaneous structure and electrochemical potential measurement with a multi- probe STM, and atomic resolution image of a graphene monolayer- bilayer boundary. (b)2D distribution of surface potential. (c)2D distribution of electric field. (d)2D distribution of electrical conductivity.

2. Two-Dimensional Mapping of Electrical Conductivity at the Atomic Scale to Examine Defects in Graphene CNMS Staff Science Highlight Scientific Achievement Significance and Impact Research Details K. W. Clark, X.-G. Zhang, I. V. Vlassiouk, G. He, R. M. Feenstra, and A.-P. Li, ACS Nano, DOI: 10.1021/nn403056k Graphene’s 2D electronic conductivity was mapped point-by- point with a scanning tunneling potentiometry (STP) method. At boundaries where graphene sheets with different orientations or thicknesses meet, the resistance is high due to both the disruption of the structure and the large change in the electron density at the boundary. This is a new approach to electrical conductivity and its correlation with atomic structure in a 2D material. The study reveals the roles of different types of imperfections in the atomic lattice of graphene, providing information on the conductivity at an unprecedented atomic level and providing insight needed for graphene based electronics. Electrical transport properties are studied by measuring the voltage changes across individual defects while a current is flowing through the graphene. Transport properties are analyzed and correlated to defect structures and electronic properties. (b) Work was performed at ORNL and at the Carnegie Mellon University (a)Schematic diagram of simultaneous structure and voltage measurements, and an atomic resolution image of a graphene monolayer- bilayer boundary. (b)2D distribution of surface potential. (c)2D distribution of electric field. (d)2D distribution of electrical conductivity.