Evidence of Chemical Functionalized Molecules Adsorbed on the Interface Region of Epitaxial Graphene: Interface Roughness and Modification of the Electronic Properties

Abstract

We investigate the variation of the electronic properties and morphological surface change of epitaxial graphene (EG) by chemically functionalizing the graphene layer with a surface-adsorbed organic free radical, 2,2,6,6-tetramethyl-1-piperridinyloxy (TEMPO) using scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and core-level photoemission spectroscopy (CLPES). STM and LEED images revealed that the adsorption of TEMPO occurred at the interface regions, observed as surface roughness in STM images and haziness in the (6(31/2) × 6(31/2))R30° LEED patterns. TEMPO molecules adsorbed onto EG through the NO radical group, as confirmed by the binding energies of the N 1s and O 1s core-level spectra. Changes in the work function, as measured by secondary electron edge, indicated that the adsorption of NO free radicals onto EG acts as an n-type dopant.