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Graphene nanoribbons show exciting electronic properties related to the exotic nature of the charge carriers and to local confinement as well as atomic-scale structural details. The local work function provides evidence for such structural, electronic, and chemical variations at surfaces. Kelvin prove force microscopy can be used to measure the local contact potential difference (LCPD) between a probe tip and a surface, related to the work function. Here we use this technique to map the LCPD of graphene nanoribbons grown on a Au(111) substrate. The LCPD data shows charge transfer between the graphene nanoribbons and the gold substrate. Our results are corroborated with density functional theory calculations, which verify that the maps reflect the doping of the nanoribbons. Our results help to understand the relation between atomic structure and electronic properties both in high-resolution images and in the distance dependence of the LCPD.

Electrostatic potentials strongly affect molecular energy levels and charge states, providing the fascinating opportunity of molecular gating. Their influence on molecular vibrations remains less explored. Here, we investigate ethyl‐diaminodicyanoquinone molecules on a monolayer of MoS2 on Au(111) using scanning tunneling and atomic force microscopy and spectroscopy. These molecules exhibit a large dipole moment in gas phase, which is found to (partially) persist on the MoS2 monolayer. The self‐assembled structures consist of chains, where the dipoles of neighboring molecules are aligned antiparallel. Thanks to the decoupling efficiency of the molecular states from the metal by the MoS2 interlayer, vibronic states of the molecules are resolved, which vary in intensity depending on the molecular surrounding. We suggest that the vibrations are strongly damped by electrostatic interactions with the environment. [ABSTRACT FROM AUTHOR]

Abstract: In the study we present results on topography, morphology, chemical composition, electronic structure and electrical properties of the (100) surface layer of KTaO3 single crystal caused by sputtering with Ar+ ion beam with energy of 1keV. Several surface sensitive techniques, i.e. X-ray photoelectron spectroscopy (XPS), local conductivity of atomic force microscopy (LC-AFM), and Kelvin Probe Force Microscopy (KPFM) were used. The observed changes in the electronic structure were explained as a result of the chemical decomposition of the surface layer. A correlation between the electronic states which appeared in the energy gap and the changes in charge state of Ta ions was found. The activation energy related to averaged local conductivity temperature dependence was estimated from Arrhenius plot. It was also found, that variations in the local contact potential difference (LCPD) indicated changes in the chemical composition in nano-scale. The chemical reconstruction of the KTaO3 surface modified by Ar+ ion beam was deduced. This non-homogeneity corresponded to 2-D non-homogeneity of the local electric conduction (LC-AFM), which occurred within nano-areas after sputtering. Chemical reactivity of the modified surface with CO2 and O2 was observed. The reversibility of the Ar+ induced loss of oxygen non-stoichiometry was observed after the sample was exposed to various doses of O2. The successful reversibility occurred after oxidation process at high temperature, i.e. 300°C. [Copyright &y& Elsevier]

Electron donor-acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled via electrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111). Depending on the adsorption site, the molecule is found either in a nearly undisturbed free state or in a bound state. In the latter case, the molecule adopts a specific adsorption site, leading to the formation of a chelate complex with a single Na + alkali cation pulled out from the insulating film. Although expected to be electronically decoupled, the charge distribution of the complex is drastically modified, leading to the loss of the intrinsic donor-acceptor character. The chelate complex formation is reversible with respect to lateral manipulations, enabling tunable donor-acceptor molecular switches activated by on-surface coordination.