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The trigonal strain-relief pattern formed by an Ag bilayer on Pt(111) is a prominent example for dislocation networks and their use as nanotemplates. However, its atomic structure has not been solved. Combining scanning tunneling microscopy, low-energy ion scattering, and x-ray photoelectron diffraction, we demonstrate that, unexpectedly, about 22% of the atoms exchange across the Ag/Pt interface, and that the partial dislocations defining the trigonal network are buried in the Pt interface layer. We present an embedded-atom-method simulation identifying the lowest energy structure compatible with all experimental findings.

The inter- and intramolecular ordering of the trimetallic nitride endohedral fullerene ${\text{Dy}}_{3}\text{N}@{\text{C}}_{80}$ with icosahedral cage symmetry ${I}_{h}$ on Cu(111) has been studied by scanning tunneling microscopy and synchrotron-based x-ray photoelectron diffraction (XPD). ${\text{Dy}}_{3}\text{N}@{\text{C}}_{80}$ $({I}_{h})$ is found to form ordered islands consisting of domains of equally oriented molecules. As for ${\text{C}}_{60}$ on the same substrate, the cage is facing with a hexagon toward the surface, which is however slightly tilted for ${\text{C}}_{80}$. The endohedral nitrogen atom remains at a position close to the geometrical center of the cage. Resonant XPD on the ${\text{M}}_{\text{V}}$ edge shows that the encaged ${\text{Dy}}_{3}\text{N}$ unit takes well-defined orientations with respect to the ${\text{C}}_{80}$ cage and the Cu(111) substrate.

Local controllable modification of the electronic structure of carbon nanomaterials is important for the development of carbon-based nanoelectronics. By combining density-functional theory simulations with Ar-ion-irradiation experiments and low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) characterization of the irradiated samples, we study the changes in the electronic structure of single-walled carbon nanotubes due to the impacts of energetic ions. As nearly all irradiation-induced defects look as nondistinctive hillocklike features in the STM images, we compare the experimentally measured STS spectra to the computed local density of states of the most typical defects with an aim to identify the type of defects and assess their abundance and effects on the local electronic structure. We show that individual irradiation-induced defects can give rise to single and multiple peaks in the band gap of the semiconducting nanotubes and that a similar effect can be achieved when several defects are close to each other. We further study the stability of defects and their evolution during STM measurements. Our results not only shed light on the abundance of the irradiation-induced defects in carbon nanotubes and their signatures in STS spectra but also suggest a way the STM can be used for engineering the local electronic structure of defected carbon nanotubes.

A low-temperature scanning tunneling microscopy (LT-STM) study of four slightly different hydrocarbons based on hexaphenylbenzene (HPB) and hexa-peri-hexabenzocoronene (HBC) on the Cu(111) surface at submonolayer coverage is presented. All molecules show a commensurate monolayer structure, with significant differences in structure and growth mode. We find that the long range order and the size of defect free domains increase when the intermolecular interaction becomes stronger with respect to the molecule-substrate interaction. Moreover, we can assign adsorption and self-ordering properties to the different chemical groups within the molecules.

The interaction of atomic hydrogen and low-energy hydrogen ions with ${\mathrm{sp}}^{2}$-bonded carbon is investigated on the surfaces of ${\mathrm{C}}_{60}$ multilayer films, single-walled carbon nanotubes, and graphite (0001). These three materials have been chosen to represent ${\mathrm{sp}}^{2}$-bonded carbon networks with different local curvatures and closed surfaces (i.e. no dangling bonds). Chemisorption of hydrogen on these surfaces reduces emission from photoemission features associated with the \ensuremath{\pi} electrons and leads to a lowering of the work function up to 1.3 eV. It is found that the energy barrier for hydrogen adsorption decreases with increasing local curvature of the carbon surface. Whereas in the case of ${\mathrm{C}}_{60}$ and single-walled carbon nanotubes, hydrogen adsorption can be achieved by exposure to atomic hydrogen, the hydrogen adsorption on graphite (0001) requires ${H}^{+}$ ions of low kinetic energy (\ensuremath{\sim}1 eV). On all three materials, the adsorption energy barrier is found to increase with coverage. Accordingly, hydrogen chemisorption saturates at coverages that depend on the local curvature of the sample and the form of hydrogen (i.e., atomic or ionic) used for the treatment.

We present photoelectron spectroscopy investigations of in-situ prepared AgO. The sample was prepared by room temperature oxidation of Ag in an electron cyclotron resonance ${\mathrm{O}}_{2}$ plasma. In contrast to other measurements based on ex situ prepared AgO powder samples, our investigations show a distinct double peak structure of the O $1s$ signal with a remarkable chemical shift of 2.9 eV between the two O $1s$ components. These two components can not be motivated from a crystallographic point of view as the oxygen sites are all equivalent in the unit cell. We interpret this double peak structure as a characteristic feature of AgO and discuss it in terms of mixed valences.

We propose a class of graphene nanoribbons showing strong intrinsic ferromagnetic behavior due to their asymmetry. Such ribbons are based on a zigzag-edged backbone surmounted by a periodic, triangular notched region of variable size. The electronic properties as a function of the topology are investigated. Interestingly, substitutional doping by boron or nitrogen induces half-metallicity. The most effective doping sites can be inferred from the band structure. Given the present rapid development of bottom-up strategies for the synthesis of atomically precise carbon nanostructures the proposed class of nanoribbons emerges as a real candidate for spintronic applications at ambient temperature.

In this paper we present a simple method accounting for tip size effects in scanning tunneling microscopy (STM) simulations. We consider the case where the tip atoms can be regarded as independent sources of $s$ orbitals and compute the tunneling current using the Bardeen formula and the approximation of incoherent scattering. By averaging over the many possible tip configurations compatible with the effective external shape of the STM probe, we show that the tunneling current is proportional, within our model, to the convolution product between the local density of states of the system and a three-dimensional step function defined by the effective tip volume. The method is tested on three systems of current scientific interest, namely, a hexabenzocoronene molecule adsorbed on Cu(111), a reconstructed Au(677) surface, and a formate molecule adsorbed on Pt(111), which we study by means of large-scale density functional theory calculations and STM experiments. An excellent agreement between experimental and simulated STM images is found. It is shown that, under typical experimental conditions, our approach recovers the results of the well-known Tersoff-Hamann modeling in the case of spherical tips, while allowing for more versatility in the choice of the shape of the STM probe. Finally we present an application of our method to one-dimensional surface models mimicking a localized defect and a surface step, thereby offering a very simple framework for the discussion of the tip-induced broadening of the surface features in the STM imaging.