NbO terminated Nb(110) and its oxidation are examined by scanning tunneling microscopy and spectroscopy (STS). The oxide structures are strongly influenced by the structural and electronic properties of the underlying NbO substrate. The NbO is terminated by one-dimensional few-nanometer nanocrystals, which form an ordered pattern. High-resolution STS measurements reveal that the nanocrystals and the regions between the nanocrystals exhibit different electronic characters. Lowdosage oxidation, sufficient for sub-monolayer coverage of the NbO, with subsequent UHV annealing results in the formation of resolved sub-nanometer clusters, positioned in-between the nanocrystals. Higher dosage oxidation results in the formation of a closed Nb 2 o 5−y layer, which is confirmed by X-ray photoelectron spectroscopy measurements. The pentoxide is amorphous at the atomic-scale. However, large scale (tens of nanometers) structures are observed with their symmetry matching that of the underlying nanocrystals.

Scanning tunneling microscopy (STM) measurements of the (110) surface of magnetite showed the coexistence of two reconstructions: the known (1 × 3) row reconstruction and a surprising atomic structure of high complexity which occupies a small fraction of the surface. Oxygen vacancies on the Fe3O4(110) B-terminated surface have previously been determined to be the most energetically favourable surface termination of those considered [Li et al., Surf. Sci. 601, 876 (2007)]. However, this study only investigated oxygen vacancies which were three-fold coordinated. Here, first principle calculations indicate that two-fold coordinated oxygen represents the most energetically stable oxygen vacancy on the B-terminated (110) surface of magnetite. STM simulations reveal that the structure that occupies a small fraction of the surface corresponds to this energetically favourable B-terminated Fe3O4(110) surface. The oxygen vacancies form an ordered array: along the [110] direction, every second two-fold coordinated oxygen atom is vacant, vacancies are separated by 6Å. In adjacent two-fold coordinated oxygen rows, the vacancies are shifted in the [110] direction by 3Å. Density functional theory (DFT) calculations of the spin density distributions indicate that surface and sub-surface octahedrally coordinated iron atoms are charge ordered. The charge ordering and existence of oxygen vacancies act to reduce the surface charge. However, other polarity compensation mechanisms may be at play to stabilize the surface.

Defects introduced to the surface of Bi(111) break the translational symmetry and modify the surface states locally. We present a theoretical and experimental study of the 2D defects on the surface of Bi(111) and the states that they induce. Bi crystals cleaved in ultrahigh vacuum (UHV) at low temperature (110 K) and the resulting ion-etched surface are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) as well as spectroscopy (STS) techniques in combination with density functional theory (DFT) calculations. STS measurements of cleaved Bi(111) reveal that a commonly observed bilayer step edge has a lower density of states (DOS) around the Fermi level as compared to the atomic-flat terrace. Following ion bombardment, the Bi(111) surface reveals anomalous behavior at both 110 and 300 K: Surface periodicity is observed by LEED, and a significant increase in the number of bilayer step edges and energetically unfavorable monolayer steps is observed by STM. It is suggested that the newly exposed monolayer steps and the type A bilayer step edges result in an increase to the surface Fermi density as evidenced by UPS measurements and the Kohn–Sham DOS. These states appear to be thermodynamically stable under UHV conditions.

We report on a transition in a monolayer of C60 molecules deposited on a WO2/W(110) substrate. The transition from a static state, where the molecules are rigidly bound to the surface by a coordination bond, to a state where the molecules are loosely bound to the surface by van der Waals force and rotate continuously, has been studied using scanning tunnelling microscopy (STM). The separation between the molecules and the surface increases by 1.2 Å across the transition. The transition from the static state into the rotating state takes place at 259 K. The energy of the spinning state with respect to the lowest energy state, having a single coordinated bond, can be obtained from the statistics of the molecules switching. The binding energy of the molecule in the spinning state can be easily altered by changing the polarity of the bias voltage applied between the STM tip and the surface. The binding energy decreases by 80 meV when the bias polarity of the sample changes from positive to negative with respect to the tip. The results are consistent with the Coulomb blockade model: when electrons travel from the surface to the C60 molecule, and then to the tip; charge accumulates on the molecule due to the Coulomb blockade. This increases the electrostatic interaction between the molecule’s charge and a corresponding image charge generated on the metallic surface.

Herein, we report a simple method for a covalent modification of surface supported graphene with photoactive dyes. Graphene was fabricated on cubic-SiC/Si(001) wafers due to their low cost and suitability for mass-production of continuous graphene fit for electronic applications on millimetre scale. Functionalisation of the graphene surface was carried out in solution via white light induced photochemical generation of phenazine radicals from phenazine diazonium salt. The resulting covalently bonded phenazine-graphene hybrid structure was characterised by scanning tunnelling microscopy (STM) and spectroscopy (STS), Raman spectroscopy and density functional theory (DFT) calculations. It was found that phenazine molecules form an overlayer, which exhibit a short range order with a rectangular unit cell on the graphene surface. DFT calculations based on STM results reveal that molecules are standing up in the overlayer with the maximum coverage of 0.25 molecules per graphene unit cell. Raman spectroscopy and STM results show that the growth is limited to one monolayer of standing molecules. STS reveals that the phenazine-graphene hybrid structure has a band gap of 0.8 eV.

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We present a study of (110)-terminated magnetite using a range of surface-sensitive techniques, the foremost of those being reflectance anisotropy spectroscopy (RAS). The anisotropic optical response of the as-polished and row-reconstructed terminations are investigated. The responses are interpreted to result from termination-induced anisotropic shifts in energy of the bulklike optical transitions. Density functional theory (DFT) calculations demonstrate that the row reconstruction of Fe 3 O 4 (110) exhibits anisotropic strain in its terminating layers, and this strain is concluded to be the origin of the RAS response. X-ray photoelectron spectroscopy measurements demonstrate that the row reconstruction is reduced and the stoichiometry in the surface region is relatively easily altered by in situ preparation procedures. This is correlated to altered surface electronic properties identified by scanning tunneling spectroscopy measurements. RAS is sensitive to this change in surface structure, with the magnitude of the RAS response being altered.

Oxygen adatoms on the MoO 2+ x /Mo(110) surface are observed to be removed when a sufficiently large bias is applied between the scanning tunneling microscope tip and the surface. Experimental observations, such as the bias polarity dependence of adatom removal and the observation of an intermediate state, indicate that the adatom penetrates the surface oxide layer. Through the comparison of finite element method simulations with various experimental relationships, the electric field is concluded to be the sole contributor to adatom penetration into the surface oxide layer. The energetic barrier to this process is estimated to be approximately 0.45 eV in magnitude. Furthermore, the resolution of this phenomenon is on the atomic scale: individual adatoms can undergo surface penetration whilst their nearest neighbour adatoms, separated by 5 Å, are unaffected. The mechanism reported here has the advantages of not strongly influencing the substrate and is exceptionally localised, which can be beneficial for the synthesis of single atom devices.