S. Modesti

Novel features of potassium and sodium vibrations on copper surfaces observed by high-resolution electron-energy-loss spectroscopy

High-resolution electron-energy-loss spectra of alkali metals adsorbed on Cu show three unexpected features: the adsorbate-substrate stretching frequency does not change with coverage, within 1 meV on Cu(111) and Cu(110), in agreement with the covalent picture of chemisorption; the spectra show an unusual overtone which is interpreted as a consequence of a strongly non linear relationship between the surface dipole moment and the adsorbate-substrate distance; the dynamical dipole moment is strongly coverage dependent.

Photoemission and photoabsorption study of the high-temperature phases of the Ge(111) surface

Abstract The Ge(111) surface has been studied by photoemission and photoabsorption spectroscopies as a function of temperature up to 1200 K. Up to 1020 K the data indicate the presence of an adatom-restatom reconstruction, with a gradual weak metallization of the surface between 600 and 1020 K. Evidence for a high-temperature phase transition is found between 1020 and 1085 K from core-level spectroscopy. Valence-band photoemission spectra and photoabsorption data indicate a metallic surface layer above this phase transition. About 0.7–1 atomic bilayer is estimated to undergo the semiconductor to metal transition. All these data can be interpreted consistently with an incomplete surface-melting scenario.

Kondo conductance across the smallest spin 1/2 radical molecule

Significance Molecular electronics, with molecules functioning as the basic building blocks of circuits, is considered by some to be one of the contenders for next-generation electronics. Radical molecules are interesting because a quantum phenomenon, the Kondo effect, involving the radical’s unpaired electron and its spin, has the potential to enhance and control conductance. Examples of molecular Kondo are known experimentally in geometries including mechanical break junctions and scanning tunneling spectroscopy (STS), but so far it has not been possible to make accurate theoretical predictions. Here we predict the Kondo effect expected for the simplest molecular radical, nitric oxide, on a gold surface. Subsequently we verify that experimentally by STS. Both agreements and discrepancies offer a quantitative lesson of considerable future use. Molecular contacts are generally poorly conducting because their energy levels tend to lie far from the Fermi energy of the metal contact, necessitating undesirably large gate and bias voltages in molecular electronics applications. Molecular radicals are an exception because their partly filled orbitals undergo Kondo screening, opening the way to electron passage even at zero bias. Whereas that phenomenon has been experimentally demonstrated for several complex organic radicals, quantitative theoretical predictions have not been attempted so far. It is therefore an open question whether and to what extent an ab initio-based theory is able to make accurate predictions for Kondo temperatures and conductance lineshapes. Choosing nitric oxide (NO) as a simple and exemplary spin 1/2 molecular radical, we present calculations based on a combination of density functional theory and numerical renormalization group (DFT+NRG), predicting a zero bias spectral anomaly with a Kondo temperature of 15 K for NO/Au(111). A scanning tunneling spectroscopy study is subsequently carried out to verify the prediction, and a striking zero bias Kondo anomaly is confirmed, still quite visible at liquid nitrogen temperatures. Comparison shows that the experimental Kondo temperature of about 43 K is larger than the theoretical one, whereas the inverted Fano lineshape implies a strong source of interference not included in the model. These discrepancies are not a surprise, providing in fact an instructive measure of the approximations used in the modeling, which supports and qualifies the viability of the density functional theory and numerical renormalization group approach to the prediction of conductance anomalies in larger molecular radicals.

Computational and experimental imaging of Mn defects on GaAs (110) cross-sectional surfaces

We present a combined experimental and computational study of the (110) cross-sectional surface of Mn

Metallic, magnetic and molecular nanocontacts

\ensuremath{\delta}

Dissociation of CH Species on Ni(111): A HREELS Study

-doped GaAs samples. We focus our study on three different selected Mn defect configurations not previously studied in detail, namely surface interstitial Mn, isolated and in pairs, and substitutional Mn atoms on cationic sites

The EEL epectrum of the triplet exciton of C60 and the theoretical analysis of its vibronic structure

({\mathrm{Mn}}_{\mathrm{Ga}})

The surface triplet exciton of C60(111)

in the first subsurface layer. The sensitivity of the scanning tunneling microscopy (STM) images to the specific local environment allows us to distinguish between Mn interstitials with nearest-neighbor As atoms

Temperature dependence of the Ge(1 1 1) 3d threshold near the 1050 K surface order-disorder transition

({\mathrm{Int}}_{\mathrm{As}})

Multipole and spin-flip interband transitions in the electron energy loss of ferromagnetic Fe

rather than Ga atoms