Search

Detailed measurements of state resolved inelastic scattering of N[SUB2] from Ru (0001) are reported for a wide range of initial energies (0-3 eV) and angles of incidence. The ion time-of-flight resonantly enhanced multiphoton ionization (REMPI) detection scheme developed here and used with cw molecular beams simultaneously measures the internal quantum state and translational energy normal to the sample surface. Doppler broadening of the REMPI spectrum of scattered particles (yields the dispersion in scattering out of plane. The results are qualitatively similar to inelastic N[SUB2] scattering studies for a wide variety of other metal surfaces; i.e., no observable vibrational excitation, weak rotational excitation described as a Boltzmann distribution, strong surface excitation depending upon the incident normal energy, and an anticorrelation between rotational and surface excitation. The absence of any vibrational excitation at E≈3 eV is inconsistent with adiabatic model dynamics based on the ab initio potential-energy surface. It is, however, consistent with a strong nonadiabatic damping of vibration to electron-hole pairs in the region of the barrier. This same suggestion was previously found necessary to rationalize unusual dissociative adsorption and associative desorption of N[SUB2] on Ru(0001). [ABSTRACT FROM AUTHOR]

Experiments on quantum transport in a low temperature scanning tunneling microscope provide the possibility to study atomic and molecular contacts with well-defined electrode-geometry at least for one of the contacts, the surface. Here, we show for a number of examples, the strength of transport studies by STM. For single cobalt adatoms, we demonstrate the abrupt change in the width of the Kondo resonance of the cobalt adatom once the contact regime is reached. Differences of the mechanical properties of junctions with cobalt and gold adatoms are discussed. Finally, we show transport measurements and imaging with individual PVBA molecules. Configurations in which we have investigated quantum transport: through a junction consisting of a single gold adatom, a single cobalt adatom, and a PVBA molecule between the tip of an STM and the surface. [ABSTRACT FROM AUTHOR]

We report on an atomic-scale study of the Kondo lattice compound YbAl3 using scanning tunneling microscopy (STM) and spectroscopy (STS). An analysis of the surface orientation and structure is performed based on STM images containing more than one crystal facet. We compare tunneling spectra acquired on different facets and discuss their relation with the temperature scales observed in measurements of bulk quantities and the states observed in photoemission spectra. On specific facets, we observe strong additional resonances close to the Fermi energy which are not consistent with the characteristic energy scales found in bulk measurements, and which we interpret in terms of a modified Kondo stale of the near-surface Ytterbium atoms. [ABSTRACT FROM AUTHOR]

The influence of the coordination on the Kondo temperature of a magnetic impurity at a noble metal surface and the line shape observed in low temperature scanning tunneling spectroscopy (STS) is investigated for single cobalt atoms adsorbed on and embedded in copper surfaces. Surprisingly, the Kondo temperature for substitutional cobalt atoms is almost the same as that of adatoms on the Cu(100) surface. This is in stark contrast to the behaviour observed at the Cu(111) surface. DFT calculations reveal that in the case of Cu(100) the coupling of the spin of the cobalt atom to the conduction band is not substantially increased by the incorporation of the cobalt atom. At the same time the observed line shape differs strongly from what is observed on adatom systems. [ABSTRACT FROM AUTHOR]

Scanning tunneling spectroscopy has developed into a powerful spectroscopic technique that has found wide application in the atomic scale characterization of the electronic properties of clean surfaces as well as adsorbates and defects at surfaces. However, it still lacks the standard methods for data treatment and removal of artifacts in spectra as they are, e.g., common in photoemission spectroscopy. The properties of the atomic scale tip apex—the probe of the instrument—tend to introduce spurious background signals into tunneling spectra. We present and discuss two methods which permit to extract tip-independent information from low temperature tunneling spectra acquired on single atoms and molecules on single crystal surfaces by background subtraction. The methods rely on a characterization of the tip on the clean metal surface. The performance of both methods is demonstrated and compared for simulated and experimental tunneling spectra. [ABSTRACT FROM AUTHOR]