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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]

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]

We use scanning tunneling microscopy and spectroscopy to study the energy dependence of hot-electron scattering processes on metal surfaces via the determination of the energy-dependent phase-coherence length. From this an electron lifetime can be determined, which in the case of electrons in the surface state of Ag(111) and in the case of the n=1 image-potential state on Cu(100) shows good agreement with theoretical modeling and other experimental data. The method is based on the quantitative analysis of electron interference patterns. A theoretical analysis shows that the phase-coherence length can be determined in confining nanostructures of a characteristic length scale smaller than the phase-coherence length. [ABSTRACT FROM AUTHOR]

We use scanning tunneling microscopy and spectroscopy to study the properties of magnetic Co adatoms on noble metal surfaces at 6 K. Due to spin-flip scattering of the substrate electrons at the impurity the many-body Kondo state forms. This state is characterized by an energy, the Kondo temperature TK. We measure TK of adatom systems and a resonant scattering phase shift locally and are thus able to discuss the coupling of the Co adatom to the metal electronic system. From the resonant scattering phase shift of the surface-state electrons scattering off a Co adatom on Ag(111), we find that the coupling to the surface state is rather weak. On the other hand, increasing the number of nearest neighbor substrate atoms increases the coupling of a Co adatom to the host metal and increases TK. This shows the dominant character of the coupling of the Co atom to the bulk states of the substrate crystal. [ABSTRACT FROM AUTHOR]

Scanning tunneling spectroscopy (STS) reveals a distinct asymmetry in the scattering properties of an isolated step for the n=1 image-potential state on Cu(001). The elastic scattering probability for an electron traveling downstairs is determined from the strength of density oscillations in front of a step edge and is found to be approximately two times higher than for the opposite upstairs direction. A one-dimensional scattering model is extended to the case of asymmetric transmission and reflection coefficients. The calculations using the asymmetry measured by STS explain the dispersion and the decay rate of the n=1 band on Cu(119) measured by two-photon photoemission. In particular, the asymmetry of the decay rate can be described quantitatively with a minimum of adjustable parameters. While the results can also be transferred successfully to the Cu(1115) surface, the limit of applicability is reached for Cu(117) with a step separation of 3.5 nearest-neighbor distances. [ABSTRACT FROM AUTHOR]