arXiv subjects

R. Berndt

Publications and source records attributed to R. Berndt.

24 records · Page 2Linked to original sources

arXiv2004

Electron dynamics in vacancy islands

The dynamics of Ag(111) surface state electrons confined to nanoscale hexagonal and triangular vacancy islands are investigated using scanning tunneling spectroscopy. The lifetimes of quantised states with significant amplitude near the centers of the vacancies are weakly affected by the geometry of the confining cavity. A model that includes the dependence of the lifetime on electron energy, vacancy size, step reflectivity and the phase coherence length describes the results well. For vacancy islands with areas in the range $\approx 40$--$220 {\rm nm}^2$ lossy scattering is the dominant lifetime-limiting process. This result and a corrected analysis of published experimental data improve the consistency of experimental and calculated surface state lifetimes.

cond-mat.other↗

arXiv2004

Surface-State Localization at Adatoms

Low-temperature scanning tunneling spectroscopy of magnetic and non-magnetic metal atoms on Ag(111) and on Cu(111) surfaces reveals the existence of a common electronic resonance at an energy below the binding energies of the surface states. Using an extended Newns-Anderson model, we assign this resonance to an adsorbate-induced bound state, split off from the bottom of the surface-state band, and broadened by the interaction with bulk states. A lineshape analysis of the bound state indicates that native adatoms decrease the surface-state lifetime, while a cobalt adatom causes no significant change.

cond-mat.str-el↗

arXiv2004

Chiral structures of lander molecules on Cu(100)

Supramolecular assemblies of lander molecules (C$_{90}$H$_{98}$) on Cu(100) are investigated with low-temperature scanning tunneling microscopy. The energetically most favourable conformation of the adsorbed molecule is found to exist in two mirror symmetric enantiomers or conformers. At low coverage, the molecules align in enantiomerically pure chains along the chiral directions $[01\bar{2}],[02\bar{1}],[012]$ and $[021]$. The arrangement is proposed to be mainly governed by intermolecular van-der-Waals interaction. At higher coverages, the molecular chains arrange into chiral domains, for which a structural model is presented.

cond-mat.other↗

arXiv2004

Stark effect of the Au(111) and Cu(111) surface states

We present a low-temperature scanning tunneling spectroscopy study of the Au(111) and of the Cu(111) surface states showing that their binding energy increases when the tip is approached towards the surface. This result, supported by a one-dimensional model calculation and by a comparison to existing photoemission spectroscopy measurements, confirms the existence of a tip-induced Stark effect as previously reported for Ag(111) [L. Limot et al., Phys. Rev. Lett. 91, 196801 (2003)], and suggests that this effect is a general feature of scanning tunneling spectroscopy.

cond-mat.other↗

arXiv2003

Kondo Effect and Surface-State Electrons

We have used low temperature scanning tunneling spectroscopy and atomic manipulation to study the role of surface-state electrons in the Kondo effect of an isolated cobalt atom adsorbed on Ag(111). We show that the observed Kondo signature remains unchanged in close proximity of a monoatomic step, where the local density of states of the surface-state electrons is strongly perturbed. This result indicates a minor role for surface-state electrons in the Kondo effect of cobalt, compared to bulk electrons. A possible explanation for our findings is presented.

cond-mat↗

arXiv2003

Surface State Stark Shift in a Scanning Tunneling Microscope

We report a quantitative low-temperature Scanning Tunneling Spectroscopy (STS)study on the Ag(111) surface state over an unprecedented range of currents (50 pA to 6 $μ$A)through which we can tune the electric field in the tunnel junction of the microscope. We show that in STS a sizeable Stark effect causes a shift of the surface state binding energy $E_{0}$.Data taken are reproduced by a one-dimensional potential model calculation, and are found to yield a Stark-free energy $E_{0}$ in agreement with recent state-of-the-art Photoemission Spectroscopy measurements.

cond-mat.str-el↗