2006 - 2010

Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111)
Y. Wang, X. Ge, G. Schull, R. Berndt, H. Tang, C. Bornholdt, F. Koehler, R. Herges, J. Am. Chem. Soc. 132, 1196 (2010)

Abstract:
4,4-Azopyridine trimers and 4-phenylazopyridine dimers have been reversibly switched in ordered arrays on Au(111). During the switching process, single weak C-H...N hydrogen bonds are broken and reformed.

[BibTeX]
@article{YFW_JACS10,
  author = {Y. Wang and X. Ge and G. Schull and R. Berndt and H. Tang and C. Bornholdt and F. Koehler and R. Herges},
  title = {Switching Single Azopyridine Supramolecules in Ordered Arrays on Au(111)},
  journal = {J. Am. Chem. Soc.},
  volume = {132},
  pages = {1196},	
  year = {2010},
  url = {http://pubs.acs.org/doi/abs/10.1021/ja9080277},
  doi = {http://doi.org/10.1021/ja9080277}
}
 
 
Kondo effect of a Co atom on Cu(111) in contact with an iron tip
N. Néel, J. Kröger, R. Berndt, Phys. Rev. B 82, 233401 (2010)

Abstract:
Single Co atoms, which exhibit a Kondo effect on Cu(111), are contacted with Cu and Fe tips in a low-temperature scanning tunneling microscope. With Fe tips, the Kondo effect persists with the Abrikosov-Suhl resonance significantly broadened. In contrast, for Cu-covered W tips, the resonance width remains almost constant throughout the tunneling and contact ranges. The distinct changes in the line width are interpreted in terms of modifications of the Co d state occupation owing to hybridization with the tip apex atoms.

[BibTeX]
@article{NNE_PRB10,
  author = {N. Néel and J. Kröger and R. Berndt},
  title = {Kondo effect of a Co atom on Cu(111) in contact with an iron tip},
  journal = {Phys. Rev. B},
  volume = {82},
  pages = {233401},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRB/v82/p233401},
  doi = {http://doi.org/10.1103/PhysRevB.82.233401}
}
 
 
Conductance of atom-sized Pb contacts
M. Becker, R. Berndt, New J. Phys. 12, 113010 (2010)

Abstract:
The contact formation of a metallic tip approaching Pb thin films supported on Ag(111) substrates is investigated with a cryogenic scanning tunnelling microscope. While contacts to thicker Pb films are formed rather abruptly, the transition between tunnelling and contact is gradual for the first Pb monolayer on Ag(111). This behaviour may be understood in terms of diifferent vertical bonding-strengths due to a charge-transfer induced surface dipole. Owing to the gradual evolution of tip-surface contacts on the first Pb(111) ML imaging can be performed at contact. Furthermore, we show that for atomic-sized Pb contacts, the interpretation of peaks in conventional conductance histograms in terms of single-atom point-contact conductances yields an overestimation of contact conductances.

[BibTeX]
@article{MBE_NJP10,
  author = {M. Becker and R. Berndt},
  title = {Conductance of atom-sized Pb contacts},
  journal = {New J. Phys.},
  volume = {12},
  pages = {113010},	
  year = {2010},
  url = {http://stacks.iop.org/NJP/12/113010},
  doi = {http://doi.org/10.1088/1367-2630/12/11/113010}
}
 
 
Graphene on Ru(0001): Contact Formation and Chemical Reactivity on the Atomic Scale
S. Altenburg, J. Kröger, B. Wang, M.-L. Boquet, N. Lorente, R. Berndt, Phys. Rev. Lett. 105, 236101 (2010)

Abstract:
Graphene on Ru(0001) is contacted with Au tips of a cryogenic scanning tunneling microscope. The formation and conductance of single-atom contacts vary within the moiré unit cell. Density functional calculations reveal that elastic distortions of the graphene lattice occur at contact due to a selectively enhanced chemical reactivity of C atoms at hollow sites of Ru(0001). Concomitant quantum transport calculations indicate that the graphene-Ru distance determines the conductance variations.

[BibTeX]
@article{SAL_PRL10,
  author = {S.J. Altenburg and J. Kröger and B. Wang and M.-L. Boquet and N. Lorente and R. Berndt},
  title = {Graphene on Ru(0001): Contact Formation and Chemical Reactivity on the Atomic Scale},
  journal = {Phys. Rev. Lett.},
  volume = {105},
  pages = {236101},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRL/v105/p236101},
  doi = {http://doi.org/10.1103/PhysRevLett.105.236101}
}
 
 
Coverage Driven Formation of Homochiral Domains of an Achiral Molecule on Au(111)
T. Gopakumar, F. Matino, B. Schwager, A. Bannwarth, F. Tuczek, J. Kröger, R. Berndt, J. Phys. Chem. C 114, 18247 (2010)

Abstract:
Adsorption of achiral Ni-tetramethyl-tetraazaannulene on Au(111) leads to the assembly of chiral trimers, which serve as building blocks for larger chiral patterns. A racemic mixture is observed at low coverages. Beyond a critical coverage, extraordinarily large homochiral domains occur and cover entire substrate terraces. The chiral structures and the formation of homochiral domains are induced by steric interactions.

[BibTeX]
@article{GOP_JPCC10,
  author = {T.G. Gopakumar and F. Matino and B. Schwager and A. Bannwarth and F. Tuczek and J. Kröger and R. Berndt},
  title = {Coverage Driven Formation of Homochiral Domains of an Achiral Molecule on Au(111)},
  journal = {J. Phys. Chem. C},
  volume = {114},
  pages = {18247},	
  year = {2010},
  url = {http://dx.doi.org/10.1021/jp106973p},
  doi = {http://doi.org/10.1021/jp106973p}
}
 
 
Molecular Nanocrystals on Ultrathin NaCl Films on Au(111)
Y. Wang, J. Kröger, R. Berndt, H. Tang, J. Am. Chem. Soc. 132, 12546 (2010)

Abstract:
Direct comparison of SnPc growth on a metal and a nearly insulating surface was achieved by adsorption of SnPc on Au(111) partially covered with NaCl. While on Au(111), SnPc lies flat and grows in a Stranski-Krastanov mode; on NaCl, Volmer-Weber growth of three-dimensional molecular nanocrystals occurs. On NaCl, intermolecular interactions dominate over the molecule-NaCl coupling and result in a tilted adsorption configuration.

[BibTeX]
@article{JFW_JACS10_2,
  author = {Y. Wang and J. Kröger and R. Berndt and H. Tang},
  title = {Molecular Nanocrystals on Ultrathin NaCl Films on Au(111)},
  journal = {J. Am. Chem. Soc.},
  volume = {132},
  pages = {12546},	
  year = {2010},
  url = {http://dx.doi.org/10.1021/ja105110d},
  doi = {http://doi.org/10.1021/ja105110d}
}
 
 
CoPc adsorption on Cu(111): origin of the C4 to C2 symmetry reduction
J.C. R. Cuadrado, Y. Wang, G. Xin, R. Berndt, H. Tang, J. Chem. Phys. 133, 154701 (2010)

Abstract:
Adsorption of phthalocyanines (Pc) to various surfaces has recently been reported to lead to a lowering of symmetry from C4 to C2 in scanning tunneling microscope (STM) images. Possible origins of the reduced symmetry involve the electronic structure or geometric deformation of the molecules. Here the origin of the reduction is clarified from a comprehensive theoretical study of CoPc adsorbed to the Cu(111) surface along with experimental STM data. Total energy calculations using different schemes for the exchange-correlation energy and STM simulations are compared against experimental data. We find that the symmetry reduction is only reproduced when van der Waals corrections are included into the formalism. It is caused by a deformation along the two perpendicular molecular axes, one of them coming closer to the surface by around 0.2 �A. An electronic structure analysis reveals (i) the relevance of the CoPc interaction with the Cu(111) surface state and, (ii) that intramolecular features in dI/dV maps clearly discriminate a Co-derived state from the rest of the Pc states.

[BibTeX]
@article{RCU_JCP10,
  author = {R. Cuadrado, J.I. Cerdá and Y. Wang and G. Xin and R. Berndt and H. Tang},
  title = {CoPc adsorption on Cu(111): origin of the C4 to C2 symmetry reduction},
  journal = {J. Chem. Phys.},
  volume = {133},
  pages = {154701},	
  year = {2010},
  url = {http://link.aip.org/link/?JCP/133/154701},
  doi = {http://doi.org/10.1063/1.3502682}
}
 
 
Optical Probe of Quantum Shot-Noise Reduction at a Single-Atom Contact
N. Schneider, G. Schull, R. Berndt, Phys. Rev. Lett. 105, 026601 (2010)

Abstract:
Visible and infrared light emitted at a Ag-Ag(111) junction has been investigated from tunneling to single-atom contact conditions with a scanning tunneling microscope. The light intensity varies in a highly nonlinear fashion with the conductance of the junction and exhibits a minimum at conductances close to the conductance quantum. The data are interpreted in terms of current noise at optical frequencies, which is characteristic of partially open transport channels.

[BibTeX]
@article{NSC_PRL10,
  author = {N. Schneider and G. Schull and R. Berndt},
  title = {Optical Probe of Quantum Shot-Noise Reduction at a Single-Atom Contact},
  journal = {Phys. Rev. Lett.},
  volume = {105},
  pages = {026601},	
  year = {2010},
  note = {Editors' Suggestion.},
  url = {http://link.aps.org/abstract/PRL/v105/p026601},
  doi = {http://doi.org/10.1103/PhysRevLett.105.026601}
}
 
Editors' Suggestion.
 
Adatom-induced Lateral Inhomogeneity of Quantum Well States in Metal Multilayers
U. Schwingenschlögl, T. Uchihashi, C.D. Paloa, R. Berndt, Phys. Rev. B 82, 33406 (2010)

Abstract:
The influence of Co adatoms on the quantum well states (QWSs) existing in Cu/Co (100) multilayers is investigated by means of ab initio calculations. The typical oscillations of the density of states at the Fermi level as a function of the number of Cu layers are found to be strongly perturbed by the presence of adatoms on the surface. In a lateral direction, the QWSs exhibit atomic-scale variations, which depend on the number of Cu layers. These results suggest that the phase accumulation model, which is often used for analyzing QWS, is not sufficient to interpret electronic features near adatoms and call for experimental real-space investigations of QWS.

[BibTeX]
@article{USC_PRB10,
  author = {U. Schwingenschlögl and T. Uchihashi and C. Di Paloa and R. Berndt},
  title = {Adatom-induced Lateral Inhomogeneity of Quantum Well States in Metal Multilayers},
  journal = {Phys. Rev. B},
  volume = {82},
  pages = {33406},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRB/v82/p33406},
  doi = {http://doi.org/10.1103/PhysRevB.82.033406}
}
 
 
Single azopyridine-substituted porphyrin molecules for configurational and electronic switching
F. Matino, G. Schull, U. Jana, F. Köhler, R. Berndt, R. Herges, Chem. Comm. 46, 6780 (2010)

Abstract:
A new azopyridine functionalized Ni-porphyrin was synthesized as a model compound for deposition and switch on surfaces. Two geometrically and electronically different states of single molecules on Au(111) were found by scanning tunneling microscopy/spectroscopy and analyzed with density functional calculations

[BibTeX]
@article{FMA_CCO10,
  author = {F. Matino and G. Schull and U. Jana and F. Köhler and R. Berndt and R. Herges},
  title = {Single azopyridine-substituted porphyrin molecules for configurational and electronic switching},
  journal = {Chem. Comm.},
  volume = {46},
  pages = {6780},	
  year = {2010},
  url = {http://dx.doi.org/10.1039/C0CC00959H},
  doi = {http://doi.org/10.1039/C0CC00959H}
}
 
 
Scattering and lifetime broadening of quantum well states in Pb films on Ag(111)
M. Becker, R. Berndt, Phys. Rev. B 81, 205438 (2010)

Abstract:
Quantum well states in thin Pb(111) metal films on Ag(111) surfaces were investigated using low-temperature scanning tunneling spectroscopy. Quantitative analysis of the spectra yields the bulk-band dispersion in G-L direction, scattering phase shifts at interface and vacuum barrier as well as the lifetime broadening.

[BibTeX]
@article{MBE_PRB10_2,
  author = {M. Becker and R. Berndt},
  title = {Scattering and lifetime broadening of quantum well states in Pb films on Ag(111)},
  journal = {Phys. Rev. B},
  volume = {81},
  pages = {205438},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRB/v81/p205438},
  doi = {http://doi.org/10.1103/PhysRevB.81.205438}
}
 
 
Control of spin-polarized current in a scanning tunneling microscope by single-atom transfer
M. Ziegler, N. Ruppelt, N. Néel, J. Kröger, R. Berndt, Appl. Phys. Lett. 96, 132505 (2010)

Abstract:
The spin polarization of the tunneling current between a Cr-covered scanning tunneling microscope tip and a Fe-covered W(110) surface was controllably modified by transferring single Cr atoms from the tip to the surface. Reproducible reversal of the spin polarization enables the discrimination of magnetic from electronic properties without the need of an external magnetic field.

[BibTeX]
@article{MZI_APL10,
  author = {M. Ziegler and N. Ruppelt and N. Néel and J. Kröger and R. Berndt},
  title = {Control of spin-polarized current in a scanning tunneling microscope by single-atom transfer},
  journal = {Appl. Phys. Lett.},
  volume = {96},
  pages = {132505},	
  year = {2010},
  url = {http://link.aip.org/link/?APPLAB/96/132505},
  doi = {http://doi.org/10.1063/1.3377917}
}
 
 
Atomic resolution in tunneling induced light emission from GaAs(110)
M. Reinhardt, G. Schull, P. Ebert, R. Berndt, Appl. Phys. Lett. 96, 152107 (2010)

Abstract:
A cryogenic scanning tunneling microscope is used to induce band edge luminescence from GaAs(110). The emission intensity varies within the unit mesh of the surface. This atomic resolution reflects variations of the efficiency of hole injection into states at the valence band maximum. Moreover, the hole injection efficiency is modulated by local potential fluctuations due to dopants

[BibTeX]
@article{MRE_APL10,
  author = {M. Reinhardt and G. Schull and P. Ebert and R. Berndt},
  title = {Atomic resolution in tunneling induced light emission from GaAs(110)},
  journal = {Appl. Phys. Lett.},
  volume = {96},
  pages = {152107},	
  year = {2010},
  url = {http://link.aip.org/link/?APPLAB/96/152107},
  doi = {http://doi.org/10.1063/1.3360203}
}
 
 
Atomic-Scale Control of Electron Transport through Single Molecules
Y. Wang, J. Kröger, R. Berndt, H. Vázquez, M. Brandbyge, M. Paulsson, Phys. Rev. Lett. 104, 176802 (2010)

Abstract:
Tin-phthalocyanine molecules adsorbed on Ag(111) were contacted with the tip of a cryogenic scanning tunneling microscope. Orders-of-magnitude variations of the single-molecule junction conductance were achieved by controllably dehydrogenating the molecule and by modifying the atomic structure of the surface electrode. Non-equilibrium Green's function calculations reproduce the trend of the conductance and visualize the current flow through the junction, which is guided through molecule-electrode chemical bonds.

[BibTeX]
@article{YFW_PRL10,
  author = {Y. Wang and J. Kröger and R. Berndt and H. Vázquez and M. Brandbyge and M. Paulsson},
  title = {Atomic-Scale Control of Electron Transport through Single Molecules},
  journal = {Phys. Rev. Lett.},
  volume = {104},
  pages = {176802},	
  year = {2010},
  note = {Editors' Suggestion. cf. S. Kancharla, Tuning conductance, in Physics - spotlighting exceptional research.},
  url = {http://link.aps.org/abstract/PRL/v104/p176802},
  doi = {http://doi.org/10.1103/PhysRevLett.104.176802}
}
 
Editors' Suggestion.
cf. S. Kancharla, Tuning conductance, in Physics - spotlighting exceptional research.
 
Contrast inversion of the apparent barrier height of Pb thin films in scanning tunneling microscopy
M. Becker, R. Berndt, Appl. Phys. Lett. 96, 33112 (2010)

Abstract:
Scanning tunneling microscopy measurements of the apparent height of the tunneling barrier are analyzed for Pb islands on Ag(111). The apparent barrier height (ABH) significantly varies with the bias voltage. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of the ABH. Using model calculations, these variations are interpreted in terms of the strongly modulated local density of states of thin Pb films, which is caused by quantum well states.

[BibTeX]
@article{MBE_APL10,
  author = {M. Becker and R. Berndt},
  title = {Contrast inversion of the apparent barrier height of Pb thin films in scanning tunneling microscopy},
  journal = {Appl. Phys. Lett.},
  volume = {96},
  pages = {33112},	
  year = {2010},
  url = {http://link.aip.org/link/?APPLAB/96/33112},
  doi = {http://doi.org/10.1063/1.3291114}
}
 
 
Conductance of Ag atoms and clusters on Ag(111): Spectroscopic and time-resolved data
A. Sperl, J. Kröger, R. Berndt, Phys. Status Solidi B 247, 1077 (2010)

Abstract:
The evolution of the electronic structure of linear atomic Ag chains on Ag(111) has been explored atom by atom using low-temperature scanning tunnelling microscopy and spectroscopy. Electronic states confined to the linear chains are well described within a particle-in-a-box model. The evolution of an unoccupied Ag monomer resonance during the synthesis of a Ag dimer reveals that the Ag-Ag interaction is predominantly direct owing to the large spatial extension of p wave functions of the adsorbed atoms. Diffusion dynamics of a single Ag atom adsorbed on Ag(111) have been monitored by two-level conductance fluctuations of the tunnel junctions. Effective temperatures of the junction and diffusion barrier heights in the presence of the tip were extracted from a voltage-dependent analysis of the fluctuation rate.

[BibTeX]
@article{ASP_PSSB10,
  author = {A. Sperl and J. Kröger and R. Berndt},
  title = {Conductance of Ag atoms and clusters on Ag(111): Spectroscopic and time-resolved data},
  journal = {Phys. Status Solidi B},
  volume = {247},
  pages = {1077},	
  year = {2010},
  url = {http://dx.doi.org/10.1002/pssb.200945485},
  doi = {http://doi.org/10.1002/pssb.200945485}
}
 
 
Influence of band structure on the apparent barrier height in scanning tunneling microscopy
M. Becker, R. Berndt, Phys. Rev. B 81, 035426 (2010)

Abstract:
The apparent height of the tunneling barrier in scanning tunneling microscopy measured on Au(111), Ag(111), and Cu(111) surfaces is found to vary significantly with the bias voltage. In particular, the apparent barrier height Phi_a is asymmetric with respect to the bias polarity on all three surfaces, in contrast to simple interpretations of Phi_a in terms of an average work function of tip and sample. Model calculations of the tunneling current, which take band-structure effects into account, describe the experimental observations.

[BibTeX]
@article{MBE_PRB10,
  author = {M. Becker and R. Berndt},
  title = {Influence of band structure on the apparent barrier height in scanning tunneling microscopy},
  journal = {Phys. Rev. B},
  volume = {81},
  pages = {035426},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRB/v81/p035426},
  doi = {http://doi.org/10.1103/PhysRevB.81.035426}
}
 
 
Direct observation of conductance fluctuations of a single-atom tunneling contact
A. Sperl, J. Kröger, R. Berndt, Phys. Rev. B 81, 035406 (2010)

Abstract:
Using the tip of a cryogenic scanning tunneling microscope, the dynamics of lateral translations of a single silver atom adsorbed on Ag(111) were investigated with a time resolution of 10 ns. Elevated tunneling currents passed through the tip close to the adsorbed atom induce sudden adsorption site changes, which are reflected by two-level fluctuations of the tunneling conductance. The voltage dependence of the fluctuation rate reveals different local heating of the adsorbed atom in different adsorption sites.

[BibTeX]
@article{ASP_PRB10,
  author = {A. Sperl and J. Kröger and R. Berndt},
  title = {Direct observation of conductance fluctuations of a single-atom tunneling contact},
  journal = {Phys. Rev. B},
  volume = {81},
  pages = {035406},	
  year = {2010},
  url = {http://link.aps.org/abstract/PRB/v81/p035406},
  doi = {http://doi.org/10.1103/PhysRevB.81.035406}
}
 
 
Molecular switches on surfaces explored with a scanning tunneling miscroscope
J. Kröger, Y. Wang, N. Néel, R. Berndt, in Molecular and Organic Devices, D. Aswal and J. Yakhmi (Hrsg.) , 85-108 (Nova Science Publishers, 2010)
[BibTeX]
@inbook{JKR_NSP10,
  author = {J. Kröger and Y. Wang and N. Néel and R. Berndt},
  chapter = {Molecular switches on surfaces explored with a scanning tunneling miscroscope},
  title = {Molecular and Organic Devices},
  editor = {D.K. Aswal and J.V. Yakhmi},
  pages = {85--108},
  publisher = {Nova Science Publishers},	
  year = {2010},
  isbn = {978-60876-594-2}
}
 
 
Controlled single atom and single molecule contacts
R. Berndt, J. Kröger, N. Néel, G. Schull, Phys. Chem. Chem. Phys. 12, 1022 (2010)

Abstract:
The scanning tunnelling microscope (STM) may be used to prepare contacts to single atoms or molecules on surfaces and to investigate the transport of electrons through these junctions. The imaging capabilities of STM along with spectroscopic modes of measurement enable a rather detailed characterisation of the geometric and electronic properties of the contacts. This perspective presents recent investigations into the quantum transport through magnetic atoms and C60 molecules.

[BibTeX]
@article{RBE_PCCP10,
  author = {R. Berndt and J. Kröger and N. Néel and G. Schull},
  title = {Controlled single atom and single molecule contacts},
  journal = {Phys. Chem. Chem. Phys.},
  volume = {12},
  pages = {1022},	
  year = {2010},
  url = {http://dx.doi.org/10.1039/b908672m},
  doi = {http://doi.org/10.1039/b908672m}
}
 
 
Scanning tunneling microscopic investigations into the conductance of single-atom junctions
J. Kröger, A. Sperl, N. Néel, R. Berndt, J. Adv. Mic. Res. 4, 49 (2009)

Abstract:
Experiments using a scanning tunneling microscope to controllably fabricate single-atom contacts are reviewed. An important feature of this approach is that the electronic and geometric properties of the junctions can be characterized prior to and after contact formation. Investigations on magnetic contacts have led to the observation of unusual conductance values. Spectroscopy of the electronic states of single atoms in contact with the tip is demonstrated through the observation of the Kondo effect and of surface state localization at adsorbed atoms. Time-resolved two-level fluctuations of a single-atom tunneling contact reveal heating of the junction in an otherwise cryogenic environment.

[BibTeX]
@article{JKR_JSPM09,
  author = {J. Kröger and A. Sperl and N. Néel and R. Berndt},
  title = {Scanning tunneling microscopic investigations into the conductance of single-atom junctions},
  journal = {J. Adv. Mic. Res.},
  volume = {4},
  pages = {49},	
  year = {2009},
  url = {http://dx.doi.org/10.1166/jspm.2009.1009},
  doi = {http://doi.org/10.1166/jspm.2009.1009}
}
 
 
Single-Atom Contacts with a Scanning Tunnelling Microscope
J. Kröger, N. Néel, A. Sperl, Y. Wang, R. Berndt, New J. Phys. 11, 125006 (2009)

Abstract:
The tip of a cryogenic scanning tunnelling microscope is used to controllably contact single atoms adsorbed on metal surfaces. By deliberately choosing the materials of tip and surface, a variety of electrode combinations may be used to investigate conventional and spin-polarized electron transport through non-magnetic and magnetic atoms. The junctions are stable and enable spectroscopic measurements of localized electronic states and correlated electron systems.

[BibTeX]
@article{JKR_NJP09,
  author = {J. Kröger and N. Néel and A. Sperl and Y. Wang and R. Berndt},
  title = {Single-Atom Contacts with a Scanning Tunnelling Microscope},
  journal = {New J. Phys.},
  volume = {11},
  pages = {125006},	
  year = {2009},
  url = {http://stacks.iop.org/NJP/11/125006},
  doi = {http://doi.org/10.1088/1367-2630/11/12/125006}
}
 
 
Local heating at a ferromagnet-metal interface
N. Néel, J. Kröger, M. Ziegler, R. Berndt, Appl. Phys. Lett. 95, 203103 (2009)

Abstract:
The electronic structure of individual Co islands on Cu(111) was investigated by a cryogenic scanning tunneling microscope. An irreversible shift of the occupied Co d band toward the Fermi level was induced by elevated tunneling currents and voltages. Heating of the Co-Cu interface most likely induces local alloying and a concomitant modification of the island electronic structure.

[BibTeX]
@article{NNE_APL09,
  author = {N. Néel and J. Kröger and M. Ziegler and R. Berndt},
  title = {Local heating at a ferromagnet-metal interface},
  journal = {Appl. Phys. Lett.},
  volume = {95},
  pages = {203103},	
  year = {2009},
  url = {http://link.aip.org/link/?APPLAB/95/203103},
  doi = {http://doi.org/10.1063/1.3262949}
}
 
 
Spatial modulation of d states in a nanoscale Co island
T. Gopakumar, N. Néel, J. Kröger, R. Berndt, Chem. Phys. Lett. 484, 59 (2009)

Abstract:
A cryogenic scanning tunnelling microscope was used to probe the electronic properties of a moiré pattern observed from cobalt islands on Ag(111). Spatially resolved spectroscopy reveals that the moiré lattice gives rise to a periodic electronic pattern of cobalt d states. The arrangement of magnetic molecules on the moiré lattice suggests an electronic template effect.

[BibTeX]
@article{GOP_CHL09,
  author = {T.G. Gopakumar and N. Néel and J. Kröger and R. Berndt},
  title = {Spatial modulation of d states in a nanoscale Co island},
  journal = {Chem. Phys. Lett.},
  volume = {484},
  pages = {59},	
  year = {2009},
  url = {http://dx.doi.org/10.1016/j.cplett.2009.11.012},
  doi = {http://doi.org/10.1016/j.cplett.2009.11.012}
}
 
 
Passing current through touching molecules
G. Schull, T. Frederiksen, M. Brandbyge, R. Berndt, Phys. Rev. Lett. 103, 206803 (2009)

Abstract:
The charge flow from a single C60 molecule to another one has been probed. The conformation and electronic states of both molecules on the contacting electrodes have been characterized using a cryogenic scanning tunneling microscope. While the contact conductance of a single molecule between two Cu electrodes can vary up to a factor of three depending on electrode geometry, the conductance of the C60-C60 contact is consistently lower by two orders of magnitude. First-principles transport calculations reproduce the experimental results, allow a determination of the actual C60-C60 distances, and identify the essential role of the intermolecular link in bi- and trimolecular chains.

[BibTeX]
@article{GSC_PRL09_2,
  author = {G. Schull and T. Frederiksen and M.  Brandbyge and R. Berndt},
  title = {Passing current through touching molecules},
  journal = {Phys. Rev. Lett.},
  volume = {103},
  pages = {206803},	
  year = {2009},
  note = {Editors' Suggestion. cf. D. Monroe, Molecular Currents, in Physics - spotlighting exceptional research.},
  url = {http://link.aps.org/abstract/PRL/v103/p206803},
  doi = {http://doi.org/10.1103/PhysRevLett.103.206803}
}
 
Editors' Suggestion.
cf. D. Monroe, Molecular Currents, in Physics - spotlighting exceptional research.
 
Supramolecular Patterns controlled by Electron Interference and Direct Intermolecular Interactions
Y. Wang, X. Ge, C. Manzano, J. Kröger, R. Berndt, W. Hofer, H. Tang, J. Cerda, J. Am. Chem. Soc. 131, 10400 (2009)

Abstract:
Whereas all 230 three-dimensional space groups occur in molecular crystals, out of only 17 plane groups some highly symmetric ones such as p31m have not yet been observed in two-dimensional (2D) crystals of organic molecules. Here a kagome network with p31m symmetry is reported for cobalt phthalocyanine on Cu(111). This unusual structure results from substrate-induced reduction of molecular symmetry and substrate-mediated interaction via quantum-interference of surface electrons. These interactions provide additional control over the symmetry of 2D crystals of phthalocyanines and lead to a variety of other symmetries in self-assembled arrays.

[BibTeX]
@article{JFW_JACS09_2,
  author = {Y. Wang and X. Ge and C. Manzano and J. Kröger and R. Berndt and W.A. Hofer and H. Tang and J. Cerda},
  title = {Supramolecular Patterns controlled by Electron Interference and Direct Intermolecular Interactions},
  journal = {J. Am. Chem. Soc.},
  volume = {131},
  pages = {10400},	
  year = {2009},
  url = {http://dx.doi.org/10.1021/ja903506s},
  doi = {http://doi.org/10.1021/ja903506s}
}
 
 
Local density of states from constant-current tunneling spectra
M. Ziegler, N. Néel, A. Sperl, J. Kröger, R. Berndt, Phys. Rev. B 80, 125402 (2009)

Abstract:
Scanning tunneling spectroscopy of the differential conductance (dI/dV) is performed at constant current and at constant distance. These modes of operation significantly affect peak positions and line shapes in spectra as well as patterns in spatial maps of dI/dV. A normalization procedure for constant-current data, which relies on experimental current-distance data, is shown to yield spectral information on the local density of states.

[BibTeX]
@article{MZI_PRB09_2,
  author = {M. Ziegler and N. Néel and A. Sperl and J. Kröger and R. Berndt},
  title = {Local density of states from constant-current tunneling spectra},
  journal = {Phys. Rev. B},
  volume = {80},
  pages = {125402},	
  year = {2009},
  url = {http://link.aps.org/abstract/PRB/v80/p125402},
  doi = {http://doi.org/10.1103/PhysRevB.80.125402}
}
 
Erratum: Local density of states from constant-current tunneling spectra , Phys. Rev. B 91, 039902 (2015)
 
Evolution of unoccupied resonance during the synthesis of a silver dimer on Ag(111)
A. Sperl, J. Kröger, R. Berndt, A. Franke, E. Pehlke, New J. Phys. 11, 63020 (2009)

Abstract:
Silver dimers were fabricated on Ag(111) by single-atom manipulation using the tip of a cryogenic scanning tunnelling microscope. An unoccupied electronic resonance was observed to shift toward the Fermi level with decreasing atom-atom distance as monitored by spatially resolved scanning tunnelling spectroscopy. Density functional calculations were used to analyse the experimental observations and revealed that the coupling between the adsorbed atoms is predominantly direct rather than indirect via the Ag(111) substrate.

[BibTeX]
@article{ASP_NJP09,
  author = {A. Sperl and J. Kröger and R. Berndt and A. Franke and E. Pehlke},
  title = {Evolution of unoccupied resonance during the synthesis of a silver dimer on Ag(111)},
  journal = {New J. Phys.},
  volume = {11},
  pages = {63020},	
  year = {2009},
  url = {http://stacks.iop.org/NJP/11/63020},
  doi = {http://doi.org/10.1088/1367-2630/11/6/063020}
}
 
 
Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer
X. Ge, C. Manzano, R. Berndt, L. Anger, F. Köhler, R. Herges, J. Am. Chem. Soc. 131, 6096 (2009)

Abstract:
Isolated Co-phthalocyanine (CoPc) molecules were moved on a monolayer of CoPc on Cu(111) using an STM tip. If placed almost on top of another, the CoPc molecule in the second layer locks in place and the STM image at negative bias changes substantially. Density functional theory calculations explain the nature of the bonding mode and the change in STM.

[BibTeX]
@article{XGE_JACS09,
  author = {X. Ge and C. Manzano and R. Berndt and L.T. Anger and F. Köhler and R. Herges},
  title = {Controlled Formation of an Axially Bonded Co-Phthalocyanine Dimer},
  journal = {J. Am. Chem. Soc.},
  volume = {131},
  pages = {6096--6098},	
  year = {2009},
  url = {http://dx.doi.org/10.1021/ja900484c},
  doi = {http://doi.org/10.1021/ja900484c}
}
 
 
Surface reconstruction and energy gap of superconducting V_3Si(001)
N. Hauptmann, M. Becker, J. Kröger, R. Berndt, Phys. Rev. B 79, 144522 (2009)

Abstract:
Scanning tunneling microscopy of V_3Si(001) reveals a yet unknown surface reconstruction which is most likely induced by carbon. We suggest a structural model for the reconstructed surface, which is consistent with experimental data obtained by scanning tunneling microscopy and Auger electron spectroscopy. Superconductivity of the reconstructed sample persists as monitored by scanning tunneling spectroscopy of the superconducting energy gap. The evolution of the energy gap with decreasing tip-sample distance from the tunneling to the contact regime indicates Andreev reflections in contact spectroscopy.

[BibTeX]
@article{NHA_PRB09,
  author = {N. Hauptmann and M. Becker and J. Kröger and R. Berndt},
  title = {Surface reconstruction and energy gap of superconducting V_3Si(001)},
  journal = {Phys. Rev. B},
  volume = {79},
  pages = {144522},	
  year = {2009},
  url = {http://link.aps.org/abstract/PRB/v79/p144522},
  doi = {http://doi.org/10.1103/PhysRevB.79.144522}
}
 
 
Quantized Conductance of a Single Magnetic Atom
N. Néel, J. Kröger, R. Berndt, Phys. Rev. Lett. 102, 086805 (2009)

Abstract:
A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is contacted with non-magnetic W or ferromagnetic Ni tips in a scanning tunneling microscope. When the Co atom bridges two non-magnetic electrodes conductances of 2e^2/h are found. With two ferromagnetic electrodes a conductance of e^2/h is observed which may indicate fully spin-polarized transport.

[BibTeX]
@article{NNE_PRL09,
  author = {N. Néel and J. Kröger and R. Berndt},
  title = {Quantized Conductance of a Single Magnetic Atom},
  journal = {Phys. Rev. Lett.},
  volume = {102},
  pages = {086805},	
  year = {2009},
  url = {http://link.aps.org/abstract/PRL/v102/p086805},
  doi = {http://doi.org/10.1103/PhysRevLett.102.086805}
}
 
 
Electron-plasmon and electron-electron interactions at a single atom contact
G. Schull, N. Néel, P. Johansson, R. Berndt, Phys. Rev. Lett. 102, 057401 (2009)

Abstract:
The transition from tunneling to contact is investigated by detecting light emitted from Au(111) in a scanning tunneling microscope. Optical spectra reflect single and multielectron processes andtheir distinct evolutions as a a single atom contact is formed. The experimental data are analyzed in terms of plasmon excitation and hot-hole processes.

[BibTeX]
@article{GSC_PRL09,
  author = {G. Schull and N. Néel and P. Johansson and R. Berndt},
  title = {Electron-plasmon and electron-electron interactions at a single atom contact},
  journal = {Phys. Rev. Lett.},
  volume = {102},
  pages = {057401},	
  year = {2009},
  url = {http://link.aps.org/abstract/PRL/v102/p057401},
  doi = {http://doi.org/10.1103/PhysRevLett.102.057401}
}
 
 
Pushing and Pulling a Sn Ion through an Adsorbed Phthalocyanine Molecule
Y. Wang, J. Kröger, R. Berndt, W. Hofer, J. Am. Chem. Soc. 131, 3639 (2009)

Abstract:
Molecule-based functional devices on surfaces may take advantage of bistable molecular switches. The conformational dynamics and efficiency of switches are radically different on surfaces compared to liquid phase. We present a design of molecular layers, which enables bistable switching on a surface, and, for the first time, demonstrate control of a single switch in a dense and ordered array at the spatial limit. Up and down motion of a central Sn ion through the frame of a phthalocyanine molecule is achieved via resonant electron or hole injection into molecular orbitals.

[BibTeX]
@article{YFW_JACS09,
  author = {Y. Wang and J. Kröger and R. Berndt and W.A. Hofer},
  title = {Pushing and Pulling a Sn Ion through an Adsorbed Phthalocyanine Molecule},
  journal = {J. Am. Chem. Soc.},
  volume = {131},
  pages = {3639},	
  year = {2009},
  url = {http://dx.doi.org/10.1021/ja807876c},
  doi = {http://doi.org/10.1021/ja807876c}
}
 
 
Structural and Electronic Properties of Ultrathin Tin-Phthalocyanine Films on Ag(111) at the Single-Molecule Level
Y. Wang, J. Kröger, R. Berndt, W. Hofer, Angew. Chem. 48, 1287 (2009)

Abstract:
Organic electronic and optoelectronic devices such as light-emitting diodes, field-effect transistors and photovoltaic devices have received considerable attention recently because organic materials can be cheap, light and flexible. The device performance is intimately coupled to charge transfer at inorganic-organic as well as at organic-organic interfaces. Understanding the structural and electronic properties of organic thin films supported on surfaces is thus of fundamental interest. In this context, phthalocyanines are molecules with unique optical and electrical properties. They have been investigated by low-energy electron and X-ray diffraction, scanning electron microscopy, and photoelectron spectroscopy. Using scanning tunnelling microscopy (STM) with its unique subnanometer resolution, the geometric arrangement and electronic properties may be studied at the single molecule level. However, stable imaging is often hampered by an enhanced mobility of the molecules. Up to now, STM investigations mainly focussed on molecule aggregates with coverages around a single molecular layer.

[BibTeX]
@article{YFW_ACH09,
  author = {Y. Wang and J. Kröger and R. Berndt and W. Hofer},
  title = {Structural and Electronic Properties of Ultrathin Tin-Phthalocyanine Films on Ag(111) at the Single-Molecule Level},
  journal = {Angew. Chem.},
  volume = {48},
  pages = {1287 -- 1291},	
  year = {2009},
  url = {http://dx.doi.org/10.1002/ange.200803305},
  doi = {http://doi.org/10.1002/ange.200803305}
}
 
 
Linewidth of a Cesium Adatom Resonance on Ag(111)
M. Ziegler, J. Kröger, R. Berndt, A. Borisov, J. Gauyacq, Phys. Rev. B 79, 075401 (2009)

Abstract:
Single Cs atoms adsorbed on Ag(111) induce a resonance appearing just below the threshold of the quasi-two-dimensional Shockley-type surface state continuum. Spectroscopic analysis using a cryogenic scanning tunneling microscope and theoretical modeling are used to identify the importance of the various contributions to the linewidth and to the decay of the resonance: resonant charge transfer, inelastic transitions, and adsorbate vibrations perpendicular to the surface.

[BibTeX]
@article{MZI_PRB09,
  author = {M. Ziegler and J. Kröger and R. Berndt and A.G. Borisov and J.P. Gauyacq},
  title = {Linewidth of a Cesium Adatom Resonance on Ag(111)},
  journal = {Phys. Rev. B},
  volume = {79},
  pages = {075401},	
  year = {2009},
  url = {http://link.aps.org/abstract/PRB/v79/p075401},
  doi = {http://doi.org/10.1103/PhysRevB.79.075401}
}
 
 
Probing the Conductance of Single Atoms and Molecules
N. Néel, J. Kröger, L. Limot, R. Berndt, J. Scann. Probe Microsc. 3, 9 (2008)

Abstract:
Contact between the tip of a low-temperature scanning tunnelling microscope and single atoms and molecules is investigated. In a controlled and reproducible way clean Ag(111) surfaces, individual silver atoms on Ag(111) as well as individual Co atoms and buck molecules adsorbed on Cu(100) are contacted. Upon contact the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime. Spectroscopy in the contact regime on Co atoms on Cu(100) shows significant change of the Kondo temperature. Conductance curves of buck molecules indicate fluctuations induced by heating of the junction.

[BibTeX]
@article{NNE_JSPM08,
  author = {N. Néel and J. Kröger and L. Limot and R. Berndt},
  title = {Probing the Conductance of Single Atoms and Molecules},
  journal = {J. Scann. Probe Microsc.},
  volume = {3},
  pages = {9--12},	
  year = {2008},
  url = {http://dx.doi.org/10.1166/jspm.2008.006},
  doi = {http://doi.org/10.1166/jspm.2008.006}
}
 
 
Controlling the Kondo Effect in CoCu_n Clusters Atom by Atom
N. Néel, J. Kröger, R. Berndt, T. Wehling, A. Lichtenstein, M. Katsnelson, Phys. Rev. Lett. 101, 266803 (2008)

Abstract:
Clusters containing a single magnetic impurity were investigated by scanning tunneling microscopy, spectroscopy, and /ab initio/ electronic structure calculations. The Kondo temperature of a Co atom embedded in Cu clusters on Cu(111) exhibits a non-monotonic variation with the cluster size. Calculations model the experimental observations and demonstrate the importance of the local and anisotropic electronic structure for correlation effects in small clusters.

[BibTeX]
@article{NNE_PRL08,
  author = {N. Néel and J. Kröger and R. Berndt and T. Wehling and A. Lichtenstein and M.I. Katsnelson},
  title = {Controlling the Kondo Effect in CoCu_n Clusters Atom by Atom},
  journal = {Phys. Rev. Lett.},
  volume = {101},
  pages = {266803},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRL/v101/p266803},
  doi = {http://doi.org/10.1103/PhysRevLett.101.266803}
}
 
 
Scanning tunneling microscopy and kinetic Monte-Carlo investigation of Cesium superlattices on Ag(111)
M. Ziegler, J. Kröger, R. Berndt, A. Filinov, M. Bonitz, Phys. Rev. B 78, 245427 (2008)

Abstract:
Cesium adsorption structures were characterized in a low-temperature scanning tunneling microscopy experiment. At low coverages, atomic resolution of individual Cs atoms is occasionally suppressed in interstitial regions of an otherwise hexagonally ordered adsorbate film on terraces. Close to step edges Cs atoms appear as elongated protrusions along the step edge direction. At higher coverages, Cs superstructures with atomically resolved hexagonal lattices are observed. Kinetic Monte-Carlo simulations model the observed adsorbate structures on a qualitative level.

[BibTeX]
@article{MZI_PRB08,
  author = {M. Ziegler and J. Kröger and R. Berndt and A. Filinov and M. Bonitz},
  title = {Scanning tunneling microscopy and kinetic Monte-Carlo investigation of Cesium superlattices on Ag(111)},
  journal = {Phys. Rev. B},
  volume = {78},
  pages = {245427},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRB/v78/p245427},
  doi = {http://doi.org/10.1103/PhysRevB.78.245427}
}
 
 
Imaging confined electrons with plasmonic light
G. Schull, M. Becker, R. Berndt, Phys. Rev. Lett. 101, 136801 (2008)

Abstract:
Variations of the spectra of plasmonic light emitted from the junction of a scanning tunneling microscope (STM) have been observed for different lateral position of the STM tip on a Au(111) surface. Sub-nanometer spatial variations of the light emission intensity over triangular island and in the vicinity of surface step edges have been recorded at different photon energies. They reveal surface standing wave patterns characteristic for two-dimensional confined electrons.

[BibTeX]
@article{GSC_PRL08,
  author = {G. Schull and M. Becker and R. Berndt},
  title = {Imaging confined electrons with plasmonic light},
  journal = {Phys. Rev. Lett.},
  volume = {101},
  pages = {136801},	
  year = {2008},
  note = {cf. D. Voss, Racking up the electron billiards. http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.101.136801 cf. A. Sandhu, Plasmonic light: Imaging electrons, Nature Nanotechnology, Research Highlights, 3. Oktober 2008 doi: 10.1038/nnano.2008.317},
  url = {http://link.aps.org/abstract/PRL/v101/p136801},
  doi = {http://doi.org/10.1103/PhysRevLett.101.136801}
}
 
cf. D. Voss, Racking up the electron biliards in Physics - spotlighting exceptional research.
cf. A. Sandhu, Plasmonic light: Imaging electrons, Nat. Nanotechnol., Research Highlights, 3. Oktober 2008
 
Spectroscopy of an atom between two electrodes
N. Néel, J. Kröger, R. Berndt, E. Pehlke, Phys. Rev. B 78, 233402 (2008)

Abstract:
The electronic structure induced by an atom between two metal electrodes is probed by adsorbing atoms on a Ag(111) surface and contacting them with the tip of a scanning tunneling microscope. Spectra of the differential conductance exhibit distinct structure and are different from spectra recorded at tunneling distances. A single-particle Newns-Anderson like model reproduces the experimental line shape. The coupling of the adsorbed atom to the atom at the apex of the tip electrode induces an additional bond, which shifts and broadens the spectral features of the unperturbed atom-substrate system.

[BibTeX]
@article{NNE_PRB08_2,
  author = {N. Néel and J. Kröger and R. Berndt and E. Pehlke},
  title = {Spectroscopy of an atom between two electrodes},
  journal = {Phys. Rev. B},
  volume = {78},
  pages = {233402},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRB/v78/p233402},
  doi = {http://doi.org/10.1103/PhysRevB.78.233402}
}
 
 
Quantum modulation of the Kondo resonance of Co adatoms on Cu/Co/Cu(100)
T. Uchihashi, J. Zhang, J. Kröger, R. Berndt, Phys. Rev. B 78, 33402 (2008)

Abstract:
Low-temperature scanning tunneling spectroscopy reveals that the Kondo temperature T_K of Co atoms adsorbed on Cu/Co/Cu(100) multilayers varies between 60 K and 134 K as the Cu film thickness decreases from 20 to 5 atomic layers. The observed change of T_K is attributed to a variation of the density of states at the Fermi level K induced by quantum well states confined to the Cu film. A model calculation based on the quantum oscillations of K at the belly and the neck of the Cu Fermi surface reproduces most of the features in the measured variation of T_K.

[BibTeX]
@article{TUC_PRB08,
  author = {T. Uchihashi and J. Zhang and J. Kröger and R. Berndt},
  title = {Quantum modulation of the Kondo resonance of Co adatoms on Cu/Co/Cu(100)},
  journal = {Phys. Rev. B},
  volume = {78},
  pages = {33402},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRB/v78/p33402},
  doi = {http://doi.org/10.1103/PhysRevB.78.033402}
}
 
 
A rigid sublimable naphthalenediimide cyclophane as model compound for UHV STM experiments
S. Gabutti, M. Knutzen, M. Neuburger, G. Schull, R. Berndt, M. Mayor, Chem. Comm. 20, 2370 (2008)

Abstract:
The design, synthesis and characterization of a rigid naphthalenediimide cyclophane as a model compound for ultrahigh vacuum (UHV) STM experiments are described together with first self-assembly investigations on an Au(111) substrate displaying the formation of densely packed parallel rows of molecules.

[BibTeX]
@article{SGA_CCO08,
  author = {S. Gabutti and M. Knutzen and M. Neuburger and G. Schull and R. Berndt and M. Mayor},
  title = {A rigid sublimable naphthalenediimide cyclophane as model compound for UHV STM experiments},
  journal = {Chem. Comm.},
  volume = {20},
  pages = {2370 -- 2372},	
  year = {2008},
  url = {http://www.rsc.org/Publishing/Journals/CC/article.asp?doi=b719796a},
  doi = {http://doi.org/10.1039/b719796a}
}
 
 
Azo Supramolecules on Au(111) with Controlled Size and Shape
Y. Wang, X. Ge, G. Schull, R. Berndt, C. Bornholdt, F. Koehler, R. Herges, J. Am. Chem. Soc. 130, 4218 (2008)

Abstract:
Using a subtle balance between weak intermolecular C-H...N hydrogen bonds and molecule-surface interactions, supramolecules of azobenzene-related molecules on Au surfaces were prepared. For analysis, modeling based on first-principles calculations was performed.

[BibTeX]
@article{YFW_JACS08,
  author = {Y. Wang and X. Ge and G. Schull and R. Berndt and C. Bornholdt and F. Koehler and R. Herges},
  title = {Azo Supramolecules on Au(111) with Controlled Size and Shape},
  journal = {J. Am. Chem. Soc.},
  volume = {130},
  pages = {4218},	
  year = {2008},
  url = {http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2008/130/i13/abs/ja710414b.html},
  doi = {http://doi.org/10.1021/ja710414b%20S0002-7863(71)00414-1}
}
 
 
Spatially resolved conductance of oriented C_60
G. Schull, N. Néel, M. Becker, J. Kröger, R. Berndt, New J. Phys. 10, 065012 (2008)

Abstract:
The conductance of oriented C_60 molecules on Au(111) and Cu(100) was investigated using a low-temperature scanning tunnelling microscope. A remarkable dependence of spectra of the differential conductance on the adsorption orientation is observed for Au(111) which is absent for Cu(100). For C_60 adsorbed on Au(111) the spatial distribution of the three lowest unoccupied molecular orbitals is revealed by maps of the differential conductance.

[BibTeX]
@article{GSC_NJP08,
  author = {G. Schull and N. Néel and M. Becker and J. Kröger and R. Berndt},
  title = {Spatially resolved conductance of oriented C_60 },
  journal = {New J. Phys.},
  volume = {10},
  pages = {065012},	
  year = {2008},
  url = {http://stacks.iop.org/NJP/10/065012},
  doi = {http://doi.org/10.1088/1367-2630/10/6/065012}
}
 
 
Tunneling spectroscopy of lander molecules on coinage metal surfaces
X. Ge, J. Kuntze, R. Berndt, H. Tang, A. Gourdon, Chem. Phys. Lett. 458, 161 (2008)

Abstract:
"Lander molecules" adsorbed on Ag, Cu and Au(111)-surfaces are investigated with scanning tunneling spectroscopy at 5 K. Density functional calculations are used to analyse the experimental data. Clear spectral features are attributed to the highest occupied molecular orbital (HOMO) and a group of lowest unoccupied molecular orbitals (LUMO). The orbital energies and the HOMO-LUMO gaps of molecules at steps and on terraces differ. The experimental observations are consistent with calculated results for the local work function and charge transfer.

[BibTeX]
@article{XGE_CPL08,
  author = {X. Ge and J. Kuntze and R. Berndt and H. Tang and A. Gourdon},
  title = {Tunneling spectroscopy of lander molecules on coinage metal surfaces},
  journal = {Chem. Phys. Lett.},
  volume = {458},
  pages = {161--165},	
  year = {2008},
  url = {http://dx.doi.org/10.1016/j.cplett.2008.04.093},
  doi = {http://doi.org/10.1016/j.cplett.2008.04.093}
}
 
 
Conductance of oriented C_60 molecules
N. Néel, J. Kröger, L. Limot, R. Berndt, Nano Lett. 8, 1291 (2008)

Abstract:
The tip of a cryogenic scanning tunneling microscope is used to contact C_60 molecules with various adsorption orientations on Cu(100). By imaging C_60 molecules with submolecular resolution, a direct relation between the molecule conductance and its orientation is provided. We find that despite the high symmetry of C_60 the orientation significantly affects the contact conductance.

[BibTeX]
@article{NNE_NLE08,
  author = {N. Néel and J. Kröger and L. Limot and R. Berndt},
  title = {Conductance of oriented C_60  molecules},
  journal = {Nano Letters},
  volume = {8},
  pages = {1291},	
  year = {2008},
  url = {http://dx.doi.org/10.1021/nl073074i},
  doi = {http://doi.org/10.1021/nl073074i}
}
 
 
Rotation of C_60 in a single-molecule contact
N. Néel, L. Limot, J. Kröger, R. Berndt, Phys. Rev. B 77, 125431 (2008)

Abstract:
The orientation of individual C_60 molecules adsorbed on Cu(100) is reversibly switched when the tip of a scanning tunneling microscope is approached to contact the molecule. The probability of switching rises sharply upon displacing the tip beyond a threshold. A mechanical mechanism is suggested to induce the rotation of the molecule.

[BibTeX]
@article{NNE_PRB08,
  author = {N. Néel and L. Limot and J. Kröger and R. Berndt},
  title = {Rotation of C_60  in a single-molecule contact},
  journal = {Phys. Rev. B},
  volume = {77},
  pages = {125431},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRB/v77/e125431},
  doi = {http://doi.org/10.1103/PhysRevB.77.12543}
}
 
 
Reply to Comment on Electronic structure of C_60 on Au(887)
F. Schiller, M. Ruiz-Osés, J.E. Ortega, P. Segovia, J. Martínez-Blanco, B. Doyle, V.Pérez-Dieste, L. Lobo, N. Néel, R. Berndt, J. Kröger, J. Chem. Phys. 128, 037101 (2008)
[BibTeX]
@article{FSC_JCP08,
  author = {F. Schiller and M. Ruiz-Osés and J. E. Ortega and P. Segovia and J. Martínez-Blanco and B.P. Doyle and V.Pérez-Dieste and L. Lobo and N. Néel and R. Berndt and J. Kröger},
  title = {Reply to Comment on Electronic structure of C_60  on Au(887)},
  journal = {J. Chem. Phys.},
  volume = {128},
  pages = {037101},	
  year = {2008},
  url = {http://link.aip.org/link/?JCPSA6/128/037101/1},
  doi = {http://doi.org/10.1063/1.2813437}
}
 
 
Unoccupied states of individual silver clusters and chains on Ag(111)
A. Sperl, J. Kröger, N. Néel, H. Jensen, R. Berndt, A. Franke, E. Pehlke, Phys. Rev. B 77, 085422 (2008)

Abstract:
Size-selected silver clusters on Ag(111) were fabricated with the tip of a scanning tunneling microscope. Unoccupied electron resonances give rise to image contrast and spectral features which shift toward the Fermi level with increasing cluster size. Linear assemblies exhibit higher resonance energies than equally sized compact assemblies. Density functional theory calculations reproduce the observed energies and enable an assignment of the resonances to hybridized atomic 5s and 5p orbitals with silver substrate states.

[BibTeX]
@article{ASP_PRB08,
  author = {A. Sperl and J. Kröger and N. Néel and H. Jensen and R. Berndt and A. Franke and E. Pehlke},
  title = {Unoccupied states of individual silver clusters and chains on Ag(111)},
  journal = {Phys. Rev. B},
  volume = {77},
  pages = {085422},	
  year = {2008},
  url = {http://link.aps.org/abstract/PRB/v77/e085422},
  doi = {http://doi.org/10.1103/PhysRevB.77.085422}
}
 
 
Mott-Hubbard transition on 1T-TaS2 induced by rubidium adsorption
P. Schmidt, J. Kröger, B. Murphy, R. Berndt, New J. Phys. 10, 013022 (2008)

Abstract:
The effect of rubidium deposition on 1T-TaS2 was investigated by scanning tunnelling microscopy and spectroscopy at room temperature. While the clean surface is characterized by a charge density wave with hexagonal symmetry, the rubidium-covered surface exhibits a rectangular symmetry of the charge density wave. The spectroscopy data signals a Mott-Hubbard phase transition by an energy gap between upper and lower Hubbard bands. Rubidium adsorption further leads to the formation of a network of linear wires which are interpreted as substrate folds induced by relief of surface stress.

[BibTeX]
@article{PSC_NJP08,
  author = {P. Schmidt and J. Kröger and B.M. Murphy and R. Berndt},
  title = {Mott-Hubbard transition on 1T-TaS2 induced by rubidium adsorption},
  journal = {New J. Phys.},
  volume = {10},
  pages = {013022},	
  year = {2008},
  url = {http://stacks.iop.org/NJP/10/013022},
  doi = {http://doi.org/10.1088/1367-2630/10/1/013022}
}
 
 
Orientationally Ordered (7x7) Superstructure of C_60 on Au(111)
G. Schull, R. Berndt, Phys. Rev. Lett. 99, 226105 (2007)

Abstract:
Long range orientational order within C_60 monolayers on Au(111) is observed with low-temperature scanning tunneling microscopy. A unit cell comprised of 49 molecules which adopt 11 different orientations is found. It can be divided in a faulted and an unfaulted half similar to the (7x7) reconstruction of Si(111). A model is proposed which shows how, through a Moiré-like effect, the substrate induces minute changes in the orientation of the C_60 molecules. Intermolecular interactions are shown to play a major role in stabilizing the superlattice.

[BibTeX]
@article{GSC_PRL07,
  author = {G. Schull and R. Berndt},
  title = {Orientationally Ordered (7x7) Superstructure of C_60  on Au(111)},
  journal = {Phys. Rev. Lett.},
  volume = {99},
  pages = {226105},	
  year = {2007},
  note = {cf. P. Rodgers, Made to order, Nature Nanotechnology 2, 672 (2007)},
  url = {http://link.aps.org/abstract/PRL/v99/p226105},
  doi = {http://doi.org/10.1103/PhysRevLett.99.226105}
}
 
cf. P. Rodgers, Made to order, Nature Nanotechnology 2, 672 (2007)
 
Ultraviolet light emission from Si in a scanning tunneling micrscope
P. Schmidt, R. Berndt, M. Vexler, Phys. Rev. Lett. 99, 246103 (2007)

Abstract:
Ultraviolet and visible radiation is observed from the contacts of a scanning tunneling microscope with Si(100) and (111) wafers. This luminescence relies on the presence of hot electrons in silicon, which are supplied, at positive bias on n- and p-type samples, through the injection from the tip, or, at negative bias on p samples, by Zener tunneling. Measured spectra reveal a contribution of direct optical transitions in Si bulk. The necessary holes well below the valence band edge are injected from the tip or generated by Auger processes.

[BibTeX]
@article{PSC_PRL07,
  author = {P. Schmidt and R. Berndt and M.I. Vexler},
  title = {Ultraviolet light emission from Si in a scanning tunneling micrscope},
  journal = {Phys. Rev. Lett.},
  volume = {99},
  pages = {246103},	
  year = {2007},
  url = {http://link.aps.org/abstract/PRL/v99/p246103},
  doi = {http://doi.org/10.1103/PhysRevLett.99.246103}
}
 
 
Conductance of tip-surface and tip-atom junctions on Au(111) explored by a scanning tunnelling microscope
J. Kröger, H. Jensen, R. Berndt, New J. Phys. 9, 153 (2007)

Abstract:
The conductance between the tip of a scanning tunnelling microscope and a Au(111) surface is measured at tip-surface distances comprising tunnelling and contact regions. Contact between the tip and the flat sample surface as well as between the tip and an individual gold atom can be performed reproducibly without deteriorating the imaging capability of the instrument. Conductance measurements performed on the face-centered cubic and hexagonal close-packed stacking domains of the Au(111) surface reconstruction lead to similar results. The conductivity of mono- and diatomic gold wires bridging the tip-surface junction is given by a quantum of conductance.

[BibTeX]
@article{JKR_NJP07,
  author = {J. Kröger and H. Jensen and R. Berndt},
  title = {Conductance of tip-surface and tip-atom junctions on Au(111) explored by a scanning tunnelling microscope},
  journal = {New J. Phys.},
  volume = {9},
  pages = {153},	
  year = {2007},
  url = {http://www.iop.org/EJ/abstract/1367-2630/9/5/153/},
  doi = {http://doi.org/10.1088/1367-2630/9/5/153}
}
 
 
Silver oligomer and single fullerene electronic properties revealed by a scanning tunnelling microscope
H. Jensen, J. Kröger, N. Néel, R. Berndt, Eur. Phys. J. D 45, 465 (2007)

Abstract:
Clusters on surfaces have been investigated with low-temperature scanning tunnelling microscopy and spectroscopy. Constant current spectra acquired on Ag oligomers and one-dimensional chains on a Ag(111) reveal a single resonance peak whose energy shifts towards the Fermi level with increasing cluster size. Next, controlled and reproducible contact between a STM tip and a buck molecule adsorbed on Cu(100) is reported. The transition from tunnelling to contact is discussed in terms of local heating of the tip-molecule junction.

[BibTeX]
@article{HJE_EPJD07,
  author = {H. Jensen and J. Kröger and N. Néel and R. Berndt},
  title = {Silver oligomer and single fullerene electronic properties revealed by a scanning tunnelling microscope},
  journal = {Eur. Phys. J. D},
  volume = {45},
  pages = {465--469},	
  year = {2007},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1140/epjd/e2007-00157-x},
  doi = {http://doi.org/10.1140/epjd/e2007-00157-x}
}
 
 
Conductance and Kondo Effect in a Controlled Single-Atom Contact
N. Néel, J. Kröger, L. Limot, K. Palotas, W. Hofer, R. Berndt, Phys. Rev. Lett. 98, 016801 (2007)

Abstract:
The tip of a low-temperature scanning tunneling microscope is brought into contact with individual cobalt atoms adsorbed on Cu(100). A smooth transition from the tunneling regime to contact occurs at a conductance of G≈G0. Spectroscopy in the contact regime, i.e., at currents in a μA range, was achieved and indicated a significant change of the Kondo temperature T_K. Calculations indicate that the proximity of the tip shifts the cobalt d band and thus affects T_K.

[BibTeX]
@article{NNE_PRL07_2,
  author = {N. Néel and J. Kröger and L. Limot and K. Palotas and W.A. Hofer and R. Berndt},
  title = {Conductance and Kondo Effect in a Controlled Single-Atom Contact},
  journal = {Phys. Rev. Lett.},
  volume = {98},
  pages = {016801},
  publisher = {American Physical Society},	
  year = {2007},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.98.016801},
  doi = {http://doi.org/10.1103/PhysRevLett.98.016801}
}
 
 
Dynamics of surface-localised electronic excitations studied with the scanning tunnelling microscope
J. Kröger, M. Becker, H. Jensen, T. von Hofe, N. Néel, L. Limot, R. Berndt, S. Crampin, E. Pehlke, C. Corriol, V. Silkin, D. Sanchez-Portal, A. Arnau, E. Chulkov, P. Echenique, Prog. Surf. Sci. 82, 29 (2007)

Abstract:
The decay rates of electron-like and hole-like excitations at metal surfaces as determined by a scanning tunnelling microscope are presented and discussed. Surface-localised electron states as diverse as Shockley-type surface states and quantum well states confined to ultrathin alkali metal adsorption layers are covered. Recent developments in the analysis of the experimental procedures that are used to determine decay rates with the scanning tunnelling microscope, namely the analysis of line shapes and the spatial decay of standing wave patterns, are discussed.

[BibTeX]
@article{JKR_PSS07,
  author = {J. Kröger and M. Becker and H. Jensen and T. von Hofe and N. Néel and L. Limot and R. Berndt and S. Crampin and E. Pehlke and C. Corriol and V.M. Silkin and D. Sanchez-Portal and A. Arnau and E.V. Chulkov and P.M. Echenique},
  title = {Dynamics of surface-localised electronic excitations studied with the scanning tunnelling microscope},
  journal = {Prog. Surf. Sci.},
  volume = {82},
  pages = {29},	
  year = {2007},
  url = {http://dx.doi.org/10.1016/j.progsurf.2007.03.003},
  doi = {http://doi.org/10.1016/j.progsurf.2007.03.003}
}
 
 
Self-organization of cobalt-phthalocyanine on a vicinal gold surface revealed by scanning tunnelling microscopy
J. Kröger, H. Jensen, N. Néel, R. Berndt, Surf. Sci. 601, 4180 (2007)

Abstract:
Adsorption of cobalt-phthalocyanine on Au(788) in the sub-monolayer coverage regime leads to a preferential occupation of step edges with the molecule plane tilted such as to bridge adjacent terraces. Molecules which adsorb on terraces leave the surface reconstruction of Au(788) unchanged and exhibit the propensity to occupy face-centered cubic stacking domains. Tunnelling spectroscopy in the centre of the molecule reveals cobalt d-orbital related features, while spectroscopy on the benzene rings shows the lowest unoccupied molecular orbital.

[BibTeX]
@article{JKR_SSI07,
  author = {J. Kröger and H. Jensen and N. Néel and R. Berndt},
  title = {Self-organization of cobalt-phthalocyanine on a vicinal gold surface revealed by scanning tunnelling microscopy},
  journal = {Surf. Sci.},
  volume = {601},
  pages = {4180--4184},	
  year = {2007},
  url = {http://dx.doi.org/10.1016/j.susc.2007.04.091},
  doi = {http://doi.org/10.1016/j.susc.2007.04.091}
}
 
 
Lifetimes of electrons in the Shockley surface state band of Ag(111)
M. Becker, S. Crampin, R. Berndt, Appl. Phys. A 88, 555 (2007)

Abstract:
We present a theoretical many-body analysis of the electron-electron (e-e) inelastic damping rate Γ of electron-like excitations in the Shockley surface state band of Ag(111). It takes into account ab initio band structures for both bulk and surface states. Γ is found to increase more rapidly as a function of surface state energy E than previously reported, thus leading to an improved agreement with experimental data.

[BibTeX]
@article{MBE_APA07,
  author = {M. Becker and S. Crampin and R. Berndt},
  title = {Lifetimes of electrons in the Shockley surface state band of Ag(111)},
  journal = {Appl. Phys. A},
  volume = {88},
  pages = {555--557},	
  year = {2007},
  note = {cf. cond-mat/0609080},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00339-007-4059-9},
  doi = {http://doi.org/10.1007/s00339-007-4059-9}
}
 
 
Structure of in vacuo Rb intercalated 1T-TaS_2
P. Schmidt, B. Murphy, J. Kröger, H. Jensen, R. Berndt, Phys. Rev. B 74, 193407 (2006)

Abstract:
Rb adsorption in ultra-high vacuum on the transition metal dichalcogenide 1T-TaS_2 is investigated by scanning tunneling microscopy at 9 K and at room temperature. Comparison of step heights on clean and Rb-covered surface provides direct evidence that the adsorbed Rb atoms intercalate between the topmost layers of the substrate. This result resolves the current uncertainty about the structure of these widely investigated surfaces. The increase of the van der Waals gap between the substrate layers is discussed on the basis of a sphere model.

[BibTeX]
@article{PSC_PRB06,
  author = {P. Schmidt and B. Murphy and J. Kröger and H. Jensen and R. Berndt},
  title = {Structure of in vacuo Rb intercalated 1T-TaS_2},
  journal = {Phys. Rev. B},
  volume = {74},
  pages = {193407},	
  year = {2006},
  url = {http://link.aps.org/abstract/PRB/v74/p193407},
  doi = {http://doi.org/10.1103/PhysRevB.74.193407}
}
 
 
Conductance of single atoms and molecules studied with a scanning tunnelling microscope
N. Néel, J. Kröger, L. Limot, R. Berndt, Nanotechnology 18, 044027 (2007)

Abstract:
The conductance of single atoms and molecules is investigated with a low-temperature scanning tunnelling microscope. In a controlled and reproducible way clean Ag(111) surfaces, individual silver atoms on Ag(111)as well as individual buck molecules adsorbed on Cu(100) are contacted with the tip of the microscope. Upon contact formation the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime.

[BibTeX]
@article{NNE_NTEC07,
  author = {N. Néel and J. Kröger and L. Limot and R. Berndt},
  title = {Conductance of single atoms and molecules studied with a scanning tunnelling microscope},
  journal = {Nanotechnology},
  volume = {18},
  pages = {044027},	
  year = {2007},
  url = {http://www.iop.org/EJ/abstract/0957-4484/18/4/044027},
  doi = {http://doi.org/10.1088/0957-4484/18/4/044027}
}
 
 
Controlled Contact to a C_60 Molecule
N. Néel, J. Kröger, L. Limot, T. Frederiksen, M. Brandbyge, R. Berndt, Phys. Rev. Lett. 98, 065502 (2007)

Abstract:
The conductance of C_60 on Cu(100) is investigated with a low-temperature scanning tunneling microscope. At the transition from tunneling to the contact regime the conductance of C_60 adsorbed with a pentagon-hexagon bond rises rapidly to 0,25 conductance quanta G0. An abrupt conductance jump to G0 is observed upon further decreasing the distance between the instrument's tip and the surface. Ab-initio calculations within density functional theory and non-equilibrium Green's function techniques explain the experimental data in terms of the conductance of an essentially undeformed From a detailed analysis of the crossover from tunneling to contact we conclude that the conductance in this region is strongly affected by structural fluctuations which modulate the tip-molecule distance.

[BibTeX]
@article{NNE_PRL07,
  author = {N. Néel and J. Kröger and L. Limot and T. Frederiksen and M. Brandbyge and R. Berndt},
  title = {Controlled Contact to a C_60  Molecule},
  journal = {Phys. Rev. Lett.},
  volume = {98},
  pages = {065502},	
  year = {2007},
  note = {cf. cond-mat/0608476},
  url = {http://link.aps.org/abstract/PRL/v98/p065502},
  doi = {http://doi.org/10.1103/PhysRevLett.98.065502}
}
 
 
Electronic structure of C_60 on Au(887) C60!!!
F. Schiller, M. Ruiz-Osés, J. Ortega, P. Segovia, J. Martinez-Blanco, B. Doyle, V. Pérez-Dieste, J. Lobo, N. Néel, R. Berndt, J. Kröger, J. Chem. Phys. 125, 144719 (2006)

Abstract:
We present an analysis of the electronic structure of C_60 adsorbed on a vicinal Au(111) surface at different fullerene coverages using Photoemission, X-ray Absorption and Scanning Tunnelling Microcopy/Spectroscopy (STM/STS). STS provides a straightforward determination of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels with respect to the Fermi energy. At C_60 coverages of half and one monolayer (ML) a 2.7 eV wide HOMO-LUMO gap is found. The near-edge X-ray absorption fine structure (NEXAFS) spectrum for the 0.5 ML buck nanomesh structure displays a significant intensity at the low energy side of the LUMO exciton peak, which is explained as due to absorption into HOMO-LUMO gap states localized at individual C_60 cluster edges. From 0.5 ML to 1 ML we observe a rigid shift of the HOMO-LUMO peaks in the STS spectra and an almost complete quenching of the gap states feature in NEXAFS.

[BibTeX]
@article{FSC_JCP06,
  author = {F. Schiller and M. Ruiz-Osés and J.E. Ortega and P. Segovia and J. Martinez-Blanco and B.P. Doyle and V. Pérez-Dieste and J. Lobo and N. Néel and R. Berndt and J. Kröger},
  title = {Electronic structure of C_60  on Au(887) C60!!!},
  journal = {J. Chem. Phys.},
  volume = {125},
  pages = {144719},	
  year = {2006},
  url = {http://link.aip.org/link/?JCP/125/144719},
  doi = {http://doi.org/10.1063/1.2354082}
}
 
 
Dynamics of electronic states at metal surfaces
R. Berndt, J. Kröger, in Handbook of Surface Science, Band 3, E. Hasselbrink and B. Lundqvist (Hrsg.) , 525-574 (Elsevier, 2008)
[BibTeX]
@inbook{RBE_ELS08,
  author = {R. Berndt and J. Kröger},
  chapter = {Dynamics of electronic states at metal surfaces},
  title = {Handbook of Surface Science, Band 3},
  editor = {E. Hasselbrink and B.I. Lundqvist},
  pages = {525--574},
  publisher = {Elsevier},	
  year = {2008},
  url = {https://www.elsevier.com/books/dynamics/author/978-0-444-52056-2},
  doi = {http://doi.org/10.1016/S1573-4331(08)00011-5}
}
 
 
Theoretical analysis of STM-derived lifetimes of excitations in the Shockley surface-state band of Ag(111)
M. Becker, S. Crampin, R. Berndt, Phys. Rev. B 73, 081402 (2006)

Abstract:
We present a quantitative many-body analysis using the GW approximation of the decay rate due to electron-electron scattering of excitations in the Shockley surface state band of Ag(111), as measured using the scanning tunneling microscope (STM). The calculations include the perturbing influence of the STM, which causes a Stark-shift of the surface state energy E and concomitant increase in. We find varies more rapidly with E than recently found for image potential states, where the STM has been shown to significantly afect measured lifetimes. For the Shockley states, the Stark shifts that occur under normal tunneling conditions are relatively small, and previous STM-derived lifetimes need not be corrected.

[BibTeX]
@article{MBE_PRB06,
  author = {M. Becker and S. Crampin and R. Berndt},
  title = {Theoretical analysis of STM-derived lifetimes of excitations in the Shockley surface-state band of Ag(111)},
  journal = {Phys. Rev. B},
  volume = {73},
  pages = {081402},	
  year = {2006},
  url = {http://link.aps.org/abstract/PRB/v73/p081402},
  doi = {http://doi.org/10.1103/PhysRevB.73.081402}
}
 
 
Adsorption geometry of Cu(111)-Cs studied by scanning tunneling microscopy
T. von Hofe, J. Kröger, R. Berndt, Phys. Rev. B 73, 245434 (2006)

Abstract:
Using scanning tunneling microscopy at low temperatures we investigated cesium adsorbed on Cu(111). At low coverages we observe a hexagonally ordered Cs adsorption layer with a mutual adsorbate distance of 1,1 nm. This distance is discussed in terms of a commensurate adsorption superstructure which is stabilised by long-range adsorbate interactions mediated by Cu(111) surface state electrons. Intermediate coverages are characterised by incommensurate superstructures which are rotated with respect to the substrate lattice. The rotation angle varies with coverage and follows a trend which is consistent with models of epitaxial rotation. With increasing coverage the adsorption layers are found to rotate toward alignment with the substrate.

[BibTeX]
@article{TVH_PRB06,
  author = {T. von Hofe and J. Kröger and R. Berndt},
  title = {Adsorption geometry of Cu(111)-Cs studied by scanning tunneling microscopy},
  journal = {Phys. Rev. B},
  volume = {73},
  pages = {245434},	
  year = {2006},
  note = {cf. http://arxiv.org/cond-mat/0603 Nr. 551},
  url = {http://link.aps.org/abstract/PRB/v73/p245434},
  doi = {http://doi.org/10.1103/PhysRevB.73.245434}
}
 
 
Fullerene nanowires on a vicinal gold surface
N. Néel, J. Kröger, R. Berndt, Appl. Phys. Lett. 88, 163101 (2006)

Abstract:
Deposition of fullerene molecules on vicinal gold surface was investigated by scanning tunneling microscopy. Fullerene stripes of few nanometers width and extending over hundreds of nanometers have been fabricated on the gold surface by utilizing faceting of Au(433) substrates upon buck adsorption and subsequent annealing. The observed step bunching is attributed to a lowering of the facet free energy. This surface morphology is a promising template candidate for subsequent deposition of functional units.

[BibTeX]
@article{NNE_APL06,
  author = {N. Néel and J. Kröger and R. Berndt},
  title = {Fullerene nanowires on a vicinal gold surface},
  journal = {Appl. Phys. Lett.},
  volume = {88},
  pages = {163101},	
  year = {2006},
  url = {http://link.aip.org/link/?APL/88/163101},
  doi = {http://doi.org/10.1063/1.2195530}
}
 
 
Molecules on vicinal Au surfaces studied by scanning tunnelling microscopy
J. Kröger, N. Néel, H. Jensen, R. Berndt, R. Rurali, N. Lorente, J. Phys.: Condens. Matter 18, S51 (2006)

Abstract:
Using low-temperature scanning tunnelling microscopy and spectroscopy we investigated the adsorption characteristics of 3,4,9,10-perylenetetracarboxylic-dianhydride and fullerenes on Au(788), Au(433), and Au(778). On Au(788) and Au(778) 3,4,9,10-perylenetetracarboxylic-dianhydride exhibits three coexisting superstructures, which do not reflect the periodicity of the hosting substrate. The adsorption on Au(433) leads to the formation of molecule chains along the step edges after annealing the sample. Fullerene molecules on Au(788) arrange in a mesh of islands, which extends over several hundreds of nanometres with an extraordinarily high periodicity. A combination of fullerene adsorption and annealing leads to facetting of Au(433) and the formation of extraordinarily long fullerene stripes.

[BibTeX]
@article{JKR_JPCM06,
  author = {J. Kröger and N. Néel and H. Jensen and R. Berndt and R. Rurali and N. Lorente},
  title = {Molecules on vicinal Au surfaces studied by scanning tunnelling microscopy},
  journal = {J. Phys.: Condens. Matter},
  volume = {18},
  pages = {S51--S66},	
  year = {2006},
  url = {http://stacks.iop.org/JPhysCM/18/S51},
  doi = {http://doi.org/10.1088/0953-8984/18/13/S04}
}
 
 
Molecular Orbital Shift of Perylenetetracarboxylic-Dianhydride
J. Kröger, H. Jensen, R. Berndt, R. Rurali, N. Lorente, Chem. Phys. Lett. 438, 249 (2007)

Abstract:
Scanning tunneling microscopy and spectroscopy reveals that the energy of orbitals of individual perylenetetracarboxylic-dianhydride molecules depends on their adsorption geometry. Internal molecular structure appears at characteristic energies for each of the coexisting adsorption domains on Au(788) and Au(111). Tunneling spectroscopy on single molecules belonging to different adsorption domains exhibits an energy shift of the lowest and second-to-lowest unoccupied molecular orbital of 0.35 eV. On the basis of density functional theory calculations this shift is attributed to hydrogen bond-mediated intermolecular interaction. Hence, tunneling spectroscopy can be used as an efficient tool to discriminate between phases of organic molecular layers.

[BibTeX]
@article{JKR_CPL07,
  author = {J. Kröger and H. Jensen and R. Berndt and R. Rurali and N. Lorente},
  title = {Molecular Orbital Shift of Perylenetetracarboxylic-Dianhydride},
  journal = {Chem. Phys. Lett.},
  volume = {438},
  pages = {249},	
  year = {2007},
  note = {first published on cond-mat/0506025 (2005)},
  url = {http://dx.doi.org/10.1016/j.cplett.2007.03.001},
  doi = {http://doi.org/10.1016/j.cplett.2007.03.001}
}
 
first published on cond-mat/0506025 (2005)
 
Highly Periodic Fullerene Nanomesh
N. Néel, J. Kröger, R. Berndt, Adv. Mater. 18, 174 (2006)

Abstract:
The last decade has witnessed many efforts to realise the parallel fabrication of long-range-ordered nanostructures on surfaces. The controlled fabrication of highly periodic metal, semiconductor, or molecular nanostructures at surfaces remains, however, a challenging endeavour in nanoscience research. Large quantities of structures can be created in parallel by self-organised growth, either in the kinetic, or the thermodynamic regime, and the controlled deposition of size-selected clusters from the gas phase. Owing to the statistical nature of deposition and diffusion processes it is difficult to achieve lateral order by this approach. Consequently, pre-structured samples have been studied intensely to enhance ordering on a large scale. On planar surfaces, for instance, the use of strained layers and dislocations as templates for subsequent depositions led to a self-organization on the scale of several dozens of nanometers. Supramolecular surface assemblies can be guided using hydrogen bonding, to control and guide new surface phases formed by subsequently deposited molecules. A highly regular mesh of hexagonal boron nitride was recently fabricated by self-assembly on a Rh(111) single crystalline surface and lead to ordering of buck molecules. An alternative approach is to use vicinal surfaces, i.e., surfaces which correspond to small deviations from the most symmetric crystallographic planes. They represent periodic arrays of steps at the nanometer scale with adjustable dimensions and thus are of great interest for the fabrication of arrays of nanowires or dots.

[BibTeX]
@article{NNE_ADMA06,
  author = {N. Néel and J. Kröger and R. Berndt},
  title = {Highly Periodic Fullerene Nanomesh},
  journal = {Adv. Mater.},
  volume = {18},
  pages = {174--177},	
  year = {2006},
  url = {http://dx.doi.org/10.1002/adma.200500913},
  doi = {http://doi.org/10.1002/adma.200500913}
}
 
 
Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)
J. Kliewer, R. Berndt, J. Minár, H. Ebert, Appl. Phys. A 82, 63 (2006)

Abstract:
Small Mn clusters (Mn_1-Mn_4) are prepared by manipulation of Mn adatoms on Ag(111) with the tip of a scanning tunnelling microscope. The apparent heights of the clusters are observed to increase monotonously from 1.6 Å for a monomer to 2.2 Å for a tetramer. Self-consistent calculations of the electronic structure of these clusters are in encouraging agreement with the experimental data.

[BibTeX]
@article{JKL_APA06,
  author = {J. Kliewer and R. Berndt and J. Minár and H. Ebert},
  title = {Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)},
  journal = {Appl. Phys. A},
  volume = {82},
  pages = {63--66},	
  year = {2006},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00339-005-3380-4},
  doi = {http://doi.org/10.1007/s00339-005-3380-4}
}