2011 - 2015

Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope
S. Mühlenberend, M. Gruyters, R. Berndt, Appl. Phys. Lett. 107, (2015)

Abstract:
The electroluminescence from p-type GaAs(110) in a scanning tunneling microscope has been investigated at 6 K. Unexpectedly, high degrees of circular polarization have often been observed with ferromagnetic Ni tips and also with paramagnetic W and Ag tips. The data are interpreted in terms of two distinct excitation mechanisms. Electron injection generates intense luminescence with low polarization. Plasmon-mediated generation of electron-hole pairs leads to less intense emission, which, however, is highly polarized for many tips.

[BibTeX]
@article{SMU_APL15,
  author = {Mühlenberend, Svenja and Gruyters, Markus and Berndt, Richard},
  title = {Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope},
  journal = {Applied Physics Letters},
  volume = {107},
  number = {24},	
  year = {2015},
  url = {http://scitation.aip.org/content/aip/journal/apl/107/24/10.1063/1.4938167},
  doi = {http://doi.org/10.1063/1.4938167}
}
 
 
Low-temperature scanning tunneling microscopy study on the electronic properties of a double-decker DyPc2 molecule at the surface
Y. Zhang, P. Liao, J. Kan, C. Yin, N. Li, J. Liu, Q. Chen, Y. Wang, W. Chen, G.Q. Xu, J. Jiang, R. Berndt, K. Wu, Phys. Chem. Chem. Phys. 17, 27019 (2015)

Abstract:
To fully achieve potential applications of the double-decker molecules containing rare earth elements as single-molecule magnets in molecular spintronics, it is crucial to understand the 4f states of the rare earth atoms sandwiched in the double-decker molecules by metal electrodes. In this study, low-temperature scanning tunneling microscopy and spectroscopy were employed to investigate the isolated double-decker DyPc2 molecule adsorbed on Au(111) via its differential conductance measurements. The experimental results revealed that the differential conductance maps acquired at a constant height mode simply depicted the authentic molecular orbitals; moreover, the differential conductance maps achieved at a constant current mode could not directly probe the 4f states of the sandwiched Dy atom. This was consistent with the spectra obtained over the molecule center around the Fermi level, indicative of no Kondo feature. Upon decreasing the tip-molecule distance, the CH-mode images presented high-resolution structure but no information of the 4f states. All results indicated that the Dy atom barely contributed to the tunneling current because of the absence of coupling with the microscope tip, echoing the inaccessibility of the Dy 4f states in the double-decker DyPc2 molecule.

[BibTeX]
@article{YZH_PCCP15,
  author = {Zhang, Yajie and Liao, Peilin and Kan, Jinglan and Yin, Cen and Li, Na and Liu, Jing and Chen, Qiwei and Wang, Yongfeng and Chen, Wei and Xu, Guo Qin and Jiang, Jianzhuang and Berndt, Richard and Wu, Kai},
  title = {Low-temperature scanning tunneling microscopy study on the electronic properties of a double-decker DyPc2 molecule at the surface},
  journal = {Phys. Chem. Chem. Phys.},
  volume = {17},
  pages = {27019--27026},
  publisher = {The Royal Society of Chemistry},	
  year = {2015},
  url = {http://dx.doi.org/10.1039/C5CP03925H},
  doi = {http://doi.org/10.1039/C5CP03925H}
}
 
 
Interactions between two C 60 molecules measured by scanning probe microscopies
N. Hauptmann, C. González, F. Mohn, L. Gross, G. Meyer, R. Berndt, Nanotechnology 26, 445703 (2015)

Abstract:
C_60 -functionalized tips are used to probe C_60 molecules on Cu(111) with scanning tunneling and atomic force microscopy. Distinct and complex intramolecular contrasts are found. Maximal attractive forces are observed when for both molecules a [6,6] bond faces a hexagon of the other molecule. Density functional theory calculations including parameterized van der Waals interactions corroborate the observations.

[BibTeX]
@article{NHA_NTEC15,
  author = {Nadine Hauptmann and César González and Fabian Mohn and Leo Gross and Gerhard Meyer and Richard Berndt},
  title = {Interactions between two C 60 molecules measured by scanning probe microscopies},
  journal = {Nanotechnology},
  volume = {26},
  number = {44},
  pages = {445703},	
  year = {2015},
  url = {http://stacks.iop.org/0957-4484/26/i=44/a=445703},
  doi = {http://doi.org/10.1088/0957-4484/26/44/445703}
}
 
 
Investigating the differences between Co adatoms states on surfaces of selected bismuth chalcogenides
M. Wasniowska, M. Sikora, M. Dobrzanski, T. Eelbo, M.M. Soares, M. Rams, I. Miotkowski, R. Wiesendanger, R. Berndt, Z. Kąkol, A. Kozłowski, Phys. Rev. B 92, 115412 (2015)

Abstract:
We report on the electronic and magnetic properties of Co atoms adsorbed on topological insulator (TI) surfaces, such as Bi2Se3, Bi2Te3, and on magnetically doped Bi1.9Mn0.1Te3 and Bi1.98Fe0.02Se3 in comparison to a nontopological insulator surface, Bi2S3. Co atoms are used as probes of impurity affected surface electronic properties of TI and non-TI tetradymite semiconductors. X-ray spectroscopy, x-ray magnetic circular dichroism, and scanning tunneling microscopy and spectroscopy were employed. We found that the electronic properties of Co adatoms do not depend much on the substrate. In particular, no TI specific phenomenon was found. Magnetic dichroism measurements reveals an in-plane easy axis of adsorbed Co atoms on all topological insulators and Bi2S3, but not on the ferromagnetic substrate Bi1.9Mn0.1Te3, for which an out-of-plane easy axis was found.

[BibTeX]
@article{MWA_PRB15,
  author = {Wasniowska, M. and Sikora, M. and Dobrzanski, M. and Eelbo, T. and Soares, M. M. and Rams, M. and Miotkowski, I. and Wiesendanger, R. and Berndt, R. and Kąkol, Z. and Kozłowski, A.},
  title = {Investigating the differences between Co adatoms states on surfaces of selected bismuth chalcogenides},
  journal = {Phys. Rev. B},
  volume = {92},
  pages = {115412},
  publisher = {American Physical Society},	
  year = {2015},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.92.115412},
  doi = {http://doi.org/10.1103/PhysRevB.92.115412}
}
 
 
Competing Forces during Contact Formation between a Tip and a Single Molecule
N.M. Caffrey, K. Buchmann, N. Hauptmann, C. Lazo, P. Ferriani, S. Heinze, R. Berndt, Nano Lett. 15, 5156 (2015)

Abstract:
Sn-phthalocyanine adsorbs on Ag(111) in a physisorbed or a chemisorbed configuration. Both structures are contacted with the tip of a combined scanning tunneling and atomic force microscope. The tunneling conductances of both configurations exhibit similar exponential variations with the tip–molecule distance. The short-range forces, however, display nontrivial distance dependencies. First-principles calculations reproduce the experimental results. Both attractive and repulsive interactions occur between the tip and different parts of the molecule due to a combination of bond formation and electrostatic interactions with the tip electric dipole. Consequently, deformations occur and the force varies in the resulting unexpected fashion.

[BibTeX]
@article{NCA_NLE15,
  author = {Nuala M. Caffrey and Kristof Buchmann and Nadine Hauptmann and Cesar Lazo and Paolo Ferriani and Stefan Heinze and Richard Berndt},
  title = {Competing Forces during Contact Formation between a Tip and a Single Molecule},
  journal = {Nano Letters},
  volume = {15},
  number = {8},
  pages = {5156-5160},	
  year = {2015},
  note = {PMID: 26218345},
  url = {http://dx.doi.org/10.1021/acs.nanolett.5b01383},
  doi = {http://doi.org/10.1021/acs.nanolett.5b01383}
}
 
 
Reaction of Phthalocyanines with Graphene on Ir(111)
S.J. Altenburg, M. Lattelais, B. Wang, M.-L. Bocquet, R. Berndt, J. Am. Chem. Soc. 137, 9452 (2015)

Abstract:
Iron phthalocyanine (FePc) is adsorbed to graphene on Ir(111) at cryogenic temperature. In addition to mobile FePc with four lobes, imaging and spectroscopy with a scanning tunneling microscope reveal immobile molecules that exhibit fewer lobes. A reversible transformation between four- and three-lobed molecules has been induced by current injection. The data are consistent with chemical bonding of lobes to graphene on Ir, pinning down the graphene area toward Ir. Similar observations are made from NiPc, CoPc, CuPc, and H2Pc. The experimental findings can be explained by ab initio calculations, which suggest that a Diels-Alder-type reaction may be involved with an allyl unit of graphene in the top-fcc moiré registry.

[BibTeX]
@article{SAL_JACS15,
  author = {Simon J. Altenburg and Marie Lattelais and Bin Wang and Marie-Laure Bocquet and Richard Berndt},
  title = {Reaction of Phthalocyanines with Graphene on Ir(111)},
  journal = {Journal of the American Chemical Society},
  volume = {137},
  number = {29},
  pages = {9452--9458},	
  year = {2015},
  note = {PMID: 26147789},
  url = {http://dx.doi.org/10.1021/jacs.5b05558},
  doi = {http://doi.org/10.1021/jacs.5b05558}
}
 
 
Electronic and Vibrational States of Single Tin-Phthalocyanine Molecules in Double Layers on Ag(111)
F. Schwarz, Y. Wang, W. Hofer, R. Berndt, E. Runge, J. Kröger, J. Phys. Chem. C 119, 15716 (2015)

Abstract:
Electronic and vibrational properties of the two stable molecular configurations of Sn-phthalocyanine adsorbed on an ultrathin Sn-phthalocyanine buffer film on Ag(111) have been investigated with scanning tunneling microscopy and density functional calculations. Complex submolecular patterns are experimentally observed in unoccupied states images. The calculations show that they result from a superposition of Sn p orbitals. Furthermore, the characteristic features in spectra of the differential conductance are reproduced by the calculations together with a remarkable difference between the two configurations. First-principles calculations show that rather than a single vibrational mode and its higher harmonics the excitations of different molecular vibrational quanta induce replica of orbital spectroscopic signatures. The replicated orbital features appear for the configuration with a low molecule-surface coupling. To model spectra of molecules with a larger coupling to the surface it is sufficient to consider elastic tunneling to orbital resonances alone.

[BibTeX]
@article{FSC_JPCC15,
  author = {F. Schwarz and Y.F. Wang and W.A. Hofer and R. Berndt and E. Runge and J. Kröger},
  title = {Electronic and Vibrational States of Single Tin-Phthalocyanine Molecules in Double Layers on Ag(111)},
  journal = {J. Phys. Chem. C},
  volume = {119},
  number = {27},
  pages = {15716--15722},	
  year = {2015},
  url = {http://dx.doi.org/10.1021/acs.jpcc.5b03392},
  doi = {http://doi.org/10.1021/acs.jpcc.5b03392}
}
 
 
Shifting the Voltage Drop in Electron Transport Through a Single Molecule
S. Karan, D. Jacob, M. Karolak, C. Hamann, Y. Wang, A. Weismann, A.I. Lichtenstein, R. Berndt, Phys. Rev. Lett. 115, 016802 (2015)

Abstract:
A Mn-porphyrin was contacted on Au(111) in a low-temperature scanning tunneling microscope (STM). Differential conductance spectra show a zero-bias resonance that is due to an underscreened Kondo effect according to many-body calculations. When the Mn center is contacted by the STM tip, the spectrum appears to invert along the voltage axis. A drastic change in the electrostatic potential of the molecule involving a small geometric relaxation is found to cause this observation.

[BibTeX]
@article{SKA_PRL15,
  author = {Karan, Sujoy and Jacob, David and Karolak, Michael and Hamann, Christian and Wang, Yongfeng and Weismann, Alexander and Lichtenstein, Alexander I. and Berndt, Richard},
  title = {Shifting the Voltage Drop in Electron Transport Through a Single Molecule},
  journal = {Phys. Rev. Lett.},
  volume = {115},
  pages = {016802},
  publisher = {American Physical Society},	
  year = {2015},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.115.016802},
  doi = {http://doi.org/10.1103/PhysRevLett.115.016802}
}
 
cf. K. Wright , Molecular Voltage Shift, in APS Physics - spotlighting exceptional research.
 
Surface Trapping and STM Observation of Conformational Isomers of a Bis(Terpyridine) Ligand from Metallosupramolecular Grids
S. Karan, C. Hamann, H. Tang, A.R. Stefankiewicz, J.-M. Lehn, R. Berndt, ChemPhysChem 16, 1370 (2015)

Abstract:
Tetranuclear Co-grid complexes incorporating bis-tridentate ligands, namely 4,6-bis(2,2'-bipyrid-6-yl)-2-phenylpyrimidine, were electrosprayed onto a Au(111) substrate under an ultrahigh vacuum. Fragmentation occurs leaving the ligands in four different conformations. Most ligands are found to form H-bonded dimers. The most abundant conformer of the ligand on the Au surface is an asymmetric form, which has not been observed before. The present results indicate that the fragmentation of coordination compounds during the deposition process, in principle, allows for surface trapping, identification, and investigation of high energy, out-of-equilibrium conformations of the ligand molecules at low temperatures, which otherwise would not be observable.

[BibTeX]
@article{SKA_CPC15,
  author = {Karan, Sujoy and Hamann, Christian and Tang, Hao and Stefankiewicz, Artur R. and Lehn, Jean-Marie and Berndt, Richard},
  title = {Surface Trapping and STM Observation of Conformational Isomers of a Bis(Terpyridine) Ligand from Metallosupramolecular Grids},
  journal = {ChemPhysChem},
  volume = {16},
  number = {7},
  pages = {1370--1373},
  publisher = {WILEY-VCH Verlag},	
  year = {2015},
  url = {http://dx.doi.org/10.1002/cphc.201500100},
  doi = {http://doi.org/10.1002/cphc.201500100}
}
 
 
Shot Noise as a Probe of Spin-Polarized Transport through Single Atoms
A. Burtzlaff, A. Weismann, M. Brandbyge, R. Berndt, Phys. Rev. Lett. 114, 016602 (2015)

Abstract:
Single atoms on Au(111) surfaces have been contacted with the Au tip of a low temperature scanning tunneling microscope. The shot noise of the current through these contacts has been measured up to frequencies of 120 kHz and Fano factors have been determined to characterize the transport channels. The noise at Fe and Co atoms, the latter displaying a Kondo effect, indicates spin-polarized transport through a single channel. Transport calculations reproduce this observation.

[BibTeX]
@article{ABU_PRL15,
  author = {Burtzlaff, Andreas and Weismann, Alexander and Brandbyge, Mads and Berndt, Richard},
  title = {Shot Noise as a Probe of Spin-Polarized Transport through Single Atoms},
  journal = {Phys. Rev. Lett.},
  volume = {114},
  pages = {016602},
  publisher = {American Physical Society},	
  year = {2015},
  note = {Editors' Suggestion.},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.114.016602},
  doi = {http://doi.org/10.1103/PhysRevLett.114.016602}
}
 
Editors' Suggestion.
 
High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex
N. Hauptmann, L. Gro K. Buchmann, K. Scheil, C. Schütt, F.L. Otte, R. Herges, C. Herrmann, R. Berndt, New J. Phys. 17, 013012 (2015)

Abstract:
The conductances of molecular model junctions comprising a triazatriangulenium platform with or without an ethynyl spacer and an upright Zn-porphyrin are probed with a low-temperature scanning probe microscope. The platform alone is found to be highly conductive. The ethynyl-linked Zn-porphyrin moiety reduces the conductance by three orders of magnitude and leads to an unexpected, non-monotonous variation of the force that was measured simultaneously at the tip of the microscope. Density functional theory calculations show that this variation results from an induced tilting of the porphyrin.

[BibTeX]
@article{NHA_NJP15,
  author = {Nadine Hauptmann and Lynn Groß and Kristof Buchmann and Katharina Scheil and Christian Schütt and Franziska L Otte and Rainer Herges and Carmen Herrmann and Richard Berndt},
  title = {High-conductance surface-anchoring of a mechanically flexible platform-based porphyrin complex},
  journal = {New J. Phys.},
  volume = {17},
  number = {1},
  pages = {013012},	
  year = {2015},
  url = {http://stacks.iop.org/1367-2630/17/i=1/a=013012},
  doi = {http://doi.org/10.1088/1367-2630/17/1/013012}
}
 
 
Spectroscopy of transmission resonances through a C 60 junction
N. Schneider, N. Néel, N. Andersen, J. Lü, M. Brandbyge, J. Kröger, R. Berndt, J. Phys.: Condens. Matter 27, 015001 (2015)

Abstract:
Electron transport through a single C 60 molecule on Cu(111) has been investigated with a scanning tunnelling microscope in tunnelling and contact ranges. Single-C 60 junctions have been fabricated by establishing a contact between the molecule and the tip, which is reflected by a down-shift in the lowest unoccupied molecular orbital resonance. These junctions are stable even at elevated bias voltages enabling conductance measurements at high voltages and nonlinear conductance spectroscopy in tunnelling and contact ranges. Spectroscopy and first principles transport calculations clarify the relation between molecular orbital resonances and the junction conductance. Due to the strong molecule-electrode coupling the simple picture of electron transport through individual orbitals does not hold.

[BibTeX]
@article{NSC_JPCM14,
  author = {N.L. Schneider and N. Néel and N.P. Andersen and J.T. Lü and M. Brandbyge and J. Kröger and R. Berndt},
  title = {Spectroscopy of transmission resonances through a C 60 junction},
  journal = {J. Phys.: Condens. Matter},
  volume = {27},
  number = {1},
  pages = {015001},	
  year = {2015},
  url = {http://stacks.iop.org/0953-8984/27/i=1/a=015001},
  doi = {http://doi.org/10.1088/0953-8984/27/1/015001}
}
 
 
Tungsten - hydrogen complexes on graphene on Ir(111)
S. Altenburg, R. Berndt, New J. Phys. 16, 093047 (2014)

Abstract:
W and W-H complexes on graphene on Ir(111) were studied by means of low temperature scanning tunneling microscopy. H is found to coadsorb at the sample surface during W evaporation. Five different W-related structures on graphene on Ir(111) were found and characterized. They are identified as WH_n , with n=0,1,2,3,4 , as shown by electric field induced dehydrogenation. They exhibit a number of peculiar effects, such as electric field induced shifts of spectroscopic features as well as reversible switching and charging effects. In addition, two different structures of H on Ir(111) were characterized.

[BibTeX]
@article{SAL_NJP14_2,
  author = {S.J. Altenburg and R. Berndt},
  title = {Tungsten - hydrogen complexes on graphene on Ir(111)},
  journal = {New J. Phys.},
  volume = {16},
  number = {9},
  pages = {093047},	
  year = {2014},
  url = {http://stacks.iop.org/1367-2630/16/i=9/a=093047},
  doi = {http://doi.org/10.1088/1367-2630/16/9/093047}
}
 
 
Structure and dynamics of C_60 molecules on Au(111)
H. Shin, A. Schwarze, R.D. Diehl, K. Pussi, A. Colombier, É. Gaudry, J. Ledieu, G.M. McGuirk, L.N. Serkovic Loli, V. Fournée, L.L. Wang, G. Schull, R. Berndt, Phys. Rev. B 89, 245428 (2014)

Abstract:
Earlier studies of C60 adsorption on Au(111) reported many interesting and complex features. We have performed coordinated low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory studies to elucidate some of the details of the monolayer commensurate (2 sqrt(3) x 2 sqrt(3))R30° phase. We have identified the adsorption geometries of the two states that image as dim and bright in STM. These consist of a C60 molecule with a hexagon side down in a vacancy (hex-vac) and a C60 molecule with a carbon-carbon 6:6 bond down on a top site (6:6-top), respectively. We have studied the detailed geometries of these states and find that there is little distortion of the C60 molecules, but there is a rearrangement of the substrate near the C60 molecules. The two types of molecules differ in height, by about 0.7 Å, which accounts for most of the difference in their contrast in the STM images. The monolayer displays dynamical behavior, in which the molecules flip from bright to dim, and vice versa. We interpret this flipping as the result of the diffusion of vacancies in the surface layers of the substrate. Our measurements of the dynamics of this flipping from one state to the other indicate that the activation energy is 0.66 ± 0.03 eV for flips that involve nearest-neighbor C60 molecules, and 0.93 ± 0.03 for more distant flips. Based on calculated activation energies for vacancies diffusing in Au, we interpret these to be a result of surface vacancy diffusion and bulk vacancy diffusion. These results are compared to the similar system of Ag(111)-(2 sqrt(3) x 2 sqrt(3))R30°-C60. In both systems, the formation of the commensurate C60 monolayer produces a large number of vacancies in the top substrate layer that are highly mobile, effectively melting the interfacial metal layer at temperatures well below their normal melting temperatures.

[BibTeX]
@article{HSH_PRB14,
  author = {Shin, Heekeun and Schwarze, A. and Diehl, R. D. and Pussi, K. and Colombier, A. and Gaudry, É. and Ledieu, J. and McGuirk, G. M. and Serkovic Loli, L. N. and Fournée, V. and Wang, L. L. and Schull, G. and Berndt, R.},
  title = {Structure and dynamics of C_60 molecules on Au(111)},
  journal = {Phys. Rev. B},
  volume = {89},
  pages = {245428},
  publisher = {American Physical Society},	
  year = {2014},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.89.245428},
  doi = {http://doi.org/10.1103/PhysRevB.89.245428}
}
 
 
Electronic and magnetic states of Mn 2 and Mn 2 H on Ag(111)
T. Sachse, N. Néel, S. Meierott, R. Berndt, W. Hofer, J. Kröger, New J. Phys. 16, 063021 (2014)

Abstract:
Manganese dimers on Ag(111) are investigated with scanning tunneling microscopy and density functional calculations. Two species of dimers coexist that differ in their apparent heights and the absence or presence of submolecular structure. These species can be interconverted by electron and hole injection from the microscope tip. Calculations identify the two kinds of dimers as pristine Mn_2 and Mn_2H and show that hydrogen attachment to Mn_2 leads to marked changes in the dimer electronic and magnetic structure. Antiferromagnetic coupling between Mn magnetic moments in Mn_2H leaves its spectroscopic signature in the electronic structure of the monohydride compound.

[BibTeX]
@article{TSA_NJP14,
  author = {T. Sachse and N. Néel and S. Meierott and R. Berndt and W.A. Hofer and J. Kröger},
  title = {Electronic and magnetic states of Mn 2 and Mn 2 H on Ag(111)},
  journal = {New J. Phys.},
  volume = {16},
  number = {6},
  pages = {063021},	
  year = {2014},
  url = {http://stacks.iop.org/1367-2630/16/i=6/a=063021},
  doi = {1367-2630/16/i=6/a=063021}
}
 
 
Local work function and STM tip-induced distortion of graphene on Ir(111)
S. Altenburg, R. Berndt, New J. Phys. 16, 053036 (2014)

Abstract:
The contact conductance and the apparent barrier height Φ of graphene on Ir(111) are measured with a cryogenic scanning tunneling microscope. A strong dependence of Φ on the tip-sample distance is found and explained by a local lifting of the graphene film by van-der-Waals forces. Variations of Φ observed within the moiré unit cell of the graphene layer are interpreted in terms of differences in the local work function and the buckling of the graphene film. Comparison to results based on density functional theory indicates that a modulation of the charge transfer between graphene and Ir(111) is the origin of the work function variations.

[BibTeX]
@article{SAL_NJP14,
  author = {S.J. Altenburg and R. Berndt},
  title = {Local work function and STM tip-induced distortion of graphene on Ir(111)},
  journal = {New J. Phys.},
  volume = {16},
  number = {5},
  pages = {053036},	
  year = {2014},
  url = {http://stacks.iop.org/1367-2630/16/i=5/a=053036},
  doi = {http://doi.org/10.1088/1367-2630/16/5/053036}
}
 
 
Remotely Triggered Geometrical Isomerization of a Binuclear Complex
S. Karan, T.G. Gopakumar, H. Jacob, S. Meyer, F. Tuczek, R. Berndt, J. Am. Chem. Soc. 136, 6163 (2014)

Abstract:
Binuclear organometallic molecules are model systems for investigating intramolecular spin-coupling and charge-transfer processes. Using electrospray ionization, Fe(salten) dimers linked by dipyridyl disulfide are deposited on gold for probing with a low-temperature scanning tunneling microscope. Each monomer constitutes a multistable switch owing to its geometric isomerism. Controlled and reversible remote switching within a single dimer is demonstrated. The process is attributed to intramolecular electron transfer.

[BibTeX]
@article{SKA_JACS14,
  author = {Sujoy Karan and Thiruvancheril G. Gopakumar and Hanne Jacob and Sven Meyer and Felix Tuczek and Richard Berndt},
  title = {Remotely Triggered Geometrical Isomerization of a Binuclear Complex},
  journal = {J. Am. Chem. Soc.},
  volume = {136},
  number = {17},
  pages = {6163-6166},	
  year = {2014},
  note = {PMID: 24730362},
  url = {http://dx.doi.org/10.1021/ja500154g},
  doi = {http://doi.org/10.1021/ja500154g}
}
 
 
Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope
H. Zheng, A. Weismann, R. Berndt, Nat. Commun. 5, 2992 (2014)

Abstract:
In devices like the single-electron transistor the detailed transport properties of a nanostructure can be measured by tuning its energy levels with a gate voltage. The scanning tunnelling microscope in contrast usually lacks such a gate electrode. Here we demonstrate tuning of the levels of a donor in a scanning tunnelling microscope without a third electrode. The potential and the position of the tip are used to locally control band bending. Conductance maps in this parameter space reveal Coulomb diamonds known from three-terminal data from single-electron transistors and provide information on charging transitions, binding energies and vibrational excitations. The analogy to single-electron transistor data suggests a new way of extracting these key quantities without making any assumptions about the unknown shape of the scanning tunnelling microscope tip.

[BibTeX]
@article{HZH_NCOM14,
  author = {Hao Zheng and Alexander Weismann and Richard Berndt},
  title = {Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope},
  journal = {Nat. Commun.},
  volume = {5},
  pages = {2992},	
  year = {2014},
  url = {http://www.nature.com/ncomms/2014/140103/ncomms3992/full/ncomms3992.html},
  doi = {http://doi.org/10.1038/ncomms3992}
}
 
 
MOCVD of Fe atoms on H/Si(111) surfaces using Fe-phthalocyanine
M. Gruyters, T. Pingel, R. Berndt, Appl. Phys. A 114, 363 (2014)

Abstract:
Single Fe atoms are deposited on hydrogen-passivated Si(111) surfaces by decomposition of FePc molecules. The metal-organic molecules are evaporated from powder in a heated crucible of an electron beam source. Scanning tunneling microscopy (STM) indicates the incorporation of the central Fe atom of the molecule into H/Si(111) in the near-surface region. This provides a possible precursor state for implantation deeper into the semiconductor substrate.

[BibTeX]
@article{MGR_APA14,
  author = {Gruyters, Markus and Pingel, Torben and Berndt, Richard},
  title = {MOCVD of Fe atoms on H/Si(111) surfaces using Fe-phthalocyanine},
  journal = {Applied Physics A},
  volume = {114},
  number = {2},
  pages = {363--366},	
  year = {2014},
  url = {http://dx.doi.org/10.1007/s00339-013-8177-2},
  doi = {http://doi.org/10.1007/s00339-013-8177-2}
}
 
 
Atom für Atom: Oberflächenchemie
A. Sperl, J. Kröger, R. Berndt, Chem. unserer Zeit 47, 296 (2013)

Abstract:
Mit Hilfe der Spitze eines Rastertunnelmikroskops wird ein einzelnes metallfreies Phthalocyanin-Molekül in ein Silber-Phthalocynanin auf einer Obefläche umgewandelt. Die Reaktionsschritte erfolgen Atom für Atom. Jedes Zwischenprodukt kann mit Hilfe von rastertunnelmikroskopischen Aufnahmen analysiert werden. Neben der schrittweisen Molekülumwandlung sind die Tautomerisierung und das H-Hüpfen, die kontrolliert durch Injektion von Elektronen induziert werden, weitere Beispiele für die Präzision eines modernen Rastertunnelmikroskops.

Using the tip of a scanning tunnelling microscope a metal-free phthalocyanine has been transformed into a silver-phthalocyanine on a surface. The individual reactions have been performed atom by atom. Each product has been imaged with the scanning tunnelling microscope. Along with the transformation of the molecule, controlled tautomerization and H hopping have been induced by injection of electrons and demonstrate the precision a state-of-the-art scanning tunnelling microscope has reached.

[BibTeX]
@article{ASP_CIUZ13,
  author = {Sperl, Alexander and Kröger, Jörg and Berndt, Richard},
  title = {Atom für Atom: Oberflächenchemie},
  journal = {Chemie in unserer Zeit},
  volume = {47},
  number = {5},
  pages = {296--299},
  publisher = {WILEY-VCH Verlag},	
  year = {2013},
  url = {http://dx.doi.org/10.1002/ciuz.201300617},
  doi = {http://doi.org/10.1002/ciuz.201300617}
}
 
 
Surface-Supported Supramolecular Pentamers
S. Karan, Y. Wang, R. Robles, N. Lorente, R. Berndt, J. Am. Chem. Soc. 135, 14004 (2013)

Abstract:
Chiral pentamers of all-trans-retinoic acid molecules have been prepared on Au(111) surfaces and on a molecular monolayer. Over a range of coverages, pentamers are the building blocks of larger arrays that become increasingly enantiopure. The stability of pentamers is analyzed from experiments on an isomer and a more reactive substrate as well as from density functional theory. The linear shape of the molecule and suitable densities are crucial for the formation of pentamers, driven by cyclic hydrogen bonding between carboxylic acid moieties.

[BibTeX]
@article{SKA_JACS13,
  author = {Sujoy Karan and Yongfeng Wang and Roberto Robles and Nicolás Lorente and Richard Berndt},
  title = {Surface-Supported Supramolecular Pentamers},
  journal = {J. Am. Chem. Soc.},
  volume = {135},
  number = {38},
  pages = {14004--14007},	
  year = {2013},
  note = {PMID: 24007411},
  url = {http://dx.doi.org/10.1021/ja405456k},
  doi = {http://doi.org/10.1021/ja405456k}
}
 
 
Fe impurity-induced electronic states at the GaAs(110) surface
S. Mühlenberend, M. Gruyters, R. Berndt, Phys. Rev. B 88, 115301 (2013)

Abstract:
The electronic properties of single Fe atoms in the surface of p-type GaAs(110) are investigated by scanning tunneling microscopy (STM) and spectroscopy. In STM images, Fe atoms show a characteristic structure with an orientation that matches the GaAs substrate lattice. Fe is assumed to occupy substitutional sites in the surface. Spectra of the differential conductance on Fe reveal several distinct peaks. They are discussed in the context of electronic states that originate from hybridization between d orbitals of the Fe atom and p-like orbitals of neighboring As atoms.

[BibTeX]
@article{SMU_PRB13,
  author = {Mühlenberend, Svenja and Gruyters, Markus and Berndt, Richard},
  title = {Fe impurity-induced electronic states at the GaAs(110) surface},
  journal = {Phys. Rev. B},
  volume = {88},
  pages = {115301},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.88.115301},
  doi = {http://doi.org/10.1103/PhysRevB.88.115301}
}
 
 
A Spin-Crossover Complex on Au(111): Structural and Electronic Differences Between Mono- and Multilayers
T. Gopakumar, M. Bernien, H. Naggert, F. Matino, C. Hermanns, A. Bannwarth, S. Mühlenberend, A. Krüger, D. Krüger, F. Nickel, W. Walter, R. Berndt, W. Kuch, F. Tuczek, Chem. Eur. J. 19, 15702 (2013)

Abstract:
Submono-, mono- and multilayers of the Fe(II) spin-crossover (SCO) complex [Fe(bpz)2(phen)] (bpz=dihydrobis(pyrazolyl)borate, phen=1,10-phenanthroline) have beenprepared by vacuum deposition on Au(111) substrates and investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). As evidenced by NEXAFS, molecules of the second layer exhibit a thermal spin crossover transition, although with a more gradual characteristics than in the bulk. For mono- and submonolayers of [Fe(bpz)2(phen)] deposited on Au(111) substrates at room temperature both NEXAFS and STM indicate a dissociation of [Fe(bpz)2(phen)] on Au(111) into four-coordinate complexes, [Fe(bpz)2], and phen molecules. Keeping the gold substrate at elevated temperatures ordered monolayers of intact molecules of [Fe(bpz)2(phen)] are formed which can be spin-switched by electron-induced excited spin-state trapping (ELIESST).

[BibTeX]
@article{GOP_CEJ13,
  author = {T.G. Gopakumar and M. Bernien and H. Naggert and F. Matino and C.F. Hermanns and A. Bannwarth and S. Mühlenberend and A. Krüger and D. Krüger and F. Nickel and W. Walter and R. Berndt and W. Kuch and F. Tuczek},
  title = {A Spin-Crossover Complex on Au(111): Structural and Electronic Differences Between Mono- and Multilayers},
  journal = {Chem. Eur. J.},
  volume = {19},
  pages = {15702--15709},	
  year = {2013},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/chem.201302241/full},
  doi = {http://doi.org/10.1002/chem.201302241}
}
 
 
"Magic" Vicinal Zinc Oxide Surfaces
H. Zheng, M. Gruyters, E. Pehlke, R. Berndt, Phys. Rev. Lett. 111, 086101 (2013)

Abstract:
The structure of (0001) oriented ZnO single crystal surfaces is investigated by scanning tunneling microscopy. Depending on the preparation conditions, faceting of the crystals into large areas of {1 0 -1 4} surface orientation occurs. This restructuring of the surface is shown to be a consequence of dipole compensation and charge neutralization. A new stabilization mechanism of polar oxide surfaces is found which is based on the formation of vicinal surfaces with special electronic and structural properties.

[BibTeX]
@article{HZH_PRL13_2,
  author = {Zheng, Hao and Gruyters, Markus and Pehlke, Eckhard and Berndt, Richard},
  title = {"Magic" Vicinal Zinc Oxide Surfaces},
  journal = {Phys. Rev. Lett.},
  volume = {111},
  pages = {086101},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.111.086101},
  doi = {http://doi.org/10.1103/PhysRevLett.111.086101}
}
 
 
Broken Symmetry of an Adsorbed Molecular Switch Determined by Scanning Tunneling Spectroscopy
T.G. Gopakumar, T. DavranCandan, J. Bahrenburg, R.J. Maurer, F. Temps, K. Reuter, R. Berndt, Angewandte Chemie 125, 11213 (2013)

Abstract:
Asymmetrische Drehung: Die Struktur von Tris[4(phenylazo)phenyl)]amin auf einer Au(111)Oberfläche wurde mit Rastertunnelspektroskopie untersucht. Ein entarteter Markerzustand dient als empfindliche Sonde für die Struktur der adsorbierten Moleküle.

[BibTeX]
@article{GOP_ACH13,
  author = {Gopakumar, Thiruvancheril G. and DavranCandan, Tugba and Bahrenburg, Julia and Maurer, Reinhard J. and Temps, Friedrich and Reuter, Karsten and Berndt, Richard},
  title = {Broken Symmetry of an Adsorbed Molecular Switch Determined by Scanning Tunneling Spectroscopy},
  journal = {Angewandte Chemie},
  volume = {125},
  number = {42},
  pages = {11213--11216},	
  year = {2013},
  url = {http://www.ingentaconnect.com/content/bpl/ange/2013/00000125/00000042/art00018},
  doi = {http://doi.org/10.1002/ange.201305027}
}
 
 
Force and conductance spectroscopy of second-layer tin-phthalocyanine on Ag(111)
N. Hauptmann, R. Berndt, physica status solidi (b) 250, 2403 (2013)

Abstract:
The conductance, frequency shift, and energy dissipation are measured during the formation of a contact to a single tin-phthalocyanine (SnPc) molecule. The molecule is located on top of a first SnPc layer on Ag(111). The data show that subtle changes of the adsorption geometry cause drastic differences of the conductance, force, and dissipation signals.
Site-dependent averaged conductance shift versus piezo displacement.

[BibTeX]
@article{NHA_PSSB13,
  author = {Hauptmann, Nadine and Berndt, Richard},
  title = {Force and conductance spectroscopy of second-layer tin-phthalocyanine on Ag(111)},
  journal = {physica status solidi (b)},
  volume = {250},
  number = {11},
  pages = {2403--2407},	
  year = {2013},
  url = {http://dx.doi.org/10.1002/pssb.201349210},
  doi = {http://doi.org/10.1002/pssb.201349210}
}
 
 
Antimicrobial activity of silica coated silicon nano-tubes (SCSNT) and silica coated silicon nano-particles (SCSNP) synthesized by gas phase condensation.
C. Tank, S. Raman, S. Karan, S. Gosavi, N. Lalla, V.S.R. Berndt, W. Gade, S. Bhoraskar, V. Mathe, J. Mater. Sci.: Mater. Med. 24, 1483 (2013)

Abstract:
Silica-coated, silicon nanotubes (SCSNTs) and silica-coated, silicon nanoparticles (SCSNPs) have been synthesized by catalyst-free single-step gas phase condensation using the arc plasma process. Transmission electron microscopy and scanning tunneling microscopy showed that SCSNTs exhibited a wall thickness of less than 1 nm, with an average diameter of 14 nm and a length of several 100 nm. Both nano-structures had a high specific surface area. The present study has demonstrated cheaper, resistance-free and effective antibacterial activity in silica-coated silicon nano-structures, each for two Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) was estimated, using the optical densitometric technique, and by determining colony-forming units. The MIC was found to range in the order of micrograms, which is comparable to the reported MIC of metal oxides for these bacteria. SCSNTs were found to be more effective in limiting the growth of multidrug-resistant Staphylococcus aureus over SCSNPs at 10 μg/ml (IC 50 = 100 μg/ml).

[BibTeX]
@article{CHT_JMSC13,
  author = {Ch. Tank and S. Raman and S. Karan and S. Gosavi and N.P. Lalla and V. Sathe R. Berndt and W.N. Gade and S.V. Bhoraskar and V.L. Mathe},
  title = {Antimicrobial activity of silica coated silicon nano-tubes (SCSNT) and silica coated silicon nano-particles (SCSNP) synthesized by gas phase condensation.},
  journal = {J. Mater. Sci.: Mater. Med.},
  volume = {24},
  pages = {1483--1490},	
  year = {2013},
  url = {http://www.ncbi.nlm.nih.gov/pubmed/23494617#},
  doi = {http://doi.org/10.1007/s10856-013-4896-3}
}
 
 
Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification
N. Hauptmann, K. Scheil, T.G. Gopakumar, F.L. Otte, C. Schütt, R. Herges, R. Berndt, J. Am. Chem. Soc. 135, 8814 (2013)

Abstract:
Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.

[BibTeX]
@article{NHA_JACS13,
  author = {Nadine Hauptmann and Katharina Scheil and Thiruvancheril G. Gopakumar and Franziska L. Otte and Christian Schütt and Rainer Herges and Richard Berndt},
  title = {Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification},
  journal = {Journal of the American Chemical Society},
  volume = {135},
  number = {24},
  pages = {8814-8817},	
  year = {2013},
  note = {PMID: 23724828},
  url = {http://dx.doi.org/10.1021/ja4036187},
  doi = {http://doi.org/10.1021/ja4036187}
}
 
 
Manipulation of Subsurface Donors in ZnO
H. Zheng, A. Weismann, R. Berndt, Phys. Rev. Lett. 110, 226101 (2013)

Abstract:
Single donors close to the ZnO(0001) surface are investigated with scanning tunneling microscopy. Their binding energies and depths are determined from spatially resolved spectra of the differential conductance. At elevated bias of the STM tip, vertical motion of the donors can be induced. The direction of the motion can be controlled by the bias polarity.

[BibTeX]
@article{HZH_PRL13,
  author = {Zheng, Hao and Weismann, Alexander and Berndt, Richard},
  title = {Manipulation of Subsurface Donors in ZnO},
  journal = {Phys. Rev. Lett.},
  volume = {110},
  pages = {226101},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.110.226101},
  doi = {http://doi.org/10.1103/PhysRevLett.110.226101}
}
 
 
Switching and charging of a ruthenium dye on Ag(111)
N. Hauptmann, C. Hamann, H. Tang, R. Berndt, Phys. Chem. Chem. Phys. 15, 10326 (2013)

Abstract:
The ruthenium dye N3, cis-bis(isothiocyanato)bis(2,2[prime or minute]-bipyridyl-4,4[prime or minute]-dicarboxylato)-ruthenium(ii), deposited on Ag(111) by ultra-high vacuum electrospray ionization is investigated using low-temperature scanning tunneling microscopy. Scanning tunneling spectroscopy of single molecules reveals vibronic excitations that are related to the lowest unoccupied molecular orbital (LUMO). Switching of N3 may be induced and modifies the energy of the negative ion resonance as well as the vibrational progression. Moreover, charging of the molecule is induced at reverse bias. These data suggest a surprisingly weak electronic coupling of N3 to the Ag substrate. A double-barrier model reproduces the essential spectral features.

[BibTeX]
@article{NHA_PCCP13,
  author = {Hauptmann, Nadine and Hamann, Christian and Tang, Hao and Berndt, Richard},
  title = {Switching and charging of a ruthenium dye on Ag(111)},
  journal = {Phys. Chem. Chem. Phys.},
  volume = {15},
  pages = {10326-10330},
  publisher = {The Royal Society of Chemistry},	
  year = {2013},
  url = {http://dx.doi.org/10.1039/C3CP51023A},
  doi = {http://doi.org/10.1039/C3CP51023A}
}
 
 
Soft-Landing Electrospray Deposition of the Ruthenium Dye N3 on Au(111)
N. Hauptmann, C. Hamann, H. Tang, R. Berndt, The Journal of Physical Chemistry C 117, 9734 (2013)

Abstract:
Ruthenium dyes (N3) are deposited by in situ ultrahigh vacuum (UHV) electrospray ionization on a Au(111) surface and investigated using scanning tunneling microscopy and spectroscopy. The molecules exhibit some fragmentation at deposition energies around 7 eV, while deposition of intact molecules is feasible with energies of 2.5 eV. A variety of adsorption geometries is found that are analyzed using spectroscopy of vibronic excitations and DFT calculations.

[BibTeX]
@article{NHA_JPCC13,
  author = {Nadine Hauptmann and Christian Hamann and Hao Tang and Richard Berndt},
  title = {Soft-Landing Electrospray Deposition of the Ruthenium Dye N3 on Au(111)},
  journal = {The Journal of Physical Chemistry C},
  volume = {117},
  number = {19},
  pages = {9734-9738},	
  year = {2013},
  url = {http://dx.doi.org/10.1021/jp311420d},
  doi = {http://doi.org/10.1021/jp311420d}
}
 
 
Subsurface sites of Fe in H/Si(111) studied by scanning tunneling microscopy
M. Gruyters, T. Pingel, R. Berndt, Phys. Rev. B 87, 165405 (2013)

Abstract:
The structural and electronic properties of Fe atoms in the subsurface region of hydrogen-passivated Si(111) surfaces are investigated by scanning tunneling microscopy (STM). In the STM images, Fe atoms show a characteristic triangular structure with orientation and dimensions that match the Si host lattice. Comparison between atomically resolved microscopy images and the crystalline structure of the H/Si(111) surface indicate that Fe atoms occupy substitutional sites which are located in the third Si layer underneath the surface.

[BibTeX]
@article{MGR_PRB13,
  author = {Gruyters, Markus and Pingel, Torben and Berndt, Richard},
  title = {Subsurface sites of Fe in H/Si(111) studied by scanning tunneling microscopy},
  journal = {Phys. Rev. B},
  volume = {87},
  pages = {165405},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.87.165405},
  doi = {http://doi.org/10.1103/PhysRevB.87.165405}
}
 
 
Scanning tunneling spectroscopy of Ni/W(110): bcc and fcc properties in the second atomic layer
J. Schöneberg, A. Weismann, R. Berndt, Appl. Phys. A 111, 285 (2013)

Abstract:
Nickel islands are grown on W(110) at elevated temperatures. Islands with a thickness of two layers are investigated with scanning tunneling microscopy. Spectroscopic measurements reveal that nanometer sized areas of the islands exhibit distinctly different apparent heights and dI/dVspectra. Spin polarized and paramagnetic band structure calculations indicate that the spectral features are due to fcc(111) and bcc(110) orientations of the Ni film, respectively.

[BibTeX]
@article{JSC_APA13,
  author = {Schöneberg, Johannes and Weismann, Alexander and Berndt, Richard},
  title = {Scanning tunneling spectroscopy of Ni/W(110): bcc and fcc properties in the second atomic layer},
  journal = {Applied Physics A},
  volume = {111},
  number = {1},
  pages = {285--288},	
  year = {2013},
  url = {http://dx.doi.org/10.1007/s00339-012-7523-0},
  doi = {http://doi.org/10.1007/s00339-012-7523-0}
}
 
 
Hot electron cascades in the scanning tunneling microscope
N.L. Schneider, P. Johansson, R. Berndt, Phys. Rev. B 87, 045409 (2013)

Abstract:
The nonequilibrium distribution of electrons at the junction of a scanning tunneling microscope is investigated by detecting photons with energies hν > eV, where V is the bias voltage. Electrons are found at energies exceeding the Fermi level by almost eV. While their distribution deviates from a Fermi-Dirac function it is consistent with a model of hot electrons and holes that diffuse in energy and real space.

[BibTeX]
@article{NSC_PRB13,
  author = {Schneider, Natalia L. and Johansson, Peter and Berndt, Richard},
  title = {Hot electron cascades in the scanning tunneling microscope},
  journal = {Phys. Rev. B},
  volume = {87},
  pages = {045409},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.87.045409},
  doi = {http://doi.org/10.1103/PhysRevB.87.045409}
}
 
 
Tunneling Anisotropic Magnetoresistance at the Single-Atom Limit
N. Néel, S. Schröder, N. Ruppelt, P. Ferriani, J. Kröger, R. Berndt, S. Heinze, Phys. Rev. Lett. 110, 037202 (2013)

Abstract:
The tunneling anisotropic magnetoresistance (TAMR) of single Co atoms adsorbed on a double-layer Fe film on W(110) is observed by scanning tunneling spectroscopy. Without applying an external magnetic field the TAMR is found by comparing spectra of atoms that are adsorbed on the domains and domain walls of the Fe film. The TAMR can be as large as 12% and repeatedly changes sign as a function of bias voltage. First-principles calculations show that the hybridization between Co d states of different orbital symmetries depends on the magnetization direction via spin-orbit coupling. This leads to an anisotropy of the density of states and thus induces a TAMR.

[BibTeX]
@article{NNE_PRL13,
  author = {Néel, N. and Schröder, S. and Ruppelt, N. and Ferriani, P. and Kröger, J. and Berndt, R. and Heinze, S.},
  title = {Tunneling Anisotropic Magnetoresistance at the Single-Atom Limit},
  journal = {Phys. Rev. Lett.},
  volume = {110},
  pages = {037202},
  publisher = {American Physical Society},	
  year = {2013},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.110.037202},
  doi = {http://doi.org/10.1103/PhysRevLett.110.037202}
}
 
 
Tunneling magnetoresistance and exchange interaction in single-atom contacts
C. Lazo, N. Néel, J. Kröger, R. Berndt, S. Heinze, Phys. Rev. B 86, 180406(R) (2012)

Abstract:
The tunneling magnetoresistance of single-atom junctions is shown to depend on the electrode separation owing to exchange forces and the resulting geometric relaxations. An analytical model is proposed to extract relaxations from the magnetoresistances measured with a scanning tunneling microscope. Exchange forces and relaxations calculated within density functional theory demonstrate the validity of the model for a range of distances between tip and sample which extends from tunneling close to the point of maximal attraction.

[BibTeX]
@article{CLA_PRB12,
  author = {Lazo, Cesar and Néel, Nicolas and Kröger, Jörg and Berndt, Richard and Heinze, Stefan},
  title = {Tunneling magnetoresistance and exchange interaction in single-atom contacts},
  journal = {Phys. Rev. B},
  volume = {86},
  pages = {180406(R)},
  publisher = {American Physical Society},	
  year = {2012},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.86.180406},
  doi = {http://doi.org/10.1103/PhysRevB.86.180406}
}
 
 
Review Article: Structures of phthalocyanine molecules on surfaces studied by STM
Y. Wang, K. Wu, J. Kröger, R. Berndt, AIP Adv. 2, 041402 (2012)

Abstract:
This review mainly focuses on progress recently achieved in the growth of phthalocyanine molecules on single-crystal surfaces of sub-monolayer up to few-monolayer thin films studied by scanning tunneling microscopy in our groups. On metallic surfaces such as Au(111), Ag(111) and Cu(111), molecular superstructures are determined by combining directional intermolecular interactions caused by symmetry reduction, molecule-substrate interactions and indirect long-range interactions due to quantum interference of surface state electrons. On semiconducting TiO2surface, molecular assembling structures are dictated by the strong molecule-substrate interaction. However, on insulating NaCl film, molecule-molecule interaction dominates over the molecule-NaCl coupling, leading to molecular growth behavior. Knowledge obtained from these studies would help people better understand the physicochemical properties of the phthalocyanine molecules at surfaces so that their new applications could be further explored and uncovered in the future.

[BibTeX]
@article{YFW_AIPA12,
  author = {Wang, Yongfeng and Wu, Kai and Kröger, Jörg and Berndt, Richard},
  title = {Review Article: Structures of phthalocyanine molecules on surfaces studied by STM},
  journal = {AIP Advances},
  volume = {2},
  number = {4},
  pages = {041402},	
  year = {2012},
  url = {http://scitation.aip.org/content/aip/journal/adva/2/4/10.1063/1.4773458},
  doi = {http://doi.org/10.1063/1.4773458}
}
 
 
Plasmon-induced fluorescence and electroluminescence from porphine molecules on GaAs(110) in a scanning tunneling microscope
S. Mühlenberend, N.L. Schneider, M. Gruyters, R. Berndt, Appl. Phys. Lett. 101, 203107 (2012)

Abstract:
Surface plasmon polaritons of the tip of a scanning tunneling microscope are used to induce fluorescence from (5,10,15,20)-tetraphenyl-21 H,23 H-porphine molecules on GaAs(110) surfaces at very low coverages. Fluorescence spectra exhibiting vibrationally resolved Q-band transitions show that the luminescence is of molecular origin. The emission is not directly induced by the tunneling current. Rather, radiationless energy transfer from plasmon modes of the tip leads to molecular excitation.

[BibTeX]
@article{SMU_APL12,
  author = {Mühlenberend, Svenja and Schneider, Natalia L. and Gruyters, Markus and Berndt, Richard},
  title = {Plasmon-induced fluorescence and electroluminescence from porphine molecules on GaAs(110) in a scanning tunneling microscope},
  journal = {Applied Physics Letters},
  volume = {101},
  number = {20},
  pages = {203107},	
  year = {2012},
  url = {http://scitation.aip.org/content/aip/journal/apl/101/20/10.1063/1.4767351},
  doi = {http://doi.org/10.1063/1.4767351}
}
 
 
Light Emission Probing Quantum Shot Noise and Charge Fluctuations at a Biased Molecular Junction
N.L. Schneider, J.T. Lü, M. Brandbyge, R. Berndt, Phys. Rev. Lett. 109, 186601 (2012)

Abstract:
The emission of plasmonic light from a single C60 molecule on Cu(111) is probed in a scanning tunneling microscope from the weak-coupling, tunneling range to strong coupling of the molecule to the electrodes at contact. At positive sample voltage the photon yield decreases owing to shot-noise suppression in an increasingly transparent quantum contact. At reversed bias an unexpected nonlinear increase occurs. First-principles transport calculations reveal that ultrafast charge fluctuations on the molecule give rise to additional noise at optical frequencies beyond the shot noise of the current that is injected to the tip.

[BibTeX]
@article{NSC_PRL12,
  author = {Schneider, N. L. and Lü, J. T. and Brandbyge, M. and Berndt, R.},
  title = {Light Emission Probing Quantum Shot Noise and Charge Fluctuations at a Biased Molecular Junction},
  journal = {Phys. Rev. Lett.},
  volume = {109},
  pages = {186601},
  publisher = {American Physical Society},	
  year = {2012},
  note = {Editors' Suggestion.},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.186601},
  doi = {http://doi.org/10.1103/PhysRevLett.109.186601}
}
 
Editors' Suggestion.
 
Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy
M. Gruyters, T. Pingel, T. Gopakumar, N. Néel, C. Schütt, F. Köhler, R. Herges, R. Berndt, J. Phys. Chem. C 116, 20882 (2012)

Abstract:
The electronic properties of FePc molecules adsorbed on hydrogen-passivated Si(111) surfaces are investigated by scanning tunneling microscopy at low temperatures. Spatially resolved spectroscopy reveals a significant variation of the electronic states at different positions above the molecule. The highest occupied ligand- and metal-based orbitals of FePc are determined by pronounced peaks in the tunneling spectra and voltage-dependent changes in the microscopic images. Comparison with density functional theory calculations indicates that the electronic ground state is an 3A1g state.

[BibTeX]
@article{MGR_JPCC12,
  author = {M. Gruyters and T. Pingel and T.G. Gopakumar and N. Néel and Ch. Schütt and F. Köhler and R. Herges and R. Berndt},
  title = {Electronic Ground-State and Orbital Ordering of Iron Phthalocyanine on H/Si(111) Unraveled by Spatially Resolved Tunneling Spectroscopy},
  journal = {J. Phys. Chem. C},
  volume = {116},
  number = {39},
  pages = {20882--20886},	
  year = {2012},
  url = { 

        http://dx.doi.org/10.1021/jp3058433

    

},
  doi = {http://doi.org/10.1021/jp3058433}
}
 
 
Plasmonic excitation of light emission and absorption by porphyrine molecules in a scanning tunneling microscope
N.L. Schneider, R. Berndt, Phys. Rev. B 86, 035445 (2012)

Abstract:
Light emission from a scanning tunneling microscope is investigated from Ag(111) surfaces using tips with a clean metallic apex and a molecule-covered shaft. The measurements are conducted such that no molecules are located in the tunneling gap. Nevertheless, spectra of the emission exhibit absorption and emission features of the tetraphenyl-H2-porphyrine molecules used. The experimental data show that molecules in the vicinity of the tunneling gap are excited through tip-induced plasmons and their radiative decay. The excitation of plasmons is due to inelastic tunneling and does not involve an external light source.

[BibTeX]
@article{NSC_PRB12,
  author = {N.L. Schneider, and R. Berndt},
  title = {Plasmonic excitation of light emission and absorption by porphyrine molecules in a scanning tunneling microscope},
  journal = {Phys. Rev. B},
  volume = {86},
  pages = {035445},
  publisher = {American Physical Society},	
  year = {2012},
  note = {Editors' Suggestion.},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.86.035445},
  doi = {http://doi.org/10.1103/PhysRevB.86.035445}
}
 
Editors' Suggestion.
 
Transfer of Cl Ligands between Adsorbed Iron Tetraphenylporphyrin Molecules
T.G. Gopakumar, H. Tang, J. Morillo, R. Berndt, J. Am. Chem. Soc. 134, 11844 (2012)

Abstract:
Iron tetraphenylporphyrin chloride (FeTPPCl) adsorbed on a Au(111) substrate is investigated using low-temperature scanning tunneling microscopy. Cl is controllably transferred between the Fe center of a selected molecule and the tip of the microscope without disrupting the surrounding molecular pattern. Cl abstraction from FeTPPCl is triggered by removing an electron from the highest occupied molecular orbital. Density functional calculations suggest that the reaction involves a change in the oxidation state of the Fe ion.

[BibTeX]
@article{GOP_JACS12,
  author = {Thiruvancheril G. Gopakumar and Hao Tang and Joseph Morillo and Richard Berndt},
  title = {Transfer of Cl Ligands between Adsorbed Iron Tetraphenylporphyrin Molecules},
  journal = {Journal of the American Chemical Society},
  volume = {134},
  number = {29},
  pages = {11844--11847},	
  year = {2012},
  note = {PMID: 22746822},
  url = { 

        http://dx.doi.org/10.1021/ja302589z

    

},
  doi = {http://doi.org/10.1021/ja302589z}
}
 
 
Force and conductance during contact formation to a C 60 molecule
N. Hauptmann, F. Mohn, L. Gross, G. Meyer, T. Frederiksen, R. Berndt, New J. Phys. 14, 073032 (2012)

Abstract:
Force and conductance were simultaneously measured during the formation of Cu-C60 and C60-C60 contacts using a combined cryogenic scanning tunneling and atomic force microscope. The contact geometry was controlled with submolecular resolution. The maximal attractive forces measured for the two types of junctions were found to differ significantly. We show that the previously reported values of the contact conductance correspond to the junction being under maximal tensile stress.

[BibTeX]
@article{NHA_NJP12,
  author = {Nadine Hauptmann and Fabian Mohn and Leo Gross and Gerhard Meyer and Thomas Frederiksen and Richard Berndt},
  title = {Force and conductance during contact formation to a C 60 molecule},
  journal = {New J. Phys.},
  volume = {14},
  number = {7},
  pages = {073032},	
  year = {2012},
  url = {http://stacks.iop.org/1367-2630/14/i=7/a=073032},
  doi = {http://doi.org/10.1088/1367-2630/14/7/073032}
}
 
 
Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold
T. Gopakumar, F. Matino, H. Naggert, A. Bannwarth, F. Tuczek, R. Berndt, Angew. Chem. Int. Ed. 51, 6262 (2012)

Abstract:
Single molecules of the iron(II) complex [Fe(bpz)2phen] (phen=1,10-phenanthroline, bpz=dihydrobis(pyrazolyl)borate) are reversibly switched between low spin and high spin by electron-induced spin crossover (ELIESST) in a bilayer on gold, as revealed by STM.

[BibTeX]
@article{GOP_ACIE12,
  author = {T.G. Gopakumar and F. Matino and H. Naggert and A. Bannwarth and F. Tuczek and R. Berndt},
  title = {Electron-Induced Spin Crossover of Single Molecules in a Bilayer on Gold},
  journal = {Angew. Chem. Int. Ed.},
  volume = {51},
  pages = {6262--6266},	
  year = {2012},
  doi = {http://doi.org/10.1002/anie.201201203}
}
 
 
Energy-resolved spin-polarized tunneling and exchange coupling of Co and Cr atoms on Fe islands on W(110)
N. Néel, P. Ferriani, M. Ziegler, S. Heinze, J. Kröger, R. Berndt, Phys. Rev. B 85, 155406 (2012)

Abstract:
Co and Cr atoms adsorbed to Fe islands on W(110) are investigated with spin-resolved scanning tunneling spectroscopy and first-principles calculations. The spin polarization of the current to Cr adatoms exhibits the same sign as above Fe islands over a wide range of energies. In contrast, it exhibits sign reversals at Co adatoms. These data do not suggest a simple relation between the spin polarization of the current and the orientation of the magnetic moment of the adatom. First-principles calculations reveal that the different spatial decay into the vacuum of majority s and minority d states of the Co adatom is at the origin of the sign reversals of the spin polarization of the current. The different behavior of Cr adatoms is due to their larger exchange splitting and antiferromagnetic coupling to the Fe islands.

[BibTeX]
@article{NNE_PRB12,
  author = {N. Néel and P. Ferriani and M. Ziegler and S. Heinze and J. Kröger and R. Berndt},
  title = {Energy-resolved spin-polarized tunneling and exchange coupling of Co and Cr atoms on Fe islands on W(110)},
  journal = {Phys. Rev. B},
  volume = {85},
  pages = {155406},
  publisher = {American Physical Society},	
  year = {2012},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.85.155406},
  doi = {http://doi.org/10.1103/PhysRevB.85.155406}
}
 
 
Local Gating of an Ir(111) Surface Resonance by Graphene Islands
S. Altenburg, J. Kröger, T. Wehling, B. Sachs, A. Lichtenstein, R. Berndt, Phys. Rev. Lett. 108, 206805 (2012)

Abstract:
The influence of graphene islands on the electronic structure of the Ir(111) surface is investigated. Scanning tunneling spectroscopy (STS) indicates the presence of a two-dimensional electron gas with a binding energy of -160 meV and an effective mass of -0.18me underneath single-layer graphene on the Ir(111) surface. Density functional calculations reveal that the STS features are predominantly due to a holelike surface resonance of the Ir(111) substrate. Nanometer-sized graphene islands act as local gates, which shift and confine the surface resonance.

[BibTeX]
@article{SAL_PRL12,
  author = {S.J. Altenburg and J. Kröger and T.O. Wehling and B. Sachs and A.I. Lichtenstein and R. Berndt},
  title = {Local Gating of an Ir(111) Surface Resonance by Graphene Islands},
  journal = {Phys. Rev. Lett.},
  volume = {108},
  pages = {206805},	
  year = {2012},
  url = {http://link.aps.org/abstract/PRL/v108/p206805},
  doi = {http://doi.org/10.1103/PhysRevLett.108.206805}
}
 
 
Spectroscopy of single donors at ZnO(0001) surfaces
H. Zheng, J. Kröger, R. Berndt, Phys. Rev. Lett. 108, 076801 (2012)

Abstract:
Donors near the polar (0001) surface of nominally undoped ZnO were investigated with scanning tunneling microscopy at 5 K. Spatially resolved spectroscopy reveals single and double charging. Equidistant peaks in spectra of ionized donors are attributed to polaron excitation. The data are consistent with doping due to Zn interstitials or complexes.

[BibTeX]
@article{HZH_PRL12,
  author = {H. Zheng and J. Kröger and R. Berndt},
  title = {Spectroscopy of single donors at ZnO(0001) surfaces},
  journal = {Physical Review Letters},
  volume = {108},
  pages = {076801},	
  year = {2012},
  url = {http://link.aps.org/abstract/PRL/v108/p076801},
  doi = {http://doi.org/10.1103/PhysRevLett.108.076801}
}
 
 
Voltage-dependent conductance states of a single-molecule junction
Y. Wang, N. Néel, J. Kröger, H. Vázquez, M. Brandbyge, B. Wang, R. Berndt, J. Phys.: Condens. Matter 24, 394012 (2012)

Abstract:
Ag Sn-phthalocyanine Ag junctions are shown to exhibit three conductance states. While the junctions are conductive at low bias, their impedance drastically increases above a critical bias. Two-level fluctuations occur at intermediate bias. These characteristics may be used to protect a nanoscale circuit. Further experiments along with calculations reveal that the self-limiting conductance of the junctions is due to reversible changes of the junction geometry.

[BibTeX]
@article{YFW_JPCM12,
  author = {Y. Wang and N. Néel and J. Kröger and H Vázquez and M Brandbyge and B Wang and R Berndt},
  title = {Voltage-dependent conductance states of a single-molecule junction},
  journal = {J. Phys.: Condens. Matter},
  volume = {24},
  number = {39},
  pages = {394012},	
  year = {2012},
  url = {http://stacks.iop.org/0953-8984/24/i=39/a=394012},
  doi = {http://doi.org/10.1088/0953-8984/24/39/394012}
}
 
IOP select.
 
Light emission from a double-decker molecule on a metal surface
N. Schneider, F. Matino, G. Schull, S. Gabutti, M. Mayor, R. Berndt, Phys. Rev. B 84, 153403 (2011)

Abstract:
A scanning tunneling microscope is used to induce the emission of light from a monolayer of naphtalenediimide cyclophane, a molecule comprising two separate p-electron systems. Spectra of the emission exhibit clear features related to vibrational molecular states. They are interpreted in terms of the unusual density of unoccupied states of the molecule, which causes a drastic preference of inelastic tunneling to the molecular affinity level.

[BibTeX]
@article{NSC_PRB11,
  author = {N. Schneider and F. Matino and G. Schull and S. Gabutti and M. Mayor and R. Berndt},
  title = {Light emission from a double-decker molecule on a metal surface},
  journal = {Phys. Rev. B},
  volume = {84},
  pages = {153403},	
  year = {2011},
  url = {http://link.aps.org/abstract/PRB/v84/p153403},
  doi = {http://doi.org/10.1103/PhysRevB.84.153403}
}
 
 
Two-Site Kondo Effect in Atomic Chains
N. Néel, R. Berndt, J. Kröger, T.O. Wehling, A.I. Lichtenstein, M.I. Katsnelson, Phys. Rev. Lett. 107, 106804 (2011)

Abstract:
Linear CoCu_nCo clusters on Cu(111) are fabricated by means of atomic manipulation. They represent a two-site Kondo system with tunable interaction. Scanning tunneling spectroscopy reveals oscillations of the Kondo temperature T_K with the number n of Cu atoms for n>=3. Density functional calculations show that the Ruderman-Kittel-Kasuya-Yosida interaction mediated by the Cu chains causes the oscillations. Calculations find ferromagnetic and antiferromagnetic interaction for n=1 and 2, respectively. Both interactions lead to a decrease of T_K as experimentally observed.

[BibTeX]
@article{NNE_PRL11,
  author = {N. Néel and R. Berndt and J. Kröger and T. O. Wehling and A. I. Lichtenstein and M. I. Katsnelson},
  title = {Two-Site Kondo Effect in Atomic Chains},
  journal = {Phys. Rev. Lett.},
  volume = {107},
  pages = {106804},	
  year = {2011},
  url = {http://arxiv.org/abs/1105.3301},
  doi = {http://doi.org/10.1103/PhysRevLett.107.106804}
}
 
 
Two-level conductance fluctuations of a single-molecule junction
N. Néel, J. Kröger, R. Berndt, NanoLetters 11, 3593 (2011)

Abstract:
The conductance of a single-molecule junction in a low-temperature scanning tunneling microscope has been measured at nanosecond time resolution. In a transition region between tunneling and contact the conductance exhibits rapid two-level fluctuations which are attributed to different geometries of the junction. The voltage dependence of the fluctuations indicates that electrons injected into the lowest unoccupied molecular orbital may efficiently couple to molecular vibrations.

[BibTeX]
@article{NNE_NLE11,
  author = {N. Néel and J. Kröger and R. Berndt},
  title = {Two-level conductance fluctuations of a single-molecule junction},
  journal = {NanoLetters},
  volume = {11},
  pages = {3593--3596},	
  year = {2011},
  url = {http://dx.doi.org/10.1021/nl201327c},
  doi = {http://doi.org/10.1021/nl201327c}
}
 
 
Charge injection through single and double carbon bonds
G. Schull, Y.J. Dappe, C. González, H. Bulou, R. Berndt, NanoLetters 11, 3142 (2011)

Abstract:
The contact conductance of oriented C60 molecules is probed with a scanning tunnel ing microscope as a function of the lateral position of the tip in contact to the molecular cage. Together with first principles calculations, these measurements reveal variations of the effciency of charge injection to the fullerene mo lecule with the order of the contacted carbon-carbon bond.

[BibTeX]
@article{GSC_NLE11,
  author = {G. Schull and Y. J. Dappe and C. González and H. Bulou and R. Berndt},
  title = {Charge injection through single and double carbon bonds},
  journal = {NanoLetters},
  volume = {11},
  pages = {3142--3146},	
  year = {2011},
  url = {http://dx.doi.org/10.1021/nl201185y},
  doi = {http://doi.org/10.1021/nl201185y}
}
 
 
Spin Valve Effect in Single-Atom Contacts
M. Ziegler, N. Néel, C. Lazo, P. Ferriani, S. Heinze, J. Kröger, R. Berndt, New J. Phys. 13, 85011 (2011)

Abstract:
Magnetic single-atom contacts have been controllably fabricated with a scanning tunnelling microscope. A voltage-dependent spin valve effect with conductance variations of ≈ 40% is reproducibly observed from contacts comprising a Cr-covered tip and Co and Cr atoms on ferromagnetic nanoscale islands on W(110) with opposite magnetization. The spin-dependent conductances are interpreted from first-principles calculations in terms of the orbital character of the relevant electronic states of the junction.

[BibTeX]
@article{MZI_NJP11,
  author = {M. Ziegler and N. Néel and C. Lazo and P. Ferriani and S  Heinze and J. Kröger and R. Berndt},
  title = {Spin Valve Effect in Single-Atom Contacts},
  journal = {New J. Phys.},
  volume = {13},
  pages = {85011},	
  year = {2011},
  url = {http://stacks.iop.org/NJP/13/85011},
  doi = {http://doi.org/10.1088/1367-2630/13/8/085011}
}
 
 
30 Jahre Rastertunnelmikroskopie
R. Berndt, Editorial, Physik in unserer Zeit 42, 159 (2011)
[BibTeX]
@article{RBE_PIUZ11,
  author = {R. Berndt},
  title = {30 Jahre Rastertunnelmikroskopie},
  journal = {Editorial, Physik in unserer Zeit},
  volume = {42},
  pages = {159},	
  year = {2011},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/piuz.201190038/abstract},
  doi = {http://doi.org/10.1002/piuz.201190038}
}
 
 
Demetalation of an organometallic complex
A. Sperl, J. Kröger, R. Berndt, J. Am. Chem. Soc. 133, 11007 (2011)

Abstract:
Single lead-phthalocyanine molecules adsorbed to ultrathin lead islands on Ag(111) are demetalized by trans-ferring the lead atom of the inner macrocycle to the tip of a scanning tunneling microscope. Reactants and products are discriminated by their images and spectroscopic fingerprints.

[BibTeX]
@article{ASP_JACS11,
  author = {A. Sperl and J. Kröger and R. Berndt},
  title = {Demetalation of an organometallic complex},
  journal = {J. Am. Chem. Soc.},
  volume = {133},
  pages = {11007--11009},	
  year = {2011},
  url = {http://dx.doi.org/10.1021/ja203199q},
  doi = {http://doi.org/10.1021/ja203199q}
}
 
 
Controlled Metalation of a Single Adsorbed Phthalocyanine
A. Sperl, J. Kröger, R. Berndt, Angew. Chem. 123, 5406 (2011)

Abstract:
Silvered molecules: The controlled metalation of individual phthalocyanine (H_2Pc) molecules to form AgPc was observed by low-temperature scanning tunneling microscopy (STM). Stepwise dehydrogenation was followed by Ag+ implantation; tautomerization and hydrogen atom hopping within the H_2Pc inner ring were also induced by electron injection from the STM tip.

[BibTeX]
@article{ASP_ACH11,
  author = {A. Sperl and J. Kröger and R. Berndt},
  title = {Controlled Metalation of a Single Adsorbed Phthalocyanine},
  journal = {Angew. Chem.},
  volume = {123},
  pages = {5406},	
  year = {2011},
  url = {http://dx.doi.org/10.1002/ange.201100950},
  doi = {http://doi.org/10.1002/ange.201100950}
}
 
 
Coverage-Driven Electronic Decoupling of Fe-Phthalocyanine from a Ag(111) Substrate
T. Gopakumar, T. Brumme, J. Kröger, C. Toher, G. Cuniberti, R. Berndt, J. Phys. Chem. C 115, 12173 (2011)

Abstract:
Coverage-dependent structural and electronic properties of Fe-phthalocyanine (FePc) molecules adsorbed on Ag(111) have been investigated by scanning tunneling microscopy/spectroscopy and density functional calculations. While spectra of single FePc molecules are dominated by a broad signature of Fe d orbitals, spectra of molecules in an ordered superstructure resolve spectroscopic contributions from individual dz2 and dxz/dyz orbitals. Calculations suggest that an increased molecule-surface distance in the superstructure and a change of the Ag(111) surface electronic structure cause the spectral changes, which are consistent with a partial electronic decoupling of the molecules from the substrate. A progressive evolution toward a gap around the Fermi level is observed for molecules on the first and second molecular layer.

[BibTeX]
@article{GOP_JPCC11,
  author = {T.G. Gopakumar and T. Brumme and J. Kröger and C. Toher and G. Cuniberti and R. Berndt},
  title = {Coverage-Driven Electronic Decoupling of Fe-Phthalocyanine from a Ag(111) Substrate},
  journal = {J. Phys. Chem. C},
  volume = {115},
  pages = {12173},	
  year = {2011},
  url = {http://dx.doi.org/10.1021/jp2038619},
  doi = {http://doi.org/10.1021/jp2038619}
}
 
 
Electronic superstructure of lead phthalocyanine on lead islands
A. Sperl, J. Kröger, R. Berndt, J. Phys. Chem. A 115, 6973 (2011)

Abstract:
Lead phthalocyanine (PbPc) deposited on lead islands on Ag(111) forms two-dimensional crystals of densely packed molecules. For particular orientations, the molecular arrays exhibit an electronic superstructure with an extraordinarily large unit cell. The molecules induce a shift of quantum well states, which are confined to the Pb islands. Patterns formed by PbPc on Ag(111) are drastically different.

[BibTeX]
@article{ASP_JPCA11,
  author = {A. Sperl and J. Kröger and R. Berndt},
  title = {Electronic superstructure of lead phthalocyanine on lead islands},
  journal = {J. Phys. Chem. A},
  volume = {115},
  pages = {6973},	
  year = {2011},
  url = {http://dx.doi.org/10.1021/jp112169s},
  doi = {http://doi.org/10.1021/jp112169s}
}
 
 
Ultra high vacuum deposition of organic molecules by electrospray ionization
C. Hamann, R. Woltmann, I. Hong, N. Hauptmann, S. Karan, R. Berndt, Rev. Sci. Instrum. 82, 33903 (2011)

Abstract:
An electrospray apparatus for deposition of organic molecules on surfaces in ultra high vacuum is presented. The kinetic energy at the impact and mass to charge ratio of deposited ions can be controlled by an electrostatic quadrupole deflector and an in-line quadrupole mass spectrometer. With an ion funnel in the first two vacuum stages a high ion transmission is achieved. Experiments on porphyrin cations and deoxyribonucleic acid deposited on a Au(111) surface demonstrate the capabilities of the instrument.

[BibTeX]
@article{CCH_RSI11,
  author = {Ch. Hamann and R. Woltmann and I. Hong and N. Hauptmann and S. Karan and R. Berndt},
  title = {Ultra high vacuum deposition of organic molecules by electrospray ionization},
  journal = {Rev. Sci. Instrum.},
  volume = {82},
  pages = {33903},	
  year = {2011},
  url = {http://dx.doi.org/10.1063/1.3553010},
  doi = {http://doi.org/10.1063/1.3553010}
}
 
 
Atomic-scale engineering of electrodes for single-molecule contacts
G. Schull, T. Frederiksen, A. Arnau, D. Sánchez-Portal, R. Berndt, Nat. Nanotech. 6, 23 (2011)

Abstract:
The transport of charge through a conducting material depends on the intrinsic ability of the material to conduct current and on the charge injection efficiency at the contacts between the conductor and the electrodes carrying current to and from the material. According to theoretical considerations, this concept remains valid down to the limit of single-molecule junctions. Exploring this limit in experiments requires atomic-scale control of the junction geometry. Here we present a method for probing the current through a single C60 molecule while changing, one by one, the number of atoms in the electrode that are in contact with the molecule. We show quantitatively that the contact geometry has a strong influence on the conductance. We also find a crossover from a regime in which the conductance is limited by charge injection at the contact to a regime in which the conductance is limited by scattering at the molecule. Thus, the concepts of 'good' and 'bad' contacts, commonly used in macro- and mesoscopic physics, can also be applied at the molecular scale.

[BibTeX]
@article{GSC_NNAT11,
  author = {G. Schull and Th. Frederiksen and A. Arnau and D. Sánchez-Portal and R. Berndt},
  title = {Atomic-scale engineering of electrodes for single-molecule contacts},
  journal = {Nat. Nanotech.},
  volume = {6},
  pages = {23},	
  year = {2011},
  url = {http://dx.doi.org/10.1038/nnano.2010.215},
  doi = {http://doi.org/10.1038/nnano.2010.215}
}
 
published online 14. Nov. 2010
cf. A. Heinrich, Closing in on molecular junctions, news & views Nature Nanotech. 6, 6-7 (2011)
 
Electronic decoupling of a cyclophane from a metal surface
F. Matino, G. Schull, F. Köhler, S. Gabutti, M. Mayor, R. Berndt, PNAS 108, 961 (2011)

Abstract:
Electronic self-decoupling of an organic chromophore from a metal substrate is achieved using a naphtalenediimide cyclophane to spatially separate one chromophore unit of the cyclophane from the substrate. Observations of vibronic excitations in scanning tunneling spectra demonstrate the success of this approach. These excitations contribute a significant part of the tunneling current and give rise to clear structure in scanning tunneling microscope images. We suggest that this approach may be extended to implement molecular functions at metal surfaces.

[BibTeX]
@article{FMA_PNAS11,
  author = {F. Matino and G. Schull and F. Köhler and S. Gabutti and M. Mayor and R. Berndt},
  title = {Electronic decoupling of a cyclophane from a metal surface},
  journal = {PNAS},
  volume = {108},
  pages = {961--964},	
  year = {2011},
  url = {http://dx.doi.org/10.1073/pnas.1006661107},
  doi = {http://doi.org/10.1073/pnas.1006661107}
}