Publikationen

2016-2017

Ligand-Induced Energy Shift and Localization of Kondo Resonances in Cobalt-Based Complexes on Cu(111)
T. Knaak, M. Gruber, C. Lindström, M.-L. Bocquet, J. Heck, R. Berndt, Nano Lett.

Abstract:
Magnetic sandwich complexes are of particular interest for molecular spintronics. Using scanning tunneling microscopy, we evidence the successful deposition of 1,3,5-tris(η6-borabenzene-η5-cyclopentadienylcobalt) benzene, a molecule composed of three connected magnetic sandwich units, on Cu(111). Scanning tunneling spectra reveal two distinct spatial-dependent narrow resonances close to the Fermi level for the trimer molecules as well as for molecular fragments composed of one and two magnetic units. With the help of density functional theory, these resonances are interpreted as two Kondo resonances originating from two distinct nondegenerate d-like orbitals. These Kondo resonances are found to have defined spatial extents dictated by the hybridization of the involved orbitals with that of the ligands. These results opens promising perspectives for investigating complex Kondo systems composed of several "Kondo" orbitals.

[BibTeX]
@article{TKN_NLE17,
  author = {Knaak, Thomas and Gruber, Manuel and Lindström, Christoph and Bocquet, Marie-Laure and Heck, Jürgen and Berndt, Richard},
  title = {Ligand-Induced Energy Shift and Localization of Kondo Resonances in Cobalt-Based Complexes on Cu(111)},
  journal = {Nano Letters},
  url = {http://dx.doi.org/10.1021/acs.nanolett.7b04181},
  doi = {http://doi.org/10.1021/acs.nanolett.7b04181}
}
 
Publication Date (Web): October 18, 2017
 
Robust and Selective Switching of an FeIII Spin-Crossover Compound on Cu2N/Cu(100) with Memristance Behavior
T. Jasper-Toennies, M. Gruber, S. Karan, H. Jacob, F. Tuczek, R. Berndt, Nano Lett. (2017)

Abstract:
The switching between two spin states makes spin-crossover molecules on surfaces very attractive for potential applications in molecular spintronics. Using scanning tunneling microscopy, the successful deposition of [Fe(pap)2]+ (pap = N-2-pyridylmethylidene-2-hydroxyphenylaminato) molecules on Cu2N/Cu(100) surface is evidenced. The deposited FeIII spin-crossover compound is controllably switched between three different states, each of them exhibiting a characteristic tunneling conductance. The conductance is therefore employed to readily read the state of the molecules. A comparison of the experimental data with the results of density functional theory calculations reveals that all Fe(pap)2 molecules are initially in their high-spin state. The two other states are compatible with the low-spin state of the molecule but differ with respect to their coupling to the substrate. As a proof of concept, the reversible and selective nature of the switching is used to build a two-molecule memory.

[BibTeX]
@article{TJT_NLE17,
  author = {Jasper-Toennies, Torben and Gruber, Manuel and Karan, Sujoy and Jacob, Hanne and Tuczek, Felix and Berndt, Richard},
  title = {Robust and Selective Switching of an FeIII Spin-Crossover Compound on Cu2N/Cu(100) with Memristance Behavior},
  journal = {Nano Letters},	
  year = {2017},
  url = {http://dx.doi.org/10.1021/acs.nanolett.7b02481},
  doi = {http://doi.org/10.1021/acs.nanolett.7b02481}
}
 
Publication Date (Web): October 12, 2017
 
A minimal double quantum dot
H. Zheng, J. Zhang, R. Berndt, Scientific Reports 7, 10764 (2017)

Abstract:
Double quantum dots (DQDs) are a versatile platform for solid-state physics, quantum computation and nanotechnology. The micro-fabrication techniques commonly used to fabricate DQDs are difficult to extend to the atomic scale. Using an alternative approach, which relies on scanning tunneling microscopy and spectroscopy, we prepared a minimal DQD in a wide band-gap semiconductor matrix. It is comprised of a pair of strongly coupled donor atoms that can each be doubly charged. The donor excitation diagram of this system mimicks the charge stability diagram observed in transport measurements of DQDs. We furthermore illustrate how the charge and spin degrees of freedom of the minimal DQD may be used to obtain a single quantum bit and to prepare a Bell state. The results open an intriguing perspective for quantum electronics with atomic-scale structures.

[BibTeX]
@article{HZH_SIR17,
  author = {Hao Zheng and Junyi Zhang and Richard Berndt},
  title = {A minimal double quantum dot},
  journal = {Scientific Reports},
  volume = {7},
  pages = {10764},	
  year = {2017},
  doi = {http://doi.org/10.1038/s41598-017-10814-z}
}
 
Published online: 07 September 2017
 
Submolecular resolution in scanning probe images of Sn-phthalocyanines on Cu(100) using metal tips
K. Buchmann, N. Hauptmann, A.S. Foster, R. Berndt, J. Phys.: Condens. Matter 29, 394004 (2017)

Abstract:
Single Sn-phthalocyanine (SnPc) molecules adsorb on Cu(100) with the Sn ion above (Sn-up) or below (Sn-down) the molecular plane. Here we use a combination of atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and first principles calculations to understand the adsorption configuration and origin of observed contrast of molecules in the Sn-down state. AFM with metallic tips images the pyrrole nitrogen atoms in these molecules as attractive features while STM reveals a chirality of the electronic structure of the molecules close to the Fermi level EF, which is not observed in AFM. Using density functional theory calculations, the origin of the submolecular contrast is analysed and, while the electrostatic forces turn out to be negligible, the van der Waals interaction between the phenyl rings of SnPc and the substrate deform the molecule, push the pyrrole nitrogen atoms away from the substrate and thus induce the observed submolecular contrast. Simulated STM images reproduce the chirality of the electronic structure near EF.

[BibTeX]
@article{KBU_JPCM17,
  author = {Kristof Buchmann and Nadine Hauptmann and Adam S Foster and Richard Berndt},
  title = {Submolecular resolution in scanning probe images of Sn-phthalocyanines on Cu(100) using metal tips},
  journal = {Journal of Physics: Condensed Matter},
  volume = {29},
  number = {39},
  pages = {394004},	
  year = {2017},
  url = {http://stacks.iop.org/0953-8984/29/i=39/a=394004},
  doi = {http://doi.org/10.1088/1361-648X/aa7dbd}
}
 
 
Quantum Coherent Multielectron Processes in an Atomic Scale Contact
P.-J. Peters, F. Xu, K. Kaasbjerg, G. Rastelli, W. Belzig, R. Berndt, Phys. Rev. Lett. 119, 066803 (2017)

Abstract:
The light emission from a scanning tunneling microscope operated on a Ag(111) surface at 6 K is analyzed from low conductances to values approaching the conductance quantum. Optical spectra recorded at sample voltages V reveal emission with photon energies hν > 2eV. A model of electrons interacting coherently via a localized plasmon-polariton mode reproduces the experimental data, in particular, the kinks in the spectra at eV and 2eV as well as the scaling of the intensity at low and intermediate conductances.

[BibTeX]
@article{PPE_PRL17,
  author = {Peters, Peter-Jan and Xu, Fei and Kaasbjerg, Kristen and Rastelli, Gianluca and Belzig, Wolfgang and Berndt, Richard},
  title = {Quantum Coherent Multielectron Processes in an Atomic Scale Contact},
  journal = {Phys. Rev. Lett.},
  volume = {119},
  pages = {066803},
  publisher = {American Physical Society},	
  year = {2017},
  url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.066803},
  doi = {http://doi.org/10.1103/PhysRevLett.119.066803}
}
 
 
On-surface synthesis of heptacene and its interaction with a metal surface
M. Zugermeier, M. Gruber, M. Schmid, B.P. Klein, L. Ruppenthal, P. Muller, R. Einholz, W. Hieringer, R. Berndt, H.F. Bettinger, J.M. Gottfried, Nanoscale 9, 12461 (2017)

Abstract:
Heptacene was generated by surface-assisted didecarbonylation of an α-diketone precursor on a Ag(111) surface. Monitoring of the surface reaction and characterization of the adsorbed heptacene was performed with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. The surface-assisted formation of heptacene occurs around 460 K. Both the heptacene and the precursor molecules are oriented along the high-symmetry directions of the (111) surface and their molecular π systems face towards the substrate. The interaction with the Ag(111) substrate is not laterally uniform, but appears to be strongest on the central part of the molecule, in line with the expectations from Clar's rule. In the STM images, heptacene shows a dumbbell shape, which may correspond to the substantial out-of-plane deformations of heptacene on Ag(111). As revealed by DFT, the center of the molecule is closer to the surface than the outer parts. In addition, the inner rings are most affected by charge redistribution between surface and molecule. Heptacene acts as an acceptor and receives a negative charge of -0.6e from the Ag(111) surface. Since vacuum-sublimable α-diketone precursors for even larger acenes are available, the approach is promising for the on-surface synthesis of higher acene homologues such as octacene and nonacene.

[BibTeX]
@article{MZU_NSC17,
  author = {Zugermeier, Malte and Gruber, Manuel and Schmid, Martin and Klein, Benedikt P. and Ruppenthal, Lukas and Muller, Philipp and Einholz, Ralf and Hieringer, Wolfgang and Berndt, Richard and Bettinger, Holger F. and Gottfried, J. Michael},
  title = {On-surface synthesis of heptacene and its interaction with a metal surface},
  journal = {Nanoscale},
  volume = {9},
  pages = {12461-12469},
  publisher = {The Royal Society of Chemistry},	
  year = {2017},
  url = {http://dx.doi.org/10.1039/C7NR04157H},
  doi = {http://doi.org/10.1039/C7NR04157H}
}
 
 
13-cis-Retinoic acid on coinage metals: hierarchical self-assembly and spin generation
X. Zhang, N. Li, Y. Zhang, R. Berndt, Y. Wang, Phys. Chem. Chem. Phys. 19, 14919 (2017)

Abstract:
Hierarchical self-assembly of 13-cis-retinoic acid on Au(111) and Ag(111) was investigated using low-temperature scanning tunnelling microscopy. On both surfaces, molecules form dimers by hydrogen bonds and the dimers arrange into ordered two-dimensional arrays through van der Waals forces. Three packing modes are observed on Au(111) and only one on Ag(111). We tentatively attribute the different patterns on the two surfaces to a stronger molecule-substrate interaction on Ag(111) and site-dependent molecular adsorption on different atomic lattices. In addition, 13-cis-ReA on Au(111) can be made to carry a localized spin.

[BibTeX]
@article{XZH_PCCP17,
  author = {Zhang, Xue and Li, Na and Zhang, Yajie and Berndt, Richard and Wang, Yongfeng},
  title = {13-cis-Retinoic acid on coinage metals: hierarchical self-assembly and spin generation},
  journal = {Phys. Chem. Chem. Phys.},
  volume = {19},
  pages = {14919-14923},
  publisher = {The Royal Society of Chemistry},	
  year = {2017},
  url = {http://dx.doi.org/10.1039/C7CP01568B},
  doi = {http://doi.org/10.1039/C7CP01568B}
}
 
 
Conductance of a Freestanding Conjugated Molecular Wire
T. Jasper-Tönnies, A. Garcia-Lekue, T. Frederiksen, S. Ulrich, R. Herges, R. Berndt, Phys. Rev. Lett. 119, 066801 (2017)

Abstract:
A freestanding molecular wire is placed vertically on Au(111) using a platform molecule and contacted by a scanning tunneling microscope. Despite the simplicity of the single-molecule junction, its conductance G reproducibly varies in a complex manner with the electrode separation. Transport calculations show that G is controlled by a deformation of the molecule, a symmetry mismatch between the tip and molecule orbitals, and the breaking of a C≡C triple in favor of a Au–C–C bond. This tip-controlled reversible bond formation or rupture alters the electronic spectrum of the junction and the states accessible for transport, resulting in an order of magnitude variation of the conductance.

[BibTeX]
@article{TJT_PRL17,
  author = {Jasper-T\"onnies, Torben and Garcia-Lekue, Aran and Frederiksen, Thomas and Ulrich, Sandra and Herges, Rainer and Berndt, Richard},
  title = {Conductance of a Freestanding Conjugated Molecular Wire},
  journal = {Phys. Rev. Lett.},
  volume = {119},
  pages = {066801},
  publisher = {American Physical Society},	
  year = {2017},
  url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.066801},
  doi = {http://doi.org/10.1103/PhysRevLett.119.066801}
}
 
 
Deposition of a Cationic FeIII Spin-Crossover Complex on Au(111): Impact of the Counter Ion
T. Jasper-Tönnies, M. Gruber, S. Karan, H. Jacob, F. Tuczek, R. Berndt, J. Phys. Chem. Lett. 8, 1569 (2017)

Abstract:
Spin-crossover molecules on metallic substrates have recently attracted considerable interest for their potential applications in molecular spintronics. Using scanning tunneling microscopy, we evidence the first successful deposition of a charged FeIII spin-crossover complex, [Fe(pap)2]+ (pap = N-2-pyridylmethylidene-2-hydroxyphenylaminato), on Au(111). Furthermore, the bulk form of the molecules is stabilized by a perchlorate counterion, which depending on the deposition technique may affect the quality of the deposition and the measurements. Finally, we evidence switching of the molecules on Au(111).

[BibTeX]
@article{TJT_JPCL17,
  author = {Jasper-T\"onnies, Torben and Gruber, Manuel and Karan, Sujoy and Jacob, Hanne and Tuczek, Felix and Berndt, Richard},
  title = {Deposition of a Cationic FeIII Spin-Crossover Complex on Au(111): Impact of the Counter Ion},
  journal = {J. Phys. Chem. Lett.},
  volume = {8},
  number = {7},
  pages = {1569-1573},	
  year = {2017},
  note = {PMID: 28319403},
  url = { http://dx.doi.org/10.1021/acs.jpclett.7b00457},
  doi = {http://doi.org/10.1021/acs.jpclett.7b00457}
}
 
 
Vacuum-Evaporable Spin-Crossover Complexes in Direct Contact With a Solid Surface: Bismuth vs. Gold
S. Ossinger, H. Naggert, L. Kipgen, T. Jasper-Toennies, A. Rai, J. Rudnik, F. Nickel, L.M. Arruda, M. Bernien, W. Kuch, R. Berndt, F. Tuczek, J. Phys. Chem. C 121, 1210 (2017)

Abstract:
To investigate the ability for spin-state switching of spin-crossover (SCO) complexes adsorbed to solid substrates, the SCO complex [Fe(H2B(pz)2)2(phenme4)] (pz = pyrazole, phenme4 = 3,4,7,8-tetramethyl-1,10-phenanthroline) is prepared. The new complex is investigated by magnetic susceptibility measurements and Mössbauer spectroscopy in the solid state and by temperature-dependent UV/Vis-spectroscopy in a thin film deposited by physical vapour deposition (PVD) on quartz glass. Thermal and light-induced SCO are observed in the bulk and the film on glass. Submonolayers of this complex obtained by PVD are studied by temperature-dependent near-edge x-ray absorption fine structure (NEXAFS) on Au(111) as well as Bi(111) and by scanning tunneling microscopy (STM) on Au(111). NEXAFS shows thermal and light-induced spin-state switching of the complex on Bi(111), however, with a large temperature-independent high-spin fraction (≈ 50%). On the other hand, combined evidence from NEXAFS and STM indicates that on Au(111) the complex dissociates into [Fe(H2B(pz)2)2] and phenme4. Similar observations are made with the parent complex [Fe(H2B(pz)2)2(phen)], which on Bi(111) stays intact and exhibits thermal as well as light-induced SCO, but on Au(111) dissociates into [Fe(H2B(pz)2)2] and phen.

[BibTeX]
@article{SOS_JPCC16,
  author = {Ossinger, Sascha and Naggert, Holger and Kipgen, Lalminthang and Jasper-Toennies, Torben and Rai, Abhishek and Rudnik, Julian and Nickel, Fabian and Arruda, Lucas M. and Bernien, Matthias and Kuch, Wolfgang and Berndt, Richard and Tuczek, Felix},
  title = {Vacuum-Evaporable Spin-Crossover Complexes in Direct Contact With a Solid Surface: Bismuth vs. Gold},
  journal = {J. Phys. Chem. C},
  volume = {121},
  number = {2},
  pages = {1210-1219},	
  year = {2017},
  url = {http://dx.doi.org/10.1021/acs.jpcc.6b10888},
  doi = {http://doi.org/10.1021/acs.jpcc.6b10888}
}
 
Publication Date (Web): December 21, 2016
 
Charging single Co atoms on ultrathin NaCl films
N. Li, H. Wang, D.-L. Song, C. Li, R. Li, S.-M. Hou, Y.-F. Wang, R. Berndt, Dalton Trans. 45, 16566 (2016)

Abstract:
Single Co adatoms adsorbed on a double-layer NaCl film supported by Cu(111) were negatively charged after applying a positive voltage pulse to the sample in a scanning tunnelling microscope. Density functional calculations showed that the magnetic moment of Co changed from 3μB to 2.2μB after charge state manipulation.

[BibTeX]
@article{NLI_DTR16,
  author = {Li, Na and Wang, Hao and Song, Dao-Liang and Li, Chao and Li, Ruoning and Hou, Shi-Min and Wang, Yong-Feng and Berndt, Richard},
  title = {Charging single Co atoms on ultrathin NaCl films},
  journal = {Dalton Trans.},
  volume = {45},
  pages = {16566-16569},
  publisher = {The Royal Society of Chemistry},	
  year = {2016},
  url = {http://dx.doi.org/10.1039/C6DT01963C},
  doi = {http://doi.org/10.1039/C6DT01963C}
}
 
 
Distance- and spin-resolved spectroscopy of iridium atoms on an iron bilayer
J. Schöneberg, N.M. Caffrey, P. Ferriani, S. Heinze, R. Berndt, Phys. Rev. B 94, 115418 (2016)

Abstract:
The induced spin-polarization of Ir atoms on a ferromagnetic Fe double layer on W(110) has been investigated with spin-polarized scanning tunneling microscopy. An unoccupied state is observed with a spin-polarization exceeding 60% that is inverted with respect to the Fe layer. This inversion is due to the tunneling gap acting as an orbital and spin filter. Distance dependent measurements show that the spin-polarization remains approximately constant over the entire experimentally accessible range, from far in the tunneling regime to 1Å from the point of contact formation. This is corroborated by density functional theory calculations which show that the inversion of spin-polarization occurs within 0.5Å of the adatom.

[BibTeX]
@article{JSC_PRB16,
  author = {Schöneberg, Johannes and Caffrey, Nuala Mai and Ferriani, Paolo and Heinze, Stefan and Berndt, Richard},
  title = {Distance- and spin-resolved spectroscopy of iridium atoms on an iron bilayer},
  journal = {Phys. Rev. B},
  volume = {94},
  pages = {115418},	
  year = {2016},
  url = {http://link.aps.org/doi/10.1103/PhysRevB.94.115418},
  doi = {http://doi.org/10.1103/PhysRevB.94.115418}
}
 
 
Vacuum synthesis of magnetic aluminum phthalocyanine on Au(111)
I.-P. Hong, N. Li, Y.-J. Zhang, H. Wang, H.-J. Song, M.-L. Bai, X. Zhou, J.-L. Li, G.-C. Gu, X. Zhang, M. Chen, J.M. Gottfried, D. Wang, J.-T. Lu, L.-M. Peng, S.-M. Hou, R. Berndt, K. Wu, Y.-F. Wang, Chem. Commun. 52, 10338 (2016)

Abstract:
Air-unstable magnetic aluminum phthalocyanine (AlPc) molecules are prepared by an on-surface metalation reaction of phthalocyanine with aluminum (Al) atoms on Au(111) in ultrahigh vacuum. Experiments and density functional theory calculations show that an unpaired spin is located on the conjugated isoindole lobes of the molecule rather than at the Al position.

[BibTeX]
@article{IHO_CCO16,
  author = {Hong, I-Po and Li, Na and Zhang, Ya-Jie and Wang, Hao and Song, Huan-Jun and Bai, Mei-Lin and Zhou, Xiong and Li, Jian-Long and Gu, Gao-Chen and Zhang, Xue and Chen, Min and Gottfried, J. Michael and Wang, Dong and Lu, Jing-Tao and Peng, Lian-Mao and Hou, Shi-Min and Berndt, Richard and Wu, Kai and Wang, Yong-Feng},
  title = {Vacuum synthesis of magnetic aluminum phthalocyanine on Au(111)},
  journal = {Chem. Commun.},
  volume = {52},
  pages = {10338-10341},
  publisher = {The Royal Society of Chemistry},	
  year = {2016},
  url = {http://dx.doi.org/10.1039/C6CC03359H},
  doi = {http://doi.org/10.1039/C6CC03359H}
}
 
 
Manipulation of Cyclohexene-Based Organic Molecules on Various Metallic Substrates
M. Gruber, R. Berndt, J. Phys. Chem. C 120, 18642 (2016)

Abstract:
Shikimic-acid and beta-carotene molecules were investigated on various metallic substrates using scanning tunneling microscopy at ~5 K. We studied the potential ability of these metal-free organic molecules to be switched into a magnetic state as it was recently evidenced for retinoic acid and cholesterol on Au(111). While our attempts to generate spin within shikimic-acid and beta-carotene molecules proved unsuccessful, switching attempts for different molecule/substrate pairs were thoroughly analyzed so as to tentatively elucidate the underlying causes of the vain attempts. We speculate that, by avoiding the identified causes, other organic molecule/substrate pairs can be found for spin manipulation.

[BibTeX]
@article{GRU_JPCC16,
  author = {Manuel Gruber and Richard Berndt},
  title = {Manipulation of Cyclohexene-Based Organic Molecules on Various Metallic Substrates},
  journal = {J. Phys. Chem. C},
  volume = {120},
  number = {33},
  pages = {18642-18650},	
  year = {2016},
  url = {http://dx.doi.org/10.1021/acs.jpcc.6b06089},
  doi = {http://doi.org/10.1021/acs.jpcc.6b06089}
}
 
 
Surface cis Effect: Influence of an Axial Ligand on Molecular Self-Assembly
T. Knaak, T.G. Gopakumar, B. Schwager, F. Tuczek, R. Robles, N. Lorente, R. Berndt, J. Am. Chem. Soc. 138, 7544 (2016)

Abstract:
Adding ligands to molecules can have drastic and unforeseen consequences in the final products of a reaction. Recently a surface trans effect due to the weakening of a molecule-surface bond was reported. Here, we show a surface cis effect where an axial ligand at adsorbed transition-metal complexes enables lateral bonding among the molecules. In the absence of this ligand, the intermolecular interaction is repulsive and supramolecular patterns are not observed. Fe-tetramethyl-tetraazaannulene on Au(111) was investigated using low-temperature scanning tunneling microscopy and spectroscopy along with density functional theory calculations. At low coverages, the molecules remain isolated. Exposure to CO leads to axial CO bonding and induces reordering into extended clusters of chiral molecular trimers. The changed self-assembly pattern is due to a CO-induced modification of the molecular structure and the corresponding charge transfer between the molecule and the substrate, which in turn changes the lateral intermolecular forces.

[BibTeX]
@article{TKN_JACS16,
  author = {Thomas Knaak and Thiruvancheril G. Gopakumar and Bettina Schwager and Felix Tuczek and Roberto Robles and Nicolás Lorente and Richard Berndt},
  title = {Surface cis Effect: Influence of an Axial Ligand on Molecular Self-Assembly},
  journal = {J. Am. Chem. Soc.},
  volume = {138},
  number = {24},
  pages = {7544 -- 7550},	
  year = {2016},
  url = {http://dx.doi.org/10.1021/jacs.6b03710},
  doi = {http://doi.org/10.1021/jacs.6b03710}
}
 
 
Switching of an Azobenzene-Tripod Molecule on Ag(111)
K. Scheil, T.G. Gopakumar, J. Bahrenburg, F. Temps, R.J. Maurer, K. Reuter, R. Berndt, J. Phys. Chem. Lett. 7, 2080 (2016)

Abstract:
The trans-cis isomerization makes azobenzene (AB) a robust molecular switch. Once adsorbed to a metal, however, the switching is inefficient or absent due to rapid excited-state quenching or loss of the trans-cis bistability. We find that tris-[4-(phenylazo)-phenyl]-amine is a rather efficient switch on Ag(111). Using scanning tunneling and atomic force microscopy at submolecular resolution along with density functional theory calculations, we show that the switching process is no trans-cis isomerization but rather a reorientation of the N-N bond of an AB unit. It proceeds through a twisting motion of the azo-bridge that leads to a lateral shift of a phenyl ring. Thus, the role of the Ag substrate is ambivalent. While it suppresses the original bistability of the azobenzene units, it creates a new one by inducing a barrier for the rotation of the N-N bond.

[BibTeX]
@article{KSC_JPCL16,
  author = {Katharina Scheil and Thiruvancheril G. Gopakumar and Julia Bahrenburg and Friedrich Temps and Reinhard Johann Maurer and Karsten Reuter and Richard Berndt},
  title = {Switching of an Azobenzene-Tripod Molecule on Ag(111)},
  journal = {J. Phys. Chem. Lett.},
  volume = {7},
  number = {11},
  pages = {2080--2084},	
  year = {2016},
  note = {PMID: 27193044},
  url = {http://dx.doi.org/10.1021/acs.jpclett.6b01011},
  doi = {http://doi.org/10.1021/acs.jpclett.6b01011}
}
 
 
AFM Imaging of Mercaptobenzoic Acid on Au(110): Submolecular Contrast with Metal Tips
N. Hauptmann, R. Robles, P. Abufager, N. Lorente, R. Berndt, J. Phys. Chem. Lett. 7, 1984 (2016)

Abstract:
A self-assembled monolayer of mercaptobenzoic acid (MBA) on Au(110) is investigated with scanning tunneling and atomic force microscopy (STM and AFM) and density functional calculations. High-resolution AFM images obtained with metallic tips show clear contrasts between oxygen atoms and phenyl moieties. The contrast above the oxygen atoms is due to attractive covalent interactions, which is different than previously reported high-resolution images, where Pauli repulsion dominated the image contrast. We show that the bonding of MBA to the substrate occurs mainly through dispersion interactions, whereas the thiol-Au bond contributes only a quarter of the adsorption energy. No indication of Au adatoms mediating the thiol-Au interaction was found in contrast to other thiol-bonded systems. However, MBA lifts the Au(110)-(2x1) reconstruction.

[BibTeX]
@article{NHA_JPCL16,
  author = {Nadine Hauptmann and Roberto Robles and Paula Abufager and Nicolas Lorente and Richard Berndt},
  title = {AFM Imaging of Mercaptobenzoic Acid on Au(110): Submolecular Contrast with Metal Tips},
  journal = {J. Phys. Chem. Lett.},
  volume = {7},
  number = {11},
  pages = {1984-1990},	
  year = {2016},
  note = {PMID: 27183144},
  url = {http://dx.doi.org/10.1021/acs.jpclett.6b00684},
  doi = {http://doi.org/10.1021/acs.jpclett.6b00684}
}
 
 
Isolated supramolecules on surfaces studied with scanning tunneling microscopy
C. Xie, Q.-M. Wu, R.-N. Li, G.-C. Gu, X. Zhang, N. Li, R. Berndt, J. Kröger, Z.-Y. Shen, S.-M. Hou, Y.-F. Wang, Chin. Chem. Lett. 27, 807 (2016)

Abstract:
Abstract To date, supramolecular chemistry is an ever growing research field owing to its crucial role in molecular catalysis, recognition, medicine, data storage and processing as well as artificial photosynthetic devices. Different isolated supramolecules were prepared by molecular self-assembly on surfaces. This review mainly focuses on supramolecular aggregations on noble metal surfaces studied by scanning tunneling microscopy, including dimers, trimers, tetramers, pentamers, wire-like assemblies and Sierpinski triangular fractals. The variety of self-assembled structures reflects the subtle balance between intermolecular and molecule-substrate interactions, which to some extent may be controlled by molecules, substrates and the molecular coverage. The comparative study of different architectures helps identifying the operative mechanisms that lead to the structural motifs. The application of these mechanisms may lead to novel assemblies with tailored physicochemical properties.

[BibTeX]
@article{CXI_CCL16,
  author = {Chao Xie and Qi-Meng Wu and Ruo-Ning Li and Gao-Chen Gu and Xue Zhang and Na Li and Richard Berndt and Jörg Kröger and Zi-Yong Shen and Shi-Min Hou and Yong-Feng Wang},
  title = {Isolated supramolecules on surfaces studied with scanning tunneling microscopy},
  journal = {Chin. Chem. Lett.},
  volume = {27},
  number = {6},
  pages = {807 - 812},	
  year = {2016},
  url = {http://www.sciencedirect.com/science/article/pii/S1001841716300511},
  doi = {http://doi.org/10.1016/j.cclet.2016.03.022}
}
 
 
Generation of spin in single cholesterol molecules on gold
S. Karan, R. Berndt, Phys. Chem. Chem. Phys. 18, 9334 (2016)

Abstract:
Compact islands of cholesterol on Au(111) were investigated with scanning tunneling microscopy at ∼ 5 K. Single molecules have been switched among several states, three of which exhibit a sharp spectroscopic feature at the Fermi level. This feature signals the presence of a localized spin and suggests that the molecule may be controllably switched between paramagnetic and diamagnetic states.

[BibTeX]
@article{SKA_PCCP16,
  author = {Karan, Sujoy and Berndt, Richard},
  title = {Generation of spin in single cholesterol molecules on gold},
  journal = {Phys. Chem. Chem. Phys.},
  volume = {18},
  pages = {9334--9337},
  publisher = {The Royal Society of Chemistry},	
  year = {2016},
  url = {http://dx.doi.org/10.1039/C5CP07410J},
  doi = {http://doi.org/10.1039/C5CP07410J}
}
 
 
Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts
J. Schöneberg, F. Otte, N. Néel, A. Weismann, Y. Mokrousov, J. Kröger, R. Berndt, S. Heinze, Nano Lett. 16, 1450 (2016)

Abstract:
Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.

[BibTeX]
@article{JSC_NLE16,
  author = {J. Schöneberg and F. Otte and N. Néel and A. Weismann and Y. Mokrousov and J. Kröger and R. Berndt and S. Heinze},
  title = {Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts},
  journal = {Nano Letters},
  volume = {16},
  number = {2},
  pages = {1450-1454},	
  year = {2016},
  note = {PMID: 26783634},
  url = {http://dx.doi.org/10.1021/acs.nanolett.5b05071},
  doi = {http://doi.org/10.1021/acs.nanolett.5b05071}
}
 
 
Spin Manipulation by Creation of Single-Molecule Radical Cations
S. Karan, N. Li, Y. Zhang, Y. He, I.-P. Hong, H. Song, J.-T. Lü, Y. Wang, L. Peng, K. Wu, G.S. Michelitsch, R.J. Maurer, K. Diller, K. Reuter, A. Weismann, R. Berndt, Phys. Rev. Lett. 116, 027201 (2016)

Abstract:
All-trans-retinoic acid (ReA), a closed-shell organic molecule comprising only C, H, and O atoms, is investigated on a Au(111) substrate using scanning tunneling microscopy and spectroscopy. In dense arrays single ReA molecules are switched to a number of states, three of which carry a localized spin as evidenced by conductance spectroscopy in high magnetic fields. The spin of a single molecule may be reversibly switched on and off without affecting its neighbors. We suggest that ReA on Au is readily converted to a radical by the abstraction of an electron.

[BibTeX]
@article{SKA_PRL16,
  author = {Karan, Sujoy and Li, Na and Zhang, Yajie and He, Yang and Hong, I-Po and Song, Huanjun and Lü, Jing-Tao and Wang, Yongfeng and Peng, Lianmao and Wu, Kai and Michelitsch, Georg S. and Maurer, Reinhard J. and Diller, Katharina and Reuter, Karsten and Weismann, Alexander and Berndt, Richard},
  title = {Spin Manipulation by Creation of Single-Molecule Radical Cations},
  journal = {Phys. Rev. Lett.},
  volume = {116},
  pages = {027201},
  publisher = {American Physical Society},	
  year = {2016},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.116.027201},
  doi = {http://doi.org/10.1103/PhysRevLett.116.027201}
}
 
 
Shot noise from single atom contacts in a scanning tunneling microscope
A. Burtzlaff, N.L. Schneider, A. Weismann, R. Berndt, Surf. Sci. 643, 10 (2016)

Abstract:
Abstract The shot noise of the current through single-atom contacts has been measured in a scanning tunneling microscope at a temperature of 5 K. Electrical measurements at frequencies up to 120 kHz were performed on Au, Fe, and Co atoms on Au(111) using Au tips. The data from Fe and Co indicate spin polarized transmission through a single conductance channel. Optical measurements at sub-petahertz frequencies were carried out on Cu adatoms on Cu(111) using Cu tips. The data are consistent with previous observations from coinage metal contacts.

[BibTeX]
@article{ABU_SSI16,
  author = {Andreas Burtzlaff and Natalia L. Schneider and Alexander Weismann and Richard Berndt},
  title = {Shot noise from single atom contacts in a scanning tunneling microscope},
  journal = {Surf. Sci.},
  volume = {643},
  pages = {10 -- 12},	
  year = {2016},
  note = {Present challenges in surface science, a special issue in honour of Dietrich Menzel},
  url = {http://www.sciencedirect.com/science/article/pii/S0039602815001983},
  doi = {http://doi.org/10.1016/j.susc.2015.07.006}
}