1996 - 2000

Controlled Modification of Individual Adsorbate Electronic Structure
J. Kliewer, R. Berndt, S. Crampin, Phys. Rev. Lett. 85, 4936 (2000)

Abstract:
Modification of the electronic structure of a single Mn adsorbate placed within a geometrical array of adatoms on Ag(111) is observed using local spectroscopy with the scanning tunneling microscope. The changes result from coupling between the adsorbate level and surface electronic states of the substrate. These surface states are scattered coherently within the adatom array, mediating the presence and shape of the array to the adsorbate within. The dimension and geometry of the adatom array thus provide a degree of control over the induced changes.

[BibTeX]
@article{JKL_PRL00,
  author = {J. Kliewer and R. Berndt and S. Crampin},
  title = {Controlled Modification of Individual Adsorbate Electronic Structure},
  journal = {Phys. Rev. Lett.},
  volume = {85},
  pages = {4936--4939},	
  year = {2000},
  url = {http://link.aps.org/abstract/PRL/v85/p4936},
  doi = {http://doi.org/10.1103/PhysRevLett.85.4936}
}
 
 
Heiße Löcher leben länger
R. Berndt, J. Kliewer, Phys. Unserer Zeit 4, 178 (2000)

Abstract:
Halbleiter und Metalle lassen sich einfacher beschreiben, wenn man neben den negativen Elektronen auch so genannte Quasiteilchen einführt, zum Beispiel positive Löcher. Diese Löcher, insbesondere solche, die sich an Kristalloberflächen aufhalten, sind sehr kurzlebig. Eine präzise Messung ihrer Lebensdauer und eine mit den Messwerten konsistente theoretische Berechnungen gelang kürzlich Physikern der Universität Kiel und der RWTH Aachen.

[BibTeX]
@article{RBE_PIUZ00,
  author = {R. Berndt and J. Kliewer},
  title = {Heiße Löcher leben länger},
  journal = {Phys. Unserer Zeit},
  volume = {4},
  pages = {178},	
  year = {2000}
}
 
 
Schein oder Sein - Elektronische Struktur kohärent projiziert in einem Quantenresonator
R. Berndt, Phys. Bl. 56, 16 (2000)
[BibTeX]
@article{RBE_PHBL00,
  author = {R. Berndt},
  title = {Schein oder Sein - Elektronische Struktur kohärent projiziert in einem Quantenresonator},
  journal = {Phys. Bl.},
  volume = {56},
  number = {4},
  pages = {16},	
  year = {2000}
}
 
 
Two-dimensional self-assembly of supramolecular structures
M. Böhringer, W.-D. Schneider, R. Berndt, Surf. Rev. Lett. 7, 661 (2000)

Abstract:
We briefly review recent low temperature scanning tunneling microscopy (STM) investigations performed in our laboratory1-5 on the self-assembly of the dipolar organic molecule 1-nitronaphthalene (NN) adsorbed on the reconstructed Au(111) surface. NN becomes chiral upon planar adsorption on the gold surface. We observe several coverage-driven structural transformations which are associated with simultaneous changes in the enantiomeric composition of the self-assembled molecular structures. At low coverages almost exclusively decamers with an 8:2 ratio of the enantiomers are formed. In a medium coverage range enantiopure one-dimensional molecular double chains prevail on the surface. Subsequently, molecules with opposite handedness are admixed until at monolayer coverage racemic one- and two-dimensional structures coexist. Modeling shows that hydrogen bonding causes the observed self-assembly. A subtle interplay between the electrostatic interactions among the molecules and their interaction with the reconstructed metal surface is the origin of the observed coverage-driven chiral phase transition in two dimensions.

[BibTeX]
@article{MBO_SRL00,
  author = {M. Böhringer and W.-D. Schneider and R. Berndt},
  title = {Two-dimensional self-assembly of supramolecular structures},
  journal = {Surf. Rev. Lett.},
  volume = {7},
  pages = {661--666},	
  year = {2000},
  url = {http://journals.wspc.com.sg/149/07/0705n06/S0218625X00000749.html},
  doi = {http://doi.org/10.1142/S0218625X00000749}
}
 
 
Role of the tip shape in light emission from the scanning tunneling microscope
J. Aizpurua, S. Apell, R. Berndt, Phys. Rev. B 62, 2065 (2000)

Abstract:
The influence of tip shape on the light produced by scanning tunneling microscopy (STM) is analyzed theoretically for the case of nobel metals where collective modes enhance the photon emission. We investigate a hyperbolic tip geometry where the aperture of the tip and its apex curvature can be changed independently. The electromagnetic field in the tip-sample region is calculated with use of the boundary charge method. The tunneling current is treated in a modified Tersoff and Hamann's theory. The aperture of the tip is found to control the overall shape of the emission spectrum while the radius of curvature of the apex is more important for the intensity. Experimentally observed variations of emission spectra may be understood in terms of different tip shapes. The lateral extent of the tip-induced charge density is strongly dependent on the tip shape and may reach near-atomic scale for sufficiently sharp tips. This spatial localization has direct implications for the resolution in photonic maps.

[BibTeX]
@article{JAV_PRB00,
  author = {J. Aizpurua and S.P. Apell and R. Berndt},
  title = {Role of the tip shape in light emission from the scanning tunneling microscope},
  journal = {Phys. Rev. B},
  volume = {62},
  pages = {2065--2073},	
  year = {2000},
  url = {http://link.aps.org/abstract/PRB/v62/p2065},
  doi = {http://doi.org/10.1103/PhysRevB.62.2065}
}
 
 
Dimensionality effects in the lifetime of surface states
J. Kliewer, R. Berndt, E. Chulkov, V. Silkin, P. Echenique, S. Crampin, Science 288, 1399 (2000)

Abstract:
A long standing discrepancy between experimental and theoretical values for the lifetimes of holes in the surface state electron bands on noble metal surfaces is resolved, with both found to have been in error. The ability of the scanning tunneling microscope to verify surface quality before taking spectroscopic measurements is exploited to remove the effects of defect scattering on experimental lifetimes, found to have been a significant contribution to prior determinations. A theoretical treatment of inelastic electron-electron scattering is developed which explicitly includes intra-band transitions within the surface state band. In our model two-dimensional decay channels dominate the electron-electron interactions that contribute to the hole decay, screened by the electron states of the underlying three-dimensional electron system.

[BibTeX]
@article{JKL_SCI00,
  author = {J. Kliewer and R. Berndt and E.V. Chulkov and V.M. Silkin and P.M. Echenique and S. Crampin},
  title = {Dimensionality effects in the lifetime of surface states},
  journal = {Science},
  volume = {288},
  pages = {1399--1402},	
  year = {2000},
  note = {cf. Electron Dynamics at Surfaces, M. Wolf, G. Ertl, Science 288, 1352-1353 (2000)},
  url = {http://dx.doi.org/10.1126/science.288.5470.1399},
  doi = {http://doi.org/10.1126/science.288.5470.1399}
}
 
cf. Electron Dynamics at Surfaces M. Wolf, G. Ertl, Science 288, 1352-1353 (2000)
 
Reversed surface corrugation in STM images on Au(111) by field-induced lateral motion of adsorbed molecules
M. Böhringer, K. Morgenstern, W.-D. Schneider, R. Berndt, Surf. Sci. 457, 37 (2000)

Abstract:
Submonolayer coverages of the organic molecule 1-nitronaphthalene adsorbed on the reconstructed Au(111) surface were investigated by scanning tunneling microscopy at 50 and 10 K. At 50 K, upon switching the polarity of the tunneling voltage a peculiar change in the image contrast is observed. At negative sample-tip bias voltage the dislocation lines of the Au(111) surface reconstruction are imaged as protrusions and molecular aggregates appear 0.15 nm higher than the substrate. At reversed bias, the interior of the fcc and hcp domains exhibits the same height as the molecular clusters, while the domain walls of the surface reconstruction appear as depressions with a strongly increased corrugation amplitude. At 10 K, for the same tunneling parameters, no such contrast reversal is observed. Controlled manipulation experiments at 10 K demonstrate that contrast reversal at 50 K is due to long-range attractive tip-molecule interactions which assemble small molecular aggregates below the tip apex.

[BibTeX]
@article{MBO_SSI00_2,
  author = {M. Böhringer and K. Morgenstern and W.-D. Schneider and R. Berndt},
  title = {Reversed surface corrugation in STM images on Au(111) by field-induced lateral motion of adsorbed molecules},
  journal = {Surf. Sci.},
  volume = {457},
  pages = {37--50},	
  year = {2000},
  url = {http://dx.doi.org/10.1016/S0039-6028(00)00368-X},
  doi = {http://doi.org/10.1016/S0039-6028(00)00368-X}
}
 
 
Low-temperature scanning tunnelling spectroscopy: Kondo effect and surface state lifetimes
W.-D. Schneider, R. Berndt, J. Electron. Spectrosc. Relat. Phenom. 109, 19 (2000)

Abstract:
The present review focusses on a local view of two important phenomena in condensed matter physics, the lifetime of electrons in surface states on noble metals and the scattering of conduction electrons at magnetic impurities: the Kondo effect. Spectroscopic signatures of both effects have been observed in the past by high-resolution photoemission which, however, has the drawback of averaging over a typical surface area of 1 mm^2. By combining the atomic-scale spatial resolution of the scanning tunneling microscope (STM) with meV energy resolution achievable in scanning tunneling spectroscopy (STS) the gap between predicted and measured surface state lifetimes has been closed and our understanding of the interaction of a single magnetic impurity with the conduction electrons of the non-magnetic host has been deepened.

[BibTeX]
@article{WDS_JESP00,
  author = {W.-D. Schneider and R. Berndt},
  title = {Low-temperature scanning tunnelling spectroscopy: Kondo effect and surface state lifetimes},
  journal = {J. Electron. Spectrosc. Relat. Phenom.},
  volume = {109},
  pages = {19--31},	
  year = {2000},
  url = {http://www.sciencedirect.com/science/article/pii/S0368204800001043},
  doi = {http://doi.org/10.1016/S0368-2048(00)00104-3}
}
 
 
Real Space Observation of a Chiral Phase Transition in a Two-Dimensional Organic Layer,\ Direkte Beobachtung eines chiralen Phasen�berganges in einer zweidimensionalen Molek�lschicht
M. Böhringer, W.-D. Schneider, R. Berndt, Angew. Chem. Int. Ed. 39, 792 (2000)

Abstract:
1-Nitronaphthalene adsorbs planar on Au(111) leading to two-dimensional chirality. The handedness of individual molecules is determined by high-resolution scanning tunnelling microscopy. At low coverages enantiopure linear molecular chains are observed. With increasing coverage molecules with opposite handedness are admixed until at monolayer coverage racemic structures prevail. The chiral phase transition is due to an interplay between electrostatic interactions among the molecules and their interaction with the Au(111) surface.

[BibTeX]
@article{MBO_ACIE00,
  author = {M. Böhringer and W.-D. Schneider and R. Berndt},
  title = {Real Space Observation of a Chiral Phase Transition in a Two-Dimensional Organic Layer,\ Direkte Beobachtung eines chiralen Phasen�berganges in einer zweidimensionalen Molek�lschicht},
  journal = {Angew. Chem. Int. Ed.},
  volume = {39},
  pages = {792--795},	
  year = {2000},
  url = {http://dx.doi.org/10.1002/(SICI)1521-3773(20000218)39:4<792::AID-ANIE792>3.0.CO;2-2},
  doi = {http://doi.org/10.1002/(SICI)1521-3773(20000218)39:4%3C792::AID-ANIE792%3E3.0.CO;2-2}
}
 
 
Direkte Beobachtung eines chiralen Phasenüberganges in einer zweidimensionalen Molekülschicht
M. Böhringer, W.-D. Schneider, R. Berndt, Angew. Chem. 112, 821 (2000)

Abstract:
1-Nitronaphthalin ist aufgrund einer planaren Adsorptionsgeometrie auf Au(111) 2D-chiral. Die Händigkeit der Moleküle lässt sich durch hochauflösende Rastertunnelmikroskopie direkt bestimmen. Bei niedriger Moleküldichte bilden sich enantiomerenreine molekulare Doppelketten. Mit zunehmender Bedeckung werden immer mehr Moleküle mit entgegengesetzter Händigkeit in das Konglomerat eingebaut, bis bei der vollen Monolage razemische Strukturen überwiegen. Der beobachtete chirale Phasenübergang ist die Folge eines Wechselspiels von elektrostatischen Wechselwirkungen zwischen den Molekülen und ihrer Wechselwirkung mit der Au(111)-Oberfläche.

[BibTeX]
@article{MBO_ACH00,
  author = {Böhringer, Matthias and Schneider, Wolf-Dieter and Berndt, Richard},
  title = {Direkte Beobachtung eines chiralen Phasenüberganges in einer zweidimensionalen Molekülschicht},
  journal = {Angew. Chem.},
  volume = {112},
  number = {4},
  pages = {821--825},
  publisher = {WILEY-VCH Verlag GmbH},	
  year = {2000},
  url = {http://dx.doi.org/10.1002/(SICI)1521-3757(20000218)112:4<821::AID-ANGE821>3.0.CO;2-N},
  doi = {http://doi.org/10.1002/(SICI)1521-3757(20000218)112:4%3C821::AID-ANGE821%3E3.0.CO;2-N}
}
 
 
Self-assembly of 1-nitronaphthalene on Au(111)
M. Böhringer, K. Morgenstern, W.-D. Schneider, M. Wühn, C. Wöll, R. Berndt, Surf. Sci. 444, 199 (2000)

Abstract:
We report low-temperature scanning tunneling microscopy and near-edge X-ray absorption fine structure investiga-tions of the organic molecule 1-nitronaphthalene adsorbed on the reconstructed Au(111) surface. Depending on the coverage, molecular structures of distinct dimensionality are observed. After saturation of the step edges with molecules, clusters form on the substrate terraces at coverages up to 0.15 monolayers (ML). The smallest clusters consist of three molecules and are stable at specific surface reconstruction sites only. In contrast, pinwheel-shaped clusters comprised of ten molecules are observed on various inequivalent sites of the reconstructed Au surface. For coverages larger than 0.2 ML one-dimensional molecular double chains prevail. The structure of the decamers and the chains is determined by intermolecular electrostatic forces, whereas their position and orientation are affected by the surface reconstruction. At saturation coverage a periodic two-dimensional close-packed arrangement of molecules that is independent of the surface reconstruction occurs simultaneously with one-dimensional structures along the uniaxial reconstruction domains. The structural features are discussed in terms of competing effects of intermolecular forces and the interaction with the substrate.

[BibTeX]
@article{MBO_SSI00,
  author = {M. Böhringer and K. Morgenstern and W.-D. Schneider and M. Wühn and Ch. Wöll and R. Berndt},
  title = {Self-assembly of 1-nitronaphthalene on Au(111)},
  journal = {Surf. Sci.},
  volume = {444},
  pages = {199--210},	
  year = {2000},
  url = {http://dx.doi.org/10.1016/S0039-6028(99)01039-0},
  doi = {http://doi.org/10.1016/S0039-6028(99)01039-0}
}
 
 
Low-Temperature Scanning Tunnelling Spectroscopy
R. Berndt, in Structure and Dynamics of heterogeneous Systems, P. Entel and D. Wolf (Hrsg.) , 116-123 (World Scientific, 2000)
[BibTeX]
@inbook{RBE_WSC00,
  author = {R. Berndt},
  chapter = {Low-Temperature Scanning Tunnelling Spectroscopy},
  title = {Structure and Dynamics of heterogeneous Systems},
  editor = {P. Entel and D.E. Wolf},
  pages = {116--123},
  publisher = {World Scientific},	
  year = {2000},
  url = {http://www.worldscientific.com/worldscibooks/10.1142/4370},
  doi = {http://doi.org/10.1142/9789812793652_0010},
  isbn = {978-981-02-4251-0}
}
 
 
Comment on "Physical Picture for Light Emission in Scanning Tunneling Microscopy''
P. Johansson, R. Berndt, J. Gimzewski, S. Apell, Phys. Rev. Lett. 84, 2034 (2000)

Abstract:
A Comment on the Letter by Mufei Xiao, Phys. Rev. Lett. 82, 1875 (1999). The authors of the Letter offer a Reply.

[BibTeX]
@article{PJO_PRL00,
  author = {P. Johansson and R. Berndt and J.K. Gimzewski and S.P. Apell},
  title = {Comment on "Physical Picture for Light Emission in Scanning Tunneling Microscopy''},
  journal = {Phys. Rev. Lett.},
  volume = {84},
  pages = {2034},	
  year = {2000},
  url = {http://link.aps.org/abstract/PRL/v84/p2034},
  doi = {0.1103/PhysRevLett.84.2034}
}
 
 
Two-dimensional self-assembly of magic supramolecular clusters
M. Böhringer, K. Morgenstern, W.-D. Schneider, R. Berndt, J. Phys. Cond. Mat. 11, 9871 (1999)

Abstract:
We report low-temperature scanning tunnelling microscope (STM) observations of magic two-dimensional supramolecular clusters formed after low-coverage deposition of 1-nitro-naphthalene (NN) molecules on a reconstructed Au(111) substrate. The clusters that consist predominantly of ten NN molecules are chiral and form a racemic mixture on the surface. STM manipulation of the clusters shows that their internal structure does not depend on the atomistic details of the substrate. Manipulation of individual molecules within the clusters hints at utility for nanoscale devices. The enantiomers of these supramolecular clusters are discriminated and separated in a molecular-scale analogue to Pasteur's experiment.

[BibTeX]
@article{MBO_JPCM99,
  author = {M. Böhringer and K. Morgenstern and W.-D. Schneider and R. Berndt},
  title = {Two-dimensional self-assembly of magic supramolecular clusters},
  journal = {J. Phys. Cond. Mat.},
  volume = {11},
  pages = {9871--9878},	
  year = {1999},
  url = {http://stacks.iop.org/JPhysCM/11/9871},
  doi = {http://doi.org/10.1088/0953-8984/11/49/305}
}
 
 
Stability of two-dimensional nanostructures
K. Morgenstern, E.L. gsgaard null, I. Stensgaard, F. Besenbacher, M. Böhringer, R. Berndt, F. Mauri, A. de Vita, R. Car, W.-D. Schneider, Appl. Phys. A 69, 559 (1999)

Abstract:
We investigate atomic and molecular nanostructures on metal surfaces by variable low temperature scanning tunnelling microscopy. In combination with molecular dynamics calculations we achieve a detailed understanding of the stability of these structures. Atomic nanostructures in homoepitaxial metallic systems are thermodynamically only metastable. Two-dimensional islands on Ag(110) decay above a threshold temperature of T_l=175 K. Caused by the anisotropy of the surface distinct decay behaviours exist above and below a critical temperature of T_c=220 K. Calculations based on effective medium potentials of the underlying rate limiting atomic processes allow us to identify the one-dimensional decay below T_c as well as the two-dimensional decay above T_c. In contrast to atoms, the intermolecular electrostatic interaction of polar molecules leads to thermodynamically stable structures. On the reconstructed Au(111) surface, the pseudo-chiral 1-Nitronaphthalin forms two-dimensional supermolecular clusters consisting predominantly of ten molecules. Comparison of images with submolecular resolution to local density calculations elucidates the thermodynamical stability as well as the internal structure of the decamers.

[BibTeX]
@article{KMO_APA99,
  author = {K. Morgenstern and E. Læ gsgaard and I. Stensgaard and F. Besenbacher and M. Böhringer and R. Berndt and F. Mauri and A. de Vita and R. Car and W.-D. Schneider},
  title = {Stability of two-dimensional nanostructures},
  journal = {Appl. Phys. A},
  volume = {69},
  pages = {559--569},	
  year = {1999},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s003390051472},
  doi = {http://doi.org/10.1007/s003390051472}
}
 
 
Surface-State Linewidth from Scanning Tunnelling Spectroscopy
R. Berndt, J. Li, W.-D. Schneider, S. Crampin, Appl. Phys. A 69, 503 (1999)

Abstract:
The STM can be used to investigate lifetimes of hot holes in a surface state at low temperatures. We analysed dI/dV-data from Ag(111) using detailed tunnelling calculations and a simple model and found an electron self-energy of Sigma = 4.9 ± 0.6 meV. The corresponding lifetime tau = 67 ± 8 fs is considerably higher than those determined by angle-resolved photoemission, although it remains below theoretical predictions. Spatially resolved dI/dV spectra reveal that the lifetime decreases drastically in proximity to defects such as surfaces steps.

[BibTeX]
@article{RBE_APA99,
  author = {R. Berndt and J. Li and W.-D. Schneider and S. Crampin},
  title = {Surface-State Linewidth from Scanning Tunnelling Spectroscopy},
  journal = {Appl. Phys. A},
  volume = {69},
  pages = {503--506},	
  year = {1999},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s003390051453},
  doi = {http://doi.org/10.1007/s003390051453}
}
 
 
Scanning Tunnelling Spectroscopy of Kondo Scattering from a Single Magnetic Impurity
R. Berndt, J. Li, W.-D. Schneider, B. Delley, Phys. Status Solidi B 215, 845 (1999)

Abstract:
Using low-temperature scanning tunnelling spectroscopy we investigate electron scattering from isolated Ce adatoms on Ag(111). d I/d V tunnelling spectra reveal a characteristic antiresonance around the Fermi energy which is not observed for nonmagnetic Ag adatoms. We interpret this spectrum as a Fano interference between delocalised sp-derived Ag states and the localised f-derived Kondo resonance.

[BibTeX]
@article{RBE_PSSB99,
  author = {R. Berndt and J. Li and W.-D. Schneider and B. Delley},
  title = {Scanning Tunnelling Spectroscopy of Kondo Scattering from a Single Magnetic Impurity},
  journal = {Phys. Status Solidi B},
  volume = {215},
  pages = {845--848},	
  year = {1999},
  url = {http://dx.doi.org/10.1002/(SICI)1521-3951(199909)215:1<845::AID-PSSB845>3.0.CO;2-0},
  doi = {http://doi.org/10.1002/(SICI)1521-3951(199909)215:1%3C845::AID-PSSB845%3E3.0.CO;2-0}
}
 
 
Tunneling spectroscopy of surface state scattering and confinement
J. Li, W.-D. Schneider, R. Berndt, S. Crampin, Surf. Sci. 422, 95 (1999)

Abstract:
Using low-temperature scanning tunnelling microscopy we have investigated confinement of electronic surface states to hexagonal islands and other nanoscale structures on Ag(111). Local spectroscopy and spatial maps of the differential conductance are analysed using simple models of the electronic structure. We find that the concept of confinement of a two-dimensional surface state applies down to very small structures, and observe in real space how proximity to defects affects surface state lifetimes.

[BibTeX]
@article{JTL_SSI99,
  author = {J. Li and W.-D. Schneider and R. Berndt and S. Crampin},
  title = {Tunneling spectroscopy of surface state scattering and confinement},
  journal = {Surf. Sci.},
  volume = {422},
  pages = {95--106},	
  year = {1999},
  url = {http://dx.doi.org/10.1016/S0039-6028(98)00890-5},
  doi = {http://doi.org/10.1016/S0039-6028(98)00890-5}
}
 
 
Separation of a Racemic Mixture of Two-Dimensional Molecular Clusters by Scanning Tunneling Microscopy,\ Trennung eines racemischen Gemisches zweidimensionaler molekularer Cluster mit dem Rastertunnelmikroskop
M. Böhringer, K. Morgenstern, W.-D. Schneider, R. Berndt, Angew. Chem. Int. Ed. 38, 821 (1999)

Abstract:
Adsorption of sub-monolayer amounts of 1-nitronaphthalene (NN) onto Au(111) leads to the aggregation of NN decamers which exhibit two-dimensional chirality. Using a scanning tunneling microscope the enantiomers of these supramolecular clusters are discriminated and separated from the racemic mixture present on the surface. The experiment is a molecular scale analogon to Pasteur's experiment.

[BibTeX]
@article{MBO_ACIE99,
  author = {M. Böhringer and K. Morgenstern and W.-D. Schneider and R. Berndt},
  title = {Separation of a Racemic Mixture of Two-Dimensional Molecular Clusters by Scanning Tunneling Microscopy,\ Trennung eines racemischen Gemisches zweidimensionaler molekularer Cluster mit dem Rastertunnelmikroskop},
  journal = {Angew. Chem. Int. Ed.},
  volume = {38},
  pages = {821--823},	
  year = {1999},
  note = {cf. glqq Highlightsgrqq in Angew. Chem. Int.Ed. 38, 2533-2536 (1999) und Angew. Chem. 111, 2691-2694 (1999)},
  url = {http://dx.doi.org/10.1002/(SICI)1521-3773(19990315)38:6<823::AID-ANIE823>3.0.CO;2-2},
  doi = {http://doi.org/10.1002/(SICI)1521-3773(19990315)38:6%3C823::AID-ANIE823%3E3.0.CO;2-2}
}
 
cf. Highlight in Angew. Chem. Int.Ed. 38, 2533-2536 (1999)
 
Trennung eines racemischen Gemisches zweidimensionaler molekularer Cluster mit dem Rastertunnelmikroskop
M. Böhringer, K. Morgenstern, W.-D. Schneider, R. Berndt, Angew. Chem. 111, 832 (1999)

Abstract:
Die Adsorption von Submonolagen von 1-Nitronaphthalin (NN) auf Au(111) führt zur Aggregation von NN-Decameren, die eine zweidimensionale Chiralität aufweisen und als racemisches Gemisch anfallen. In Analogie zu Pasteurs Experiment von 1848 werden mit einem Rastertunnelmikroskop auf molekularer Ebene die Enantiomere unterschieden und getrennt.

[BibTeX]
@article{MBO_ACH99,
  author = {Böhringer, Matthias and Morgenstern, Karina and Schneider, Wolf-Dieter and Berndt, Richard},
  title = {Trennung eines racemischen Gemisches zweidimensionaler molekularer Cluster mit dem Rastertunnelmikroskop},
  journal = {Angew. Chem.},
  volume = {111},
  number = {6},
  pages = {832--834},
  publisher = {WILEY-VCH Verlag GmbH},	
  year = {1999},
  note = {cf. glqq Highlightsgrqq in Angew. Chem. Int.Ed. 38, 2533-2536 (1999) und Angew. Chem. 111, 2691-2694 (1999)},
  url = {http://dx.doi.org/10.1002/(SICI)1521-3757(19990315)111:6<832::AID-ANGE832>3.0.CO;2-B},
  doi = {http://doi.org/10.1002/(SICI)1521-3757(19990315)111:6%3C832::AID-ANGE832%3E3.0.CO;2-B}
}
 
cf. Highlight in Angew. Chem. 111, 2691-2694 (1999)
 
Two-dimensional self-assembly of ``magic'' molecular clusters on a metal surface
M. Böhringer, K. Morgenstern, W.-D. Schneider, R. Berndt, F. Mauri, V. de Vita, R. Car, Phys. Rev. Lett. 83, 324 (1999)

Abstract:
Two-dimensional supramolecular clusters and chains are observed upon submonolayer deposition of 1-nitronaphthalene (NN) onto reconstructed Au(111). The molecules become pseudochiral upon adsorption. Their handedness is determined from high-resolution scanning tunneling microscope images and local-density calculations. Modeling shows that hydrogen bonds cause the observed self-assembly. Clusters and chains mutually interact via electrostatic repulsion.

[BibTeX]
@article{MBO_PRL99,
  author = {M. Böhringer and K. Morgenstern and W.-D. Schneider and R. Berndt and F. Mauri and V. de Vita and R. Car},
  title = {Two-dimensional self-assembly of ``magic'' molecular clusters on a metal surface},
  journal = {Phys. Rev. Lett.},
  volume = {83},
  pages = {324--327},	
  year = {1999},
  url = {http://link.aps.org/abstract/PRL/v83/p324},
  doi = {http://doi.org/10.1103/PhysRevLett.83.324}
}
 
 
Ordered surface alloying of Co monolayers on Cu(001)
F. Nouvertné, U. May, A. Rampe, M. Gruyters, U. Korte, R. Berndt, G. Güntherodt, Surf. Sci. 436, L653 (1999)

Abstract:
Monolayer films of Co on Cu(001) annealed at 180° C exhibit ordered c(2x2) regions as evidenced by STM images. The ordered surface alloy formation of Co-Cu(001) in the monolayer regime occurs in spite of the bulk immiscibility of Co-Cu and in contrast to the theoretically predicted instability of a c(2x2) ordered monolayer. RHEED and LEED exhibit superstructure-related reflections that corroborate this interpretation.

[BibTeX]
@article{FNO_SSI99,
  author = {F. Nouvertné and U. May and A. Rampe and M. Gruyters and U. Korte and R. Berndt and G. Güntherodt},
  title = {Ordered surface alloying of Co monolayers on Cu(001)},
  journal = {Surf. Sci.},
  volume = {436},
  pages = {L653--L660},	
  year = {1999},
  url = {http://dx.doi.org/10.1016/S0039-6028(99)00638-X},
  doi = {http://doi.org/10.1016/S0039-6028(99)00638-X}
}
 
 
Adsorption site determination of PTCDA on Ag(110) by manipulation of adatoms
M. Böhringer, W.-D. Schneider, K. Glöckler, E. Umbach, R. Berndt, Surf. Sci. 419, L95 (1998)

Abstract:
Simultaneous imaging of organic molecules and an underlying metallic substrate lattice is often hampered by tip-induced molecular motion, even at low temperatures. In the case of perylene-tetracarboxylic acid-dianhydride (PTCDA) on Ag(110), this problem is circumvented by using tip-induced motion of a coadsorbed Ag atom to obtain convenient markers of the substrate lattice. A model for the registry of PTCDA on Ag(110) is deduced.

[BibTeX]
@article{MBO_SSI98_2,
  author = {M. Böhringer and W.-D. Schneider and K. Glöckler and E. Umbach and R. Berndt},
  title = {Adsorption site determination of PTCDA on Ag(110) by manipulation of adatoms},
  journal = {Surf. Sci.},
  volume = {419},
  pages = {L95--L99},	
  year = {1998},
  url = {http://dx.doi.org/10.1016/S0039-6028(98)00733-X},
  doi = {http://doi.org/10.1016/S0039-6028(98)00733-X}
}
 
 
Surface state lifetime measured by scanning tunneling spectroscopy
J. Li, W.-D. Schneider, R. Berndt, O. Bryant, S. Crampin, Phys. Rev. Lett. 81, 4464 (1998)

Abstract:
Quasiparticle interactions broaden spectral features at surfaces, which can be measured using the scanning tunneling microscope (STM). We report the first study of lifetime effects on Shockley surface-state electrons using low-temperature STM spectroscopy. Data taken from Ag(111) are analyzed using detailed tunneling calculations and a simple model, and are found to correspond to a self-energy of Σ = 4.9 ± 0.6 meV. This is considerably below values determined by angle-resolved photoemission, but remains higher than theoretical predictions.

[BibTeX]
@article{JTL_PRL98_3,
  author = {J. Li and W.-D. Schneider and R. Berndt and O. Bryant and S. Crampin},
  title = {Surface state lifetime measured by scanning tunneling spectroscopy},
  journal = {Phys. Rev. Lett.},
  volume = {81},
  pages = {4464--4467},	
  year = {1998},
  url = {http://link.aps.org/abstract/PRL/v81/p4464},
  doi = {http://doi.org/10.1103/PhysRevLett.81.4464}
}
 
 
Photon emission induced by the scanning tunneling microscope
R. Berndt, M. Böhringer, Proc. SPIE 3272, 66 (1998)

Abstract:
The tunneling of electrons between the tip of a scanning tunneling microscopy (STM) and a sample is accompanied by the emission of photons. This luminescence phenomenon can be used to study local radiative processes at surfaces by combining the high spatial resolution of the STM and optical techniques. In this way, spatial maps of photon intensity modulations can be measured with lateral resolutions of less than 1 nm. Here we review the basic concepts of STM induced light emission and discuss recent results from adsorbed molecules.

[BibTeX]
@article{RBE_SPIE98,
  author = {R. Berndt and M. Böhringer},
  title = {Photon emission induced by the scanning tunneling microscope},
  journal = {Proc. SPIE},
  volume = {3272},
  pages = {66},
  publisher = {Int'l Society of Optical Engineers (SPIE), San Jose, Kalifornien},	
  year = {1998},
  url = {http://dx.doi.org/10.1117/12.307148},
  doi = {http://doi.org/10.1117/12.307148}
}
 
 
Scanning tunneling microscope-induced molecular motion and its effect on the image formation
M. Böhringer, W.-D. Schneider, R. Berndt, Surf. Sci. 408, 72 (1998)

Abstract:
The effect of tip-induced molecular motion on the appearance ofscanning tunneling microscope (STM) images of anthracene on Ag(110)was investigated for various tunneling parameters and at varioustemperatures. At 50 K isolated molecules can be imaged at hightunneling resistance. For increased tip - molecule interactionapparent one-dimensional and two-dimensional molecularsuperstructures arise in the STM images which are due to tip-inducedmotion, transient binding at specific substrate sites and repeatedimaging of a molecule. At still higher tip-molecule interactionstrength molecules can be dragged over the surfacesuch that an atomically resolved substrate lattice is discernible.The slid molecule acts as amplifier of the charge corrugation of themetallic surface.

[BibTeX]
@article{MBO_SSI98,
  author = {M. Böhringer and W.-D. Schneider and R. Berndt},
  title = {Scanning tunneling microscope-induced molecular motion and its effect on the image formation},
  journal = {Surf. Sci.},
  volume = {408},
  pages = {72--85},	
  year = {1998},
  url = {http://dx.doi.org/10.1016/S0039-6028(98)00151-4},
  doi = {http://doi.org/10.1016/S0039-6028(98)00151-4}
}
 
 
Electron confinement to nanoscale Ag islands on Ag(111): a quantitative study
J. Li, W.-D. Schneider R. Berndt, S. Crampin, Phys. Rev. Lett. 80, 3332 (1998)

Abstract:
Lateral confinement has been suggested as a possible mechanism for depopulation of surface state levels and concomitant modification of metal surface related properties. Studies to date give conflicting accounts of the effectiveness of confinement due to scattering at step edges. We present a quantitative study of surface states on nanoscale Ag islands on Ag(111), using low-temperature scanning tunneling microscopy and electronic structure calculations. These results confirm the validity of the confinement picture down to the smallest of island sizes.

[BibTeX]
@article{JTL_PRL98_2,
  author = {J. Li and W.-D. Schneider and R. Berndt and S. Crampin},
  title = {Electron confinement to nanoscale Ag islands on Ag(111): a quantitative study},
  journal = {Phys. Rev. Lett.},
  volume = {80},
  pages = {3332--3335},	
  year = {1998},
  url = {http://link.aps.org/abstract/PRL/v80/p3332},
  doi = {http://doi.org/10.1103/PhysRevLett.80.3332}
}
 
 
Low-temperature manipulation of Ag atoms and clusters on Ag(110) surfaces
J. Li, W.-D. Schneider, R. Berndt, Appl. Phys. A 66, S675 (1998)

Abstract:
We report on manipulation experiments performed with a scanning tunneling microscope (STM) on Ag(110) at T=50 K. At high tunneling currents (I=50 nA) the tip can move individual atoms and small clusters preferentially through troughs between densely packed atomic rows. At lower tunneling currents cross-channel motion along the diagonal of the surface unit cell occurs which may indicate adatom-surface atom exchange processes during the tip-induced motion. The interaction between the tip and the Ag adatom is shown to be attractive or repulsive depending on the polarity of the bias voltage. The transfer of Ag adatoms to the tip and the subsequent redeposition are characterized in terms of current versus distance measurements.

[BibTeX]
@article{JTL_APA98_2,
  author = {J. Li and W.-D. Schneider and R. Berndt},
  title = {Low-temperature manipulation of Ag atoms and clusters on Ag(110) surfaces},
  journal = {Appl. Phys. A},
  volume = {66},
  pages = {S675--S678},	
  year = {1998},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s003390051220},
  doi = {http://doi.org/10.1007/s003390051220}
}
 
 
Size-dependent light emission from mass-selected clusters
M.-H. Schaffner, F. Patthey, U. Heiz, W.-D. Schneider, O. Kuffer, H.-V. Roy, P. Fayet, J. Gimzewski, R. Berndt, Eur. Phys. J. D 2, 79 (1998)

Abstract:
The emission of photons in the visible wavelength range from mass-selected Ag^+_n, Cu^+_n, Pt^+_n and Pd^+_n (n = 1....5) clusters is observed. Photons are detected  10^-4$ s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy sputtering process used for the generation of these clusters.

[BibTeX]
@article{MHS_EPJD98,
  author = {M.-H. Schaffner and F. Patthey and U. Heiz and W.-D. Schneider and O. Kuffer and H.-V. Roy and P. Fayet and J.K. Gimzewski and R. Berndt},
  title = {Size-dependent light emission from mass-selected clusters},
  journal = {Eur. Phys. J. D},
  volume = {2},
  pages = {79--82},	
  year = {1998},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s100530050114},
  doi = {http://doi.org/10.1007/s100530050114}
}
 
 
Corrugation reversal in scanning tunneling microscope images of organic molecules
M. Böhringer, W.-D. Schneider, R. Berndt, K. Glöckler, M. Sokolowski, E. Umbach, Phys. Rev. B 57, 4081 (1998)

Abstract:
Submonolayer coverages of perylene-tetracarboxylic-dianhydride on Ag(110) were investigated with scanning tunneling microscopy (STM) at 295 and 50 K. The molecules form highly ordered rhombic islands which at 295 K coexist with molecules diffusing on the substrate terraces. At 50 K the molecular islands appear 1.4 Å higher than the Ag substrate in STM images, independent of the tunneling voltages and currents. At 295 K this apparent height is observed only at high tunneling resistances. Lowering of the resistance decreases the height difference until finally the contrast between islands and the surrounding substrate is reversed. At the same time, vacancies within islands show no contrast reversal. We explain the contrast reversal by trapping of molecules below the tip apex.

[BibTeX]
@article{MBO_PRB98,
  author = {M. Böhringer and W.-D. Schneider and R. Berndt and K. Glöckler and M. Sokolowski and E. Umbach},
  title = {Corrugation reversal in scanning tunneling microscope images of organic molecules},
  journal = {Phys. Rev. B},
  volume = {57},
  pages = {4081--4087},	
  year = {1998},
  url = {http://link.aps.org/abstract/PRB/v57/p4081},
  doi = {http://doi.org/10.1103/PhysRevB.57.4081}
}
 
 
Kondo scattering at a single magnetic impurity
J. Li, W.-D. Schneider, R. Berndt, B. Delley, Phys. Rev. Lett. 80, 2893 (1998)

Abstract:
Electron scattering of isolated Ce adatoms on Ag(111) surfaces was studied with a low-temperature scanning tunneling microscope. Tunneling spectra obtained on and near Ce reveal a characteristic dip around the Fermi energy which is absent for nonmagnetic Ag adatoms. This feature is detected over a few atomic diameters around Ce atoms at the surface. The transition matrix element from the localised f electron to the tunnel-current carrying continuum states bears a strong resemblance to discrete autoionised states. We interpret the dip spectrum as a Fano interference for the limit where the f orbital has a very small matrix element.

[BibTeX]
@article{JTL_PRL98,
  author = {J. Li and W.-D. Schneider and R. Berndt and B. Delley},
  title = {Kondo scattering at a single magnetic impurity},
  journal = {Phys. Rev. Lett.},
  volume = {80},
  pages = {2893--2896},	
  year = {1998},
  url = {http://link.aps.org/abstract/PRL/v80/p2893},
  doi = {http://doi.org/10.1103/PhysRevLett.80.2893}
}
 
 
Analysis of spectroscopic scanning tunneling microscope images
J. Li, W.-D. Schneider, R. Berndt, Appl. Phys. A 66, S167 (1998)

Abstract:
Electron scattering from steps on the Ag(111) surface has been studied by spectroscopic scanning tunneling microscope (STM) images of the differential conductance (d I/d V). Modeling shows that near steps the features of dI/dV deviate significantly from those of the underlying local density of states. These deviations are due to variations of the vertical tip position which exponentially affect the tunneling barrier transmission and, hence, d I/d V.

[BibTeX]
@article{JTL_APA98,
  author = {J. Li and W.-D. Schneider and R. Berndt},
  title = {Analysis of spectroscopic scanning tunneling microscope images},
  journal = {Appl. Phys. A},
  volume = {66},
  pages = {S167--S169},	
  year = {1998},
  url = {http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s003390051123},
  doi = {http://doi.org/10.1007/s003390051123}
}
 
 
Highly ordered structures and submolecular scanning tunneling microscopy contrast of PTCDA and DM-PBDCI monolayers on Ag(111) and Ag(110)
K. Glöckler, C. Seidel, A. Soukopp, M. Sokolowski, E. Umbach, M. Böhringer, W.-D. Schneider, R. Berndt, Surf. Sci. 405, 1 (1998)

Abstract:
Highly ordered monolayers of two perylene derivatives (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride ( PTCDA) and N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DM-PBDCI)) were prepared by vacuum sublimation on Ag(111) and Ag(110) surfaces. Using scanning tunnelling microscopy (STM) and low energy electron diffraction, the nucleation, growth, step site interaction, and superstructures were investigated and compared. All adsorbate structures are commensurate, with the exception of DM-PBDCI on Ag( 111). A similar, but not identical, submolecular STM resolution was obtained for both molecules and on both surfaces. The local distribution shows ten dominant intensity maxima per molecule and corresponds to that of the lowest unoccupied orbital. From these results we draw conclusions concerning the tunnelling mechanism, the adsorbate-substrate, and the adsorbate-adsorbate interactions, which are discussed in relation to the formerly published results on the electronic structure of PTCDA/Ag(111).

[BibTeX]
@article{KGL_SSI98,
  author = {K. Glöckler and C. Seidel and A. Soukopp and M. Sokolowski and E. Umbach and M. Böhringer and W.-D. Schneider and R. Berndt},
  title = {Highly ordered structures and submolecular scanning tunneling microscopy contrast of PTCDA and DM-PBDCI monolayers on Ag(111) and Ag(110)},
  journal = {Surf. Sci.},
  volume = {405},
  pages = {1--20},	
  year = {1998},
  url = {http://dx.doi.org/10.1016/S0039-6028(97)00888-1},
  doi = {http://doi.org/10.1016/S0039-6028(97)00888-1}
}
 
 
Light measurements
R. Berndt, in Procedures in Scanning Probe Microscopies, R. Colton (Hrsg.) , (John Wiley and Sons Ltd., Chichester, UK, 1998)
[BibTeX]
@inbook{RBE_WIL98,
  author = {R. Berndt},
  chapter = {Light measurements},
  title = {Procedures in Scanning Probe Microscopies},
  editor = {R.J. Colton},
  publisher = {John Wiley and Sons Ltd., Chichester, UK},	
  year = {1998},
  isbn = {978-0471959120}
}
 
 
Photon emission from the scanning tunneling microscope
R. Berndt, in Scanning Probe Microscopy, R. Wiesendanger (Hrsg.) , 97-134 (Springer, Heidelberg, 1998)
[BibTeX]
@inbook{RBE_SPR98,
  author = {R. Berndt},
  chapter = {Photon emission from the scanning tunneling microscope},
  title = {Scanning Probe Microscopy},
  editor = {R. Wiesendanger},
  series = {Springer Series on Nanoscience and Technology},
  pages = {97--134},
  publisher = {Springer, Heidelberg},	
  year = {1998}
}
 
 
Local density of states from spectroscopic scanning tunneling microscope images: Ag(111)
J. Li, W.-D. Schneider, R. Berndt, Phys. Rev. B 56, 7656 (1997)

Abstract:
Electron scattering from steps on the Ag(111) surface has been studied by scanning tunneling microscopy (STM) and spectroscopic STM images of the differential conductance (dI/dV). The amplitudes and positions of maxima of dI/dV deviate significantly from those of the local density of states (LDOS). These deviations are due to variations of the vertical tip position which exponentially affect the tunneling barrier transmission and, hence, dI/dV. We show that the LDOS can be recovered from simultaneous topographic and spectro-scopic measurements.

[BibTeX]
@article{JTL_PRB97,
  author = {J. Li and W.-D. Schneider and R. Berndt},
  title = {Local density of states from spectroscopic scanning tunneling microscope images: Ag(111)},
  journal = {Phys. Rev. B},
  volume = {56},
  pages = {7656--7659},	
  year = {1997},
  url = {http://link.aps.org/abstract/PRB/v56/p7656},
  doi = {http://doi.org/10.1103/PhysRevB.56.7656}
}
 
 
Transition from three-dimensional to two-dimensional faceting of Ag(110) induced by Cu-phthalocyanine
M. Böhringer, R. Berndt, W.-D. Schneider, Phys. Rev. B 55, 1384 (1997)

Abstract:
At submonolayer coverages Cu-phthalocyanine (CuPc) induces faceting of misoriented Ag(110) into three coexisting orientational phases. CuPc-decorated kinks precipitate into an azimuthally rotated facet, while the interaction of CuPc with the remaining kink-depleted steps causes step bunching in a polar transition. Local deviations from the CuPc-induced equilibrium surface morphology are caused by kinetic constraints attributed to the dominating interaction with kinks. At monolayer coverage a rigid molecular superstructure prevents large scale mass transport and allows only for microfaceting.

[BibTeX]
@article{MBO_PRB97,
  author = {M. Böhringer and R. Berndt and W.-D. Schneider},
  title = {Transition from three-dimensional to two-dimensional faceting of Ag(110) induced by Cu-phthalocyanine},
  journal = {Phys. Rev. B},
  volume = {55},
  pages = {1384--1387},	
  year = {1997},
  url = {http://link.aps.org/abstract/PRB/v55/p1384},
  doi = {http://doi.org/10.1103/PhysRevB.55.1384}
}
 
 
Light emission induced by the scanning tunneling microscope
R. Berndt, E.L. Bullock, in Physics of Surfaces, A. Hoareau (Hrsg.) , 51-60 (Editions Frontières, Gif-sur-Yvette, 1996)
[BibTeX]
@inbook{RBE_EFR96,
  author = {R. Berndt and E. L. Bullock},
  chapter = {Light emission induced by the scanning tunneling microscope},
  title = {Physics of Surfaces},
  editor = {A. Hoareau},
  pages = {51--60},
  publisher = {Editions Frontières, Gif-sur-Yvette},	
  year = {1996}
}
 
 
STM induced photon emission from Au(110) - the role of the topography
R. Berndt, in Near field optics: Imaging and Storing with Photonic Fields, M. Nieto-Vesperinas (Hrsg.) NATO ASI Series E 319, 175-180 (Kluwer, Dordrecht, 1996)
[BibTeX]
@inbook{RBE_NASI96,
  author = {R. Berndt},
  chapter = {STM induced photon emission from Au(110) - the role of the topography},
  title = {Near field optics: Imaging and Storing with Photonic Fields},
  editor = {M. Nieto-Vesperinas},
  series = {NATO ASI Series E},
  volume = {319},
  pages = {175--180},
  publisher = {Kluwer, Dordrecht},	
  year = {1996}
}
 
 
Tip-Assisted Diffusion on Ag(110) in Scanning Tunneling Microscopy
J. Li, R. Berndt, W.-D. Schneider, Phys. Rev. Lett. 76, 1888 (1996)

Abstract:
The influence of the tip in a scanning tunneling microscope on the atomic motion of Ag on Ag(110) is investigated at T = 50 and 295 K. At T = 50 K the tip can move single Ag atoms preferentially along [110] via an attractive interaction. At T = 295 K, the tip can displace monatomic steps over distances as large as several hundred Å. The structures thus created decay on a time scale of minutes. In contrast to prevailing assumptions significant tip-induced disturbances of the equilibrium shape of steps are observed even at sub-nA tunneling currents.

[BibTeX]
@article{JTL_PRL96,
  author = {J. Li and R. Berndt and W.-D. Schneider},
  title = {Tip-Assisted Diffusion on Ag(110) in Scanning Tunneling Microscopy},
  journal = {Phys. Rev. Lett.},
  volume = {76},
  pages = {1888--1891},	
  year = {1996},
  note = {cf. J.K. Gimzewski, Atoms get a big push, or is that a pull? in Physics World, Nov. 1997, pp. 27-28},
  url = {http://link.aps.org/abstract/PRL/v76/p1888},
  doi = {http://doi.org/10.1103/PhysRevLett.76.1888}
}
 
cf. J.K. Gimzewski, Atoms get a big push, or is that a pull? in Physics World, Nov. 1997, pp. 27-28
 
Discommensurations, epitaxial growth and island formation in Ge(111):Cu
M. Böhringer, Q. Jiang, R. Berndt, W.-D. Schneider, J. Zegenhagen, Surf. Sci. 367, 245 (1996)

Abstract:
We investigated surface reconstructions induced by monolayer coverages of Cu on Ge(111) using scanning tunneling microscopy (STM) at room temperature (RT) and 50 K. Following annealing to moderate temperatures (≈ 100°C) a discommensurate, two-dimensional domain superlattice with hexagonal symmetry is observed. Within the domains, atomic resolution showing a hexagonal arrangement of surface atoms with slightly increased lattice parameter compared to the substrate is observed by STM, but only at cryogenic temperatures. We attribute this to dynamic processes happening at RT which are prohibited at 50 K. Three alternative microscopic models for the interior of the domains of the discommensurate phase are proposed. The first with stoichiometry CuGe and Cu substituting for Ge in the surface layer and a stacking fault in half of the domains. The second with stoichiometry CuGe_2 and Cu imbedded in the Ge surface layer. The third model with stoichiometry Cu_2Ge and two Cu atoms per (1 × 1) surface unit cell in substitutional and H_3 sites. The increased lattice constant produces the discommensurations which are thus the result of adsorbate induced stress. Upon raising the annealing temperature, larger and larger parts of the surface are depleted of Cu and exhibit the c(2 × 8) reconstruction of clean Ge(111). Decreasing areas show the domain superstructure, which thus proves to be thermodynamically unstable and most of the Cu appears to be incorporated in 3-D islands, probably consisting of an epitaxial Cu germanide.

[BibTeX]
@article{MBO_SSI96,
  author = {M. Böhringer and Q. Jiang and R. Berndt and W.-D. Schneider and J. Zegenhagen},
  title = {Discommensurations, epitaxial growth and island formation in Ge(111):Cu},
  journal = {Surf. Sci.},
  volume = {367},
  pages = {245--260},	
  year = {1996},
  url = {http://dx.doi.org/10.1016/S0039-6028(96)00874-6},
  doi = {http://doi.org/10.1016/S0039-6028(96)00874-6}
}
 
 
Vicinal surfaces of Au(110) and Ag(110) investigated by scanning tunneling microscopy
J. Li, R. Gaisch, R. Berndt, W.-D. Schneider, J. Vac. Sci. Technol. B 14, 1149 (1996)

Abstract:
We report scanning tunneling microscopy results obtained on nominally (110) oriented, slightly miscut Au and Ag surfaces studied in ultrahigh vacuum at ambient and low temperatures (50 K). On these surfaces extended areas comprised of vicinal planes were observed and they exhibit intriguing step structures. An analysis of these planes in terms of their orientation, atomic structures, and steps is presented.

[BibTeX]
@article{JTL_JVSTB96,
  author = {J. Li and R. Gaisch and R. Berndt and W.-D. Schneider},
  title = {Vicinal surfaces of Au(110) and Ag(110) investigated by scanning tunneling microscopy},
  journal = {J. Vac. Sci. Technol. B},
  volume = {14},
  pages = {1149--1152},	
  year = {1996},
  url = {http://link.aip.org/link/?JVB/14/1149},
  doi = {http://doi.org/10.1116/1.588418}
}