Jouko Nieminen

Imaging water on Ag(111): Field induced reorientation and contrast inversion

Water adsorbed on Ag(111) at 70 K forms circular clusters that consist of six molecules. In scanning tunneling microscopy, this cyclic hexamer is imaged as a protrusion for voltages below V(SS)=-93 meV and as a depression for voltages above V(SS). The electronic density of states, however, increases around V(SS). We explain this counterintuitive result with the aid of calculated images by a change from constructive to destructive interference between different tunneling channels due to a field induced reorientation of the molecule under the tunneling tip.

Far-ranged transient motion of “hot” oxygen atoms upon dissociation

Scanning tunneling microscopy at low temperature reveals that upon dissociative adsorption of oxygen on Ag(001) “hot” adatoms have separated in a far-ranged transient motion to two different intrapair distances around 2 and 4 nm, corresponding to 7 and 14 surface lattice constants, respectively. Manipulation experiments on oxygen atoms displaying different contrasts in the images and model calculations suggest that the transient motion ends up not only in the stable fourfold hollow site but also in two metastable sites.

Origin of the high-energy kink in the photoemission spectrum of the high-temperature superconductor Bi2Sr2CaCu2O8

Susmita Basak, Tanmoy Das, Hsin Lin, J. Nieminen, M. Lindroos, R.S. Markiewicz, and A. Bansil 1 Physics Department, Northeastern University, Boston MA 02115, USA 2 Institute of Physics, Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland SMC-INFM-CNR, Dipartimento di Fisica, Università di Roma “La Sapienza”, P. Aldo Moro 2, 00185 Roma, Italy. ISC-CNR, Via dei Taurini 19, 00185 Roma

Role of translational and vibrational energy in the dissociative chemisorption of methane on Pd{110}

Abstract Dissociative adsorption of methane has been investigated on Pd {1 1 0} by using molecular beam surface scattering. The initial sticking probability has been determined in the translational energy range of 7–95 kJ/mol and at selected vibrational energies from 300 to 700 K. The measured initial sticking probability is found to increase strongly with both translational and vibrational energy of CH4 molecules. The activation of the dissociative chemisorption of CH4 induced by the vibrational energy is shown to depend on the translational energy and is attributed to the excitation of the bending modes of the incident molecule. We have also performed molecular dynamics simulations to investigate the dissociation mechanism theoretically. The simulations clearly demonstrate that an efficient energy transfer occurs upon adsorption between the translational and vibrational energies of the incident CH4 molecule, which thereby facilitates the deformation of the molecular structure of CH4 resulting in dissociation.

Mechanism of lubrication by a thin solid film on a metal surface

Molecular dynamics simulations of frictional sliding of a tip over a flat substrate in the presence of a lubricating solid film of one or two atomic layers thickness are presented. The role of adhesion in promoting wear is discussed by reference to earlier simulations of frictional sliding in the absence of a lubricating layer. Two conditions for lubrication are identified. First, the shear strength of the interface between the tip and the film must be lower than the shear strength of the tip or the underlying substrate. Secondly, the film must have a sufficient strength in compression to prevent penetration of the film by the tip. The importance of lubrication in obtaining images from the frictional force microscope is also discussed.

Temperature dependence of surface reconstructions of Au on Pd(110).

Surface reconstructions of Au film on Pd(110) substrate are studied using a local Einstein approximation to quasiharmonic theory with the Sutton-Chen interatomic potential. Temperature dependent surface free energies for different coverages and surface structures are calculated. Experimentally observed transformations from

Electrically tunable localized tunneling channels in silicene nanoribbons

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Submolecular imaging of chloronitrobenzene isomers on Cu(111).

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Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS 2

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Nanoscale interplay of strain and doping in a high-temperature superconductor

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