1987 - 1990

Scanning tunneling optical microscopy (STOM) of silver nanostructures
R. Berndt, A. Baratoff, J. Gimzewski, in Scanning Tunneling Microscopy and Related Methods, R. Behm, N. Garcia and H. Rohrer (Hrsg.) NATO ASI Series E 184, 269-280 (Kluwer, Dordrecht, 1990)

Abstract:
Local photon emission properties in the visible range of granular and island silver films have been characterized using STM. The experimental data are discussed in the light of model calculations. The observed fluorescence spectra and their dependence on tunnel voltage are interpreted theoretically in terms of radiative decay of local surface Plasmons excited dominantly via inelastic tunneling. Spatial mapping of the resulting integrated light intensity (photon maps) reveals a close relation to topographic features. The sharp spatial contrast, lack of significant polarity dependence, and the detection of fieid emission resonances in isochromat photon spectra favor inelastic tunneling as the dominant process.

[BibTeX]
@inbook{RBE_NASI90,
  author = {R. Berndt and A. Baratoff and J.K. Gimzewski},
  chapter = {Scanning tunneling optical microscopy (STOM) of silver nanostructures},
  title = {Scanning Tunneling Microscopy and Related Methods},
  editor = {R.J. Behm and N. Garcia and H. Rohrer},
  series = {NATO ASI Series E},
  volume = {184},
  pages = {269--280},
  publisher = {Kluwer, Dordrecht},
  address = {Dordrecht},	
  year = {1990},
  url = {http://dx.doi.org/10.1007/978-94-015-7871-4_13},
  doi = {http://doi.org/10.1007/978-94-015-7871-4},
  isbn = {978-94-015-7871-4}
}
 
 
Evidence for coupled rotational and phonon quantum excitations in the scattering of a nearly monoenergetic HD beam from the Ni(001) surface
R. Berndt, J. Toennies, C. Wöll, J. Chem. Phys. 92, 1468 (1990)

Abstract:
Angular distributions and time-of-flight spectra of a nearly monoenergetic (Δ v/v ≈ 2 % FWHM) He seeded HD beam (k_i = 6.80 -1, E_i = 32 meV) have been measured after scattering from a Ni(001) single-crystal surface along the left⟨ 100 right⟩ azimuth. The most intense peaks in the angular distributions are attributed to diffraction with rotational excitation while the rotationally elastic diffraction peaks are an order of magnitude smaller. All the time-of-flight distributions reveal intense peaks at Δ E=-11.06 meV corresponding to the HD rotational transition j_i = 0 → j_f = 1. The rotational energy loss observed at angles between the diffraction peaks is attributed to incoherent inelastic scattering at defects. The other inelastic peaks in the time-of-flight spectra can be assigned to phonons which are created or annihilated in the rotationally inelastic collisions. The measured phonon dispersion curves suggest a predominant interaction with the transverse bulk edge and not with the Rayleigh mode. These results provide the first direct evidence for a coupling of rotational transitions to the phonons of a metal surface. The pronounced rotational inelasticity at step edges does not support the widely held view that nonactivated chemisorption occurs at step edges.

[BibTeX]
@article{RBE_JCP90_2,
  author = {R. Berndt and J.P. Toennies and Ch. Wöll},
  title = {Evidence for coupled rotational and phonon quantum excitations in the scattering of a nearly monoenergetic HD beam from the Ni(001) surface},
  journal = {J. Chem. Phys.},
  volume = {92},
  pages = {1468--1477},	
  year = {1990},
  url = {http://link.aip.org/link/?JCP/92/1468},
  doi = {http://doi.org/10.1063/1.458105}
}
 
 
Helium atom scattering from CO adsorbed at steps on Ni(001)
R. Berndt, B. Hinch, J. Toennies, C. Wöll, J. Chem. Phys. 92, 1435 (1990)

Abstract:
Diffraction of helium atoms from randomly distributed step edges on the otherwise smooth (001) surface of Ni has been observed. Measurements for different azimuths near the left⟨ 100 right⟩ direction indicate that the step edges are lined up perpendicular to the left⟨ 100 right⟩ direction. The effect of CO adsorption on both the amplitude of the diffraction oscillations and also on specular scattering has been studied. The in-plane diffraction oscillations from the steps and the specular peak intensity show a similar attenuation with CO adsorption. This is interpreted in terms of a simple model for the effect of adsorption on the step diffraction oscillations. With increasing CO adsorption, the step edge diffraction patterns are also found to be slightly shifted suggesting a continuous change in step edge shape with adsorption.

[BibTeX]
@article{RBE_JCP90,
  author = {R. Berndt and B.J. Hinch and J.P. Toennies and Ch. Wöll},
  title = {Helium atom scattering from CO adsorbed at steps on Ni(001)},
  journal = {J. Chem. Phys.},
  volume = {92},
  pages = {1435--1441},	
  year = {1990},
  url = {http://link.aip.org/link/?JCP/92/1435},
  doi = {http://doi.org/10.1063/1.458102}
}
 
 
Helium atom scattering studies of thermal energy vibrations on clean and adsorbate-covered Ni(100) surfaces
R. Berndt, J. Toennies, C. Wöll, J. Electron. Spectrosc. Relat. Phenom. 44, 183 (1987)

Abstract:
Vibrations at a Ni(100) surface have been studied by Helium atom scattering. Adsorption of various adsorbates (CO,H,O) leads to characteristic changes and new features in the phonon spectrum of the clean surface. The dispersion curves for the clean substrate are compared to recent EELS data. Experimentally determined values for the frequency of the hindered translation of adsorbed CO-molecules strongly deviate from theoretical predictions.

[BibTeX]
@article{RBE_JESP87,
  author = {R. Berndt and J.P. Toennies and Ch. Wöll},
  title = {Helium atom scattering studies of thermal energy vibrations on clean and adsorbate-covered Ni(100) surfaces},
  journal = {J. Electron. Spectrosc. Relat. Phenom.},
  volume = {44},
  pages = {183--196},	
  year = {1987},
  url = {http://dx.doi.org/doi:10.1016/0368-2048(87)87019-6},
  doi = {http://doi.org/10.1016/0368-2048(87)87019-6}
}