Université de Neuchâtel

On the search for Fermi surface nesting in quasi-2D materials

Aebi, Philipp ; Pillo, Th. ; Berger, Helmuth ; Lévy, F.

In: Journal of Electron Spectroscopy and Related Phenomena, 2001, vol. 117-118, p. 433-449

We investigate a number of isostructural, quasi-two dimensional transition metal dichalcogenides with respect to Fermi surface nesting. Using angle-resolved photoemission we find no clear evidence for Fermi surface nesting as a key scenario for charge density wave formation in these materials. However, interesting and unusual behavior has been discovered. For 1T-TaS2 in the...

Université de Neuchâtel

A monochromatized multiple energy laboratory UV source for k-space imaging

Pillo, Th. ; Patthey, L. ; Boschung, E. ; Hayoz, J. ; Aebi, Philipp ; Schlapbach, Louis

In: Journal of Electron Spectroscopy and Related Phenomena, 1998, vol. 97, no. 3, p. 243-252

A laboratory set-up for ultraviolet (UV) photoelectron spectroscopy combining a high intensity UV source and a toroidal UV monochromator, both being commercially available, is described. The source is modified in order to maximize the solid angle collected by the monochromator. Scanning its exit arm length allows for the optimization of the photon intensity as well as the energy resolution by...

Université de Neuchâtel

Geometrical and electronic structure of Pd clusters on graphite

Bovet, M. ; Boschung, E. ; Hayoz, J. ; Pillo, Th. ; Dietler, G. ; Aebi, Philipp

In: Surface Science, 2001, vol. 473, no. 1-2, p. 17-24

Pd clusters formed by physical vapor deposition at room temperature (RT) on highly oriented pyrolytic graphite were investigated by a combination of X-ray photoelectron spectroscopy and diffraction, angle-resolved ultraviolet photoelectron spectroscopy, scanning tunneling microscopy and calculations based on the local density functional theory. Different coverages with nominally 3, 5 and 10 Å...

Université de Neuchâtel

Growth of Au on Ag(110): electronic structure by photoemission

Hayoz, J. ; Pillo, Th. ; Naumovic, D. ; Aebi, Philipp ; Schlapbach, Louis

In: Surface Science, 1999, vol. 433-435, p. 104-108

Au films, from the submonolayer range up to eight monolayers, have been deposited in situ at 300 K. The electronic structure has been probed by ultra-violet valence-band photoemission. The discussion of our findings is based on a detailed knowledge of the geometrical structure of each film. With increasing Au coverage the valence-band structure changes from Ag- to Au-bulk-like. At intermediate Au...

Université de Neuchâtel

Photoelectron emission from nitrogen- and boron-doped diamond (100) surfaces

Diederich, L. ; Küttel, O. M. ; Ruffieux, P. ; Pillo, Th. ; Aebi, Philipp ; Schlapbach, Louis

In: Surface Science, 1998, vol. 417, no. 1, p. 41-52

The nitrogen-doped (N-doped), type Ib, synthetic diamond (100) surface was investigated by means of X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Photoelectron emission data from the boron-doped (B-doped) and the N-doped diamond (100) surfaces were compared and permitted the energy band diagrams for these differently terminated surfaces to be drawn. We...

Université de Neuchâtel

Angle-scanned photoemission: Fermi surface mapping and structural determination

Aebi, Philipp ; Fasel, Roman ; Naumovic, D. ; Hayoz, J. ; Pillo, Th. ; Bovet, M ; Agostino, R. G. ; Patthey, L. ; Schlapbach, Louis ; Gil, F. P. ; Berger, Helmuth ; Kreutz, T. J. ; Osterwalder, Jürg

In: Surface Science, 1998, vol. 402-404, p. 614-622

A brief survey of the angle-scanned photoemission technique is given. It incorporates two complementary methods in one: 1. Mapping of X-ray excited photoelectron intensities over virtually the complete hemisphere above the sample surface results in extended data sets where important surface-geometrical structure information is extracted and even “fingerprinting” is possible. This...

Université de Neuchâtel

Fine structure in high-resolution photoemission spectra of quasi-two-dimensional 1T-TaS2

Pillo, Th. ; Hayoz, J. ; Naumovic, D. ; Berger, Helmuth ; Perfetti, L. ; Gavioli, L. ; Taleb-Ibrahimi, A. ; Schlapbach, Louis ; Aebi, Philipp

In: Physical Review B, 2001, vol. 64, no. 245105, p. 1-4

Using high-resolution angle-resolved photoemission spectroscopy (ARPES), we examined the charge density wave (CDW) compound 1T-TaS2 as a function of the photon energy (energy range from 11 up to 33 eV) for both quasicommensurate (QC) and commensurate (C) CDW phases. While the QC-phase normal emission ARPES spectra coincide with previous results, normal emission spectra of the C...

Université de Neuchâtel

Photoemission of bands above the Fermi level: The excitonic insulator phase transition in 1T-TiSe2

Pillo, Th. ; Hayoz, J. ; Berger, Helmuth ; Lévy, F. ; Schlapbach, Louis ; Aebi, Philipp

In: Physical Review B, 2000, vol. 61, no. 23, p. 16213-16222

High-resolution angle-resolved photoemission spectroscopy (ARPES) was used to investigate the transition metal dichalcogenide (TMC) 1T-TiSe2 above and below the phase transition. We find that this system fulfills special conditions such as narrow band width and flat dispersion for bands within 5kBT of the Fermi energy. These prerequisites allow ARPES to observe...

Université de Neuchâtel

Interplay between electron-electron interaction and electron-phonon coupling near the Fermi surface of 1T-TaS2

Pillo, Th. ; Hayoz, J. ; Berger, Helmuth ; Fasel, Roman ; Schlapbach, Louis ; Aebi, Philipp

In: Physical Review B, 2000, vol. 62, no. 7, p. 4277-4287

We present a detailed high-resolution angle-resolved photoemission study of the electronic band structure of the room-temperature quasicommensurate charge-density-wave phase of 1T-TaS2. In particular, we show that no crossings of the Fermi level are visible in the complete Brillouin zone, indicating that an electron-electron correlation-induced pseudogap in the Ta 5d...

Université de Neuchâtel

Experimental evidence for kinetically determined intermixed Volmer-Weber growth in thin-film deposition of Au on Ag(110)

Hayoz, J. ; Pillo, Th. ; Fasel, R. ; Schlapbach, Louis ; Aebi, Philipp

In: Physical Review B, 1999, vol. 59, no. 24, p. 15975-15989

Au films, from the submonolayer range up to 11 ML, have been deposited in situ at 300 K. The geometrical structures of these films have been investigated combining full-hemispherical x-ray photoelectron diffraction, low-energy electron diffraction (LEED), low-energy ion-scattering spectroscopy, and scanning tunneling microscopy leading to an intermixed Volmer-Weber growth model. The results...