Publications

2004

• Spin-dependent magnetoresistance in multiwall carbon nanotubes
  
  • Hoffer X.
  • Klinke C.
  • M. Bonard J.
  • Gravier L.
  • E. Wegrowe J.
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2004, 67, pp.103. The spin-dependent transport in multiwall carbon nanotubes, obtained by chemical vapour deposition in porous alumina membranes, has been investigated. The zero-bias anomaly is shown to follow the typical power law GT(-alpha) (eV/kT). In the nanotubes contacted with Ni pads, the magnetoresistance due to the spin-polarised current (SD-MR) is destroyed. In the case of those contacted with Co pads, however, the SD-MR is observed. These measurements show that both the observation of a typical scaling law of the conductance (for nanotubes tip to 1.5 mum) and a short spin diffusion length (less than 0.15 mum with nickel contacts and 0.7 mum with cobalt contacts) coexist through the nanotube. This observation may be interpreted in terms of a reminiscence of the Luttinger-liquid behaviour with spin-charge separation
• Spin-dependent thermopower in Co/Cu multilayer nanowires
  
  • Gravier L.
  • Fabian A.
  • Rudolf A.
  • Cachin A.
  • E. Wegrowe J.
  • P. Ansermet J.
  Journal of Magnetism and Magnetic Materials, Elsevier, 2004, 271, pp.153. The magnetic field dependence of the thermoelectrical power of a series of Co/Cu multilayered nanowires grown by electrodeposition in a polymer matrix is almost that predicted by the Mott formula in the temperature range of 15300 K. Application of the two-current model to thermopower yields (S-up arrow - S-down arrow)/(S-up arrow + S-down arrow) the relative difference between the thermopower of each spin channel
• Observation of high energy photoelectrons from solids at moderate laser intensity
  
  • N. Belsky A.
  • Bachau H.
  • Gaudin J.
  • Geoffroy G.
  • Guizard S.
  • Martin P.
  • Petite G.
  • Philippov A.
  • Vasil'Ev A.N.
  • N. Yatsenko B.
  Applied Physics B - Laser and Optics, Springer Verlag, 2004, 78, pp.989. We investigate the photoemission for a set of wide band-gap crystals irradiated by femtosecond Ti-Sapphire laser pulses at intensities varying from 0.5 to 6 TW/cm(2) (below the optical breakdown threshold). The measured total electron yield increases linearly with the laser intensity in this intensity range. An intense and wide plateau of high energy electrons appears in the photoelectron spectra at excitation intensities larger than 1 TW/cm(2). The exponential cut-off of this plateau reaches 40 eV at maximal applied intensities. In order to explain such a behavior, we propose a mechanism where the heating is due to a sequence of direct interbranch one- and multi-photon transitions in the conduction band
• Spatially periodical structures, under femtosecond pulsed excitation of irradiated AI203 crystals
  
  • F. Martynovitch E.
  • Petite G.
  • P. Dresvianski V.
  • A. Starchenko A.
  Applied Physics Letters, American Institute of Physics, 2004, 84, pp.4550. Measuring the luminescence intensity of specially prepared irradiation defects induced in crystals, we observe that the longitudinal structure of quasi-interferences induced by two orthogonally polarized femtosecond pulses propagating together with different velocities is insensitive to the spatial broadening due to velocity dispersion in the crystals. On the contrary, it does depend on the pulse duration when it is changed by varying the spectral width of the radiation. It thus allows a direct measurement of the coherence time of such pulses. Stability of the axial selectivity is a good sign, taking away a number of serious limitations concerning possible applications
• Track formation in fluorapatite irradiated with energetic cluster ions
  
  • Jaskierowicz G.
  • Dunlop A.
  • Jonckheere R.
  Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier, 2004, 222, pp.213. We present preliminary transmission electron microscopy observations on apatite samples irradiated at 300 K with 30 MeV C60 cluster ions up to fluences ranging from 1 × 1010 to 3 × 1011 cm-2. Each incoming projectile generates strong structural modifications in the vicinity of its path as a consequence of the very high density of energy deposited in electronic processes. It will be shown that a wide variety of morphologies is found in neighbouring tracks, some of them appearing as "continuous", whereas in the same sample region many consist of one or several alignments of droplets, which could be either voids or gas filled bubbles. Electron diffraction patterns seem to indicate that the core of the track do not consist of amorphous solid matter. The tracks induced under cluster irradiation evolve under the beam in the electron microscope. Some faceting of the damaged regions appears as the discontinuity along the track length increases
• Comment on "Molecular dynamics study of the threshold displacement energy in vanadium
  
  • Vajda P.
  , 2004. The simulation study on Frenkel pair creation in vanadium by L.A. Zepeda-Ruiz et al. (Phys. Rev. B 67, 134114, 2003) is criticized for its lack of reference to existing experimental work and for generally inadequate treatment of literature data. Hence, the validity of the ensuing discussion of various results (e.g. the value of the minimum TDE and the Frenkel pair stability in V) is questioned.