Mössbauer study of the amorphization process in ion-implanted diamond

⁵⁷Co is implanted at different doses in diamond and graphite. It is found that, in contrast with the mearements of⁵⁷Co implanted Si and Ge, the damage production in diamond can not be described by a direct amorphization model.     

Hyperfine interactions: the past, the present and the future

Five major hyperfine interaction techniques, detected by nuclear radiation, originated in the short time span between 1950 and 1965. The coincidence with the demographic expansion, especially in Europe, of university education led to the creation of many new research laboratories applying these promising techniques in solid state physics, chemistry and biology. Since the turn of century many of the early pioneers are going into retirement, leading to a decline in activities in Europe, compensated in some degree by an increase in activities outside Europe. The organisation of the 2007 HI/NQI-conference was impeccable and took place in a superb setting. Thanks to all those involved in its organization.     

The strain-hardening behaviour of linear and long-chain-branched polyolefin melts in extensional flows

By generalizing the Doi-Edwards model to the Molecular Stress Function theory of Wagner and Schaeffer, the extensional viscosities of polyolefin melts in uniaxial, equibiaxial and planar constant strain-rate experiments starting from the isotropic state can be described quantitatively. While the strain hardening of four linear polymer melts (two high-density polyethylenes, a polystyrene and a polypropylene) can be accounted for by a tube diameter that decreases affinely with the average stretch, the two long-chain-branched polymer melts considered (a low-density polyethylene and a long-chain branched polypropylene) show enhanced strain hardening in extensional flows due to the presence of long-chain branches. This can be quantified by a molecular stress function, the square of which is quadratic in the average stretch and which follows from the junction fluctuation theory of Flory. The ultimate magnitude of the strain-hardening effect is governed by a maximum value of the molecular stress, which is specific to the polymer melt considered and which is the only free non-linear parameter of the theory. Received: 1 June 1999/Accepted: 24 November 1999     

Properties of Ga2-X-Te3 investigated by129I Mössbauer spectroscopy

¹²⁹I Mössbauer spectroscopy was used to study the properties of^129mTe labeled Ga₂Te₃. and alloyed (Ga₂Te₃)_xAu_y and (Ga₂Te₃)_xAs_y, sources. A satisfactory fit to the Ga₂Te₃ spectrum could only be obtained by introducing a distribution in the hyperfine interaction parameters. This is interpreted in favor of the hypothesis of a random distribution of the structural vacancies in the deficit cubic Ga₂Te₃. The addition of atomic percents of As to the compound did not change significantly the pure Ga₂Te₃ spectrum. The spectrum of Ga₂Te₃ alloyed with atomic percents of Au, on the contrary, could be fitted with only one component with a satisfactory narrow linewidth, suggesting that due to Au doping ordering is induced in the stoichiometric vacancies of the Ga₂Te₃ lattice structure.     

New phases and chemical short range order in co-deposited CoFe thin films with bcc structure: an NMR study

A ⁵⁹Co NMR study has been carried out on several series of co-evaporated Co₁-_xFe_x thin-film alloys prepared on MgO (001), GaAs (100), and GaAs (110) substrates at deposition temperatures between 175°C and 500°C. The sample thicknesses varied between 100 Å and 1000 Å and the alloy concentrations were in the range 0:1 < x < 0:3. X-ray diffraction and NMR show that the stability limits of the bcc phase in CoFe alloys is shifted from the x = 0:25 observed in the bulk alloys down to about x = 0:11 in thin films. For x = 0:27 and at the deposition temperature of 500°C, a new ordered phase has been stabilised where Co has two Fe atoms only in its first coordination shell. Other samples, grown at lower temperatures, also exhibit an exotic chemical short range order (CSRO) where Co coordinations with zero and two Fe neighbours dominate. A mixture of bcc Co (and not fcc Co as in the bulk alloys) and unknown ordered bcc intermetallics can account for the observed CSRO. Theoretical ground-state phases for the bcc lattice are considered in order to explain the observations.     

Formation and microstructure of cubic metastable iron silicides synthesized during pulsed laser annealing

Hyperfine Interactions - The phase formation and crystallization processes of metastable [CsCl]Fe1?x Si phases were investigated by irradiating?-FeSi/Si(111) thin films with a pulsed...     

Iron in reduced charge montmorillonites

Reduced charge Camp-Berteau Montmorillonites (R.C.M.) have been studied. The Cation Exchange Capacity (C.E.C.) resulting from these samples with different Li/Na ratios decreased linearly from the original value of about 1 meq/g to 0.6 meq/g. Diffused Li⁺ ended in octahedral layer nearby Mg²⁺. Iron was as Fe³⁺ and mainly in octahedral sites. A small additional quantity of tetrahedral configuration was detected. Only minor modifications on Mössbauer parameters of R.C.M. samples were observed as a consequence of charge reduction.