On the stability of bcc Co in Co/Fe superlattices an NMR and XRD study

While RHEED observations show that 10 to 11 As is the stability limit for an open bcc Co layer when grown on an Fe substrate, our XRD and NMR studies have shown that, in MBE grown Co/Fe superlattices, cobalt can be stabilised in a bcc structure up to a critical Co thickness of 21 Ås. In order to understand this apparent discrepancy, NMR experiments have been carried out in Co_x/Fe_y multilayers with thickness varying in the range 5 Å < x < 42 Å and 24 Å < y < 60 Å, grown on GaAs (1 1 0) as well as on MgO (1 0 0) substrates. The analysis of the chemical short range order by NMR concludes that the larger bcc Co thickness observed in superlattices results from the formation of a rather homogeneous CoFe_20% bcc alloy which contains the supplementary 10–11 As of Co and which coexists with pure Co grains. The concentration of about 20% Fe in the alloyed part of the Co layer happens to be close to the stability limit for a bcc structure in the equilibrium phase diagram of bulk CoFe alloys. However, while a mixture of bcc and fcc phases is observed in bulk alloys, the bcc structure is preserved in all phases under the MBE growth conditions and below the critical thickness. Above the critical thickness amixture of bcc Co, bcc CoFe and hcp Co is observed.     

Mössbauer study of the disorder in crystalline and amorphous Ge implanted with 125mTe ions

Crystalline and amorphous Ge and amorphous Ge_0.8Te_0.2 were implanted with ^125mTe. The Mössbauer spectra showed quadrupole split doublets. The isomer shift and quadrupole split values suggested that the atomic configuration around Te after implantation in Ge is similar to that of amorphous GeTe.     

Lattice location and stability of ion implanted Cu in Si

We report on the lattice location of ion implanted Cu in Si using the emission channeling technique. The angular distribution of beta(-) particles emitted by the radioactive isotope 67Cu was monitored following room temperature implantation into Si single crystals and annealing up to 600 degrees C. The majority of Cu was found close to substitutional sites, however, with a significant displacement, most likely 0.50(8) A along the <111> directions towards the bond center position. The activation energy for the dissociation of near-substitutional Cu is estimated to be 1.8-2.2 eV.     

Lattice displacement waves in AuTe2

¹²⁵Te and¹²⁹I Mössbauer spectra were studied of AuTe₂, AuAgTe₄, and AuCuTe₄. A distribution in hyperfine parameters is needed to obtain a satisfactory fit of the¹²⁹I spectra, and is interpreted in favor of lattice displacement waves recently observed in these compounds.     

57Co implanted in reactive and non-reactive frozen gases

⁵⁷Co was implanted in different reactive and non reactive frozen gases like Ne, Ar, N₂, Xe, CH₄ and C₂H₄. Higher ionization states of Fe and cryochemical compounds are detected.     

Amorphization of diamond by low temperature133Xe ion implantation

The structure of the amorphous layer in¹³³Xe implanted diamond is investigated by Mössbauer spectroscopy. Very different Debye Waller factors are measured after room temperature and liquid nitrogen temperature implantation.     

Weyl fermions on strings embedded in three dimensions

It is shown that the determinant of the Weyl operator introduced by Kavalov, Kostov and Sedrakyan is determined by the extrinsic geometry of the embedding. The effective action is anomalous under bendings of the surface.     

The Mössbauer search for Fe in Si

In this review paper, a series of Mössbauer experiments on Fe in Si, spread over almost thirty years, is discussed. In early Mössbauer experiments, the role of precipitate formation during diffusion was insufficiently realized. Later, an apparent inconsistency was observed between ion implantation experiments by recoil implantation of Coulomb excited atoms and by conventional ion implantation. This inconsistency is removed by recent high-resolution Coulomb excitation recoil implantation studies and by ion implantation experiments at the temperature of liquid helium. These studies lead to an unambiguous identification of interstitial Fe and Co in Si. Finally, the present status of the theoretical predictions on the isomer shift of Fe in Si is reviewed.