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.     

Mössbauer study of iron in sp-metals and semimetals

Bi, In, Pb, Sb, α- and β-Sn were implanted with⁵⁷Co and⁵⁷Fe. The results of the analysis suggested strongly hybridized bonds between the iron and the host atoms. An upturn of the isomer shift (δ) values relative to the δ values in hosts with completed d-shell was not justified. Charge states of Fe²⁺ or Fe⁺ also appeared. The possible role of the native surface oxide layers in the formation of these states was investigated.     

Master equation approach to the dynamical critical behaviour of the Schlögl model

Starting from the multivariate master equation we construct a reduced model that gives the critical theory. The relation to the static problem is studied using the minimal subtraction technique and the critical exponents are calculated up to O(?²).     

Structural information about tellurium and iodine implanted in semiconductors from analysis of Mössbauer nuclear quadrupole interaction data

We have analyzed through electronic structure investigations, based on a model of an impurity atom trapped close to a substitutional site adjacent to a vacancy, the nuclear quadrupole interactions of¹²⁵Te and¹²⁹I implanted in a number of group IV and III–V semiconductors. Our analysis supports the proposed model for these impurity systems and leads to distances between the impurity and nearest neighbour host atoms close to the normal covalent bond distance, with one exception,¹²⁹I in GaSb, a possible physical reason for which is pointed out. The general nature of our conclusion for the impurity-host bond distances, in particular, its relationship to bond lengths associated with adsorbed halogen atoms at surfaces of semiconductors is discussed.     

Location of 125I implanted in silicon and germanium

A Mössbauer study of ¹²⁵I implanted into silicon and germanium lattices with various dose values was performed. The spectra measured after thermal annealing suggested an off-substitutional site population for I in the silicon lattice. The Mössbauer spectra showed no difference in the hyperfine splitting of ¹²⁵Te after electron capture of ¹²⁵I in comparison with that obtained after the isomeric transition of implanted ^125mTe. The site populations of Te and I atoms after implantation and thermal annealings were concluded as being the same.     

Emission Mössbauer spectroscopy study of fluence dependence of paramagnetic relaxation in Mn/Fe implanted ZnO

Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope ⁵⁷Mn⁺ (T _1/2= 1.5 min) into ZnO single crystals at ISOLDE/CERN shows that a large fraction of ⁵⁷Fe atoms produced in the ⁵⁷Mn beta decay is created as paramagnetic Fe³⁺ with relatively long spin-lattice relaxation times. Here we report on ZnO pre-implanted with ⁵⁶Fe to fluences of 2×10¹³, 5×10 ¹³ and 8 × 10¹³ ions/cm² in order to investigate the dependence of the paramagnetic relaxation rate of Fe³⁺ on fluence. The spectra are dominated by magnetic features displaying paramagnetic relaxation effects. The extracted spin-lattice relaxation rates show a slight increase with increasing ion fluence at corresponding temperatures and the area fraction of Fe³⁺ at room temperature reaches a maximum contribution of 80(3)% in the studied fluence range.     

Synchrotron Mössbauer reflectometry

Grazing incidence nuclear resonant scattering of synchrotron radiation can be applied to perform depth-selective phase analysis and to determine the isotopic and magnetic structure of thin films and multilayers. Principles and recent experiments of this new kind of reflectometry are briefly reviewed. Methodological aspects are discussed. Model calculations demonstrate how the orientations of the sublattice magnetisation in ferro- and antiferromagnetic multilayers affect time-integral and time-differential spectra. Experimental examples show the efficiency of the method in investigating finite-stacking, in-plane and out-of-plane anisotropy and spin-flop effects in magnetic multilayers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low temperature ion beam mixing of Co/Si systems

Co/Si systems were ion beam mixed at 77 K using a 100 keV Ar beam. The formation of different phases as a function of irradiation dose has been studied, using Mössbauer spectroscopy (MS) and Rutherford backscattering spectroscopy (RBS). It was found that Co₂Si, CoSi and CoSi₂ are formed subsequently in parallel layers. After high dose irradiation, a phase with stoichiometry Co∶Si equal to 1∶3 was observed, suggesting CoSi₃ has been formed. However, MS gave clear evidence that this phase consists of precipitates of CoSi₂ and Si. Finally, we found that the amount of mixing scales linearly with the square root of the fluence, with a mixing rate of 1.0×10⁴Å⁴.