Papers by Heinz Carstanjen
Physics Letters A, 1981
We report on the first observation of the lattice steering ("channeling") of 4.12 MeV positive mu... more We report on the first observation of the lattice steering ("channeling") of 4.12 MeV positive muons (iii), resulting from the decay of thermalized positive pions (ir~)implanted in Ta single crystals. The steering effect manifests itself as a peak in the~intensity (relative height 1.25, FWHM 0.3°)in a (100) crystal direction. Conclusions on the behaviour of~in Ta as well as potential future applications of the technique are discussed.
physica status solidi (a), 2009
ABSTRACT
Nuclear Instruments and Methods in Physics Research, 1982
Abstract We report on the first observation of channeling phenomena in a blocking experiment with... more Abstract We report on the first observation of channeling phenomena in a blocking experiment with 4.12 MeV positive muons (μ+) resulting from the decay of thermalized pions (π +) implanted into Ta single crystals. The channeling manifests itself as a peak in the μ+ intensity (relative height 1.25, fwhm 0.3°) along the 〈100〉 direction of the Ta crystals. In addition, first results of a similar experiment involving the blocking of relativistic positrons from the decay of muons (μ+) implanted into an Au crystal are presented. We describe the principles of the method together with the experimental set-up and discuss conclusions to be drawn from the experimental findings as well as potential applications of the technique.
Zeitschrift f�r Physik A Atomic Nuclei, 1988
A monoenergetic positron (e § beam (A T/T< 5.10-4) from the Stuttgart pelletron accelerator and a... more A monoenergetic positron (e § beam (A T/T< 5.10-4) from the Stuttgart pelletron accelerator and a 4.6mg/cm 2 Be target has been employed to investigate e § e-scattering in the MeV region in a large solid angle with high statistics by means of a novel positionsensitive detector system. Superimposed on the Bhabha scattering, a structure has been found at an e § kinetic energy of 2263 keV (810keV excitation energy in the e+e-rest frame). From the energy-integrated resonance cross-section of ares' Fr;~ e-_____ 30 b. eV (c.m.) and the standard resonance cross-section we estimate partial resonance widths Fr~ e-~-72 meV or 24 meV for total angular momenta J = 0 or J = i, respectively. The structure, which has not been predicted within the framework of quantum electrodynamics, coincides with one of the sum energies of the correlated e § e-lines observed in heavy-ion collisions.
Physical Review Letters, 1999
Chemistry and Physics of Fracture, 1987
The distribution of interstitial atoms around dislocations has to be described by Fermi-Dirac sta... more The distribution of interstitial atoms around dislocations has to be described by Fermi-Dirac statistics, in order to take site saturation into account. Calculations for hydrogen in the case of elastic interaction /1,2/ as well as experimental results /2,3/ have shown that local concentrations near the dislocation core must be rather high. Thus H-H interaction should play an important role which, however, complicates the theoretical discription remarkably /4/.
Radiation Effects, 1983
From a compilation of known literature, the substitutional fraction of boron in silicon is depict... more From a compilation of known literature, the substitutional fraction of boron in silicon is depicted in a diagram as a function of implantation dose and annealing temperature. Samples implanted at 1 1016 B/cm2 and annealed at 900, 1000 and 1100°C for 1 hour each are examined by the (n, α) method and compared to the RBS signal of the host
Zeitschrift Fur Metallkunde, 1998
The behaviour of spherical and cylindrical voids in a solid under irradiation is investigated. Th... more The behaviour of spherical and cylindrical voids in a solid under irradiation is investigated. The irradiation is assumed to result only in the creation of point defects - vacancies and interstitials. In the stationary stage of the process, i. e. for the time when the point defects have already taken their stationary distributions, the irradiation tends to increase the sizes of the voids. Special attention was paid to the nonstationary stage of the void evolution. Because the diffusion coefficient of interstitials is larger than the diffusion coefficient of vacancies, a fast decrease of the void size is observed during nonstationary stage. A critical void radius is found: voids with radii smaller than the critical one disappear during the nonstationary stage; voids with radii larger than the critical one will fail to disappear during the nonstationary stage. The radii of these voids will increase during the stationary stage later on. The influence of the finite size of the sample on...
Philosophical Magazine A, 1979
Vacancies in high–purity gold Single crystals have been investigated after quenching from tempera... more Vacancies in high–purity gold Single crystals have been investigated after quenching from temperatures between 900 and 960°C and after Several steps of an isochronal annealing programme by measurements of the diffuse X–ray scattering intensity close to Bragg reflections, of the lattice parameter change and of the electrical resistivity. From the combined results the volume relaxation of a vacancy was determined
The present note describes an electron microscopy and ion beam analysis study of the bonding of t... more The present note describes an electron microscopy and ion beam analysis study of the bonding of thin-film Au bicrystals. The single crystal Au films were grown on (001) surfaces of cleaved NaCl single crystals containing cleavage steps of various heights, some of which are as high as 10[mu]m. They were then partially bonded under pressure at 195 C in ambient
We report on the first observation of the lattice steering ("channeling") of 4.12 MeV positive mu... more We report on the first observation of the lattice steering ("channeling") of 4.12 MeV positive muons (iii), resulting from the decay of thermalized positive pions (ir~)implanted in Ta single crystals. The steering effect manifests itself as a peak in the~intensity (relative height 1.25, FWHM 0.3°)in a (100) crystal direction. Conclusions on the behaviour of~in Ta as well as potential future applications of the technique are discussed.
Nuclear Physics Methods in Materials Research, 1980
A precise knowlegde of the surface positions of adsorbed atoms on crystal surfaces is fundamental... more A precise knowlegde of the surface positions of adsorbed atoms on crystal surfaces is fundamental for a variety of surface investigations. Among the techniques developped for the location of surface atoms LEED is the most elaborate and efficient method at the moment. But, laborious and extensive calculations are necessary in order to extract the surface positions of the investigated impurities. Morover, it can not be applied at very low impurity concentrations.
Nuclear Physics Methods in Materials Research, 1980
Most location studies are done by Low Energy Electron Diffraction (LEED) which primarily yields t... more Most location studies are done by Low Energy Electron Diffraction (LEED) which primarily yields the symmetry and structure of the adsorbed layers. Moreover, LEED requires a regular arrangement of the adsorbed atoms. Here we present a direct technique for the location of adsorbed foreign atoms on a monocrystalline surface /1/ by applying “surface channeling” /2/ where fast ions at grazing angles are incident along low index directions of the surface. Then, the scattering of the ions arises from successive correlated collisions with many atoms of the low index surface rows. This allows us to describe surface channeling with continuum row potentials analogous to axial channeling in bulk /3/. Fig.1 shows the projection of the pertinent interaction potential of a (101) Ni-surface with deuterons obtained by superposition of three neighbouring [101] continuum row potentials. At grazing incidence along the [101] direction the ions experience strong steering by this repulsive potential. The important aspect for the atom location experiments is that thereby the ion flux density is reduced at the rows and enhanced between the rows. This effect can be used to locate the position of foreign atoms at the surface, since their interaction with incident ions (e.g. nuclear reactions, characteristic X-ray production) occurs with cross sections which decrease with increasing impact parameter. Therefore, we obtain a reduction in the reaction yield, if the foreign atoms are shadowed by the atomic rows and an increase, if their position is between the rows.
Radiation Effects, 1972
Abstract A computer simulation of the channeling of 300 keV deuterons in a niobium lattice has be... more Abstract A computer simulation of the channeling of 300 keV deuterons in a niobium lattice has been performed. The model calculations included: binary Thomas-Fermi interaction between projectiles and lattice atoms, thermal displacements of the lattice atoms in the transverse plane of particle motion, electron scattering of the deuterons dependent on the local electron density, and electronic energy loss dependent on the local electron density. Flux distributions and mean particle energy distributions of the deuterons were calculated in their development with penetration depth. Flux peaking and energy peaking was found to depend sensitively on the local variation of the electron density in the crystal.
At the Max-Planck-Institut fu¨r Metallphysik in Stuttgart, Germany, a 6 MV Pelletron accelerator ... more At the Max-Planck-Institut fu¨r Metallphysik in Stuttgart, Germany, a 6 MV Pelletron accelerator is being used for surface analysis using high resolution RBS and ERD of hydrogen by means of an electrostatic spectrometer. While for ERD analysis of hydrogen a thin foil in front of the detector is sufficient to eliminate the background of backscattered particles, for the ERD analysis of heavier elements, e.g., oxygen, the recording of a second parameter of the detected particles is necessary to separate particles of the same energy, but of different mass and charge state. For this purpose a set-up was installed that combines the high energy resolution of the spectrometer with a measurement of the time of flight of the ions through the spectrometer using a chopped ion beam. The measurement of depth profiles of elements lighter than argon, with a depth resolution in the few monolayer range, is now possible. The technique is demonstrated by the analysis of the oxidation of aluminum single crystal surfaces. The experiments revealed a strong anisotropy in the oxidation. The technique also allows to measure charge state dependent depth profiles. Measurements of backscattering of Ne and Ar ions on Au and of recoil O ions from Ta2O5 and Al2O3 have been performed. From the measurements charge state distributions after the ion-atom collision and mean free path lengths for electron capture and loss are derived.
Radiation Effects, 1982
Abstract The angular distribution of 2.8 MeV helium ions backscattered from silicon crystals cont... more Abstract The angular distribution of 2.8 MeV helium ions backscattered from silicon crystals containing self-interstitials has been calculated by channeling computer simulations for a double alignment channeling configuration. The structures of the self-interstitial defects are assumed to be the split interstitial and the split di-interstitial with various inter-atomic distances. The obtained profiles of the backscattering yield are found to show shapes characteristic for each structure which can be used for differentiating between these structures. When comparing these profiles with experimental profiles obtained with the same double alignment channeling configuration in a previous study one finds reasonable agreement for the split interstitial defect with an inter-atomic distance of 1.76 A.
Nuclear Instruments and Methods in Physics Research, 1983
Berichte der Bunsengesellschaft für physikalische Chemie, 1972
Channeling provides a new technique for determining the lattice positions of deuterium atoms in s... more Channeling provides a new technique for determining the lattice positions of deuterium atoms in single crystals at low concentrations. In the present investigation the D(d,p)T reaction yield was measured around the 〈100〉 and the 〈111〉 incidence directions of a 300 keV deuteron beam penetrating through niobium loaded with 2 atomic percent deuterium. In combination with flux and energy distribution calculations of the channeled deuterons the conclusion was reached that at 150 K the dissolved deuterium atoms are located at tetrahedral lattice sites. Measurements at room temperature indicate that deuterium at 295 K occupies the same sites. Channeling liefert eine neue Methode zur Bestimmung der Gitterpositionen von Deuteriumatomen in Einkristallen bei niedrigen Konzentrationen. In der vorliegenden Arbeit wurde die Protonenausbeute aus einer D(d, p) T-Kernreaktion zwischen Deuteriumatomen, gelost in einem Niobeinkristall (Konzentration: 2 Atomprozent), und einem 300 keV-Deuteronenstrahl in Abhangigkeit vom Einfallswinkel der Deuteronen zur 〈100〉 und 〈111〉)-Achse des Kristalls gemessen. Durch Vergleich dieser Protonenausbeuteprofile, deren Struktur empfindlich von der jeweiligen Zwischengitterposition der Deuteriumatome abhangt, mit Profilen, die aus der Deuteronenflus- und energieverteilung fur verschiedene Deuteriumpositionen berechnet wurden, konnte geschlossen werden, daO Deuterium bei 150°K und einer Konzentration von 2 Atomprozent in Niob Tetraederplatze einnimmt. Messungen bei Zimmertemperatur ergaben, das Deuterium bei 295°K die gleichen Platze besetzt.
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Papers by Heinz Carstanjen