Spark source mass spectrometric assessment of boron and nitrogen concentrations in crystalline gallium arsenide

The residual or doped element concentration [E] in GaAs measured by SSMS is only accurate with respect to the relative sensitivity coefficient RSC_E. For a trace element concentration, the RSC_E = [E]_SSMS/[E]_TRUE is set to unity, if no reference material or method is available to approximate the concentration to the true value. For boron a relative sensitivity coefficient of RSC_B = 0.94 ± 0.08 was obtained using TI-IDMS as a reference method. RSC_N = 1 is used for nitrogen determinations. A boron and nitrogen detection limit of 4.4 × 10¹³ cm^–3 is achieved. SSMS was used as reference method to calibrate the FTIR factor f_E = [E] / I_α due to the integrated local vibrational mode absorption I_α of atomic boron and nitrogen in GaAs. A factor of f_B = (12.0 × 2.7) × 10¹⁶ cm^–1 (517 cm^–1) and f_N = (7.4 ± 0.1) × 10¹⁵ cm^–1 (472 cm^–1) was obtained for a boron and nine nitrogen containing GaAs samples at 77 K and 10 K, respectively. Received: 15 December 1998 / Revised: 8 April 1999 / Accepted: 13 April 1999     

Radiofrequency spark source mass spectrometric analysis of oxygen in undoped silicon crystals and of carbon in undoped and carbon doped gallium arsenide crystals

Radiofrequency spark source mass spectrometry is a reliable and precise analytical method to measure the amount of oxygen in silicon grown by the Czochralski technique from SiO₂ crucibles in the common range from 2ppm(atomic) to 20ppm(atomic) and in silicon grown by the floating zone technique below 0.1ppm(atomic). The technique is also excellent for the measurement of the amount of carbon in semi-insulating gallium arsenide grown under low and high pressure N₂ ambient gas by the B₂O₃ encapsulated Czochralski technique from pyrolytic BN crucibles in the common range from 0.02ppm(atomic) to 0.4ppm(atomic). The results are in rather good agreement with concentrations measured by charged particle activation analysis and consistent with those obtained using other methods.     

Relating high-energy Lepton-Hadron, proton-nucleus, and nucleus-nucleus collisions through geometric scaling

A characteristic feature of small-x lepton-proton data from HERA is geometric scaling: the fact that in the region of small Bjorken variable x, x less, similar 0.01, all data can be described by a single variable Q(2)/Q(2)(s,p)(x), with all x dependence encoded in the so-called saturation momentum Q(s,p)(x). Here, we observe that the same scaling ansatz accounts for nuclear photoabsorption cross sections and favors the nuclear dependence Q(2)(s,A) proportional, variant A(alpha)Q(2)(s,p), alpha approximately 4/9. We then make the empirical finding that the same A dependence accounts for the centrality evolution of the multiplicities measured in Au+Au collisions at RHIC. It also allows one to parametrize the high-p(t) particle suppression in d+Au collisions at forward rapidities. If these geometric scaling properties have a common dynamical origin, then this A dependence of Q(2)(s,A) should emerge as a consequence of the underlying dynamical model.     

Hyperfeinstrukturaufspaltung von rückstoßfreien Gammalinien

The temperature dependence of the hyperfine splitting of the 8.42 keVγ-ray of Tm¹⁶⁹ in oxide crystals was investigated using the Mößbauer-effect. The quadrupole splitting of the first excited state in Tm¹⁶⁹ showed a pronounced increase with decreasing temperature. This manifests a contribution of various Stark levels, which are occupied according to their Boltzmann factors, to an average field gradient at the nucleus. It is shown in a model calculation for the temperature dependence of the field gradient that the data can be explained using a maximum splitting of about 400 cm^?1 of the electronic groundstate by the crystal field. The emission pattern of the Er₂O₃-source is broadened below 20° K. This is possibly produced by an interaction with a residual magnetic field from the surrounding Er-ions.     

Magnetisches Moment und Quadrupolmoment des 8,42 keV-Zustandes von Tm169 aus der Hyperfeinstrukturaufspaltung in Tm-Metall

The hyperfine transition from the 8·42 kev level to the groundstate of Tm¹⁶⁹ was investigated using the Mössbauer-Effect in Tm-metal in the temperature range between 5° K and 60° K. Well resolved hyperfine spectra were found between 5° K and 25° K indicating an internal magnetic field of about 7×10⁶ Oe and a large electric fieldgradient. The ratio of the magnetic moments of the 8·42 keV rotational state to the groundstateμ _a /μ _g =?2·33±0·04 was deduced from these measurements. The magnetic moment of the groundstate and the quadrupole moment of the 8·42 kev level were deduced from calculated internal fields. These data were analyzed in terms of the “Unified Nuclear Model” and the results compared with other known magnetic moments andM-1-transition probabilities in theK=1/2 rotational band of Tm¹⁶⁹. The complicated hyperfine spectra obtained above 25° K reveal the influence of complex magnetic ordering on the internal fields in Tm-metal.     

Kernresonanzabsorption nicht Doppler-verbreiterter Gammastrahlung in Re187

Nuclear resonant absorption of gamma-rays has been observed in nuclei of Re¹⁸⁷ bound in a crystal lattice. At a temperature of 20° K a small fraction of the gammaquanta of the 134 keV transition to the ground state is emitted with essentially no energy lost to recoil, the recoil momentum being taken up by the entire crystal, not by the individual nucleus. Nuclei of Re¹⁸⁷ similarly bound in a crystal lattice have been irradiated with such gamma-rays emitted without loss of energy, resulting in an oberservable resonance absorption. Using a relative velocity of the order of 10 cm/sec the line emitted with the natural line width has been shifted away from the absorption line, resulting in the destruction of the resonance phenomena. Analysis of the variation in transmission as a function of the Doppler shift of the emitted gamma-ray yields a value ofτ=(1,5±0,2) · 10^?11 sec for the lifetime of the 134 keV excited state in Re¹⁸⁷.