Electrodynamics of the vortex lattice in untwinned YBaCuO by complex impedance measurements

We report complex impedance measurements in an untwinned YBaCuO crystal. Our broad frequency range covers both the quasi static response and the resistive response of the vortex lattice. It allow us to characterize the irreversibility line without the need of any frequency dependent pinning parameters. We confirm the validity of the two modes model of vortex dynamic, and extract both the surface critical current and the flux flow resistivity around the first order transition T_m. This latter is identified by the abrupt loss of pinning and by an unexpected step of (T) at T_m. Received 22 November 2002 / Received in final form 17 February 2003 Published online 20 June 2003 RID="a" ID="a"e-mail: alain.pautrat@ismra.fr RID="b" ID="b"UMR 6508 associée au CNRS     

Photoluminescence studies in N,P, As implanted cadmium telluride

High purity p-type Cdte crystals have been implanted with N⁺, P⁺ and As⁺⁺ ions. After appropriate low temperature annealing, samples have been studied with high resolution photoluminescence technique, and with a tunable dye laser as the excitation source. A chemical doping effect by the acceptors N, P and As on tellurium site, has been evidenced. The bound exciton lines, the two-hole transitions, the donor acceptor pairs bands and the free electron-neutral acceptor transitions have been identified for the first time. The ground state of the acceptors N, P and As are respectively at 56.0 meV, 68.2 meV and 92.0 meV from the valence band.     

The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.     

Magnetic moments of the 12+ isomeric states in 194, 196, 198Pb

The g-factor of the 12⁺ isomeric state in lead isotopes with A = 194, 196, 198 was measured using the time-differential perturbed angular distribution method (TDPAD). The values obtained are respectively g(194) = ?0.158(6); g(196) = ?0.157(7); g(198) = ?0.144(11). A more precise determination of the 12⁺ level half-life is also made. The g-factprs of these nuclear states, which are described with v(i_{$\text{13}\text{2}$})^?2 as the main configuration, are surprisingly constant over a large mass range (between A = 206 and 194). A core polarization analysis explains this trend: the polarization induced on neutrons in i_{$\text{13}\text{2}$} orbit decreases with the mass number A (blocking effect), but a compensation is provided by the other spin-orbit partners f_{$\text{7}\text{2}$}-f_{$\text{5}\text{2}$} and P_{$\text{3}\text{2}$}-P_{$\text{1}\text{2}$}.     

Low-energy transitions in the 197Pb and 198Pb isotopes

The ¹⁹⁸Pb and ¹⁹⁷Pb isotopes are produced through the ¹⁸⁶W(¹⁶O, 4n, 5n) reactions. Conversion-electron, γ- and X-ray spectra are measured using the compound-nucleus recoil method. Conversion coefficients and multipolarities are deduced for a large number of transitions. Together with angular distribution measurements and the results of γγt multidimensional coincidences they lead to decay schemes for the two isotopes. Microscopic calculations, performed in the two- or three-quasiparticle approximation with a surface delta interaction, fail to reproduce completely the observed properties, showing similar defects for the odd and even isotope.     

Electronic and optical parameters of an oxygen-related center in Zn-Te

An electron trapping center (E_c ? 0.44 eV) has been characterized by the photocapacitance technique. This center appears in oxygen contaminated crystals after ion implantation and annealing in Zn vapour. It has also been created by oxygen implantation in oxygen-free crystals. This center might result of an O_Te-D⁺ associate.     

Electrical and optical identification of the persistent acceptor as copper in ZnTe

Capacitance, photoluminescence and infra-red absorption experiments have been performed on copper doped ZnTe single crystals. Comparative measurements on samples treated at various temperatures show clearly that Cu introduces a single acceptor level with high solubility. Spectroscopic results allow to identify the persistent acceptor “a” at 149 meV as copper on substitutional zinc site confirming that native defects are not responsible for the p-type conductivity of undoped ZnTe.