S. Cottenier

Tuning of CeO2 buffer layers for coated superconductors through doping

D.E.P. Vanpoucke, S. Cottenier, V. Van Speybroeck, P. Bultinck, I. Van Driessche
Applied Surface Science
260, 32-35
2012
A1

Abstract 

The appearance of microcracks in cerium oxide (CeO 2) buffer layers, as used in buffer layer architectures for coated superconductors, indicates the presence of stress between this buffer layer and the substrate. This stress can originate from the differences in thermal expansion or differences in lattice parameters between the CeO 2 buffer layer and the substrate. In this article, we study, by means of ab initio density functional theory calculations, the influence of group IV doping elements on the lattice parameter and bulk modulus of CeO 2. Vegard's law behavior is found for the lattice parameter in systems without oxygen vacancies, and the Shannon crystal radii for the doping elements are retrieved from the lattice expansions. We show that the lattice parameter of the doped CeO 2 can be matched to that of the La 2Zr 2O 7 coated NiW substrate substrate for dopant concentrations of about 5%, and that bulk modulus matching is either not possible or would require extreme doping concentrations. [All rights reserved Elsevier].

Open Access version available at UGent repository

Classical toy models for the monopole shift and the quadrupole shift

K. Rose, S. Cottenier
Physical Chemistry Chemical Physics (PCCP)
2012 (14) 11308-11317
2012
A1

Abstract 

The penetration of s- and p1/2-electrons into the atomic nucleus leads to a variety of observable effects. The presence of s-electrons inside the nucleus gives rise to the isotope shift in atomic spectroscopy, and to the isomer shift in Mössbauer spectroscopy. Both well-known phenomena are manifestations of the more general monopole shift. In a recent paper (Koch et al., Phys. Rev. A, 2010, 81, 032507), we discussed the existence of the formally analogous quadrupole shift: a tensor correction to the electric quadrupole interaction due to the penetration of relativistic p1/2-electrons into the nucleus. The quadrupole shift is predicted to be observable by high-accuracy molecular spectroscopy on a set of 4 molecules (the quadrupole anomaly). The simple physics behind all these related phenomena is easily obscured by an elaborate mathematical formalism that is required for their derivation: a multipole expansion in combination with perturbation theory, invoking quantum physics and ideally relativity. In the present paper, we take a totally different approach. We consider three classical ‘toy models’ that can be solved by elementary calculus, and that nevertheless contain all essential physics of the monopole and quadrupole shifts. We hope that this intuitive (yet exact) analysis will increase the understanding about multipole shift phenomena in a broader community.

Electronic structure of transparent oxides with the Tran–Blaha modified Becke–Johnson potential

H. Dixit, R. Saniz, S. Cottenier, D. Lamoen, B. Partoens
Journal of Physics: Condensed Matter
24 (20), 205503
2012
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Abstract 

We present electronic band structures of transparent oxides calculated using the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. We studied the basic n-type conducting binary oxides In2O3, ZnO, CdO and SnO2 along with the p-type conducting ternary oxides delafossite CuXO2 (X=Al, Ga, In) and spinel ZnX2O4 (X=Co, Rh, Ir). The results are presented for calculated band gaps and effective electron masses. We discuss the improvements in the band gap determination using TB-mBJ compared to the standard generalized gradient approximation (GGA) in density functional theory (DFT) and also compare the electronic band structure with available results from the quasiparticle GW method. It is shown that the calculated band gaps compare well with the experimental and GW results, although the electron effective mass is generally overestimated.

Lattice position and thermal stability of diluted As in Ge

S. Decoster, U. Wahl, S. Cottenier, J.G. Correia, T. Mendonça, L.M. Amorim, L.M.C. Pereira, A. Vantomme
Journal of Applied Physics
111, 053528
2012
A1

Abstract 

We present a lattice location study of the n-type dopant arsenic after ion implantation into germanium. By means of electron emission channeling experiments, we have observed that the implanted As atoms substitute the Ge host atoms and that, in contrast to several implanted metal impurities in Ge, no significant fraction of As is found on interstitial sites. The substitutional As impurities are found to be thermally stable up to 600 C. After 700 C annealing a strong reduction of emission channeling effects was observed, in full accordance with the expected diffusioninduced broadening of the As profile.

Is the 7/2− 1 isomeric state of 43S spherical?

R. Chevrier, J.M. Daugas, L. Gaudefroy, Y. Ichikawa, H. Ueno, M. Hass, H. Haas, S. Cottenier, N. Aoi, K. Asahi, D.L. Balabanski, N. Fukuda, T. Furukawa, G. Georgiev, H. Hayashi, H. Iijima, N. Inabe, T. Inoue, M. Ishihara, Y. Ishii, D. Kameda, T. Kubo, T. Nanao, G. Neyens, T. Ohnishi, M.M. Rajabali, K. Suzuki, H. Takeda, M. Tsuchiya, N. Vermeulen, H. Watanabe, A. Yoshimi
Physical Review Letters
108 (16), 162501
2012
A1

Abstract 

We report on the spectroscopic quadrupole moment measurement of the 7/21- isomeric state in 1643S27 [E*=320.5(5)  keV, T1/2=415(3)  ns], using the time dependent perturbed angular distribution technique at the RIKEN RIBF facility. Our value, ∣Qs∣=23(3)  efm2, is larger than that expected for a single-particle state. Shell model calculations using the modern SDPF-U interaction for this mass region reproduce remarkably well the measured ∣Qs∣, and show that non-negligible correlations drive the isomeric state away from a purely spherical shape.

Open Access version available at UGent repository

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