Aca - Departamento de Física - Universidad Técnica Federico Santa ...

More documents

Recommendations

Info

$Difracción e Interferencia - Departamento de Física - Universidad ...$

V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Nonetheless, we demonstrate proceeding further that not only the binary but also the recoil peak may be supressed when transitions involve the first excited (ungerade) state of the residual target. A similar effect was discovered for emission of photoelectrons: at definite photon energies, electron ejection in the classical direction given by the polarization vector is forbidden for molecules aligned with the polarization vector [12,13]. Unfortunately, no experiments with oriented molecules are available at present to contrast with our predictions. Notwithstanding, in the age of the COLTRIMS and reaction microscopes [14] is possible to envisage in the near future the coming of experimental work to corroborate (or not) our findings. [11] O. Al-Hagan et al, Nature Physics 5, 59 (2009). [12] J. Fernández, O. Fojón, A. Palacios and F. Martín, Phys. Rev. Lett. 98, 043005 (2007). [13] J. Fernández, O. Fojón and F. Martín, Phys. Rev. A 79, 023420 (2009). [14] Ten years of COLTRIMS and reaction microscopes, collection of papers edited by J. Ullrich, Max Planck Institute für Kernphysik Heidelberg (2004). References [1] H. D. Cohen and U. Fano, Phys. Rev. 150, 30 (1966). [2] N. Stolterfoht et al, Phys. Rev. Lett. 87, 023201 (2001). [3] C. R. Stia, O. A. Fojón, P. Weck, J. Hanssen, and R. D. Rivarola, J. Phys. B: At. Mol. Opt. Phys. 36, L257 (2003). [4] O. Kamalou, J.-Y. Chesnel, D. Martina, F. Frémont, J. Hanssen, C. R. Stia, O. A. Fojón, R. D. Rivarola, Phys. Rev. A 71, 010702(R) (2005). [5] S. Chatterjee, D. Misra, A. H. Kelkar, L. Tribedi, C. R. Stia, O. A. Fojón and R. D. Rivarola, Phys. Rev. A 78, 052701 (2008). [6] S. Chatterjee, S. Kasthurirangan, A. H. Kelkar, C. R. Stia, O. A. Fojón, R. D. Rivarola and L. Tribedi, J. Phys. B: At. Mol. Opt. Phys. 42, 065201 (2009). [7] S. Chatterjee, A. N. Agnihotri, C. R. Stia, O. A. Fojón, R. D. Rivarola and L. Tribedi, Phys. Rev. A (2010) in press. [8] P. Weck, O. A. Fojón, J. Hanssen, B. Joulakian and R. D. Rivarola, Phys. Rev. A 63, 042709 (2001). [9] M. Brauner, J. S. Briggs and H. Klar, J. Phys. B: At. Mol. Opt. Phys. 22, 2265 (1989). [10] C. R. Stia, O. A. Fojón, Ph. Weck, J. Hanssen, B. Joulakian and R. D. Rivarola, Phys. Rev. A 66, 052709 (2002). 58 Valparaíso, Chile
V Encuentro Sud Americano de Colisiones Inelásticas en la Materia The role of electronic excitations in the energy loss of hydrogen clusters in dielectric and metallic materials S. M. Shubeita 1 , R. C. Fadanelli 1 , J. F. Dias 1 , P. L. Grande 1 , C. D. Denton 2 , I. Abril 2 , R. Garcia-Molina 3 and N. R. Arista 4 1 Instituto de Física da Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil 2 Departamento de Física Aplicada, Universidad d’Alicante, Alicante, Spain 3 Departamento de Física – CIOyN, Universidad de Murcia, Murcia, Spain 4 Centro Atômico Bariloche, Instituto Balseiro, San Carlos de Bariloche, Rio Negro, Argentina e-mail address corresponding author: samir.shubeita@ufrgs.br The aim of this work is to study the signature of plasmon excitations induced by H + 2 and H + 3 ionic clusters when interacting with thin (10-50 Å) layers of dielectric (SiO 2 , LaScO 3 , HfO 2 ) and metallic (Au) materials. For this purpose, high energy resolution backscattering experiments were carried out as a function of the incoming projectile energy, covering an energy range between 40 and 200 keV/nucleon. The ratio R n between the energy loss of the cluster and the sum of the energy loss of its constituents provides the information about the plasmon excitation threshold, which is characteristic for each material. The results obtained for the high-k dielectrics (LaScO 3 and HfO 2 ) and Au do not show any clear evidence of plasmon excitations induced by H + 2 ionic clusters (see fig. 1 for HfO 2 ). These results are supported by calculations based on the dielectric formalism. However, for the SiO 2 thin film (fig. 2), the plasmon excitation threshold is observed at about 70 keV/nucleon for both cluster ions (H + 2 and H + 3 ) [1]. In fact, unlike SiO 2 where a dominant long-range electronic excitation is present, the HfO 2 , LaScO 3 and Au have several and equally important excitation energies (mix of plasmon excitations, excitons and interband transitions). They lead to different onset projectile-energies, which explains the smoothly increase of stopping ratio [2]. Also, the results obtained for Au are compared with previous results [3]. Figure 1. The experimental energy loss ratio R 2 (squares) for HfO 2 as a function of the incident cluster energy, in comparison with different theoretical approaches. Figure 2. The experimental stopping ratio R 2 (full squares) as a function of the incident H + 2 cluster energy. The thick lines represent the dielectric formalism calculations including plasmon excitations (full line) and without plasmon excitations (dotted lines) after averaging over charge-state fractions of H + and H 0 . 59 Valparaíso, Chile
Page 2 and 3:
V Encuentro Sud Americano de Colisi
Page 4 and 5:
Page 6 and 7:
Page 8 and 9: V Encuentro Sud Americano de Colisi
Page 76 and 77: Counts V Encuentro Sud Americano de
Page 78 and 79: Py (a.u.) V Encuentro Sud Americano
Page 102 and 103: Intensidade Intensidade V Encuentro
Page 108 and 109:
Page 110:
show all

Aca - Departamento de Física - Universidad Técnica Federico Santa ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?