1. F. *Gonella and P. Mazzoldi, "Metal Nanocluster Composite Glasses", in: Handbook of Nanostructured Materials and Nanotechnology, H.S. Nalwa, ed., Vol. 4, p. 81-158, Academic Press, S. Diego 2000. * C. Maurizio, ‘Multielemental nanocluster formation by ion implantation in silica’, Nucl. Instr. Meth. B, to be published. * G. Mattei, C. Maurizio, C. Sada, P. Mazzoldi, C. de Julian, E. Cattaruzza, G. Battaglin, ‘Au-Cu and Pd-Cu nanoclusters obtained by ion implantation in silica: stability under thermal annealing’ J. Non-Cryst. Solids, to be published. * C. Maurizio, F. Gonella, E. Cattaruzza, P. Mazzoldi, F. D'Acapito “Implanted dielectrics: synchrotron radiation studies by absorption and diffraction techniques”, Nucl. Instr. Meth. B, 200 (2003) 126-137. * F.D'Acapito, F.Zontone “Grazing-incidence X-ray diffraction in the study of metallic clusters buried in glass obtained by ion implantation” J. Appl. Cryst., 32 (1999) 234-240. Au-Cu and Pd-Cu nanoclusters in silica: stability under thermal annealing C. Maurizio (maurizio@esrf.fr), F. D’Acapito*- P. Mazzoldi, G. Mattei, S. Padovani, C. Sada, E. Cattaruzza, C. de Julian **, F. Gonella *** * INFM, Italian beamline GILDA, ESRF ** INFM and Physics Dept., Univ. of Padova (I), *** INFM and Phys-Chem. Dept., Univ. of Venezia (I), METAL ALLOY NANOCLUSTER COMPOSITE GLASSES physical interest- optical properties, nonlinearity (  (3) ) - classical and quantum confinement - aggregation and stability techn. applications- optoelectronics - cathalysis - magnetic recording alloy clustersone further possibility to tailor the system structure ion implantation A+B A:B A+A+ B+B+ core-shell Pd+Cu and Au+Cu sequential implantation in silica Annealing in 4% H 2 or air for 1 h at 900 °C implantation energy: 90 keV for Cu + 130 keV for Pd + 190 keV for Au + fluence = 3·10 16 ions/cm 2  2  A/cm 2  70 nm  25 nm * Which are the structural modification upon heating? * Which are the physical and chemical processes that drive the alloy decomposition? * How do they depend on the annealing atmosphere and/or on the alloy components? * Is it possible to exploit them for tailoring the composite structure? Open questions The sequential ion implantation leads to the formation of solid solition binary alloy nanoclusters embedded in silica The alloy clusters are poor in Cu (TEM, EXAFS, SAED) because part of Cu atoms remain dispersed in the matrix F. Gonella et al., APL 75 (1999) 55. Solid solution fcc Au 0.68 Cu 0.32 alloy clusters Au L III -edge Cu K-edge G. Battaglin et al., NIMB 191 (2002) 392. fcc Pd 0.6 Cu 0.4 alloy clusters Pd K-edge Cu K-edge Au+Cu Cu K-edge AuCu tetragonal alloy G. Mattei et al. PRL 90 (2003) 085501. 15 min air annealing Cu 2 O (cubic crystals aligned with fcc alloy) Au-Cu fcc alloy CuO clusters Au clusters + 60 min air annealing CuO fcc-Au GIXRD EXAFS * most of Cu is oxidized * further aggregation of Pd in metallic clusters * Pd-Cu coordination still present * No LRO oxide correlation as-implanted annealed R (Cu-Cu) = 2.95 ± 0.02 A, N>6 -> possible cubic Cu 2 O R (Cu-Pd) = 2.71 ± 0.02 A -> Pd-Cu alloy B Cu-Cu Cu-Pd B EXAFS at Cu K-edge Cu-O A First shell around Cu A N=2.1±0.4 N=2.9±0.3 B Heat of formationCuO = -155.3 Kj/mol AuCu s.s. = -5.32 Kj/mol PdCu s.s. = -12.6 Kj/mol a=4.06 Å a=4.27 Å CuO clusters Au clusters Cu 2 OAu-Cu clusters WORK IN PROGRESS: * to monitor the structural modification during air annealing * to investigate other pathways for selective de-alloying Au+Cu implanted SiO 2 Pd+Cu implanted SiO 2 Cu K-edge Pd+Cu The heating in reducing atmosphere of nanocluster-doped silica determines: - dopant aggregation in metallic clusters - increasing of cluster size (TEM) - modification of the alloy composition: Cu atoms diffuse into the alloy clusters - the chemical ordering is favored. Heating in reducing atmosphere (H 2 4%, T = 900 C for 1h) EXAFS analysis Sequential ion implantation for nanoclusters formation Heating in oxidizing atmosphere (air, T=900C for 1 h) Au+Cu Effect of heating in oxidizing atmosphere of Au-Cu alloy clusters in silica: - after 15 min Cu 2 O cubic nanoclusters are formed, on the template of the cubic Au-Cu alloy clusters - after 1 h only CuO and Au clusters are present, the de-alloying process is completed Pd+Cu Effect of heating in oxidizing atmosphere of Pd-Cu alloy clusters in silica: - after 1 h most of Cu is oxidized - further aggregation of Pd in metallic cluster - Pd-Cu coordination after 1 h is still present - no evidence of long range order oxide correlation - the Co oxidation occurs especially near the glass surface Pd-Cu clusters possible Cu oxidation via core-shell structure a  3.89 Å the nanocrystalline structure drives the cluster evolution during oxidation TEM