Electron Dynamics in Transition Metal Granular Film

N.E. MASSA; J.C. DENARDIN; L.M. SOCOLOVSKY; M. KNOBEL; X.X. ZHANG

Denver, Colorado, USA

Congreso; American Physical Society March Meeting; 2007

American Physical Society

Electron Dynamics in Transition Metal Granular FilmsN.E. MASSA, LANAIS EFO-CEQUINOR, UNLP, CP 962, 1900 LaPlata, Argentina, J.C. DENARDIN, Dpto de F¶³sica, USACh, Santiago,Chile, L.M. SOCOLOVSKY, Inst. de F¶³sica, UFG, Goi^ania, Brazil, M.KNOBEL, Inst. de F¶³sica, UNICAMP, Campinas, Brazil, X.X. ZHANG,Inst. of Nanoscience and Technology, UST, Hong Kong, China | Nearnormal incidence re°ectivity spectra of transition metal »500 nm thickcosputtered granular ¯lms on SiO2 subtracts were measured from 30to 11000 cm¡1 and at temperatures from 30 to 490 K. The re°ectiv-ity for Co0:85(SO2)0:15 has a frequency and temperature behavior ac-cording to conducting metal oxides. The electron scattering rate de-notes an unique relaxation time characteristic of a single type of carriersand has a very strong temperature dependence due to strong electron-phonon interactions. Using small polaron ¯ts we individualize these asrelated to glass stretching vibrational modes. The optical conductiv-ity of Ni0:61(SO2)0:39, undergoing a metal-insulator transition at »77K, has a Drude mode (freer carriers) and a mid-IR band (mid-infraredcarriers"). This last disorder related strong resonance drives the phasetransition by localization decreasing in magnitude as the temperature islowered and points to a double relaxation process (two di®erent scatter-ing mechanisms). On the other hand, Co0:51(SO2)0:49 has an insulatorre°ectivity in which a distinctive band at »1450cm¡1 originates in elec-tron promotion, localization, and defect induced quasiparticle formation.