CEQUINOR   05415
CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
artículos
Título:
Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance
Autor/es:
NÉSTOR E. MASSA; JULIANO C. DENARDIN; LEANDRO M. SOCOLOVSKY; MARCELO KNOBEL; FERNANDO P. DE LA CRUZ; XIXIANG ZHANG
Revista:
JOURNAL OF APPLIED PHYSICS
Editorial:
American Institute of Physics
Referencias:
Lugar: Melville; Año: 2009 vol. 105 p. 114306 - 114306
ISSN:
0021-8979
Resumen:
We report on near normal infrared  reflectivity spectra of  ~550 nm thick  transition metal and SiO2 cosputtered granular films having a wide range of metal fractions. Co0.85(SiO2)0.15 with conductivity well above the percolation threshold has a frequency and temperature behavior according to conducting metal oxides. The electron scattering rate displays an unique relaxation time characteristic of  single type of carriers experiencing strong electron-phonon interactions. Using small polaron fits we individualize those phonons as glass vibrational modes. A film as Ni0.61(SiO2)0.39, with a metal fraction closer to the percolation threshold,  undergoes a metal-non metal transition at ~77 K . As it is suggested by the scattering rate quadratic dependence we identify two carrier contributions associated to a Drude mode and a mid-infrared overdamped band. Disorder induced, the mid-infrared contribution drives the phase transition by thermal electron localization. Co0.51(SiO2)0.49 has the reflectivity of an insulator with a distinctive band at ~1450cm−1 originating in electron promotion, localization, and defect induced polaron formation. Angle dependent oblique reflectivity of globally insulating Co0.38(SiO2)0.62, Fe0.34(SiO2)0.66, and  Ni0.28(SiO2)0.72, reveals a remarkable resonance at that band threshold due to  the excitation by normal electric fields of  electrons in metallic nanoparticles. At higher oblique angles, this localized plasma couples to SiO2 longitudinal optical Berreman phonons. Singular to a globally insulating phase, we believe that this Mie-like resonance might be a useful tool for tracking metal-insulator phase transitions in inhomogeneous materials.