CEQUINOR   05415
CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
artículos
Título:
Far Infrared near normal specular reflectivty of Nix(SiO2)1-x (x=1.0,0.84,0.75,0.61,0.54,0.28) granular films
Autor/es:
NESTOR E. MASSA; JULIANO C. DENARDIN; LEANDRO M. SOCOLOVSKY; MARCELO KNOBEL; FERNANDO P. DE LA CRUZ; XIXIANG ZHANG
Revista:
JOURNAL OF ALLOYS AND COMPOUNDS
Editorial:
Elsevier
Referencias:
Lugar: New York; Año: 2010 vol. 495 p. 638 - 641
ISSN:
0925-8388
Resumen:
One of the current issues at the basis of the understanding of novel materials is the degree of the role
played by spatial inhomogeneities due to subtle phase separations. To clarify this picture herewecompare
the plain glass network response of transition metal granular films with different metal fractions against
what is known for conducting oxides. Films for Nix(SiO2)1−x (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) were
studied by temperature dependent far infrared measurements. While for pure Ni the spectrum shows
a flat high reflectivity, those for x∼0.84 and ∼0.75 have a Drude component, vibrational modes mostly
carrier screened, and a long tail that extents toward near infrared. This is associated with hopping electron
conductivity and strong electronphonon interactions. The relative reduction of the number of carriers in
Ni0.75(SiO2)0.25 allows less screened phonon bands on the top of a continuum and a wide and overdamped
oscillator at mid-infrared frequencies. Ni0.54(SiO2)0.46 and Ni0.28(SiO2)0.72 have well defined vibrational
bands and a sharp threshold at ∼1450cm−1. It is most remarkable that a distinctive resonant peak at
∼1250cm−1 found for p-polarized angle dependent specular reflectivity. It originates in an electron cloud
traced to electrons that are not able to overcome the metaldielectric interface that, beating against the
positive background, generates the electric dipole. Overall, we conclude that the spectra are analogous
to those regularly found in conducting oxides where with a suitable percolating network polarons are
forme