Far infrared near normal specular reflectivity of Ni sub(x)(SiO sub(2)) sub(1-x) (x = 1.0, 0.84, 0.75, 0.61, 0.54, 0.28) granular films

• Published in: Journal of alloys and compounds 2010-04, Vol.495 (2), p.638-641
• Main Authors: Massa, Nestor E, Denardin, Juliano C, Socolovsky, Leandro M, Knobel, Marcelo, De la Cruz, Fernando P, Zhang, XiXiang
• Format: Article
• Language: English
• Subjects: Bands; Carriers; Conduction; Infrared; Networks; Oxides; Reflectivity
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2009.10.228

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 here we compare the plain glass network response of transition metal granular films with different metal fractions against what is known for conducting oxides. Films for Ni sub(x)(SiO sub(2)) sub(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 [inline image] 0.84 and [inline image]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 electron-phonon interactions. The relative reduction of the number of carriers in Ni sub(0.75)(SiO sub(2)) sub(0.25) allows less screened phonon bands on the top of a continuum and a wide and overdamped oscillator at mid-infrared frequencies. Ni sub(0.54)(SiO sub(2)) sub(0.46) and Ni sub(0.28)(SiO sub(2)) sub(0.72) have well defined vibrational bands and a sharp threshold at [inline image]1450 cm super(-1). It is most remarkable that a distinctive resonant peak at [inline image]1250 cm super(-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 metal-dielectric 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 formed.