Electronic Properties

CoxC1—x (x = 0.18, 0.25, 0.39) nanogranular films were prepared by pulsed filtered vacuum arc deposition [592]. The as-deposited films with various Co concentrations were amorphous. Upon annealing, nanocrystalline Co grains were formed, while the carbon content remained amorphous. The electrical resistance of the films was measured as a function of temperature between 20 and 300 K. While the as-deposited films were metallic in the measured temperature range, annealed films showed complicated transport properties, depending on both the Co concentration and the annealing temperature. Experimental results were compared to the general predictions of theories of weak localization and/or electron-electron interaction on the metallic side of the metal-insulator transition and thermally assisted hopping or tunneling on the insulating side of the transition.

Composites of silica glass and metal nanoparticles of copper or nickel were synthesized by the hot compaction of sol-gel-derived glass-metal powders [593]. The metal particle sizes ranged from 5.1 to 7.2 nm. The electrical resistivity of the composites was characterized by semiconductor-like behavior in the temperature range 235-340 K. This was believed to arise due to electron hopping between localized states within the bandgap of amorphous silica formed by the dispersed metal atoms.

Electrically conducting films of thickness approximately 2 /m were prepared on ordinary glass slides by growing nanoparticles of iron and copper, respectively, from a suitable precursor sol [594, 595]. The diameters of metal particles varied from 3 to 13 nm by controlling the heat-treatment schedule of the sol coating. The resistivity values in the range 0.0001-0.0039 H/cm over the temperature range 80-300 K were obtained depending on the particle diameter and the type of metal used. The effective Debye temperature 6d for the different nanoparticle systems was estimated by fitting the experimental data to the Ziman equation. 6D varied from 346 to 408 K for iron with the particle size in the range 3.4-9.5 nm. The values obtained for copper are 243-307 K with particle diameters covering a range of 5.9-12.6 nm.

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