Abstract
Granular metals are composites consisting of a random mixture of nanometer-sized metal and insulator grains. As a function of metal volume fraction, the structure and electrical properties of the granular metals can be divided into two regimes, separated by the percolation threshold. In the metal-rich regime, metal grains form a connected network, and electrical conduction is by electron percolation through the metallic channels. The physical basis and formulation of an effective-medium theory are described for the calculation of this percolative aspect of the electrical transport. The role of microstructure in the effective medium property is particularly emphasized. In the insulator-rich regimes, metal grains are dispersed in the matrix of the insulator. Electrical conduction in this dielectric regime is via the hopping mechanism, which is a term coined to denote the combination of thermal activation and tunneling. A critical-path method is presented to show that activation and tunneling, nominally independent, can actually couple to give a -ℓn σ ∝ T-α type of temperature dependence for the conductivity σ. For granular metals, the widely observed -ℓn σ ∝ 1 / √T behavior is ascribed to be an interpolation between the high-temperature activated behavior and the low-temperature α = 1/4 behavior. The alternative mechanism of the correlation gap is also discussed.
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© 1994 Springer Science+Business Media Dordrecht
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Sheng, P. (1994). Electronic Transport in Granular Metal Films. In: Hadjipanayis, G.C., Siegel, R.W. (eds) Nanophase Materials. NATO ASI Series, vol 260. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-1076-1_43
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DOI: https://doi.org/10.1007/978-94-011-1076-1_43
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