AC conductivity and correlation effects in nano-granular Pt/C

Abstract

Nano-granular metals are materials that fall into the general class of granular electronic systems in which the interplay of electronic correlations, disorder and finite size effects can be studied. The charge transport in nano-granular metals is dominated by thermally-assisted, sequential and correlated tunneling over a temperature-dependent number of metallic grains. Here we study the frequency-dependent conductivity (AC conductivity) of nano-granular Platinum with Pt nano-grains embedded into amorphous carbon (C). We focus on the transport regime on the insulating side of the insulator metal transition reflected by a set of samples covering a range of tunnel-coupling strengths. In this transport regime polarization contributions to the AC conductivity are small and correlation effects in the transport of free charges are expected to be particularly pronounced. We find a universal behavior in the frequency dependence that can be traced back to the temperature-dependent zero-frequency conductivity (DC conductivity) of Pt/C within a simple lumped-circuit analysis. Our results are in contradistinction to previous work on nano-granular Pd/$$\hbox {ZrO}_2$$ ZrO 2 in the very weak coupling regime where polarization contributions to the AC conductivity dominated. We describe possible future applications of nano-granular metals in proximity impedance spectroscopy of dielectric materials.

The effect of metal–insulator interface interactions on electrical transport in granular metals

“…where T 0 is the characteristic temperature, ∼100 K for many GMs [84]. The decreases in GM conductivity at 75 K compared to 300 K indicate that ϕ c ∼ 0.4-0.5 for both Co-YSZ and Mo-YSZ.…”

Granular metals with SiN x dielectrics

“…GMs have been studied for >50 years [12,13] for both fundamental and applied research in nanoelectronics [14], plasmonics [15], superconductivity [16], and magnetism [17]. While GMs with various metals have been investigated, nearly all GM studies employed oxide-based insulators, such as SiO 2 , Al 2 O 3 , or yttria-stabilized zirconia (YSZ), with notable non-oxides including MgF 2 [18], BN [19], and carbon-based [20,21] GMs. Recently, we found that GMs with non-noble metals and oxide insulators form metal-oxides, which deleteriously increase GM conductivity at j < j c [5].…”

Novel Dielectric Nanogranular Materials with an Electrically Tunable Frequency Response

“…[4] Tunable frequency filters may cover multiple frequencies to meet different scenarios in multiple band operations.Nanogranular materials comprise disordered nanometer-sized granular metals dispersed in a host matrix and are a robust platform for studying complex disordered solids. [10,11] Based on this platform, a variety of intriguing phenomena have been discovered that involve the interplay of electronic, [12,13] magnetic, [14,15] optical, [16,17] and thermal properties, [18,19] as well as quantum [20] and superconductive behavior. [21] At diluted granular fractions (typically less than the percolation threshold of 50 vol%), the materials are in the dielectric regime, whereby both DC [22,23] and AC [24,25,26,27] electrical transport properties have been widely studied in this regime.…”