Theory of percolation and tunneling regimes in nanogranular metal films

Grimaldi, Claudio

doi:10.1103/physrevb.89.214201

Cited by 37 publications

(64 citation statements)

References 54 publications

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“…[33]. Tunneling processes [37,38] and related soft percolation problems [39] have been studied for some time, but it has only recently been demonstrated [33,40,41] that when tunneling is allowed the system conductance depends exponentially on surface coverage p below the percolation threshold, p c = 0.676336 [42] and that for p > p c the system conductance obeys the power law:…”

Section: Simulation Detailsmentioning

confidence: 99%

Neuromorphic behavior in percolating nanoparticle films

Fostner

Brown

2015

Phys. Rev. E

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We show that the complex connectivity of percolating networks of nanoparticles provides a natural solid-state system in which bottom-up assembly provides a route to realization of neuromorphic behavior. Below the percolation threshold the networks comprise groups of particles separated by tunnel gaps; an applied voltage causes atomic scale wires to form in the gaps, and we show that the avalanche of switching events that occurs is similar to potentiation in biological neural systems. We characterize the level of potentiation in the percolating system as a function of the surface coverage of nanoparticles and other experimentally relevant variables, and compare our results with those from biological systems. The complex percolating structure and the electric field driven switching mechanism provide several potential advantages in comparison to previously reported solid-state neuromorphic systems.

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Section: Simulation Detailsmentioning

confidence: 99%

Neuromorphic behavior in percolating nanoparticle films

Fostner

Brown

2015

Phys. Rev. E

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“…The conduction depends on particle-to-particle paths that are not in straight lines but follow various detours (Jiang et al, 2015;Grimaldi et al, 2001;Grimaldi, 2014) due to the random arrangement of particles. If strain is applied transverse to the current direction, the transverse detour-components of the conduction paths are strained as well, resulting in a resistance change with a transverse gauge factor k T .…”

Section: Longitudinal and Transversal Gauge Factorsmentioning

confidence: 99%

Granular metal–carbon nanocomposites as piezoresistive sensor films – Part 1: Experimental results and morphology

Schultes¹,

Schmid-Engel²,

Schwebke³

et al. 2018

J. Sens. Sens. Syst.

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Abstract.We have produced granular films based on carbon and different transition metals by means of plasma deposition processes. Some of the films possess an increased strain sensitivity compared to metallic films. They respond to strain almost linearly with gauge factors of up to 30 if strained longitudinally, while in the transverse direction about half of the effect is still measured. In addition, the film's thermal coefficient of resistance is adjustable by the metal concentration. The influence of metal concentration was investigated for the elements Ni, Pd, Fe, Pt, W, and Cr, while the elements Co, Au, Ag, Al, Ti, and Cu were studied briefly. Only Ni and Pd have a pronounced strain sensitivity at 55 ± 5 at. % (atomic percent) of metal, among which Ni-C is far more stable. Two phases are identified by transmission electron microscopy and X-ray diffraction: metal-containing nanocolumns densely packed in a surrounding carbon phase. We differentiate three groups of metals, due to their respective affinity to carbon. It turns out that only nickel has the capability to bond and form a stable and closed encapsulation of GLC around each nanoparticle. In this structure, the electron transport is in part accomplished by tunneling processes across the basal planes of the graphitic encapsulation. Hence, we hold these tunneling processes responsible for the increased gauge factors of Ni-C composites. The other elements are unable to form graphitic encapsulations and thus do not exhibit elevated gauge factors.

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“…Standard percolation theories [9] assume that the host matrix is a perfect insulator, which is an abrupt assumption in many real systems. Recent progresses on percolation phenomena in systems with matrixes that can be penetrated by electron quantum mechanical tunneling [10] describe better PVP/NGP composites.…”

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confidence: 99%

Dynamics of electric charge transport and determination of the percolation insulator-to-metal transition in polyvinyl-pyrrolidone/nano-graphene platelet composites

Lampadaris

Sakellis

Papathanassiou

2017

Applied Physics Letters

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Polyvinyl-pyrrolidone (PVP) loaded with different fractions of dispersed nanographene platelets (NGP) were studied by Broadband Dielectric Spectroscopy in the frequency range from 1 mHz to 1 MHz. Complex permittivity and dynamic ac conductivity as a function of frequency, temperature and composition were explored. The concentration-dependent insulator-to-conductor transition was traced through dependence of the dc conductivity and the onset of the dispersive ac ac conductivity. The temperature evolution of the dielectric spectra, below and above the fractional threshold exhibits different dynamics and signs the critical percolation threshold. Percolation is dictated by quantum penetration of the effective potential barrier set by the polymer matrix operating in parallel with conduction along physical contact of NGP, in accordance with predictions for systems consisting of a semi-conducting matrix and dispersed conducting inclusions.* Corresponding author; e-mail address: antpapa@phys.uoa.gr 2 Functional polymers with dispersed nano-structures exhibit properties of significant technological importance, broad applicability and low production cost. Polyvinyl-pyrrolidone (PVP) is a polymer wide known for its pharmaceutical applications. It can be used as binder, coating and disintegrate for tablets stabilizer [1]. PVP is easily dissolved in water; both PVP and water are non-toxic, environmentally friendly and bio-compatible materials. Graphene is an excellent conductor of electricity and can be dispersed into water. Nano-graphene platelets combine the advantageous properties of graphene and the low production cost (e.g., in relation with single layered graphene). Thus, controlling the PVP/NGP composition, one can tune the properties of the composite, respectively, and achieve the desired optimum properties respectively. In this way, novel ambitious devices can be innovated. For example, water solutions PVP/ NGP composite can be used as bio-compatible link between electrodes and skin or tissues. As a result, various coated functional polymers with graphene [2, 3] have been prepared in order to analyse the mechanisms of charge transfer [4], to find the critical nanoparticle concentration to achieve percolation of electric charge carriers along the volume of the composite [5,6,7] and generally to inspect the electrical properties for those various matrices.Lastly, PVA (polyvinyl-alcohol) is a relevant material with polyvinyl-pyrrolidone that has been studied significantly [8]. In such studies, the dc conductivity vs composition is examined to find the percolation threshold. Standard percolation theories [9] assume that the host matrix is a perfect insulator, which is an abrupt assumption in many real systems. Recent progresses on percolation phenomena in systems with matrixes that can be penetrated by electron quantum mechanical tunneling [10] describe better PVP/NGP composites.Aqueous polymer solutions were formed by dissolving PVP K30 (ASG SCIENTIFICCAS 9003-39-8) in de-ionized doubly distilled water and aque...

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Theory of percolation and tunneling regimes in nanogranular metal films

Cited by 37 publications

References 54 publications

Neuromorphic behavior in percolating nanoparticle films

Neuromorphic behavior in percolating nanoparticle films

Granular metal–carbon nanocomposites as piezoresistive sensor films – Part 1: Experimental results and morphology

Dynamics of electric charge transport and determination of the percolation insulator-to-metal transition in polyvinyl-pyrrolidone/nano-graphene platelet composites

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