Transport properties of progressively reduced graphene oxide (GO) are described Evolution of the electronic properties reveals that as-synthesized GO undergoes insulator−semiconductor−semimetal transitions with reduction The apparent transport gap ranges from 10 to 50 meV and approaches zero with extensive reduction Measurements at varying degrees of reduction reveal that transport in reduced GO occurs via variable-range hopping and further reduction leads to an increased number of available hopping sites

/pdf/insulator-to-semimetal-transition-in-graphene-oxide-gorvz1q17g.pdf

Insulator to semimetal transition in graphene oxide

The well-known enhanced conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films that is obtained by addition of high-boiling solvents like sorbitol to the aqueous dispersion used for film deposition is shown to be associated with a rearrangement of PEDOT-rich clusters into elongated domains, as evidenced from STM and AFM. Consistently, temperature dependent conductivity measurements for sorbitol-treated films reveal that charge transport occurs via quasi ID variable range hopping (VRH), in contrast to 3D VRH for untreated PEDOT:PSS films. The typical hopping distance of 60-90 nm, extracted from the conductivity measurements is consistent with hopping between the 30-40 nm sized grains observed with scanning probe microscopy.

A Morphological Model for the Solvent-Enhanced Conductivity of PEDOT:PSS Thin Films**

We have performed a detailed study of the intrinsic electrical conduction process in individual monolayers of chemically reduced graphene oxide down to a temperature of 2 K. The observed conductance can be consistently interpreted in the framework of two-dimensional variable-range hopping in parallel with electric-field-driven tunneling. The latter mechanism is found to dominate the electrical transport at very low temperatures and high electric fields. Our results are consistent with a model of highly conducting graphene regions interspersed with disordered regions, across which charge carrier hopping and tunneling are promoted by strong local electric fields.

/pdf/electrical-conduction-mechanism-in-chemically-derived-5dke0sulkz.pdf

Electrical Conduction Mechanism in Chemically Derived Graphene Monolayers

Hopping conductivity in ordered and disordered solids (II)

Measurements of the conductivity sigma xx in the minima of the Shubnikov-de Haas oscillations on GaAs-AlxGa1-xAs heterostructures show that at helium temperatures a strong non-ohmic behaviour is observed with an instability in the current-voltage characteristic at electric field values of about 100 V cm-1 at B=7T. The data are analysed on the basis of an electric-field-dependent electron temperature.

https://iopscience.iop.org/article/10.1088/0022-3719/16/28/012/pdf

Two-dimensional magneto-quantum transport on GaAs-AlxGa1-xAs heterostructures under non-ohmic conditions

A previous percolation theory for hopping conduction is extended to high fields, and applied specifically to the Mott (1969) model (a constant density of states). The importance of nearest-neighbour pair correlations, the local chemical potential, and certain spatial correlations are discussed. The directional constraints created by the spatial correlations and by the nature of the percolation cluster are included approximately. The effect of the local chemical potential is included in an approximation similar to the mean field approximation. The theory is worked out primarily in the moderate field regime. The conductance is found to be proportional to exp (-A+eFl/kT), where exp(-A) is the low field conductance, F the electric field, and l a fraction of the characteristic low-field hopping distance rm. For three dimensions, l=0.17 rm, and for two dimensions, l=0.18 rm. Expressions are also derived for the high-field limit, and agree functionally with derivations by others.

http://iopscience.iop.org/article/10.1088/0022-3719/9/12/017/pdf

M Pollak

Papers

A percolation treatment of high-field hopping transport