Electronic applications of large-area graphene films require rapid and accurate methods to map their electrical properties. Here we present the first electrical resistance tomography (ERT) measurements on large-area graphene samples, obtained with a dedicated measurement setup and reconstruction software. The outcome of an ERT measurement is a map of the graphene electrical conductivity. The same setup allows to perform van der Pauw (vdP) measurements of the average conductivity. We characterised the electrical conductivity of chemical-vapour deposited graphene samples by performing ERT, vdP and scanning terahertz time-domain spectroscopy (TDS), the last one by means of a commercial instrument. The measurement results are compared and discussed, showing the potential of ERT as an accurate and reliable technique for the electrical characterization of graphene samples.

We propose a simple algorithm to locate the ‘corner’ of an L-curve, a function often used to select the regularisation parameter for the solution of ill-posed inverse problems. The algorithm involves the Menger curvature of a circumcircle and the golden section search method. It efficiently finds the regularisation parameter value corresponding to the maximum positive curvature region of the L-curve. The algorithm is applied to some commonly available test problems and compared to the typical way of locating the l-curve corner by means of its analytical curvature. The application of the algorithm to the data processing of an electrical resistance tomography experiment on thin conductive films is also reported.

Metallic nanowire (NW) networks have attracted great attention as promising transparent conductive materials thanks to the low sheet resistance, high transparency, low cost production, and compatibility with flexible substrates. Despite many efforts having been devoted to investigating the conduction mechanism, a quantitative characterization of local electrical properties of nanowire networks at the macroscale still represents a challenge. In this work, we report on the investigation of local electrical properties and their evolution over time of Ag NW networks by means of electrical resistance tomography (ERT). Spatial correlation of local conductivity properties and optical transparency revealed that the nonscanning and rapid ERT technique allows to probe local electrical inhomogeneities in the NW network, differently from conventional measurement techniques such as van der Pauw and the four-point probe. In addition, ERT mapping over time was employed for in situ monitoring the evolution of Ag NW networks conductivity, elucidating the dependence of the degradation of local electrical properties under ambient exposure on the initial conductivity. Our results shed light on the importance of the characterization of local electrical properties of NW networks where uniformity and stability represent the main challenges to overcome for their use as transparent conductive materials.

The electrical resistance tomography (ERT) technique is applied to the measurement of sheet conductance maps of both uniform and patterned conductive thin films. Images of the sheet conductance spatial distribution and local conductivity values are obtained. Test samples are tin-oxide films on glass substrates, with electrical contacts on the sample boundary. Some samples are deliberately patterned in order to induce null conductivity zones of known geometry, while others contain higher conductivity inclusions. Four-terminal resistance measurements among the contacts are performed with a scanning setup. The ERT reconstruction is performed by a numerical algorithm based on the total variation regularization and the L-curve method. ERT correctly images the sheet conductance spatial distribution of the samples. The reconstructed conductance values are in good quantitative agreement with independent measurements performed with the van der Pauw and the four-point probe methods

Characterization of intrinsic electrical properties of large surface area materials like mesoporous nanocrystalline (nc-TiO 2 ), requires to avoid sensor-like response to external agents. Both an appropriate sample configuration and a suitable measurement protocol are mandatory. In this work both stack and planar contacts configuration were studied, the latter giving evidence to be potentially useful for space charge limited (SCL) current investigations in order to study the band-gap states (BGS) properties in nc-TiO 2 . Moreover in absence of a suitable measurement protocol, standard dye sensitized solar cells (DSSC) electrode films show apparent SCL current behavior, as consequence of surface electrical transport contribution due to physisorbed water on the hydroxylated metal oxide large surface area. This feature recalls the typical results of electrolyte filled systems, in which an exponential distribution of trap states is reported, and it is not expected to be the intrinsic feature of nc-TiO 2 trap states distribution. In absence of adsorbates, no deviation from ohmic regime is observed in standard electrodes, while in planar configuration samples the SCL regime is accessible and shows a different BGS signature. The nature of the electrical contacts, ohmic in the present situation, is also discussed.