Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping

Cheah, Chun Yee; Gómez-Navarro, Cristina; Jaurigue, Lina; Kaiser, A. B.

doi:10.1088/0953-8984/25/46/465303

Cited by 10 publications

(18 citation statements)

References 28 publications

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“…On the range of temperatures studied, there is not an unequivocal behaviour (See Figure S12-S19 in supporting information), however for all the composites the maximum adjustment for  is 1/4 ( Figure 18), which is in accordance with other CNT [57] and graphite composites reported results [58,59]. In the case of disorder deposited graphene materials [60,61] it follows a 2D system behaviour. We have observed that relaxation time,, decreases (calculated from p in the Z´´ plots) with an increasing on temperature and RH ( figure 19).…”

Section: Dielectric Relaxationsupporting

confidence: 82%

Testing the influence of the temperature, RH and filler type and content on the universal power law for new reduced graphene oxide TPU composites

Gómez

Villaro

Navas

et al. 2017

Mater. Res. Express

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In this paper, 6 different reduced graphene oxide (rGO) were prepared by a modified Hummers' method and reduced by thermochemical methods. rGO materials were intentionally prepared to obtain different BET and thickness and oxygen content maintaining constant the lateral size to compare its performance on thermoplastic polyurethane (TPU) matrix. Microstructure and the effect of the incorporation of rGO on the hardness and electrical properties of TPU were investigated. It has been studied the temperature and humidity dependence of the electrical conductivity and the sensitivity and the response time to humidity changes have been determined. Influence of the filler content, temperature and humidity on the Jonscher's universal power law (UPL) for ac conductivity vs frequency and its fitting parameters A and n were determined. It has been observed an anomalous behaviour (according to UPL) and a linear correlation between log A and n independently of the filler content, humidity and temperature, however there is an influence of the rGO used for the preparation of the composite. To study the transport mechanisms the experimental results were adjusted to the equation = 0 exp[-(TMott/T)] and the maximum adjustment for  = 1/4 like other carbon nanocomposites however there is not an unequivocal behaviour.

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Section: Dielectric Relaxationsupporting

confidence: 82%

Testing the influence of the temperature, RH and filler type and content on the universal power law for new reduced graphene oxide TPU composites

Gómez

Villaro

Navas

et al. 2017

Mater. Res. Express

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“…Such a behavior is well known for disordered systems, including disordered graphene. It can be understood in terms of Anderson localization and variable range hopping (VRH) transport [34,35,36,37,38]. The fit in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…With decreasing sample temperature the sheet resistance is exponentially increasing from 2 kΩ/2 up to 20 kΩ/2. This behavior is well known for disordered systems and especially also for disordered graphene and can be understood in terms of Anderson localization [34,35,36,37]. To verify this assumption we fit the data according to the model of variable range hopping (VRH) which is the basic transport mechanism in Anderson localized systems [38].…”

Section: Si 3 Electrical Measurementsmentioning

confidence: 99%

Graphene grown on Ge(0 0 1) from atomic source

Lippert

Dąbrowski

Schroeder

et al. 2014

Carbon

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Among the many anticipated applications of graphene, some -such as transistors for Si microelectronics -would greatly benefit from the possibility to deposit graphene directly on a semiconductor grown on a Si wafer. We report that Ge(001) layers on Si(001) wafers can be uniformly covered with graphene at temperatures between 800 • C and the melting temperature of Ge. The graphene is closed, with sheet resistivity strongly decreasing with growth temperature, weakly decreasing with the amount of deposited C, and reaching down to 2 kΩ/2. Activation energy of surface roughness is low (about 0.66 eV) and constant throughout the range of temperatures in which graphene is formed. Density functional theory calculations indicate that the major physical processes affecting the growth are: (1) substitution of Ge in surface dimers by C, (2) interaction between C clusters and Ge monomers, and (3) formation of chemical bonds between graphene edge and Ge(001), and that the processes 1 and 2 are surpassed by CH 2 surface diffusion when the C atoms are delivered from CH 4 . The results of this study indicate that graphene can be produced directly at the active region of the transistor in a process compatible with the Si technology.

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“…Despite the higher quality, the resulting graphene film still contains a high density of defects based on electrical measurements [Lippert et al 2014, Fig. 6], and due to these disorders, the transport mechanism across the disordered graphene is explained by variable-range hopping (see Chapter 2.1) and in fact the authors have cited our paper [Cheah et al 2013] in support of their observed electronic conduction.…”

Section: Potential Applications Of Graphene-based Materialsmentioning

confidence: 51%

“…(As an aside, we note that in the literature review of [Muchhala et al 2014], their sentence, "They reported two possible conduction processes: 2D-VRH conduction mechanism at higher temperatures with low bias and at lowest temperatures with high biases, a temperature-independent field-driven tunneling process" attributed to [Kaiser et al 2009] should have been rightly attributed instead to [Cheah et al 2013] as it is one of the main results of this thesis (see Chapter 5) i.e. that of a crossover between two VRH conduction regimes, and was not discussed in the older paper.…”

Section: Recent Advances In the Synthesis Of Reduced Graphene Oxidementioning

confidence: 99%

Electronic Conduction in Disordered Carbon Materials

Cheah¹

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<p>Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction.</p>

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Conductance of partially disordered graphene: crossover from temperature-dependent to field-dependent variable-range hopping

Cited by 10 publications

References 28 publications

Testing the influence of the temperature, RH and filler type and content on the universal power law for new reduced graphene oxide TPU composites

Testing the influence of the temperature, RH and filler type and content on the universal power law for new reduced graphene oxide TPU composites

Graphene grown on Ge(0 0 1) from atomic source

Electronic Conduction in Disordered Carbon Materials

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