Carrier Transport in Reduced Graphene Oxide Probed Using Raman

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C: Energy Conversion and Storage; Energy and Charge Transport

Carrier Transport in Reduced Graphene Oxide Probed Using Raman Spectroscopy Duvvuri Surya Bhaskaram, and Gurusamy Govindaraj J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b01311 • Publication Date (Web): 24 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018

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The Journal of Physical Chemistry

Carrier Transport in Reduced Graphene Oxide Probed Using Raman Spectroscopy D. Surya Bhaskaram and G. Govindaraj* Department of Physics, School of Physical, Chemical and Applied Sciences, Pondicherry University, R.V. Nagar, Kalapet, Pondicherry -605 014, India

Email: [email protected]

Abstract In the present work, we have investigated the temperature dependent electronic conduction in hydrazine reduced graphene oxide in the temperature range of 300K to 5K. The Raman spectroscopy and transport measurements are used to probe the conduction mechanism. It is observed that the carrier transportation takes place via variable range hopping. For variable range hopping, various parameters such as density of states, hopping distance and hopping energy have been calculated. The conduction behaviours across the temperature range show three different regions with three different characteristic temperatures. Temperature-dependent Raman spectra have been successfully studied for ID/IG ratio, which uncovers the length scales of defect sites and number of defects. Further, the linewidth of the G band is studied to get an insight of electronphonon interaction. The quantitative analysis of transport mechanism is done using electronphonon coupling and ID/IG ratio.

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Introduction More than a decade has passed since the advent of the wonder material graphene. Still, graphene attracts the attention of researchers due to its extraordinary properties such as high electric and thermal conductivity, optical transparency and mechanical strength. Functionalizing graphene sheets or doping the graphene sheet bring in new opportunities in semiconductor electronic devices. So far, various methods have been used for its synthesis such as chemical vapor deposition, micromechanical exfoliation, liquid phase exfoliation and chemical oxidationreduction. The need for a high yield and low-cost method brought into limelight the reduction of age-old material graphene oxide. The product obtained by such a method is termed as reduced graphene oxide (rGO). The reduction of GO using hydrazine is one such common approach when it comes to high yield at low cost. The rGO is the choice not only because of its low cost and high yield but also for its desirable properties such as wettability and defective nature. These properties are useful in energy storage industry,(1) electronics,(2) sensors, biomedical,(3) and printable graphene electronics.(4) The rGO obtained by thermal or chemical reduction contains nanometer range sp2 carbon atoms arranged in a honeycomb lattice. To this long array of carbon atoms, are attached the oxygen functional groups. The content of oxygen functional groups is decided by the degree of reduction.(5) Hydrazine is a strong reducing agent; it reduces the GO to rGO leaving behind very few oxygen functional groups. This process leaves the sp2 carbon array with defects. Electron transport in graphene layers has been investigated for several years. The rGO is an analogue to pristine graphene but the charge transport behaviour in rGO is quite different from pristine graphene. A thorough understanding of the carrier transport mechanism in rGO layers is needed to access the rGO based device application. Ho-Jong Kim et al.,(6) has explained the charge transport in thick rGO layers using parallel percolating conductive pathways consisting of sp2 conducting channels and defect mediated transport. Muchharla et al.,(7) gave an account on temperature-dependent electrical transport properties of rGO films in a wide temperature range of 50K to 400K. The electrical conduction in rGO was displayed in two different temperature regimes. At higher temperatures, band gap dominating transport behaviour was observed while at lower temperatures, the rGO sample showed a conduction mechanism consistent with Mottʼs variable range hopping. Neustroev et al.,(8) also studied the conductivity of thermally reduced graphene oxide and inferred similar results as those by Muchharla et al. Cheah et al.,(9) gave an account on VRH in disordered carbon and electric field driven VRH. Go´ mez-Navarro et al.,(10) described the conduction in chemically derived graphene using hopping conduction between 2 ACS Paragon Plus Environment

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defect sites. Junsheng Ma et al., (11) performed the temperature dependent conductivity studies on rGO film and showed the semiconducting behavior of rGO, following Mott’s 3D VRH and thermal conduction at different temperature regions. Raman spectroscopy is one of the tools, which has been extensively used to study graphene. It is a fast and non-destructive tool and provides maximum information on structural and electronic properties of graphene.(12) The technique in addition to throwing light on various vibrational modes can also be used for quantifying the purity of graphene layer. Thorough studies combined with phonon dispersion relation of graphene has brought into knowledge the types of phonons involved in electron scattering events giving rise to various bands. The Raman spectra of carbon materials are quite simple to look at with few intense bands and their overtone. The shape, size and position of these bands are loaded with information. The most prominent band in graphene’s Raman spectra are 2D and G band. The 2D band also known as G' Raman band of pristine graphene has been studied by researchers to extract the information on the purity of sample.(13) There are studies available on change in line width, peak position and shape of the 2D band to analyze the number of layers and get an insight of the optical process. The position and FWHM of G band have been studied by various groups to get an insight of electron-phonon coupling in graphene. Further temperature dependence of these bands reveals the information of temperature coefficient of G band and anharmonic properties of graphene.(14) In chemically derived graphene, G band and D band are of prime importance. Sometimes the 2D band is also observed. The D band is a defect-activated band. The position of D band shifts with excitation energy.(15) Based on ID/IG ratio, reduction of graphene oxide to graphene is monitored.(16) An estimation of the number of layers is done through this ratio. This ratio is also used to quantify defects in graphene such as the distance between defects and number of defects. (17) The intensity of the G band, peak broadening and a shift in the frequency of the G band due to change in laser power, temperature and excitation energy are of great interest as they can uncover many of the physical properties such as thermal conductivity,(18) thermal expansion coefficient, shear and stress incorporated due to a substrate.(19) Electron and hole doping can also be monitored using the G band. Further information on electron-phonon coupling can be quantitatively analyzed using linewidth of the G band.(20) Few reports have used Raman spectroscopy to connect to transport properties of graphene qualitatively.(10)



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In the present work, we have studied the electronic transport behaviour of chemically reduced graphene, as a function of temperature. The dc conductivity data in a wide range of 5K to 300K has been explored. The Mott’s VRH transport mechanism is incorporated to analyze the conductivity data. Various parameters such as density of states, hopping length and energies have been calculated. Further, to have a quantitative study of hopping mechanism, temperature dependent Raman spectroscopy is used. The contribution of electron-phonon coupling to conduction is calculated with the aid of Raman spectroscopy.

Experimental Graphite oxide was prepared following modified Hummer’s method as reported in ref. (21) To prepare rGO, 100 mg of as prepared graphite oxide was dispersed in 100 ml of DI water. This solution was poured into an RB flask and set for heating at 100 °C. The RB flask was connected to the water-cooled condenser to reflux the solution mixture. Then, one ml of hydrazine hydrate was added to the above solution and nitrogen gas was slowly purged into the solution. The inflow of nitrogen was stopped after 30 seconds of purging. This solution was stirred for 24 hours and Reduced GO was cast out as a bulk solid. The solid product was isolated and washed using DI water and methanol. This was vacuum dried in an oven for 4 hours.(22)

Results and Discussion The X-ray diffraction was performed to confirm the reduction of GO to rGO as a primary step. The disappearance of sharp GO peak at 11° and appearance of a broad hump around 25° confirms the reduction process. The transmission electron microscopy (TEM) Fig.1 shows the TEM image of as-prepared rGO sample. In the TEM image, we can see a single to few layers of the disordered sheet with folding appearing as dark lines.(23)

Raman Spectroscopy The Raman spectra were recorded with Renishaw confocal Raman microscopy with an excitation source of 785 nm. The temperature dependent Raman spectroscopy was performed 4 ACS Paragon Plus Environment

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using cold-hot temperature control cell attached to the instrument with temperature varying from 123K to 423K. The demand of rGO in varied applications such as energy storage and sensors is in its bulk state. Thus, the characterization of the bulk sample needs to be done for the extraction of its potential benefits. To accomplish this the sample was pressed into the form of a small disc of 0.9 mm thickness and subject to laser excitation, using confocal Raman spectroscopy. Raman Spatial mapping and depth analysis were performed to check the homogeneity of the pellet. To understand the Raman spectra obtained, first we need to understand the phonon dispersion relation. Graphene has two non-equivalent atoms per unit cell, thus six normal modes with two degenerate modes at Γ point (Brillouin zone centre): A2u+B2g+E1u+E2g. Out of them only the E2g mode has a second order notation in the Cartesian coordinates system when referred to character table of D6h point group. Thus, E2g mode is Raman active. The phonon dispersion of graphene contains six phonon bands out of which three are optical (O) and three are acoustic (A). Based on the kind of vibrations executed by phonons w.r.t. carbon plane they are further divided as inplane (i): vibrations, parallel to carbon plane and out of plane (o): vibrations perpendicular to carbon plane. Based on vibrations along and transverse to nearest carbon-carbon distance phonons are further classified as longitudinal (L) and transverse (T). Hence the six various modes are oTO, oTA, iLO, iTO, iLA, iTA. Specific Raman band in graphene is a result of scattering through either of these phonons and/or defects.(12,24)

Fig.2 shows the room temperature Raman spectra of rGO. It consists of two prominent bands at 1310 cm-1 and 1590 cm-1 that corresponds to the D and G band. A hump like feature is observed around 2613 cm-1 and 2900 cm-1which correspond to 2D and D+D' band. The G band originates due to the first order Raman scattering process with phonon wave vector q as zero. They are associated with E2g symmetry phonon mode, which is doubly degenerate. The G band has a finite broadening associated with it. For the prepared rGO, a finite broadening of nearly 46 cm-1 is observed in the G band. The broadening (𝛾) could be due to the electron-phonon coupling, anharmonic term and defects.(25)

𝛾 = 𝛾𝑎𝑛 + 𝛾𝐸𝑃𝐶 + 𝛾𝑑𝑒𝑓𝑒𝑐𝑡 The broadening contribution due to anharmonic term is very small in comparison to other sources, thus can be neglected. The contribution to the broadening due to electron-phonon coupling is calculated according to the formula given below(26) 5 ACS Paragon Plus Environment


𝛾 𝐸𝑃𝐶 = 𝛾0𝐸𝑃𝐶 {𝑓 [− (

ℏ𝜔Γ 2

ℏ𝜔Γ

+ ℇ𝐹 )] − 𝑓 (

2

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− ℇ𝐹 )}.……………………………………………(1)

Where 𝑓(𝑥) is Fermi Dirac distribution., 𝛾 𝐸𝑃𝐶 is the broadening due to electron phonon coupling when Fermi energy is not zero, 𝛾0𝐸𝑃𝐶 is the broadening due to electron phonon coupling when Fermi energy is zero, 𝜔Γ , the peak position of the G band for single layer pristine graphene is 1580 cm-1. The 𝛾 𝐸𝑃𝐶 calculated is 10.97 cm-1 at 300K and increases to 11.5cm-1 at 5K. From literature, it is perceived that the linewidth value of 11.5 cm-1 is the electron-phonon coupling contribution to the broadening in the single layer pristine graphene with zero band gap i.e. ℇ𝐹 = 0. For the as prepared rGO we observed from fermi energy measurements that, ℇ𝐹 changes from 1.16x10-4 to 1.7x10-5 eV as the temperature changes from 300K to 5K. The ℇ𝐹 value at low temperatures is quite small and this could be the reason behind obtaining similar line width as found in literature due to electron phonon coupling at ℇ𝐹 =

0 .(27) The spectral resolution contributes nearly 1cm-1 to broadening thus making a total of 11.97 cm-1 (10.97+1 cm-1) broadening at 300K. Out of the 46 cm-1 broadening obtained, we have accounted for 11.97 cm-1 using electron phonon coupling. The remaining 35.03 cm-1 could be due to the defects and multiple electron transition for more than one layer.(28) As we know from the TEM images that the rGO obtained is highly disordered, therefore the D' peak is expected immediately next to the G band. The D' band originates due to the intravalley transition activated by a defect and an iLO phonon. However, no such feature is seen in the obtained Raman spectrum. This could be due to the merging of D' band with G band making it appear wider.(29) The other prominent band in the Raman spectra obtained is the D band. The D band is due to the breathing mode of the carbon ring. This band requires an iTO phonon and one defect for its activation. It is a second-order process. The intensity ratio of D and G band, ID/IG is used to find the distance between defects (LD) and defect density nD in prepared rGO by following the relations,(17) −1 𝐼 𝐿2𝐷 (𝑛𝑚2 ) = (1.8 ± 0.5) × 109 𝜆4𝐿 ( 𝐷⁄𝐼 ) …………………………………………..2(a) 𝐺

1 𝐼𝐷 𝑛𝐷 (𝑐𝑚−2 ) = (1.8 ± 0.5) × 1022 𝜆−4 𝐿 ( ⁄𝐼 ) …………………………………………2(b) 𝐺

With the increase in temperature, it is found that 𝐼𝐷 ⁄𝐼𝐺 ratio increases hence LD decreases. This has

been shown in fig. 3. It is observed that the change in LD with temperature is not uniform throughout the temperature region; it shows a steep variation above 263K and tends to remain almost same below 263K. 6 ACS Paragon Plus Environment

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Conductivity Studies The conductivity measurement was performed using a quantum design physical property measurement system-AC transport probe. Fig. 4 shows the conductivity variation as a function of temperature. We have fit the data using power law given by Eq.(3). (30) 1

𝜎𝑑𝑐 = 𝜎1 𝑒

⁄4 𝑇 −( 0 ) 𝑇

…………………………………………………………………………(3)

T0 is the characteristic temperature coefficient, it is directly related to the degree of disorder. T0 depends on the localization length 𝜉 and density of states near the Fermi level 𝑁(𝜀𝑓 ), which is assumed to be constant around the Fermi level. 24

𝑇0 =

𝜋𝑘𝐵 𝑁(𝜀𝑓 )𝜉 3

……………………………………………………………………………..4(a)

To find the localization length 𝜉, which is the integration of all possible tunneling paths between hop sites, the following relation is used.(31) 2.8𝑒 2

𝑇0 =

4𝜋𝜀0 𝜀𝜉𝑘𝐵

………………………………………………………………………………4(b)

Where 𝜀 is the permittivity of rGO taken as three. To understand the mechanism of carrier transport, the temperature region from 300K to 5 K is divided into three regimes, regime I being 300K-183K, regime II from 182 to 23 K and regime III from 22 to 5 K. In all the three regimes conductivity dependence on temperature is observed to follow Eq.(3). The plot of conductivity data of the three different regimes fitted using Eq.(3), is shown in Fig.5. The characteristic temperatures T0, localization length and density of states are calculated and tabulated in table 1. Further to quantify the mechanism of hopping, hopping distance R and hopping energy W are calculated using the following formulae: (30) 𝑅=(

1⁄ 4

𝜉

)

8𝜋𝑘𝐵 𝑇𝑁(𝜀𝑓 )

…………………………………………………………………………5(a)

3

𝑊 = 4𝜋𝑅3 𝑁(𝜀 )……………………………………………………………………………….5(b) 𝑓

The variation of R as a function of temperature in the first two regimes are shown in Fig.6. It is observed that in regime I as the temperature decreases from 300K to 183K the conductivity gradually decreases. In regime II also a similar response is observed but below 23K there is a sudden drop in conductivity, observed up to 5K. To understand the conductivity mechanism we 7 ACS Paragon Plus Environment


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need to understand the structure of disordered rGO. The rGO layers are composed of continuous sp2 planes with sp3 clusters randomly dispersed on these planes. These sp3 clusters are formed due to the covalently attached oxygen functional groups to carbon atoms. The potential energy of these traps is much higher than that of sp2 domains. The charge carriers, specifically electrons are trapped inside these potential wells created by the sp3 cluster. Inside this potential well, there is a large network of sp2 bonded carbon atoms. There are numerous hurdles on this sp2 network such as edges and defects, which opposes the swift flow of electrons. These hurdles have lower potential as compared to sp3 clusters. Therefore, the carriers prefer to hop across these defects contributing to variable range hopping conduction. This is shown in Fig.7.

As calculated from Raman spectra the LD at 300K is 17.8 nm and R at 300K is 1.8 nm. The LD is the distance between two high potential defects; R is the distance between hops executed inside the well. Once the electron is trapped inside the potential well created by two sp3 matrices, it executes multiple hops across the defects present on sp2 planes bound inside the sp3 potential well. Thus from the above analogy, it is calculated using LD/R , that a carrier can execute nearly 10 hops inside a potential well at room temperature. As the temperature decreases to 182 K, the LD increases to 19.4 nm and R increases to 2.1 nm thus the number of hops decreases to 8 or 9. When the temperature reaches to 123K LD remains almost constant (~19.4 nm) as inferred from Raman data, but R increases to ~6 nm, thus the carrier executes only 3 to 4 hops before encountering a high potential barrier. Hence, there is a decrease in conductivity of rGO and this trend continues until 23K. On decreasing the temperature further, a sharp decrease in conductivity is observed. The electron-phonon coupling also plays an important role in electron conduction as discussed earlier in the Raman section. The G band broadening (𝛾) in Raman spectra points towards the electron-phonon coupling. The contribution of electron-phonon coupling to 𝛾 can be used to derive the coupling strength using Eq.(6),(26) 𝛾0𝐸𝑃𝐶 =

√3𝑎02 𝐸𝑃𝐶(Γ)2 …………………………………………………………………………(6) 2 4𝑀𝜐𝐹

𝐸𝑃𝐶(Γ)2 is the coupling strength, M is the atomic mass of the carbon atom, a0 is 2.46Å i.e. graphite lattice spacing and 𝜐𝐹 =2.4x103 m/s. In the temperature region 170K and below, the prepared sample shows the fermi energy (ℇ𝐹 ) of order 10-5 eV and corresponding broadening contribution of 11.5 cm-1 which is same as reported in literature for ℇ𝐹 = 0. Hence taking the value of 11.5 8 ACS Paragon Plus Environment

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cm-1 as 𝛾0𝐸𝑃𝐶 , the calculated 𝐸𝑃𝐶(Γ) = .05 𝑒𝑉/Å. This is comparable to,(20) though much less than the coupling strength obtained for pristine graphene. This is due to low Fermi velocity of electrons in rGO. Thus a finite electron-phonon coupling exists in the rGO layers due to which phonon couples to the electron and thus electron can no longer move freely until the interaction persists.

Conclusion In brief, we have synthesized rGO using hydrazine as the reducing agent. The characterization is done on the bulk sample pressed into the form of a pellet. Combining the Raman data and conductivity data the inference was drawn about the mode of conduction in rGO. It is observed that throughout the temperature region, carriers in rGO tend to execute variable range hopping. Raman fingerprint serves as a backbone for quantitative analysis of hopping mechanism and contribution of electron-phonon coupling to conduction mechanism.

Acknowledgement Authors would like to thank Central Instrumentation Facility, Pondicherry University for characterization facilities.

References (1) (2)

(3)

(4)

(5) (6)

Zhu, J.; Yang, D.; Yin, Z.; Yan, Q.; Zhang, H. Graphene and Graphene-Based Materials for Energy Storage Applications. Small 2014, 10, 3480–3498. Naderi, H. R.; Sobhani-Nasab, A.; Rahimi-Nasrabadi, M.; Ganjali, M. R. Decoration of Nitrogen-Doped Reduced Graphene Oxide with Cobalt Tungstate Nanoparticles for Use in High-Performance Supercapacitors. Appl. Surf. Sci. 2017, 423, 1025–1034. Yao, Z.; Yang, X.; Niu, Y.; Wu, F.; Hu, Y.; Yang, Y. Voltammetric Dopamine Sensor Based on a Gold Electrode Modified with Reduced Graphene Oxide and Mn3O4 on Gold Nanoparticles. Microchim. Acta 2017, 184, 2081–2088. Wang, S.; Ang, P. K.; Wang, Z.; Tang, A. L. L.; Thong, J. T. L.; Loh, K. P. High Mobility, Printable, and Solution-Processed Graphene Electronics. Nano Lett. 2010, 10, 92–98. Eda, G.; Mattevi, C.; Yamaguchi, H.; Kim, H.; Chhowalla, M. Insulator to Semimetal Transition in Graphene Oxide. J. Phys. Chem. C 2009, 113, 15768–15771. Kim, H.J.; Kim, D.; Jung, S.; Yi, S. N.; Yun, Y. J.; Chang, S. K.; Ha, D. H. Charge 9 ACS Paragon Plus Environment


(7) (8)

(9)

(10)

(11)

(12) (13) (14) (15) (16) (17)

(18)

(19) (20) (21)

(22)

(23)

(24)

Page 10 of 22

Transport in Thick Reduced Graphene Oxide Film. J. Phys. Chem. C 2015, 119, 28685– 28690. Muchharla, B.; Narayanan, T.N.;Balakrishnan, K.; Ajayan, P. Temperature Dependent Electrical Transport of Disordered Reduced Graphene Oxide. 2D Mater. 2014, 1, 11008. Neustroev, E. P.; Nogovitsyna, M. V; Solovyova, Y. S.; Alexandrov, G. N.; Burtseva, Е. K. Study of Electrical Conductivity of Thermally Reduced Graphene Oxide. Nanosystems. 2015, 7, 162–167. Cheah, C. Y.; Kaiser, A. B. Variable-Range Hopping Transport : Crossovers from Temperature Dependence to Electric Field Dependence in Disordered Carbon Materials. Int. J. Nanotechnol. 2009, 11, 412-418. Gómez-Navarro, C.; Weitz, R. T.; Bittner, A. M.; Scolari, M.; Mews, A.; Burghard, M.; Kern, K. Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets. Nano Lett. 2007, 7, 3499–3503. Ma, J.; Hou, X.; Yu, M.; Hua, J.; Ren, X.; Qiu, H.; Wang, R. Functional Chemically Modified Graphene Film: Microstructure and Electrical Transport Behavior. J. Phys. D: Appl. Phys. 2017, 50, 435101–435110. Ferrari, A. C.; Basko, D. M. Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene. Nat. Nanotechnol. 2013, 8, 235–246. Tang, B.; Guoxin, H.; Gao, H. Raman Spectroscopic Characterization of Graphene. Appl. Spectrosc. Rev. 2010, 45, 369–407. Calizo, I.; Balandin, A. A.; Bao, W.; Miao, F.; Lau, C. N. Temperature Dependence of the Raman Spectra of Graphene and Graphene Multilayers. Nano Lett. 2007, 7, 2645–2649. Sood, A. K.; Gupta, R.; Asher, S. A. Origin of the Unusual Dependence of Raman D Band on Excitation Wavelength in Graphite-like Materials. J. Appl. Phys. 2001, 90, 4494–4497. Tang, B.; Guoxin, H.; Gao, H. Raman Spectroscopic Characterization of Graphene. Appl. Spectrosc. Rev. 2010, 45, 369–407. Cançado, L. G.; Jorio, A.; Ferreira, E. H. M.; Stavale, F.; Achete, C. A.; Capaz, R. B.; Moutinho, M. V. O.; Lombardo, A.; Kulmala, T. S.; Ferrari, A. C. Quantifying Defects in Graphene via Raman Spectroscopy at Different Excitation Energies. Nano Lett. 2011, 11, 3190–3196. Balandin, A. A.; Ghosh, S.; Bao, W.; Calizo, I.; Teweldebrhan, D.; Miao, F.; Lau, C. N. Superior Thermal Conductivity of Single-Layer Graphene 2008. Nano Lett. 2008, 8, 902– 907. Tan, P.; Han, W.; Zhao, W.; Wu, Z. The Shear Mode of Multilayer Graphene. Nat. Mater. 2012, 11, 294–300. Park, C.-H.; Giustino, F.; Cohen, M. L.; Louie, S. G. Electron−Phonon Interactions in Graphene, Bilayer Graphene, and Graphite. Nano Lett. 2008, 8, 4229–4233. Surya Bhaskaram, D.; Cheruku, R.; Govindaraj, G. Reduced Graphene Oxide Wrapped V2O5 Nanoparticles: Green Synthesis and Electrical Properties. J. Mater. Sci. Mater. Electron. 2016, 27, 10855–10863. Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of Graphene-Based Nanosheets via Chemical Reduction of Exfoliated Graphite Oxide. Carbon. 2007, 45, 1558–1565. Ferrari, A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K. S.; Roth, S.; et al. Raman Spectrum of Graphene and Graphene Layers. Phys. Rev. Lett. 2006, 97, 187401. Malard, L. M.; Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S. Raman Spectroscopy 10 ACS Paragon Plus Environment

Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25)

(26) (27) (28)

(29) (30) (31)

in Graphene. Phys. Rep. 2009, 473, 51–87. Late, D. J.; Maitra, U.; Panchakarla, L. S.; Waghmare, U. V; Rao, C. N. R. Temperature Effects on the Raman Spectra of Graphenes: Dependence on the Number of Layers and Doping. J. Phys. Condens. Matter 2011, 23, 55303. Ferrari, A. C. Raman Spectroscopy of Graphene and Graphite: Disorder, Electron–phonon Coupling, Doping and Nonadiabatic Effects. Solid State Commun. 2007, 143, 47–57. Lazzeri, M.; Mauri, F. Nonadiabatic Kohn Anomaly in a Doped Graphene Monolayer. Phys. Rev. Lett. 2006, 97, 266407. Park, J. S.; Reina, A.; Saito, R.; Kong, J.; Dresselhaus, G.; Dresselhaus, M. S. G′ Band Raman Spectra of Single, Double and Triple Layer Graphene. Carbon. 2009, 47, 1303– 1310. Kaniyoor, A.; Ramaprabhu, S. A Raman Spectroscopic Investigation of Graphite Oxide Derived Graphene. AIP Adv. 2012, 2, 32183-13. Zhang, L.;Tang, Z. J. Polaron Relaxation and Variable Range Hopping Conductivity in the Giant-Dielectric-Constant Material CaCu3Ti4O12. Phys. Rev. B. 2004, 70, 471306. Santos, E. J. G.; Kaxiras, E. Electric-Field Dependence of the Effective Dielectric Constant in Graphene. Nano Lett. 2013, 13, 898–902.



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Table 1: Summary of the characteristic temperature obtained in three different temperature regimes and the calculated localization length (𝜉) and density of states 𝑁(𝜀𝑓 ). 𝑁(𝜀𝑓 ) (/eV cm3)

Temperature

T0 (K)

𝜉(nm)

300K-183K

4.4x103

3.5

4.56 × 1020

182K-23K

1.2x103

12

3.86 × 1019

22K-5K

2.8x103

5.4

1.21 × 1020


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Figure 1: The Transmission electron micrograph of reduced graphene oxide obtained by hydrazine reduction.



D band

rGO G band

Counts(A.U)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1000

1500

2000

2500 Raman shift (cm-1)

3000

Figure 2: Raman spectrum of as-prepared reduced graphene oxide with D and G band marked.


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19.5 19.0 18.5 18.0 LD(nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17.5 17.0 16.5 16.0 15.5 100 150 200 250 300 350 400 450 Temperature(K)

Figure 3: Variation of LD the distance between two Raman active defects as a function of temperature.



200

150 dc(S/cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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100

50

0 0

50

100

150

200

250

300

Temperature(K)

Figure 4: The dc conductivity as a function of temperature ranging from 300K to 5K.


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2.30

(a)

300K to 183K linear fit

2.25

log dc(S/cm)

2.20

2.15 0.24

0.25 0.26 1/4 -1/4 1/T (K )

0.27

2.2

(b) log dc(S/cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.0

182K-23K Linear fit

1.8

1.6 0.25

0.30 0.35 0.40 1/T1/4(K-1/4)

0.45



1.8 (c)

1.6

log dc(S/cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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22K-5K linear fit

1.4 1.2 1.0 0.5 1/4 -1/4 0.6 1/T (K )

0.7

Figure 5: Plot of DC conductivity as a function of T-1/4 in three different temperature regimes (a) 300K-183K, (b) 182K-23K, (c) 22K-5K.


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2.10

9.0

(a)

(a)

8.5

Rhop (300K-183K)

2.05 2.00 1.95 1.90

Rhop(182K-23K)

8.0 Rhop(nm)

R hop(nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7.5 7.0 6.5 6.0 5.5

1.85

5.0 180

200

220

240

260

280

300

20 40 60 80 100 120 140 160 180 200

Temperature(K)

Temperature(K)

Figure 6: The variation of hopping distance Rhop as a function of temperature in (a)Temperature regime I- 300K-183K (b) Temperature regime II-182K-23K.

        19 ACS Paragon Plus Environment


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

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Figure 7: Illustration of an electron executing variable range hopping trapped inside a potential well created by various defects present on the graphene plane.        20 ACS Paragon Plus Environment

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Table of Content Image

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160x120mm (150 x 150 DPI)

ACS Paragon Plus Environment

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Carrier Transport in Reduced Graphene Oxide Probed Using Raman

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