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The Effect of Thickness and Chemical Reduction of Graphene Oxide on Nanoscale Friction Sangku Kwon, Kyung Eun Lee, Hyunsoo Lee, Sang Joon Koh, JaeHyeon Ko, Yong-Hyun Kim, Sang Ouk Kim, and Jeong Young Park J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b04609 • Publication Date (Web): 19 Sep 2017 Downloaded from http://pubs.acs.org on September 21, 2017

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The Journal of Physical Chemistry

The Effect of Thickness and Chemical Reduction of Graphene Oxide on Nanoscale Friction

Sangku Kwon†,‡,§, Kyung Eun Lee⊥,§, Hyunsoo Lee†,§, Sang Joon Koh†,‡, Jae-Hyeon Ko#, Yong-Hyun Kim#, Sang Ouk Kim*,⊥ and Jeong Young Park*,†,‡

†Center

for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS),

Daejeon 34141, South Korea ‡Graduate

School of EEWS, Korea Advanced Institute of Science and Technology (KAIST),

Daejeon 34141, South Korea ⊥National

Creative Research Initiative Center for Multi-Dimensional Directed Nanoscale

Assembly, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea #

Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and

Technology (KAIST), Daejeon 34141, South Korea

ABSTRACT The tribological properties of two-dimensional (2D) atomic layers are quite different from three-dimensional continuum materials because of the unique mechanical responses of 2D layers. It is known that friction on graphene shows a remarkable decreasing behavior as the number of layers increases, which is caused by the puckering effect. On other graphene derivatives, such as graphene oxide (GO) or reduced graphene oxide (rGO), the thickness dependence of friction is important because of the possibilities for technical applications. In this report, we demonstrate unexpected layer-dependent friction behavior on GO and rGO layers. Friction force microscopy measurements show that nanoscale friction on GO does not depend on the number of layers; however, after reduction, friction on rGO shows an inverse 1

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thickness dependence compared with pristine graphene. We show that the friction on rGO is higher than that on SiO2 at low load, and that an interesting crossover behavior at higher load occurs because of the lower friction coefficient and higher adhesion of the rGO. We provide a relevant interpretation that explains the effect of thickness and chemical reduction on nanoscale friction.

INTRODUCTION Understanding the nanoscale tribological and mechanical properties of 2-dimensional (2D) layered materials1,2 (e.g., graphene, h-BN, and MoS2) has attracted a great deal of research interest because of their unique behavior.3-5 Friction on 2D layered materials is highly dependent on the thickness,6-9 substrate,10,11 chemical composition,12-14 and atomic structure (e.g., ripples15). It has been shown that the friction on 2D layered materials is inversely proportional to the thickness when the thickness is close to atomic scale.7-10 Lee et al. reported that 2D layered materials that are suspended or loosely bound to the substrate have layer-dependent frictional properties that originate from the puckering effect.7 The puckering effect gradually decreases as the thickness increases because the bending stiffness of the 2D layered materials is monotonically proportional to the thickness, which thus results in layer-dependent frictional behavior. The thickness dependence of friction was not observed in the case of graphene on mica because of strong adhesion between the graphene and the mica.10 Furthermore, friction on 2D materials increases drastically (i.e., more than fourfold) following chemical modification. To understand these phenomena, various theories (e.g., surface corrugation14,16 and lateral stiffness12,13) have been introduced. Graphene oxide (GO), an oxidized single graphitic layer, has gained attention for its unique physical, electrical, and chemical properties.17-22 Graphene oxidation can be achieved by an electrostatic field23 or flow of charge,24 which proposes an intriguing potential for GObased electronics. Thus far, there have been very limited tribological studies of GO. H. Lee et al. observed sp2 and sp3 domains using friction mapping.25 In spite of the technical relevance and importance, the thickness dependence of friction on GO has not been studied previously. In this letter, we report the unique layer-dependent frictional behavior observed on GO and 2


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reduced graphene oxide (rGO) layers. After oxidation of the graphene, the friction increases; however, after reduction, the friction decreases, which is consistent with previous friction studies on chemically modified graphene.12,13 We show that the layer-dependence of the friction properties of GO and rGO are quite different from those of graphene.

EXPERIMENTAL METHODS GO was prepared by the oxidative exfoliation of graphite powder (Sigma Aldrich, Flake) following a modified Hummers method, as described elsewhere.26,27 Briefly, 1 g of graphite powder was stirred into 45ml of a H2SO4 : H3PO4 (8:1, v/v) solution in an ice bath; 3.5 g of potassium permanganate was then added to this mixture, while keeping it in the ice bath. The mixture was then continuously stirred for 24 h at 35 °C. After thorough oxygenation, 250 ml of deionized water and 20 ml of 35% H2O2 were slowly added to the mixture in the ice bath. The final yellow mixture was thoroughly filter washed 5 times with a 1 M HCl solution and re-dispersed in 500 ml of deionized water under mild mixing. Subsequent purification was performed by dialysis and centrifugation to remove any ionic impurities and unexfoliated graphite oxides. A predetermined amount of the concentrated dispersion was diluted in deionized water to prepare the monolayer GO dispersions at the desired composition. Afterwards, GO flakes were spin-casted on ultraviolet/ozone-treated SiO2/Si substrates. To prepare the rGO, the spin-casted GO flakes were thermally reduced at 750 °C under H2 (60 sccm) atmosphere for 20 min. Prior to the atomic force microscopy (AFM) experiments, we characterized the chemical functionalities of the as-prepared GO and rGO using X-ray photoelectron spectroscopy (XPS, Sigma Probe from Thermo VG Scientific) measurements under ultrahigh vacuum employing an Al KR X-ray source (1486.3 eV). We also compared the Raman spectra of the rGO with pristine graphene on silicon substrates, as shown in Figure S1 in the Supporting Information. The Raman spectra show two main peaks: the D- and G-bands between wavenumbers 1100 ~ 2400 cm−1. The D- and G-bands are associated with the presence of structural defects and distortions in the crystal structure that decrease the sp2 carbon domain and the C–C bond stretch with sp2 carbon formation.28-30 The degree of defect 3



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loading and disorder in the structure can be determined by the intensity ratio of the D- to Gbands (ID/IG). The D-band in pristine graphene is absent, which means that it is free of defects, while the D-band was observed with high intensity and a broadened peak in rGO, as shown in Figure S1. Thus, the rGO had a higher ID/IG ratio (0.87) than that of pristine graphene, indicating that the rGO has small domains of oxygen functional groups mixed with sp2 carbon in the graphitic planes. Friction force microscopy (FFM) measurements were carried out using an environmental AFM (AFM 5500, Agilent) at ambient conditions (~45% RH and 23 °C). We performed friction measurements on several different flakes of GO and rGO on silica (e.g., mono-, bi-, and trilayer flakes). We used TiN-coated AFM tips (NSG10, NT-MDT) with a spring constant of 3 N/m for the simultaneous measurement of friction with topography. We also obtained the identical friction behavior using different AFM tips, such as Si tips (PPPCONT-50, PPP-LFMR-50) with a polygon-based pyramid and typical force constant of 0.2 N/m. To compare the thickness dependence of the friction, the same tip was utilized on both the GO and rGO in the data set and SiO2 was used for a reference. In addition, we confirmed the same adhesion between the tip and the SiO2 for both the GO and rGO on SiO2 samples, which means that there is no wear effect from the tip during AFM scanning. A low normal load was used in the FFM experiments such that there was no sample damage; therefore, the FFM experiments were performed in the elastic deformation regime and the measured friction values did not show any time-dependent characteristics. The friction was estimated by subtracting the lateral signal from the retrace to trace in the friction loops. The quantitative friction analysis was performed by averaging the values of the measured areas.

RESULTS AND DISCUSSION Once we prepared the samples, we carried out XPS measurements (Figure 1a). The XPS spectra of the GO sample show peaks at 288.6, 286.8, and 284.8 eV, which correspond to C=O, sp3, and sp2, respectively. After thermal reduction, the sp3 and C=O peaks disappeared. Figure 1b,c shows large-area (40 µm × 40 µm) topography and friction images of the rGO samples that show many rGO flakes on the surface. 4


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Figure 1. (a) XPS spectra of GO and rGO showing that the sp3 and C=O peaks disappeared after thermal reduction. (b) AFM topography and (c) friction images measured on rGO on SiO2/Si.

For quantitative analysis, we took topography and friction images on single-, bi-, and trilayer GO and rGO on silica substrate. Figure 2a,b shows the AFM topography and friction images, respectively, measured on GO layers deposited on SiO2/Si substrate. The thickness of the GO is 0.8 ± 0.04 nm, from the height profile from the topography image, which is consistent with the literature.31 Due to the presence of covalent bonding with oxygen,21,32,33 it is known that GO is significantly thicker than pristine graphene (~0.34 nm). Interestingly, the GO layers do not show any layer-dependent friction behavior (Figure 2c,d). This is contrary to pristine graphene, in which friction decreases as the number of layers increases.7 Friction on GO is higher than that on SiO2, which is consistent with a previous report.13 The absence 5



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of thickness dependence on GO is also clearly visible in the plot of friction vs applied load (Figure 2e). Finally, Figure 2f shows a plot of the normalized friction behavior of GO as a function of the number of GO layers (i.e., mono-, bi-, and trilayer GO). The friction was normalized to 1, which corresponds to the friction on SiO2, and error bars are included in each plot. Arbitrary units for friction in the plot are used to avoid any confusion that could occur from different lateral force calibrations caused by the variation of contributing factors (e.g., the mechanical properties of the tip, optical deflection sensitivity, and humidity).34,35 The absence of friction dependence on GO is related to the high adhesion between the GO and the SiO2 substrate. In the case of graphene, it was also demonstrated that the high adhesion between the graphene and the substrate (mica) results in no thickness dependence for friction.10 In the case of GO on SiO2, many oxygen-containing functional groups on the GO can give rise to a stronger interaction with the substrate, resulting in the absence of the puckering effect, and thus no thickness dependence.

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Figure 2. (a) 3 µm × 2 µm AFM topographical image and (b) corresponding friction image measured on mono- and bilayer GO flakes on SiO2/Si measured at 15 nN. Line profiles along the white line in (a) showing (c) the height of the GO layers and (d) the variation of friction. Plots of (e) friction vs applied load measured on the GO and (f) normalized friction as a function of the number of GO layers (i.e., mono-, bi-, and trilayer) at an applied load of 20 nN. SiO2 is included for reference.

After thermal reduction of the GO, the frictional properties of the GO sheets changed substantially. The main difference is that the friction is reduced and the rGO now shows layer-dependent frictional behavior. Figure 3a,b shows an AFM topographical image and 7



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corresponding friction image, respectively, measured on rGO flakes on SiO2/Si. As shown in the height profile (Figure 3c), the thickness of one layer is reduced close to the value of pristine graphene (~0.35 nm) after the reduction process. From the friction image and the line profile of the friction (Figure 3d), the thickness dependence of the friction is clearly visible, showing higher friction on bilayer rGO compared with monolayer rGO.

Figure 3. (a) 5 µm × 4 µm AFM topographical image and (b) corresponding friction image measured on mono- and bilayer rGO flakes on silicon oxide measured at an applied load of 0 nN. Line profiles along the white line in (a) showing (c) the height of the rGO layers and (d) the variation in friction. Plots of (e) friction vs applied load measured on the rGO. and (f) normalized friction as a function of the number of rGO layers (i.e., mono-, bi-, and trilayer), measured at an applied load of 20 nN. 8


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As shown in Figure 3d, the friction contrast between the mono- and bilayer rGO is clearly observed and distinct from the GO. The frictional force on the bilayer rGO is ~15% higher than that of monolayer rGO. It is known that most 2D layered materials that are deposited onto a SiO2 substrate or suspended have a maximal frictional force at the thinnest layer because of puckering.6-8 This puckering effect is diminished when the adhesion is strong between the 2D layered materials and the substrate.10 In our case, because of the high adhesion force between the GO and the substrate, unlike graphene, monolayer rGO shows the minimum friction value and friction increases slightly as the number of layers increases. To quantify the frictional differences and examine any observable phenomena, such as the negative friction coefficient observed on chemically modified graphite,36 we measured the friction as a function of applied load at the mono- and bi-layer boundary while varying the applied load from high to low (Figure 3e). A plot of the normalized friction behavior of rGO as a function of the number of rGO layers (i.e., mono-, bi-, and trilayer rGO) is shown in Figure 3f. The thickness dependence of friction is clearly shown in Figure 3f. The friction increase is clearly observed as the rGO thickness increased. In this paper, the exact mechanism for the friction dependence on the thickness of rGO is still unclear; possible explanations are: (i) the adhesion is weaker compared with GO-SiO2, which gives rise to the thickness effect, and (ii) the bending stiffness is higher for thicker layers, which gives rise to higher friction forces.12,13 Since the bending stiffness of the 2D materials increases proportionally to the number of layers, we can simply assume that the thicker layers have higher bending stiffness, which is attributed to the higher frictional force. The stronger layer– layer interaction in rGO than in pristine graphene may result in the inverse thickness dependence of friction compared with pristine graphene. In previous studies, we demonstrated that the higher out-of-plane bending stiffness of 2D materials leads to higher friction behavior between pristine graphene and chemically modified graphene using AFM experiments and density functional theory calculations.37,38 The relatively high adhesive force is considered at the interface of the rGO layers and between the rGO and SiO2 because of the presence of oxygen functional groups, while pristine graphene has a lower van der Waals interaction with neighboring graphene layers and the SiO2 substrate. Thus, we think that the 9



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puckering effect does not play a role in this study. In addition, the influence of contact quality might be a possible explanation for the thickness dependence of the friction on 2D materials,39 even though the atomic structure of rGO is not clearly defined because of the random dispersion of a mixture of oxygen-containing functional groups and sp2 carbon domains. The friction curves measured on SiO2 and mono- and bilayer rGO (Figure 3e) also indicate that the friction on SiO2 is higher than that on rGO at the high load, but there is a crossover of friction contrast at the low load (i.e., the friction on SiO2 is lower than that on rGO). This crossover behavior is related to the higher adhesion force and lower friction coefficient of rGO compared with that of SiO2. The adhesion force can be estimated from the regions of negative normal force in the plots of friction vs applied load on GO and rGO, as shown in Figures 2e and 3e. In addition, we directly measured the adhesion force of monoand bilayer GO and rGO and the SiO2 substrate for reference using the pull-off force in the force–distance curves, as shown in Figure S2 in the Supporting Information. Higher adhesion in rGO (~20 nN) than in GO (~14.4 nN) and SiO2 (~9.1 nN) is clearly observed in Figure S2. In other words, at low load, high adhesion in the rGO dominates the higher friction force; meanwhile, at high load, the SiO2 exhibits the higher friction force because of its higher friction coefficient. This interesting crossover in friction between rGO and SiO2 is shown in the series of friction images taken at different loads. Figure 4a–c shows friction images measured on rGO as the applied load was varied (i.e., −5, 5, and 20 nN) on the same region. Figure 4a shows that the friction of monolayer rGO is always smaller than that of bilayer rGO. As the load increases, the friction on SiO2 increases; at 5 nN, the friction on SiO2 is similar to that of bilayer rGO, and higher than that of monolayer rGO, as shown in Figure 4b and the profile in Figure 4e. Finally, at the higher load (20 nN), the friction on SiO2 is higher than on both mono- and bilayer rGO (Figure 4c,f).

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Figure 4. Friction images (3 µm x 2 µm) of mono- and bilayer rGO on SiO2 substrate measured with applied loads of (a) −5, (b) 5, and (c) 20 nN. (d–f) Corresponding line profiles across the white line in (a).

Overall, this study shows that chemical modification and the thickness of graphene significantly impact nanoscale friction. Adhesion between the graphene oxide and substrate also plays an important role in determining the thickness dependence of the friction force. In the case of rGO on SiO2, the interplay between adhesion and the friction coefficient can allow us to change the relative friction of the rGO compared with the substrate, which indicates the intriguing possibility of local control of lubrication using 2D atomic layers.

CONCLUSIONS We have presented the nanoscale tribological properties of GO and rGO. By using friction force microscopy, the friction of GO and rGO were studied while changing the number of GO and rGO layers. We found that the friction on GO does not exhibit thickness 11



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dependence, while friction on rGO shows a clear inverse thickness dependence compared with pristine graphene. These results can be associated with the strong adhesion between GO and substrates induced by abundant surface functional groups on GO, which may diminish the puckering effect. In contrast, the weaker surface adhesion and higher bending stiffness of rGO can be associated with the increase in friction as the number of rGO layers increased. We observed an interesting inverse behavior of friction on rGO compared with that of SiO2, which suggests an intriguing possibility for controllable nanoscale friction using 2D atomic sheets.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Raman spectra of rGO and pristine graphene, comparison of adhesion force on GO and rGO (PDF)

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] Author Contributions §

Sangku Kwon and Kyung Eun Lee and Hyunsoo Lee contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the Institute for Basic Science (IBS) [IBS-R004-A2-2017-a00]. K.E.L. and S.O.K were financially supported by the Nano-Material Technology Developme nt Program through the National Research Foundation of Korea (NRF) funded by the 12


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Ministry of Science, ICT and Future Planning (2016M3A7B4905613). J.-H.K. and Y.H.K. were supported by the National Research Foundation of Korea (2015R1A2A2A0 5027766) and Science Research Center (2016R1A5A1008184) programs.

REFERENCES 1. Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Two-Dimensional Gas of Massless Dirac Fermions in Graphene. Nature 2005, 438, 197-200. 2. Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666-669. 3. Park, J. Y.; Kwon, S.; Kim, J. H. Nanomechanical and Charge Transport Properties of Two-Dimensional Atomic Sheets. Adv. Mater. Interfaces 2014, 1, 1300089. 4. Park, J. Y.; Salmeron, M. Fundamental Aspects of Energy Dissipation in Friction. Chem. Rev. 2014, 114, 677-711. 5. Feng, X.; Kwon, S.; Park, J. Y.; Salmeron, M. Superlubric Sliding of Graphene Nanoflakes on Graphene. ACS Nano 2013, 7, 1718-1724. 6. Li, Q. Y.; Lee, C.; Carpick, R. W.; Hone, J. Substrate Effect on Thickness-Dependent Friction on Graphene. Phys. Status Solidi B 2010, 247, 2909-2914. 7. Lee, C.; Li, Q.; Kalb, W.; Liu, X. Z.; Berger, H.; Carpick, R. W.; Hone, J. Frictional Characteristics of Atomically Thin Sheets. Science 2010, 328, 76-80. 8. Lee, H.; Lee, N.; Seo, Y.; Eom, J.; Lee, S. Comparison of Frictional Forces on Graphene and Graphite. Nanotechnology 2009, 20, 325701. 9. Filleter, T.; McChesney, J. L.; Bostwick, A.; Rotenberg, E.; Emtsev, K. V.; Seyller, T.; Horn, K.; Bennewitz, R. Friction and Dissipation in Epitaxial Graphene Films. Phys. Rev. Lett. 2009, 102, 086102. 10. Cho, D. H.; Wang, L.; Kim, J. S.; Lee, G. H.; Kim, E. S.; Lee, S.; Lee, S. Y.; Hone, J.; Lee, C. Effect of Surface Morphology on Friction of Graphene on Various Substrates. Nanoscale 2013, 5, 3063-3069. 11. Deng, Z.; Klimov, N. N.; Solares, S. D.; Li, T.; Xu, H.; Cannara, R. J. Nanoscale Interfacial Friction and Adhesion on Supported Versus Suspended Monolayer and Multilayer Graphene. Langmuir 2013, 29, 235-243. 12. Kwon, S.; Ko, J. H.; Jeon, K. J.; Kim, Y. H.; Park, J. Y. Enhanced Nanoscale Friction on Fluorinated Graphene. Nano Lett. 2012, 12, 6043-6048. 13. Ko, J. H.; Kwon, S.; Byun, I. S.; Choi, J. S.; Park, B. H.; Kim, Y. H.; Park, J. Y. Nanotribological Properties of Fluorinated, Hydrogenated, and Oxidized Graphenes. Tribol. Lett. 2013, 50, 137-144. 14. Li, Q. Y.; Liu, X. Z.; Kim, S. P.; Shenoy, V. B.; Sheehan, P. E.; Robinson, J. T.; Carpick, R. W. Fluorination of Graphene Enhances Friction Due to Increased Corrugation. Nano Lett. 2014, 14, 5212-5217. 15. Choi, J. S.; Kim, J-.S.; Byun, I.-S.; Lee, D. H.; Lee, M. J.; Park, B. H.; Lee, C.; Yoon, D.; Cheong, H.; Lee, K. H. et al. Friction Anisotropy-Driven Domain Imaging on Exfoliated 13



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Monolayer Graphene. Science 2011, 333, 607-610. 16. Dong, Y. L.; Wu, X. W.; Martini, A. Atomic Roughness Enhanced Friction on Hydrogenated Graphene. Nanotechnology 2013, 24, 375701. 17. Sofo, J. O.; Suarez, A. M.; Radovic, L. R.; Bar-Ziv, E. Gate-Voltage Control of Oxygen Diffusion on Graphene. Phys. Rev. Lett. 2011, 106, 146802. 18. Eda, G.; Fanchini, G.; Chhowalla, M. Large-Area Ultrathin Films of Reduced Graphene Oxide as a Transparent and Flexible Electronic Material. Nat. Nanotechnol. 2008, 3, 270-274. 19. Dikin, D. A.; Stankovich, S.; Zimney, E. J.; Piner, R. D.; Dommett, G. H. B.; Evmenenko, G.; Nguyen, S. T.; Ruoff, R. S. Preparation and Characterization of Graphene Oxide Paper. Nature 2007, 448, 457-460. 20. Robinson, J. T.; Zalalutdinov, M.; Baldwin, J. W.; Snow, E. S.; Wei, Z. Q.; Sheehan, P.; Houston, B. H. Wafer-Scale Reduced Graphene Oxide Films for Nanomechanical Devices. Nano Lett. 2008, 8, 3441-3445. 21. Mkhoyan, K. A.; Contryman, A. W.; Silcox, J.; Stewart, D. A.; Eda, G.; Mattevi, C.; Miller, S.; Chhowalla, M. Atomic and Electronic Structure of Graphene-Oxide. Nano Lett. 2009, 9, 1058-1063. 22. Eda, G.; Chhowalla, M. Chemically Derived Graphene Oxide: Towards Large-Area Thin-Film Electronics and Optoelectronics. Adv. Mater. 2010, 22, 2392-2415. 23. Kwon, S.; Lee, E.-S.; Seo, H.; Jeon, K.-J.; Hwang, C. C.; Kim, Y.-H.; Park, J. Y. Reversible Oxidation States of Single Layer Graphene Tuned by Electrostatic Potential. Surf. Sci. 2013, 612, 37-41. 24. Lee, Y. K.; Choi, H.; Lee, C.; Lee, H.; Goddeti, K. C.; Moon, S. Y.; Doh, W. H.; Baik, J.; Kim, J.-S.; Choi, J. S. et al. Charge Transport-Driven Selective Oxidation of Graphene. Nanoscale 2016, 8, 11494-11502. 25. Lee, H.; Son, N.; Jeong, H. Y.; Kim, T. G.; Bang, G. S.; Kim, J. Y.; Shim, G. W.; Goddeti, K. C.; Kim, J. H.; Kim, N. et al. Friction and Conductance Imaging of Sp2- and Sp3Hybridized Subdomains on Single-Layer Graphene Oxide. Nanoscale 2016, 8, 4063-4069. 26. Kim, J. E.; Han, T. H.; Lee, S. H.; Kim, J. Y.; Ahn, C. W.; Yun, J. M.; Kim, S. O. Graphene Oxide Liquid Crystals. Angew. Chem. Int. Ed. 2011, 50, 3043-3047. 27. Lee, K. E.; Kim, J. E.; Maiti, U. N.; Lim, J.; Hwang, J. O.; Shim, J.; Oh, J. J.; Yun, T.; Kim, S. O. Liquid Crystal Size Selection of Large-Size Graphene Oxide for Size-Dependent N-Doping and Oxygen Reduction Catalysis. ACS Nano 2014, 8, 9073-9080. 28. Krishnamoorthy, K.; Veerapandian, M.; Mohan, R.; Kim, S.-J. Investigation of Raman and Photoluminescence Studies of Reduced Graphene Oxide Sheets. Appl. Phys. A 2012, 106, 501-506. 29. Dresselhaus, M. S.; Jorio, A.; Hofmann, M.; Dresselhaus, G.; Saito, R. Perspectives on Carbon Nanotubes and Graphene Raman Spectroscopy. Nano Lett. 2010, 10, 751-758. 30. Perumbilavil, S.; Sankar, P.; Priya Rose, T.; Philip, R. White Light Z-Scan Measurements of Ultrafast Optical Nonlinearity in Reduced Graphene Oxide Nanosheets in the 400–700 Nm Region. Appl. Phys. Lett. 2015, 107, 051104. 31. Park, S.; Ruoff, R. S. Chemical Methods for the Production of Graphenes. Nat. Nanotechnol. 2010, 5, 309-309. 32. 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. 14


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33. Byun, I. S.; Yoon, D.; Choi, J. S.; Hwang, I.; Lee, D. H.; Lee, M. J.; Kawai, T.; Son, Y.-W.; Jia, Q.; Cheong, H. et al. Nanoscale Lithography on Monolayer Graphene Using Hydrogenation and Oxidation. ACS Nano 2011, 5, 6417-6424. 34. Ogletree, D. F.; Carpick, R. W.; Salmeron, M. Calibration of Frictional Forces in Atomic Force Microscopy. Rev. Sci. Instrum. 1996, 67, 3298-3306. 35. Varenberg, M.; Etsion, I.; Halperin, G. An Improved Wedge Calibration Method for Lateral Force in Atomic Force Microscopy. Rev. Sci. Instrum. 2003, 74, 3362-3367. 36. Deng, Z.; Smolyanitsky, A.; Li, Q. Y.; Feng, X. Q.; Cannara, R. J. AdhesionDependent Negative Friction Coefficient on Chemically Modified Graphite at the Nanoscale. Nat. Mater. 2012, 11, 1032-1037. 37. Kwon, S.; Ko, J.-H.; Jeon, K.-J.; Kim, Y.-H.; Park, J. Y. Enhanced Nanoscale Friction on Fluorinated Graphene. Nano Lett. 2012, 12, 6043-6048. 38. Ko, J.-H.; Kwon, S.; Byun, I.-S.; Choi, J. S.; Park, B. H.; Kim, Y.-H.; Park, J. Y. Nanotribological Properties of Fluorinated, Hydrogenated, and Oxidized Graphenes. Tribol. Lett. 2013, 50, 137-144. 39. Li, S.; Li, Q.; Carpick, R. W.; Gumbsch, P.; Liu, X. Z.; Ding, X.; Sun, J.; Li, J. The Evolving Quality of Frictional Contact with Graphene. Nature 2016, 539, 541-545.

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