Research Article www.acsami.org
Anisotropic Friction of Wrinkled Graphene Grown by Chemical Vapor Deposition Fei Long,† Poya Yasaei,‡ Wentao Yao,† Amin Salehi-Khojin,*,‡ and Reza Shahbazian-Yassar*,†,‡ †
Department of Mechanical Engineering and Engineering Mechanics, Michigan Technological University, Houghton, Michigan 49931, United States ‡ Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois 60607, United States ACS Appl. Mater. Interfaces 2017.9:20922-20927. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 11/09/18. For personal use only.
S Supporting Information *
ABSTRACT: Wrinkle structures are commonly seen on graphene grown by the chemical vapor deposition (CVD) method due to the different thermal expansion coefficient between graphene and its substrate. Despite the intensive investigations focusing on the electrical properties, the nanotribological properties of wrinkles and the influence of wrinkle structures on the wrinkle-free graphene remain less understood. Here, we report the observation of anisotropic nanoscale frictional characteristics depending on the orientation of wrinkles in CVD-grown graphene. Using friction force microscopy, we found that the coefficient of friction perpendicular to the wrinkle direction was ∼194% compare to that of the parallel direction. Our systematic investigation shows that the ripples and “puckering” mechanism, which dominates the friction of exfoliated graphene, plays even a more significant role in the friction of wrinkled graphene grown by CVD. The anisotropic friction of wrinkled graphene suggests a new way to tune the graphene friction property by nano/microstructure engineering such as introducing wrinkles. KEYWORDS: graphene, friction, anisotropy, chemical vapor deposition, atomic force microscopy
1. INTRODUCTION The frictional property of two-dimensional (2D) materials at nanoscale has significant importance not only for the fundamental understanding of nanotribology1 but also for the design and application of nanoelectrical and mechanical systems (NEMs).2−4 Recent friction force microscopy (FFM) studies have revealed that the frictional properties of exfoliated graphene and other 2D materials on Si/SiO2 substrate strongly depend on the number of layers. In general, it is observed that monolayer sheets exhibit friction higher than that of multilayers, which is attributed to a higher elastic compliance and moderate layer−substrate adhesion.5 Theoretical modeling of the single asperity contact between a sliding atomic force microscope probe and graphene has shown that monolayer graphene locally buckles at the probe contact area, which effectively increases the friction.5,6 This phenomenon is referred to as the “puckering” effect. As the 2D materials get thicker, the interlayer adhesion and bending stiffness increase, which depresses the puckering and results in lower friction. For sharp probes, Brownian dynamics (BD) simulations suggested © 2017 American Chemical Society
the contributing mechanism of this layer dependency can also be the decreased sample deformation energy due to increased local contact stiffness.7 In addition to the thickness dependency, residual stress in exfoliated monolayer graphene sheets introduces ripple structures when transferring to Si/SiO2 substrate, which lead to anisotropic frictional behavior.8−10 The friction is reported to be lower along the ripple lines because the out-of-plane puckering is prohibited by the higher bending stiffness with 215% anisotropy.10 Despite the intensive studies on exfoliated graphene, the nanotribological properties of chemical vapor deposition (CVD)-grown graphene remain less understood.1,11,12 CVD is currently the most promising method for the growth of large area graphene.13 Due to the negative thermal expansion coefficient in graphene and the positive values in typical growth substrates (e.g., copper), “wrinkles” are commonly formed within the grains of the Received: January 16, 2017 Accepted: May 17, 2017 Published: May 17, 2017 20922
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
Research Article
ACS Applied Materials & Interfaces monolayer graphene during the cooling process.14−16 These wrinkles are believed to alter the electrical and mechanical properties of graphene.17−19 In our current work, CVD-grown graphene with highly anisotropic wrinkles was synthesized and transferred onto the Si/SiO2 substrate. The effects of wrinkle structures on the friction property of graphene were systematically investigated using FFM under ambient conditions. Experimental friction measurements revealed strong dependency on the orientation of wrinkles. In detail, lower friction was observed along the wrinkle direction, while higher friction was measured perpendicular to the wrinkle direction. The anisotropy is on average ∼194%, which is similar to exfoliated graphene, suggesting that the ripples and puckering mechanism also dominates the friction of CVD-grown graphene.
The size of the wrinkles varies from 1 to 5 nm in height, 7 to 18 nm in width, and up to micrometers in length. More importantly, most of the wrinkles are almost parallel with each other at the submicrometer scale, which results in a unique structural anisotropy at the nano/microscopic scale. FFM was employed to investigate the frictional property of the wrinkled graphene. In FFM, the cantilever scan direction is perpendicular to its axial direction. The friction force between the AFM tip and the sample produces a torsional moment that laterally twists the cantilever (Figure S1). This lateral twisting signal is usually coupled with the sample topography and introduces artifacts. These artifacts can be minimized by subtracting the forward scan signal by the backward scan signal.10,23,24 Experimentally, the half width of the lateral force loop formed by the forward and backward scan is commonly used as a measure of the frictional force (Figure S2). Two FFM measurements were carried out by aligning the high-density wrinkle direction perpendicular and parallel to the scanning direction of the probe, respectively. The topography images are shown in Figures 2a and c. The scanning direction of the probe
2. RESULTS AND DISCUSSION Monolayer graphene samples were synthesized on copper foils by the ambient pressure CVD technique20,21 and then transferred onto the Si/SiO2 substrate using the poly(methyl methacrylate) (PMMA)-assisted technique as previously described.22 Scanning electron microscopy (SEM) was employed to check the sample morphology. As illustrated in Figure 1a, the low magnification SEM image shows partially
Figure 2. (a) Topography and (b) friction force mapping when the probe scans perpendicular to the high-density wrinkle direction. (c) Topography and (d) friction force mapping when the probe scans parallel to the high-density wrinkle direction. Wrinkles perpendicular and parallel to the probe scanning direction are indicated with green and yellow arrows, respectively. The friction force profiles along the red and blue dashed lines are shown in Figure 3. Figures in panels e and f are schematics of the interaction between the probe and wrinkle along perpendicular and parallel directions, respectively.
Figure 1. (a) Typical SEM image of CVD-grown graphene after transfer onto Si/SiO2 substrate. (b) Raman spectra obtained from the single crystalline graphene with an I2D/IG ratio of ∼2, which is characteristic for monolayer graphene. (c) AFM topography of monolayer graphene on Si/SiO2 substrate. Most wrinkles are aligned along the same direction, which is referred to as high-density wrinkle direction, as indicated with a red arrow. (d) Zoom-in AFM topography of wrinkles along the high-density wrinkle direction.
is horizontal. The corresponding friction force images were captured simultaneously with the topography and are shown in Figures 2b and d, respectively. Wrinkles perpendicular and parallel to the probe scanning direction are indicated with green and yellow arrows, respectively. When the wrinkles were aligned perpendicular to the probe scanning direction, they exhibited friction (brighter contrast in Figure 2b) higher than that of the wrinkle-free graphene. However, when the wrinkles were aligned parallel to probe scanning direction, they exhibited friction (darker contrast in Figure 2d) lower than that of the wrinkle-free graphene. The friction of wrinkles can be explained by the mechanism proposed as follows. There is interlayer adhesion within the wrinkle structure due to van der Waals interaction, as shown in Figure S3. This interlayer adhesion keeps the stable wrinkle morphology from collapsing. For the perpendicular probe scan direction with respect to the wrinkle,
covered individual hexagonal graphene grains. Figure 1b gives the Raman spectra of the graphene sample. The I2D/IG ratio is close to 2, confirming that the graphene is a monolayer. Figure 1c shows a typical atomic force microscopy (AFM) topography of the graphene samples on the Si/SiO2 substrate. Most wrinkles are formed along the same direction, while only a few of them sitting approximately orthogonal. The preferred wrinkle orientation is referred to as high-density wrinkle direction in the following context, as indicated with red arrow in Figure 1c. Figure 1d shows higher magnification AFM topography of the wrinkles along the high-density direction. 20923
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
Research Article
ACS Applied Materials & Interfaces
substrate. Moreover, the observation also implies that the direction of the ripple texture is aligned along the wrinkles. This anisotropic surface texture results in an anisotropic out-of-plane bending stiffness, which is more rigid along the parallel direction than the perpendicular direction. As shown in Figure 3a, when the probe scans perpendicular to the ripple lines, the monolayer graphene can be easily deformed and puckered around the probe due to the lower bending stiffness. The increased contact area leads to higher friction, as can be seen in Figure 3a, where the area enclosed by red lines is larger than that enclosed by blue lines. Moreover, as the probe moves forward, the work done by the probe is converted to the strain energy stored in the puckered graphene. When the strain energy overcomes the friction force, it suddenly dissipates, resulting in the minor peaks observed in Figure 3a red lines. On the other hand, the bending stiffness along the ripple lines is higher. Therefore, puckering is prohibited, as illustrated in Figure 3c, so that the friction along the parallel direction is not only lower but also more uniform, as observed in Figure 3a (blue lines). We also noticed that the lateral force peaks produced by wrinkles can be reproduced well in both forward and backward scans, but the minor peaks on wrinkle-free graphene area exhibited variations. It has been reported that the sliding of an AFM tip on graphene surface would induce changes of graphene’s interfacial geometry, which locally delaminates the graphene layer on the substrate.25 Although this sliding history dependency was developed to explain the adhesion variation between an AFM tip and graphene, we believe a similar mechanism also plays an important role in our FFM experiments. As illustrated in Figure S4, when the AFM tip scans in the forward direction, it applies uniaxial stress to the graphene along the scanning direction. The friction redistributes the graphene residual strain along the same direction, which creates rippling texture in the scan direction.26 This in effect increases the bending rigidity; therefore, the displacement of graphene is reduced when the tip scans in the backward direction, resulting in lower friction detection. However, this redistribution of the residual strain does not change the overall anisotropic friction of the wrinkle-free graphene because the wrinkle structures dominate over the sliding history of the AFM tip in our experiments. The results support our discussion that the frictions of wrinkles and wrinkle-free graphene have different origins. The friction of wrinkles is originated from their morphology, while the friction of wrinkle-free graphene is due to anisotropic residual strain. Further computational simulations based on the finite element method and molecular dynamics will be performed for the detailed understanding of the underlying mechanism. To further characterize the anisotropic friction of CVDgrown graphene, we investigated the dependency of friction on the applied normal load, as shown in Figure 4a. Six parallel samples were measured, and each data point gives the average value of friction forces measured from 10 wrinkle-free areas. The friction curves measured perpendicular to the high-density wrinkle direction are shown in red, while frictions measured along the parallel direction are shown in blue. Consistent with our previous observation, the friction along the perpendicular direction (red curves) is on average higher than that along the parallel direction (blue curves). More importantly, the slopes of the curves correspond to the coefficient of friction (COF). The average COF value measured along the perpendicular direction was 0.035, which was ∼194% of the COF value of 0.018 measured along the parallel direction. The magnitude of the
the interlayer adhesion does not prohibit the bending deformation. Therefore, the contact area between the probe and wrinkle is much larger than the single asperity contact between the probe and wrinkle-free graphene, as illustrated in Figure 2e. Therefore, higher friction was observed. When the probe scans parallel to the wrinkle and especially when the probe scans right on top of the wrinkle, as shown in Figure 2f, the probe needs to overcome the interlayer adhesion to create deformation. Because the wrinkle structure is more rigid vertically due to the interlayer adhesion, less deformation is allowed. As a result, lower friction was observed. In addition to the direction dependency of wrinkle friction, we observed that the friction of the wrinkle-free graphene depends strongly on the high-density wrinkle direction. Friction force profiles obtained from the red and blue dashed lines in Figures 2b and d are shown in Figure 3a with red and blue solid
Figure 3. (a) Friction force profiles from the dashed lines illustrated in Figures 2b and d. Both forward and backward scan profiles are shown. The sharp peaks correspond to the high friction of wrinkles. Perpendicular to the probe scan direction, the wrinkle-free graphene exhibits minor peaks originated from ripples and puckers, as indicated on the red profile. Meanwhile, on the blue profile, no obvious ripples are observed. The schematics in panels b and c show graphene puckering at the probe contact area. More graphene deformation is produced perpendicular to the ripple lines due to the lower bending stiffness.
lines, respectively. The peaks in the profiles correspond to the wrinkles perpendicular to the probe scan direction. The values between the peaks correspond to the friction of the wrinkle-free graphene areas. Under the same normal load of 150 nN, the friction of the wrinkle-free graphene was greater when measured perpendicular to the high-density wrinkle direction (red solid line) compared to that measured in the parallel direction (blue solid line). More importantly, the friction force profile of the wrinkle-free graphene exhibits minor peaks perpendicular to the high-density wrinkle direction, while the profile is much smoother along the parallel direction. The increased waviness in the friction signal suggests the existence of ripple texture on the wrinkle-free graphene due to the inhomogeneous adhesion between the graphene and its 20924
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
Research Article
ACS Applied Materials & Interfaces
Figure 4. (a) Friction force as a function of normal load. The friction of graphene perpendicular to the high-density wrinkle direction is on average higher than that along the parallel direction. The COF is measured as the slope of the curves. The average COF value perpendicular to the high-density wrinkle direction is 0.035, and the COF value of the parallel direction is 0.018. The anisotropy is 194%. (b) COFs as a function of angle θ between probe scanning direction and high-density wrinkle direction. θ = ±90° corresponds to perpendicular and θ = 0° corresponds to parallel direction. The data are well-fitted by a sinusoidal regression which shows 180° periodicity. Figure 5. (a) Graphene friction at the graphene/SiO2 boundary area with various scan angles. (a, c, e, and g) Topography images and (b, d, f, and h) friction force images of 0, 60, 120, and 180°, respectively. (i) Friction force profiles at the graphene/SiO2 boundary area with various scan angles. (j) COF on Si/SiO2 substrate as a function of AFM probe scan angle. The average COF is 0.251, which is an order of magnitude higher than that of graphene. More importantly, the COF does not show dependency of scanning angle. Scale bar 1 μm.
friction along with the COFs shows strong anisotropic dependency on the wrinkle direction. The probe wear is always a concern in FFM. To measure the probe wear quantitatively, a polycrystalline titanium roughness sample was used as the AFM tip characterizer.27 The basic principle of this characterization process is shown in Figures S5a and b. The AFM image obtained on the sharp features can be used to evaluate the tip morphology. The images of a new probe and three probes after the friction measurements are shown in Figures S5c−f. The corresponding tip profiles and the estimated tip radii are shown in Figure S5g. The radius of the new tip is Rnew = 11.52 nm, which agrees with the nominal value of 8−12 nm provided by the manufacturer. The tip radius after the friction measurement is 13.8 ± 0.4 nm, which is ∼20% larger than that of the new tip. This result indicates moderate wear of the AFM probes. However, comparing to the ∼194% anisotropic friction of graphene, the tip wear has only a minor influence on the experiments and does not change our conclusions. To confirm that the observed anisotropic friction was induced by wrinkle structures instead of the graphene intrinsic atomic lattice, the COF values of the same area along various wrinkle orientations were measured. If the COF shows 60° periodicity, then the anisotropy could be originated from the hexagonal carbon lattice. On the other hand, if the COF shows 180° periodicity, then the anisotropy must be induced by the wrinkle structures. Figure 4b shows the measured COFs as well as the fitting curve of A*sin|θ|, where θ = ±90° indicates that the probe scans perpendicular to high-density wrinkle direction and θ = 0° corresponds to parallel direction. The data fit well with a periodicity of 180°, which shows strong evidence that the anisotropic friction observed on CVD-grown graphene is indeed induced by wrinkle structures. In addition, we measured the friction at the graphene/SiO2 boundary, as shown in Figure 5. Figures 5a, c, e, and g are the topography images and b, d, f, and h are the corresponding friction force images of 0, 60, 120, and 180°, respectively. Figure 5i shows the friction force profiles of the same graphene/SiO2 boundary area with various scan angles. The graphene shows no friction anisotropy near the boundary. We attribute this to the weak adhesion between graphene and SiO2 substrate at the boundary area. As can be seen from the
topography images, the graphene near the boundary is slightly scratched after multiple scans. In other words, at the boundary area, the morphology of graphene changes significantly, and the wrinkle structure no longer dominates the friction. At areas far from the boundary, no obvious scratch can be seen on graphene; therefore, to study the wrinkle induced anisotropic friction, all the data in the manuscript were measured away from the boundary areas. The coefficient of friction of the SiO2 substrate is shown in Figure 5j. The SiO2 substrate does not exhibit anisotropic friction, and the average COF is 0.251, which is an order of magnitude higher than that of graphene. More importantly, the orientations of the graphene grains are random during CVD, although the wrinkles are aligned in the cooling process. Therefore, measuring several grains on the same substrate would eliminate the possibility that the anisotropic friction is induced by the various alignments with respect to the substrates. Also, we transferred the graphene onto several SiO2 substrates with random orientations and observed the same anisotropic friction of graphene. This indicates that the frictional property of the substrate does not play a dominate role in our experiments. Furthermore, the environmental conditions may also alter the frictional property of graphene such as humidity, temperature, vacuum, or ambient conditions. While we believe that these factors are not likely to induce anisotropic nature to the friction on graphene, it is important to deconvolute these effects in future studies of friction on graphene and other two-dimensional materials.
3. CONCLUSIONS In summary, we systematically investigated the friction of monolayer CVD-grown graphene with FFM. Experimental results show that the frictional behavior of CVD-grown graphene depends on the orientation of wrinkle structures. Higher friction was observed perpendicular to the wrinkle 20925
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
Research Article
ACS Applied Materials & Interfaces Author Contributions
direction, while lower friction was observed parallel to the wrinkle direction. The friction anisotropy can be as high as ∼194%, indicating that anisotropic nano/microstructures such as wrinkles have significant impact on the frictional property of monolayer graphene. The observed anisotropic friction is originated from the formation of ripples and can be explained by the puckering mechanism. Our results suggest the potential of tuning graphene friction by nano/microstructure engineering, which could benefit applications such as nano/microelectromechanical systems, where tunable friction is desirable.
F.L. and R.S.Y. conceived the idea. F.L. and W.T.Y. performed FFM measurements under the supervision of R.S.Y. P.Y. synthesized graphene samples and performed SEM and Raman characterizations under the supervision of A.S.K. All authors have given approval of the final version of the manuscript. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS Financial support from the National Science Foundation is acknowledged (Award CMMI-1200383 to R.S.Y., F.L., and W.T.Y. and EFMA-1542864 to A.S.K. and P.Y.).
4. METHODS 4.1. Graphene Synthesis. The graphene growth was carried out using an ambient pressure chemical vapor deposition (AP-CVD) method similar to that in our previous reports.22,28 In short, the copper substrates (from Alfa Aesar, product no. 46365) were cleaned in 10% hydrochloric acid (in deionized water) for 10−20 min and eventually rinsed in acetone and isopropanol, dried under N2 flow, and loaded into the CVD chamber. Next, the chamber was evacuated (down to 1 mTorr) and purged with 5% hydrogen in argon forming gas to reach the ambient pressure. The samples were heated up to 1050 °C under the same flow for 60 min. Next, 20 ppm of methane (CH4) was added for 40−90 min, and the chamber was then rapidly cooled to room temperature. The samples were then coated with poly(methyl methacrylate) (PMMA), floated on copper etchant (CE-100) for 24 h, and then floated on several DI water baths to remove the solvent residue. Finally, the floating samples were scooped out by the target (Si/SiO2) substrates and annealed in vacuum at 350 °C for 2 h under flow of 5% forming gas to remove the polymer residue and enhance adhesion to the surface. 4.2. AFM. The experimental setup is shown in Figure S1. All AFM experiments were carried out with Dimension ICON system (Bruker, CA.) in ambient conditions. RFESP (Bruker, CA) cantilevers were selected with a nominal spring constant of 3 N/m. The normal and lateral spring constants were calibrated using Sader’s method.29 The calibrated normal and torsional spring constants of the 3 cantilevers are 4.5 ± 0.3 and 185 ± 10 N/m, respectively. AFM images were analyzed with Nanoscope Analysis software (Bruker, CA), and the line profiles were replotted with Origin 9.0. When measuring friction at various probe scanning angles, the graphene samples were physically rotated, while the probe scanning direction remained unchanged. 4.3. SEM. All SEM images were obtained with an integrated Carl Zeiss microscope in a Raith e-LiNE plus electron beam lithography system. We used the acceleration voltage of 10 kV and working distance of 10 mm for imaging. 4.4. Raman. The Raman spectra were obtained with a Horiba LabRAM HR Evolution confocal Raman microscope with a 532 nm laser wavelength, 1200 g/mm grating, and a 100× objective lens. The laser power was in the range of 1−4 mW.
■
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b00711. Additional experimental data and analysis graphs (PDF)
■
REFERENCES
(1) Kim, K. S.; Lee, H. J.; Lee, C.; Lee, S. K.; Jang, H.; Ahn, J. H.; Kim, J. H.; Lee, H. J. Chemical Vapor Deposition-Grown Graphene: The Thinnest Solid Lubricant. ACS Nano 2011, 5, 5107−5114. (2) Novoselov, K. S.; Jiang, D.; Schedin, F.; Booth, T. J.; Khotkevich, V. V.; Morozov, S. V.; Geim, A. K. Two-Dimensional Atomic Crystals. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 10451−10453. (3) Meric, I.; Han, M. Y.; Young, A. F.; Ozyilmaz, B.; Kim, P.; Shepard, K. L. Current Saturation in Zero-Bandgap, Top-Gated Graphene Field-Effect Transistors. Nat. Nanotechnol. 2008, 3, 654− 659. (4) Chen, C.; Rosenblatt, S.; Bolotin, K. I.; Kalb, W.; Kim, P.; Kymissis, I.; Stormer, H. L.; Heinz, T. F.; Hone, J. Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout. Nat. Nanotechnol. 2009, 4, 861−867. (5) 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. (6) Ye, Z.; Tang, C.; Dong, Y.; Martini, A. Role of Wrinkle Height in Friction Variation with Number of Graphene Layers. J. Appl. Phys. 2012, 112, 116102. (7) Smolyanitsky, A.; Killgore, J. P.; Tewary, V. K. Effect of Elastic Deformation on Frictional Properties of Few-Layer Graphene. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 85, 035412. (8) Choi, J. S.; Chang, Y. J.; Woo, S.; Son, Y. W.; Park, Y.; Lee, M. J.; Byun, I. S.; Kim, J. S.; Choi, C. G.; Bostwick, A.; Rotenberg, E.; Park, B. H. Correlation between Micrometer-Scale Ripple Alignment and Atomic-Scale Crystallographic Orientation of Monolayer Graphene. Sci. Rep. 2015, 4, 7263. (9) Rastei, M. V.; Heinrich, B.; Gallani, J. L. Puckering Stick-Slip Friction Induced by a Sliding Nanoscale Contact. Phys. Rev. Lett. 2013, 111, 084301. (10) 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.; Son, Y. W.; Park, J. Y.; Salmeron, M. Friction Anisotropy−Driven Domain Imaging on Exfoliated Monolayer Graphene. Science 2011, 333, 607−610. (11) Egberts, P.; Han, G. H.; Liu, X. Z.; Johnson, A. T. C.; Carpick, R. W. Frictional Behavior of Atomically Thin Sheets: HexagonalShaped Graphene Islands Grown on Copper by Chemical Vapor Deposition. ACS Nano 2014, 8, 5010−5021. (12) Demirbaş, T.; Baykara, M. Z. Nanoscale Tribology of Graphene Grown by Chemical Vapor Deposition and Transferred onto Silicon Oxide Substrates. J. Mater. Res. 2016, 31, 1914−1923. (13) Yazyev, O. V.; Chen, Y. P. Polycrystalline Graphene and Other Two-Dimensional Materials. Nat. Nanotechnol. 2014, 9, 755−767. (14) Hattab, H.; N’Diaye, A. T.; Wall, D.; Klein, C.; Jnawali, G.; Coraux, J.; Busse, C.; van Gastel, R.; Poelsema, B.; Michely, T.; Meyer zu Heringdorf, F. J.; Horn-von Hoegen, M. Horn-von Hoegen, M. Interplay of Wrinkles, Strain, and Lattice Parameter in Graphene on Iridium. Nano Lett. 2012, 12, 678−682. (15) Paronyan, T. M.; Pigos, E. M.; Chen, G.; Harutyunyan, A. R. Formation of Ripples in Graphene as a Result of Interfacial Instabilities. ACS Nano 2011, 5, 9619−9627.
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Fei Long: 0000-0002-5245-6961 Reza Shahbazian-Yassar: 0000-0002-7744-4780 20926
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
Research Article
ACS Applied Materials & Interfaces (16) Zhang, Y.; Gao, T.; Gao, Y.; Xie, S.; Ji, Q.; Yan, K.; Peng, H.; Liu, Z. Defect-Like Structures of Graphene on Copper Foils for Strain Relief Investigated by High-Resolution Scanning Tunneling Microscopy. ACS Nano 2011, 5, 4014−4022. (17) Bao, W.; Miao, F.; Chen, Z.; Zhang, H.; Jang, W.; Dames, C.; Lau, C. N. Controlled Ripple Texturing of Suspended Graphene and Ultrathin Graphite Membranes. Nat. Nanotechnol. 2009, 4, 562−566. (18) Zhang, K.; Arroyo, M. Understanding and Strain-Engineering Wrinkle Networks in Supported Graphene through Simulations. J. Mech. Phys. Solids 2014, 72, 61−74. (19) Vázquez de Parga, A. L.; Calleja, F.; Borca, B.; Passeggi, M. C. G.; Hinarejos, J. J.; Guinea, F.; Miranda, R. Periodically Rippled Graphene: Growth and Spatially Resolved Electronic Structure. Phys. Rev. Lett. 2008, 100, 056807. (20) Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Role of Hydrogen in Chemical Vapor Deposition Growth of Large Single-Crystal Graphene. ACS Nano 2011, 5, 6069− 6076. (21) Yu, Q.; Jauregui, L. A.; Wu, W.; Colby, R.; Tian, J.; Su, Z.; Cao, H.; Liu, Z.; Pandey, D.; Wei, D.; Chung, T. F.; Peng, P.; Guisinger, N. P.; Stach, E. A.; Bao, J.; Pei, S.-S.; Chen, Y. P. Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 443−449. (22) Yasaei, P.; Kumar, B.; Hantehzadeh, R.; Kayyalha, M.; Baskin, A.; Repnin, N.; Wang, C.; Klie, R. F.; Chen, Y. P.; Král, P.; SalehiKhojin, A. Chemical Sensing with Switchable Transport Channels in Graphene Grain Boundaries. Nat. Commun. 2014, 5, 4911. (23) Deng, Z.; Smolyanitsky, A.; Li, Q.; Feng, X.-Q.; Cannara, R. J. Adhesion-Dependent Negative Friction Coefficient on Chemically Modified Graphite at the Nanoscale. Nat. Mater. 2012, 11, 1032− 1037. (24) Marsden, A. J.; Phillips, M.; Wilson, N. R. Friction Force Microscopy: A Simple Technique for Identifying Graphene on Rough Substrates and Mapping the Orientation of Graphene Grains on Copper. Nanotechnology 2013, 24, 255704. (25) Liu, X.-Z.; Li, Q.; Egberts, P.; Carpick, R. W. Nanoscale Adhesive Properties of Graphene: The Effect of Sliding History. Adv. Mater. Interfaces 2014, 1, 1300053. (26) Bao, W.; Miao, F.; Chen, Z.; Zhang, H.; Jang, W.; Dames, C.; Lau, C. N. Controlled Ripple Texturing of Suspended Graphene and Ultrathin Graphite Membranes. Nat. Nanotechnol. 2009, 4, 562−566. (27) Vorselen, D.; Kooreman, E. S.; Wuite, G. J. L.; Roos, W. H. Controlled Tip Wear on High Roughness Surfaces Yields Gradual Broadening and Rounding of Cantilever Tips. Sci. Rep. 2016, 6, 36972. (28) Yasaei, P.; Fathizadeh, A.; Hantehzadeh, R.; Majee, A. K.; ElGhandour, A.; Estrada, D.; Foster, C.; Aksamija, Z.; Khalili-Araghi, F.; Salehi-Khojin, A. Bimodal Phonon Scattering in Graphene Grain Boundaries. Nano Lett. 2015, 15, 4532−4540. (29) Green, C. P.; Lioe, H.; Cleveland, J. P.; Proksch, R.; Mulvaney, P.; Sader, J. E. Normal and Torsional Spring Constants of Atomic Force Microscope Cantilevers. Rev. Sci. Instrum. 2004, 75, 1988−1996.
20927
DOI: 10.1021/acsami.7b00711 ACS Appl. Mater. Interfaces 2017, 9, 20922−20927
