Enhanced Graphene Mechanical Properties ... - ACS Publications

Subscriber access provided by UNIV OF YORK

Communication

Enhanced Graphene Mechanical Properties through Ultra-Smooth Copper Growth Substrates Mark Griep, Emil Sandoz-Rosado, Travis Tumlin, and Eric Wetzel Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.5b04531 • Publication Date (Web): 16 Feb 2016 Downloaded from http://pubs.acs.org on February 17, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Nano Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 19

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

Nano Letters

Enhanced Graphene Mechanical Properties through Ultra-Smooth Copper Growth Substrates Mark H. Griep*, Emil Sandoz-Rosado, Travis M. Tumlin, and Eric Wetzel U.S. Army Research Laboratory, 4600 Deer Creek Loop, APG, MD 21005. The combination of extraordinary strength and stiffness in conjunction with exceptional electronic and thermal properties in lightweight 2D materials has propelled graphene research towards a wide array of applications including flexible electronics and functional structural components. Tailoring graphene’s properties towards a selected application requires precise control of the atomic layer growth process, transfer, and post-processing procedures. To date, the mechanical properties of graphene are largely controlled through post-process defect engineering techniques. In this work, we demonstrate the role of varied catalytic surface morphologies on the tailorability of subsequent graphene film quality and breaking strength, providing a mechanism to tailor the physical, electrical, and mechanical properties at the growth stage. A new surface planarization methodology that results in over a 99% reduction in Cu surface roughness allows for smoothness parameters beyond that reported to date in literature and clearly demonstrates the role of Cu smoothness towards a decrease in the formation of bi-layer graphene defects, altered domain sizes, monolayer graphene sheet resistance values down to 120 Ω/□, and a 78% improvement in breaking strength.

The combined electrical and mechanical

ACS Paragon Plus Environment

1

Nano Letters

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

Page 2 of 19

enhancements achieved through this methodology allows for the direct growth of application quality flexible transparent conductive films with monolayer graphene.

Keywords: Graphene, Breaking Strength, Electropolishing, 2D-Nanomaterial


2

Page 3 of 19

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

Nano Letters

The ability to precisely control the electrical and mechanical properties of graphene is a key foundational attribute towards tailoring it for selected applications. Graphene’s mechanical properties in particular have been of intense study in recent years to isolate the impact of multiple variables including the role of grain boundaries

1

and their associated tilt

2, 3

, domain

size 4, defect quantities 5, and material wrinkling 6 on the resulting strength characteristics. More recently, the process of defect engineering through controlled plasma treatments has created a methodology to tailor graphene breaking strength

7, 8

and crack propagation mechanisms

9

through the tailoring of defect densities. Although counter-intuitive, controlled defect creation has demonstrated the capability to enhance graphene’s elastic modulus and inhibit crack propagation. In addition to strengthening graphene at low defect concentrations, the strength parameter can be tailored to precise levels to fit the desired application through O2/Ar plasma treatment. In this work we demonstrate a growth methodology that allows for direct tuning and improvement of graphene’s breaking strength through engineering of the growth foil, without the need for any post-processing treatment of the graphene film. Recent literature has begun to elucidate the effect of catalytic metal surface roughness on the subsequent quality of CVD grown 2D nanomaterials 10-12. Increased surface coverage, control of nucleation density, and larger single crystalline domains has resulted for graphene 2D nanomaterials utilizing planarized copper growth substrates

11, 12

. Similar effects on increased

domain size has also recently been shown with h-BN 13 in addition to altered growth mechanisms due to substrate roughness variations

14

. To date, however, standard electropolishing (EP)

methodologies reported in literature for CVD graphene growth have yielded only moderate reductions in surface roughness and have not systematically elucidated the impact of varying morphologies on subsequent material properties. Here, we report a new EP methodology that


3

Nano Letters

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

Page 4 of 19

allows tailored preparations of ultrasmooth Cu substrates with >99% reduction in surface roughness, far beyond that reported in literature to date

11, 12, 15

, which also allows for highly

reproducible production of select planarization levels ranging for 10 to 100 fold roughness reduction from control.

The ability to precisely control Cu surface morphology to select

roughness levels allows for the systematic evaluation of the role of varying planarization levels on graphene growth dynamics and resulting material properties As shown in Figure 1, a high degree of Cu surface morphology control has been attained through an optimized EP setup (EP methods discussed in the SI), yielding the ability to control surface planarization levels from 10 to 100 fold roughness reductions from control. A multitude of variables that affect the electropolishing process are precisely controlled including the electrolyte composition (acid concentration, solution viscosity) and the electropolishing setup (electrolyte temperature, stirring speed, sample geometry, electrolyte volume, shape/size of the bath, and arrangement of the electrodes). Unlike previous reports which affix the Cu foil in a beaker of electrolyte solution, this setup flows the electrolyte past a fixed area window exposing only the desired polishing area on the Cu; allowing repeatable/stable current densities for every sample. For the electrolyte composition it was found that lower viscosity solutions

12

, as opposed to

solutions containing polyethylene glycol 11, were required to achieve a smooth, continuous flow between the electrodes and avoid current fluctuations.

Although previous reports utilized

electropolishing protocols in the 1.0-2.0V range to remain below oxygen evolution regions which can promote pitting 16, our studies revealed a higher level of surface roughness reduction and overall surface consistency is achieved at a secondary plateau in the 8V range while maintaining a stable current density of 0.40-0.45 A/cm2 throughout the process. In this EP methodology, rapid dissolution of the Cu ridges occurs in under 30 seconds, after which uniform,


4

Page 5 of 19

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

Nano Letters

repeatable surface planarization levels were achieved with processing times up to 120s. Further EP beyond 120s yielded an increase in surface roughness due to the rapid formation of pits and areas of complete copper dissolution (ie. hole formation in the foil).

With the optimized

configuration, surface roughness reductions from control (Ra 390nm) of 93% (60s EP, Ra 27.3nm), 98.7% (90s EP, Ra 4.9nm), and 99.3% (120s EP, Ra 2.8nm) were produced to study the effect of variable surface roughness levels on graphene growth dynamics and ultimate material properties. Further AFM images highlighting surface topography at each planarization level are shown in Figure S1. The Cu planarization levels achieved in this process are far smoother than that reported in previous electropolishing literature

11, 12

and is comparable to roughness levels

achieved through more complex methodologies including template stripped

17

, epitaxially

sputtered 18, electron beam evaporated 19, and single-point diamond turned 20 Cu substrates.


5

Nano Letters

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

Page 6 of 19

Figure 1. Schematic of (a) electropolishing setup and (b) planarization mechanism during polishing. (c) Roughness values and correlating AFM images (30um x 30um) of control, 60s, 90s, and 120s EP Cu. Inset table displays measured roughness values and calculated roughness reduction from control.

Graphene growth on the EP substrates was achieved through standard protocols (growth methods described in the SI). Following graphene nucleated growth, roughness values for the substrate were measured to be 95.9nm, 10.5nm, 6.4nm, and 5.8nm for the control, 60s, 90s, and 120s EP samples, respectively (Figure S2).

Therefore at the point of graphene growth, the highly

planarized samples saw an increase in surface roughness due to the LPCVD processing, consistent with that seen in previous literature

20

. Although the control and 60s samples saw a

reduction in roughness due to processing near the Cu melting point, the overall roughness reduction trend is maintained across the planarized samples during graphene growth.


6

Page 7 of 19

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

Nano Letters

The varying planarization levels yielded markedly different graphene growth dynamics, particularly with regards to nucleation. The importance of controlling nucleation is a key factor to the final graphene quality, as demonstrated through the control of Cu surface oxygen to tailor nucleation kinetics

21

. In the nucleation phase on the highly planarized substrates, as shown in

Figure 2, it can be noted that substantial reduction in domain nucleation sites is achieved on the EP substrates. In fact, a decrease in domain nucleation sites is seen within the EP samples, following the trend that smoother substrates yield less domain sites. Compared to the control foil nucleation density of 42.4 ± 14.9 domain sites in a 128um x 96um scan area, the planarized samples yielded domain counts of, 5.4 ± 1.1, 4.6 ± 1.5, and 2.4 ± 1.1 for the 60s, 90s, and 120s polished foils (Table S1). As graphene islands tend to nucleate at surface imperfections such as grooves or grain boundaries 22, 23, a reduction in nucleation density is achieved through reducing the defect points on the Cu surface. The reduction in nucleation density confirms the reduced quantity of defect points on the foil, allowing for the growth of higher quality graphene materials. The improved quality of the graphene film with respect to subdued bilayer formation is also confirmed (Figure 2), which shows a direct increase in monolayer graphene coverage and reduction in bilayer islands with increased EP time. RAMAN analysis, as shown in Figure 2(e), reveal an I2D/IG ratio for all samples averages around 2.25 and suggest predominantly monolayer graphene within the local probe region measured. Although the increased presence of bilayers is noted in the optical images, the small bilayer structures are not reflected in the local probe area (1 kΩ/□; far above the theoretical sheet resistance of ‘perfect’ graphene at ~30 Ω/□

25

.

Here, in addition to the

demonstrated reduction in defective bilayer islands, the ultra-smooth surface planarization levels eliminate the large growth substrate ridges that translate into defective wrinkles upon transfer. This decrease in defects directly translates to a reduction in monolayer graphene sheet resistance that is comparable to more complex optimization techniques including multi-layer stacking incorporation of Ag nanowires substrates

28

24

, addition of graphene nanopatches

27

26

,

, and tailored BN

. It could be expected that the coupling of this planarization approach with the

aforementioned optimization techniques would achieve flexible graphene transparent conductive films (TCF) on par or superior to the current indium tin oxide (ITO) standard. Beyond electrical performance, this work evaluated the role of growth substrate planarization on the resulting graphene’s mechanical properties. Graphene was mechanically characterized through AFM indentation of a monolayer suspended over a well. Previous work of indentation of suspended monolayer graphene concluded that the in-plane elastic stiffness of small-grain CVD, large-grain CVD, and pristine exfoliated graphene were not differentiable through statistical analysis; however, breaking force was statistically different between the various types of graphene 1. As such, we compared the average breaking force of graphene grown on unpolished, 60, 90, and 120 second electro-polished copper using the same diamond AFM tip for indentation (nominal tip radius of 40nm, spring constant of 198 N/m). The breaking force is governed by the stress concentration under the hemisphere of the AFM tip as well as the presence of defects in the graphene, ensuring that indentation using the same tip yielded quantifiable data for


9

Nano Letters

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

Page 10 of 19

mechanical comparison between graphene grown on substrates of differing polish preparation. Indentation experiments were performed on graphene suspended over circular and square wells with lengths of 0.5, 1, and 2 µm. Due to the highly localized stress concentration underneath, which is at least an order of magnitude smaller than the dimensions of the well, both the location of indentation on the monolayer over the well and the well geometry did not impact the breaking force. The mean breaking forces and standard deviations are reported in Figure 3 for graphene grown on each copper EP time. Results demonstrate a steady increase in graphene breaking strength directly correlating to increased surface planarizations levels at each EP timepoint. Analysis demonstrated that the mean breaking forces of all four graphene types were statistically different with a confidence of over 95% 29. The graphene samples were tested in the order of 90s, control, 120s, 60s to ensure that tip wear did not create a systematic increase in breaking force. Given that the mean breaking forces monotonically increase from control through 120s e-polished samples, it is safe to assume that the tip wear was not a significant factor for the increasing breaking force.


10

Page 11 of 19

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

Nano Letters

Figure 3. (a) Mean breaking force for graphene grown on each copper EP timepoint from 0s (control) to 120s. (b) Mean breaking force for the bimodal fits and a potential trimodal fit at 120s.

Examining the histograms of the break force for each scenario reveals a bimodal behavior (Figure 4). The data sets were curve fit with bimodal normal distributions with differing variances, governed by mixture parameter, p. The quality of the bimodal fits was verified utilizing the Akaike information criterion (AIC) function.

The AIC values for potential

unimodel, bimodal, and trimodal fits to the breaking force datasets is shown in Table S2, with the bimodal fit providing the lowest AIC values for each dataset. We hypothesize that the existence of two primary peaks is related to the proximity of grain boundaries to the loading tip.


11

Nano Letters

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

Page 12 of 19

During membrane testing, the AFM tip is a stress concentrator and failures are initiated local to the tip. If grain boundaries have less strength than the bulk planar crystal, the presence of a grain boundary near the tip could trigger failure at lower loads. The frequency of the first failure case is governed by the size of the grains and the frequency of the second failure case is governed by the overall graphene quality and presence of defects such as voids and cracks. Additional quality enhancements relates to the conformation of synthesized graphene on a rough metal surface which has been shown to induce uneven strain within the film and defects in the carbon lattice 30, 31

. Since graphene growth follows the morphology of growth substrate, when the graphene is

removed from the non-planar underlying metal it is unable to lay flat on the target surface and results in cracking and wrinkling within the transferred graphene film

32

. As wrinkled regions

have been shown to modulate the local mechanical and electronic environment 33, the reduction of wrinkle defects through ultra-smooth EP foils is a likely factor.


12

Page 13 of 19

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

Nano Letters

Figure 4: Histograms of the graphene breaking forces fit with bimodal distributions (red) for graphene grown on Cu foils treated at a) 0s, b) 60s, c) 90s and d) 120s EP timepoints. Potential emergence of a trimodal distribution (blue) included in the 120s EP sample.


13

Nano Letters

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

Page 14 of 19

The individual bimodal peak averages can be seen in Figure 3(b). The mean breaking forces for the first peaks are all about 1µN, indicating that for all e-polishing times there exists a defect that has the same ultimate stress. This supports the idea of grain boundaries causing the lower defect peak, since grain boundaries would have nearly the same ultimate stress, but vary in frequency depending on e-polishing time. The mixture parameter, p, which indicates the relative likelihood of a sample falling on the first distribution relative to the second distribution curve, decreases monotonically with e-polishing time (Figure S3). A lower mixture parameter indicates that the lower breaking peak occurs less frequently compared to the higher breaking peak. We would expect that as the e-polishing times increased, the graphene grain sizes would increase and the frequency of failure at a grain boundary would decrease. In the singular case of the graphene grown on 120 second polished copper an unusual trend was observed suggesting the possibility of trimodal behavior, shown in Figure 4d. While further studies are needed to definitively indicate three distinct normal peaks in the population of breaking forces, there is certainly a significant shift in the number of instances of failure greater than a breaking force value of 3µN (also seen in Figure 3b). If trimodal behavior is indeed present, then it could indicate a third mode of failure consistent with a pristine sheet of graphene. The significant increase in breaking strength of the 120 second sample could be the result of a decrease in defects caused by wrinkles and folds in the graphene as a result of extra material grown on rougher surfaces. The Ra values of the copper substrate monotonically drops from 390nm at 0 seconds EP time to 2.8nm at 120 seconds EP time, corresponding to 12.71% extra copper surface (and extra graphene) and 0.002% extra copper surface compared to a perfectly flat substrate. With 12.71% extra material, the 0 second EP graphene (control) is more likely to fold and wrinkle during transfer, possibly leading to lower breaking forces.


14

Page 15 of 19

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

Nano Letters

In summary, the role of ultra-smooth Cu growth surface morphologies towards the improvement of graphene quality in terms of electrical sheet resistance and mechanical breaking strength is shown. A systematic approach to evaluate the impact of 10-fold and 100-fold reductions in surface roughness over control foils verified a direct trend of improved graphene properties. A substantial reduction in monolayer graphene sheet resistance values down to 120 Ω/□ was achieved, allowing for the direct CVD growth of viable TCF materials.

From a strength

viewpoint, interestingly, the mechanical analysis not only revealed enhancements in breaking strength of over 76%, but also a bimodal behavior that isolates a common fracture characteristic across the samples that is distinctly separate from the noted strength enhancements. Additionally, by tailoring the mechanical properties at the growth phase, these results present new opportunities to optimize and tune graphene modulus without the need for post-processing procedures. With the simultaneous material enhancements of improved sheet resistance and increased mechanical strength demonstrated in CVD-grown monolayer graphene with this methodology, a direct approach to produce application quality materials can be achieved without the need for further optimization.


15

Nano Letters

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

Page 16 of 19

AUTHOR INFORMATION Corresponding Author * Email: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Funding for this work was provided by the U.S. Army Research Laboratory. This research was supported in part by an appointment to the Postgraduate Research Participation Program at the U.S. Army Research Laboratory administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and U.S. ARL. ACKNOWLEDGMENT We gratefully acknowledge the input and advice of Dr. James Hannon and Dr. Joshua Smith at IBM regarding graphene growth dynamics. We also thank Dr. Kris Behler, Dr. Rad Balu, and Dr. Ross Sausa for helpful discussions on the preparation/analysis of Cu foils. We also acknowledge Prof. Pullickel Ajayan and Dr. Robert Vajtai of Rice University for their aid in the development of the graphene growth process. ABBREVIATIONS AFM, Atomic Force Microscopy; CI, Confidence Index; Cu, Copper; CVD, Chemical Vapor Deposition; EP, Electropolish; ITO, Indium Tin Oxide; TCF, Transparent Conductive Film


16

Page 17 of 19

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

Nano Letters

SUPPORTING INFORMATION Methodology: Electropolishing of Cu foil Methodology: Characterization of Cu foil Methodology: Graphene growth and transfer process S1. AFM images of electropolished Cu foils prior to graphene growth. S2. AFM images of electropolished Cu foils post graphene growth. S3. Bimodal mixture parameter at varying electropolishing timepoints. Table S1. Average domain count, domain size, and area coverage for nucleated graphene growth on varying electropolishing timepoint foils. Table S2. Akaike information criterion analysis for polymodal fittings of graphene breaking strength values.

REFERENCES 1. Lee, G.-H.; Cooper, R. C.; An, S. J.; Lee, S.; van der Zande, A.; Petrone, N.; Hammerberg, A. G.; Lee, C.; Crawford, B.; Oliver, W.; Kysar, J. W.; Hone, J. Science 2013, 340, (6136), 1073-1076. 2. Zhang, J.; Zhao, J.; Lu, J. ACS Nano 2012, 6, (3), 2704-2711. 3. Grantab, R.; Shenoy, V. B.; Ruoff, R. S. Science 2010, 330, (6006), 946-948. 4. Chen, M. Q.; Quek, S. S.; Sha, Z. D.; Chiu, C. H.; Pei, Q. X.; Zhang, Y. W. Carbon 2015, 85, 135-146. 5. Song, Z.; Artyukhov, V. I.; Wu, J.; Yakobson, B. I.; Xu, Z. ACS Nano 2015, 9, (1), 401408. 6. Ruiz-Vargas, C. S.; Zhuang, H. L.; Huang, P. Y.; van der Zande, A. M.; Garg, S.; McEuen, P. L.; Muller, D. A.; Hennig, R. G.; Park, J. Nano Letters 2011, 11, (6), 2259-2263. 7. Lopez-Polin, G.; Gomez-Navarro, C.; Parente, V.; Guinea, F.; Katsnelson, M. I.; PerezMurano, F.; Gomez-Herrero, J. Nat Phys 2015, 11, (1), 26-31. 8. Zandiatashbar, A.; Lee, G.-H.; An, S. J.; Lee, S.; Mathew, N.; Terrones, M.; Hayashi, T.; Picu, C. R.; Hone, J.; Koratkar, N. Nat Commun 2014, 5, 3186. 9. López-Polín, G.; Gómez-Herrero, J.; Gómez-Navarro, C. Nano Letters 2015, 15, (3), 2050-2054. 10. Kim, K. K.; Hsu, A.; Jia, X.; Kim, S. M.; Shi, Y.; Hofmann, M.; Nezich, D.; RodriguezNieva, J. F.; Dresselhaus, M.; Palacios, T.; Kong, J. Nano Letters 2011, 12, (1), 161-166.


17

Nano Letters

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

Page 18 of 19

11. Luo, Z.; Lu, Y.; Singer, D. W.; Berck, M. E.; Somers, L. A.; Goldsmith, B. R.; Johnson, A. T. C. Chemistry of Materials 2011, 23, (6), 1441-1447. 12. Zhang, B.; Lee, W. H.; Piner, R.; Kholmanov, I.; Wu, Y.; Li, H.; Ji, H.; Ruoff, R. S. ACS Nano 2012, 6, (3), 2471-2476. 13. Lee, K. H.; Shin, H.-J.; Lee, J.; Lee, I.-y.; Kim, G.-H.; Choi, J.-Y.; Kim, S.-W. Nano Letters 2012, 12, (2), 714-718. 14. Tay, R. Y.; Griep, M. H.; Mallick, G.; Tsang, S. H.; Singh, R. S.; Tumlin, T.; Teo, E. H. T.; Karna, S. P. Nano Letters 2014, 14, (2), 839-846. 15. Lee, D.; Kwon, G. D.; Kim, J. H.; Moyen, E.; Lee, Y. H.; Baik, S.; Pribat, D. Nanoscale 2014, 6, (21), 12943-12951. 16. Shieh, J.-M.; Chang, S.-C.; Wang, Y.-L.; Dai, B.-T.; Cheng, S.-S.; Ting, J. Journal of The Electrochemical Society 2004, 151, (7), C459-C462. 17. Pavel, P.; Jindřich, M.; Dominik, B.; Zuzana, L.; Petr, D.; Marek, V.; Pauline, S.; Anastasia, V.; Dušan, H.; Martin, P.; Lukáš, K.; Miroslav, B.; Klaus, E.; Peter, V.; Jan, Č.; Tomáš, Š. Nanotechnology 2014, 25, (18), 185601. 18. Jacobberger, R. M.; Arnold, M. S. Chemistry of Materials 2013, 25, (6), 871-877. 19. Tao, L.; Lee, J.; Chou, H.; Holt, M.; Ruoff, R. S.; Akinwande, D. ACS Nano 2012, 6, (3), 2319-2325. 20. Dhingra, S.; Hsu, J.-F.; Vlassiouk, I.; D’Urso, B. Carbon 2014, 69, 188-193. 21. Hao, Y.; Bharathi, M. S.; Wang, L.; Liu, Y.; Chen, H.; Nie, S.; Wang, X.; Chou, H.; Tan, C.; Fallahazad, B.; Ramanarayan, H.; Magnuson, C. W.; Tutuc, E.; Yakobson, B. I.; McCarty, K. F.; Zhang, Y.-W.; Kim, P.; Hone, J.; Colombo, L.; Ruoff, R. S. Science 2013, 342, (6159), 720723. 22. Luo, Z.; Kim, S.; Kawamoto, N.; Rappe, A. M.; Johnson, A. T. C. ACS Nano 2011, 5, (11), 9154-9160. 23. Nie, S.; Wofford, J. M.; Bartelt, N. C.; Dubon, O. D.; McCarty, K. F. Physical Review B 2011, 84, (15), 155425. 24. Kholmanov, I. N.; Magnuson, C. W.; Aliev, A. E.; Li, H.; Zhang, B.; Suk, J. W.; Zhang, L. L.; Peng, E.; Mousavi, S. H.; Khanikaev, A. B.; Piner, R.; Shvets, G.; Ruoff, R. S. Nano Letters 2012, 12, (11), 5679-5683. 25. Chen, J.-H.; Jang, C.; Xiao, S.; Ishigami, M.; Fuhrer, M. S. Nat Nano 2008, 3, (4), 206209. 26. Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J.-S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Ri Kim, H.; Song, Y. I.; Kim, Y.-J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J.-H.; Hong, B. H.; Iijima, S. Nat Nano 2010, 5, (8), 574-578. 27. Song, W.; Kim, K. W.; Chang, S.-J.; Park, T. J.; Kim, S. H.; Jung, M. W.; Lee, G.; Myung, S.; Lim, J.; Lee, S. S.; An, K.-S. Journal of Materials Chemistry C 2015, 3, (4), 725728. 28. Gannett, W.; Regan, W.; Watanabe, K.; Taniguchi, T.; Crommie, M. F.; Zettl, A. Applied Physics Letters 2011, 98, (24), 242105. 29. Welch, B. L. Biometrika 1947, 34, (1/2), 28-35. 30. Zhang, Y.; Gao, T.; Gao, Y.; Xie, S.; Ji, Q.; Yan, K.; Peng, H.; Liu, Z. ACS Nano 2011, 5, (5), 4014-4022. 31. Rasool, H. I.; Song, E. B.; Allen, M. J.; Wassei, J. K.; Kaner, R. B.; Wang, K. L.; Weiller, B. H.; Gimzewski, J. K. Nano Letters 2010, 11, (1), 251-256.


18

Page 19 of 19

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

Nano Letters

32. Li, X.; Zhu, Y.; Cai, W.; Borysiak, M.; Han, B.; Chen, D.; Piner, R. D.; Colombo, L.; Ruoff, R. S. Nano Letters 2009, 9, (12), 4359-4363. 33. Xu, K.; Cao, P.; Heath, J. R. Nano Letters 2009, 9, (12), 4446-4451.

Table of Contents Graphic


19

Enhanced Graphene Mechanical Properties ... - ACS Publications

Recommend Documents