Effects of ultraviolet nanosecond laser irradiation on structural modification and optical transmission of single layer graphene

Applied Surface Science 398 (2017) 89–96

Contents lists available at ScienceDirect

Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc

Full Length Article

Effects of ultraviolet nanosecond laser irradiation on structural modification and optical transmission of single layer graphene Chunhong Li ∗ , Xiaoli Kang, Qihua Zhu, Wanguo Zheng Research Center of Laser Fusion, China Academy of Engnieering Physics, Mianyang 621900, China

a r t i c l e

i n f o

Article history: Received 21 August 2016 Received in revised form 19 November 2016 Accepted 5 December 2016 Available online 6 December 2016 Keywords: Single layer graphene Ultraviolet nanosecond laser irradiation Structural modification Raman spectra Optical transmittance

a b s t r a c t Structural modifications and optical transmission change of single layer graphene (SLG) on transparent SiO2 substrate induced by nanosecond 355 nm laser irradiation were systematically studied by scanning electron microscopy (SEM), laser-excited Raman, X-ray photon spectroscopy (XPS) and UV–vis transmission spectra. In this study, to avoid damage to graphene, the selected irradiation fluence was set to be smaller than the laser damage threshold of SLG. Laser-driven formation of nano-dots, carbon clusters and spherical carbon morphologies were clearly presented using SEM magnification images, and the formation mechanism of such structures were discussed. Raman spectra revealed formation of D’ peak and the continuously increasing of ID /IG intensity ratio with the concurrent increase of laser fluence, indicating the increase in amount of structural defects and disordering in SLG. XPS results disclosed that the oxygen content in SLG increases with laser fluence. The formation and relative content increase of C O, C O C and O C O bonds in SLG induced by laser irradiation were also revealed by XPS. Laser-driven micro-structure modifications of crystalline graphene to nano-crystalline graphene and photo-chemical reactions between graphene and O2 and H2 O in air environment were suggested to be responsible for the Raman and XPS revealed modifications in SLG. It is worthy to point out that the above mentioned structural modifications only caused a slight decrease (<2% @ 550 nm) in the optical transmittance of SLG. These results may provide more selections for the batch processing of large scale graphene aiming at modifying its structure and thus taiorling its properties. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Graphene has been attracting considerable attention because of its outstanding electric [1], optical [2,3], mechanical [4] and thermal [5] properties. These properties make graphene good candidates for many applications such as field effect transistors, transparent conducting electrodes, non-linear optical components, photodetectors and thermal management materials. For the application of graphene-based devices, the processing or modification of graphene is an important issue. Laser irradiation treatment is a very good solution for the processing [6–9] and modification [10–12] of such thin films like graphene. Compared with other methods, laser treatment has unique advantages. For example, the processing precision can be very high, and the treatment location can be arbitrarily selected according to specific requirements by controlling the laser beam paremeters. Also, unnecessary contamination can be avoided during laser-based

∗ Corresponding author. E-mail address: [email protected] (C. Li). http://dx.doi.org/10.1016/j.apsusc.2016.12.026 0169-4332/© 2016 Elsevier B.V. All rights reserved.

processing. Due to the practical importance, investigating the laserinduced effects on graphene is very necessary. Recently, influence of CW laser [13,14] and short pulsed femtosecond laser [15–17] as well as nanosecond laser [18–21] irradiation on graphene has been reported. These results showed that the damage threshold, structure modification and the properties of graphene were closely related to the laser parameters (e.g. wavelength, pulse duration and pulse energy), the type of the substrate and the characteristics of graphene. However, most of these studies focused on the laser-induced damage effect or laser-induced chemical modifications on graphene, while little attention was paid to the low energy laser-induced modifications rather than damage on pure single layer graphene (SLG), especially in the case of nanosecond laser irradiation. Therefore, more investigation is needed to extend understanding on this point, so that the specific properties of SLG can be tailored through modifying its microstructure. In this paper, we present a study of the structural modifications of SLG during nanosecond pulsed laser irradiation at fluence lower than its damage threshold using sacnning electron microscopy (SEM), Raman spectrum and X-ray photoelectron spectroscopy(XPS). Also, the optical transmittance variation of SLG with

90

C. Li et al. / Applied Surface Science 398 (2017) 89–96

Table 1 The tested LIDT and the irradiated laser fluence for SLG samples. Sample Name

a

b

c

d

e

Tested LIDT

Laser fluence (mJ/cm2 )

0

10.5

31.6

51.8

70.3

78.0

of Renishaw Raman system, using a 514 nm Ar+ laser as excitation light source with a power of 5 mW. The diameter of the excited laser beam was about 2 mm, and thus the laser power density on the sample plane was about 0.158 W/cm2 . This low level power density won’t induce destroy to graphene during Raman test. All Raman spectra were obtained in the 90◦ scattering configuration. The Raman spectra were measured over the range from 1000 to 3500 cm−1 . XPS spectra were acquired on a thermal electron ESCALAB 250 system. The X-ray source was a monochromatic Mg Ka (1253.6 eV) beam with an analysis area of ∼3 mm2 on sample surface. The optical transmittance of samples were characterized by the UV–vis NIR optical transmission spectra.

3. Results and discussions Fig. 1. Experimental setup of the pulsed UV laser beam irradiation system.

laser irradiation fluences is measured and analyzed. Additional features of our work include: (1) the 355 nm ultra-violet laser is used by considering the relatively strong absorption of graphene at this wavelength, which possibly means higher treatment efficiency than using lasers with longer wavelengths; (2) the SLG used is on the transparent fused silica substrate, as is rarely reported. 2. Experiment SLG was prepared by chemical vapor deposition method on high purity copper foil and then transferred onto a foreign substrate. UV grade Corning 7980 fused silica with dimensions of 25.4 × 25.4 × 2 mm3 was used as the substrate. The substrate was first carefully polished using CeO2 slurry and the surface roughness was controlled to be less than 1 nm. Then the substrate was washed thoroughly with distilled de-ionized water and absolute ethanol to rinse off any dusts and particles induced by polishing and storage. After that, poly methyl methacrylate (PMMA) was spin-coated on the surface of graphene on copper foil. The copper substrate was dissolved in a warm (70 ◦ C) etchant solution (30% FeCl3 and 5% HCl) and rinsed in deionized water. Then the PMMA-based graphene was transferred onto the as-polished fused silica substrate. Finally, the PMMA cover layer was completely removed in warm (70 ◦ C) dimethylethylene solution and then dried. The as-prepared SLG samples were irradiated with a nanosecond pulse laser (Nd-YAG Q-swithched solid laser). The wavelength was 355 nm and the pulse length (full width at half maximum, FWHM) was ∼6.8 ns. The incident laser energy of each shot was measured by a Ophir calorimeter in front of the test sample with a wedge. The beam profile was measured with an Ophir & Spiricon beam analyzer. The temporal and spatial profile of laser beam was both near Gaussian with a 1/e2 diameter of 10 mm at the sample plane. Prior to laser irradiation experiment, the laser-induced damage threshold (LIDT) of the prepeared SLG samples was tested strictly according to Interanational Standard ISO 11254. Using the R-on-1 method, the tested LIDT for the as-produced SLG samples was 78 mJ/cm2 at 355 nm. Thus, in order to avoid distinct laserinduced damage, the examined laser energy density in this study was set as 0, 10.5, 31.6, 51.8, 70.3 mJ/cm2 , respectively (seen in Table 1). To study the effect of laser fluence, for one SLG sample, only one pulse of laser shot was irradiated. The setup of the laser irradiation facility was depicted in Fig. 1. Sacnning electron microscopy (SEM) was used to observe the typical morphological variations of SLG induced by laser irradiation. Raman and XPS spectra were employed to annalyze the structural modifications and surface functional groups of SLG samples. Raman spectra were performed with a Fourier-transform mode

Fig. 2 systematically presented the morphology modifications of graphene induced by laser pulse at different fluence. Fig. 2(a,b) showed the morphology of pristine state graphene. It demonstrated good surface quality, though some isolated nano-scale cracks/wrinkles were also observed. Fig. 2(c–f) clearly presented the morphology of SLG after laser irradiation. Unlike the folds [15] and nanometer-scale patterning [22] induced by femtosecond laser ablation, it is interesting to observe that nano-scale spherical carbon was formed on the SLG surface after UV nanosecond laser irradiation. Particularly, discrete carbon clusters looking like flower buds were observed for the graphene irradiated by laser pulse at 10.5 mJ/cm2 . When the laser fluence increased to 31.6 mJ/cm2 , nanometric-sized carbon balls were discovered. Larger size spherical carbon could be seen in images of Fig. 2e (51.8 mJ/cm2 ) and Fig. 2f (70.3 mJ/cm2 ). Besides, a small amount of folds and nanoscale holes presented on the surface of graphene irradiated by high laser fluence of 70.3 mJ/cm2 . The morphology modification revealed that graphene surface experienced high temperature, material melting, gasification and carbon atom re-deposition processes during irradiation-induced photon energy absorption. In detail, nanosecond laser irradiation caused photon energy deposition and transient temperature rise on graphene layer. Then, the irradiated graphene gasified quickly, producing carbon plasma with high temperature and high density. At the end of laser pulse, the cooling process began and deposition of carbon atoms/ions on graphene surface occurred, resulting in nano-sized carbon with different morphologies. The morphology of deposited nano-carbon depended on several factors such as the density and diffusion of carbon plasma as well as the property of the substrate. The density of carbon plasma was closely related with the laser fluence. Due to relatively large surface tension of the graphene and the difficulty in diffusion of carbon atoms, spherical carbon was easily formed during the condensation process. Fig. 3 simultaneously presented morphologies of three types of carbon on the surface of laser-irradiated graphene, i.e. nano-sized dots, carbon clusters and spherical carbon. It was inferred that the spherical carbon was formed by the growth of small size nano-dots and carbon clusters. Fig. 4 showed Raman spectra of the pristine state and laser irradiated SLG. The pristine graphene showed typical G peak (1585 cm−1 ) and 2D peak (2700 cm−1 ) belonging to SLG. The G band corresponds to the strethching virbration mode, E2g phonon at the Brillouin zone center [23]. The 2D band, which is also called G’ in literature, originates from a second order Raman process involving a double resonance (DR) scattering event between K and K’ points [24]. After laser irradiation, structural disorder-induced D peak (1350 cm−1 ) immediately appearred, revealing defects and disorder created in graphene [25]. When the laser fluence increased to 50.8 mJ/cm2 , another defect-related D’ peak (1620 cm−1 ) appeared. Also, G peak broadened obviously at laser fluence of 70.3 mJ/cm2 .

C. Li et al. / Applied Surface Science 398 (2017) 89–96

91

Fig. 2. Morphology modifications of single layer graphene irradiated by nanosecond pulsed laser at different fluence. (a-b) pristine state of the as-produced SLG surface. (c) showing carbon clusters on the graphene surface induced by 10.5 mJ/cm2 laser (d) morphology induced by laser fluence at 31.6 mJ/cm2 , (e) morphology induced by laser fluence at 51.8 mJ/cm2 , (f) morphology induced by laser fluence at 70.3 mJ/cm2 .

Fig. 5 showed the fitted G peak corresponding to laser fluence of 70.3 mJ/cm2 by using Lorentzian functions. The component centered at 1550 cm−1 , 1580 cm−1 and 1620 cm−1 was assigned as hydrogenated amorphous carbon [26], graphene and defect-related D’ peak in graphene, respectively. Besides, the weak peak near 1525 cm−1 and 1665 cm−1 were also attributed to the amorphous carbon formed in laser-irradiated zones [26]. This result was in consistent with morphology modifications (existence of amorphous carbon) revealed by SEM. Fig. 6 showed evolution of D peak intensity, intensity ratios of D peak to G peak (ID /IG ), 2D peak to G peak (I2D /IG ) as well as the position and width (FWHM) of G and 2D peak as a function of the laser irradiation density. The D and 2D bands were also fitted using Lorentzian functions. It was seen that the intensity of D band only had a slight increase when laser fluence was lower than 51.8 mJ/cm2 , but it dramatically increased by ∼10 times when

the laser fluence increased to 70.3 mJ/cm2 . Ratio of ID /IG continuously increased with concurrent increasing laser fluence, while I2D /IG ratio had opposite change tendency. The position of both G and 2D peak gradually shifted towards higher wavenumbers, and their maximum shift value was 7.64 cm−1 and 20.9 cm−1 , respectively. FWHM of G and 2D band significantly increased under higher dose of laser irradiation (>10.5 mJ/cm2 ). The maximum broadening for G and 2D band was 38 cm−1 and 24 cm−1 , respectively. It was suggested that there was a threshold of about 51.8 mJ/cm2 , since the appearance of typical spherical carbon balls just began at laser fluence of 51.8 mJ/cm2 (Fig. 2). Increasing intensity of D peak indicated increasing amounts of structural disorder in irradiated graphene. According to the suggested amorphization trajectory proposed by Ferrari [27], the structural disorder in graphite material includes three stages. In the study of graphene, the first two stages were most relevant due

92

C. Li et al. / Applied Surface Science 398 (2017) 89–96

to its two dimensional nature. In stage 1, crystalline graphite was transformed into nano-crystalline graphite. D peak intensity as well as ID /IG increased, and FWHM of all peaks become large. In stage 2, nano-crystalline graphite was transformed into sp3 amorphous carbon. D peak intensity as well as ID /IG decreased with increasing disorder. Apparently, the change of ID /IG ratio and G peak position in our work was only in accordance with the transformation from graphene to nano-crystalline graphene. However, Raman spectra in Fig. 4 confirmed the existence of amorphous carbon in the graphene irradiated by 70.3 mJ/cm2 laser, implyling that the second transformation stage (formation of amorphous carbon) has started. This contradiction could be explained as follows. The ratio I(D)/I(G) cannot be viewed as the only consideration to identify the two stages since a given I(D)/I(G) ratio may correspond to two different defects concentrations [28]. The critical point between the stage 1 and stage 2 may present when the laser fluence was between 51.8 mJ/cm2 and 70.3 mJ/cm2 . On the other hand, it was reported that the intensity ratio of Raman D to G peaks was inversely proportional to square of the carrier mean free path [29]. Thus, the carrier mobility of irradiated graphene will probably decrease with increasing laser fluence. In fact, Fujio Wakaya [30] showed that the electrical resistance of Fig. 3. Micro-structure of the laser-driven spherical carbon.

Fig. 4. Raman spectra of the pristine state and UV laser-irradiated SLG samples.

Fig. 5. G band of Raman specta for pristine state sample (a) and laser-irradiated (70.3 mJ/cm2 ) SLG sample (b).

C. Li et al. / Applied Surface Science 398 (2017) 89–96

93

Fig. 6. Evoultion of D band intensity (a) intensity ratios of ID /IG and I2D /IG (b) FWHM of G and 2D band (c) position of G and 2D band (d) with the increase of laser fluence.

graphene irradiated by the ultra-violet laser (248 nm) increased by about 25% when the laser power density reached 1.4 MW/cm2 . This point should be taken into account when using nanosecond laser to treat graphene. Ratio of I2D /IG was reported to be a signature of the charge carrier doping in graphene. This intensity ratio reduced with increasing carrier concentration [31]. At low level doping, the intensity of 2D peak was 3–5 times stronger than the G peak, depending on the excitation wavelength; at high level doping, (for a G peak position above 1592 cm−1 ), the intensity ratio was ∼1 [32]. The doping in graphene was reasonable because our experiments were carried out in air atmosphere, and the functionalization by oxygen was very likely to occur, leading to a p-type doping [33]. The decreasing I2D /IG ratio from 3.44 (10.5 mJ/cm2 ) to 1.21(70.3 mJ/cm2 ) indicated increasing doping level with increasing laser density. However, G and 2D peak were also sensitive to strain, and this will cause ambiguous effects like the doping. Considering that graphene’s negative thermal expansion coefficient [34] causes a geometric mismatch with most supporting substrates, strain probably exists in the irradiated graphene. To distinguish the concurrent effects of doping and strain in graphene [35], the correlation of 2D and G shifts in Raman spectra was plotted. Fig. 7 showed a linear variation between ␻G and ␻2D , and the calculated slope (␻2D /␻G ) was 2.82. This value was very close to the reported bi-axially strained graphene [36]. Hence, it was deduced that strain effect was the main contributor to the observed changes in G and 2D modes and the effect of doping was negligible due to its low level. The low level of doping could also be inferred from the variation of FWHM of G peak. As was reported by Das, et al. [31], G peak became narrow with increasing doping level. But G peak in this work broadened with increasing laser irradiation density. Further, the simultaneous blue-shift in both G and 2D line shifts revealed the strain was compressive [37]. This result may be very meaningful for the application of laser-induced strain engineering in graphene based devices.

Fig. 7. Correlatation of positions of G and 2D band as the function of laser fluence.

Fig. 8 showed C-1s and O-1s peaks of XPS spectra for the pristine and as-irradiated SLG. It was found that the oxygen content in SLG increased with the laser fluence. As the laser fluence increased to 70.3 mJ/cm2 , the oxygen content in SLG increased from 1.5% (pristine state) to 17.8%, indicating an increasing degree of oxidation of SLG. To understand the origin of the oxidation process, the C-1s peak in Fig. 8 was further deconvoluted and analyzed with a XPS peak synthesis procedure. Pearson VII function was used to fit the experimental data. Peak fitting and peak area analysis results were shown in Fig. 9. C-1s peak was best fitted with five independent peaks. The peak at binding energy of 284.5 eV was attributed to the C C bonds of graphene [38,39]. The other four peaks corresponded to four kinds of carbon-oxygen bonds: C OH (285.3–285.8 eV), C O C (286.1 ∼ 286.9 eV), C O (288.2 ∼ 288.5 eV), O C O (289.2–289.5 eV), respectively.

94

C. Li et al. / Applied Surface Science 398 (2017) 89–96

Fig. 8. XPS spectra of the pristine state and laser-irradiated SLG samples. Baseline shift of 2 eV was verified in the obtained spectra. The actual binding energy should plus 2 eV on the spectra showing data.

The presence of these functional groups in pristin SLG might be caused by the adsorption of oxygen-containing molecula in air. In the laser irradiated samples, the photo-induced chemical reactions between graphene and O2 , H2 O, etc. in air should be the major reason. Based on the peak fitting results, the relative content of the above mentioned five components was caculated and summarized in Table 2. Obviously, the relative content of sp2 C C bonds

belonging to graphene decreased after irradiation, which indicated that the basic crystalline structure of graphene was gradually modified by laser irradiation. This was in agreement with the results in Raman spectra. The content of O C O bond showed a continuous increase with a concurrent increase of laser fluence, but its values were generally lower than other carbon-oxygen bonds. The content of C OH, C O C and C O bond all showed fluctuations with the increase of laser fluence. This suggested that some of these oxygencontaining species were not stable, so that they transformed into other more stable species during laser irradiation process. This result may be very useful for realizing the tailoring of functional groups on suface of SLG. Since one of the applications of SLG was related to its high optical transmittance, in this case, it was expected that the modification of SLG doesn’t cause obvious decrease in its optical transmittance. In order to examine this point, the transmission spectra in the range of 200–800 nm of as-irradiated samples were compared with the prinstine state SLG. It was found in Fig. 10 that the transmittance at all wavelengths showed a decreasing trend with increasing laser fluence, but the amplitude was very limitted. For example, compared to the pristine state SLG, the transmission loss at 550 nm for the sample irradiated by laser at 70.3 mJ/cm2 was about 2.1%. Besides, a broad transition band centered at 260–270 nm was observed in the transmission spectra, which was resulted from the ␲-␲* electron transition of graphene. The band intensity showed a relatively large decrease after laser irradiation (51.8 mJ/cm2 ), suggesting that the ␲-␲* electronic structure has been modified or disrupted. The modification of ␲-␲* electronic structure indicated the decreased mobility of electrons, and thus the electron resistance would increase after laser irradiation.

4. Conclusions Effects of 355 nm nanosecond laser irradiation on SLG on fused silica substrate have been carefully studied. It was found that when

Fig. 9. Deconvoluted peaks of the C-1s peak for the (a) pristine SLG and (b)-(d) SLG irradiated by aser at different fluences of 31.6, 51.8 and 70.3 mJ/cm2 . Baseline shift of 2 eV was verified in the obtained spectra. The actual binding energy should plus 2 eV on the spectra showing data.

C. Li et al. / Applied Surface Science 398 (2017) 89–96

95

Table 2 Fitting results of peak area and oxygen content for the pristine and laser irraidated SLG samples.

Pristine 10.5 J/cm2 31.6 J/cm2 51.8 J/cm2 70.3 J/cm2

C C (%)

C OH (%)

C O C (%)

C O (%)

O C O (%)

Oxygen (%)

73.5 66.3 59.0 53.0 43.7

9.8 10.9 8.3 7.4 13.6

14.7 16.4 27.3 34.1 17.0

2.0 5.1 2.1 1.9 21.0

0.0 1.3 3.3 3.6 4.7

1.5 5.1 9.6 16.0 17.8

Fig. 10. UV–vis absortption and transmission spectra for the pristine SLG and laserirradiated SLG samples.

SLG was irradiated with laser energy densities smaller than its damage threshold, modifications in its morphology, crystal structural as well as surface chemical composition could be induced. Nanometer spherical carbon presented on irradiated SLG, which was probably caused by laser-induced high temperature, material melting, gasification and carbon atoms re-deposition processes. Structural disorder in irradiated SLG mainly included the formation of nanocrystalline graphene and amorphous carbon. Also, compressive strain was generated in irradiated graphene. Due to oxidation reaction, different types of oxygen-containing functional groups were produced on surface of SLG with varied laser fluences. Simutaneously, it was found that the optical transmittance of irradiated SLG only had a slight decrease. These results may provide useful references for modification of graphene by low-energy nanosecond short-wavelengh laser irradiation, which would possibly bring great convinience for the batch processing of large scale graphene. Acknowledgments This work is financially supported by the Natural Science Foundation of China under Grant No. 51306165 and No. 61605188. We specially thank Prof. Lei Ding at Research Center of Laser Fusion for pulsed UV laser-irradiation experiment and thoughtful discussions. References [1] F. Bonaccorso, Z. Sun, T. Hasan, A.C. Ferrari, Graphene photonics and optoelectronics, Nat. Photon. 4 (9) (2012) 611–622. [2] R.R. Nair, P. Blake, A.N. Grigorenko, K.S. Novoselov, T.J. Booth, T. Stauber, N.M.R. Peres, A.K. Geim, Fine structure constant defines visual transparency of grapheme, Science 320 (5881) (2008) 1308. [3] Q.L. Bao, H. Zhang, Y. Wang, Z.H. Ni, Y.L. Yan, Z.X. Shen, K.P. Loh, D.Y. Tang, Atomic-layer graphene as a saturable absorber for ultrafast pulsed lasers, Adv. Funct. Mater. 19 (19) (2009) 3077–3083. [4] C.G. Lee, X.D. Wei, J.W. Kysar, H. James, Measurements of the elastic properties and intrinsic strength of monolayer graphene, Science 321 (5887) (2008) 385–388.

[5] A.A. Balandin, S. Ghosh, W.Z. Bao, I. Calizo, D. Teweldebrhan, F. Miao, Superior thermal conductivity of single layer graphene, Nano Lett. 8 (3) (2008) 902–907. [6] D.W. Li, Y.S. Zhou, X. Huang, L. Jiang, J.F. Silvain, Y.F. Lu, In situ imaging and control of layer-by-layer femtosecond laser thinning of grapheme, Nanoscale 7 (8) (2015) 3651–3659. [7] Z. Lin, T. Huang, X. Ye, M. Zhong, L. Li, J. Jiang, W. Zhang, L. Fan, H. Zhu, Thinning of large-area graphene film from multilayer to bilayer with a low-power CO2 laser, Nanotechnology 24 (27) (2016) 275302. [8] J.H. Yoo, J.B. Park, S. Ahn, C.P. Grigoropoulos, Laser-induced direct graphene patterning and simultaneous transferring method for graphene sensor platform, Small 9 (24) (2013) 4269–4275. [9] V. Strong, S. Dubin, M.F. El-Kady, A. Lech, Y. Wang, B.H. Weiller, R.B. Kaner, Patterning and electronic tuning of laser scribed graphene for flexible all-carbon devices, ACS Nano 6 (2012) 1395–1403. [10] W.H. Lee, J.W. Suk, H. Chou, J.H. Lee, Y.F. Hao, Y.P. Wu, R. Piner, D. Akinwande, K.S. Kim, R.S. Ruoff, Selective area fluorination of graphene with fluoropolymer and laser irradiation, Nano Lett. 12 (2012) 2374–2378. [11] V.D. Frolov, P.A. Pivovarov, E.V. Zavedeev, A.A. Khomich, A.N. Grigorenko, V.I. Konov, Laser-induced local profile transformation of multilayered graphene on a substrate, Opt. Laser Technol. 69 (2015) 34–38. [12] W.B. Cai, B.Q. Zeng, J.L. Liu, J. Guo, N.N. Li, L. Chen, H.W. Chen, Improved field emission property of graphene by laser irradiation, Appl. Surf. Sci. 284 (2013) 113–117. [13] B. Krauss, T. Lohmann, D.H. Chae, M. Haluska, K. von Klitzing, J.H. Smet, Laser-induced disassembly of a graphene single crystal into a nanocrystalline network, Phys. Rev. B 79 (16) (2009) 897–899. [14] T. Huang, J.Y. Long, M.L. Zhou, J. Jiang, X.H. Ye, Z. Lin, L. Li, The effects of low power density CO2 laser irradiation on graphene properties, Appl. Surf. Sci. 273 (2013) 502–506. [15] J.H. Yoo, J.B. In, J.B. Park, H. Jeon, C.P. Grigoropoulos, Graphene folds by femtosecond laser ablation, Appl. Phys. Lett. 100 (2012) 233124. [16] A. Roberts, D. Cormode, C. Reynolds, T. Newhouse-Illige, B.J. LeRoy, A.S. Sandhu, Response of graphene to femtosecond high-intensity laser irradiation, Appl. Phys. Lett. 99 (2011) 051912. [17] M. Currie, J.D. Caldwell, F.J. Bezares, J. Robinson, T. Anderson, H. Chun, M. Tadjer, Quantifying pulsed laser induced damage to graphene, Appl. Phys. Lett. 99 (2011) 211909. [18] F. Herziger, R. Mirzayev, E. Poliani, J. Maultzsch, In-situ Raman study of laser-induced graphene oxidation, Phys. Status Solidi B 252 (11) (2015) 2451–2455. [19] V. Kiisk, T. Kahro, J. Kozlova, L. Matisen, H. Alles, Nanosecond laser treatment of grapheme, Appl. Surf. Sci. 276 (4) (2013) 133–137. [20] F. Wakaya, T. Teraoka, T. Kisa, T. Manabe, S. Abo, M. Takai, Effects of ultra-violet laser irradiation on graphene, Microelectron. Eng. 97 (6) (2012) 144–146. [21] F. Wakaya, T. Kurihara, S. Abo, M. Takai, Ultra-violet laser processing of graphene on SiO2 /Si, Microelectron. Eng. 110 (20) (2013) 358–360. [22] R. Sahin, E. Simseck, S. Akturk, Nanoscale patterning of graphene through femtosecond laser ablation, Appl. Phys. Lett. 104 (2014) 053118. [23] L.M. Malard, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene, Phys. Rep. 473 (2009) 51–87. [24] C. Thomsen, S. Reich, Double resonant Raman scattering in graphite, Phys. Rev. Lett. 85 (2000) 5214–5217. [25] R.J. Nemanich, S.A. Solin, First- and second-order Raman scattering from finite-size crystals of graphite, Phys. Rev. B 20 (2) (1979) 392–401. [26] A.C. Ferrari, J. Robertson, Raman spectroscopy of amorphous, nanostructured, diamond-like carbon, and nanodiamond, Phil. Trans. R. Soc. Lond. A 362 (2004) 2477–2512. [27] A.C. Ferrari, Raman spectroscopy of graphene and graphite: disorder, electron-phonon coupling, doping and nonadiabatic effects, Solid State Commun. 143 (1–2) (2007) 47–57. [28] A. Eckmann, A. Felten, I. Verzhbitskiy, R. Davey, C. Casiraghi, Raman study on defective graphene: effect of the excitation energy, type, and amount of defects, Phys. Rev. B 88 (2013) 035426. [29] T.M.G. Mohiuddin, A. Lombardo, R.R. Nair, A. Bonetti, G. Savini, R. Jalil, N. Bonini, D.M. Basko, C. Galiotis, N. Marzari, K.S. Novoselov, A.K. Geim, A.C. Ferrari, Phys. Rev. B. 79 (2009) 205433. [30] J. Zabel, R.R. Nair, A. Ott, T. Georgiou, A.K. Geim, K.S. Novoselov, C. Casiraghi, Nano Lett. 12 (2012) 617. [31] A. Das, S. Pisana, B. Chakraborty, S. Piscanec, S.K. Saha, U.V. Waghmare, K.S. Novoselov, H.R. Krishnamurthy, A.K. Geim, A.C. Ferrari, A.K. Sood, Monitoring dopants by Raman scattering in an electrochemically top-gated graphene transistor, Nat. Nanotechnol. 3 (4) (2008) 210–215.

96

C. Li et al. / Applied Surface Science 398 (2017) 89–96

[32] C. Casiraghia, S. Pisana, K.S. Novoselov, A.K. Geim, A.C. Ferrarib, Raman fingerprint of charged impurities in graphene, Appl. Phys. Lett. 91 (2007) 233108. [33] D. Abdula, T. Ozel, K. Kang, D.G. Cahill, M. Shim, Environment-induced effects on the temperature dependence of Raman spectra of single-layer graphene, J. Phys. Chem. C 112 (51) (2008) 20131–20134. [34] D. Yoon, Y.W. Son, H. Cheong, Negative thermal expansion coefficient of graphene measured by Raman spectroscopy, Nano Lett. 11 (8) (2011) 3227–3231. [35] J.E. Lee, G. Ahn, J. Shim, Y.S. Lee, S. Ryu, Optical separation of mechanical strain from charge doping in graphene, Nat. Commun. 3 (8) (2012) 2543–2544.

[36] F. Ding, H. Ji, Y. Chen, A. Herklotz, K. Dörr, Y.F. Mei, A. Rastelli, O.G. Schmidt, Stretchable graphene: a close look at fundamental parameters through biaxial straining, Nano Lett. 10 (9) (2010) 3453–3458. [37] J. Zabel, R.R. Nair, A. Ott, T. Georgiou, A.K. Geim, K.S. Novoselov, C. Casiraghi, Raman spectroscopy of graphene and bilayer under biaxial strain: bubbles and balloons, Nano Lett. 12 (2) (2011) 617–621. [38] M.J. Webb, P. Palmgren, P. Pal, O. Karis, H. Grennberg, A simple method to produce almost perfect graphene on highly oriented pyrolytic graphite, Carbon 49 (10) (2011) 3242–3249. [39] R. Larciprete, P. Lacovig, A. Gardonio, A. Baraldi, S. Lizzit, Atomic oxygen on graphite: chemical characterization and thermal reduction, J. Phys. Chem. C 116 (18) (2012) 9900–9908.