- Email: [email protected]
Laser-induced reduction of graphene oxide powders by high pulsed ultraviolet laser irradiations
Applied Surface Science 444 (2018) 578–583
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full Length Article
Laser-induced reduction of graphene oxide powders by high pulsed ultraviolet laser irradiations Chii-Rong Yang a, Shih-Feng Tseng b,⇑, Yu-Ting Chen a a b
Department of Mechatronic Engineering, National Taiwan Normal University, Taipei 10610, Taiwan Department of Mechanical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan
a r t i c l e
i n f o
Article history: Received 7 February 2018 Revised 7 March 2018 Accepted 11 March 2018 Available online 14 March 2018 Keywords: Laser-induced reduction Graphene oxide powders Raman spectroscopy X-ray photoelectron spectroscopy Surface area analyzer
a b s t r a c t This study aims to develop a laser-induced reduction approach for graphene oxide (GO) powders fabricated by using high pulsed ultraviolet laser irradiations. Before and after the laser irradiation with different fluences, the physical and electrical properties of homemade GO powders and reduced graphene oxide (rGO) powders were measured and analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area analyzer, and four-point probe instrument. The laser irradiation parameters included the pulse repetition frequency of 100 kHz, the scanning speed of galvanometers of 50 mm/s, the number of laser irradiated cycles of 10, and the laser fluences of ranging from 0.153 mJ/cm2 to 0.525 mJ/ cm2. The laser reduction experiments of GO powders demonstrated that the largest relative intensity of the 2D peak and specific surface area were found at the laser fluence of 0.438 mJ/cm2. Moreover, the electrical resistance sharply decreased from 280 MX in the initial GO powders to 0.267 MX in rGO powders at a laser irradiation fluence of 0.438. The C/O ratio was increased from 0.232 in the initial GO powders to 1.86 in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2; furthermore, the C/O ratios increased with increasing the laser fluences. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Graphene is a two-dimensional and hexagonal lattice material with a single atomic layer or few atomic layers. Due to its high room-temperature carrier mobility of up to 2 105 cm2/Vs [1,2], high thermal conductivity of 5300 W/mK [3,4], high optical transmittance of more than 90% [5–7], and high mechanical strength with Young’s modulus of 1 TPa [8,9], graphene materials have widely promising applications in solar cells, light-emitting diodes (LEDs), touch-screen panels, energy storage devices, single molecule gas detection, and other transparent electrodes [10–14]. Various approaches of manufacturing graphene materials include chemical vapor deposition (CVD), micromechanical cleavage of highly oriented pyrolytic graphite (HOPG), electrochemical exfoliation of HOPG, chemical exfoliation, photo exfoliation, epitaxial growth method, reduction of graphene oxide (GO), and so on [15–18]. Recently, several methods of thermal and electrical reduction of GO to graphene for mass production have been proposed. Trusovas et al. [19] used a picoseconds pulsed laser (wavelength of 1064 nm) processing system combined with a galvanometric ⇑ Corresponding author. E-mail address: [email protected] (S.-F. Tseng). https://doi.org/10.1016/j.apsusc.2018.03.090 0169-4332/Ó 2018 Elsevier B.V. All rights reserved.
scanner to reduce graphite oxide to graphene. After the laser irradiation on graphite oxide films with the laser power of 50 mW and the scanning speed of 30 mm/s, the largest relative intensity of 2Dpeak (2656 cm1) and the minimum structural defects of D-peak (1331 cm1) of reduced graphite oxide films were clearly observed by a Raman spectroscopy. The experimental and analytic results revealed that a single laser pulse with a fluence of 0.04 J/cm2 (50 mW) of local temperature increased up to 1400 °C for a few nanoseconds that can sufficient and effective reduction of graphite oxide to graphene by using laser irradiation. Ghadim et al. [20] reported the reduction of GO sheets in the ammonia solution at room temperature by an Nd:YAG pulsed laser system with a wavelength of 532 nm and a average power of 0.3 W. After laser irradiation of 10 min, the 2D-peak (2680 cm1) of reduced graphene oxide (rGO) sheets was slightly higher than GO ones measured by the Raman spectroscopy. A calculated 2D/G intensity ratio (I2D/IG) of rGO sheets was 0.038 that had no significant interaction for the pulsed laser reduced sheets in the ammonia solution. By using X-ray photoelectron spectroscopy (XPS) analysis, an oxygen/carbon atomic ratio (O/C) of GO sheets reduced from 49% down to 21% after laser irradiation of 10 min. Teoh et al. [21] presented a versatile technique to reduce three dimensional (3D) GO with micropatterned multilayered structures by the focused laser
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
beam (wavelength of 532 nm) irradiation and hierarchical control method. Petridis et al. [22] reported on the development of a KrF excimer pulsed laser (wavelength of 248 nm) induced reduction method for the photoreduction of GO field effect transistors (FETs). To irradiate GO FETs with a laser fluence of 80 mJ/cm2, the electrical conductivity increased with increasing the laser pulse numbers. The O/C ratio was reduced from 61% in the initial GO to 16% in rGO treated by 120 laser pulses at the fluence 80 mJ/cm2. Zhou et al. [23] proposed an electrochemical method to produce rGO films with an O/C ratio of less than 6.26%. Moreover, this method combined with a spray-coating technique could accomplish the controllable synthesis of large-area and patterned rGO films with thickness ranging from a single atomic layer to several microns coated on various substrate surfaces, such as flexible plastic, glass, Au, glassy carbon (GC), and indium tin oxide (ITO). In this study, we used the improved Hummers’ method to prepare GO powders. To obtain the reduction of GO powders with a fast, convenient, environmentally friendly, and efficient method, this study focused on the development of a laser-induced reduction technique using an ultraviolet (UV) laser-induced reduction apparatus combined with a high-speed galvanometric scanner. The laser-induced reduction parameters consisted of laser fluences, pulse repetition frequencies, scan speeds of the galvanometric scanner, and number of irradiated cycles. Before and after the laser irradiation with different processing parameters, the Raman spectra, O/C ratio, and specific surface area of GO and rGO powders were observed and analyzed using the Raman spectroscopy, XPS, and surface area analyzer. Moreover, the electrical resistances of GO and rGO powders were measured using a four-point probe instrument.
2. Experimental 2.1. Preparation of GO powders The homemade GO powders were fabricated by using preoxidized, improved Hummers’ method, and post-treatment procedures. In the pre-oxidized process, 3 g graphite flakes were dissolved in a solution containing 180 mL H2SO4 and heated to 80 °C for 4.5 h to promote the oxidation of the graphite. Then, the graphite oxides were exfoliated using an ultrasonic atomizer for 2 h. The pre-oxidized graphite flakes were obtained using the qualitative filter papers with hole diameter of 1 lm to filter the micro flakes and using a hotplate with 100 °C to dry flakes. Depending on the improved Hummers’ method, 360 mL H2SO4 was added slowly to the 40 mL H3PO4 as a mixture. Afterward 3 g pre-oxidized graphite flakes were added to the mixture, which was cooled to 0 °C in an ice bath for 30 min. Finally, 18 g KMnO4 was added slowly to the mixture and stirred for 1 h. Moreover, the mixture was heated to 50 °C and stirred for 12 h. Then, the mixture was cooled to room temperature, and 30 wt% H2O2 was added slowly into the mixture. The completely reacted mixture was a graphene oxide suspension. Fig. 1 shows digital pictures of graphene oxide suspensions with concentration of 0.4 mg/ml (a) and 1 mg/ml (b) created by GO powders dispersed in 100 ml of deionized water. In the post-treatment process, 1000 mL HCl (10 wt%) was added to the graphene oxide suspension and stirred for 2 h. To remove the supernatants, the GO suspension was centrifuged at 6000 rpm for 30 min. After removing completely metal ions (i.e. Mn and K ions), the GO flakes were washed in distillate water and centrifuged at 6000 rpm for 2 h. The filtered GO flakes were dried in a vacuum oven at 60 °C for 24 h. The GO powders with a diameter of 200 lm were fabricated using a ball grinding mill with zirconia balls of 2 mm diameter for 72 h.
579
Fig. 1. Digital pictures of graphene oxide suspensions with concentration of 0.4 mg/ml (a) and 1 mg/ml (b) created by GO powders dispersed in 100 ml of deionized water.
2.2. UV laser-induced reduction apparatus and method GO powders were reduced using the UV pulsed laser (Model: AVIA 355-14, Coherent Inc., USA) working at the 355 nm wengthlength. The specifications of UV laser were following: the laser beam diameter at the exit port of 3.5 mm, the maximal pulse repetition frequency of 300 kHz, the maximal power of 14 W, and the pulse width of 28 ns at the pulse repetition frequency of 100 kHz. Experimental apparatus included a UV laser source, three reflective mirrors, a beam expander with 2 times magnification, a galvanometric scanner with a telecentric lens of 110 mm focusing length and of 60 mm 60 mm field size, and an XYZ-axes movable stage with ball-screw mechanism, as shown in Fig. 2. The GO powders were placed inside a quartz tube. The laser beam was directly focused through the quartz tube due to the quartz material with high transmittance at the 355 nm waveband. The laser processing conditions for the irradiated GO powders were carried out as following. The defocused laser beam away from the focused point of 20 mm was irradiated towards GO powder surfaces to avoid damaging and burning those powders with high laser fluences. The defocused spot diameter (D) was approximately 5 mm. The incident laser fluence (F) in J/cm2 could be calculated by the following equation:
F¼
E A
ð1Þ
where E is the laser pulse energy, and A is the area of laser spots. The laser fluences were adjusted from 0.153 mJ/cm2 to 0.525 mJ/ cm2 for this study. Moreover, the GO powders were reduced by scanning laser beams with a cross line of the laser processing path in X and Y directions of equal line-scan space of 20 lm. Fig. 3 shows schematically the laser irradiation paths. The overlapping rates (OR) of the laser spot could be defined and estimated as follows [24].
OR ¼ 1
V 100% P RF D
ð2Þ
where D, V, and PRF are the laser spot diameter, the scanning speed of galvanometers, and the laser pulse repetition rate, respectively. During the tests, the pulse repetition frequencies, scan speeds of
580
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
2.3. Characterization and measurement Raman spectroscopy (Model: NRS-4100, JASCO Inc., Japan), XPS (Model: Theta Probe, Thermo Fisher Scientific Inc., UK), and surface area analyzer (Model: ASAP 2020, Micromeritics Inc., USA) were used to measure the physical properties of samples before and after UV laser irradiation. Raman spectrum measurements were performed with an excitation laser wavelength of 532 nm at room temperature. The laser power was restricted to 2 mW to avoid laser-induced heating on the sample surface. The O/C ratio of samples was performed using the XPS with X-ray spot size ranging from 15 to 400 mm. The Theta Probe XPS instrument had a fully motorized stage, and the maximum field of view (FOV) was 70 mm 70 mm. The specific surface area of samples was performed using the surface area and porosity analyzer. In addition, the fourpoint probe instrument was used to measure the electrical properties of samples.
3. Results and discussion 3.1. Raman spectra analysis
Fig. 2. Schematic of experimental apparatus for UV laser-induced reduction of graphene oxide powders.
Fig. 3. Schematic of the laser irradiation paths.
Table 1 Summary of the laser irradiation parameters used to reduce GO powders on the quartz tube. Laser irradiation parameters
Values or methods
Laser fluence (J/cm2) Defocused laser spot diameter (mm) Pulse repetition frequency (kHz) Scanning speed (mm/s) Overlapping rate (%) Number of irradiated cycles Laser scanning path Line-scan space (lm)
0.153 5
0.255
0.357
0.438
0.525
100 50 99.9 10 Cross lines in X and Y directions 20
the galvanometric scanner, and number (t) of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Hence, the calculated OR was a high value of more than 99%. Table 1 presents a summary of the laser irradiation parameters used to reduce GO powders on the quartz tube.
Fig. 4 shows a picture of the GO powders in the quartz tube taken by a digital camera. Before and after the UV laser irradiated samples of GO powders were characterized with the Raman spectroscopy. The laser irradiated parameters of the pulse repetition frequency, scan speeds of the galvanometric scanner, and number of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Moreover, the applied laser fluences included 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2 for this study. Fig. 5 shows the Raman spectra measured on GO and rGO powders with different laser fluences for the Raman shift ranging from 800 cm1 to 3300 cm1. The measured spectra demonstrated three characteristic peaks of D, G, and 2D bands of samples centered averagely at 1344 cm1, 1586 cm1, and 2669 cm1, respectively. The D, G, and 2D bands represented the defects, in-plane vibration of sp2 carbon atoms, and the stacking order, respectively [25]. Before laser irradiations, the measured Raman spectrum of GO powders only appeared D and G bands. After UV laser irradiations on GO powders, the measured results of Raman spectra showed that the 2D band appearing corresponded to graphene formation because of the laser-induced reduction reaction. Moreover, the intensity of D band of rGO powders significantly increased more than that of GO powders. This is due to rGO powders with lots of defects produced by UV laser irradiations. D/G intensity ratio (ID/IG) and 2D/G intensity ratio (I2D/IG) were often used to quantify defects in graphene materials and to qualify the number of stacked graphene layers, respectively. The ID/IG and I2D/IG ratios of GO and rGO powders with different laser fluences were summarized in Table 2. The ID/IG ratio of GO powders was 0.77; furthermore, the ID/IG ratios of rGO powders were 0.874, 1.175, 1.033, 0.922, and 1.23 when the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, respectively. The ID/IG ratios of rGO powders were signifi-
Fig. 4. A photo of the GO powders in the quartz tube.
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
581
mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, respectively. The measured results revealed that the I2D/IG ratios of rGO powders increased with increasing laser fluences ranging from 0.153 mJ/ cm2 to 0.438 mJ/cm2. However, the peak intensity of 2D band was lowering when the laser fluence increased to 0.525 mJ/cm2. This implied that the local accumulated temperature of rGO powders produced the thermal denaturation for these rGO powders [19]. In the previous studies, the I2D/IG ratios of less than 1, 1–2, and 2–3 were for multilayer graphene, bilayer graphene, and monolayer graphene, respectively [26,27]. Consequently, this clearly indicated the rGO powders were multilayer graphene structures. 3.2. Specific surface area and electrical resistance analysis
Fig. 5. Raman spectrum measured on GO and rGO powders with different laser fluences.
Table 2 Summary of the ID/IG and I2D/IG ratios of GO and rGO powders with different laser fluences. Types of powder
GO
rGO
Laser fluence (mJ/cm2) ID/IG I2D/IG
– 0.77 –
0.153 0.874 0.05
0.255 1.175 0.15
0.375 1.033 0.316
0.438 0.922 0.569
0.525 1.23 0.438
Before and after the laser irradiation with different laser fluences, the specific surface area and electrical resistance of GO and rGO powders were measured using the surface area analyzer and four-point probe instrument, respectively. The measured results revealed that the specific surface area and electrical resistance values of GO powders were 0.1148 m2/g and 280 MX, respectively. When the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, the specific surface area and electrical resistance values of rGO powders were 1.178 m2/g, 7.139 m2/g, 10.73 m2/g, 16.86 m2/g, and 15.24 m2/g and 18.2 MX, 16.5 MX, 10.71 MX, 0.267 MX, and 80.3 MX, respectively. The specific surface area and electrical resistance of GO and rGO powders versus different laser fluences were shown in Fig. 7. After the UV laser irradiation, the specific surface area and electrical resistance values of rGO powders were slightly larger and sharply lower than GO ones, respectively. When the laser fluences increased from 0.153 mJ/cm2 to 0.438 mJ/cm2, the specific surface area values gradually increased from 1.178 m2/g to 16.86 m2/g and the electrical resistance values gently decreased from 18.2 MX to 0.267 MX. The laser reduction zone was shown in the left side of Fig. 7. When the laser fluence increased to 0.525 mJ/cm2, the specific surface area value was a decreasing trend and the electrical resistance value was an increasing trend compared with the laser fluence of 0.438 mJ/cm2. This indicated that the situation was due to the higher laser fluence produced bondbreaking of the G-G bonds, namely, the freshly formed rGO powders would be ablated by subsequent laser irradiating, which induced an abnormal increase in electrical resistance of laserirradiated tracks during the laser processing of multiple repeated scans [28]. The laser ablation zone was shown in the right side of Fig. 7.
Fig. 6. The ID/IG and I2D/IG ratios of rGO powders versus different laser fluences.
cantly greater than GO ones caused by the laser irradiation to produce a few defects. The ID/IG and I2D/IG ratios of rGO powders versus different laser fluences were shown in Fig. 6. Because Raman spectrum taken on rGO powders indicated the apparent 2D bands, the I2D/IG ratio of rGO powders were 0.05, 0.15, 0.316, 0.569, and 0.438 when the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357
Fig. 7. Specific surface area and electrical resistance of GO and rGO powders versus different laser fluences.
582
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
Fig. 8. XPS analysis of GO and typical rGO powders for different laser fluences.
Table 3 Summary of the oxygen and carbon contents and C/O ratios of GO and typical rGO powders with different laser fluences. Types of powder
GO
rGO
Laser fluence (mJ/cm2) Oxygen content (%) Carbon content (%) C/O ratio
– 81.15 18.85 0.232
0.153 58.05 41.95 0.722
0.375 41.76 58.24 1.39
0.525 34.94 65.06 1.86
3.3. XPS analysis To investigate the degree of reduction of GO powders, XPS was employed to analyze the chemical composition before and after the UV laser irradiation with different fluences. Fig. 8 shows the C1s (284.8 eV peak) and O1s (532 eV peak) XPS spectra of GO and typical rGO powders. The the oxygen and carbon contents and C/O ratios of GO and typical rGO powders with different laser fluences were summarized in Table 3. The carbon and oxygen contents of GO powders were 18.85% and 81.15%, respectively, shown in Fig. 8a. It could be seen that the O1s peak was obviously higher than the C1s peak for GO powders. While the applied laser fluences were 0.153 mJ/cm2, 0.357 mJ/cm2, and 0.525 mJ/cm2, the oxygencontaining rGO powders were down to 58.05%, 41.76%, and 34.94%, respectively, shown in Fig. 8b–c. It was clear that the oxygen content was reduced from 81.15% in the initial GO powders to 34.94% in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2. This indicated that the majority of oxygen content was removed and efficient reduction occurred after the UV laser irradiation on GO powders [22]. The carbon to oxygen (C/O) ratios of rGO powders were 0.722, 1.39, and 1.86 when the applied laser fluences were 0.153 mJ/cm2, 0.357 mJ/cm2, and 0.525 mJ/cm2, respectively. The measured resulted showed that the C/O ratios were increased with increasing the laser fluences. Furthermore, the C/O ratio was increased from 0.232 in the initial GO powders to 1.86 in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2. 4. Conclusion This study focused to investigate the laser-induced reduction of GO powders using the pulsed UV laser at 355 nm wavelength pro-
duced significant changes in graphene properties. The pulse repetition frequency, scan speeds of the galvanometric scanner, and number of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Moreover, the applied laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2. The measured and analyzed results showed that the homemade GO powders had the higher electrical resistance of 280 MX and oxygen content of 81.15%, the lower specific surface area of 0.1148 m2/g and ID/IG ratio of 0.77, and no Raman 2D peak. By using the nanosecond pulsed UV laser irradiated GO powders, the electrical resistance sharply dropped to 0.267 MX, the specific surface area increased to 16.86 m2/g, and I2D/IG ratio had a high value of 0.569 while the laser fluence was set in 0.438 mJ/ cm2. Furthermore, the oxygen content of rGO powders decreased with increasing the laser fluences. Laser-induced reduction of GO powders was successfully developed by pulsed ultraviolet laser irradiations. These approaches are potentially used for mass production of graphene powders in the future. Acknowledgements The authors thank the Ministry of Science and Technology of Taiwan for financially supporting this research under projects MOST 106-2622-E-027-026-CC3 and MOST 106-2221-E-027-147. References [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306 (2004) 666–669. [2] K.I. Bolotin, K.J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H.L. Stormer, Ultrahigh electron mobility in suspended graphene, Solid State Commun. 146 (2008) 351–355. [3] H. Tang, G.J. Ehlert, Y. Lin, H.A. Sodano, Highly efficient synthesis of graphene nanocomposites, Nano Lett. 12 (2012) 84–90. [4] A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C.N. Lau, Superior thermal conductivity of single-layer graphene, Nano Lett. 8 (2008) 902–907. [5] D. Li, M.B. Muller, S. Gilje, R.B. Kaner, G.G. Wallace, Processable aqueous dispersions of graphene nanosheets, Nat. Nanotechnol. 3 (2008) 101–105. [6] G. Eda, G. Fanchini, M. Chhowalla, Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material, Nat. Nanotechnol. 3 (2008) 270–274. [7] S. Bae, H. Kim, Y. Lee, X. Xu, J.S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H.R. Kim, Y.I. Song, Y.J. Kim, K.S. Kim, B. Özyilmaz, J.H. Ahn, B.H. Hong, S. Iijima, Roll-to-
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
[8] [9] [10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
roll production of 30-inch graphene films for transparent electrodes, Nat. Nanotechnol. 5 (2010) 574–578. C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the elastic properties and intrinsic strength of monolayer graphene, Science 321 (2008) 385–388. V. Singh, D. Joung, L. Zhai, S. Das, S.I. Khondaker, S. Seal, Graphene based materials: Past, present and future, Prog. Mater Sci. 56 (2011) 1178–1271. J. Wu, H.A. Becerril, Z. Bao, Z. Liu, Y. Chen, P. Peumans, Organic solar cells with solution-processed graphene transparent electrodes, Appl. Phys. Lett. 92 (2008) 263302. E.C. Cho, J.H. Huang, C.P. Li, C.W. Chang-Jian, K.C. Lee, Y.S. Hsiao, J.H. Huang, Graphene-based thermoplastic composites and their application for LED thermal management, Carbon 102 (2016) 66–73. K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y. Choi, B.H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature 457 (2009) 706–710. C. Berger, Z.M. Song, T.B. Li, X.B. Li, A.Y. Ogbazghi, R. Feng, Z. Dau, A.N. Marchenkov, E.H. Conrad, P.N. First, W.A. de Heer, Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics, J. Phys. Chem. B 108 (2004) 19912–19916. S.F. Tseng, W.T. Hsiao, C.K. Chung, T.L. Chang, Investigation the interaction between the pulsed ultraviolet laser beams and PEDOT:PSS/graphene composite films, Appl. Surf. Sci. 356 (2015) 486–491. F. Bonaccorso, A. Lombardo, T. Hasan, Z. Sun, L. Colombo, A.C. Ferrari, Production and processing of graphene and 2d crystals, Mater. Today 15 (2012) 564–589. C.Y. Su, A.Y. Lu, Y. Xu, F.R. Chen, A.N. Khlobystov, L.J. Li, High-quality thin graphene films from fast electrochemical exfoliation, ACS Nano 5 (2011) 2332–2339. U. Khan, H. Porwal, A. O’Neill, K. Nawaz, P. May, J.N. Coleman, Solventexfoliated graphene at extremely high concentration, Langmuir 27 (2011) 9077–9082. S.R. Kim, M.K. Parvez, M. Chhowalla, UV-reduction of graphene oxide and its application as an interfacial layer to reduce the back-transport reactions in dye-sensitized solar cells, Chem. Phys. Lett. 483 (2009) 124–127.
583
[19] R. Trusovas, K. Ratautas, G. Racˇiukaitis, J. Barkauskas, I. Stankevicˇiene˙, G. Niaura, R. Mazˇeikiene˙, Reduction of graphite oxide to graphene with laser irradiation, Carbon 52 (2013) 574–582. [20] E.E. Ghadim, N. Rashidi, S. Kimiagar, O. Akhavan, F. Manouchehri, E. Ghaderi, Appl. Surf. Sci. 301 (2014) 183–188. [21] H.F. Teoh, Y. Tao, E.S. Tok, G.W. Ho, C.H. Sow, Direct laser-enabled graphene oxide-Reduced graphene oxide layered structures with micropatterning, J. Appl. Phys. 112 (2012) 064309. [22] C. Petridis, Y.H. Lin, K. Savva, G. Eda, E. Kymakis, T.D. Anthopoulos, E. Stratakis, Post-fabrication, in situ laser reduction of graphene oxide devices, Appl. Phys. Lett. 102 (2013) 093115. [23] M. Zhou, Y. Wang, Y. Zhai, J. Zhai, W. Ren, F. Wang, S. Dong, Controllable synthesis of large-area and patterned electrochemically reduced graphene oxide films, Chem. Eur. J. 15 (2009) 6116–6120. [24] S.F. Tseng, W.T. Hsiao, K.C. Huang, D. Chiang, The effect of laser patterning parameters on fluorine-doped tin oxide films deposited on glass substrates, Appl. Surf. Sci. 257 (2011) 8813–8819. [25] C. Faugeras, A. Nerriere, M. Potemski, A. Mahmood, E. Dujardin, C. Berger, W.A. de Heer, Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study, Appl. Phys. Lett. 92 (2008) 011914. [26] A. Reina, X.T. Jia, J. Ho, D. Nezich, H.B. Son, V. Bulovic, M.S. Dresselhaus, J. Kong, Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition, Nano Lett. 9 (2009) 30–35. [27] V.T. Nguyen, H.D. Le, V.C. Nguyen, T.T.T. Ngo, D.Q. Le, X.N. Nguyen, N.M. Phan, Synthesis of multi-layer graphene films on copper tape by atmospheric pressure chemical vapor deposition method, Adv. Nat. Sci.: Nanosci. Nanotechnol. 4 (2013) 035012. [28] K.C. Yung, H. Liem, H.S. Choy, Z.C. Chen, K.H. Cheng, Z.X. Cai, Laser direct patterning of a reduced-graphene oxide transparent circuit on a graphene oxide thin film, J. Appl. Phys. 113 (2013) 244903.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full Length Article
Laser-induced reduction of graphene oxide powders by high pulsed ultraviolet laser irradiations Chii-Rong Yang a, Shih-Feng Tseng b,⇑, Yu-Ting Chen a a b
Department of Mechatronic Engineering, National Taiwan Normal University, Taipei 10610, Taiwan Department of Mechanical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan
a r t i c l e
i n f o
Article history: Received 7 February 2018 Revised 7 March 2018 Accepted 11 March 2018 Available online 14 March 2018 Keywords: Laser-induced reduction Graphene oxide powders Raman spectroscopy X-ray photoelectron spectroscopy Surface area analyzer
a b s t r a c t This study aims to develop a laser-induced reduction approach for graphene oxide (GO) powders fabricated by using high pulsed ultraviolet laser irradiations. Before and after the laser irradiation with different fluences, the physical and electrical properties of homemade GO powders and reduced graphene oxide (rGO) powders were measured and analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area analyzer, and four-point probe instrument. The laser irradiation parameters included the pulse repetition frequency of 100 kHz, the scanning speed of galvanometers of 50 mm/s, the number of laser irradiated cycles of 10, and the laser fluences of ranging from 0.153 mJ/cm2 to 0.525 mJ/ cm2. The laser reduction experiments of GO powders demonstrated that the largest relative intensity of the 2D peak and specific surface area were found at the laser fluence of 0.438 mJ/cm2. Moreover, the electrical resistance sharply decreased from 280 MX in the initial GO powders to 0.267 MX in rGO powders at a laser irradiation fluence of 0.438. The C/O ratio was increased from 0.232 in the initial GO powders to 1.86 in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2; furthermore, the C/O ratios increased with increasing the laser fluences. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Graphene is a two-dimensional and hexagonal lattice material with a single atomic layer or few atomic layers. Due to its high room-temperature carrier mobility of up to 2 105 cm2/Vs [1,2], high thermal conductivity of 5300 W/mK [3,4], high optical transmittance of more than 90% [5–7], and high mechanical strength with Young’s modulus of 1 TPa [8,9], graphene materials have widely promising applications in solar cells, light-emitting diodes (LEDs), touch-screen panels, energy storage devices, single molecule gas detection, and other transparent electrodes [10–14]. Various approaches of manufacturing graphene materials include chemical vapor deposition (CVD), micromechanical cleavage of highly oriented pyrolytic graphite (HOPG), electrochemical exfoliation of HOPG, chemical exfoliation, photo exfoliation, epitaxial growth method, reduction of graphene oxide (GO), and so on [15–18]. Recently, several methods of thermal and electrical reduction of GO to graphene for mass production have been proposed. Trusovas et al. [19] used a picoseconds pulsed laser (wavelength of 1064 nm) processing system combined with a galvanometric ⇑ Corresponding author. E-mail address: [email protected] (S.-F. Tseng). https://doi.org/10.1016/j.apsusc.2018.03.090 0169-4332/Ó 2018 Elsevier B.V. All rights reserved.
scanner to reduce graphite oxide to graphene. After the laser irradiation on graphite oxide films with the laser power of 50 mW and the scanning speed of 30 mm/s, the largest relative intensity of 2Dpeak (2656 cm1) and the minimum structural defects of D-peak (1331 cm1) of reduced graphite oxide films were clearly observed by a Raman spectroscopy. The experimental and analytic results revealed that a single laser pulse with a fluence of 0.04 J/cm2 (50 mW) of local temperature increased up to 1400 °C for a few nanoseconds that can sufficient and effective reduction of graphite oxide to graphene by using laser irradiation. Ghadim et al. [20] reported the reduction of GO sheets in the ammonia solution at room temperature by an Nd:YAG pulsed laser system with a wavelength of 532 nm and a average power of 0.3 W. After laser irradiation of 10 min, the 2D-peak (2680 cm1) of reduced graphene oxide (rGO) sheets was slightly higher than GO ones measured by the Raman spectroscopy. A calculated 2D/G intensity ratio (I2D/IG) of rGO sheets was 0.038 that had no significant interaction for the pulsed laser reduced sheets in the ammonia solution. By using X-ray photoelectron spectroscopy (XPS) analysis, an oxygen/carbon atomic ratio (O/C) of GO sheets reduced from 49% down to 21% after laser irradiation of 10 min. Teoh et al. [21] presented a versatile technique to reduce three dimensional (3D) GO with micropatterned multilayered structures by the focused laser
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
beam (wavelength of 532 nm) irradiation and hierarchical control method. Petridis et al. [22] reported on the development of a KrF excimer pulsed laser (wavelength of 248 nm) induced reduction method for the photoreduction of GO field effect transistors (FETs). To irradiate GO FETs with a laser fluence of 80 mJ/cm2, the electrical conductivity increased with increasing the laser pulse numbers. The O/C ratio was reduced from 61% in the initial GO to 16% in rGO treated by 120 laser pulses at the fluence 80 mJ/cm2. Zhou et al. [23] proposed an electrochemical method to produce rGO films with an O/C ratio of less than 6.26%. Moreover, this method combined with a spray-coating technique could accomplish the controllable synthesis of large-area and patterned rGO films with thickness ranging from a single atomic layer to several microns coated on various substrate surfaces, such as flexible plastic, glass, Au, glassy carbon (GC), and indium tin oxide (ITO). In this study, we used the improved Hummers’ method to prepare GO powders. To obtain the reduction of GO powders with a fast, convenient, environmentally friendly, and efficient method, this study focused on the development of a laser-induced reduction technique using an ultraviolet (UV) laser-induced reduction apparatus combined with a high-speed galvanometric scanner. The laser-induced reduction parameters consisted of laser fluences, pulse repetition frequencies, scan speeds of the galvanometric scanner, and number of irradiated cycles. Before and after the laser irradiation with different processing parameters, the Raman spectra, O/C ratio, and specific surface area of GO and rGO powders were observed and analyzed using the Raman spectroscopy, XPS, and surface area analyzer. Moreover, the electrical resistances of GO and rGO powders were measured using a four-point probe instrument.
2. Experimental 2.1. Preparation of GO powders The homemade GO powders were fabricated by using preoxidized, improved Hummers’ method, and post-treatment procedures. In the pre-oxidized process, 3 g graphite flakes were dissolved in a solution containing 180 mL H2SO4 and heated to 80 °C for 4.5 h to promote the oxidation of the graphite. Then, the graphite oxides were exfoliated using an ultrasonic atomizer for 2 h. The pre-oxidized graphite flakes were obtained using the qualitative filter papers with hole diameter of 1 lm to filter the micro flakes and using a hotplate with 100 °C to dry flakes. Depending on the improved Hummers’ method, 360 mL H2SO4 was added slowly to the 40 mL H3PO4 as a mixture. Afterward 3 g pre-oxidized graphite flakes were added to the mixture, which was cooled to 0 °C in an ice bath for 30 min. Finally, 18 g KMnO4 was added slowly to the mixture and stirred for 1 h. Moreover, the mixture was heated to 50 °C and stirred for 12 h. Then, the mixture was cooled to room temperature, and 30 wt% H2O2 was added slowly into the mixture. The completely reacted mixture was a graphene oxide suspension. Fig. 1 shows digital pictures of graphene oxide suspensions with concentration of 0.4 mg/ml (a) and 1 mg/ml (b) created by GO powders dispersed in 100 ml of deionized water. In the post-treatment process, 1000 mL HCl (10 wt%) was added to the graphene oxide suspension and stirred for 2 h. To remove the supernatants, the GO suspension was centrifuged at 6000 rpm for 30 min. After removing completely metal ions (i.e. Mn and K ions), the GO flakes were washed in distillate water and centrifuged at 6000 rpm for 2 h. The filtered GO flakes were dried in a vacuum oven at 60 °C for 24 h. The GO powders with a diameter of 200 lm were fabricated using a ball grinding mill with zirconia balls of 2 mm diameter for 72 h.
579
Fig. 1. Digital pictures of graphene oxide suspensions with concentration of 0.4 mg/ml (a) and 1 mg/ml (b) created by GO powders dispersed in 100 ml of deionized water.
2.2. UV laser-induced reduction apparatus and method GO powders were reduced using the UV pulsed laser (Model: AVIA 355-14, Coherent Inc., USA) working at the 355 nm wengthlength. The specifications of UV laser were following: the laser beam diameter at the exit port of 3.5 mm, the maximal pulse repetition frequency of 300 kHz, the maximal power of 14 W, and the pulse width of 28 ns at the pulse repetition frequency of 100 kHz. Experimental apparatus included a UV laser source, three reflective mirrors, a beam expander with 2 times magnification, a galvanometric scanner with a telecentric lens of 110 mm focusing length and of 60 mm 60 mm field size, and an XYZ-axes movable stage with ball-screw mechanism, as shown in Fig. 2. The GO powders were placed inside a quartz tube. The laser beam was directly focused through the quartz tube due to the quartz material with high transmittance at the 355 nm waveband. The laser processing conditions for the irradiated GO powders were carried out as following. The defocused laser beam away from the focused point of 20 mm was irradiated towards GO powder surfaces to avoid damaging and burning those powders with high laser fluences. The defocused spot diameter (D) was approximately 5 mm. The incident laser fluence (F) in J/cm2 could be calculated by the following equation:
F¼
E A
ð1Þ
where E is the laser pulse energy, and A is the area of laser spots. The laser fluences were adjusted from 0.153 mJ/cm2 to 0.525 mJ/ cm2 for this study. Moreover, the GO powders were reduced by scanning laser beams with a cross line of the laser processing path in X and Y directions of equal line-scan space of 20 lm. Fig. 3 shows schematically the laser irradiation paths. The overlapping rates (OR) of the laser spot could be defined and estimated as follows [24].
OR ¼ 1
V 100% P RF D
ð2Þ
where D, V, and PRF are the laser spot diameter, the scanning speed of galvanometers, and the laser pulse repetition rate, respectively. During the tests, the pulse repetition frequencies, scan speeds of
580
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
2.3. Characterization and measurement Raman spectroscopy (Model: NRS-4100, JASCO Inc., Japan), XPS (Model: Theta Probe, Thermo Fisher Scientific Inc., UK), and surface area analyzer (Model: ASAP 2020, Micromeritics Inc., USA) were used to measure the physical properties of samples before and after UV laser irradiation. Raman spectrum measurements were performed with an excitation laser wavelength of 532 nm at room temperature. The laser power was restricted to 2 mW to avoid laser-induced heating on the sample surface. The O/C ratio of samples was performed using the XPS with X-ray spot size ranging from 15 to 400 mm. The Theta Probe XPS instrument had a fully motorized stage, and the maximum field of view (FOV) was 70 mm 70 mm. The specific surface area of samples was performed using the surface area and porosity analyzer. In addition, the fourpoint probe instrument was used to measure the electrical properties of samples.
3. Results and discussion 3.1. Raman spectra analysis
Fig. 2. Schematic of experimental apparatus for UV laser-induced reduction of graphene oxide powders.
Fig. 3. Schematic of the laser irradiation paths.
Table 1 Summary of the laser irradiation parameters used to reduce GO powders on the quartz tube. Laser irradiation parameters
Values or methods
Laser fluence (J/cm2) Defocused laser spot diameter (mm) Pulse repetition frequency (kHz) Scanning speed (mm/s) Overlapping rate (%) Number of irradiated cycles Laser scanning path Line-scan space (lm)
0.153 5
0.255
0.357
0.438
0.525
100 50 99.9 10 Cross lines in X and Y directions 20
the galvanometric scanner, and number (t) of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Hence, the calculated OR was a high value of more than 99%. Table 1 presents a summary of the laser irradiation parameters used to reduce GO powders on the quartz tube.
Fig. 4 shows a picture of the GO powders in the quartz tube taken by a digital camera. Before and after the UV laser irradiated samples of GO powders were characterized with the Raman spectroscopy. The laser irradiated parameters of the pulse repetition frequency, scan speeds of the galvanometric scanner, and number of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Moreover, the applied laser fluences included 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2 for this study. Fig. 5 shows the Raman spectra measured on GO and rGO powders with different laser fluences for the Raman shift ranging from 800 cm1 to 3300 cm1. The measured spectra demonstrated three characteristic peaks of D, G, and 2D bands of samples centered averagely at 1344 cm1, 1586 cm1, and 2669 cm1, respectively. The D, G, and 2D bands represented the defects, in-plane vibration of sp2 carbon atoms, and the stacking order, respectively [25]. Before laser irradiations, the measured Raman spectrum of GO powders only appeared D and G bands. After UV laser irradiations on GO powders, the measured results of Raman spectra showed that the 2D band appearing corresponded to graphene formation because of the laser-induced reduction reaction. Moreover, the intensity of D band of rGO powders significantly increased more than that of GO powders. This is due to rGO powders with lots of defects produced by UV laser irradiations. D/G intensity ratio (ID/IG) and 2D/G intensity ratio (I2D/IG) were often used to quantify defects in graphene materials and to qualify the number of stacked graphene layers, respectively. The ID/IG and I2D/IG ratios of GO and rGO powders with different laser fluences were summarized in Table 2. The ID/IG ratio of GO powders was 0.77; furthermore, the ID/IG ratios of rGO powders were 0.874, 1.175, 1.033, 0.922, and 1.23 when the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, respectively. The ID/IG ratios of rGO powders were signifi-
Fig. 4. A photo of the GO powders in the quartz tube.
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
581
mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, respectively. The measured results revealed that the I2D/IG ratios of rGO powders increased with increasing laser fluences ranging from 0.153 mJ/ cm2 to 0.438 mJ/cm2. However, the peak intensity of 2D band was lowering when the laser fluence increased to 0.525 mJ/cm2. This implied that the local accumulated temperature of rGO powders produced the thermal denaturation for these rGO powders [19]. In the previous studies, the I2D/IG ratios of less than 1, 1–2, and 2–3 were for multilayer graphene, bilayer graphene, and monolayer graphene, respectively [26,27]. Consequently, this clearly indicated the rGO powders were multilayer graphene structures. 3.2. Specific surface area and electrical resistance analysis
Fig. 5. Raman spectrum measured on GO and rGO powders with different laser fluences.
Table 2 Summary of the ID/IG and I2D/IG ratios of GO and rGO powders with different laser fluences. Types of powder
GO
rGO
Laser fluence (mJ/cm2) ID/IG I2D/IG
– 0.77 –
0.153 0.874 0.05
0.255 1.175 0.15
0.375 1.033 0.316
0.438 0.922 0.569
0.525 1.23 0.438
Before and after the laser irradiation with different laser fluences, the specific surface area and electrical resistance of GO and rGO powders were measured using the surface area analyzer and four-point probe instrument, respectively. The measured results revealed that the specific surface area and electrical resistance values of GO powders were 0.1148 m2/g and 280 MX, respectively. When the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2, the specific surface area and electrical resistance values of rGO powders were 1.178 m2/g, 7.139 m2/g, 10.73 m2/g, 16.86 m2/g, and 15.24 m2/g and 18.2 MX, 16.5 MX, 10.71 MX, 0.267 MX, and 80.3 MX, respectively. The specific surface area and electrical resistance of GO and rGO powders versus different laser fluences were shown in Fig. 7. After the UV laser irradiation, the specific surface area and electrical resistance values of rGO powders were slightly larger and sharply lower than GO ones, respectively. When the laser fluences increased from 0.153 mJ/cm2 to 0.438 mJ/cm2, the specific surface area values gradually increased from 1.178 m2/g to 16.86 m2/g and the electrical resistance values gently decreased from 18.2 MX to 0.267 MX. The laser reduction zone was shown in the left side of Fig. 7. When the laser fluence increased to 0.525 mJ/cm2, the specific surface area value was a decreasing trend and the electrical resistance value was an increasing trend compared with the laser fluence of 0.438 mJ/cm2. This indicated that the situation was due to the higher laser fluence produced bondbreaking of the G-G bonds, namely, the freshly formed rGO powders would be ablated by subsequent laser irradiating, which induced an abnormal increase in electrical resistance of laserirradiated tracks during the laser processing of multiple repeated scans [28]. The laser ablation zone was shown in the right side of Fig. 7.
Fig. 6. The ID/IG and I2D/IG ratios of rGO powders versus different laser fluences.
cantly greater than GO ones caused by the laser irradiation to produce a few defects. The ID/IG and I2D/IG ratios of rGO powders versus different laser fluences were shown in Fig. 6. Because Raman spectrum taken on rGO powders indicated the apparent 2D bands, the I2D/IG ratio of rGO powders were 0.05, 0.15, 0.316, 0.569, and 0.438 when the laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357
Fig. 7. Specific surface area and electrical resistance of GO and rGO powders versus different laser fluences.
582
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
Fig. 8. XPS analysis of GO and typical rGO powders for different laser fluences.
Table 3 Summary of the oxygen and carbon contents and C/O ratios of GO and typical rGO powders with different laser fluences. Types of powder
GO
rGO
Laser fluence (mJ/cm2) Oxygen content (%) Carbon content (%) C/O ratio
– 81.15 18.85 0.232
0.153 58.05 41.95 0.722
0.375 41.76 58.24 1.39
0.525 34.94 65.06 1.86
3.3. XPS analysis To investigate the degree of reduction of GO powders, XPS was employed to analyze the chemical composition before and after the UV laser irradiation with different fluences. Fig. 8 shows the C1s (284.8 eV peak) and O1s (532 eV peak) XPS spectra of GO and typical rGO powders. The the oxygen and carbon contents and C/O ratios of GO and typical rGO powders with different laser fluences were summarized in Table 3. The carbon and oxygen contents of GO powders were 18.85% and 81.15%, respectively, shown in Fig. 8a. It could be seen that the O1s peak was obviously higher than the C1s peak for GO powders. While the applied laser fluences were 0.153 mJ/cm2, 0.357 mJ/cm2, and 0.525 mJ/cm2, the oxygencontaining rGO powders were down to 58.05%, 41.76%, and 34.94%, respectively, shown in Fig. 8b–c. It was clear that the oxygen content was reduced from 81.15% in the initial GO powders to 34.94% in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2. This indicated that the majority of oxygen content was removed and efficient reduction occurred after the UV laser irradiation on GO powders [22]. The carbon to oxygen (C/O) ratios of rGO powders were 0.722, 1.39, and 1.86 when the applied laser fluences were 0.153 mJ/cm2, 0.357 mJ/cm2, and 0.525 mJ/cm2, respectively. The measured resulted showed that the C/O ratios were increased with increasing the laser fluences. Furthermore, the C/O ratio was increased from 0.232 in the initial GO powders to 1.86 in the rGO powders at a laser irradiation fluence of 0.525 mJ/cm2. 4. Conclusion This study focused to investigate the laser-induced reduction of GO powders using the pulsed UV laser at 355 nm wavelength pro-
duced significant changes in graphene properties. The pulse repetition frequency, scan speeds of the galvanometric scanner, and number of irradiated cycles were fixed at 100 kHz, 50 mm/s, and 10 times, respectively. Moreover, the applied laser fluences were 0.153 mJ/cm2, 0.255 mJ/cm2, 0.357 mJ/cm2, 0.438 mJ/cm2, and 0.525 mJ/cm2. The measured and analyzed results showed that the homemade GO powders had the higher electrical resistance of 280 MX and oxygen content of 81.15%, the lower specific surface area of 0.1148 m2/g and ID/IG ratio of 0.77, and no Raman 2D peak. By using the nanosecond pulsed UV laser irradiated GO powders, the electrical resistance sharply dropped to 0.267 MX, the specific surface area increased to 16.86 m2/g, and I2D/IG ratio had a high value of 0.569 while the laser fluence was set in 0.438 mJ/ cm2. Furthermore, the oxygen content of rGO powders decreased with increasing the laser fluences. Laser-induced reduction of GO powders was successfully developed by pulsed ultraviolet laser irradiations. These approaches are potentially used for mass production of graphene powders in the future. Acknowledgements The authors thank the Ministry of Science and Technology of Taiwan for financially supporting this research under projects MOST 106-2622-E-027-026-CC3 and MOST 106-2221-E-027-147. References [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films, Science 306 (2004) 666–669. [2] K.I. Bolotin, K.J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H.L. Stormer, Ultrahigh electron mobility in suspended graphene, Solid State Commun. 146 (2008) 351–355. [3] H. Tang, G.J. Ehlert, Y. Lin, H.A. Sodano, Highly efficient synthesis of graphene nanocomposites, Nano Lett. 12 (2012) 84–90. [4] A.A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C.N. Lau, Superior thermal conductivity of single-layer graphene, Nano Lett. 8 (2008) 902–907. [5] D. Li, M.B. Muller, S. Gilje, R.B. Kaner, G.G. Wallace, Processable aqueous dispersions of graphene nanosheets, Nat. Nanotechnol. 3 (2008) 101–105. [6] G. Eda, G. Fanchini, M. Chhowalla, Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material, Nat. Nanotechnol. 3 (2008) 270–274. [7] S. Bae, H. Kim, Y. Lee, X. Xu, J.S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H.R. Kim, Y.I. Song, Y.J. Kim, K.S. Kim, B. Özyilmaz, J.H. Ahn, B.H. Hong, S. Iijima, Roll-to-
C.-R. Yang et al. / Applied Surface Science 444 (2018) 578–583
[8] [9] [10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
roll production of 30-inch graphene films for transparent electrodes, Nat. Nanotechnol. 5 (2010) 574–578. C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the elastic properties and intrinsic strength of monolayer graphene, Science 321 (2008) 385–388. V. Singh, D. Joung, L. Zhai, S. Das, S.I. Khondaker, S. Seal, Graphene based materials: Past, present and future, Prog. Mater Sci. 56 (2011) 1178–1271. J. Wu, H.A. Becerril, Z. Bao, Z. Liu, Y. Chen, P. Peumans, Organic solar cells with solution-processed graphene transparent electrodes, Appl. Phys. Lett. 92 (2008) 263302. E.C. Cho, J.H. Huang, C.P. Li, C.W. Chang-Jian, K.C. Lee, Y.S. Hsiao, J.H. Huang, Graphene-based thermoplastic composites and their application for LED thermal management, Carbon 102 (2016) 66–73. K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y. Choi, B.H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature 457 (2009) 706–710. C. Berger, Z.M. Song, T.B. Li, X.B. Li, A.Y. Ogbazghi, R. Feng, Z. Dau, A.N. Marchenkov, E.H. Conrad, P.N. First, W.A. de Heer, Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics, J. Phys. Chem. B 108 (2004) 19912–19916. S.F. Tseng, W.T. Hsiao, C.K. Chung, T.L. Chang, Investigation the interaction between the pulsed ultraviolet laser beams and PEDOT:PSS/graphene composite films, Appl. Surf. Sci. 356 (2015) 486–491. F. Bonaccorso, A. Lombardo, T. Hasan, Z. Sun, L. Colombo, A.C. Ferrari, Production and processing of graphene and 2d crystals, Mater. Today 15 (2012) 564–589. C.Y. Su, A.Y. Lu, Y. Xu, F.R. Chen, A.N. Khlobystov, L.J. Li, High-quality thin graphene films from fast electrochemical exfoliation, ACS Nano 5 (2011) 2332–2339. U. Khan, H. Porwal, A. O’Neill, K. Nawaz, P. May, J.N. Coleman, Solventexfoliated graphene at extremely high concentration, Langmuir 27 (2011) 9077–9082. S.R. Kim, M.K. Parvez, M. Chhowalla, UV-reduction of graphene oxide and its application as an interfacial layer to reduce the back-transport reactions in dye-sensitized solar cells, Chem. Phys. Lett. 483 (2009) 124–127.
583
[19] R. Trusovas, K. Ratautas, G. Racˇiukaitis, J. Barkauskas, I. Stankevicˇiene˙, G. Niaura, R. Mazˇeikiene˙, Reduction of graphite oxide to graphene with laser irradiation, Carbon 52 (2013) 574–582. [20] E.E. Ghadim, N. Rashidi, S. Kimiagar, O. Akhavan, F. Manouchehri, E. Ghaderi, Appl. Surf. Sci. 301 (2014) 183–188. [21] H.F. Teoh, Y. Tao, E.S. Tok, G.W. Ho, C.H. Sow, Direct laser-enabled graphene oxide-Reduced graphene oxide layered structures with micropatterning, J. Appl. Phys. 112 (2012) 064309. [22] C. Petridis, Y.H. Lin, K. Savva, G. Eda, E. Kymakis, T.D. Anthopoulos, E. Stratakis, Post-fabrication, in situ laser reduction of graphene oxide devices, Appl. Phys. Lett. 102 (2013) 093115. [23] M. Zhou, Y. Wang, Y. Zhai, J. Zhai, W. Ren, F. Wang, S. Dong, Controllable synthesis of large-area and patterned electrochemically reduced graphene oxide films, Chem. Eur. J. 15 (2009) 6116–6120. [24] S.F. Tseng, W.T. Hsiao, K.C. Huang, D. Chiang, The effect of laser patterning parameters on fluorine-doped tin oxide films deposited on glass substrates, Appl. Surf. Sci. 257 (2011) 8813–8819. [25] C. Faugeras, A. Nerriere, M. Potemski, A. Mahmood, E. Dujardin, C. Berger, W.A. de Heer, Few layer graphene on SiC, pyrolitic graphite and graphene: a Raman scattering study, Appl. Phys. Lett. 92 (2008) 011914. [26] A. Reina, X.T. Jia, J. Ho, D. Nezich, H.B. Son, V. Bulovic, M.S. Dresselhaus, J. Kong, Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition, Nano Lett. 9 (2009) 30–35. [27] V.T. Nguyen, H.D. Le, V.C. Nguyen, T.T.T. Ngo, D.Q. Le, X.N. Nguyen, N.M. Phan, Synthesis of multi-layer graphene films on copper tape by atmospheric pressure chemical vapor deposition method, Adv. Nat. Sci.: Nanosci. Nanotechnol. 4 (2013) 035012. [28] K.C. Yung, H. Liem, H.S. Choy, Z.C. Chen, K.H. Cheng, Z.X. Cai, Laser direct patterning of a reduced-graphene oxide transparent circuit on a graphene oxide thin film, J. Appl. Phys. 113 (2013) 244903.