- Email: [email protected]
Direct evidence of advantage of Cu(111) for graphene synthesis by using Raman mapping and electron backscatter diffraction
Materials Letters 65 (2011) 2864–2867
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Direct evidence of advantage of Cu(111) for graphene synthesis by using Raman mapping and electron backscatter diffraction Masatou Ishihara, Yoshinori Koga, Jaeho Kim, Kazuo Tsugawa, Masataka Hasegawa ⁎ Nanotube Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
a r t i c l e
i n f o
Article history: Received 28 April 2011 Accepted 14 June 2011 Available online 21 June 2011 Keywords: Single-layer graphene Few-layer graphene Thermal chemical vapor deposition Raman EBSD
a b s t r a c t The advantageous crystallographic orientation of Cu surface for graphene synthesis by using thermal chemical vapor deposition (CVD) is examined by Raman mapping and electron backscatter diffraction. It is found that Cu(111) predominates over (110) and (100) for single- (SLG) or few-layer graphene (FLG) growth. To confirm this result we attempt the synthesis of graphene on Cu(111) single crystal film surfaces. We confirmed the formation of high quality and high uniformity SLG or FLG over more than 97% of the substrate surface area of 10 mm × 10 mm by Raman mapping. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Large-scale graphene with extraordinary transport properties has been demanded to realize the electronic devices of ultimate functions. For the realization of the integration of graphene devices high quality graphene films of at least millimeter size are indispensable. Several techniques have been developed to synthesize graphene on metal surfaces by using chemical vapor deposition (CVD) which is suitable for large-scale synthesis of the film. In particular recent success of the development of the synthesis method by using CVD on metal foils such as Ni and Cu increases the possibility to apply graphene for industries [1–4]. Recently the epitaxial growth of graphene on single crystal Cu (111) has been attempted [5,6]. Gao et al. have been found that there are two predominant orientations of graphene with respect to the underlying Cu(111) from the observation of the Moiré patterns by scanning tunneling microscopy and spectroscopy [5]. Reddy et al. reported that the large-area graphene can be grown on epitaxial single-crystal Cu surfaces using a quartz-tube-furnace CVD reactor [6]. These results indicate that Cu(111) is the convenient surface for graphene growth. On the other hand the polycrystalline Cu foils have been generally used as the substrate for graphene CVD. Thus the direct observation of the dependence of graphene growth on the crystallographic orientation using polycrystalline Cu foils is indispensable. In this work we compare the CVD graphene growth on Cu(111), (110) and (100) surfaces of polycrystalline Cu foils by using electron
⁎ Corresponding author. E-mail address: [email protected] (M. Hasegawa). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.047
backscatter diffraction (EBSD) and Raman mapping, and show that Cu (111) predominates over other surfaces. To confirm the advantage of Cu(111), in addition, we show the synthesis of high quality and high uniformity large-scale single- (SLG) or few-layer graphene (FLG) on Cu(111) single crystal films which are epitaxially grown on Al2O3 (0001) substrates with the step-and-terrace structure.
2. Experimental We search for the advantageous crystallographic orientations of Cu surfaces to graphene growth. Graphene films are deposited on Cu foils by thermal CVD using methane–hydrogen at 1000 °C which was originally reported by Li et al. [2]. The distribution of graphene and the crystallographic orientation of Cu surface are measured by Raman map (RabRAM HR-800, HORIBA) using an Ar ion laser with a wavelength of 514.5 nm and EBSD (OIM system, EDAX), respectively. We attempt the synthesis of graphene on Cu(111) single crystal film surfaces. Cu(111) single crystal films for the substrate of SLG or FLG synthesis are obtained by the epitaxial growth of Cu(111) on Al2O3(0001) using magnetron sputtering at substrate temperatures ranging from 100 to 200 °C. The size of the substrates is 10 mm × 10 mm × 0.5 mm. To obtain flat surface of Cu film, Al2O3 (0001) substrates with the step-and-terrace surface structure [7], provided by SHINKOSHA Co., Ltd., are used. The mis-orientation angle of the surface from (0001) is smaller than 0.1° (typically 0.07°). The thickness of deposited Cu(111) film is 1 μm, and the surface roughness, Ra, is 1 nm. The crystalline quality of Cu(111) single crystal film has been confirmed by using the pole figure measurement of x-ray diffraction. The deposited Cu(111) film has exhibited six-fold
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
a
b
2865
d
c
2D
(101)
Intensity (arb. units)
G
(100)
Cu(111)
Cu(100)
(111)
Cu(101)
1 µm
1 µm
1000 1500 2000 2500 3000
Raman shift (cm-1)
5µm
Fig. 1. Distribution of single- (SLG) or few-layer graphene (FLG) grown on surface domains of a Cu foil. (a) Optical microscope image of surface domains of the Cu foil. (b) EBSD image with a color map from Cu(111) (blue), Cu(101) (green), Cu(100) (pink) of the area shown in (a). (c) Raman map of the 2D to G peak intensity ratio (I2D/IG) over a 14 μm × 18 μm area overlapping with the optical microscope image. The scanning step is 2 μm and the blue cross markers describe the measurement points. Light-blue areas are associated with SLG or FLG (I2D/IG N 1). (d) Raman spectra from graphene films grown on the three different crystal orientations of Cu foil.
3. Results and discussion Fig. 1(a) shows the optical microscope image of the Cu foil after graphene growth at the measurement area of EBSD map and Raman spectroscopy. Fig. 1(b) shows a EBSD map of the Cu foil with a triple junction of grain boundary edges and the three crystallographic orientations of Cu(111), (101) and (100) are identified. Reina [1] and Ismach [8] have discussed that in the case of the CVD graphene I2D/IG is the indication of the number of graphene layers. According to their discussion when I2D/IG is larger than one the number of layers of CVD derived graphene is estimated to be smaller than three, i.e., SLG or FLG is obtained. In the Raman map, Fig. 1(c), we show the distribution of SLG or FLG which is obtained from the points at which I2D/IG is larger than one. Fig. 1(d) shows Raman spectra from three different points marked in Fig. 1(c) by the colored arrows and dots. The distribution of SLG or FLG on the Cu foil obtained from the Raman map is verified with that of the surface orientation of Cu domains obtained from EBSD map. We find that SLG or FLG is formed preferentially on Cu(111) domain, which suggests Cu(111) is the most appropriate face for SLG or FLG growth. On the other hand almost no Raman signals related to graphene, such as G, 2D, and D peaks, are observed on Cu(101) domain except grain boundary edges, on which graphene growth is
suppressed. In the case of Cu(100) domain although some graphenerelated Raman signals are obtained, almost no Raman measurement points at which I2D/IG is more than one are found. This indicates that multilayer (4 or more) graphene growth on Cu(100) is preferential [1]. It is considered that the grain boundary is one of the point of graphene nucleation because of the observation of the formation of graphene among Cu(100), (101) and (111) domains, but the growth of SLG or FLG is depressed on (100) and (110) rapidly. From these results we conclude that Cu(111) is the best substrate for the CVD growth of SLG or FLG. Fig. 2 shows a typical Raman spectrum of the graphene film deposited on Cu(111) single crystal surface. The disorder-induced D peak, which appears at ~1350 cm− 1 is not observed in the spectrum. The spectrum exhibits 2D peak at 2671 cm− 1 and G peak at 1589 cm− 1 on the smooth background from the fluorescence of Cu substrate. The 2D peak is symmetric with a full width at half maximum of 39 cm− 1. The I2D/IG ratio for the graphene is ~3.3, which indicates the formation of SLG or FLG [1,8]. The uniformity of graphene on Cu(111) films is examined by using Raman map. First we select five areas of 20 μm × 20 μm at the center and four corners on the substrate surface, and measure Raman spectra with 1 μm mesh (441 points in each area). Fig. 3 shows the Raman 1800
2D(2671 cm-1) 1600
Intensity (a. u.)
symmetrical diffraction pattern, which indicates the film has doubledomain structure. The CVD of graphene on Cu(111) single crystal surfaces is performed by using an infrared gold image furnace (MILA3000-P-N, ULVAC-RIKO). The Cu(111) single crystal film on Al2O3 substrate is placed on a quartz sample holder in the furnace. Then the furnace is evacuated under 3 × 10 − 4 Pa. Next the temperature of the substrate is raised from room temperature to 1000 °C in 5 min with flowing 2 sccm hydrogen at a pressure of 5.3 Pa. The graphene CVD is started by flowing 35 sccm methane at 66.5 Pa immediately after the substrate temperature reached to 1000 °C. The duration of the CVD of graphene is 20 min, and the temperature is kept at 1000 °C during the CVD. The furnace is evacuated immediately after the CVD process. The substrate is cooled down under the pressure less than 1 × 10 − 3 Pa. It takes about 6 min to cool down to 300 °C, and 19 min to 100 °C. The quality and uniformity of graphene on Cu(111) films are examined by Raman map (XploRA, HORIBA) using a diode laser with a wavelength of 638 nm and a spot size of 1 μm.
1400 1200 1000
G(1589 cm-1)
800 600 400 1000
1500
2000
2500
3000
Raman shift (cm-1) Fig. 2. Typical Raman spectrum of graphene films grown on Cu(111) single crystal surface by thermal CVD.
2866
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
ID
a
I2D/IG
50
ID
b
5.0
I2D/IG
50
5.0
4.0
4.0
40
40 3.0
30
1 µm
3.0 30
2.0 1 µm
20
1.0
1 µm
2.0 1 µm
20
0.0
Intensity (a. u.)
f
2500
0.0
c
2D
ID
2000 1500
I2D/IG
50
D
1.0
5.0
G 4.0 40 3.0
1000 30
2.0
500 1 µm
0 1000
1500
2000
2500
1 µm
20
1.0 0.0
3000
Raman shift (cm-1)
d
ID
e
I2D/IG
50
ID
I2D/IG
50
5.0
5.0
4.0
4.0
40
40 3.0
30
1 µm
20
3.0 30
2.0 1 µm
1.0
1 µm
2.0 1 µm
20
0.0
1.0 0.0
Fig. 3. Raman map of the graphene films grown on Cu(111) single crystal surface measured with 1 μm mesh for selected five areas of 20 μm × 20 μm using a 100× objective lens. (a–e) Raman maps of the intensity of D peak (ID) and the 2D to G peak intensity ratio (I2D/IG). (f) Typical two Raman spectra measured from the white and blue areas in (c).
maps of the intensity of D peak (ID) and the ratio I2D/IG. Fig. 3(f) shows typical Raman spectra observed from the white and the dark blue area in the Raman map of D peak intensity together with amorphous carbon which produces broad G and D peaks with a very weak 2D intensity [9]. It is suggested that amorphous carbon is formed by the reaction of residual carbon in the cooling process. This area, however, is less than 1%, and may originate from defects of Cu film. In Fig. 3(b), (d) and (e), the ratios I2D/IG are more than one at almost all measurement points. The disorder-induced D peaks are not observed in these three areas. In Fig. 3(a) and (c), the ratios I2D/IG are more than one over almost whole areas except several points identified by the arrows, where small amount of amorphous carbon are observed in graphene layers in Raman spectra. Fig. 4(a) shows the Raman map observed for the area of 150 μm × 150 μm with a mesh of 1 μm (22801 points) at the center of the sample. The ratios I2D/IG are more than one at 99% of the data
a
points, which indicates that almost whole area of the sample surface is covered with SLG or FLG. Fig. 4(b) shows the Raman map of 10 mm × 10 mm with a mesh of 200 μm, which covers the whole sample surface. Although some damages are observed at the edges of the substrate the Raman signals from SLG or FLG are confirmed at 97% of all data points, which indicate that SLG or FLG was deposited over whole Cu(111) substrate surface. These results prove that the Cu(111) single crystal surface is useful to synthesize SLG or FLG with high uniformity and high quality. 4. Conclusion In this study the advantageous crystallographic orientation of Cu surface for SLG or FLG synthesis by using thermal chemical vapor deposition is examined for the first time by EBSD pattern and Raman mapping. It is found that Cu(111) predominates over (110) and (100)
b
I2D/IG
I2D/IG
5.0
5.0
4.0
4.0
3.0
3.0
2.0
2.0
1.0 10 µm
1.0 500 µm
0.0
0.0
Fig. 4. Raman map of the 2D to G peak intensity ratio (I2D/IG) measured with (a) 1 μm mesh for an area of 150 μm × 150 μm and (b) 200 μm mesh over whole substrate surface of 10 mm × 10 mm.
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
for SLG or FLG synthesis. To confirm this result we examine the synthesis of SLG or FLG on Cu(111) single crystal film surfaces which are epitaxially grown on Al2O3(0001) substrates with the step-andterrace structure. We confirmed the high quality and high uniformity SLG or FLG formation by Raman mapping over more than 97% of the substrate surface area of 10 mm × 10 mm. Acknowledgment The authors thank Naobumi Saito and Yutaka Maruyama for their assistances with EBSD and Raman spectroscopy, respectively.
2867
References [1] [2] [3] [4] [5] [6]
Reina A, Jia X, Ho J, Nezich D, Son H, Bulovic V, et al. Nano Lett 2009;9:30–5. Li X, Cai X, An J, Kim S, Nah J, Yang D, et al. Science 2009;324:1312–4. Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, et al. Nature 2009;457:706–10. Li X, Zhu Y, Cai W, Borysiak M, Han B, Chen D, et al. Nano Let 2009;9:4359–63. Gao L, Guest JR, Guisinger NP. Nano Lett 2010;10:3512–6. Reddy KM, Gledhill AD, Chen C-H, Drexler JM, Padture NP. App Phys Lett 2011;98: 113117. [7] Yoshimoto M, Maeda T, Ohnishi T, Koinuma H, Ishiyama O, Shinohara M, et al. Appl Phys Lett 1995;67:2615–7. [8] Ismach A, Druzgalski C, Penwell S, Schwartzberg S, Zheng M, Javey A, et al. Nano Lett 2010;10:1542–8. [9] Knight DS, White WB. J Mater Res 1989;4:385–93.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Direct evidence of advantage of Cu(111) for graphene synthesis by using Raman mapping and electron backscatter diffraction Masatou Ishihara, Yoshinori Koga, Jaeho Kim, Kazuo Tsugawa, Masataka Hasegawa ⁎ Nanotube Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
a r t i c l e
i n f o
Article history: Received 28 April 2011 Accepted 14 June 2011 Available online 21 June 2011 Keywords: Single-layer graphene Few-layer graphene Thermal chemical vapor deposition Raman EBSD
a b s t r a c t The advantageous crystallographic orientation of Cu surface for graphene synthesis by using thermal chemical vapor deposition (CVD) is examined by Raman mapping and electron backscatter diffraction. It is found that Cu(111) predominates over (110) and (100) for single- (SLG) or few-layer graphene (FLG) growth. To confirm this result we attempt the synthesis of graphene on Cu(111) single crystal film surfaces. We confirmed the formation of high quality and high uniformity SLG or FLG over more than 97% of the substrate surface area of 10 mm × 10 mm by Raman mapping. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Large-scale graphene with extraordinary transport properties has been demanded to realize the electronic devices of ultimate functions. For the realization of the integration of graphene devices high quality graphene films of at least millimeter size are indispensable. Several techniques have been developed to synthesize graphene on metal surfaces by using chemical vapor deposition (CVD) which is suitable for large-scale synthesis of the film. In particular recent success of the development of the synthesis method by using CVD on metal foils such as Ni and Cu increases the possibility to apply graphene for industries [1–4]. Recently the epitaxial growth of graphene on single crystal Cu (111) has been attempted [5,6]. Gao et al. have been found that there are two predominant orientations of graphene with respect to the underlying Cu(111) from the observation of the Moiré patterns by scanning tunneling microscopy and spectroscopy [5]. Reddy et al. reported that the large-area graphene can be grown on epitaxial single-crystal Cu surfaces using a quartz-tube-furnace CVD reactor [6]. These results indicate that Cu(111) is the convenient surface for graphene growth. On the other hand the polycrystalline Cu foils have been generally used as the substrate for graphene CVD. Thus the direct observation of the dependence of graphene growth on the crystallographic orientation using polycrystalline Cu foils is indispensable. In this work we compare the CVD graphene growth on Cu(111), (110) and (100) surfaces of polycrystalline Cu foils by using electron
⁎ Corresponding author. E-mail address: [email protected] (M. Hasegawa). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.047
backscatter diffraction (EBSD) and Raman mapping, and show that Cu (111) predominates over other surfaces. To confirm the advantage of Cu(111), in addition, we show the synthesis of high quality and high uniformity large-scale single- (SLG) or few-layer graphene (FLG) on Cu(111) single crystal films which are epitaxially grown on Al2O3 (0001) substrates with the step-and-terrace structure.
2. Experimental We search for the advantageous crystallographic orientations of Cu surfaces to graphene growth. Graphene films are deposited on Cu foils by thermal CVD using methane–hydrogen at 1000 °C which was originally reported by Li et al. [2]. The distribution of graphene and the crystallographic orientation of Cu surface are measured by Raman map (RabRAM HR-800, HORIBA) using an Ar ion laser with a wavelength of 514.5 nm and EBSD (OIM system, EDAX), respectively. We attempt the synthesis of graphene on Cu(111) single crystal film surfaces. Cu(111) single crystal films for the substrate of SLG or FLG synthesis are obtained by the epitaxial growth of Cu(111) on Al2O3(0001) using magnetron sputtering at substrate temperatures ranging from 100 to 200 °C. The size of the substrates is 10 mm × 10 mm × 0.5 mm. To obtain flat surface of Cu film, Al2O3 (0001) substrates with the step-and-terrace surface structure [7], provided by SHINKOSHA Co., Ltd., are used. The mis-orientation angle of the surface from (0001) is smaller than 0.1° (typically 0.07°). The thickness of deposited Cu(111) film is 1 μm, and the surface roughness, Ra, is 1 nm. The crystalline quality of Cu(111) single crystal film has been confirmed by using the pole figure measurement of x-ray diffraction. The deposited Cu(111) film has exhibited six-fold
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
a
b
2865
d
c
2D
(101)
Intensity (arb. units)
G
(100)
Cu(111)
Cu(100)
(111)
Cu(101)
1 µm
1 µm
1000 1500 2000 2500 3000
Raman shift (cm-1)
5µm
Fig. 1. Distribution of single- (SLG) or few-layer graphene (FLG) grown on surface domains of a Cu foil. (a) Optical microscope image of surface domains of the Cu foil. (b) EBSD image with a color map from Cu(111) (blue), Cu(101) (green), Cu(100) (pink) of the area shown in (a). (c) Raman map of the 2D to G peak intensity ratio (I2D/IG) over a 14 μm × 18 μm area overlapping with the optical microscope image. The scanning step is 2 μm and the blue cross markers describe the measurement points. Light-blue areas are associated with SLG or FLG (I2D/IG N 1). (d) Raman spectra from graphene films grown on the three different crystal orientations of Cu foil.
3. Results and discussion Fig. 1(a) shows the optical microscope image of the Cu foil after graphene growth at the measurement area of EBSD map and Raman spectroscopy. Fig. 1(b) shows a EBSD map of the Cu foil with a triple junction of grain boundary edges and the three crystallographic orientations of Cu(111), (101) and (100) are identified. Reina [1] and Ismach [8] have discussed that in the case of the CVD graphene I2D/IG is the indication of the number of graphene layers. According to their discussion when I2D/IG is larger than one the number of layers of CVD derived graphene is estimated to be smaller than three, i.e., SLG or FLG is obtained. In the Raman map, Fig. 1(c), we show the distribution of SLG or FLG which is obtained from the points at which I2D/IG is larger than one. Fig. 1(d) shows Raman spectra from three different points marked in Fig. 1(c) by the colored arrows and dots. The distribution of SLG or FLG on the Cu foil obtained from the Raman map is verified with that of the surface orientation of Cu domains obtained from EBSD map. We find that SLG or FLG is formed preferentially on Cu(111) domain, which suggests Cu(111) is the most appropriate face for SLG or FLG growth. On the other hand almost no Raman signals related to graphene, such as G, 2D, and D peaks, are observed on Cu(101) domain except grain boundary edges, on which graphene growth is
suppressed. In the case of Cu(100) domain although some graphenerelated Raman signals are obtained, almost no Raman measurement points at which I2D/IG is more than one are found. This indicates that multilayer (4 or more) graphene growth on Cu(100) is preferential [1]. It is considered that the grain boundary is one of the point of graphene nucleation because of the observation of the formation of graphene among Cu(100), (101) and (111) domains, but the growth of SLG or FLG is depressed on (100) and (110) rapidly. From these results we conclude that Cu(111) is the best substrate for the CVD growth of SLG or FLG. Fig. 2 shows a typical Raman spectrum of the graphene film deposited on Cu(111) single crystal surface. The disorder-induced D peak, which appears at ~1350 cm− 1 is not observed in the spectrum. The spectrum exhibits 2D peak at 2671 cm− 1 and G peak at 1589 cm− 1 on the smooth background from the fluorescence of Cu substrate. The 2D peak is symmetric with a full width at half maximum of 39 cm− 1. The I2D/IG ratio for the graphene is ~3.3, which indicates the formation of SLG or FLG [1,8]. The uniformity of graphene on Cu(111) films is examined by using Raman map. First we select five areas of 20 μm × 20 μm at the center and four corners on the substrate surface, and measure Raman spectra with 1 μm mesh (441 points in each area). Fig. 3 shows the Raman 1800
2D(2671 cm-1) 1600
Intensity (a. u.)
symmetrical diffraction pattern, which indicates the film has doubledomain structure. The CVD of graphene on Cu(111) single crystal surfaces is performed by using an infrared gold image furnace (MILA3000-P-N, ULVAC-RIKO). The Cu(111) single crystal film on Al2O3 substrate is placed on a quartz sample holder in the furnace. Then the furnace is evacuated under 3 × 10 − 4 Pa. Next the temperature of the substrate is raised from room temperature to 1000 °C in 5 min with flowing 2 sccm hydrogen at a pressure of 5.3 Pa. The graphene CVD is started by flowing 35 sccm methane at 66.5 Pa immediately after the substrate temperature reached to 1000 °C. The duration of the CVD of graphene is 20 min, and the temperature is kept at 1000 °C during the CVD. The furnace is evacuated immediately after the CVD process. The substrate is cooled down under the pressure less than 1 × 10 − 3 Pa. It takes about 6 min to cool down to 300 °C, and 19 min to 100 °C. The quality and uniformity of graphene on Cu(111) films are examined by Raman map (XploRA, HORIBA) using a diode laser with a wavelength of 638 nm and a spot size of 1 μm.
1400 1200 1000
G(1589 cm-1)
800 600 400 1000
1500
2000
2500
3000
Raman shift (cm-1) Fig. 2. Typical Raman spectrum of graphene films grown on Cu(111) single crystal surface by thermal CVD.
2866
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
ID
a
I2D/IG
50
ID
b
5.0
I2D/IG
50
5.0
4.0
4.0
40
40 3.0
30
1 µm
3.0 30
2.0 1 µm
20
1.0
1 µm
2.0 1 µm
20
0.0
Intensity (a. u.)
f
2500
0.0
c
2D
ID
2000 1500
I2D/IG
50
D
1.0
5.0
G 4.0 40 3.0
1000 30
2.0
500 1 µm
0 1000
1500
2000
2500
1 µm
20
1.0 0.0
3000
Raman shift (cm-1)
d
ID
e
I2D/IG
50
ID
I2D/IG
50
5.0
5.0
4.0
4.0
40
40 3.0
30
1 µm
20
3.0 30
2.0 1 µm
1.0
1 µm
2.0 1 µm
20
0.0
1.0 0.0
Fig. 3. Raman map of the graphene films grown on Cu(111) single crystal surface measured with 1 μm mesh for selected five areas of 20 μm × 20 μm using a 100× objective lens. (a–e) Raman maps of the intensity of D peak (ID) and the 2D to G peak intensity ratio (I2D/IG). (f) Typical two Raman spectra measured from the white and blue areas in (c).
maps of the intensity of D peak (ID) and the ratio I2D/IG. Fig. 3(f) shows typical Raman spectra observed from the white and the dark blue area in the Raman map of D peak intensity together with amorphous carbon which produces broad G and D peaks with a very weak 2D intensity [9]. It is suggested that amorphous carbon is formed by the reaction of residual carbon in the cooling process. This area, however, is less than 1%, and may originate from defects of Cu film. In Fig. 3(b), (d) and (e), the ratios I2D/IG are more than one at almost all measurement points. The disorder-induced D peaks are not observed in these three areas. In Fig. 3(a) and (c), the ratios I2D/IG are more than one over almost whole areas except several points identified by the arrows, where small amount of amorphous carbon are observed in graphene layers in Raman spectra. Fig. 4(a) shows the Raman map observed for the area of 150 μm × 150 μm with a mesh of 1 μm (22801 points) at the center of the sample. The ratios I2D/IG are more than one at 99% of the data
a
points, which indicates that almost whole area of the sample surface is covered with SLG or FLG. Fig. 4(b) shows the Raman map of 10 mm × 10 mm with a mesh of 200 μm, which covers the whole sample surface. Although some damages are observed at the edges of the substrate the Raman signals from SLG or FLG are confirmed at 97% of all data points, which indicate that SLG or FLG was deposited over whole Cu(111) substrate surface. These results prove that the Cu(111) single crystal surface is useful to synthesize SLG or FLG with high uniformity and high quality. 4. Conclusion In this study the advantageous crystallographic orientation of Cu surface for SLG or FLG synthesis by using thermal chemical vapor deposition is examined for the first time by EBSD pattern and Raman mapping. It is found that Cu(111) predominates over (110) and (100)
b
I2D/IG
I2D/IG
5.0
5.0
4.0
4.0
3.0
3.0
2.0
2.0
1.0 10 µm
1.0 500 µm
0.0
0.0
Fig. 4. Raman map of the 2D to G peak intensity ratio (I2D/IG) measured with (a) 1 μm mesh for an area of 150 μm × 150 μm and (b) 200 μm mesh over whole substrate surface of 10 mm × 10 mm.
M. Ishihara et al. / Materials Letters 65 (2011) 2864–2867
for SLG or FLG synthesis. To confirm this result we examine the synthesis of SLG or FLG on Cu(111) single crystal film surfaces which are epitaxially grown on Al2O3(0001) substrates with the step-andterrace structure. We confirmed the high quality and high uniformity SLG or FLG formation by Raman mapping over more than 97% of the substrate surface area of 10 mm × 10 mm. Acknowledgment The authors thank Naobumi Saito and Yutaka Maruyama for their assistances with EBSD and Raman spectroscopy, respectively.
2867
References [1] [2] [3] [4] [5] [6]
Reina A, Jia X, Ho J, Nezich D, Son H, Bulovic V, et al. Nano Lett 2009;9:30–5. Li X, Cai X, An J, Kim S, Nah J, Yang D, et al. Science 2009;324:1312–4. Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, et al. Nature 2009;457:706–10. Li X, Zhu Y, Cai W, Borysiak M, Han B, Chen D, et al. Nano Let 2009;9:4359–63. Gao L, Guest JR, Guisinger NP. Nano Lett 2010;10:3512–6. Reddy KM, Gledhill AD, Chen C-H, Drexler JM, Padture NP. App Phys Lett 2011;98: 113117. [7] Yoshimoto M, Maeda T, Ohnishi T, Koinuma H, Ishiyama O, Shinohara M, et al. Appl Phys Lett 1995;67:2615–7. [8] Ismach A, Druzgalski C, Penwell S, Schwartzberg S, Zheng M, Javey A, et al. Nano Lett 2010;10:1542–8. [9] Knight DS, White WB. J Mater Res 1989;4:385–93.