Continuous Growth of Highly Reproducible Single-Layer Graphene

Feb 8, 2019 - Pradeep Kumar Kashyap†‡ , Indu Sharma† , and Bipin Kumar Gupta*†. †Photonic Materials Metrology Sub Division, Advanced Materia...
2 downloads 0 Views 5MB Size
Download PDF
This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

Article Cite This: ACS Omega 2019, 4, 2893−2901

http://pubs.acs.org/journal/acsodf

Continuous Growth of Highly Reproducible Single-Layer Graphene Deposition on Cu Foil by Indigenously Developed LPCVD Setup Pradeep Kumar Kashyap,†,‡ Indu Sharma,† and Bipin Kumar Gupta*,† †

Photonic Materials Metrology Sub Division, Advanced Materials and Devices Metrology Division and ‡Academy of Scientific and Innovative Research (AcSIR), CSIR-National Physical Laboratory Campus, Dr. K. S. Krishnan Road, New Delhi 110012, India

ACS Omega 2019.4:2893-2901. Downloaded from pubs.acs.org by 5.101.222.25 on 02/11/19. For personal use only.

S Supporting Information *

ABSTRACT: Continuous growth of high-quality single-layer graphene (SLG) is highly desirable in several electronic and optoelectronic applications. To fulfill such requirements, we proposed a low-cost, highly reproducible high-quality SLG synthesized by indigenously developed low-pressure chemical vapor deposition (LPCVD) setup. The quality of SLG is examined by Raman spectroscopy, where we have probed the I2D/IG ratio for continuous 30 runs to assess the reproducibility and quality of single-layer using proposed indigenous LPCVD setup for device fabrication. The highest I2D/IG ratio of SLG (5.82) was found with full width at half maximum values of 2D peak and G peak of ∼30.10 cm−1 and ∼20.86 cm−1, respectively. Further, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy have been performed to study the quality of SLG. Thickness measurement of graphene with graphene grain size is calculated from atomic force microscopy studies, and the average grain size is found to be 1−3 μm. Moreover, I−V characteristics have also been investigated by the two-probe method to ensure the quality of SLG. The lowest resistance of the SLG (∼387 Ω) was found at room temperature. Thus, this new indigenously developed low-cost setup provides a novel alternative method to produce highly reproducible metrology-grade continuous SLG on Cu substrate for next-generation quantum devices.

■

applications.6 In spite of the short history of 2D materials, graphene has established a dynamic research area for new breakthrough in physics and novel potential industrial applications.7 Various techniques have been used so far to produce graphene on mass scale, for example, mechanical exfoliation, chemical exfoliation, thermal decomposition of silicon carbide, chemical vapor deposition (CVD), and electrochemical deposition technique.8−15 However, among these methods, CVD has been the most promising method to produce large-scale, high-quality graphene in an inexpensive and reproducible manner.16 Additionally, the major advantage of this method is that CVD-synthesized graphene may be transferred onto a desired arbitrary substrate with required dimension, which is a major shortcoming in mechanically exfoliated graphene sheets.17 There are two types of the CVD method: atmospheric-pressure CVD (APCVD) and lowpressure CVD (LPCVD). LPCVD is more advantageous than the APCVD method to achieve continuous growth on Cu foils substrate for high-quality single-layer graphene (SLG).18,19 As the mass transport velocity and the velocity of the reaction on the surface are comparable, APCVD is highly complicated due to different kinetics. As a result, an inhomogeneous graphene domain could grow on Cu substrate,

INTRODUCTION In the last few years, two-dimensional (2D) materials have been the center of attraction for all scientific communities worldwide due to their exceptional optical, chemical, physical, and structural properties. The strategic synthesis and dimensions of a 2D material control its characteristic properties to a large extent and the properties may be easily tailored according to the desired applications.1−3 The last few years have witnessed many breakthroughs in 2D materials, especially in graphene research, owing to their significant advancement in mass-scale production in a reproducible manner for quantum devices to address practical applications.4 Graphene is derived from exotic carbon forms having hexagonal lattice of monolayer sp2-hybridized carbon atoms and is a semimetal in nature, where charge carriers behave like Dirac fermions.5 Moreover, graphene exhibits outstanding electronic properties, for example, high chargecarrier mobility, ∼200 000 cm2 V−1 s−1; tunable band gap, ca. 0−2.5 eV; ballistic transport; and room-temperature quantum Hall effect. In addition to these fascinating properties, a very large theoretical specific surface area, ∼2630 m2 g−1, and the highest surface area-to-volume ratio among the known 2D layered materials make it a potential material for application in many quantum and optoelectronic devices. Furthermore, graphene has very small Johnson noise due to its high conductivity and transport properties (νF = 106 m s−1), which are desirable for many quantum devices in practical © 2019 American Chemical Society

Received: December 6, 2018 Accepted: January 24, 2019 Published: February 8, 2019 2893

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

Figure 1. Schematic of low-cost indigenously developed CVD system for growth of SLG on copper foil.

Figure 2. Photographs of (a) graphene grown by thermal LPCVD on copper substrate of different sizes, (b) graphene film, supported by PMMA, floating on diluted solution of nitric acid, and (c) graphene film transferred on p-type doped silicon substrate with oxide layer of silicon with a thickness of 300 nm.

■

RESULTS AND DISCUSSION Graphene is grown by the thermal LPCVD technique with low-cost indigenously developed setup at CSIR-NPL, New Delhi, India. This LPCVD setup was designed with a new concept of control of gas flow during the growth and pretreatment of copper foil by using two calibrated rotameters instead of a mass flow meter for argon and methane, as well as only one mass flow meter for controlling hydrogen gas flow to control the growth of SLG. Although majority of companies are using the three mass flow meter concept for commercial use, we have developed the strategic design and concept of replacing two mass flow meters with a rotameter to reduce the cost of synthesis without compromising the quality of highly reproducible SLG. The actual dimensions of the setup (Figure 1) and details are available at the “know how technology transfer” website of CSIR-NPL, New Delhi, India.29 Methane is a well-known precursor gas used by many research groups30−35 for growth of SLG by the CVD method. Additionally, methane is a reliable and primary source of carbon; hence, it is less reactive due to the presence of a strong carbon bond (alkane) and its insusceptibility to undergo chemical reaction, which make it more suitable for SLG formation by dissociation at elevated temperature on copper substrate. Further, it is well established that methane in diluted form produces SLG and gives few layers of graphene in concentrated form.33 Therefore, the number of layers can be optimized by varying the methane-to-hydrogen ratio. However, several other carbon precursor gases were also used by many groups like acetylene (C2H2), ethylene (C2H4), propene

which deviates from our aim to deposit single-layer graphene. In contrast, in LPCVD, there is an inverse proportionality relationship between the diffusion of hydrocarbon gases and pressure. This means that velocity of mass transport will decrease, as a result of which the substrate will approach more closely to hydrocarbon gas and the deposited films could grow with better quality, scalability, and uniformity, which is desirable for single-layer growth.18 Many important growth parameters affect graphene growth on copper substrate, such as gas flow rates, annealing/growth temperature, growth pressure, and the ratio of carrier hydrogen to hydrocarbon gases used for growth.20−22 Majority of the several reports published in the area of SLG deposition by the LPCVD technique23−28 used the commercially available expensive LPCVD system to deposit high-quality SLG. The major focus of the present work is to develop an indigenous low-cost LPCVD system for high-quality metrological-grade SLG growth in a reproducible manner. In this study, we report metrological-grade, low-cost, highly reproducible, high-quality SLG synthesized by an indigenously developed LPCVD setup after several statistical runs. The quality of SLG is investigated by Raman and high-resolution transmission electron microscopy (HRTEM) techniques to ensure the quality of single-layer deposited graphene for 30 sequential runs with the same experimental parameters. Further, to explore the feasibility of single-layer deposited graphene sample for quantum devices, we have plotted I−V characteristics to ensure the quality of SLG transferred on Si/ SiO2 substrate. 2894

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

(C3H6),36,37 etc., but the layer formation is difficult to control in these cases. Several research groups have used various transition metals, such as cobalt (Co),38 nickel (Ni),38−40 iron (Fe),38,41 platinum (Pt),38,42,43 and copper (Cu),38−40 as catalyst for growing high-quality graphene. However, Cu has been widely used as a catalyst for the growth of SLG due to the lowest affinity of carbon toward copper because it does not form any carbide phase and has the lowest carbon solubility compared to other transition metals (0.001−0.008 wt % at 1084 °C for copper, 0.6 wt % for nickel at ∼1326 °C, and 0.9 wt % for cobalt at ∼1320 °C).38 The low reactivity of copper with carbon is due to the fact that the former has a filled 3d electron shell {[Ar] 3d104s1} with a highly stable configuration, along with the half-filled 3d5, due to the symmetrical electron distribution, which lowers the reciprocal repulsion. Because of this, copper makes only soft bonds with carbon atoms through charge transfer from the π orbitals in the sp2-hybridized carbon to the empty 4s states of copper. Therefore, this unique combination of low affinity between carbon and Cu and ability to make intermediate soft bonds with carbon has made Cu a desired growth catalyst for graphitic carbon formations.39 Hence, copper is a more appropriate and versatile transition metal for use as catalyst in CVD graphene synthesis. Figure 2a shows the image of copper foils of different sizes after graphene growth by thermal LPCVD, while Figure 2b shows poly(methyl methacrylate) (PMMA)-coated graphene floating on the surface of etching solution during transfer and Figure 2c exhibits after transfer on p-type doped Si with 300 nm thick SiO2 layer, respectively. After successful transfer of graphene, it is further characterized by different characterization tools like optical microscopy, Raman spectroscopy, TEM/HRTEM, Xray photoemission spectroscopy (XPS), and atomic force microscopy (AFM). Figure 3a shows the optical image of the as-received copper foil, which indicates clearly visible deep scratches and deep

growth of graphene. Under the present experimental conditions, we have successfully recrystallized copper grain to a size greater than 100 μm, as shown in the optical image of annealed copper foil (Figure 3b). Figure 3c depicts the optical image of copper foil after graphene deposition. A continuous sheet of graphene with lateral sizes same as the size of copper substrate was synthesized by indigenously developed thermal LPCVD technique. After growth, graphene was transferred from copper to Si/SiO2 substrate successfully by the wet chemical method. Figure 3d depicts the optical image of graphene after it is transferred to Si/SiO2 substrate, which shows a clean, continuous, and wrinkle-free transfer of graphene on substrate. Also to observe the effect of annealing time on the grain size of copper foil, i.e., the copper foil was annealed for different time durations (1−40 min) with 5 min intervals. It was observed that at different annealing times, grain size of more than 100 μm was easily achieved, as shown in Figure S1 (Supporting Information). A number of experiments have been performed to grow CVD graphene by using our indigenously developed LPCVD system to inspect the quality and reproducibility of highquality SLG and further characterize these samples using Raman spectroscopy. Raman spectroscopy is a noninvasive technique to investigate the thickness (number of layers) and quality of LPCVD-grown graphene. Figure 4a,b shows the Raman spectrum of graphene on Cu foil and on Si/SiO2 substrate, respectively. The disorder-induced Raman D peak position at ∼1345.90 cm−1 is weak, which clearly signifies the quality of graphene. The main G band, which is the first-order Raman band, in graphene appears at ∼1583.12 cm−1, whereas the 2D peak appears at ∼2683.32 cm−1. The G band is due to in-plane doubly degenerate sp2 carbon−carbon bond-stretching mode, which is attributed to the E 2g irreducible representation. This G band exists for every sp2 carbon hybridized system, for example, graphite, amorphous carbon, and carbon nanotubes. But the line shape of the G band differs on the basis of the quality of the sample. The second-order Raman 2D or G′ peak results from the in-plane breathing mode of the hexagonal rings of carbon atoms. 2D or G′ peak is the strongest peak in graphene, which is attributed to the symmetric irreducible representation A′1 at the K or K′ point in the first Brillouin zone. The 2D peak intensity is found to be more than twice compared to the intensity of the G peak (the highest being I2D/IG ∼ 5.82 as shown in Table 1) for most of the area of the graphene sample, indicating overall SLG growth. The lowest ratio of intensities of defect D peak and G peaks (ID/IG), i.e., ∼0.01 as shown in Table 1, indicates the high quality of graphene with negligible defects. The highest I2D/IG of ∼5.82 was obtained with the full width at half maximum (FWHM) values of 2D and G peaks in the Raman spectrum of graphene on Si/SiO2 of around 30.10 cm−1and 20.86 cm−1, respectively, which is also in favor of SLG growth. Raman spectroscopy was performed on all of the 30 samples grown in different statistical runs of LPCVD, and it was found that in every growth process, high-quality SLG with minimum defects was grown, as shown in Figure S2 (Supporting Information). Table 1 shows the FWHM values and ratios of the intensities of 2D and G peaks of LPCVD-grown graphene. The narrow FWHM of 2D peaks clearly signifies that LPCVDgrown graphene was single-layer and of high crystal quality. Further, the ratios of intensities, I2D/IG and ID/IG, clearly indicate that graphene was of high-quality single-layer and with

Figure 3. Optical images of (a) copper foil without graphene deposition, (b) copper foil after annealing, (c) Cu foil after graphene growth, and (d) graphene transferred on Si/SiO2 substrate.

trenches on the rough Cu foil due to the rolling process, while Figure 3b depicts the optical image of copper foil after annealing at 950 °C. It has been observed that annealing copper foil in an inert atmosphere of hydrogen (H2) and argon (Ar) gases for 15 min produces a desired smooth surface for 2895

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

Figure 4. Raman spectra of graphene on (a) Cu foil and (b) Si/SiO2 substrate (sample A17).

The highest calculated carrier mobility (μ) of CVD-grown graphene is approximately 5797.69 cm2 V−1 s−1 with an FWHM of 2D peak of around ∼30.10 cm−1 after transferred on Si/SiO2. Table 2 clearly emphasizes the comparative study based on Raman spectroscopy to confirm the quality of SLG between

Table 1. FWHM of 2D and G Peaks, Ratios of Intensities of 2D and D Peaks with Respect to G Peaks, and Calculated Values of Mobility by Using Raman Spectrum of CVD Graphene Grown in Different Experimentsa s. no. A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30

fit FWHM

fit FWHM

2D (cm−1)

G (cm−1)

38.73 37.66 42.75 36.38 44.88 38.89 36.55 40.46 39.15 36.18 37.63 35.13 35.95 34.52 33.76 37.35 30.10 34.96 33.07 40.17 37.38 38.96 35.61 32.69 33.47 32.71 37.35 37.04 33.62 31.32

20.92 22.53 28.63 23.87 27.14 23.21 28.62 24.99 23.80 22.51 18.85 14.16 16.84 18.04 25.46 23.25 20.86 22.60 21.23 24.59 22.28 23.91 26.49 24.72 20.32 21.23 20.51 27.05 22.23 12.21

I2D/IG

ID/IG

mobility μ (cm2 V−1 s−1)

2.67 2.40 2.58 3.68 3.07 3.28 3.72 2.44 2.49 3.25 2.46 2.33 2.45 3.82 4.70 3.03 5.82 4.27 4.42 3.33 2.68 2.53 3.74 5.06 3.34 4.68 2.57 3.46 4.32 2.96

0.19 0.19 0.25 0.16 0.26 0.11 0.14 0.18 0.31 0.15 0.02 0.01 0.01 0.22 0.12 0.24 0.14 0.24 0.06 0.21 0.03 0.31 0.04 0.02 0.28 0.46 0.13 0.10 0.02 0.01

2130.14 2410.64 1336.00 2796.63 1043.35 2091.58 2741.95 1742.04 2027.28 2863.80 2418.30 3232.77 2940.37 3469.49 3789.95 2499.81 5797.69 3298.24 4105.63 1803.00 2490.61 2074.68 3057.28 4291.11 3920.01 4281.93 2498.92 2590.39 3850.85 5028.81

Table 2. Comparative Study on Quality of Graphene Produced in the Present Work and Previously Reported Works I2D/IG

2DFWHM (cm−1)

refs

Li, X. et al./2009 Bhaviripudi, S. et al./2010 Gao, L. et al./2010 Losurdo, M. et al./2011 Li, Z.; Wang, Y. et al./2013 Woo, Y. S. et al./2018 Pham, T. T. et al./2019 Fan, X. et al./2019 our work

2 2−5 2 2 3.7 >2 1.8 to >2 1.5 5.82

∼33 ∼35 ∼36 ∼49 35.8 ca. 37−40 ca. 30−35

44 45 46 47 48 49 50 51

∼30.10

the present work and previously reported published papers.44−51 Table 2 clearly reflects that the synthesized SLG in our study is of high quality. LPCVD-grown graphene had been transferred onto holey carbon TEM grid for analysis of microstructural morphology, crystallinity, and the number of layers of LPCVD-grown graphene by using TEM techniques. Figure 5a shows the TEM image of graphene, which shows folding of graphene layers on the TEM grid. To investigate the number of graphene layers, HRTEM of graphene has been performed on the TEM grid. Figure 5b shows the HRTEM image of graphene on the grid. The HRTEM image shows that the graphene grown by thermal LPCVD system is of single layer. Figure 5c shows the selected area electron diffraction (SAED) pattern with 6-fold symmetry structure of graphene, which reveals the crystalline nature of SLG. We can deduce that the LPCVD-grown graphene film is predominantly SLG. Figure S3 shows the X-ray photoemission spectroscopy (XPS) image of graphene grown by thermal LPCVD on copper foil for different elements, carbon and copper. Figure S3a shows the survey scan spectra and Figure S3b−d shows the spectra for C 1s, O 1s, Cu 2p3/2, and Cu 2p1/2, respectively. In Figure S3b, the peak at 284.6 eV corresponds to the sp2 component of C−C bonding in graphene. In Figure S3c, peaks at 530.2 and 531.8 eV correspond to binding energies of Cu2O

a Positions and intensities of 2D, G*, G, and D peaks are presented in Tables S1 and S2 (Supporting Information).

lower defect values. Raman studies also give mobility of charge carriers in graphene using an empirical formula between carrier mobility and FWHM of 2D peak shown in the Raman spectrum of CVD graphene. The empirical formula of mobility is as follows ln(μ) = 12.157 − 0.116 × (FWHM of 2D peak)

authors/publication years

(1) 2896

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

Figure 5. (a) TEM image of graphene transferred onto TEM grid (b) HRTEM image of graphene transferred onto TEM grid showing SLG, and (c) SAED pattern of SLG.

Figure 6. (a) Raman spectrum of SLG transferred onto Si/SiO2 substrate with gold contacts (sample A17) and (b) I−V characteristics of graphene transferred onto Si/SiO2 substrate with gold contacts.

and ID/IG ratios (∼5.82 and ∼0.14, respectively) clearly indicate that quality of graphene was maintained with lower defects even after device fabrication. As shown in Figure 6b, the typical linear behavior of current and voltage curves reveals that the resistance of SLG is 387 Ω, which indicates high conductivity of thermal LPCVD-grown graphene. The inset in Figure 6b shows the optical images of device used for current− voltage measurements. The black circle shows the area where the I−V measurement has been performed. The width of electrode and the distance between two electrodes were both 20 μm.

and oxygen−hydrogen related bond. Cu2O is known to form between CVD-grown graphene and copper due to oxygen intercalation after the graphene/Cu sample is removed from vacuum post growth and exposed to air. Figure S3d shows the XPS images of copper substrate after growth of graphene and binding energies at 932.6 and 952.4 eV corresponding to Cu 2p3/2 and Cu 2p1/2. For thickness measurement, a torn part of graphene layer has been selected, as shown in Figure S4a,b, and the measured thickness of graphene was found to be 3.93 nm. The thickness of graphene in AFM measurements is different from the precise thickness of graphene (0.35 nm) due to molecule adsorption between the surface of Si/SiO2 substrate and graphene layer in addition to AFM instrument offset. Figure S5 shows the AFM image of CVD-grown graphene with grain boundaries depicted by yellow dotted lines. We can observe in Figure S5 that the average grain size lies in the range of ca. 1−3 μm. Indigenously developed CVD setup has a zone length of 6 in.; hence, the maximum size of continuous graphene synthesized in this indigenously developed CVD is around 4.0 in × 2.0 in. For device application of synthesized graphene, I−V measurement is the essential characteristic to determine the quality and electronic properties of graphene. Hence, I−V measurement of SLG has been performed on Si/SiO2 substrate with electrodes (Au/Ti = 90/10 nm). A two-probe station is used to investigate the electronic properties of graphene at room temperature. As shown in Figure 6a prior to the I−V measurements, the graphene on device was further characterized by Raman spectroscopy, which clearly shows that there is no damage of graphene after device fabrication. The I2D/IG

■

CONCLUSIONS In summary, we have successfully synthesized highly reproducible SLG using indigenously developed LPCVD setup at low cost. The quality of the synthesized SLG was confirmed through the standard Raman spectroscopy method. The obtained Raman results clearly demonstrate that the as grown samples exhibit high-quality SLG with I2D/IG > 2 for continuous 30 sequential runs. Moreover, the highest I2D/IG ratio (5.82) of SLG was found with FWHM values of 2D and G peaks of 30.10 cm−1 and 20.86 cm−1, respectively. Furthermore, the HRTEM result also evidenced that the synthesized graphene is of single layer with good quality. The XPS result also shows that the synthesized graphene has good quality. Additionally, the AFM result ensures the continuous growth of SLG with average grain size of ca. 1−3 μm. The obtained I−V result shows that the lowest resistance of SLG is ∼387 Ω. Hence, high-quality SLG synthesized by using new indigenously developed low-cost CVD setup would be an 2897

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

Figure 7. Temperature profile of preannealing, annealing, and growth of graphene.

Figure 8. Different steps involved in the transfer of graphene by the wet chemical method.

two calibrated rotameters instead of MFCs for controlling the flow of CH4 and Ar gases. The copper foil was annealed for 15 min at 950 °C in the presence of hydrogen (50 sccm) and argon gases by maintaining a pressure ratio PH2/PAr of 7:1, and total pressure during annealing was maintained below ∼16 Torr. After annealing, growth was performed by introducing methane and hydrogen into the reactor with hydrogen flow at 298 sccm, and a pressure ratio (PH2/PCH4) of 4:1 was maintained by injection of methane. During growth, flow of argon gas is stopped, the total pressure of hydrogen and methane gases inside the reactor was below 50 Torr, and growth was performed for 10 min. After growth, the system was cooled in the presence of hydrogen and argon in the pressure ratio as maintained during the preannealing process, and the temperature profile of all of the processing steps, including preannealing, annealing, growth, and cooling, is shown in Figure 7. Graphene-deposited copper foil was taken

ultimate choice to industries for using graphene in new emerging quantum devices.

■

EXPERIMENTAL SECTION Thermal LPCVD Growth of SLG on Cu Substrate. A quartz tube of ID ∼ 61 mm, OD ∼ 65 mm, and length ∼ 120 cm was placed in a horizontal single-zone split furnace for establishing a low-cost thermal LPCVD system split furnace (Figure 1). After cleaning of quartz tube, a copper foil (Alfa Aesar, 99.999% metal basis, 25 μm thick) has been placed on the alumina boat at the center of furnace. To control the pressure inside the quartz tube, there is a controlling valve attached with pressure gauge on the other end of the quartz tube, which is connected to a rotary pump, and pressure was maintained at 0.1−1 torr by using a pressure-controlling valve. Flow of gases (H2, CH4, and Ar) was controlled by using a mass flow controller (MFC) and rotameters. The cost of LPCVD was reduced approximately up to 1 million Indian rupees by using 2898

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

■

out of the reactor for further characterizations and device fabrication. Wet Chemical Method Using PMMA for Graphene Transfer on Si/SiO2 Substrate. Graphene grown on copper foil has been successfully transferred onto Si/SiO2 substrate by the wet chemical method using poly(methyl methacrylate) (PMMA, MicroChem 495, PMMA A2). Figure 8 shows the stepwise schematic diagram for graphene transfer from copper foil to Si/SiO2. PMMA was spin-coated on graphene-covered Cu foil at 2500 rpm for 60 sec and baked at 170 °C for 1 min. After baking, the PMMA-coated graphene/copper foil was floated in diluted nitric acid solution for etching of copper foil. After etching, we scoop out the PMMA−graphene membrane on Si/SiO2 substrate and on holey carbon-coated TEM grid and further clean it with deionized water and isopropanol to remove acid content and to dry graphene, respectively. Several dip and lift processes in boiling acetone have been performed to remove the PMMA coating. Graphene on copper, holey carbon TEM grid, and Si/ SiO2 was further characterized by optical microscopy, Raman spectroscopy, TEM / HRTEM, and further I−V measurement was conducted on graphene transferred onto Si/SiO2 using the two-probe method with gold electrodes (Ti = 10 nm and Au = 90 nm) to measure the resistance of graphene. Characterization of Graphene. Raman analysis of graphene samples was performed to study the quality of graphene and the number of layers in graphene by using a Renishaw inVia Raman spectrometer-I by using 514.5 nm laser with a power of 5 mW with a 50× objective lens. The structural properties of graphene were investigated using highresolution transmission electron microscopy (model Tecnai G2 F30 STWIN) attached with a field emission gun. Electron diffraction patterns were used to analyze the crystalline nature of graphene. Electronic measurements were carried out using a Keithley 2634B source unit. Optical images were captured at different resolutions by using Olympus MX51. X-ray photoelectron spectroscopy (XPS) was performed to determine the chemical purity and elemental compositions of the assynthesized SLG, which was carried out in an ultra-highvacuum chamber equipped with a hemispherical electron energy analyzer (PerkinElmer, PHI1257) using nonmonochromatized Al Kα source (1486.6 eV) with a base pressure of 4 × 10−10 Torr at room temperature. The surface topography, grain size, and thickness of SLG were examined by atomic force microscopy (AFM) (model: 5500; Agilent Technologies). SLG was imaged in noncontact acoustic alternating current mode under ambient condition.

■

Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Bipin Kumar Gupta: 0000-0002-0176-0007 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the NPL director Dr. D. K. Aswal for his keen interest in this FTT mission-mode project on SLG and constant encouragement. They also thank Dr. Govind Gupta (CSIR-NPL, New Delhi) and Dr. Sarika Gupta (NII, New Delhi) for providing them their XPS and AFM lab facilities. They are grateful to Shweta Sharma (CSIR-NPL, New Delhi) for performing the Raman spectroscopy of the graphene samples and Dinesh Singh (CSIR-NPL, New Delhi) for carrying out TEM of graphene samples. P.K.K. and I.S. acknowledge Council of Scientific and Industrial Research for CSIR-SRF fellowship and CSIR-RA fellowship, respectively.

■

ABBREVIATIONS SLG, single-layer graphene; Cu, copper; MFC, mass flow controller; LPCVD, low-pressure chemical vapor deposition; APCVD, atmospheric-pressure chemical vapor deposition; 2D, two-dimensional; ID, inner diameter; OD, outer diameter

■

REFERENCES

(1) Geim, A. K.; Novoselov, K. S. The Rise of Graphene. Nat. Mater. 2007, 6, 183−191. (2) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D. A.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666−669. (3) Dwivedi, J.; Kumar, P.; Kedawat, G.; Gupta, B. K. New Emerging Rare-Earth Free Yellow Emitting 2D BCNO Nanophosphor for White Light Emitting Diodes. New J. Chem. 2015, 39, 5161−5170. (4) Novoselov, K. S.; Fal, V. I.; Colombo, K. L.; Gellert, P. R.; Schwab, M. G.; Kim, K. Nature 2012, 490, 192−200. (5) Luo, B.; Chen, B.; Wang, A.; Geng, D.; Xu, J.; Wang, H.; Zhang, Z.; Peng, L.; Xu, Z.; Yu, G. Chemical Vapor Deposition of Bilayer Graphene with Layer-Resolved Growth through Dynamic Pressure Control. J. Mater. Chem. C 2016, 4, 7464−7471. (6) Kumar, N.; Srivastava, A. K.; Patel, H. S.; Gupta, B. K.; Varma, G. D. Facile Synthesis of ZnO−Reduced Graphene Oxide Nanocomposites for NO2 Gas Sensing Applications. Eur. J. Inorg. Chem. 2015, 2015, 1912−1923. (7) Srivastava, A.; Galande, C.; Ci, L.; Song, L.; Rai, C.; Jariwala, D.; Kelly, K. F.; Ajayan, P. M. Novel Liquid Precursor-Based Facile Synthesis of Large-Area Continuous, Single, and Few-Layer Graphene Films. Chem. Mater. 2010, 22, 3457−3461. (8) Halim, U.; Zheng, C. R.; Chen, Y.; Lin, Z.; Jiang, S.; Cheng, R.; Huang, Y.; Duan, X. A Rational Design of Cosolvent Exfoliation of Layered Materials by Directly Probing Liquid−Solid Interaction. Nat. Commun. 2013, 4, No. 2213. (9) Lin, W.; Tian, B.; Zhuang, P.; Yin, J.; Zhang, C.; Li, Q.; Shih, T. M.; Cai, W. Graphene-Based Fluorescence-Quenching-Related Fermi Level Elevation and Electron-Concentration Surge. Nano Lett. 2016, 16, 5737−5741. (10) Parvez, K.; Wu, Z. S.; Li, R.; Liu, X.; Graf, R.; Feng, X.; Müllen, K. Exfoliation of Graphite into Graphene in Aqueous Solutions of Inorganic Salts. J. Am. Chem. Soc. 2014, 136, 6083−6091. (11) Singh, V.; Deshmukh, M. M. Nanoelectromechanics using Graphene. Curr. Sci. 2014, 437−446.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b03432. Complementary optical images, Raman spectra; positions of 2D, G*, G, and D peaks in Raman spectra (Table S1); intensities of 2D, G*, G, and D peaks in Raman spectra (Table S2), XPS survey scan; ratios of elements present in thermal LPCVD SLG grown on copper foil (Table S3); and thickness measurement of SLG using AFM and AFM topography (PDF) 2899

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

(12) Janssen, T. J.; Williams, J. M.; Fletcher, N. E.; Goebel, R.; Tzalenchuk, A.; Yakimova, R.; Lara-Avila, S.; Kubatkin, S.; Fal’ko, V. I. Precision Comparison of the Quantum Hall Effect in Graphene and Gallium Arsenide. Metrologia 2012, 49, 294−306. (13) Shen, T.; Wu, W.; Yu, Q.; Richter, C. A.; Elmquist, R.; Newell, D.; Chen, Y. P. Quantum Hall Effect on Centimeter Scale Chemical Vapor Deposited Graphene Films. Appl. Phys. Lett. 2011, 99, No. 232110. (14) Ribeiro-Palau, R.; Lafont, F.; Brun-Picard, J.; Kazazis, D.; Michon, A.; Cheynis, F.; Couturaud, O.; Consejo, C.; Jouault, B.; Poirier, W.; Schopfer, F. Nat. Nanotechnol. 2015, 10, 965−972. (15) Tzalenchuk, A.; Lara-Avila, S.; Kalaboukhov, A.; Paolillo, S.; Syvajarvi, M.; Yakimova, R.; Kazakova, O.; Janssen, T. J. B. M.; Fal’ko, V.; Kubatkin, S. Nat. Nanotechnol. 2010, 5, 186−189. (16) Chung, T. F.; Shen, T.; Cao, H.; Jauregui, L. A.; Wu, W.; Yu, Q.; Newell, D.; Chen, Y. P. Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils. Int. J. Mod. Phys. B 2013, 27, No. 1341002. (17) Fan, Y.; He, K.; Tan, H.; Speller, S.; Warner, J. H. Crack-free Growth and Transfer of Continuous Monolayer Graphene Grown on Melted Copper. Chem. Mater. 2014, 26, 4984−4991. (18) Yang, F.; Liu, Y.; Wu, W.; Chen, W.; Gao, L.; Sun, J. A Facile Method to Observe Graphene Growth on Copper Foil. Nanotechnology 2012, 23, No. 475705. (19) Wu, T.; Ding, G.; Shen, H.; Wang, H.; Sun, L.; Jiang, D.; Xie, X.; Jiang, M. Triggering the Continuous Growth of Graphene Toward Millimeter-Sized Grains. Adv. Funct. Mater. 2013, 23, 198−203. (20) Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Role of Hydrogen in Chemical Vapor Deposition Growth of Large Single-Crystal Graphene. ACS Nano 2011, 5, 6069− 6076. (21) Liu, L.; Zhou, H.; Cheng, R.; Yu, W. J.; Liu, Y.; Chen, Y.; Shaw, J.; Zhong, X.; Huang, Y.; Duan, X. High-yield Chemical Vapor Deposition Growth of High-Quality Large-Area AB-Stacked Bilayer Graphene. ACS Nano 2012, 6, 8241−8249. (22) Li, X.; Magnuson, C. W.; Venugopal, A.; Tromp, R. M.; Hannon, J. B.; Vogel, E. M.; Colombo, L.; Ruoff, R. S. Large-Area Graphene Single Crystals Grown by Low-Pressure Chemical Vapor Deposition of Methane on Copper. J. Am. Chem. Soc. 2011, 133, 2816−2819. (23) Li, X.; Magnuson, C. W.; Venugopal, A.; An, J.; Suk, J. W.; Han, B.; Borysiak, M.; Cai, W.; Velamakanni, A.; Zhu, Y.; Fu, L.; et al. Graphene Films with Large Domain Size by a Two-Step Chemical Vapor Deposition Process. Nano Lett. 2010, 10, 4328−4334. (24) Kamali, A. R. Eco-friendly Production of High Quality Low Cost Graphene and its Application in Lithium ion Batteries. Green Chem. 2016, 18, 1952−1964. (25) Jafari, A.; Alipour, R.; Ghoranneviss, M. The Effects of Growth Time on the Quality of Graphene Synthesized by LPCVD. Bull. Mater. Sci. 2015, 38, 707−710. (26) Zhu, S.; Li, Q.; Chen, Q.; Liu, W.; Li, X.; Zhang, J.; Wang, Q.; Wang, X.; Liu, H. Cu Hill and Graphene Grain Evolution in the Synthesis of Millimeter-Sized Single Crystal Graphene during Low Pressure Chemical Vapor Deposition. RSC Adv. 2014, 4, 32941− 32945. (27) Srivastava, A.; Galande, C.; Ci, L.; Song, L.; Rai, C.; Jariwala, D.; Kelly, K. F.; Ajayan, P. M. Novel Liquid Precursor-Based Facile Synthesis of Large-Area Continuous, Single, and Few-Layer Graphene Films. Chem. Mater. 2010, 22, 3457−3461. (28) Zhang, M.; Huang, B. C.; Wang, Y.; Woo, J. C. Selective LPCVD Growth of Graphene on Patterned Copper and its Growth Mechanism. Appl. Phys. Lett. 2016, 109, No. 253109. (29) http://www.nplindia.in/iglpdf/thermal_chemical_vapour_ deposition_(CVD).pdf. (30) Li, X.; Magnuson, C. W.; Venugopal, A.; Tromp, R. M.; Hannon, J. B.; Vogel, E. M.; Colombo, L.; Ruoff, R. S. Large-area graphene single crystals grown by low-pressure chemical vapor deposition of methane on copper. J. Am. Chem. Soc. 2011, 133, 2816− 2819.

(31) Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene. ACS Nano 2011, 5, 6069−6076. (32) Chen, Z.; Ren, W.; Liu, B.; Gao, L.; Pei, S.; Wu, Z. S.; Zhao, J.; Cheng, H. M. Bulk growth of mono-to few-layer graphene on nickel particles by chemical vapor deposition from methane. Carbon 2010, 48, 3543−3550. (33) De Arco, L. G.; Zhang, Y.; Kumar, A.; Zhou, C. Synthesis, transfer, and devices of single-and few-layer graphene by chemical vapor deposition. IEEE Trans. Nanotechnol. 2009, 8, 135−138. (34) Reina, A.; Thiele, S.; Jia, X.; Bhaviripudi, S.; Dresselhaus, M. S.; Schaefer, J. A.; Kong, J. Growth of large-area single-and bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces. Nano Res. 2009, 2, 509−516. (35) Yang, M.; Sasaki, S.; Suzuki, K.; Miura, H. Control of the nucleation and quality of graphene grown by low pressure chemical vapor deposition with acetylene. Appl. Surf. Sci. 2016, 366, 219−226. (36) Trinsoutrot, P.; Vergnes, H.; Caussat, B. Three dimensional graphene synthesis on nickel foam by chemical vapor deposition from ethylene. Mater. Sci. Eng., B 2014, 179, 12−16. (37) Gotterbarm, K.; Zhao, W.; Hofert, O.; Gleichweit, C.; Papp, C.; Steinrück, H. P. Growth and oxidation of graphene on Rh(111). Phys. Chem. Chem. Phys. 2013, 15, 19625. (38) Mattevi, C.; Kim, H.; Chhowalla, M. A review of chemical vapour deposition of graphene on copper. J. Mater. Chem. 2011, 21, 3324−3334. (39) Li, X.; Cai, W.; Colombo, L.; Ruoff, R. S. Evolution of graphene growth on Ni and Cu by carbon isotope labeling. Nano Lett. 2009, 9, 4268−4272. (40) Amini, S.; Garay, J.; Liu, G.; Balandin, A. A.; Abbaschian, R. Growth of large-area graphene films from metal-carbon melts. J. Appl. Phys. 2010, 108, No. 094321. (41) Xue, Y.; Wu, B.; Guo, Y.; Huang, L.; Jiang, L.; Chen, J.; Geng, D.; Liu, Y.; Hu, W.; Yu, G. Synthesis of large-area, few-layer graphene on iron foil by chemical vapor deposition. Nano Res. 2011, 4, 1208− 1214. (42) Gao, J. H.; Sagisaka, K.; Kitahara, M.; Xu, M. S.; Miyamoto, S.; Fujita, D. Graphene growth on a Pt (111) substrate by surface segregation and precipitation. Nanotechnology 2012, 23, No. 055704. (43) Choi, J. K.; Kwak, J.; Park, S. D.; Yun, H. D.; Kim, S. Y.; Jung, M.; Kim, S. Y.; Park, K.; Kang, S.; Kim, S. D.; Park, D. Y.; et al. Growth of wrinkle-free graphene on texture-controlled platinum films and thermal-assisted transfer of large-scale patterned graphene. ACS Nano 2015, 9, 679−686. (44) Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.; Piner, R.; Velamakanni, A.; Jung, I.; Tutuc, E.; Banerjee, S. K.; et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 2009, 324, 1312−1314. (45) Bhaviripudi, S.; Jia, X.; Dresselhaus, M. S.; Kong, J. Role of kinetic factors in chemical vapor deposition synthesis of uniform large area graphene using copper catalyst. Nano Lett. 2010, 10, 4128−4133. (46) Gao, L.; Guest, J. R.; Guisinger, N. P. Epitaxial graphene on Cu (111). Nano Lett. 2010, 10, 3512−3516. (47) Losurdo, M.; Giangregorio, M. M.; Capezzuto, P.; Bruno, G. Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure. Phys. Chem. Chem. Phys. 2011, 13, 20836− 20843. (48) Li, Z.; Wang, Y.; Kozbial, A.; Shenoy, G.; Zhou, F.; McGinley, R.; Ireland, P.; Morganstein, B.; Kunkel, A.; Surwade, S. P.; Li, L.; Liu, H. Effect of airborne contaminants on the wettability of supported graphene and graphite. Nat. Mater. 2013, 12, 925. (49) Woo, Y. S.; Lee, D. W.; Kim, U. J. General Raman-based method for evaluating the carrier mobilities of chemical vapor deposited graphene. Carbon 2018, 132, 263−270. (50) Pham, T. T.; Huynh, T. H.; Do, Q. H.; Ngo, T. K. Optimum reproduction and characterization of graphene on copper foils by low pressure chemical vapor deposition. Mater. Chem. Phys. 2019, 224, 286−292. 2900

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901

ACS Omega

Article

(51) Fan, X.; Sun, J.; Guo, W.; Ke, X.; Yan, C.; Li, X.; Dong, Y.; Xiong, F.; Fu, Y.; Wang, L.; Deng, J.; Chen, X. Chemical vapor deposition of graphene on refractory metals: The attempt of growth at much higher temperature. Synth. Met. 2019, 247, 233−239.

2901

DOI: 10.1021/acsomega.8b03432 ACS Omega 2019, 4, 2893−2901