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Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor
Accepted Manuscript Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor André do Nascimento Barbosa, N.J.S. Figueroa, C.D. Mendoza, A.L. Pinto, F.L. Freire, Jr. PII:
S0254-0584(18)30696-5
DOI:
10.1016/j.matchemphys.2018.08.031
Reference:
MAC 20874
To appear in:
Materials Chemistry and Physics
Received Date: 22 May 2018 Revised Date:
7 August 2018
Accepted Date: 12 August 2018
Please cite this article as: André.do.Nascimento. Barbosa, N.J.S. Figueroa, C.D. Mendoza, A.L. Pinto, F.L. Freire Jr., Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor, Materials Chemistry and Physics (2018), doi: 10.1016/ j.matchemphys.2018.08.031. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor
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André do Nascimento Barbosa¹*, N. J. S. Figueroa¹ C. D. Mendoza¹, A. L. Pinto2, F. L. Freire Jr.¹
¹ Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225, 22451-900, Rio de Janeiro, RJ, Brazil.
Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, 22290-180, Rio de Janeiro, RJ, Brazil.
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*Corresponding author
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*[email protected]
ACCEPTED MANUSCRIPT Abstract We report single-layer graphene synthesis using high-carbon content N-Octane as precursor. Unlike methanol, ethanol and other liquid carbon precursors, N-Octane is oxygen free and its molecular structure is simply a common hydrocarbon. Optimal
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precursor pressure for synthesis was found to be at 5-20 mTorr range, as at higher partial pressures we have achieved bilayer and few-layer coverage of the copper substrates with {111} plane parallel to the surface, as revealed by Raman spectroscopy. We could lower
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the synthesis temperature down to 850 ºC and still obtained graphene layers with low concentration of defects. For the complete coverage of the substrates, we report shorter
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than usual synthesis time, of no more than 5 minutes. Characterization of graphene layers were performed using Raman scattering spectroscopy and mapping, UV-vis transmittance as well as atomic force microscopy, scanning tunneling microscopy and
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scanning tunneling spectroscopy.
Keywords: Graphene, N-Octane, CVD, synthesis temperature, Raman spectroscopy,
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scanning tunneling spectroscopy.
ACCEPTED MANUSCRIPT 1 Introduction
Graphene is a material that has properties of great technological interest [1]. Isolated for the first time in 2004 [2], its transport, sheet resistance and malleability properties are
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differentials that motivate basic research and product development [3]. Currently, several proof-of-concept devices are being tested, such as gas sensors, field effect transistors and, in the form of oxidized graphene, water purification membranes for several purposes [4-
produced is in the synthesis process of the material.
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6]. However, the big challenge of implementing graphene in devices that can be mass-
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There are several ways to obtain graphene [7- 9]. Mechanical exfoliation produces samples with quite small areas and low density of defects by simply exfoliating the top layers of a highly oriented graphite and transferring onto a SiO2 wafer or another desired target substrate. Chemical exfoliation results in graphene oxide (GO) that can be
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reduced generating highly defective graphene, called reduced grapheme oxide (RGO). This process is very useful for high volume production and applications that makes use of its defective nature such as water purification filters and sensors [10-11]. Silicon
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carbide (SiC) graphitization at high temperatures yields large single-crystals and of quality compared to that of mechanical exfoliation. However, because of significant
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compressive strain imposed by this method, it is not possible to transfer the graphene to other arbitrary target substrates. Chemical deposition in the vapor phase (CVD) is the most promising form for
large-scale applications, since it is a well-known process and it is easy to scale up to the industry. The first reports describing the synthesis of graphene by CVD were published in 2009 [12] on Ni substrates, where multi-layered polycrystalline graphene was obtained. After that, copper foils were used as substrate and polycrystalline monolayer
ACCEPTED MANUSCRIPT graphene covered almost the entire substrate [13]. The CVD method basically consists of inserting into a quartz tube reactor a catalytic substrate made of a thin copper or nickel foil. The system is then evacuated and followed by the release of H2 gas in the reactor, while the temperature is raised to around 1000 ºC to reduce the substrate. It is expected
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that the oxide layer on the surface of the substrate will be eliminated almost completely, and simultaneously the surface copper grains grows larger, orienting the surface mainly in the {111} direction [14]. After the reduction period, one introduces in the system gases
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or vapors of hydrocarbons, usually methane, to synthesize the graphene.
In a work comparing several precursors, it has been shown that the growth of
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graphene can be accomplished using even fumes of alcohols and heavier hydrocarbons [15]. Also, the growth at low temperatures using toluene and benzene was proposed [16, 17], but the toxicity of both precursors makes this method particularly dangerous and its large-scale use provides health risks. The use of heavier alkane-like hydrocarbons is an
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alternative, since its pyrolysis leads to the complete molecule breakdown, not leaving any toxic radicals such as furans, and the possibility of lowering temperatures becomes an important factor when thinking of the overall cost of the scalability of the process, since
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the growth apparatus are basically resistive.
Also, there are several reports in the literature where very large graphene samples
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were grown [18, 19, 20]. Although they represent today’s state of the art in the sense of graphene synthesis processes and average grain size, their nontrivial approach and farfrom-production scalability are still barriers that should be overcome. In the energy, time and costs point of view there’s need for more conservative approaches to known growth techniques. In this work, we report the growth of single-layer graphene using as a new carbon source, N-octane, in the expectation that as C-C bonds breaks at lower temperatures, it
ACCEPTED MANUSCRIPT could provide more carbon atoms for synthesis and subsequently lower synthesis times. We investigated the effect of the growth temperature, the partial pressure of the octane vapor, time of growth and preparation of the sample. Samples were characterized using Raman spectroscopy and Raman mapping, scanning tunneling microscopy (STM) and
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Scanning tunneling spectroscopy (STS) and UV-vis transmittance. We also characterized the copper foil by EBSD analysis, as the annealing process is crucial for the quality of the synthesized graphene sheets. We could lower the synthesis temperature of nearly defect
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free graphene down to 850 ºC. The complete coverage of the copper substrates was
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obtained of no more than 5 minutes.
2 Experimental
The copper foils (alpha Aesar, order number 46986, 99.8% purity) were cut into squares
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of about 2 cm2 and they underwent ultrasound bath immersed in acetone for five minutes and then went through the same process immersed in isopropyl alcohol. Each sample was dried using high-purity nitrogen gas. The samples were inserted inside of a quartz tube
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reactor, where, under hydrogen atmosphere, the system started to heat at 30 ºC/min rate up to 1050ºC. After reaching this temperature the copper foils were annealed for one
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hour prior to growth. We investigated the partial pressure of N-octane to have a complete coverage of the substrate in the range from 100 mTorr to 5 mTorr. Furthermore, under the condition of minimum partial precursor pressure, the synthesis was carried out at temperatures in the range from 1050 ºC to 750º C for five minutes. At each stage of the sample's growth, five samples were synthesized. The samples were transferred to a silicon dioxide wafer using the wet transfer method [21]. The graphene on the copper foil was covered with a sacrificial layer of dissolved polyurethane (PU) in tetrahydrofuran
ACCEPTED MANUSCRIPT (THF) by using a spin coater. The copper was chemically attacked and dissolved using an iron chloride (FeCl3) solution. Then, the floating sample was "fished" using the SiO2 wafer. The final step consisted of the removing the sacrificial layer of PU by a THF bath for 40 minutes under ambient conditions.
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Raman spectroscopy and mapping were performed using a Micro-Raman spectrometer (NT-MDT, NTEGRA Spectra) equipped with a CCD detector and a solidstate laser (wavelength of 473 nm). Care was taken to avoid damage of samples and
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several measurements were performed with different laser powers to discard the shift of the bands caused by laser-induced heating. Measurements were carried out using a 100x
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ocular, leading to a focal point of the order of 1 µm with an incident power of less than 0.2 mW. In addition, Raman mapping were performed using AFM-Piezoelectric stage supplied by NT-MDT. EBSD analyses were performed on a JEOL 7100FT Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction (EBSD)
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system from Oxford. Transmittance measurements were carried out using a Perkin Elmer spectrophotometer, model LAMBDA 950 UV/Vis between 400 and 800 nm spectral region. Finally, the samples were loaded into an Ultra High Vacuum (UHV, ~10-7 Pa)
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Omicron STM. The physical and electronic graphene structures were characterized by STM/STS. These measurements were performed at room temperature using home-made
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electrochemically etched W tips
3 Results and discussion
The crystallographic orientation of the surface of polycrystalline copper substrates, as well as the grain size is crucial for the quality of the synthesized graphene sheets [22]. EBSD measurements on as-received copper foils show that they had a typical
ACCEPTED MANUSCRIPT microstructure of a material that passed through a process of rolling and recrystallization. In fact, its texture is typical of heavily rolled and recrystallized copper, in which cube {001} <100> is the main texture component. There is also the {122} <212> component that originate from crystal twinning together with S {123} <634> component as seen in
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Fig. 1. Most of the surface of the sample submitted to thermal treatment at 1050 0C for one hour presented abnormal grain growth, as seen in Fig. 1, resulting in large grains close to {111} <110> orientation which is unusual for FCC structures. Apparently, the
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treatment induced the crystal twinned regions to grow thus making the surface to be oriented in the {111} direction, as it has lower energy according to the FCC Wulff plot.
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Along the borders of the foil, other centimeter size crystalline domains orientations were found with the original Cube orientation. The copper foils were used as substrates for the
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graphene growth after this process.
Fig. 1: (a) Band contrast map; (b) orientation map from the original copper foil without any annealing treatment; (c) inverse pole figure color reference triangle; (d) Band contrast map; (e) orientation map from the annealed copper foil.
Fig. 2: AFM
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micrographies of graphene flakes on Cu obtained by using N-Octane as
precursor with 950 °C growth temperature. (a) Represents the height contrast image
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where it is possible to observe the grain boundaries. (b) Is the Lateral force image where the grain boundaries are highlighted. (c) The average distribution of the grains. We have
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obtained a mean size of 6.24 ± 1.47 µm for 950 °C grown sample.
The contact mode atomic microscopy was performed. Fig 2a and Fig 2b shows the height and lateral force image where it is possible to observe the grain boundaries. By measuring the larger axis of each flake through open source Imaging software, we have an average grain size of 6.24 micrometers, as Fig 2c. As compared with it is found in the literature [23, 24, 25, 26].
ACCEPTED MANUSCRIPT Raman spectroscopy results obtained from samples not yet transferred from the copper foils are presented in Fig 3a. The spectra taken at different points at the sample surface were almost identical revealing the homogeneity of the samples. Their main features were the presence of the G-band at around 1580 cm-1 and the 2D-band at around
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2700 cm-1 on top of a luminescence background due to the oxidation of the copper surface. It was possible to observe that the 2D-band widens for samples that were synthesized with 50 mTorr and higher precursor partial pressures grown at 1050ºC for 5
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minutes, suggesting that vapor flows that correspond to partial pressures above a threshold value favors the formation of bilayer or few-layer graphene. Also, the
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relationship of bands intensities (I2D/IG) together with the full width at half maximum (FWHM) corroborates that the graphene synthesized in these conditions was compatible with that of bilayer graphene. In contrast, it was observed that for the growths where the partial pressure of the octane vapor is less than 30 mTorr, the substrate surface was
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covered by monolayer graphene. It was observed that the intensity ratio I2d/IG was higher than 2 and the FWHM of the 2D-band was less than 35 cm-1. Fig 3b shows Raman spectra obtained from samples grown at 5 mTorr during 5
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minutes at different temperatures. By synthesizing graphene in these conditions, we observed the appearance of the D-band, which is related to defects in the crystalline
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lattice of the graphene, for samples grown at temperatures as low as 850 oC. This spectral feature suggested that these defects could be due to the incomplete breakdown of the molecule or that the energy needed to change the state of sp³ hybridization to sp² was not enough to completely cover the surface of the substrate, analogous to what happens with methane molecules. For lower temperatures (750 oC) only amorphous carbon was produced (not shown in the figure).
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Fig 3: (a) The Raman spectra of the graphene grown on copper where we can observe the influence of partial pressure on the intensity and FWHM of the 2D-band for samples grown at 1050 oC for 5 minutes; (b) Raman spectra of graphene grown at different temperatures transferred to SiO2 (300nm)/Si wafers. The
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growth was carried out with 5 mTorr for 5 minutes and the samples I2D/IG ratios were 3.1, 2.9 and 2.7 for processing temperatures of 1050 ºC, 950 ºC and 850 ºC, respectively, while the FWHM of the 2D-band was around 36.4, 30,6 and 38,6 cm-1 respectively.
In Fig. 4 we present the Raman maps obtained from samples prepared at different
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growth temperatures after being transferred to SiO2 (300nm)/Si wafers substrates.
Fig. 4: Raman maps of transferred samples prepared at: (a) 850 ºC; (b) 950 ºC; (c) 1050 ºC; (d) Histogram of the FWHM of 2D-bands of samples grown at these temperatures.
ACCEPTED MANUSCRIPT The map obtained from the sample prepared at 1050 oC shown at Fig. 4c was the most homogeneous one with an average I2d/IG ratio of 2.2. Fig. 4b shows that the map obtained from the sample prepared at 950 oC was also quite homogeneous with average I2d/IG ratio of 2.3, while the map of the sample grown at 850 oC shown in Fig. 4a revealed
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the presence of regions with I2d/IG typical bilayer or even few-layers graphene coexisting with the dominant single-layer graphene. On the other hand, the histograms of FWHM of 2D-band shown in Fig. 4d were, within the standard deviation, independent on the
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processing temperature and with an average value around 42 cm-1.
Raman spectroscopy can also be used to estimate the doping level as well as the
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increase in graphene strain by analyzing the positions of the 2D- and G bands. Fig. 5 show the positions of the 2D band versus positions of the G band taken at different points across the surface of the sample grown at 950 oC, 5 mTorr and 5 minutes of processing. Following the procedure developed by [27,28], we can estimate the type of strain
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(uniaxial or biaxial) of the sample. Most of the experimental data for this growth condition are positioned in the region of neutrality. In this same analysis, the strain (ε)
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graphene.
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was of the compressive biaxial type in the range between -0.2% and- 0.4% for the film of
2760 -0.4%
2730 -0.2%
2700
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0.0%
2670 1560
ε=0
-0.4% -0.2%
1580 1600 1620 1640 -1 G peak position (cm )
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2D peak position (cm
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)
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Fig. 5: Plot of the 2D- vs. G-band positions for the graphene film. The lines indicate the E2D and EG
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relationship for strained undoped (dash-dotted line), uniaxial strain (dotted line), and unstrained p-doped (ε = 0, full line) graphene. The neutrality point (zero point) was taken from literature [28] and corresponds to the expected 2D- and G-band positions for suspended freestanding single-layer graphene.
Counting of the number of graphene layers through Raman spectroscopy is
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widely accepted as means of characterization [29, 30], nevertheless optical measurements may also be used for the determination of the number of graphene layers as graphene absorbs light in a linear fashion up to several numbers of layers. In Fig. 6 we compare the
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UV-vis transmittance results obtained from graphene samples grown at 950 ºC and 850
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ºC and transferred to silica substrates. The transmittance results were normalized by an uncoated silica glass substrate. The transmittance results obtained from the sample prepared at 1050 oC are almost identical to the one grown at 950 oC and, to make the figure clearer, is not shown. Graphene is known to absorb about 2.5% of light at the visible spectrum [31], and it is in good agreement with the result obtained for our pristine N-Octane single-layer graphene. UV-vis transmittance results showed clearly that our synthesis process yields monolayer graphene for processing temperatures of 1050 oC and 950 oC, since absorbance of around 2.7% was measured with wavelength of 550 nm, as
ACCEPTED MANUSCRIPT can be seen in Fig. 6. The slightly lower transmission value, 2.8% for the sample grown at 850oC was attributed to the absorbance in the few bilayer and few-layers small regions
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present in this sample. The UV-vis results, in both cases, confirmed the Raman results.
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Fig. 6: UV-vis transmittance as a function of the wavelength.
Fig. 7: Topographic images and STS spectrum of graphene. (a) and (b) shows STM images of graphene on
Cu taken in different regions of sample, where in (a) we can see the Moiré linear pattern, and the conditions were V = 25mV, I = 1,0nA. In Fig. 7b there is no Moiré pattern and the conditions were V = 250mV, I = 1.0nA. Fig. 7c shows Fourier Transform (FT) of the image in (b) and in Fig. 7d we have the
ACCEPTED MANUSCRIPT STS spectrum, (dI/dV) / (I/V), of the position marked at point (1) in the image (b), dotted line is EF and red arrow is ED (where EF – ED = - 0.17 V). Black scale bar in (a) is 2 nm and in (b) 1 nm.
Fig. 7 shows typical STM images obtained from the graphene layer on top of the Cu substrate. They clearly indicate the success of the growth of single-layer graphene by
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CVD with N-octane as precursor. These images were taken in different regions of the same sample grown at 950 oC at the pressure of 5 mTorr for 5 minutes. Fig. 7a shows the Moiré linear pattern originating from the lattice mismatch between graphene and Cu
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crystal lattice. Diverse periodicities for Moiré patterns were observed depending on the specific angles between the principal directions of graphene and Cu. Fig. 7b does not
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show that pattern. However, in Fig. 7c, the hexagonal symmetry of graphene is observed by means of the Fourier Transform of the image in (b).
Fig. 7d, shows the STS curve that was taken at point indicated by a blue dot in the STM image shown in Fig. 7b. This STS curve refers to the Local Density of States
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(LDOS) of graphene/Cu in Fig. 7b, where the Moiré patterns are absent. The Dirac point (ED) is shifted 170.0 meV from the Fermi level (EF). Ideally, the energy bands in the graphene form a so-called Dirac cone at the K point of the first Brillouin zone. In this K
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point, EF and ED are supposed to coincide for freestanding graphene. Nevertheless, in the
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case where the Fermi level is located above or below the Dirac point, the graphene is nor p-type doped, respectively. In our measurement, EF was 170.0 meV above ED, which corresponds to an electron concentration of ~ 2.13 x1012 cm-2, i.e., the graphene is n-type doped. This is probably due to charge transfer from the Cu foil to the graphene. Indeed, the existence of this interaction between the graphene sheet and the copper substrate was shown by ARPES and Raman spectroscopy measurements in previous works [32].
ACCEPTED MANUSCRIPT 4 Conclusions
In this work we synthesized graphene using a new precursor N-Octane. Our results indicate that using N-Octane, we can achieve a reproducible synthesis process for single
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layer graphene where such features were corroborated through three different analysis techniques, namely, Raman spectroscopy and mapping, STM/STS and visible light transmittance. The adopted pre-annealing procedure resulted in a completely orientated
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copper foil with the {111} plane parallel to the surface, which certainly contributes to the good quality of the samples produced, as shown by Raman results. The analysis of the
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Raman mapping also indicated that the graphene foil was only slightly doped and submitted to a compressive biaxial strain in the range between -0.2% and- 0.4%. STM results clearly indicated the growth of single-layer graphene, while STS results indicated that there is an electron transfer from the Cu foil to graphene, that was responsible for the
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observed n-doping.
The graphene growth is still of good quality even at the lowest temperature, 850oC, confirmed by the low concentration of defects as was shown through Raman
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mapping of the transferred samples and UV-vis transmittance. At 950 °C, the N-Octane grown average graphene grain size are comparable to that observed in literature when
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methane gas is used at slightly higher temperatures, suggesting that our method is quicker and more controllable and the quality (and number of layers) of the grown samples are directly related to the quantity of the precursor used during the growth, as noted by our results. Also, due to the very short growth time and lower temperature characteristic of this process, it is overall more energetically efficient from a scalability perspective.
ACCEPTED MANUSCRIPT Acknowledgements This work was partially supported by Brazilian agencies: Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq), Instituto Nacional de Engenharia de Superfícies (INCT-INES), Coordenação de Aperfeiçoamento de Pessoal de Nível
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Superior (CAPES) and Fundação de Amparo à Pesquisa no Estado do Rio de Janeiro (FAPERJ). The authors would also like to thank LabNano/CBPF for the technical
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support during electron microscopy work.
References
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[1] A. C. Ferrari, c. et al. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. Nanoscale, v. 7, (2015) 4598-4810
[2] K. S. Novoselov et al. Electric field effect in atomically thin carbon films. Science, v. 306, (2004) 666-669
[3] K. S. Novoselov et al. A roadmap for graphene. Nature, v. 490, (2012) 192-200
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[4] X. Fengnian, Farmer D. B, Lin Y. M, P Avouris. Detection of individual gas molecules adsorbed on graphene. Nature Materials, v. 6, n. 9, (2007) 652 [5] X. Fengnian et al. Graphene field-effect transistors with high on/off current ratio and large
EP
transport band gap at room temperature. Nano Letters, v. 10, n. 2, (2010) 715-718 [6] S. Homaeigohar, M. Elbahri. Graphene membranes for water desalination. NPG Asia Materials, v. 9, (2017) e427
AC C
[7] P. Sutter. Epitaxial graphene: how silicon leaves the scene. Nature Materials, v. 8, (2009) 171-172
[8] S. Stankovich et al. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon, v. 45, (2007) 1558-1565 [9] C. Virojanadara et al. Homogeneous large-area graphene layer growth on 6 h-SiC (0001). Physical Review B, v. 78, (2008) 245403
[10] A. Anand, B. Unnikrishnan, J-Y Mao, H-J. Lin, C-C. Huang. Graphene-based nanofiltration membranes for improving salt rejection, water flux and anti-fouling - A review. Desalination, v. 429, (2018) 119-133.
ACCEPTED MANUSCRIPT [11] R. Kumar, D. K. Avasthi, A. Kaur. Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature. Sensors and Actuators B: Chemical, v. 242, (2017) 461468.
Chemical Physics Letters, v. 430, (2006) 56-59
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[12] P. R. Somani; S. P. Somani; M. Umeno. Planer nano-graphenes from camphor by cvd.
[13] X. Li et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science, v. 324, (2009) 1312-1314
orientation. Carbon, v. 68, (2014) 440-451
SC
[14] O. Frank et al. Interaction between graphene and copper substrate: the role of lattice
M AN U
[15] A. Guermoune et al. Chemical vapor deposition synthesis of graphene on copper with methanol, ethanol, and propanol precursors. Carbon, v. 49, (2011) 4204-4210 [16] B. Zhang et al. Low-temperature chemical vapor deposition growth of graphene from toluene on electropolished copper foils. ACS Nano, v. 6, (2012) 2471-2476 [17] J. Jang et al. Low-temperature-grown continuous graphene films from benzene by chemical
TE D
vapor deposition at ambient pressure. Scientific Reports, v. 5, (2015) 17955 [18] WU, Tianru et al. Fast growth of inch-sized single-crystalline graphene from a
controlled single nucleus on Cu–Ni alloys. Nature materials, v. 15, (2016) 43 [19] Kiani, F., et al. "Self-limited growth of large-area monolayer graphene films by low
EP
pressure chemical vapor deposition for graphene-based field effect transistors." Ceramics International 43.17 (2017): 15010-15017.
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[20] Xu, Xiaozhi, et al. "Ultrafast epitaxial growth of metre-sized single-crystal graphene on industrial Cu foil." Science Bulletin 62.15 (2017): 1074-1080.. [21] J. Suk et al. Transfer of cvd-grown monolayer graphene onto arbitrary substrates. ACS Nano, v. 5, (2011) 6916-6924 [22] Y. Ogawa et al. Domain structure and boundary in single-layer graphene grown on Cu (111) and Cu (100) films. The Journal of Physical Chemistry Letters, v. 3, (2012) 219-226
[23] Sempere, Bernat, et al. "Statistically meaningful grain size analysis of CVD graphene based on the photocatalytic oxidation of copper." Graphene Technology 2.1-2 (2017): 13-20
ACCEPTED MANUSCRIPT [24] Kim, Kwanpyo, et al. "Grain boundary mapping in polycrystalline graphene." ACS nano 5.3 (2011): 2142-2146 [25] Yu, Qingkai, et al. "Control and characterization of individual grains and grain
(2011): 443
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boundaries in graphene grown by chemical vapour deposition." Nature materials 10.6
microscopy." Nature 490.7419 (2012): 235
SC
[26] Duong, Dinh Loc, et al. "Probing graphene grain boundaries with optical
[27] J. E. Lee et al. Optical separation of mechanical strain from charge doping in graphene.
M AN U
Nature Communications, v. 3, (2012) 1024
[28] C. Metzger et al., Biaxial strain in graphene adhered to shallow depressions, Nano Letters v. 10, (2010) 6-10
[29] L. M .Malard, M. A. Pimenta, G. Dresselhaus, M. S. Dresselhaus. Raman spectroscopy in graphene. Physics Reports, v. 473, (2009) 51-87
[30] S. Berciaud et al. Intrinsic line shape of the Raman 2d-mode in freestanding graphene
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monolayers, Nano Letters v. 13, (2013) 3517–3523 [31] R. R. Nair et al. Fine structure constant defines visual transparency of graphene. Science, v. 320, (2008) 1308-1308
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[32] S. Gottardi et al. Comparing graphene growth on cu (111) versus oxidized cu (111). Nano
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Letters v. 15, (2015) 917-922
ACCEPTED MANUSCRIPT
Characterization of graphene synthesized by low-pressure
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chemical vapor deposition using N-Octane as precursor
André do Nascimento Barbosa¹*, N. J. S. Figueroa¹ C. D. Mendoza¹, A. L. Pinto2, F. L. Freire Jr.¹
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¹ Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225, 22451-900, Rio de Janeiro, RJ, Brazil. 2
Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, 22290-180, Rio de Janeiro,
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RJ, Brazil.
*Corresponding author
*[email protected]
New precursor for CVD-Grown graphene Copper surface orientation treatment for higher single-layer graphene yield. Raman, AFM and STM characterization of graphene samples Fast, homogeneous single-layer graphene growth
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1. 2. 3. 4.
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Highlights of this work
S0254-0584(18)30696-5
DOI:
10.1016/j.matchemphys.2018.08.031
Reference:
MAC 20874
To appear in:
Materials Chemistry and Physics
Received Date: 22 May 2018 Revised Date:
7 August 2018
Accepted Date: 12 August 2018
Please cite this article as: André.do.Nascimento. Barbosa, N.J.S. Figueroa, C.D. Mendoza, A.L. Pinto, F.L. Freire Jr., Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor, Materials Chemistry and Physics (2018), doi: 10.1016/ j.matchemphys.2018.08.031. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Characterization of graphene synthesized by low-pressure chemical vapor deposition using N-Octane as precursor
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André do Nascimento Barbosa¹*, N. J. S. Figueroa¹ C. D. Mendoza¹, A. L. Pinto2, F. L. Freire Jr.¹
¹ Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225, 22451-900, Rio de Janeiro, RJ, Brazil.
Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, 22290-180, Rio de Janeiro, RJ, Brazil.
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*Corresponding author
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*[email protected]
ACCEPTED MANUSCRIPT Abstract We report single-layer graphene synthesis using high-carbon content N-Octane as precursor. Unlike methanol, ethanol and other liquid carbon precursors, N-Octane is oxygen free and its molecular structure is simply a common hydrocarbon. Optimal
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precursor pressure for synthesis was found to be at 5-20 mTorr range, as at higher partial pressures we have achieved bilayer and few-layer coverage of the copper substrates with {111} plane parallel to the surface, as revealed by Raman spectroscopy. We could lower
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the synthesis temperature down to 850 ºC and still obtained graphene layers with low concentration of defects. For the complete coverage of the substrates, we report shorter
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than usual synthesis time, of no more than 5 minutes. Characterization of graphene layers were performed using Raman scattering spectroscopy and mapping, UV-vis transmittance as well as atomic force microscopy, scanning tunneling microscopy and
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scanning tunneling spectroscopy.
Keywords: Graphene, N-Octane, CVD, synthesis temperature, Raman spectroscopy,
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scanning tunneling spectroscopy.
ACCEPTED MANUSCRIPT 1 Introduction
Graphene is a material that has properties of great technological interest [1]. Isolated for the first time in 2004 [2], its transport, sheet resistance and malleability properties are
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differentials that motivate basic research and product development [3]. Currently, several proof-of-concept devices are being tested, such as gas sensors, field effect transistors and, in the form of oxidized graphene, water purification membranes for several purposes [4-
produced is in the synthesis process of the material.
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6]. However, the big challenge of implementing graphene in devices that can be mass-
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There are several ways to obtain graphene [7- 9]. Mechanical exfoliation produces samples with quite small areas and low density of defects by simply exfoliating the top layers of a highly oriented graphite and transferring onto a SiO2 wafer or another desired target substrate. Chemical exfoliation results in graphene oxide (GO) that can be
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reduced generating highly defective graphene, called reduced grapheme oxide (RGO). This process is very useful for high volume production and applications that makes use of its defective nature such as water purification filters and sensors [10-11]. Silicon
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carbide (SiC) graphitization at high temperatures yields large single-crystals and of quality compared to that of mechanical exfoliation. However, because of significant
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compressive strain imposed by this method, it is not possible to transfer the graphene to other arbitrary target substrates. Chemical deposition in the vapor phase (CVD) is the most promising form for
large-scale applications, since it is a well-known process and it is easy to scale up to the industry. The first reports describing the synthesis of graphene by CVD were published in 2009 [12] on Ni substrates, where multi-layered polycrystalline graphene was obtained. After that, copper foils were used as substrate and polycrystalline monolayer
ACCEPTED MANUSCRIPT graphene covered almost the entire substrate [13]. The CVD method basically consists of inserting into a quartz tube reactor a catalytic substrate made of a thin copper or nickel foil. The system is then evacuated and followed by the release of H2 gas in the reactor, while the temperature is raised to around 1000 ºC to reduce the substrate. It is expected
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that the oxide layer on the surface of the substrate will be eliminated almost completely, and simultaneously the surface copper grains grows larger, orienting the surface mainly in the {111} direction [14]. After the reduction period, one introduces in the system gases
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or vapors of hydrocarbons, usually methane, to synthesize the graphene.
In a work comparing several precursors, it has been shown that the growth of
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graphene can be accomplished using even fumes of alcohols and heavier hydrocarbons [15]. Also, the growth at low temperatures using toluene and benzene was proposed [16, 17], but the toxicity of both precursors makes this method particularly dangerous and its large-scale use provides health risks. The use of heavier alkane-like hydrocarbons is an
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alternative, since its pyrolysis leads to the complete molecule breakdown, not leaving any toxic radicals such as furans, and the possibility of lowering temperatures becomes an important factor when thinking of the overall cost of the scalability of the process, since
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the growth apparatus are basically resistive.
Also, there are several reports in the literature where very large graphene samples
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were grown [18, 19, 20]. Although they represent today’s state of the art in the sense of graphene synthesis processes and average grain size, their nontrivial approach and farfrom-production scalability are still barriers that should be overcome. In the energy, time and costs point of view there’s need for more conservative approaches to known growth techniques. In this work, we report the growth of single-layer graphene using as a new carbon source, N-octane, in the expectation that as C-C bonds breaks at lower temperatures, it
ACCEPTED MANUSCRIPT could provide more carbon atoms for synthesis and subsequently lower synthesis times. We investigated the effect of the growth temperature, the partial pressure of the octane vapor, time of growth and preparation of the sample. Samples were characterized using Raman spectroscopy and Raman mapping, scanning tunneling microscopy (STM) and
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Scanning tunneling spectroscopy (STS) and UV-vis transmittance. We also characterized the copper foil by EBSD analysis, as the annealing process is crucial for the quality of the synthesized graphene sheets. We could lower the synthesis temperature of nearly defect
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free graphene down to 850 ºC. The complete coverage of the copper substrates was
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obtained of no more than 5 minutes.
2 Experimental
The copper foils (alpha Aesar, order number 46986, 99.8% purity) were cut into squares
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of about 2 cm2 and they underwent ultrasound bath immersed in acetone for five minutes and then went through the same process immersed in isopropyl alcohol. Each sample was dried using high-purity nitrogen gas. The samples were inserted inside of a quartz tube
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reactor, where, under hydrogen atmosphere, the system started to heat at 30 ºC/min rate up to 1050ºC. After reaching this temperature the copper foils were annealed for one
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hour prior to growth. We investigated the partial pressure of N-octane to have a complete coverage of the substrate in the range from 100 mTorr to 5 mTorr. Furthermore, under the condition of minimum partial precursor pressure, the synthesis was carried out at temperatures in the range from 1050 ºC to 750º C for five minutes. At each stage of the sample's growth, five samples were synthesized. The samples were transferred to a silicon dioxide wafer using the wet transfer method [21]. The graphene on the copper foil was covered with a sacrificial layer of dissolved polyurethane (PU) in tetrahydrofuran
ACCEPTED MANUSCRIPT (THF) by using a spin coater. The copper was chemically attacked and dissolved using an iron chloride (FeCl3) solution. Then, the floating sample was "fished" using the SiO2 wafer. The final step consisted of the removing the sacrificial layer of PU by a THF bath for 40 minutes under ambient conditions.
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Raman spectroscopy and mapping were performed using a Micro-Raman spectrometer (NT-MDT, NTEGRA Spectra) equipped with a CCD detector and a solidstate laser (wavelength of 473 nm). Care was taken to avoid damage of samples and
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several measurements were performed with different laser powers to discard the shift of the bands caused by laser-induced heating. Measurements were carried out using a 100x
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ocular, leading to a focal point of the order of 1 µm with an incident power of less than 0.2 mW. In addition, Raman mapping were performed using AFM-Piezoelectric stage supplied by NT-MDT. EBSD analyses were performed on a JEOL 7100FT Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction (EBSD)
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system from Oxford. Transmittance measurements were carried out using a Perkin Elmer spectrophotometer, model LAMBDA 950 UV/Vis between 400 and 800 nm spectral region. Finally, the samples were loaded into an Ultra High Vacuum (UHV, ~10-7 Pa)
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Omicron STM. The physical and electronic graphene structures were characterized by STM/STS. These measurements were performed at room temperature using home-made
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electrochemically etched W tips
3 Results and discussion
The crystallographic orientation of the surface of polycrystalline copper substrates, as well as the grain size is crucial for the quality of the synthesized graphene sheets [22]. EBSD measurements on as-received copper foils show that they had a typical
ACCEPTED MANUSCRIPT microstructure of a material that passed through a process of rolling and recrystallization. In fact, its texture is typical of heavily rolled and recrystallized copper, in which cube {001} <100> is the main texture component. There is also the {122} <212> component that originate from crystal twinning together with S {123} <634> component as seen in
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Fig. 1. Most of the surface of the sample submitted to thermal treatment at 1050 0C for one hour presented abnormal grain growth, as seen in Fig. 1, resulting in large grains close to {111} <110> orientation which is unusual for FCC structures. Apparently, the
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treatment induced the crystal twinned regions to grow thus making the surface to be oriented in the {111} direction, as it has lower energy according to the FCC Wulff plot.
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Along the borders of the foil, other centimeter size crystalline domains orientations were found with the original Cube orientation. The copper foils were used as substrates for the
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graphene growth after this process.
Fig. 1: (a) Band contrast map; (b) orientation map from the original copper foil without any annealing treatment; (c) inverse pole figure color reference triangle; (d) Band contrast map; (e) orientation map from the annealed copper foil.
Fig. 2: AFM
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micrographies of graphene flakes on Cu obtained by using N-Octane as
precursor with 950 °C growth temperature. (a) Represents the height contrast image
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where it is possible to observe the grain boundaries. (b) Is the Lateral force image where the grain boundaries are highlighted. (c) The average distribution of the grains. We have
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obtained a mean size of 6.24 ± 1.47 µm for 950 °C grown sample.
The contact mode atomic microscopy was performed. Fig 2a and Fig 2b shows the height and lateral force image where it is possible to observe the grain boundaries. By measuring the larger axis of each flake through open source Imaging software, we have an average grain size of 6.24 micrometers, as Fig 2c. As compared with it is found in the literature [23, 24, 25, 26].
ACCEPTED MANUSCRIPT Raman spectroscopy results obtained from samples not yet transferred from the copper foils are presented in Fig 3a. The spectra taken at different points at the sample surface were almost identical revealing the homogeneity of the samples. Their main features were the presence of the G-band at around 1580 cm-1 and the 2D-band at around
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2700 cm-1 on top of a luminescence background due to the oxidation of the copper surface. It was possible to observe that the 2D-band widens for samples that were synthesized with 50 mTorr and higher precursor partial pressures grown at 1050ºC for 5
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minutes, suggesting that vapor flows that correspond to partial pressures above a threshold value favors the formation of bilayer or few-layer graphene. Also, the
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relationship of bands intensities (I2D/IG) together with the full width at half maximum (FWHM) corroborates that the graphene synthesized in these conditions was compatible with that of bilayer graphene. In contrast, it was observed that for the growths where the partial pressure of the octane vapor is less than 30 mTorr, the substrate surface was
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covered by monolayer graphene. It was observed that the intensity ratio I2d/IG was higher than 2 and the FWHM of the 2D-band was less than 35 cm-1. Fig 3b shows Raman spectra obtained from samples grown at 5 mTorr during 5
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minutes at different temperatures. By synthesizing graphene in these conditions, we observed the appearance of the D-band, which is related to defects in the crystalline
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lattice of the graphene, for samples grown at temperatures as low as 850 oC. This spectral feature suggested that these defects could be due to the incomplete breakdown of the molecule or that the energy needed to change the state of sp³ hybridization to sp² was not enough to completely cover the surface of the substrate, analogous to what happens with methane molecules. For lower temperatures (750 oC) only amorphous carbon was produced (not shown in the figure).
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Fig 3: (a) The Raman spectra of the graphene grown on copper where we can observe the influence of partial pressure on the intensity and FWHM of the 2D-band for samples grown at 1050 oC for 5 minutes; (b) Raman spectra of graphene grown at different temperatures transferred to SiO2 (300nm)/Si wafers. The
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growth was carried out with 5 mTorr for 5 minutes and the samples I2D/IG ratios were 3.1, 2.9 and 2.7 for processing temperatures of 1050 ºC, 950 ºC and 850 ºC, respectively, while the FWHM of the 2D-band was around 36.4, 30,6 and 38,6 cm-1 respectively.
In Fig. 4 we present the Raman maps obtained from samples prepared at different
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growth temperatures after being transferred to SiO2 (300nm)/Si wafers substrates.
Fig. 4: Raman maps of transferred samples prepared at: (a) 850 ºC; (b) 950 ºC; (c) 1050 ºC; (d) Histogram of the FWHM of 2D-bands of samples grown at these temperatures.
ACCEPTED MANUSCRIPT The map obtained from the sample prepared at 1050 oC shown at Fig. 4c was the most homogeneous one with an average I2d/IG ratio of 2.2. Fig. 4b shows that the map obtained from the sample prepared at 950 oC was also quite homogeneous with average I2d/IG ratio of 2.3, while the map of the sample grown at 850 oC shown in Fig. 4a revealed
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the presence of regions with I2d/IG typical bilayer or even few-layers graphene coexisting with the dominant single-layer graphene. On the other hand, the histograms of FWHM of 2D-band shown in Fig. 4d were, within the standard deviation, independent on the
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processing temperature and with an average value around 42 cm-1.
Raman spectroscopy can also be used to estimate the doping level as well as the
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increase in graphene strain by analyzing the positions of the 2D- and G bands. Fig. 5 show the positions of the 2D band versus positions of the G band taken at different points across the surface of the sample grown at 950 oC, 5 mTorr and 5 minutes of processing. Following the procedure developed by [27,28], we can estimate the type of strain
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(uniaxial or biaxial) of the sample. Most of the experimental data for this growth condition are positioned in the region of neutrality. In this same analysis, the strain (ε)
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graphene.
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was of the compressive biaxial type in the range between -0.2% and- 0.4% for the film of
2760 -0.4%
2730 -0.2%
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0.0%
2670 1560
ε=0
-0.4% -0.2%
1580 1600 1620 1640 -1 G peak position (cm )
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2D peak position (cm
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)
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Fig. 5: Plot of the 2D- vs. G-band positions for the graphene film. The lines indicate the E2D and EG
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relationship for strained undoped (dash-dotted line), uniaxial strain (dotted line), and unstrained p-doped (ε = 0, full line) graphene. The neutrality point (zero point) was taken from literature [28] and corresponds to the expected 2D- and G-band positions for suspended freestanding single-layer graphene.
Counting of the number of graphene layers through Raman spectroscopy is
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widely accepted as means of characterization [29, 30], nevertheless optical measurements may also be used for the determination of the number of graphene layers as graphene absorbs light in a linear fashion up to several numbers of layers. In Fig. 6 we compare the
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UV-vis transmittance results obtained from graphene samples grown at 950 ºC and 850
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ºC and transferred to silica substrates. The transmittance results were normalized by an uncoated silica glass substrate. The transmittance results obtained from the sample prepared at 1050 oC are almost identical to the one grown at 950 oC and, to make the figure clearer, is not shown. Graphene is known to absorb about 2.5% of light at the visible spectrum [31], and it is in good agreement with the result obtained for our pristine N-Octane single-layer graphene. UV-vis transmittance results showed clearly that our synthesis process yields monolayer graphene for processing temperatures of 1050 oC and 950 oC, since absorbance of around 2.7% was measured with wavelength of 550 nm, as
ACCEPTED MANUSCRIPT can be seen in Fig. 6. The slightly lower transmission value, 2.8% for the sample grown at 850oC was attributed to the absorbance in the few bilayer and few-layers small regions
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present in this sample. The UV-vis results, in both cases, confirmed the Raman results.
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Fig. 6: UV-vis transmittance as a function of the wavelength.
Fig. 7: Topographic images and STS spectrum of graphene. (a) and (b) shows STM images of graphene on
Cu taken in different regions of sample, where in (a) we can see the Moiré linear pattern, and the conditions were V = 25mV, I = 1,0nA. In Fig. 7b there is no Moiré pattern and the conditions were V = 250mV, I = 1.0nA. Fig. 7c shows Fourier Transform (FT) of the image in (b) and in Fig. 7d we have the
ACCEPTED MANUSCRIPT STS spectrum, (dI/dV) / (I/V), of the position marked at point (1) in the image (b), dotted line is EF and red arrow is ED (where EF – ED = - 0.17 V). Black scale bar in (a) is 2 nm and in (b) 1 nm.
Fig. 7 shows typical STM images obtained from the graphene layer on top of the Cu substrate. They clearly indicate the success of the growth of single-layer graphene by
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CVD with N-octane as precursor. These images were taken in different regions of the same sample grown at 950 oC at the pressure of 5 mTorr for 5 minutes. Fig. 7a shows the Moiré linear pattern originating from the lattice mismatch between graphene and Cu
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crystal lattice. Diverse periodicities for Moiré patterns were observed depending on the specific angles between the principal directions of graphene and Cu. Fig. 7b does not
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show that pattern. However, in Fig. 7c, the hexagonal symmetry of graphene is observed by means of the Fourier Transform of the image in (b).
Fig. 7d, shows the STS curve that was taken at point indicated by a blue dot in the STM image shown in Fig. 7b. This STS curve refers to the Local Density of States
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(LDOS) of graphene/Cu in Fig. 7b, where the Moiré patterns are absent. The Dirac point (ED) is shifted 170.0 meV from the Fermi level (EF). Ideally, the energy bands in the graphene form a so-called Dirac cone at the K point of the first Brillouin zone. In this K
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point, EF and ED are supposed to coincide for freestanding graphene. Nevertheless, in the
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case where the Fermi level is located above or below the Dirac point, the graphene is nor p-type doped, respectively. In our measurement, EF was 170.0 meV above ED, which corresponds to an electron concentration of ~ 2.13 x1012 cm-2, i.e., the graphene is n-type doped. This is probably due to charge transfer from the Cu foil to the graphene. Indeed, the existence of this interaction between the graphene sheet and the copper substrate was shown by ARPES and Raman spectroscopy measurements in previous works [32].
ACCEPTED MANUSCRIPT 4 Conclusions
In this work we synthesized graphene using a new precursor N-Octane. Our results indicate that using N-Octane, we can achieve a reproducible synthesis process for single
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layer graphene where such features were corroborated through three different analysis techniques, namely, Raman spectroscopy and mapping, STM/STS and visible light transmittance. The adopted pre-annealing procedure resulted in a completely orientated
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copper foil with the {111} plane parallel to the surface, which certainly contributes to the good quality of the samples produced, as shown by Raman results. The analysis of the
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Raman mapping also indicated that the graphene foil was only slightly doped and submitted to a compressive biaxial strain in the range between -0.2% and- 0.4%. STM results clearly indicated the growth of single-layer graphene, while STS results indicated that there is an electron transfer from the Cu foil to graphene, that was responsible for the
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observed n-doping.
The graphene growth is still of good quality even at the lowest temperature, 850oC, confirmed by the low concentration of defects as was shown through Raman
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mapping of the transferred samples and UV-vis transmittance. At 950 °C, the N-Octane grown average graphene grain size are comparable to that observed in literature when
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methane gas is used at slightly higher temperatures, suggesting that our method is quicker and more controllable and the quality (and number of layers) of the grown samples are directly related to the quantity of the precursor used during the growth, as noted by our results. Also, due to the very short growth time and lower temperature characteristic of this process, it is overall more energetically efficient from a scalability perspective.
ACCEPTED MANUSCRIPT Acknowledgements This work was partially supported by Brazilian agencies: Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq), Instituto Nacional de Engenharia de Superfícies (INCT-INES), Coordenação de Aperfeiçoamento de Pessoal de Nível
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Superior (CAPES) and Fundação de Amparo à Pesquisa no Estado do Rio de Janeiro (FAPERJ). The authors would also like to thank LabNano/CBPF for the technical
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support during electron microscopy work.
References
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[1] A. C. Ferrari, c. et al. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. Nanoscale, v. 7, (2015) 4598-4810
[2] K. S. Novoselov et al. Electric field effect in atomically thin carbon films. Science, v. 306, (2004) 666-669
[3] K. S. Novoselov et al. A roadmap for graphene. Nature, v. 490, (2012) 192-200
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[4] X. Fengnian, Farmer D. B, Lin Y. M, P Avouris. Detection of individual gas molecules adsorbed on graphene. Nature Materials, v. 6, n. 9, (2007) 652 [5] X. Fengnian et al. Graphene field-effect transistors with high on/off current ratio and large
EP
transport band gap at room temperature. Nano Letters, v. 10, n. 2, (2010) 715-718 [6] S. Homaeigohar, M. Elbahri. Graphene membranes for water desalination. NPG Asia Materials, v. 9, (2017) e427
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[7] P. Sutter. Epitaxial graphene: how silicon leaves the scene. Nature Materials, v. 8, (2009) 171-172
[8] S. Stankovich et al. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon, v. 45, (2007) 1558-1565 [9] C. Virojanadara et al. Homogeneous large-area graphene layer growth on 6 h-SiC (0001). Physical Review B, v. 78, (2008) 245403
[10] A. Anand, B. Unnikrishnan, J-Y Mao, H-J. Lin, C-C. Huang. Graphene-based nanofiltration membranes for improving salt rejection, water flux and anti-fouling - A review. Desalination, v. 429, (2018) 119-133.
ACCEPTED MANUSCRIPT [11] R. Kumar, D. K. Avasthi, A. Kaur. Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature. Sensors and Actuators B: Chemical, v. 242, (2017) 461468.
Chemical Physics Letters, v. 430, (2006) 56-59
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[12] P. R. Somani; S. P. Somani; M. Umeno. Planer nano-graphenes from camphor by cvd.
[13] X. Li et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science, v. 324, (2009) 1312-1314
orientation. Carbon, v. 68, (2014) 440-451
SC
[14] O. Frank et al. Interaction between graphene and copper substrate: the role of lattice
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[15] A. Guermoune et al. Chemical vapor deposition synthesis of graphene on copper with methanol, ethanol, and propanol precursors. Carbon, v. 49, (2011) 4204-4210 [16] B. Zhang et al. Low-temperature chemical vapor deposition growth of graphene from toluene on electropolished copper foils. ACS Nano, v. 6, (2012) 2471-2476 [17] J. Jang et al. Low-temperature-grown continuous graphene films from benzene by chemical
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vapor deposition at ambient pressure. Scientific Reports, v. 5, (2015) 17955 [18] WU, Tianru et al. Fast growth of inch-sized single-crystalline graphene from a
controlled single nucleus on Cu–Ni alloys. Nature materials, v. 15, (2016) 43 [19] Kiani, F., et al. "Self-limited growth of large-area monolayer graphene films by low
EP
pressure chemical vapor deposition for graphene-based field effect transistors." Ceramics International 43.17 (2017): 15010-15017.
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[20] Xu, Xiaozhi, et al. "Ultrafast epitaxial growth of metre-sized single-crystal graphene on industrial Cu foil." Science Bulletin 62.15 (2017): 1074-1080.. [21] J. Suk et al. Transfer of cvd-grown monolayer graphene onto arbitrary substrates. ACS Nano, v. 5, (2011) 6916-6924 [22] Y. Ogawa et al. Domain structure and boundary in single-layer graphene grown on Cu (111) and Cu (100) films. The Journal of Physical Chemistry Letters, v. 3, (2012) 219-226
[23] Sempere, Bernat, et al. "Statistically meaningful grain size analysis of CVD graphene based on the photocatalytic oxidation of copper." Graphene Technology 2.1-2 (2017): 13-20
ACCEPTED MANUSCRIPT [24] Kim, Kwanpyo, et al. "Grain boundary mapping in polycrystalline graphene." ACS nano 5.3 (2011): 2142-2146 [25] Yu, Qingkai, et al. "Control and characterization of individual grains and grain
(2011): 443
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boundaries in graphene grown by chemical vapour deposition." Nature materials 10.6
microscopy." Nature 490.7419 (2012): 235
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[26] Duong, Dinh Loc, et al. "Probing graphene grain boundaries with optical
[27] J. E. Lee et al. Optical separation of mechanical strain from charge doping in graphene.
M AN U
Nature Communications, v. 3, (2012) 1024
[28] C. Metzger et al., Biaxial strain in graphene adhered to shallow depressions, Nano Letters v. 10, (2010) 6-10
[29] L. M .Malard, M. A. Pimenta, G. Dresselhaus, M. S. Dresselhaus. Raman spectroscopy in graphene. Physics Reports, v. 473, (2009) 51-87
[30] S. Berciaud et al. Intrinsic line shape of the Raman 2d-mode in freestanding graphene
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monolayers, Nano Letters v. 13, (2013) 3517–3523 [31] R. R. Nair et al. Fine structure constant defines visual transparency of graphene. Science, v. 320, (2008) 1308-1308
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[32] S. Gottardi et al. Comparing graphene growth on cu (111) versus oxidized cu (111). Nano
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Letters v. 15, (2015) 917-922
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Characterization of graphene synthesized by low-pressure
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chemical vapor deposition using N-Octane as precursor
André do Nascimento Barbosa¹*, N. J. S. Figueroa¹ C. D. Mendoza¹, A. L. Pinto2, F. L. Freire Jr.¹
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¹ Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente, 225, 22451-900, Rio de Janeiro, RJ, Brazil. 2
Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, 22290-180, Rio de Janeiro,
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RJ, Brazil.
*Corresponding author
*[email protected]
New precursor for CVD-Grown graphene Copper surface orientation treatment for higher single-layer graphene yield. Raman, AFM and STM characterization of graphene samples Fast, homogeneous single-layer graphene growth
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1. 2. 3. 4.
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Highlights of this work