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Carbon scrolls from chemical vapor depositiongrown graphene

http://dx.doi.org/10.1016/j.carbon.2014.04.0760008-6223/� 2014 Elsevier Ltd. All rights reserved.

* Corresponding author.E-mail address: guangjun.cheng@nist.gov (G. Cheng).

Please cite this article in press as: Cheng G et al. Carbon scrolls from chemical vapor deposition grown graphene. Carbon (201dx.doi.org/10.1016/j.carbon.2014.04.076

Guangjun Cheng a,*, Irene Calizo a,b, Xuelei Liang a,c, Brent A. Sperling d,Aaron C. Johnston-Peck d, Wei Li a,c, James E. Maslar d, Curt A. Richter a,Angela R. Hight Walker a

a Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USAb Department of Electrical and Computer Engineering, Florida International University, Miami, FL 33174, USAc Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, Chinad Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA

A R T I C L E I N F O A B S T R A C T

Article history:

Received 7 December 2013

Accepted 21 April 2014

Available online xxxx

We present an investigation on the carbon scrolls produced from chemical vapor deposi-

tion (CVD) grown graphene. A wet, polymer-mediated process is used to transfer CVD

grown graphene from copper foil to a Si/SiO2 or metal substrate. Upon the removal of poly-

mer and drying, tearing of the graphene occurs and carbon scrolls are produced from the

ruptured graphene. We demonstrate that the optical and electronic properties of these

scrolls are comparable to those from exfoliated graphene. Optical microscopy and scanning

electron microscopy show that the isolated scrolls exhibit a similar morphology to those

formed from exfoliated graphene. Raman spectroscopy has been used to investigate the

conformational change from graphene to scrolls. The scrolls have a more pronounced

Raman D peak than graphene and display a large variation in the integrated intensity of

Raman G and G 0 peaks at different scroll locations. Raman spectroscopy and transmission

electron microscopy confirm that the graphene layers in the scrolls are non-AB stacked.

The scroll field-effect-transistor (FET) device exhibits an ambipolar behavior, resembling

the graphene FET device. This work demonstrates the possibility of fabricating carbon

scrolls using CVD grown graphene on various substrates and paves the way for advancing

their applications.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Carbon scrolls, formed structurally by rolling up a single layer

of graphene [1], not only possess the excellent electrical,

mechanical, and thermal properties of graphene but also

exhibit distinct properties from those of graphene and carbon

nanotubes [2–4]. Theoretical simulations have shown that

carbon scrolls hold promising applications in materials

storage and transport [5–8] and nano-mechanical devices

[9,10]. Carbon scrolls have been experimentally produced

using various methods, including the arc-discharge [11],

high-energy ball milling of graphite [12], sonication of interca-

lated graphite [13–15], microwave-assisted exfoliation of

graphite in liquid nitrogen [16], chemical vapor deposition

(CVD) [4,17,18], and scrolling of graphene oxides facilitated

by micro-explosion [19], Langmuir–Blodgett method [20],

4), http://

2 C A R B O N x x x ( 2 0 1 4 ) x x x – x x x

nanotubes [21], nanowires [22], nanoparticles [23,24], and

molecular combing [25,26].

Since the discovery of graphene in 2004 by mechanically

exfoliating graphite [27], exfoliated graphene has been used

to produce high-purity and high-quality carbon scrolls

[2,3,28]. Although the emergence of exfoliated graphene chal-

lenges the long-held notion that strictly two-dimensional (2D)

crystals were thermodynamically unstable and could not

exist [29], under external perturbations, exfoliated 2D graph-

ene also exhibits its instability by forming a three-dimen-

sional scroll. A thermal study on the exfoliated graphene

sandwiched in a homogeneous polymer matrix showed the

irreversibly scrolling of graphene above the polymer’s glass

transition temperature [28]. Direct observation of scrolling

of the exfoliated graphene on a Si/SiO2 substrate with the

aid of isopropyl alcohol and water was reported and the

field-effect-transistor (FET) devices were fabricated using

these scrolls [2].

Large area, continuous, monolayer graphene can be

grown on transition metal foils such as copper by CVD

[30,31]. One conventional method for transferring CVD

grown graphene from the copper substrate to other sub-

strates is the polymer-mediated approach [32,33]. A layer of

poly(methyl-methacrylate) (PMMA) is coated onto the graph-

ene, and the copper substrate is etched away. The PMMA/

graphene is then transferred onto other substrates, and

organic solvents are used to remove the PMMA. Due to the

instability of transferred graphene, the research on this

transfer process has mainly been focused on how to obtain

a ‘‘good’’ transferred graphene film, which is continuous

and free of contamination, residues, cracks, and holes

[32,33]. The carbon scrolls produced from CVD grown graph-

ene have not yet been reported.

In this paper, we demonstrate the instability of CVD

grown graphene through the tearing and scrolling of trans-

ferred graphene on a Si wafer with 300 nm SiO2 (Si/SiO2)

using this ‘‘PMMA-mediated’’ approach. A recent study on

the crack and tear formation in suspended, CVD grown

graphene using transmission electron microscopy (TEM)

has shown that the tear predominately aligns in the arm-

chair or zigzag directions of the graphene lattice [34]. Here

in our work, large-area, transferred graphene was investi-

gated, and thus optical microscopy, scanning electron

microscopy (SEM) and TEM were used to characterize the

morphology of graphene residue pieces and scrolls formed

from ruptured graphene. Raman spectroscopy and Raman

mapping were used to reveal the changes in Raman peaks

between graphene and scrolls and along the scrolls. The

scroll FET device was fabricated, and its electrical transport

properties were measured. We demonstrate that their optical

and electronic properties are comparable to those from exfo-

liated graphene. Specifically, the scrolls from CVD grown

graphene exhibit the similarities to those obtained from

exfoliated graphene in terms of morphology, changes in

Raman peaks, and transport properties [2,3,28]. Furthermore,

we show that tearing and scrolling of transferred graphene

can take place on a metal surface. This work demonstrates

that carbon scrolls can be fabricated using CVD grown graph-

ene and presents the potential for fabricating carbon scrolls

in a large scale on various substrates.

Please cite this article in press as: Cheng G et al. Carbon scrolls fromdx.doi.org/10.1016/j.carbon.2014.04.076

2. Experimental

2.1. Transfer process and device fabrication

PMMA solution (molecular weight 495,000 g/mol, 4% by vol-

ume dissolved in anisole) was spin-coated onto the CVD

grown graphene sample at 3000 rpm. Then the PMMA film

was kept at room temperature to dry. The Cu substrate was

etched in an ammonium persulphate (APS-100) solution.

The PMMA/graphene stack was then rinsed by deionized

water and transferred onto a Si/SiO2 substrate. Then acetone

was used to remove the PMMA film. TEM samples were pre-

pared by transferring PMMA/graphene onto lacey formvar/

carbon-coated Cu grids (Ted Pella, Inc.), removing PMMA

using acetone, and drying transferred graphene in air. The

back-gated FET devices were fabricated with an individual

scroll by depositing Ti (10 nm)/Au (80 nm) contacts using elec-

tron beam lithography.

2.2. Characterization

The SEM images of graphene residues and scrolls on a Si/SiO2

or metal substrate were obtained using a low-voltage SEM

(Zeiss, Ultra-60) operated at 1 kV and with an In-lens detector.

Raman spectra were acquired under ambient conditions with

a Renishaw InVia micro-Raman spectrometer equipped with

a 514.5 nm (2.41 eV) wavelength excitation laser and an

1800 lines/mm grating while operating in 180� backscattering

geometry. A 50· objective was used to focus the excitation

laser light to an approximately 1 lm spot on the samples with

an incident power of less than 2 mW to avoid local heating

effects. Raman mapping was conducted by raster scanning

the selected area with a step size of 1 lm. The Raman scatter-

ing was collected with an exposure time of 10 s for each point.

TEM images of transferred graphene and scrolls and their

selected-area electron diffraction (SAED) patterns were

obtained on a FEI Titan 80–300 analytical electron microscope

operated at 80 kV. The electrical properties of scroll FET were

measured under ambient condition at room temperature

using an Agilent 4156C semiconductor parameter analyzer.

3. Results and discussion

In our previous work on developing an optimal transfer pro-

cess for CVD grown graphene [33], we found that extra care

must be taken to obtain a ‘‘good’’ transferred graphene film,

continuous and free of contamination, residues, cracks, and

holes. For example, the ‘‘modified Radio Corporation of Amer-

ica (RCA) cleaning’’ process effectively removes the copper

residues on graphene. An increase in hydrophobicity of Si/

SiO2 substrate and the baking step greatly improve the con-

tact between the PMMA/graphene stack and Si/SiO2 substrate.

These extra steps significantly reduce the formation of cracks

and holes in graphene. Without these extra steps, the cracks

and holes in transferred graphene lead to the rupture of

graphene.

Fig. 1a shows an optical image of the transferred graphene

on a Si/SiO2 substrate using the conventional transfer process

without these extra steps. Upon the removal of PMMA and

chemical vapor deposition grown graphene. Carbon (2014), http://

Fig. 1 – (a) Optical image of scrolls from ruptured CVD grown graphene on a Si/SiO2 substrate. (b) Out-of-focus optical image of

(a). (c) SEM image of the area shown in (a). (d) SEM image of an area with less ruptured graphene. (e–g) SEM images of

graphene residue piece and scrolls. (h) Histogram of the angles between the adjacent edges of graphene residue pieces. The

scale bars in (a–d) are 10 lm and 1 lm in (e–g). (A color version of this figure can be viewed online.)

C A R B O N x x x ( 2 0 1 4 ) x x x – x x x 3

blow-drying the sample, except for a few small graphene res-

idue pieces on the substrate, the majority of the graphene has

ruptured and turned into fiber-like structures. The out-of-

focus optical image (the graphene level is above the focus

point) in Fig. 1b shows that the inner space of these fibers is

mostly transparent and appears hollow, indicating that these

fibers are the scrolls and that the graphene layers are not

tightly packed inside. The morphology of the scrolls and

graphene residue pieces on the substrate can be more clearly

visualized in the SEM image shown in Fig. 1c. Some scrolls are

isolated on the substrate and some are still attached to graph-

ene residue pieces. Both straight and curvy scrolls are visible.

In the center of the image lies a long, straight scroll with some

curvy scrolls attached to it. The SEM image shows that both

ends of this straight scroll are attached to graphene residue

pieces and that these two graphene pieces hold this scroll

straight. In another area with less ruptured graphene

(Fig. 1d), more straight scrolls with both of their ends attached

to the graphene pieces are observed. We also notice the

graphene wrinkle lines (graphene fold) [35,36] in graphene

residue pieces. The ends of some wrinkle lines are where

the scrolls are attached to graphene (as marked with the

arrows in Fig. 1d) and these scrolls appear to follow the

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wrinkle line direction. A graphene residue piece in Fig. 1e dis-

plays straight, folded, and scrolled edges. Fig. 1f highlights the

attachment of the scrolls to the graphene residue pieces. One

is held straight and the other curvy and relaxed. It is also

noticeable that tearing can cross the graphene wrinkle lines.

The morphology of an isolated scroll shown in Fig. 1g is sim-

ilar to that of the scrolls formed from exfoliated graphene

under the external perturbations [2,3,28].

These SEM images provide evidence that the ruptured

graphene forms scrolls. The edges of the graphene residue

pieces on the substrate hint at the tearing directions in the

original, continuous graphene sheet. Fig. 1h presents the his-

togram of around 200 measured angles between the adjacent

straight edges in these graphene residue pieces and reveals

that more than 160 angles measured are multiples of 30� such

as 30�, 60�, 90�, 120� and 150�. It has been reported that the

exfoliated graphene flakes on Si/SiO2 exhibit straight edges

with the angle between the adjacent edges being multiples

of 30�, indicating these edges are along the principal crystal-

lographic direction of graphene lattice, either armchair or zig-

zag direction [37–39]. Our finding shows CVD grown graphene

exhibits similar tearing feature to the exfoliated graphene in

terms of the resulting angle between edges.

chemical vapor deposition grown graphene. Carbon (2014), http://

4 C A R B O N x x x ( 2 0 1 4 ) x x x – x x x

The bending energy for scrolling of suspended graphene is

compensated by van der Waals interaction energy between

adjacent graphene layers in the scrolls [40]. Molecular dynam-

ics simulations have shown that water nanodroplets can acti-

vate and guide the folding of suspended graphene [41] and the

strong interaction between graphene and Si/SiO2 can prevent

this folding process [42]. Theoretical simulations have also

demonstrated that the equilibrium graphene morphology on

a rigid substrate is governed by the interplay between

graphene/substrate interaction energy and graphene strain

energy [43]. Therefore, for the graphene residue pieces on

the substrate in our work, the interaction between graphene

and Si/SiO2 substrate is probably strong. Meanwhile, in the

regions where the interaction between graphene and Si/SiO2

substrate is weak, tearing and scrolling of graphene occur.

The resulted van der Waals interaction energy between adja-

cent graphene layers in the scrolls is sufficient enough to

overcome the energy barriers such as the bending energy

and breaking carbon–carbon sp2 bonds along the tearing

directions.

To further characterize the scrolls and graphene residue

pieces, we performed Raman mapping measurements in an

area of 13 lm · 14 lm (the rectangular region marked in

Fig. 2a). The optical images in Fig. 2a and b show this area

with both scrolls and monolayer graphene residue pieces

on the substrate. Fig. 2e shows two representative Raman

spectra of CVD grown monolayer graphene (two dashed cir-

cles in Fig. 2c), and Fig. 2f presents two representative Raman

spectra of scrolls (two solid circles in Fig. 2c) on Si/SiO2. For

these four spectra, the two prominent peaks, centered

around 1580 cm�1 (G peak) and 2700 cm�1 (G 0 peak), are the

first and second order Raman scattering from graphene.

The former is associated with the doubly degenerate in-

plane transverse optical (iTO) phonon mode and longitudinal

optical (LO) phonon mode and at the Brillouin zone center,

the C point. The latter is associated with the intervalley dou-

ble resonance process involving two iTO phonons around the

K point of the Brillouin zone [44,45]. It is noticeable that the

two spectra for graphene in Fig. 2e overlap very well while

the two spectra for scrolls in Fig. 2f display a significant var-

iation in terms of the G and G 0 peak intensity. Those varia-

tions can be clearly observed in the Raman maps (Fig. 2c

and d). These Raman maps are generated by plotting the

integrated areas for G and G 0 peaks for each measured spot

during Raman mapping and are labeled with A(G) and

A(G0), respectively. These maps show the intensity contrast

between the graphene and scroll regions and the intensity

variation along the scrolls.

In addition to these two pronounced peaks, there exist

some weaker Raman peaks. The D peak, centered around

1350 cm�1, is due to an intervalley, double resonance process

involving iTO phonons and defects around the K point of the

Brillouin zone [44]. Since the D peak typically requires the

presence of defects in graphene [46], a very small or unde-

tected D peak in Fig. 2g indicates the high quality of CVD

grown graphene. In contrast, the D peak is much more

pronounced in the spectra of scrolls in Fig. 2i. It was demon-

strated that the spatially inhomogeneous curvature of a

graphene fold can generate a Raman D peak and this curva-

ture-induced D peak does not require the presence of the

Please cite this article in press as: Cheng G et al. Carbon scrolls fromdx.doi.org/10.1016/j.carbon.2014.04.076

structural disorder [47]. Therefore, we attribute the more pro-

nounced D peak in scrolls to the curvatures in the scrolls.

There are also some weak peaks associated with the sec-

ond-order overtone and combinational Raman modes in the

range of 1690–2150 cm�1. It was reported that monolayer

and non-AB stacked, multiple-layer graphene have the same

Raman modes in this range, and these Raman modes can

be used to distinguish them from AB stacked, multiple-layer

graphene [48,49]. In this region, the scrolls (Fig. 2j) show sim-

ilar Raman features to graphene (Fig. 2h). The appearance of

two peaks centered around 1890 cm�1 and 2040 cm�1 and

the absence of peak between 1700 cm�1 and 1800 cm�1 indi-

cate that the graphene layers in scrolls are non-AB stacked

[48,49] (for the high signal-to-noise Raman spectra in this

region with a collection time of 500 s, see Supplementary data

Fig. S1).

We performed a statistical analysis and plotted A(G 0) vs.

A(G) for graphene and scrolls from the mapping scans

(Fig. 3a). The data points for scrolls are more widely scattered

than those for graphene. Overall, the data points for scrolls

show that, with the increase of A(G), A(G 0) increases as well.

We also plot A(G 0)/A(G) vs. A(G), for graphene and scrolls

(Fig. 3b). While A(G 0)/A(G) for graphene ranges from 9.4 to

11.0 with an average value of 10.5, the ratio for scrolls ranges

from 1.9 to 4.7 with an average value of 3.1.

For our CVD grown graphene and scrolls, both G and G 0

peaks are symmetric and can be well fitted with a single

Lorentzian. Since the G 0 peak for AB-stacked, multiple-layer

graphene is typically asymmetric [44,45], the symmetric G 0

peak for scrolls indicates that the graphene layers in scrolls

are non-AB stacked, consistent with the results shown in

Fig. 2g. Fig. 3c correlates the G peak position with its width,

full-width at half maximum (FWHM), for graphene and scrolls

at different locations. For CVD grown graphene, the G peak

position and its width are narrowly distributed with the aver-

age value of 1585.5 cm�1 and 15.6 cm�1, respectively, while

the G peak position and its width for scrolls are more widely

scattered with the average values of 1581.0 cm�1 and

19.9 cm�1, respectively. Overall, the G peak position down-

shifts and its width broadens when graphene forms scrolls.

For the G 0 peak shown in Fig. 3d, the data points for scrolls

are also more scattered than those for graphene. The average

G 0 peak position for graphene is 2687.1 cm�1 and the position

upshifts to 2700.1 cm�1 for scrolls, while its average width

increases from 27.1 cm�1 for graphene to 40.4 cm�1 for scrolls.

Our results are consistent with the previous report [2] on the

scrolls produced from exfoliated graphene that the G peak

downshifts and broadens and the G 0 peak upshifts and broad-

ens after graphene is scrolled. Therefore, these changes in G

and G 0 peaks are associated with the conformational change

from graphene to scroll.

Large variation of A(G) and A(G 0) was also reported in the

scrolls formed from exfoliated graphene on Si/SiO2 [3,28].Recently, a systematic Raman study of mis-oriented double-

layer graphene obtained by consecutively transferring two

CVD grown graphene layers onto a TEM grid has been carried

out and found that the spectrum strongly depends on the rel-

ative rotation angle between these two layers [50]. Compared

to monolayer graphene, the double-layer graphene G peak

generally downshifts with a larger width and G 0 peak upshifts

chemical vapor deposition grown graphene. Carbon (2014), http://

Fig. 2 – (a and b) In- and out-of-focused optical image of graphene residue pieces and scrolls on a Si/SiO2 substrate,

respectively. (c and d) Raman map of the rectangular area (13 lm · 14 lm) marked in (a) using the integrated area of G and G 0

peaks, respectively. (e and f) Raman spectra from two graphene spots (dashed circles in (c)) and two scroll spots (solid circles

in (c)), respectively. (g and i) Zoomed-in D peak region for the spectra in (e) and (f), respectively. (h and j) Zoomed-in

1690 cm�1–2150 cm�1 region for the spectra in (e) and (f), respectively. The scale bars in (a) and (b) are 10 lm. (A color version

of this figure can be viewed online.)

C A R B O N x x x ( 2 0 1 4 ) x x x – x x x 5

with a larger width. Both A(G) and A(G 0) of double-layer graph-

ene exhibit a complex rotational-angle dependence and, con-

sequently, vary at different locations. In the scrolls formed

from CVD grown graphene, there are variations in the number

of graphene layers and in the rotation angles among the

graphene layers at different scroll locations, especially con-

sidering the small crystalline grains in CVD grown graphene.

These factors contribute to the changes in the position and

width of G and G 0 peaks from graphene to scroll and the large

variation of A(G) and A(G 0) at different scroll locations.

In order to further elucidate the structure of these scrolls,

we carried out the TEM measurements on the scrolls from the

ruptured CVD grown graphene. Fig. 4a and d show TEM

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images of the scrolls formed at the edge of graphene. Fig. 4b

and c show the magnified TEM images of the square 1 and 2

regions marked in Fig. 4a, respectively, and reveal the varia-

tion of the number of graphene layers at different scroll loca-

tions. The graphene layers are much more tightly packed in

the square 1 region than those in the square 2 region. In the

square 1 region, the fast Fourier transform (FFT, the inset in

Fig. 4b) of the selected square area in Fig. 4b does not display

the strong spots, confirming the variation of the interlayer

distance between the neighboring graphene layers and

indicating that, unlike in graphite, the interlayer distance

between the neighboring graphene layers varies in this scroll.

Fig. 4e–g show the SAED patterns from the regions 1 to 3

chemical vapor deposition grown graphene. Carbon (2014), http://

Fig. 4 – (a and d) TEM image of graphene with scrolled edges. (b and c) Magnified TEM images of the square 1 and 2 regions in

(a), respectively. Inset in (b) is the fast Fourier transform of the selected square area in (b). (e–g) Electron diffraction patterns

from the selected area 1–3 in (d), respectively.

Fig. 3 – Raman peaks analysis for graphene and scrolls. (a) Correlation between integrated intensity of G 0 and G peaks, A(G 0)

vs. A(G). (b) A(G 0)/A(G) vs. A(G). (c and d) Correlation between peak width and peak position for G and G 0 peaks, respectively. (A

color version of this figure can be viewed online.)

6 C A R B O N x x x ( 2 0 1 4 ) x x x – x x x

Please cite this article in press as: Cheng G et al. Carbon scrolls from chemical vapor deposition grown graphene. Carbon (2014), http://dx.doi.org/10.1016/j.carbon.2014.04.076

Fig. 5 – Electrical transport property of a FET fabricated with

an individual scroll. Inset is the optical image of the FET

device and the scale bar is 10 lm. (A color version of this

figure can be viewed online.)

C A R B O N x x x ( 2 0 1 4 ) x x x – x x x 7

marked in Fig. 4d, respectively. The electron diffraction

patterns in Fig. 4e from the graphene in the region 1 in

Fig. 4d display one set of hexagonal diffraction spots due to

the sixfold rotational symmetry of graphene [51]. In contrast,

in the electron diffraction patterns shown in Fig. 4f from

marked region 2 in Fig. 4d, in addition to the set of hexagonal

diffraction spots from graphene, the partial {1–210} and

{0–110} diffraction rings appear along the scroll direction,

indicating that the graphene layers in this scroll location are

non-AB stacked and have various stacking orientations

among the graphene layers [52]. A comparison between the

Fig. 6 – (a) Optical image of graphene residue pieces and scrolls o

in (a). (c) Magnified SEM image of the rectangular area marked in

circles in (c). The scale bars are 10 lm in (a) and (b) and 1 lm in

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diffraction patterns in Fig. 4f and those in Fig. 4g from marked

region 3 in Fig. 4d reveals the intensity variation in the partial

{1–210} and {0–110} diffraction rings, reflecting the variation of

the stacking orientations of graphene layers at different scroll

locations. These TEM results show the variation of the num-

ber of graphene layers and the rotation angles among the

graphene layers at different scroll locations and explain the

large variation of A(G) and A(G 0) at different scroll locations

observed in our Raman measurement.

We also fabricated a back-gated FET device with an indi-

vidual scroll (inset in Fig. 5). Fig. 5 shows the current (Ids) ver-

sus gate voltage (Vgs) data measured under ambient condition

at room temperature. The charge neutrality point (Dirac

point) is around +20 V, indicating p-type doping from O2 and

H2O molecules [33]. The current increases as the magnitude

of the gate voltage increases on both of sides of the neutrality

point, and thus this device exhibits an ambipolar (both n- and

p-type) behavior [27]. We also notice that the curve exhibits

an electron–hole conduction asymmetry, probably due to

the effect of charge transfer between the metal electrode

and the scroll [53]. Both p-type doping and ambipolar behav-

ior are commonly observed in graphene FET devices mea-

sured under ambient condition (see Supplementary data

Fig. S2) [33]. Therefore, the electrical transport property of this

scroll FET device resembles that of the CVD grown graphene

FET device, in accordance with previous report of the scrolls

produced from exfoliated graphene [2].

The tearing and scrolling of transferred graphene can also

occur on a metal surface. We fabricated numeric, fiducial

markers with Pt on our Si/SiO2 wafer. Fig. 6a shows the optical

image of scrolls formed from the ruptured graphene on both

n the Pt and Si/SiO2 substrates. (b) SEM image of area shown

(b). (d) Raman spectra from two scroll spots marked in solid

(c). (A color version of this figure can be viewed online.)

chemical vapor deposition grown graphene. Carbon (2014), http://

8 C A R B O N x x x ( 2 0 1 4 ) x x x – x x x

the Pt and Si/SiO2 surfaces. The SEM image of this region

(Fig. 6b) shows the graphene residue pieces and the scrolls

from ruptured graphene on the Pt surface. By reference to

the SEM image, the graphene residue pieces on Pt are not vis-

ible in the optical image. In contrast, the scrolls on Pt can be

observed (Fig. 6a). There are a few scrolls crossing both the Pt

and Si/SiO2 surfaces. Fig. 6c shows a magnified SEM image for

a scroll crossing these two surfaces (the rectangular region

marked in Fig. 6b) and reveals the different scroll morphology

on these two surfaces. The part of the scroll on the Pt surface

is more loosely packaged and has a larger contact area with

the substrate than the part on Si/SiO2, probably due to differ-

ent interaction strength between the outer graphene layer of

the scroll and the substrates upon drying. Fig. 6d presents two

representative Raman spectra for the scrolls on the Pt and Si/

SiO2 surfaces (as marked in Fig. 6c). For these two spectra, the

G peak position (1579.8 cm�1 and 1581.0 cm�1 for the scroll on

Pt and Si/SiO2, respectively) and its width (19.6 cm�1 and

21.0 cm�1 for scroll on Pt and Si/SiO2, respectively) are within

the range of fluctuation shown in Fig. 3c, and the G 0 peak

position (2699.0 cm�1 and 2698.0 cm�1 for the scroll on Pt

and Si/SiO2, respectively) and its width (49.8 cm�1 and

42.7 cm�1 for scroll on Pt and Si/SiO2, respectively) are within

the range of fluctuation shown in Fig. 3d. However, the spec-

trum for the scroll on Pt displays a much enhanced G peak

integrated intensity and much reduced G 0 peak integrated

intensity than the one on Si/SiO2. Thus, A(G 0)/A(G) corre-

spondingly decreases from 3.53 for the scroll on Si/SiO2 to

0.75 on Pt, which falls out of the fluctuation range shown in

Fig. 3b. This dramatic change in A(G 0)/A(G) could result from

the different scroll morphology on these two surfaces and

the variation in doping from the substrates.

4. Conclusions

We have investigated carbon scrolls produced from the CVD

grown graphene. The transferred graphene exhibits similar

tearing feature to the exfoliated graphene, with the angle

between the adjacent edges preferably being multiples of

30�. The ruptured graphene rolls up on a Si/SiO2 substrate

to form scrolls. Raman spectra of the scrolls show a more

pronounced Raman D peak than that of graphene due to

the curvature effect and that the graphene layers in the

scrolls are non-AB stacked. When graphene is scrolled, the

G peak downshifts and broadens and the G 0 peak upshifts

and broadens. A(G) and A(G 0) display a large variation at

the different scroll locations due to the variations in the

number of graphene layers and in the rotation angles among

the graphene layers. The scroll FET device exhibits an

ambipolar behavior, resembling the graphene FET device.

Finally, we show that the tearing and scrolling of transferred

graphene can also take place on a metal surface. The same

scroll crossing these two surfaces exhibits different mor-

phology due to the variation in its interactions with two sur-

faces. Since carbon scrolls hold promising applications in

materials storage, energy storage, and nano-mechanical

devices, our work lays the foundation for large-scale fabrica-

tion of carbon scrolls using CVD grown graphene on various

substrates.

Please cite this article in press as: Cheng G et al. Carbon scrolls fromdx.doi.org/10.1016/j.carbon.2014.04.076

Acknowledgments

I.C. was partially and A.C.J. is supported by the National

Research Council. Research performed in part at the NIST

Center for Nanoscale Science and Technology. We identify

certain commercial equipment, instruments, or materials in

this article to specify adequately the experimental procedure.

In no case does such identification imply recommendation or

endorsement by the National Institute of Standards and

Technology, nor does it imply that the materials or equipment

identified are necessarily the best available for the purpose.

Appendix A. Supplementary data

Supplementary data associated with this article can be found,

in the online version, at http://dx.doi.org/10.1016/j.carbon.

2014.04.076.

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