Arabian Journal of Chemistry (2015) xxx, xxx–xxx

King Saud University

Arabian Journal of Chemistry

www.ksu.edu.sawww.sciencedirect.com

ORIGINAL ARTICLE

Growth of Single-sided ZnO nanocombs/ML

graphene Heterostructures

* Corresponding author. Tel.: +968 24142308; fax: +968 24414228.

E-mail address: majidruq@squ.edu.om (M.S. Al-Ruqeishi).

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

http://dx.doi.org/10.1016/j.arabjc.2015.06.0071878-5352 ª 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Please cite this article in press as: Al-Ruqeishi, M.S., Mohiuddin, T. Growth of Single-sided ZnO nanocombs/ML graphene Heterostructures. Arabian JoChemistry (2015), http://dx.doi.org/10.1016/j.arabjc.2015.06.007

Majid S. Al-Ruqeishi *, Tariq Mohiuddin

Department of Physics, College of Science, Sultan Qaboos University, P.O. Box 36, P.C. 123, Al-Khoudh, Oman

Received 3 March 2015; accepted 3 June 2015

KEYWORDS

ZnO nanocombs;

Graphene–semiconductor

hybrid;

Chemical vapor deposition;

Photoluminescence

Abstract We report catalyst-free growth of high-density single-sided ZnO nanocombs for the first

time on a multi-layer graphene (MLG). Structural analysis based on scanning electron microscope

reveals the nanocomb ribbon average diameter and length are about 90–600 nm and 5–60 lm,

respectively, while the diameter and length of the comb tooth are about 30–100 nm and 100–

700 nm respectively. In general, the length of the teeth decreases gradually from one end of the

nanocomb ribbon to another. ZnO crystal growth seems to involve two steps which are the forma-

tion of Zn buffer layer/graphene, which works as growth nucleation sites and long nanowires ends

with nanocombs structure. Raman and PL optical transitions prove the well-faceted hexagonal

structure of ZnO nanocombs as well as the existence of defects such as O vacancies and Zn inter-

stitials. Graphene-based inorganic hybrid nanostructures provide several potential applications in

optoelectronics and nanoscale electronics such as nanogenerators, photovoltaic devices, optical

devices, and photodetectors.ª 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is

an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Zero band gap graphene and its remarkable electronic andoptical properties have fostered the fabrication of plenty of

2D–1D integrated semiconductor hybrid nanostructures(Biroju et al., 2014). In such a kind of graphene-based hybridstructure, graphene acts as the 2D substrate onto which several

1D semiconducting nanomaterials can be grown and superior

properties may be expected. Graphene-based inorganic hybridnanostructures offer additional functionality for realizingadvanced nanoscale electronics and optoelectronics applica-

tions in photovoltaics, nanogenerators and field emissiondevices (Choi et al., 2010; Hwang et al., 2010). Owing to theirunique electronic and optical properties, one dimensional ZnOnanostructures, with a wide band gap of 3.37 eV are consid-

ered to be important multifunctional building blocks for fabri-cating various nano-devices (Johnson et al., 2001; Arnoldet al., 2003; Wan et al., 2004). It is significant material for

ultraviolet and blue-light emitting devices (Nickel andTerukov, 2005). Recent studies have showed variety of ZnOnanostructures, such as nanorods, nanowires, nanotubes,

nanoneedles, nanotetrapods, nanorings, nanocombs and soforth (Dai et al., 2003; Wang, 2004, 2007; Shen et al., 2006).Therefore new devices such as nano-generators, nano-lasers,

urnal of

2 M.S. Al-Ruqeishi, T. Mohiuddin

and gas sensors could be designed from different ZnO nano-structures (Wang et al., 2006; Zhou et al., 2007; Liao et al.,2008; Qin et al., 2008a, 2008b). Due to its high surface area,

unique mechanical and optical properties of ZnO nanocombshave been utilized in many applications such as biosensors,bioreactors, nano-cantilevers, ultraviolet laser arrays, and

ultraviolet polarizers (Wang et al., 2003, 2006; Yan et al.,2003; Xu et al., 2006; Qin et al., 2008, 2008b). Thus, theZnO nanocombs/2D graphene heterojunction structure would

be highly desirable for next generation transparent, flexibleelectrical and optical devices, including flexible photovoltaics,displays, and light emitters.

So far, all ZnO nanocombs have been fabricated by using

chemical vapor deposition (CVD) (Wang et al., 2003; Yanet al., 2003; Leung et al., 2004; Liu et al., 2004; Park et al.,2004; Xu et al., 2004; Liao et al., 2005; Pan et al., 2005;

Huang et al., 2006; Lao et al., 2006; Lim et al., 2006; Shenet al., 2006; Xu et al., 2006; Zhang et al., 2006; Li et al.,2007; Song et al., 2007; Wang, 2007; Umar et al., 2008;

Yang et al., 2008; Zha et al., 2008; Zhang et al., 2008; Kimet al., 2009; Lin et al., 2010; Chang et al., 2011; Choi et al.,2011; Kumar et al., 2011). Mostly used precursors in this pro-

cess are Zn powders (Yan et al., 2003; Huang et al., 2006; Shenet al., 2006; Zhang et al., 2006; Li et al., 2007; Song et al., 2007;Umar et al., 2008), Zn foils (Zha et al., 2008), ZnO (Wanget al., 2003; Pan et al., 2005), and a mixture of ZnO and gra-

phite powders (Leung et al., 2004; Park et al., 2004; Xuet al., 2004, 2006; Lao et al., 2006; Lim et al., 2006; Wanget al., 2006). Many studies reported on the synthesis of

heterostructures, nanorods (Chang et al., 2011; Choi et al.,2011), nanowires (Kim et al., 2009; Lin et al., 2010; Kumaret al., 2011) ZnO/G, but until submitting this study no fabri-

cated combs like nanostructures over graphitic substrate werepublished. This is may be due to low concentration of growthprecursors inside the CVD chamber which is related to high

temperature and long growth deposition time. These two rea-sons may etch SLG, FLG and MLG before the synthesis ofZnO nanostructures process starts. To avoid etching graphiticsubstrate surface and provide more growth precursors, sub-

strate location and furnace temperature inside CVD chamberwere crucial (Kahng et al., 2012). In this article we focus onthe synthesis of single-side teethed ZnO nanocombs on

multi-layer graphene (MLG), 10 layers, under low depositiontemperature and without need of any catalyst. This is the firsttime ever to produce ZnO nanocombs over ML graphene. The

formation of the nanocombs is investigated by analyzing thecrystal morphology and optical properties using (SEM, scan-ning electron microscope), (EDX, energy dispersive X-rayspectroscopy), (XRD, X-ray diffraction), (RS, Raman spec-

trometer) and (PL, photoluminescence spectrometer).

2. Experimental setup

2.1. Wafer preparation

In this study, (MLG), 1–10 monolayers grown on Ni/SiO2/Sidisk with100 mm in diameter (MTI Co., item No. CVDGON-100D-US) were utilized as a substrate for the

synthesis of ZnO nanocombs. The disk was cut intosmall pieces (2 cm · 1 cm) with characteristics shown inFig. 1(a) and (b). Substrates were ultrasonically cleaned in

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successive baths of acetone and methanol for 5 min each,and then rinsed in distilled water and dried with gentle airblow.

2.2. ZnO nanocombs growth

Powders from Sigma Aldrich of graphite (99.99%, <45 lm)

and ZnO (99.9%, <5 lm), with mass ratio of (1:1) were mixedand an amount of 2 g was added each time into a combustionboat and used as source material. The source material was

loaded into the middle of a 2.4 cm-inner diameter quartz tube,which was placed at the center of a 45 cm long horizontal tubefurnace as shown in Fig. 1(c). The horizontal quartz tube was

connected to argon (99.999%) gas supply and a flow rate con-trol system at one end while the other end kept opened as it isshown in Fig. 1. Two substrates were placed 15 and 20 cmapart from the ZnO–graphite mixture inside the quartz tube,

near the open end. The Ar gas was then flushed inside thequartz tube to get rid of all other gases and kept at 10 sccm,standard centimeters cubic per minute. Furnace was switched

on and the temperature was raised up to (600 ± 15 �C) at aheating rate of 1.2 �C/s. The temperature is constant at themiddle area of the furnace but gradually decreases near its

edges, as illustrated in the temperature distribution curveshown in Fig. 1(c). Thermocouple was used to determine theexact temperature at each substrate surface during the process.At this temperature, samples were grown at different deposi-

tion time. After the source material was completely evapo-rated, the furnace was turned off and kept to cool down toroom temperature under the same Ar flow rate. The surface

of the samples was covered with a white–gray color thin layer.Then, samples were taken from the furnace for further analysisand characterizations.

2.3. Characterization

The obtained samples were then characterized by field emission

scanning electron microscopy (FESEM, JEOL JSM-7600F).The elemental composition of the samples was determined byenergy dispersive X-ray spectroscopy (EDX). The crystal struc-ture was identified using X-ray diffraction (XRD, X’Pert PRO,

Maximum generator output power: 3 kW with Cu Ka radia-tion). The optical characterization was done by micro-Ramanspectroscopy (Renishaw, RM1000-Invia) using 514 nm excita-

tion and Photoluminescence spectrometer (PerkinElmer LS55Fluorescence Spectrometer, pulsed Xenon with 3.8 eV excitedenergy).

3. Results and discussion

Two graphitic substrates A and B with 2 cm apart from each

other were subject to gradual elevating temperature up to(600 ± 15 �C) and then kept for 20 min inside the horizontalfurnace as illustrated in Fig. 1. The distribution of temperature

degrees over two substrates surfaces, TA = 600 �C and TB,was measured during deposition time. Fig. 2 shows FESEMimages of sample A surface at different magnifications. InFig. 2(a) fractured thin film over the sample A surface can

be seen. Elemental analysis of both (MLG) existence (spot 1)and disappears (spot 2) areas were taken and their relatedEDX spectra at spot (1) show elemental compositions of zinc,

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of

Graphite + ZnO mixture Ar

5cm 5 cm

Open End

T (ºC) Curve

(a) (b)

(c)

Figure 1 A schematic diagram of experiment setup for ZnO nanocombs synthesis process. (a) An inset drawing of graphene wafer

utilized for ZnO nanocombs growth.

1.8k

200x

45k

Spot (1)

Spot (2)

10 µm 100 nm

(a)

(b) (c)

100 µm

Figure 2 FESEM images of (a) sample A surface with inset EDX spectra at two spots (1 and 2), (b) and (c) magnified images of ZnO thin

layer and thick clusters grown on FLG/graphitic substrate.

Growth of Single-sided ZnO nanocombs/ML graphene Heterostructures 3

Please cite this article in press as: Al-Ruqeishi, M.S., Mohiuddin, T. Growth of Single-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal ofChemistry (2015), http://dx.doi.org/10.1016/j.arabjc.2015.06.007

4 M.S. Al-Ruqeishi, T. Mohiuddin

oxygen, nickel and carbon while EDX spectrum at spot (2)detected strong silicon signal and a weak intensity signal ofzinc. The platinum signal in both spectrums comes from sam-

ple pre-sputtering to avoid charging effect caused by electricscanning beam and sample surface interactions. InFig. 2(b) and (c) zinc rich ZnO big clusters are clearly seen

on graphitic surface. The EDS spectrum in Fig. 2(a) demon-strates the purity of the sample. Mainly zinc and oxygen aredetected with the atomic ratio of Zn to O 59.58:38.47 (1.5:1).

Carbon with low percentage may come from graphene sub-strate or graphite-ZnO mixture due to Ar gas flushing at thebeginning of each experiment, which will be verified inRaman spectrum discussion section. Full coverage of ZnO thin

film over graphene substrate may explain low EDS percentageof carbon. Also, small platinum (Pt) signals on EDS spectrumcan be related to the coating layer of Pt, which was used to

reduce the charging occurring during FESEM imaging.Due to high temperature (>600 �C), graphene layers (GL)

staked to nickel start to be unstable and some areas of GL dis-

appear, which agrees with Kahng et al. (2012) study, whichdetermined the maximum temperature of �700 �C at whichCVD-grown graphene films are almost stable (Kahng et al.,

2012). Thermal stability of CVD grown MLG is necessary toestablish good electrical contact between graphene and metalelectrodes in electronic devices. Thermal annealing of grapheneis also used to remove the supporting polymer layer applied

during the transfer of CVD-synthesized graphene (Chenget al., 2011; Nagareddy et al., 2011).

At T = 600 �C, MLG get damaged and cracks formed all

over the MLG film, see small arrows in Fig. 2(a). We suggestthat Ni catalyst began to form eutectic alloying at T = 460 �Cwith silicon, which is the middle layer of MLG substrate

(Zhang et al., 2006; Beltran-Huarac et al., 2014). This alloystarts to attract more silicon atoms from Si substrate to forma spherical droplet by solid–liquid–solid (SLS) mechanism

(Xing et al., 1999). Having different droplet sizes may crackthe MLG and due to flowing of Ar gas inside the chamber,some MLG flakes may get removed from the substrate, seespot (2) in Fig. 2(a).

The temperature-distance curve over sample B surface isdeclined due to the furnace temperature reduction near the fur-nace right side end as shown in top of Fig. 3. The temperature

was measured at a specific distance or locations apart from thehot zone or furnace center. A FESEM image taken at eachlocation a, b, c, d, e and f, is shown in Fig. 3 respectively.

Smooth and congested wire like nanostructures were obtainedas illustrated in Fig. 3(a) and (b), nearest locations to hotzone. In Fig. 3(b) small combs like structure can be seen atthe far end of ZnO nanowire, circled areas. High magnified

images in Fig. 3(c) and (d) show nanowires with thick sidedduds in one direction only or single-sided teeth structure. Itcan be noticed that these evolving nanocombs are far in dis-

tance from the sample surface. In Fig. 3(e) and (f) longsingle-sided teeth nanocombs were crowdedly seen. Eachnanocomb usually consists of two parts: the comb ribbon with

5–60 lm length and 90–600 nm width, and one row of nanor-ods (the so-called teeth) growing along one side of the ribbonas in Fig. 3(e) and (f). The diameter of the teeth is about 30–

100 nm, while their length is 100–700 nm depending on theposition of the teeth. The length of both ribbons and tooth dis-tribution diagrams is shown in Fig. 4(a) and (b) respectively.In general, the length of the teeth decreases gradually from the

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one end of the nanocomb ribbon to another as expected (Phanet al., 2011). It corresponds to the growth process and direc-tion of the nanocomb, as will be discussed in the growth mech-

anism. These different ZnO morphologies are mainly occurreddue to temperature fluctuations over the surface of same or dif-ferent substrates and to the combustion of Zn vapor in the

presence of oxygen. This work will only focus on the structuralcharacterization and growth mechanism of nanocombs fabri-cated on sample B.

3.1. Growth mechanism

It appears that zinc rich thin film first deposited over MLG

substrate and then it works as a buffer layer to grow nanowiresand then nanocombs, which was found at the end of ultra-longnanowires going away from the MLG substrate as shown inFig. 2(b) and (c). This indicates that the buffer layer was

deposited before the growth process of nanocombs took place.This is because carbon (C) atoms of graphene directly bind tothe Zn atoms of ZnO, thus Zn and O precursors can be widely

absorbed onto the C atoms of graphene during the CVD pro-cess (Choi et al., 2011), see Fig. 5(a). Zn cluster is easily struc-tured and grows over MLG substrate because Zn atoms

produce one orderly atomic layer on last grapheme layer andthey form orderly nucleation sites for the following crystalgrowth (Guo et al., 2011). It has been demonstrated that theZn buffer layer played an important role in the improvement

of crystal quality of ZnO films (Fu et al., 1998). Then, positivezinc starts to attract negative oxygen atoms in a self-catalyzedmethod and hence defined nucleated sites were developed.

Here, ZnO nuclei grow increasingly and form clusters sincethe interaction of ZnO nuclei–ZnO precursor is stronger thanthat of the ZnO precursor–graphene (Fig. 5(b)). At these sites,

ZnO stem grows along [2110] .direction and again Zn clustersform Zn-terminated ZnO (0001) polar chemically active sur-

face. The preferred orientation of clusters is determined onlyby the preferred orientations of the initial nuclei at this stage(Kim et al., 2009). Therefore, unstable Zn-terminated surface

could provide a proper site for Zn clustering or local enrich-ment of growing ZnO combs along [0001] direction on theZnO (0001) surface (Qiang et al., 2009). When more and more

Zn atoms deposited on (0001) surface, they would accumulateto form more new Zn clusters, which would catalyze thegrowth of the teeth along (0001) direction. Growth terminated

when there are no more growth precursors are supplied overthe MLG substrate.

3.2. Structural and optical results

Fig. 6 reveals XRD patterns of the as-synthesized nanocombswith related crystal structure and phase purity of the ZnOnanostructures. The intense peaks of ZnO (100), (002),

(101), (102), (110), (103) and (112) prove the existence ofwurtzite structure of ZnO. In addition, one weak zinc peaklocated at 2h = 38.34� and strong peak of silicon at

2h = 69.25�, which conforms with Zn and Si signals in theEDX spectrum for spot (2) shown in Fig. 2(b). Also, no peakis found corresponds to graphene, which is fully covered by

grown zinc thin film and ZnO nanocombs.We also studied the optical properties of resultant ZnO

nanocombs by Raman scattering spectroscopy. Fig. 7(a)

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of

(f)

(d)(c)

(b)(a)

(e)

10 µm

1.5K

2K6K

1K

17 K

1.8 K

10 µm 1 µm

1K

1 µm

10 µm 10 µm

10 µm

Tem

pera

ture

(˚C

)

Distance (mm)

Figure 3 FESEM images for sample B surface (a–b) ZnO nanowires at distance 0–5 mm from hot zone (600 �C), (c–d) ZnO nanocombs

at 5–10 mm and (e–f) nanocombs at 10–15 mm.

Growth of Single-sided ZnO nanocombs/ML graphene Heterostructures 5

shows room-temperature spectrum in the wavenumber range

of 100–3000 cm�1 for an excitation wavelength of 514 nm forboth sample A and B. To discuss the obtained spectrum of

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sample A, major Raman shift bands should be clarified. The

major Raman features of graphene and graphite are the socalled G band (�1580 cm�1) and 2D band (�2670 cm�1).

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of

100 200 300 400 500 6000

5

10

15

20

25

Cou

nts

Nanocombs tooth length (nm)0 10 20 30 40 50 60

0

5

10

15

20C

ount

s

Nanocombs ribbon length (um)

(a) (b)

Figure 4 Distribution length of nanocombs (a) ribbons and (b) tooth.

Figure 5 Schematic illustration of (a) graphene layer with Zn, O, ZnO growth precursors flowing over its surface (b) ZnO thin layer and

1D crystal growth.

*(100)

(111)•

*(002)*(101)

+ (10

0 ) *(102) *(110)*(103)

*(112)

•(400)

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsity

(a.u

.)

*ZnO Nanocombs• Si+ Zn

Figure 6 XRD patterns of sample B, where ZnO, Zn and Si

crystal planes could be detected.

6 M.S. Al-Ruqeishi, T. Mohiuddin

The G band originates from in-plane vibration of sp2 carbonatoms is a doubly degenerate (TO and LO) phonon mode(E2g symmetry) at the Brillouin zone center (Phan et al.,

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2008). The 2D band originates from a two phonon double res-

onance Raman process (Djurisic and Leung, 2006). Here, werefer the band as 2D band because it is the second order over-tone of the D band. It can be seen in Fig. 7(a) that the 2D

band becomes broader and blue-shifted when the graphenethickness is large as in our multilayer graphene (Ferrariet al., 2006). The I2D/IG intensity ratio is about 1.7 and theFWHM of the 2D peak is about 79 cm�1, which proves that

the sample is predominantly composed of multilayer. InFig. 7(a) sample B Raman scattering spectrum of sample (B)shows closed peaks at lower wavenumbers and hence, this

spectrum was illustrated separately, as in Fig. 7(b), to identifyeach peak clearly.

As it is known, the Wurtzite structure of ZnO belongs to

the space group P63mc. At the point C in the Brillouin zone,there are phonon modes of C = A1 + 2B1 + E1 + 2E2 [55].Among these, B1(H) and B1(L) modes are Raman inactive,

E2(H) and E2(L) modes are non-polar active, and the twoinfrared-active modes of A1 and E1 are polar and have longi-tudinal (LO) and transversal optical (TO) components. TheRS spectrum of the nanocombs shows conventional modes

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of

Figure 7 The corresponding room-temperature Raman spectra of (a) the as-synthesized sample A and grown ZnO nanocombs on

sample B, (b) detail spectrum of Raman peaks taken from sample B for ZnO nanocombs and (c) room temperature photoluminescence

(PL) of ZnO nanocombs grown over MLG compared to naked MLG.

Growth of Single-sided ZnO nanocombs/ML graphene Heterostructures 7

peaked at 331, 380, 409, 437 and 585 cm�1, which areassociated with processes of E2(H)–E2(L), A1(TO), E1(TO),

E2(H), and E1(LO), respectively. There are no additionalmodes related to impurities. The results prove that theresultant ZnO nanocombs have good quality in the wurtzite

structure.Fig. 7(c) shows the measured room temperature PL spectra

for the as-synthesized ZnO nanocombs over MLG substrateand MLG only samples. Here, two distinct peaks were

observed. The first peak approximately at 353 nm for ZnOnanocombs was observed in the UV region and no peak isrelated to MLG. As reported, the dominant peaks at UV

region are attributed to the near band edge emission (NBE)or recombination of free exciton (Rusli et al., 2012;Mahmood et al., 2013). The other ZnO nanocombs peaks in

the visible region appear approximately at 416, 436, and480 nm. The strong peak in the visible region, i.e., violet, blueand green emissions is associated with specific defects such as

O vacancies and Zn interstitials and these defects are responsi-ble for the recombination of the blue-green luminescence(Huang et al., 2001). This may be due to the shape transitionsto the well-faceted hexagonal structure (Rusli et al., 2012).

Low structural defects such as O vacancies and Zn interstitialsmay give sharper and stronger UV emission and weaker blue-green emissions.

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4. Conclusion

We synthesized successfully ZnO single-sided nanocombs on

multi-layers graphene using free catalyst CVD at 600 �C underatmospheric pressure. The obtained ZnO nanocombs are purewurtzite polycrystalline structure. We suggest that the growth

process of ZnO nanocombs is self-catalysis through the solid–vapor mechanism, starting from the (0001)-Zn polar surface.Zinc buffer layer played an important role to grow ZnO nano-combs and to link these nanostructures to the graphene sub-

strate. Additional assessments based on RS spectroscopy andPL revealed that the ZnO nanocombs had excellent crystalquality with interstitial defects.

References

Arnold, M.S., Avouris, P., et al, 2003. Field-effect transistors based on

single semiconducting oxide nanobelts. J. Phys. Chem. B 107, 659.

Beltran-Huarac, J., Resto, O., et al, 2014. Single-crystal c-MnS

nanowires conformally coated with carbon. ACS Appl. Mater.

Interfaces 6, 1180–1186.

Biroju, R.K. et al, 2014. Graphene-assisted controlled growth of

highly aligned ZnO nanorods and nanoribbons: growth mechanism

and photoluminescence properties. ACS Appl. Mater. Interfaces 6,

377–387.

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of

8 M.S. Al-Ruqeishi, T. Mohiuddin

Chang, H., Sun, Z., et al, 2011. A highly sensitive ultraviolet sensor

based on a facile in situ solution-grown ZnO nanorod/graphene

heterostructure. Nanoscale 3 (1), 258–264.

Cheng, Z., Zhou, Q., et al, 2011. Toward intrinsic graphene surfaces: a

systematic study on thermal annealing and wet-chemical treatment

of SiO2-supported graphene devices. Nano Lett. 11, 767–771.

Choi, D., Choi, M.Y., et al, 2010. Sound driven piezoelectric

nanowire-based nanogenerators. Adv. Mater. 22, 2187.

Choi, W.M., Shin, K.S., et al, 2011. Selective growth of Zno nanorods

on SiO2/Si substrates using a graphene buffer layer. Nano Res. 4

(5), 440–447.

Dai, Y.Z.Y. et al, 2003. The octa-twin tetraleg ZnO nanostructures.

Solid State Commun. 126, 629.

Djurisic, A.B., Leung, Y.H., 2006. Optical properties of ZnO

nanostructures. Small 2, 94.

Ferrari, A.C., Meyer, J.C., Mauri, A.C., et al, 2006. Raman spectrum

of graphene and graphene layers. Phys. Rev. Lett. 97, 187401.

Fu, Z.X., Lin, B.X., et al, 1998. Effect of Zn buffer layer on growth

and luminescence of ZnO films deposited on Si substrates. J. Cryst.

Growth 3 (193), 316.

Guo, J.Y., Xu, C.X., et al, 2011. Structure evolution of Zn cluster on

graphene for ZnOnanostructure growth. J. Appl. Phys. 109, 024307.

Huang, M.H., Wu, Y., et al, 2001. Catalytic growth of zinc oxide

nanowires by vapor transport. Adv. Mater. 13, 113–116.

Huang, Y.H., Zhang, Y., et al, 2006. Fabrication and characterization

of ZnO comblike nanostructures. Ceram. Int. 32, 561.

Hwang, J.O., Lee, D.H., et al, 2010. Vertical ZnO nanowires/graphene

hybrids for flexible transparent and field emission. J. Mater. Chem.

21, 3432.

Johnson, J.C., Yan, H.Q., et al, 2001. Nonlinear chemical imaging

nanomicroscopy: From second and third harmonic generation to

multiplex (broad-bandwidth) sum frequency generation near-field

scanning optical microscopy. J. Phys. Chem. B 105, 11387.

Kahng, Y.H., Sangchul, L., et al, 2012. Thermal stability of multilayer

graphene films synthesized by chemical vapor deposition and

stained by metallic impurities. Nanotechnology 23, 075702.

Kim, Y.J., Lee, J.H., et al, 2009. Vertically aligned ZnO nanostruc-

tures grown on graphene layers. Appl. Phys. Lett. 3 (95), 213101.

Kumar, B., Lee, K.Y., et al, 2011. Controlled growth of semiconduct-

ing nanowire, nanowall, and hybrid nanostructures on graphene

for piezoelectric nanogenerators. ACS Nano 5, 4197–4204.

Lao, C.S., Gao, P.X., et al, 2006. Formation of doubleside teethed

nanocombs of ZnO and selfcatalysis of Zn terminated polar

surface. Chem. Phys. Lett. 417, 358.

Leung, Y.H., Djurisic, A.B., et al, 2004. Zinc oxide ribbon and comb

structures synthesis and optical properties. Chem. Phys. Lett. 394,

452.

Li, X., Xu, C.X., et al, 2007. Disc-capped Zn. Chin. Phys. Lett. 24,

3495.

Liao, Z.M., Zhang, H.Z., et al, 2005. Conductive properties of comb-

like dendritic ZnO nanostructures. Chin. Phys. Lett. 22, 987.

Liao, L., Lu, H.B., et al, 2008. A novel gas sensor based on field

ionization from ZnO nanowires moderate working voltage and

high stability. Nanotechnology 19, 17550.

Lim, Y.S., Park, J.W., et al, 2006. Carbothermal synthesis of ZnO

nanocomb structure. Mater. Sci. Eng., B 129, 100.

Lin, J., Penchev, M., et al, 2010. Heterogeneous graphene nanostruc-

tures: ZnO nanostructures grown on large-area graphene layers.

Small 6, 2448–2452.

Liu, F., Cao, P.J., et al, 2004. Controlled selfassembled nanoaero-

planes nanocombs and tetrapodlike networks of zinc oxide.

Nanotechnology 15, 949.

Mahmood, K., Park, S.S., Sung, K., et al, 2013. Enhanced photolu-

minescence, Raman spectra and field-emission behavior of indium-

doped ZnO nanostructures. J. Mater. Chem. 1, 3138–3149.

Nagareddy, V.K., Nikitina, I.P., et al, 2011. High temperature

measurements of metal contacts on epitaxial graphene. Appl.

Phys. Lett. 99, 073506.

Please cite this article in press as: Al-Ruqeishi, M.S., Mohiuddin, T. Growth of SinChemistry (2015), http://dx.doi.org/10.1016/j.arabjc.2015.06.007

Nickel, N.H., Terukov, E., 2005. Zinc-oxide – a material for micro-

and optoelectronic. Applications XVI. Springer.

Pan, Z.W., Mahurin, S.M., et al, 2005. Nanowire array gratings with

ZnO. Nano Lett. 5, 723.

Park, J.H., Choi, H.J., et al, 2004. Ultrawide ZnO nanosheets. J.

Mater. Chem., 14

Phan, T.L., Vincent, R., et al, 2008. Raman scattering in Me-doped

ZnO nanorods (Me =Mn, Co, Cu, and Ni) prepared by thermal

diffusion. Nanotechnology 19, 475702.

Phan, T.L., Sun, Y., et al, 2011. Structural characterization of CVD-

grown ZnO nanocombs. J. Kor. Phys. Soc. 59 (1), 60–64.

Qiang, L., Yiqing, C., et al, 2009. Annealing effect on the morpholo-

gies and photoluminescence properties of ZnO nanocombs. J. Phys.

Chem. Solids 70, 1482.

Qin, T., Gutu, T., et al, 2008a. Photoluminescent nanocomb struc-

tures by metabolic incorporation of germanium into the biosilica of

the diatom Nitzschia frustulum. ACS Nano 2, 129.

Qin, Y., Wang, X.D., et al, 2008b. Microfibrenanowire hybrid

structure for energy scavenging. Nature 451, 809.

Rusli, N.I., Tanikawa, M., et al, 2012. Growth of high-density zinc

oxide nanorods on porous silicon by thermal evaporation.

Materials 5, 2817–2832.

Shen, G., Bando, Y., et al, 2006. Characterization and field-emission

properties of vertically aligned Zn and nanopencils fabricated by

a modified thermal-evaporation process. Adv. Funct. Mater. 16,

410.

Song, Y., Chen, Y.-Q., et al, 2007. Preparation and photolumines-

cence of ZnO comb-like structure and nanorod arrays. Chin. J.

Chem. Phys. 20, 308–314.

Umar, A., Kim, S.H., et al, 2008. Formation of hierarchical ZnO

nanostrcutures nanocombs: growth mechanism, structural and

optical properties. Curr. Appl. Phys. 8 (6), 793.

Wan, Q., Li, Q.H., et al, 2004. Fabrication and ethanol sensing

characteristics of ZnO nanowire gas sensors. Appl. Phys. Lett. 84,

3654.

Wang, Z.L., 2004. Zinc oxide nanostructures: growth, properties and

applications. J. Phys.: Condens. Matter 16, 829.

Wang, Z.L., 2007. Novel nanostructures of ZnO for nanoscale

photonics, optoelectronics, piezoelectricity, and sensing. Appl.

Phys. A 7, 88.

Wang, Z.L., Kong, X.Y., et al, 2003. Scanning electron microscope

image of doublesided nanocombs grown by a solidvapor process.

Phys. Rev. Lett. 91, 185502.

Wang, J.X., Sun, X.W., et al, 2006. Zinc oxide nanocomb biosensor

for glucose detection. Appl. Phys. Lett. 88, 233106.

Xing, Y.J., Xi, Z.H., et al, 1999. Oriented Si nanowires grown via an

SLS mechanism. MRS Proc. 581, 231.

Xu, C.X., Sun, X.W., et al, 2004. Selforganized nanocomb of ZnO

fabricated by Au-catalyzed vaporphase transport. J. Cryst. Growth

270, 498.

Xu, F., Yu, K., et al, 2006. Growth photoluminescence and field

emission of hierarchical ZnO nanostructures. J. Nanosci.

Nanotechnol. 6, 3794.

Yan, H., He, R., et al, 2003. Dendritic nanowire ultraviolet laser

array. J. Am. Chem. Soc. 125, 4728.

Yang, Y.F., Ye, Z.Z., et al, 2008. Rational synthesis and character-

ization of heterostructures of ZnO nanocombs with ZnCdO

nanocaps. J. Phys. D Appl. Phys. 41, 115410.

Zha, M.Z., Calestani, D., et al, 2008. Large area selfcatalysed and

selective growth of ZnO nanowires. Nanotechnology 19, 325603.

Zhang, Y.H., Song, X.B., et al, 2006. Symmetric and asymmetric

growth of ZnO hierarchical nanostructures nanocombs and their

optical properties. Nanotechnology 17, 1916.

Zhang, B., Zhang, X.T., et al, 2008. Ni-doped zinc oxide nanocombs

and phonon spectra properties. Phys. Lett. A 372, 2300.

Zhou, H., Wissinger, M., et al, 2007. Ordered uniformsized ZnO

nanolaser arrays. Appl. Phys. Lett. 91, 181112.

gle-sided ZnO nanocombs/ML graphene Heterostructures. Arabian Journal of