Author's Accepted Manuscript
Silicon carbide nanowires grown on graphene sheets D. Wang, C. Xue, H. Bai, N. Jiang
PII: DOI: Reference:
www.elsevier.com/locate/ceramint S0272-8842(14)02038-0 http://dx.doi.org/10.1016/j.ceramint.2014.12.117 CERI9718
To appear in:
Received date: Revised date: Accepted date:
13 November 2014 19 December 2014 20 December 2014
Cite this article as: D. Wang, C. Xue, H. Bai, N. Jiang, Silicon carbide nanowires grown on graphene sheets, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2014.12.117 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 galley proof before it is published in its final citable 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.
Silicon carbide nanowires grown on graphene sheets D. Wanga,b, C. Xuea, H. Baia, N. Jianga,* a
Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, P.R. China b Nano Science and Technology Institute, University of Science and Technology of China, Suzhou, 215123, China
Abstract Silicon carbide nanowires (SCNs) were synthesized on graphene sheets by a simple heat treatment using a mixture of Si powders and commercial graphene sheets with Fe catalyst addition. A series of analytical techniques were employed to investigate the as-grown SCNs. The SCNs were confirmed to be the cubic β-SiC and grew along their preferred direction perpendicular to (111). Most of SCNs with the average length of about 10 µm and diameter of 60 nm lay on the graphene sheets. A few SCNs several micrometers in length show twisted morphology. Solid-liquid-solid (SLS) and vapor-liquid-solid (VLS) mechanisms were proposed which interpret the SCNs' growth process on the graphene sheets and match the nucleation, growth of SCNs very well.
Keywords: silicon carbide nanowires; graphene; growth mechanism 1.
Introduction Silicon carbide, as its wide band gap, high breakout field, high mechanical and
thermal properties, and stable under high temperatures, has been widely applied in
* corresponding author Tel. +86 574 87615701 E-mail Address: [email protected]
electronics, optics, and paddles in semiconductor furnaces [1–3]. One-dimensional silicon carbides nanowires (SCNs) are expected to exhibit some unique mechanical, electronic, and optical properties in nano-devices . The promise of SCNs encouraged approaches to the synthesis of this material. To date, SCNs have been synthesized by several techniques on various substrates [5,6], such as activated carbon [7,8], carbon black [9,10], carbon fiber [11–16], carbon nanotubes [17–20] and graphite [21–23], including laser ablation , chemical vapor deposition (CVD) , molten salt synthesis [16,26,27], thermal evaporation process with metal as a catalyst . However, growth of SCNs on graphene sheets is rarely reported. Graphene, which owns high carrier mobility , high thermal conductivity (5300 W/mK), high elasticity  and optical transparency , is expected to be the potential functional material applied in the semiconductor industry. The studies on the synthesis of SCNs grown on graphene sheets are of great importance in promoting exploitation of superb graphene composites and novel nano-devices. In this article, SCNs were synthesized on graphene sheets by a simple heat treatment using a mixture of Si powders and commercial graphene sheets with Fe catalyst addition. The microstructures and the synthesis mechanisms of SCNs were also studied. 2.
Experimental The growth of SCNs on the graphene sheets was carried out by a simple
heat-treatment process, in which the mixture of commercial graphene sheets (Ningbo Morsh Technology. Co., Ltd), Si (micron-sized, purity 99%) powders and Fe
(micron-sized, purity 99%) powders were used as the source materials. The heat-treatment process was performed at 1573 K under vacuum condition (below 1×10-1 Pa). Before the heat treatment, the mixture of graphene, Si powders and Fe powders (mass ratio 1:2:3) were milled for 12 h, and then loaded in a graphite crucible and placed in the vacuum induction furnace to synthesize the products. After cooling to room temperature, the extra Fe and Si powders were simply washed and sieved out. Then the graphene sheets with SCNs was cleaned in alcohol, dried and kept in desiccators. X-ray diffraction (XRD) and Raman spectra test were taken to analyze the phase composition of the reaction products. Hitachi S-4800 scanning electron microscope (SEM) and JEM-2100F transmission electron microscope (TEM) were used and an energy dispersive X-ray spectroscopy (EDS) detector was also applied to make further observation of the crystal structure and the growth direction of SCNs on the graphene sheets. 3.
Results and discussion
3.1 Microstructure of composites Fig. 1 shows the XRD pattern of the products. Four β-SiC peaks at 35.70°, 41.38°, 60.02° and 71.80° were observed, which are diffractions from SiC (111), (200), (220) and (311) planes respectively, indicating the formation of β-SiC (JCPDS card No. 29-1129). Two peaks at 45.41° and 46.97° are attributed to the Fe-Si compound, which is very important for the growth of SCNs, and the growth mechanism will be discussed below in detail.
Further information on the nature of the SCNs grown on the graphene sheets is provided by the Raman spectra in Fig. 2. The Raman spectra were collected with a Renishaw Raman microscope (532 nm laser excitation wavelength). The peaks at 1334.9, 1567.5, 2680.4 cm-1 has been attributed to the vibration mode of inter-icosahedra C–C bonds. Peaks at 781.4 and 934.5 cm-1 shift towards the lower wavenumber than the two peaks corresponding to the optical phonon mode of β-SiC, which including the transverse optical phonon mode (796 cm-1) and longitudinal optical phonon mode (972 cm-1)  , indicating that the different crystalline structure from the SiC nanostructure materials. Fig. 3(a) shows a typical SEM image of the products revealing nanowires are densely grown on the graphene sheets. Most of SCNs lay on graphene sheets with the average length of about 10 µm and diameter of 60 nm. The magnified interface image of the SCNs/graphene from Fig. 3(b) indicating SCNs and the graphene are bonded via chemical reactions, rather than intertwined together. It is worth to note that the nanowires growth occurred on the whole surface of graphene sheets, with an estimated surface coverage of about 80%. In order to analyze the nanowires grown on the graphene sheets, the Transmission Electron Microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) are shown in Fig. 4. Fig. 4(a) provides a high-magnification TEM image of a representative as-fabricated SCN, and on it a tiny particle in dark is found to embed at the tip. The tiny particle at nanowire tip marked in (a) area was analyzed by EDS, where the intense Fe and Si intrinsic X-ray peaks were detected
meaning that this tip particle is composed of Fe-Si alloy, which is consistent with the results of XRD pattern shown in Fig. 1. A little amount of copper detected is considered to come from the Cu TEM grid, which is not the intrinsic signal of this nanowire. The middle region of nanowire marked in (b) area was analyzed by EDS as well. In contrast to the EDS spectrum taken at the tip areas, a very intense Si and C peak was recorded, which further suggested that this nanowire contains silicon carbide. Fig. 4(b) shows a HRTEM image and electron diffraction (ED) pattern of the SCN. The spacing between adjacent lattice planes is 0.25 nm, corresponding to the d spacing of the (111) plane of β-SiC, which indicated that the SiC nanowire was grown along the (111) direction. The SCN has a relatively rough surface with stacking fault planes perpendicular to the growth direction. This is one reason of the SCNs' Raman shift towards the lower wavenumber . Fig. 4(c) shows the other structure of twisted SCNs. This structure may be induced by the alternate growth of the SCNs along the different directions . Here we can clearly see the interface of the SCNs/graphene tightly bonded together. Furthermore we also found a standalone SCN with both straight and twisted structure shown on Fig. 4(e). The image of Fig. 4(f) is the surface of the graphene sheet with Fe-Si alloy on it but nanowire yet not be formed, which supports the SCNs growth mechanisms mentioned blew. 3.2 The growth mechanisms of the nanowires Several growth mechanisms for the growth of one-dimensional nanostructure have been proposed: vapor-liquid-solid (VLS) growth mechanism , vapor-solid (VS) growth mechanism  and solid-liquid-solid (SLS) growth mechanism .
For the case with metal catalysts, the growth mechanism of the nanowire usually obeys the VLS model. In this experiment the growth processes of the SCNs consist of two parts: the nucleation of the SiC crystals and the growth of crystal nucleuses. During the nucleation process, as the temperature increased, Fe and Si will react to produce the alloy droplets which are adsorbed on the graphene surface. Due to the great wettability between the Fe-Si alloy and graphene, a uniform liquid film is formed on the graphene surface. After that, the carbon atoms in the graphene diffuse into the liquid film and react with the Si to form SiC crystal. The schematic diagram for the nucleation of the SiC crystal is shown in Fig. 5 I and II. It should be noted that the formed SiC crystal exhibits the droplet-shape and adsorbs on the Fe-Si film due to the lower density of SiC with respect to the Fe-Si alloy. Thus, after the nucleation process, the SCNs will grow on Fe-Si alloy surface. Generally, the nucleation process involves the solid carbon in the graphene, the Fe-Si liquid film and the SiC crystal. Therefore, the nucleation of the SCNs is controlled by the solid-liquid-solid (SLS) model. However, this model cannot explain the growth process of the SCNs. This may attribute to the fact that the carbon content in the alloy particle is limited. Furthermore, it is very difficult for carbon in alloy liquid film spread to the tip alloy particle along long nanowire and thus long nanowire would not be formed. In fact, the SCNs are very long even beyond several microns. In the second step, namely the growth of crystal nucleuse, the SCNs are synthesized by the carbothermal reduction reaction mechanism[38,39]. Silicon and
carbon respectively react with a small amount of oxygen which existed in the commercial graphene sheets and the low vacuum atmosphere to generate gas phase SiO and CO, which are the initial and endothermic reactions: Si (s) + 1/2 O2 (g) = SiO (g)
C (s) + 1/2 O2 (g) = CO (g)
The gaseous SiO subsequently reacts with C and CO in accordance with reactions (3) and (4): SiO (g) + C (s) = SiC (s) + CO (g)
SiO (g) + CO (g) = SiC (s) + 2CO2 (g)
The generated CO2 gas will be consumed immediately by the surrounding carbon to form CO gas: CO2 (g) + C (s) = CO (g)
Reaction (5) is followed by reaction (4) to synthesize CO, which in turn reacts with SiO according to reaction (4), and the cycle continues. SiC will grow into be the nanowire morphology according to the reaction process mentioned above. Thus the growth of SCNs follows a VLS mechanism and the schematic for the growth of the SCNs is shown in Fig. 5 III and IV. 4.
Conclusions SCNs have been synthesized on the graphene sheets by a simple heat treatment
approach using the mixture of Si powders and graphene sheets with Fe catalyst addition. The as-grown SCNs have diameters in the range of 20–100 nm, lengths of several micrometers and different shapes were observed. The SCNs were confirmed
to be the cubic structural β-SiC. The SLS and VLS models were proposed to explain the nucleation of the SiC crystals and the growth of crystal nucleuses respectively, which can perfectly interpret the SCNs growth mechanism on graphene sheets and match experiment results very well.
Acknowledgements This work was financially supported by the China Postdoctoral Science Foundation (2014M550336).
J. Chen, Q. Shi, W. Tang, Field emission performance of SiC nanowires directly grown on graphite substrate, Mater. Chem. Phys. 126 (2011) 655–659.
Y.J. Wu, J.S. Wu, W. Qin, D. Xu, Z.X. Yang, Y.F. Zhang, Synthesis of β-SiC nanowhiskers by high temperature evaporation of solid reactants, Mater. Lett. 58 (2004) 2295–2298.
J. Ye, S. Zhang, W.E. Lee, Novel low temperature synthesis and characterisation of hollow silicon carbide spheres, Microporous Mesoporous Mater. 152 (2012) 25–30.
J.J. Niu, J.N. Wang, A Novel Self-Cleaning Coating with Silicon Carbide Nanowires, J. Phys. Chem. B. 113 (2009) 2909–2912.
B. Babić, D. Bučevac, A. Radosavljević-Mihajlović, A. Došen, J. Zagorac, J. Pantić, et al., New manufacturing process for nanometric SiC, J. Eur. Ceram. Soc. 32 (2012) 1901–1906.
W. Xie, G. Möbus, S. Zhang, Molten salt synthesis of silicon carbide nanorods using carbon nanotubes as templates, J. Mater. Chem. 21 (2011) 18325.
G. Li, X. Li, H. Wang, X. Xing, Y. Yang, SiC nanowires grown on activated carbon in a polymer pyrolysis route, Mater. Sci. Eng. B. 166 (2010) 108–112.
S. Dhage, H.-C. Lee, M.S. Hassan, M.S. Akhtar, C.-Y. Kim, J.M. Sohn, et al., Formation of SiC nanowhiskers by carbothermic reduction of silica with activated carbon, Mater. Lett. 63 (2009) 174–176.
F.-L. Wang, L.-Y. Zhang, Y.-F. Zhang, SiC Nanowires Synthesized by Rapidly Heating a Mixture of SiO and Arc-Discharge Plasma Pretreated Carbon Black, Nanoscale Res. Lett. 4 (2009) 153–156.
M. Wieligor, R. Rich, T.W. Zerda, Study on silicon carbide nanowires produced from carbon blacks and structure of carbon blacks, J. Mater. Sci. 45 (2010) 1725–1733.
B. Qian, H. Li, Z. Yang, Y. Zhang, Y. Su, H. Wei, et al., Inverted SiC nanoneedles grown on carbon fibers by a two-crucible method without catalyst, J. Cryst. Growth. 338 (2012) 6–11.
X. Zhang, Y. Chen, W. Liu, W. Xue, J. Li, Z. Xie, Growth of n-type 3C-SiC nanoneedles on carbon fabric: toward extremely flexible field emission devices, J. Mater. Chem. C. 1 (2013) 6479.
J. Wei, Fabrication of composite structure of carbon fibers and high density SiC nanowires, Phys. E Low-Dimensional Syst. Nanostructures. 41 (2009) 1810–1813.
W.M. Qiao, S.Y. Lim, S.H. Yoon, I. Mochida, L.C. Ling, J.H. Yang, Synthesis of crystalline SiC nanofiber through the pyrolysis of
polycarbomethylsilane coated platelet carbon nanofiber, Appl. Surf. Sci. 253 (2007) 4467–4471. 
J. Chen, R. Wu, G. Yang, Y. Pan, J. Lin, L. Wu, et al., Synthesis and photoluminescence of needle-shaped 3C–SiC nanowires on the substrate of PAN carbon fiber, J. Alloys Compd. 456 (2008) 320–323.
W. Xie, Z. Mirza, G. Möbus, S. Zhang, Novel Synthesis and Characterization of High Quality Silicon Carbide Coatings on Carbon Fibers, J. Am. Ceram. Soc. 95 (2012) 1878–1882.
E. Muñoz, A.B. Dalton, S. Collins, A.A. Zakhidov, R.H. Baughman, W.L. Zhou, et al., Synthesis of SiC nanorods from sheets of single-walled carbon nanotubes, Chem. Phys. Lett. 359 (2002) 397–402.
H.-J. Quah, K.Y. Cheong, Z. Lockman, Stimulation of silicon carbide nanotubes formation using different ratios of carbon nanotubes to silicon dioxide nanopowders, J. Alloys Compd. 475 (2009) 565–568.
W. Xie, G. Möbus, S. Zhang, Molten salt synthesis of silicon carbide nanorods using carbon nanotubes as templates, J. Mater. Chem. 21 (2011) 18325.
C.C. Tang, S.S. Fan, H.Y. Dang, J.H. Zhao, C. Zhang, P. Li, et al., Growth of SiC nanorods prepared by carbon nanotubes-confined reaction, J. Cryst. Growth. 210 (2000) 595–599.
H.J. Hwang, K.-J. Lee, Y.-T. An, B.-H. Choi, W.-S. Seo, Synthesis of β-silicon carbide nanofiber from an exfoliated graphite and amorphous silica, Mater. Chem. Phys. 134 (2012) 13–15.
J. Chen, J. Zhang, M. Wang, L. Gao, Y. Li, SiC nanowire film grown on the surface of graphite paper and its electrochemical performance, J. Alloys Compd. 605 (2014) 168–172.
J. Ding, C. Deng, W. Yuan, H. Zhu, X. Zhang, Novel synthesis and characterization of silicon carbide nanowires on graphite flakes, Ceram. Int. 40 (2014) 4001–4007.
W. Shi, Y. Zheng, H. Peng, N. Wang, C.S. Lee, S.-T. Lee, Laser Ablation Synthesis and Optical Characterization of Silicon Carbide Nanowires, J. Am. Ceram. Soc. 83 (2000) 3228–3230.
J.Z. Guo, Y. Zuo, Z.J. Li, W.D. Gao, J.L. Zhang, Preparation of SiC nanowires with fins by chemical vapor deposition, Phys. E Low-Dimensional Syst. Nanostructures. 39 (2007) 262–266.
J. Ding, C. Deng, W. Yuan, H. Zhu, J. Li, The synthesis of titanium nitride whiskers on the surface of graphite by molten salt media, Ceram. Int. 39 (2013) 2995–3000.
J. Ye, S. Zhang, W.E. Lee, Molten salt synthesis and characterization of SiC coated carbon black particles for refractory castable applications, J. Eur. Ceram. Soc. 33 (2013) 2023–2029.
Z.S. Wu, S.Z. Deng, N.S. Xu, J.J. Chen, J. Zhou, Needle-shaped silicon carbide nanowires : Synthesis and field electron emission properties Needle-shaped silicon carbide nanowires : Synthesis and field electron emission properties, Appl. Phys. Lett. 3829 (2008) 2000–2003.
K.I. Bolotin, K.J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, et al., Ultrahigh electron mobility in suspended graphene, Solid State Commun. 146 (2008) 351–355.
C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene, Science (80-. ). 321 (2008) 385–388.
K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, et al., Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature. 457 (2009) 706–710.
M. Bechelany, a. Brioude, D. Cornu, G. Ferro, P. Miele, A Raman Spectroscopy Study of Individual SiC Nanowires, Adv. Funct. Mater. 17 (2007) 939–943.
S. Rohmfeld, M. Hundhausen, L. Ley, Influence of Stacking Disorder on the Raman Spectrum of 3C-SiC, Phys. Status Solidi. 215 (1999) 115–119.
S.S. Brenner, G.W. Sears, Mechanism of whisker growth—III nature of growth sites, Acta Metall. 4 (1956) 268–270.
Y. Li, S. Xie, W. Zhou, L. Ci, Y. Bando, Cone-shaped hexagonal 6H–SiC nanorods, Chem. Phys. Lett. 356 (2002) 325–330.
X.W. Du, X. Zhao, S.L. Jia, Y.W. Lu, J.J. Li, N.Q. Zhao, Direct synthesis of SiC nanowires by multiple reaction VS growth, Mater. Sci. Eng. B. 136 (2007) 72–77.
L. Xin, Q. Shi, J. Chen, W. Tang, N. Wang, Y. Liu, et al., Morphological evolution of one-dimensional SiC nanomaterials controlled by sol–gel carbothermal reduction, Mater. Charact. 65 (2012) 55–61.
H.-P. Martin, R. Ecke, E. Müller, Synthesis of nanocrystalline silicon carbide powder by carbothermal reduction, J. Eur. Ceram. Soc. 18 (1998) 1737–1742.
X.K. Li, L. Liu, Y.X. Zhang, S.D. Shen, S. Ge, L.C. Ling, Synthesis of nanometre silicon carbide whiskers from binary carbonaceous silica aerogels, Carbon N. Y. 39 (2001) 159–165.
Figure captions Fig. 1 XRD pattern of the products. Fig. 2 Raman Spectrum of the products. Fig. 3 SEM pictures of the SCNs grown on graphene sheets: (a) low-magnification SEM image of the SCNs grown on graphene sheets, (b) high-magnification SEM image of the SCNs/graphene interface. Fig. 4 (a) High-magnification TEM image of a straight SCN and the EDS of its tip and middle region, (b) HRTEM image and ED pattern of the straight SCN, (c) High-magnification TEM image of a twisted SCN, (d) HRTEM image and ED pattern of the twisted SCN, (e) High-magnification TEM image of a standalone SCN with both straight and twisted structure, (f) TEM image of the graphene sheet surface with Fe-Si alloy on it. Fig. 5 Schematic for the SCNs growth mechanism on graphene sheets surface.
Fig. 1. XRD pattern of the products.
Fig. 2. Raman Spectrum of the products.
Fig. 3. SEM pictures of the SCNs grown on graphene sheets: (a) low-magnification SEM image of the SCNs grown on graphene sheets, (b) high-magnification SEM image of the SCNs/graphene interface.
Fig. 4. (a) High-magnification TEM image of a straight SCN and the EDS of its tip and middle region, (b) HRTEM image and ED pattern of the straight SCN, (c) High-magnification TEM image of a twisted SCN, (d) HRTEM image and ED pattern of the twisted SCN, (e) High-magnification TEM image of a standalone SCN with both straight and twisted structure, (f) TEM image of the graphene sheet surface with Fe-Si alloy on it.
Fig. 5. Schematic for the SCNs growth mechanism on graphene sheets surface.