Synthesis of Y-junction carbon nanofibres by ethanol catalytic combustion technique

Availableonlineatwww.sciencedirect.comDIRECTTransactions ofNonferrous MetalSociety of ChinaSciencePressTrans. Nonferrous Met. Soc. China 16(2006)s431-S434www.csu.edu.cn/ysxb/Synthesis of Y-junction carbon nanofibres by ethanolcatalytic combustion techniqueLI Fei(李飞)2, ZoU Xiao-ping(邹小平)2, CHENG Jin(程进)ZHANG Hong-dan(张红丹)2, REN Peng-fei(任鹏飞)21. Research Center for Sensor Technology, Beijing Information Technology Institute, Beijing 100101, China;2. Beijing Key Laboratory for Sensor, Beijing 100101, ChinaReceived 10 April 2006; accepted 25 April 2006Abstract: Y-shaped structure was synthesized by ethanol catalytic combustion(ECC) technique on the copper plate substrate, withoutdirectly seeding catalyst into the flame. The as-grown Y-junction carbon nanofibres were investigated by transmission electronmicroscopy(TEM). The very common laboratory ethanol burner was used for synthesizing carbon nanofibres. Two kinds of thecatalyst precursor, which are iron nitrate(Fe(NO3 )3)and nickel nitrate(Ni(NO3)2), were respectively employed to assist the formationof Y-junction carbon nanofibres. tEM analysis confirm the formation of Y-junction in the coiled and noncoiled carbon nanofibresThe type of the catalyst is found to be crucial to grow different Y-junction carbon nanofibres. Different Y-shaped structure maypossess different mechanical and electronic properties. These three-terminal nanofibres provide the nanoelectronics community witha novel material for the development of molecular-scale electronic devicesKey words: carbon nanofibres; Fe(NO3)3. Ni(NO3)2: Y-junction; ECC; Raman spectrananofibres are more than an order of magnitude stronger1 Introductionthan any current structure material, allowingrevolutionary advances in lightmass, high-strengthSince the discovery of carbon nanotubes in 1991applications[ 13]. Therefore, Y-shaped nanofibres can beIJIMAll, increasing interest has been attracted to the considered candidates to be the basic building unites fosynthesis of Y-like carbon nanotubes, which might be nanoeletronic devices. What's more, the fullerenes Cimportant multi-terminal nanostructures for potential and Cro were firstly identified by the carbon vapornanodevices such as single electron transistors[2], produced by laser irradiation of graphite, and haverectifying components and tunnel junctions as well as recently been produced in macroscopic quaenforcements for nanocomposites. For this purpose, vaporization of graphite with resistive heating. It has alseY-junctions have been as prototypes. To date, various been suggested that fullerenes might be formedfabrication methods have been developed to obtain the sooting flames. Their work motivated us to attempt toY-type junctions carbon nanotubes. They include the synthesize Y-junction carbon nanofibres, although therearc-discharge process for complex branching junctions have been no practical devices made of real three-point[3], template method[ 4, 5], hot-filament CVD method nanofibre junctions hithertousing vaporated copper as the catalyst[ 6], and pyrolysisIn this work, we reported on an alternative way toof hydrocarbon[7, 8 or organometallic precursors along synthesize Y-junction nanofibres with the stem andwith thiophene 9, 10]. Intion, nanowelding branches by ethanol catalytic combustion technique,echnique based on electron irradiation[11, 12] also which respectively use nickel nitrate precursor and ironthe important methods to fabricate nitrateprecursor as catalyst. Ethanol catalytic combustionY-junction carbon nanotubestechnique is a simple and cheap method for synthesizinThe same applies to the Y-shaped junctions carbon Y-junction carkibrec Comparednanofibers. For example, some groups have proved that methods, it te中国煤化工vantages asCNMHGProject(2005-2007)supported by Beijing City Education Committee Academic Innovative Team Program Sy wyFoundation item: Project(K M200510772013) supported by Beijing City Education CommitCorresponding author: ZoU Xiao-ping; Tel: +86-10-64884673-812: Fax: +86-10-64879486: E-mail: xpzou2005(@LI Fei, et al/ Trans. Nonferrous Met. Soc. China 16(2006follows. 1) The process of the synthesis can be done at kinds of Y-junctions. These images clearly show that thethe common laboratory; 2)Liquid ethanol, the very stem and the branches of the Y-junction are CNFs. Thecommon laboratory fuel, can quite naturally provide both junction we synthesized doesn't consist of a stemthe elevated temperature and the hydrocarbon reactant nanofibre connected two branch nanofibres. It seems thatfor CNFs synthesis at atmospheric pressure 3)The the branches grow from the sidewall of stem CNFS Seersynthesis was carried out, allowing controllablefrom the Fig. 1(a) the diameter of the stem is the samresidence time within a desired flame region; 4) Thethat of branches with a diameter of about 120synthesis can also tender either extended flames orHowever, it is interesting to note that the diameter ofmultiple flames for combustion, etc. Two kinds of Y-junction as shown in Fig. I(d) is much larger than thatcatalyst that were nickel nitrate catalyst precursor andiron nitrate catalyst precursor were respectivelydifference between the Y-junctions. Sometimes theemployed to assist the formation of Y-shaped structuresdifference is very large. Furthermore, we also noted thattheere is no caOur results show the possibility of growing Y-junctiontalytic particle present at junction pointcarbon nanofibres by ECCwhere branch nanofibres grow except for Fig. l(a). Fig. IObviously, each method has its own advantages andshows the different morphological Y-type junctionstructuresdisadvantages. Accordingly, in our present work,anethanol flame is induced to synthesize Y-junctions. Itides a method thatmucheconomical to meet the future broad applications2 ExperimentalThe approach to grow Y-junction carbon nanofibres based on ethanol catalytic combustion technique. Theethanol was employed as the carbon source and(Fe(NO3)3) or(Ni(NO3)2)as the catalyst precursor. Thecarbon nanofibres were synthesized by decomposition ofethanol. Firstly nickel nitrate was used as the catalyst1200mm200nrprecursor for the formation of Y-shaped structures. Thefirst step is to prepare a saturated solution of the catalystprecursor. Some quantities of nickel nitrate weredissolved in the pure ethanol. And then the solution ofcatalyst precursor was sonicated for tens of minutes toform a suspension of catalyst. One drop of the saturatedcatalyst solution was applied with a dip-pen to the copperbstrate, which was then placed in a flame withoutntroducing any other gas for the nanofibre growth. Thesurface of the substrate was faced down against the flamewhen it was inserted into the central core of the flame50nm500nmThe substrate with catalyst precursor was combusted forFig 1 TEM images of Y-junctions of different structures usingseveral minutes and then carbon deposits accumulated onthe copper plate. After a desired time, the sample wasnickel nitrate as catalyst precursorcooled to room temperature and dried in the air at roomtemperature. These deposits were removed and examinedFig 1(a) shows a spiral-shaped structure whose stemby transmission electron microscopy(TEM)with a JEOL and branches are all coiled. A spherical amorphou2010 microscope at 200 kV. The process of using iron particle is found right at the center of the junction(asnitrate as the catalyst precursor for synthesizing marked by an arrow). Fig. 1(b) shows the multipleY-junction is the same as that of using nickel nitrateY-junction structure that has multiple Y-like junctions.TEM was employed to confirm the structure ofFig 1(c) shows the combinatistructure that one ofY-junctionbranches is noncoiled and others are helix. there is necatalyst precursor凵中国煤化工 the junction3 Results and discussionFig 1(d) showsCNMHGnree branchesare noncoiledticleThe TEM images reveal the presence of severalFig. I also shows how multiple Y-junction can exit,LI Fei, et al/Trans. Nonferrous Met. Soc. China 16(2006suggesting possible multiple tunnel devices on a simple due to carbon accumulation. The lifting off of the newcarbon nanofibre. Therefore, Y-junction CNFs is very cap will resultformation of a new fibre at theseful in various fields of nanometer scale electrolsame time, in the case of a change in the direction of theapplications such as interconnect, two terminal diodes, concentration gradient, carbon atoms may accumulateand three terminal transistorsand a cap may form at a different location on the surfaceThe same is true of using iron nitrate as the catalyst of the catalytic precursor particle. As a result, the originalprecursor to grow Y-type junctions as shown in Fig. 2. fibre ceases extending, and a new fibre of differentHowever, the morphology of Y-junction is not abundant, orientation starts to grow. The final formation of thewhich is just a single noncoiled structureY-junction may result from the growth of a third fibrefrom a two-branch junction with the catalyst particlemoved away from the junction[ 15]. From Fig. I(d),wepropose a possible mechanism that the morphology ofthe CNF results from the flame perturbation during thegrowth of CNFsRaman spectroscopy is a simple and good tool foranalyzing the structure of the Y-junction. Raman spectraof Y-junction CNFs were excited with the 514.5 nm lineof a laser by a spectrometer at room temperature. Twopeaks(I 345.5 cm and 1 583. 4 cm in Fig 3; 1 349.8cm and 1 590.7 cm in Fig 4) can be observed in therange of 1 200-1 700 cm in a typical Raman spectrum,Figs.3and4.1250-1450thedisorder-induced phonon mode (D-band), whichcaused from the disordered components[ 16]. It has a high50nmsensitivity to the disordered structures in carbonmaterials. 1 550-1 600 cm is the graphite bandFig2 TEM image of Y-junction using iron nitrate as catalyst(G-band) which is produced from the high degree ofprecursorsymmetry and order of carbon materials, and generallyFrom Fig. l(a), Fig. 1(c)and Fig. 2, the mechanismused to identify well-ordered CNTs[16]. The peakcentered at 1 583.4 cm and 1 590.7 cm indicate an steps. Firstly, a carbogood arrangement of the hexagonal lattice of graphitenanofibre is formed from a nanosize catalyst precursor From Figs.3 and 4, we can clearly observe that theparticle, and then a catalyst precursor particle is G-band(1 345.5 cm anedeposited on the surface of this nanofibre, whichis all higher than their D-band(1 583.4 cm and 1 590.1subsequently causes the growth of a new attached cm). This phenomenon shows that this sample is not upnanofibre referred to as a 'branch. These twoto a high graphitization degreeproceeding can, under specific circumstances, favor thgrowth of Y-branched nanofibres. The length of the1345.5branch could be the consequence of the reactivity of thecatalyst[ 14], the concentration of the catalyst solution1583.4and growth temperature. Whereas, frem theFig 1(b), they a tip-growthmechanism[14], that is, the catalyst precursor particlesmoved with the growing CNFs tip. The formation ofY-junction may be the result of changes in growthdirection. Carbon atoms produced from thedecomposition of ethanol molecules are firstly adsorbedon a catalytic precursor particle. They diffuse along thesurface and/or in the interior of the metal particle, mainlydue to the existence of concentration gradient along the50010001500diffusion path. As carbon atoms acRaman shift/cm-IImulate, a capcomposed of the graphitic sheets forms. When the cap Fig3 RamanYH中国煤化工O3h2 as catalystlifts off the catalytic precursor particle, a nanofibre isCNMHGgenerated. As the fibre grows, a new cap may be formedLI Fei, et al/Trans. Nonferrous Met. Soc. China 16(2006)up of one noncoiled and two coiled CNFs; others are1349.8constituted of three noncoiled CNFs. Contrasting withthe widely used CVD and other methods, the presentmore economic. Thus, the technique is worthwhile to bedeveloped. Further extensive research will be on thegrowth of well-aligned Y-junction CNFs and explore theReferences[1 IIJIMA S Helical microtubules of graphitic carbon []. Nature, 1991500100015002000Raman shift/cm2 ANDRIOTIs A N, MENON M, SRIVASTAVAFig 4 Raman spectrum of sample using Fe(NO3)3 as catalystCHERNOZATONSKBallistic switching and rectification insingle wall carbon nanotube [J]. Appl Phys Lett, 2001, 79: 266-268precursor[3] ZHOU D, SERAPHIN S. Complex branching phenomena in thegrowth of carbon nanotubes []. Chem Phys Lett, 1995, 23We further characterized the y-junction nanofibres288-289by high-resolution transmission electron microscope. A 14 PAPADOPOULOS C, RAKITIN A, LI J,VEDENEEV AS, XUJMElectronic transport in Y-junction carbon nanotubes [] Phys RevHRTEM image taken at the sample is shown in Fig 8et12000,85:3476-3479The image shows the stacking of the graphene sheets [5] LI J, PAPADOPOULOS C, XU J. Growing Y-junction carbon[17]. We can also clearly observe the lattice. But there[6 GAN B, AHN J, ZHANG Q, RUSLI, YOON S F, YU J, HUANG Qare some defects on our samples, tooF, CHEW K, LIGATCHEV V A, ZHANG X B, LI W Z. Y-junctionby in situ[7 SU Lian-feng, WANG Jian-nong, YU Fan, SHENG Zhao-ming.Continuous dynthesis of Y-junction carbon nanotubes by catalyticCVD U. Chem Vap Deposition, 2005, 11: 351-354[ 8] LI WZ, WEN G REn Z F. Straight carbon nanotube Y-junctions[]. Appl Phys Lett, 2001, 79: 1879-18819 SATISH KUMAR B C, THOMAS P J, GOVINDARAJ A, RAOCNR, Y-junction carbon nanotubes [J]. Appl Phys Lett, 2000, 77[10 DEEPAK F L, GOVINDARAJ A, RAOCNR Synthetic trategiesFig 5 HRTEM image showing stacking of graphitic particles infor Y-junction carbon nanotubes [J]. Chem Phys Lett, 2001, 345sample using Fe(NO3)3 as catalyst precursor[11 TERRONES M, BANHART M F, GROBERT N, CHARLIER J CTERRONES H, AJAYAN P M. Molecular junctions by joininga great deal of production of Y-like nanofibres isingle-walled carbon nanotubes []. Phys Rev Lett, 2002, 89under investigation in our group. For further075505-1075505-4understanding of the behavior of the Y-junctions, the [12] CHENG J, ZOU X P, WANG L K A simple synthesis of carbonnanofibers[A]. The New Progress on Nanomaterials Research andstudy of the microstructure of the region around theTechnology Application[C]. Yantai, 2005. 71-75. (in Chinese)junction areas should be carried out[13 JIANG K, LI Q, FAN S Spinning continuous carbon nanotube yarns[ J. Nature,2002,419:804 Conclusions[14 ZHENG L X, OCONNELL M J, DOORN S K, LIAO X Z, ZHAOYH, AKHADOV E A, HOFFBAUER M A, ROOP B J, JIAQX,DYR C, PETERSON D E, HUANG S M, LIU J, ZHU Y T. UltralongY-junction CNFs can be synthesized by the ethanolsingle-wall carbon nanotubes [ ] Naturematerials, 2004, 3: 673-67catalytic combustion technique by employing Fe(NO3)3) [15] SU L E, WANG JN, YU F, SHENG Z MContinuous synthesis ofand(Ni(NO3)2 as catalyst precursor. In addition to, liquid351-354ethanol can be successful used as a kind of carbon source [16] LIU Y, PAN CX, WANG J Raman spectra of carbon nanotubes andor CNFs synthesis, too. Compared to CVD, pyrolysnanofibers prepared by ethanol flames []. J Mater Sci, 2004, 39and other methods, the catalyst does not need to be091-1094.exteriorly added when using ethanol flame. TEM images [17] SATISHKUMAR B C, JOHN THOMAS P, GOVINDARAJA.RAOCNR. Y-junction carbon nanotubes []. Appl Phys Lett, 2000, 77confirmed that some of the synthesized Y-junction CNFs2530-2532consist of three coiled CNfs with different diametersEdited by loNg huai-zheand some of the synthesized Y-shaped junctions are made中国煤化工CNMHG