Synthesis of carbon nanotube arrays using ethanol in porous anodic aluminum oxide template Synthesis of carbon nanotube arrays using ethanol in porous anodic aluminum oxide template

Synthesis of carbon nanotube arrays using ethanol in porous anodic aluminum oxide template

  • 期刊名字:科学通报(英文版)
  • 文件大小:342kb
  • 论文作者:YU Guojun,WANG Sen,GONG Jinlon
  • 作者单位:Shanghai Institute of Applied Physics
  • 更新时间:2020-10-22
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论文简介

ARTICLESchinese science Bulletin 2005 Vol. 50 No 11 1097=1100shape, and their aspect ratio can be changed with AAOSynthesis of carbon nanotube since their original preparation by takashi et al. in 199515.60arrays using ethanol in porous AAocNT walls are not composed of curved graphite layanodic aluminum oxideers but almost amorphous carbon 9-12.In fact,theaaocnt is only a kind of ultrafine carbon tube withtemplatenanometer size of diameter, very different from multiwalled carbon nanotubes (MWCnt) by other methodYU Guojun, WANG Sen, GONG Jinlongsuch as arc discharge or fine metal particles catalysis 3JZHU Dezhang, HE Suixia, LI Yulan ZHU ZhiyuanThis problem will greatly decrease the excellent propertiesof CNTs, such as high conductivity, and very low fieldShanghai Institute of Applied PhysiAcademy of Sciences, Shanghai 201800,emission voltage!l4 15. Tatsuya et al. 6 and Jeong et al. 1Correspondence should be addressed to Gong Jinlong(email: gjl@obtained the MWCNTs in the nano-channel arrays ofAAO, but the growth of these MWCNTs with variousAbstract Carbon nanotube(CNT)arrays confined bydiameters and lengths was driven by catalyst particles ofporous anodic aluminum oxide(AAO) template were synthe:- metal in fact. In addition, some channels of the Aao temsized using ethanol as reactant carbon source at low pressure.plate had not any CNTs. Gao et al. 8 prepared the wellgraphited AAOCNT using ethylene as carbon source atmagnification transmission electron microscopy(TEM) show 900 C and the graphitization extent of their AAOCNTs isthat these CNTs have highly uniform outer diameter and higher than the ones produced by other groups 5-7,butlength, absolutely controlled by the diameter and depth of still not so good as MWCNT. In our work, we synthesizednano-channel arrays of the AAO. High resolution transmis. CNT arrays confined by AAO template with ethanol assion electron microscopy (HRTEM) imaging indicates that reactant carbon source at low pressure, the graphitizationthe graphitization of the CNt walls is better than the resultsthough it is not so good as that of multiwalled carbon nano- by other research groups including Gao et al. 5-8, and ourtubes (MWCNTs) synthesized by catalysis CNTs synthesized synthesis temperature is 100.( lower than that of Gao'stion than those prepared using ethanol by comparing the group/18)using acetylene as reactant gas show much less graphitizaesults of HRTEM and Raman spectroscopy. The etchingxperimenteffects of decomposed OH radicals on the amorphous carbonA high purity (99.999%)aluminum sheet polishedand the roughness of AAo nano-channel arrays on the cnts electrochemically was anodized for 10 h at the voltage ofgrowth were employed to explain the graphitization and 25 V and temperature of 10 in 3% sulfuric acid solutiongrowth of the CNts.which produced the AAO template with 40 um thicknessKeywords: ethanol, porous anodic aluminum oxide template, and 30 nm average pore diameter. Aluminum substratehemical vapor deposition, carbon nanotube arrays, OH radical.between two AAO templates was removed with saturatedDOI:10.1360982004-68HgCl2 solution. Then the independent AAO template withone side open-ended was put into a horizontal CVD facil-Since their discover1991, carbon nanotubes ity stove after enough rinse with deionized water and dry-(CNTS)are always one of the hotspots of material science. ing at 70 C in atmosphere The growth of AAOCNTs wasIn the past decade, the CNTs, suggested as a promising carried out at 800!( and 10 Torr for 15-23 h underelectron-emitting material, have become one of ideal can- ethanol flow or acetylene flow of 80 mL/min. After CVDdidates for future generations of cold-cathode flat paneldisplays and various vacuum microelectronic devices be-process, the product was cooled to room temperature incause of their excellent characvacuum, then the AaOCNts were obtained after etchingcs, such as highaway the aAo template with concentrated hydrofluoricchemical inertness, high thermal stability, and high me- acid and totally rinsing with deionized water, in additionchanical strength, in addition to high aspect ratio, smallradius of curvature[2. 31. However, it is necessary to prepare to drying at 100! C in airlarge area and vertically aligned CNT arrays, if the CNtsScanning electron microscope (SEM, LEO 1530 VPcan be applied to practical emitting flat panel displays. At and low magtron microscopypresent, one of effective methods to produce large area, (TEM, JEOL中国煤化 observe the shapevertically aligned, and mono-dispersed CNT arrays is us- of the AACCNMHGon transmissionng self-assembled porous anodic aluminum oxide electron microscopy (HRTEM)and Raman spectroscopyAAO)as template to confine growth of CNT arrays. AAOCNTswere used to analyze the graphitization extent of theThe CNTs in AAO (AAOCNTs) have uniform structure orChiaese seience Bulletin Vol 50 No. 11 June 20051097ARTICLES2 Results and discussionlow magnification transmission electron microscopy image of the aaOCnts shows that these cnts are uniformFig. 1(a)shows the SEM image of AAOCNTS using in diameter and tube walls thickness, but the walls areethanol as carbon source after removing the AAo tem- very smooth and there are some small branches on them orplate, which shows that all of the CNTs are one side Fig. 2 shows HRTEM images of AAOCNTs growinopen-ended, straight and very uniform in diameter, the for 15 h using ethanol and ethylene, respectively. The re-results are consistent with refs. [5-18]. In Fig l(b), the sults indicate that the ethanol aaocnt is more orderedFig. 1. SEM image(a) and TEM image(b)of AAOCNT growing for 15 h using ethanol as carbon sourcedH中国煤化工CNMHGFig. 2. HRTEM images of AAOCNT growing for 15 h(a)and 23 h(c)using ethanol, and HRTEM images of AAOCNT growing for 15h(b)and 23 h(d) using acetylene109方数据Chinese Science Bulletin Vol 50 No. 11 June 2005ARTICLESthan the acetylene AAOCNT in graphitization of tube Then the Oh radicals form co by attacking nearbyalls. The former has dense, parallel crystal lattice with amorphous carbon atoms with a dangling bond. Thuslittle amorphous carbon compared to the latter which has amorphous carbon was etched away and high-puritynearly no crystal lattice and more amorphous carbon. Fig. SWCNTs were produced. So, we infer that the etching2(b)and(d) is hRtEM images of AAOCNTs growing for effect of OH radicals to amorphous carbon also appears in23 h using ethanol and ethylene, respectively. From the our AAOCNTs growth process. During this process, OHmages we can see that the graphitization results of radicals were also produced due to decomposition ofAAOCNT'S are similar to those of Fig. 2(a)and (b), but ethanol at high temperature, furthermore, the very lowthe thickness of tube walls increases by 2-3 nmpressure(10 Torr) and very long growth time(15-23 h)Raman spectroscopy is a very useful method to meas- created a sufficient condition for OH radicals' etching toure and estimate the structure ordering of CNTS. Usuallythere are two independent peaks called d band at aboutIn addition we find out a fact that the tube wall's thick-1350 cm and G band at about 1580 cm for CNTs. The ness of both ethanol AAOCNTs and acetylene AAOCNtsd band is an acoustics wave induced by disordered struc- growing for 23 h are thicker than the ones growing for 15tures, and the G band, which corresponds to the character- h. Obviously, the growth mode of AAOCNT is very dif-tic band of graphite monocrystflects the symmetrferent from¨tip¨ growth mode/ or“base” growthor ordering of CNTs. Thus, the integral intensity ratio of model23lof CNTs growth Up to now, there are three kindsd band to G band D/IG)can reflect the graphitization of viewpoints on the growth of AAOCNTs Firstly, theextent of CNTs. Our Raman test was carried out on Dilor AAOCNT growth is catalyzed by alumina just like thatLabRamINFINITY microscopy Raman spectroscopy me- reported in refs. [8ter, and the wavelength of excitation beam is 632.8 nm. template confining growth of CNT arrays formed by carFig. 3 gives the Raman spectroscopy of our AAoCNts bon deposition onto the channel walls of AAo(24. 251. Theproduced by ethanol and acetylene, respectively. It is ob- third viewpoint is both of the above two 26.We think ourvious that the acetylene AAOCNTs are more disordered AAOCNTs grow clingingly along the channel walls ofthan ethanol AAOCNTs from the Raman spectroscopy. AAO via layer by layer process of carbon deposition, be-The crystal size, La9,20, increased from 7 nm for the cause the tube wall thickness increases with growth time,former to 20 nm for the latter, via the formula La=44 IG/lp. and the tube length, tube diameter wondrously match theThe result is consistent with HRTEM imageschannel depth, channel diameter of the AAO. The growth24000mode of AAOCNTs is similar to"epitaxial growth"modesuggested by Im et al. and almost the same as "layer bylayer"mode reported by Yao et al. 125. The only role ofG bandAAO for CNT growth is template confining, and the micro-structure or micro-shape of the AAO channel wallsdirectly works on the deposition of carbon and the qualitof AAOCNTs. However, up to now, the roughness of theAAo channel walls is within the nanometer scale[271. sothe roughness of aaocnt walls is within this scale tooThis reason prevents AAOCNTS with poor graphitizationfrom ideal mwcnt we believe that the smoothness and00the graphitization extent will be improved greatly, if the100012001400roughness of the aao channel walls can be reduced. furRaman shift/cmher work is progressing in our groupFig. 3. Raman spectroscopy(excitation beam wavelength: 632. 8 nn3 Conclusiontaken from AAOCNTs produced by ethanol and acetylene, respectivelsummary, AAOCNT arrays were synthesized usingThe reason why ethanol is a much better carbon source ethanol as reactant carbon source at low pressure, and thefor improving graphitization of AAOCNTs than acetylene graphitization extent of the AAOCNTs is much better thanand other carbon sources[5-18]. we think is the existent of the results reported in literatures. This work may be verydecomposed OH radicals from ethanol during the growth important for preparing ideal MWCNT arrays with uniof AAOCNTs. High-purity single-walled carbon nano- form, adjustand diameter in AAo templatetubes(SWCNTs) were prepared using ethanol at very low Acknowledgeme中国煤化-y the Key project oftemperature by Maruyama et al. 2, and the etching role of Knowledge InneCNMHGemic of Sciences. thedecomposed OH radicals to amorphous carbon was ex- National Natural crtion or Cnina (urant No. 1037508plained by them. In brief, the ethanol catalyzed by metal 2003CB716901) and Shanghai Nanometer Special Foundation (Grantparticles produces elementary carbon and Oh radicals. No. 0352nm050)灼9数鸦 ence Bulletin Vol.50N.11June20051099ARTICLESReferences15. Wan. YJ. Kulkarni. N.n.K. et al.. Electric characteriza-lijima, S, Helical microtubles of graphitic carbon, Nature, 1991tion of individual carbongrown in nanoporous anodic3546348):56-58alumina templates, ApplLetters,2004,84(7):11772. 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