Hirata Yoshinori

Matsumoto Takeo

Okuno Masayuki

奥野 正幸

松本 菘生

Kanazawa University Repository for Academic Resources

Sd. Rep. Kanaza宵aUniv. Vol. 39， No.2， pp. 39 ~46 D色C巴mber1994 The syn.thesi邑ofcarbon n.3JlOpartides hy :aUernating curnmt arc -discharge evapo:ratおYOSHINORI HIRA T A， MASA YUKI OKUNO and T AKEO MA TSUMOTO Departmenl 01 Em1h Sciences， Faculty 01 Seience， l(anazawa [jらl!ve;古i~v， J(al?u昨la，Kanazawa， .920-11， ]atan Abstract: Carbon nanotubes and nanoparticles have been synthesized by th己呂lternatingcurrent (a.c.) arc-dischargeξvaporation method. A carbon rod and a carbon string werε used as the source material for carbon. The synthesis of carbon nanotubcs and nanopartj. cles was carried out und己rth巴followingconditions， a voltagεof 6~15 V， a current of 8~ 20 A and with h芭liumgas at approximately 700 Torr. As a 官邸1I1tof th担seconditions， carbon nanotubes and nanoparticles were found on th日巴lectrode目 The morphology of the nanotubεs is similar to those repol'ted from the direct curr日nt(d，c，) arc-discharge巴vaporation method (Iijima et aL (1992))，百owεver・， in the pres邑ntstudy a few nanotubes were observed to be bent in the middle sεction and completely sealed by a cap at the each encl. Two typεs of nanopal'ticles were found on the carbon el日ctrodes，(1) a spherica! nanoparti-cle with a hollow and (2) a nanopal'ticle with a similar shape as those observed on th己nanotube tips. Th紅白wereno nanotubes or nanoparticles found on th色glasssubstrat日us芭dfor the collection of carbon materials d巴posit己din the r日actionchamber 1. Introduction 39 Diamond and graphite are well known as the two "C60" ， a new form of carbon was found by Kroto et a1 of carbon， Recentlv the vaporization of a graphite disk in a density helium laser. The which is called "百buck王印E紅mins坑te臼rfullε訂re臼n児eby using a focused pulsed structure similar to a sphere呂a一ndhas 32 faces， 12of which are and 20 are hexagon. Carbon nanotubes， which are the other new form of carbon were synthesized Iijima (1991). By using a direct current arc-discharge evaporation method， he has synthesized the needles of the carbon nanotubes and the nanoparticles at the negative end of the carbon electrodes， A structural model for a carbon nanotube reported by Iijima (1991) is shown in Fig.1. However， the synthesis of carbon nanotubes and nanoparticlεs using alternating current has not previously been reported. In this paper the authors report on the synthesis of carbon nanotubes and nanoparticles by using the a.c. arc-discharge evaporation method. 40 Yoshinori HlRATA， Masayuki OKUNO ana T旦keoMATSUMOTO (b ) 2A6A |一{1 c主主エ〉下2~戸~， _1_ 3心主主主3Fig. L (a) Schematic diagram of the stfUctural model of the carbon nanotube reported by Iijima (1991) The number corr巴spondsto the roling of graphitεlayers. (b) Schematic diagram of the three sh問 tsof graphite. 20 Expel'im側 taI2.1 Appa:ratus Fig. 2 shows a schernatic diagram of the carbon nanotube synthesis apparatus， which employs the a.c. evaporation technique used in this study. This apparatus is similar to that re凹 rtedby Iijima The reaction chamber 1S made of pyrex glass， 13 cm long and 6 cm in diameter. The electrodes of the carbon the carbon and the tungsten basket heater were supported copper rods that were 0.45 cm in diameter. A of glass substrate was set up 9 mm above the electrode in the in order to collect synthesized carbon materials. 2，2 Syn1l;h.eiSlRs Three types of were undertakeno The differ肉enceswere related to the source material of the electrode. (a) Synthesis using carhon string A carhon string 5 mm indiameter was used for the Initially， the air in the reaction chamher was removed using a rotary pump and helium gas at approximately 700 Torr was introduced置 Thecarbon discharge arc was generated running a alternating current of 8-10 A at 15 V. The samp!es for TEM obsεrvation were col1ected from the carbon string in the reaction chamber. Th邑synth己sisof carbon nanotub巴sand nanoparticles by alt邑matingcurr田 tarc-discharge evaporation method. 41 A ( a) 寸BHe D 九F~E ( ) [戸引? ? ???? ???????? ?????????????????????ぃ??? ??????????????? ????????? ???。??? ? ??、?『? ??? ? ? ? ??????????????????????????、【????「????????????? ? ? ??? ? ?、?? ? ?」? ??Fig. 2. (a) Schematic diagram of a.c. arc-discharg巴evaporationmethod apparatus目 A，pressur色 gauge;B， reacion chamb巴r;C， copp邑rrod; D， substrate; E， slide rhεostat; F， voltmeter; G， ammeter; H， rotary pump (b) Close up schematic diagram of el記ctrodes(b) Synthesis using-carbon sticks Two carbon rods 6 mm indiameter for spectrum analysis (Shimazu Co Ltd) were used for this synthesis. The sharpened point of a carbon rod was contacted against another rod with a flat face for arc-discharge evaporation. Similar to be the first synthesis， the reaction chamber was filled with helium gas at approximately 700 Torr. The carbon discharge arc was generated by running a alternating current of 10-20 A at 10 V. The samples for TEM observation were collected from the carbon sticks in the reaction chamber. 42 Y oshinori HIRATA， Masayuki OKUNO and Takeo MATSUMOTO (c) tungsten basket heater A small lump of carbon approximatly 3 mm and 0，02 g in vveight was placed in a tungsten basket heateL As in the first ， the reaction chambε:r 'iNas filled with helium gas at 700 Torr. This synthesis was carried out under仕lecurrent of 13--15 A at 6 V. This using the tungsten basket heater is a type of evapora-tion method， The samples Ior TEM observation were collected from the carbon stick in the tungsten basket heater 3. Reslld印刷wl.dl:i.sclJ.ssioll The TEM (TOPCON EM 200kγ) comfirmed the carbon rod and used for the source material shovved a structure固 TheTEM revealed the products of the the carbon nanotubes and to be found on the electrodes in aH thrεe However， were not observed on the substrate， except for one nanoparticle discoverd in the synthεsis carbon sticks. 3.1 Cai"bon 1lano1);ube The straight carbon nanotubes 5~20 nm in diameter 'iJ'lere always formed on the surIace of the carbon string and carbon while no carbon nanotubes werεformed on the substrate， As the temperature of substrate is lower t11an that of electrode， this indicates that carbon nanotubes were grovvn in higher temp合ratureconditions， The of carbon nanotubes have polyhedral caps similar to those by et a10 However， some of the nanotubes in the were bent and had two capsιThe carbon nanotubes vvere bent in the middle section and were formed in 0ur>tlha，"i Fig， 3(a)， Fig， 4 and synthesis 5 show the typkal carbon nanotubes that were Iormed in and synthesis 刊 ly. Fig. 3 (a) shows the carbon nanotube 10 nm in diameter and is bent in the middle sectionロ Thistube has two caps， thus both ends of this tube are closed. The nanotube consists of nine sheets， with a inner tube (making a total of ten) that 18 closedτ20 nm from the of the nanotube. On the left side of the nanotube， the ten tubes each have a thickness of approximately 0，34 nm， which i8 constant along the length of the nanotube It is important to note the thickness of left side of the nanotube 。fgraphite is 0固335nm. Hence， the dark lines on the toεrs. 011 the right side of the nanotube the thickness of the carbon is not constant fr唱。mthe tip to the middle section of the nanotube 3(b)i. The Uuckness of each is 0.34 nm at the and 1S 0.39 nm at the middle section on average園 Visiblefrom the of the right side of the nanotubεare two distinct carbon sectionso The wider section consisits of six carbon lavers. while the narrower section conslsts of the three carbon Thεsynthεsis oI carbon nanotubes and nanoparticles by altemating curr日ntarc-discharg邑evaporationm色thod. 43 The cap of the nanotube consists of three facets. Iijima et a1. (1992) suggested that the occurrenc合 ofa pentagon in a hexagon network of a nanotube 明1mresult in strain around the pentagon， causing the tip of the nanotube to be closed by the occurrence of the six pentagons. It is considered that the apexes of the tube tip in Fig. 3(b) consist of four pεntagons. Only four pentagons are visible in Fig. 3(b) becausξTEM figure is a type of projection and may not show a1 six apexes. Fig. 4 shows the carbon nanotubes ac-companied by many nanoparticles. This figllre indicates that the nanotubes have no prefered growth direction. In addition， thεmajority of nanotubes in this figure are straight. Fig. 5 shows the two carbon nanotubes produced using the tungsten basket (synthesis method(c))， which are approximately 7.7 nm in diameter and have 10 graphite layers. Each of the nanotubes overlap each other at the upper end. Thεse two nanotubes display the same number of graphite layers and similar diameters. Therefore， itis possible that these nanotubes can be regarded as one bent tllbe， and the concentric circle shovvs a cross section of this nanotube. Iijima et a1. (1992) indicated that the f1ux density of carbon atoms decreases towards the end of the arc discharge， and as soon as the arc stop~弓， the tube tips are quickly closed by the formation of a pentagon. However， the present study used the altemating current and not the dirεct Cllrrent method. Therefore， the flux density of carbon atoms was more Fig.3目 (a)Electron micrograph showing carbon Fig. 3. (b) Clos思upmicrograph of (a). The graph. nanotube consisting of two caps. This ite layer structure {002} can be observed nanotube was formed on th邑carhonstring and is bending in the middl己Sεction.4 Yoshinori HIRATA， Masayuki OKUNO and Takeo MATSUMOTO Fig， 4， Electron micrograph oI carbon nanotubes and nanopoxticles that were formεd on the ca:rbon stringo Fig， 5， Electron micrograph of two carbon nanotubes that overlap色achothεr at the 日ndof it， Individual dark line corresponds to the graphit巴sheetsseparated by 0，34 nm， irregular than that used in the direct current method， This is consistent with the existence of many types of nanotubes in the present 3.2 Nanαllarti.de The nanoparticles 'vere formed on the surface of source carbon in 011 the existence of nanoparticles on the substrate was observed from the carbon sticks {2-2(b)} synthesis， The of the nanoparticles Vi!εre observed near the carbon nanotubes， This suggests that the nanoparticles werεgrown under the same conditions to that of the carbon nanotubes. The present identified two types of nanoparticles， The first type was nearly with a hollow (Fig， 6)， And the second type vvas a similar to those of the of the nanotubes Fig， 6， Fig， '1and Fig. 8 display the formed in synthesis (a)， synthesis (b) and The cross section of the nanotube also shows a concentric circle of Therefore it Is possible that the nanoparticles in Fig， 6 and '1 are cross sections of the nanotubes， However， if it is a cross section of nanotubes， the nanotube is orientated vertically 011 the micro There are many of the nearly spherical nanoparticles with nanotubes in Fig， 4固It1s difficult to propose that many parts of these show cross sections of the The synthesis of carbon nanotubεs and nanoparticles by alt巴rnatingcurrent arc-discharge evaporatiol1 m色thod 45 Fig.6. EIεctron micrograph of a near spherical nanoparticle with a hollow found on the carbon string. Fig.7. Ele氾tronmicrograph of a near spherical nanoparticle. This nanoparticle is 5.1 nm in diamcteL The minimum circle in the center is approximately 0.7 nm in di旦日1巴ternanotubes， becausεthe probability of the verti-cal arrangements of nanotubes 1S very sma!L Therefore， the spherical materials in Fig. 6 and Fig. 7 are not cross sections of nanotubεs but are nanoparticles. Iijima reported simi-lar to those observed in the pres-ent observed small parti-cles of graphitizεd carbon in amorphous carbon produced the vacuum deposition method. Recently， ithas been indicated that the was included in the center o:fthe spheri-cal nanoparticle. Thεsize o:f the minimum circle of the nanopartic1e in Fig. 7 ismatεly 0.7 nm in diameter‘ Given the size of C60 is 0.71 nm in diameter， this suggests that the Fig. 8. Electron micrograph of a nanoparticle simi- nanopartic1e in Fig. '7 may include C60 1n the l旦rto the tips of nanotubes. The nano- center. particle， which ov巴r1apsthe nanotube， isfound in the soot in the tungsten bask号theater. Fig. 8 shows a that overlaps 46 Yoshinori HIRATA， Masayuki OKUNO and Takeo MATSUMOTO the nanotube. Iijima et a1. (1992) report吋 thatthe nanotubes have tips similar to a ice cream corn in shape. The nanoparticle in Fig. 8 shows this characteristic ice-cream corn morphology. 11 other words， the morphology of this nanopartide i8 similar to the tip oI a nanotube. 4， C叩 cb，lsi<1JlIlSIn the present study， carbon nanotubes and nanoparticles were grown on a carbon rod， a carbon string and a carbon in a tungsten filamθnt basket， using the a.c. arc-discharge evaporation method. The morphology of the nanotube tips is approximately the same as for the d.c. evaporation method used in previous works (Iijima et a1. (1992)). However， using the a.c.εmethod a bent nanotube was produced as shovvn in 3. The observed in the present study can be classified into two types， (1)spherical with a hollow and si出 ilarto the of the nanotube. However， the variation between the nanotubes and the nanoparticles Is not significantly distinct. Admow!edgemre空ltSThe authors "wish to thank Mrs. Kate 'IiVebstεr and 1¥針。 Jody Vvebster for their careful reading of this manuscript. ReferenceぉEbbesen， T.iV. and Ajayan， P.M. (1992)， Large-scale synthesis of carbon nanotub巴s. Nature， 358， 220-222， Iijima， S.(1980). Direct observation of the tetrah巴dralbonding in graphitized carbonblack by high r邑solu回tion巴lectronmicroscopy， Jour惚alof Crystal Gグowth，50， 675-683. Hjima， S， (1991). Helica¥ microtubl巴Sof graphitic carbon. Nature， 354， 56-58 Iijima， S.， Ajayan， P.M. and Ichikashi， T.(1百92). Growth model for carbon nanotubes. Physical review letters， 3100-3103， Iijima， S.， khik21shi， T， and Ando， Y. (1992). Pentagons，heptagons and negativ，己 curvaturein graphite microtuble growth. Nature， 356， 776-778 Hjima， S.and Ichihashi， T. (1993). Single-shell carbon nanotub巴Sof l-nm diameter. 1¥Tature， 363， 603-605. Kroto， H.W.， Heath， J，R.， Obrien， S.c.， Curl， R.F， and Sm，al1εy， R忍 (1985). C60・Buckminsterfullerene.Nature， 318， 162-163， Tsang， S.c.， Harris， P.].F. ;md Gre巴n，M.L.H. (1993). Thinning and opening of carbon n旦notubesby oxidation using carbon dioxide. Na品ure，362， 520-522 

The Synthesis of Carbon nanotubes and Nanoparticles by Alternating Current Arc - discharge Evaporation Method.

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The Synthesis of Carbon nanotubes and Nanoparticles by Alternating Current Arc - discharge Evaporation Method.

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