Carbonnanohornshybridizedwithametal-includednanocapsule NoriakiSano a, * ,TakeyukiKikuchi b ,HaolanWang c ,ManishChhowalla d , GehanA.J.Amaratunga c a Department of Chemical Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji 671-2201, Japan b Department of Engineering Science, Himeji Institute of Technology, 2167 Shosha, Himeji, 671-2201, Japan c Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK d Department of Ceramic and Materials Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ 08854-8065, USA Received5July2003;accepted4October2003 Abstract Anovelnanocarbonstructure,carbonnanohorns(CNHs)particlewhichincludesoneNi-containedcarbonnanocapsule(CNC) initscenter,isproducedbysubmergedarcinliquidnitrogenusingNi-contained(0.7mol%)graphiteanode.Transmissionelectron microscopyrevealedthateachCNHsparticleinnearlysphericalshapeofdiameteraround50–100nmhasoneNinanoparticleof diameter5–20nmencapsulatedbygraphiticshellsasCNC. Ó 2003ElsevierLtd.Allrightsreserved. Keywords: A.Carbonnanotube;B.Arcdischarge;C.Transmissionelectronmicroscopy 1. Introduction Over a decade, there are a considerable number of effortstosearchnovelnanostructuralcarbonmaterials. Sucheffortshaverealizedsomeimportantdiscoveriesof fullerene-family structures such as fullerenes [1], multi- walledcarbonnanotubes(MW-CNTs)[2],single-walled carbonnanotubes(SW-CNTs)[3],single-walledcarbon nanohorns(SW-CNHs)[4],nano-onions[5],andmetal- included carbon nanocapsules (CNCs) [6]. In order to produce such materials, arc discharge in reduced-pres- sure gases [7,8], plasma-enhanced chemical vapor de- position [9,10], and thermal pyrolysis of hydrocarbon gases[11,12]haveconventionallybeenusedwidely.To growCNTsinthesemethods,Ni,FeandCocanbeused as metallic catalysts [3,9–12]. It is known that these catalysts are necessary to fabricate SW-CNTs and CNCs.Inadditiontotheabovemethods,submergedarc in cold liquid is recently reported as a cost-effective method [13–21]. By use of this method, MW-CNTs [13,15,16,18,19], SW-CNHs [20], nano-onions with C 60 core [17], MoS 2 fullerenes [21] were successfully fabri- cated. In addition to these nanomaterials, metal- includednanocarbonsarealsotriedtobeproducedby thesubmergedarcmethod.Firstly,Hsinetal.reported thatdissolvingmetallicionssuchasNiandCoinwater inthesubmergedarcmethodresultedinthefabrication ofmetal-includedCNTs[14].Also,non-elongatedmet- al-includednanoparticlesofnearlysphericalorpolyhe- dralshapesweresynthesizedusingmetal-dopedgraphite electrodes or metal-dissolved water [15,16]. In their methods to form metal-included nanoparticles, water wasusedtoquenchthehotarcwithevaporatedmate- rialsfromelectrodes.Thisstudyshowsthatnanoparti- cles unexpected in their methods can be synthesized when liquid nitrogen was used instead of water. Here, we used a composite graphite anode doped with Ni, resulting in a discovery that a novel hybrid structure, CNHs particle including one Ni-contained CNC in its center,canbeproducedinthisreactionfield. 2. Experimental Experimentalset-upusedinthisstudyisthesameas the one used in our previous work on fabrication of carbonnano-onionsandMW-CNTsbyarcdischargein water[17,18].Here,weusedliquidnitrogen(2500ml)in Dewarflask,insteadofwaterinbeaker.Theanodeused * Corresponding author. Tel.: +81-792-67-4845; fax: +81-792-67- 4845/4830. E-mail address: sano@mech.eng.himeji-tech.ac.jp (N.Sano). 0008-6223/$-seefrontmatter Ó 2003ElsevierLtd.Allrightsreserved. doi:10.1016/j.carbon.2003.10.001 Carbon42(2004)95–99 www.elsevier.com/locate/carbon