Eur. Phys. J. D 52, 79–82 (2009) DOI: 10.1140/epjd/e2009-00008-x Regular Article T HE EUROPEAN P HYSICAL JOURNAL D Raman spectral features of longer polyynes HC 2n H (n = 4–8) in SWNTs T. Wakabayashi 1, a , T. Murakami 1 , H. Nagayama 1 , D. Nishide 2, b , H. Kataura 3 , Y. Achiba 4 , H. Tabata 5, c , S. Hayashi 5 , and H. Shinohara 2 1 Department of Chemistry, School of Science and Engineering, Kinki University, Higashiosaka, 577-8502 Osaka, Japan 2 Department of Chemistry and Institute for Advanced Research, Nagoya University, 464-8602 Nagoya, Japan 3 Nanotechnology Research Institute, AIST, Tsukuba, 305-8562 Ibaraki, Japan 4 Department of Chemistry, Tokyo Metropolitan University, Hachioji, 192-0397 Tokyo, Japan 5 Department of Electrical and Electronics Engineering, Kobe University, 657-8501 Kobe, Japan Received 19 September 2008 Published online 24 January 2009 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2009 Abstract. Size-selected linear hydrocarbon molecules, polyynes HC2nH, were contacted in solutions with single-wall carbon nanotubes (SWNTs) prepared from laser-ablated metal/carbon composite rods (Rh/Pt/C) to produce polyyne-encapsulating SWNTs, HC2nH@SWNT(RhPt). New Raman spectral fea- tures were observed at 2120, 2061, 2017, 1982, and 1963 cm -1 for five polyynes of n = 4–8, respectively, and identified as the vibrational excitation of symmetric stretching modes of the molecules inside the SWNTs. The Raman spectra were compared with those observed for polyynes on Ag islands (SERS) and in solutions. The filling factor was investigated from the concentration dependence of the Raman intensity for HC10H@SWNT(NiCo) to give an estimate of one polyyne molecule per ∼350 carbon atoms of SWNTs, providing a picture for head-to-tale filling of aligned C10H2 molecules inside the SWNTs. PACS. 78.30.Na Fullerenes and related materials – 78.66.Tr Fullerenes and related materials 1 Introduction The linear hydrocarbon molecules, polyynes H(C≡C) n H (n ≥ 2), are intriguing because of their electronic prop- erties of one-dimensional π-electron systems [1]. They are stable model compounds for reactive linear carbon clus- ters, C n , and their aggregates [2–4]. Recently, polyynes have been produced by simple methods of laser abla- tion and arc discharge in liquids [5,6] and characterized by Raman spectroscopy [7,8]. Size-separated polyynes, C 2n H 2 , were studied by normal Raman and surface- enhanced Raman scattering (SERS) spectroscopy for n = 4–8 [9] and by resonance Raman spectroscopy for n =5 and 6 [10]. New optical emission spectra were detected in the visible regions for C 2n H 2 of n = 5–8 and related to the vibronic interaction in the forbidden electronic tran- sitions [11]. Very recently, polyynes of n = 4–6 were encapsulated inside single-wall carbon nanotubes (SWNTs) for stabi- lization and characterized by Raman spectroscopy [12,13]. The resonance effect in the Raman scattering intensity for polyyne@SWNTs was discussed [14]. The system can be a e-mail: wakaba@chem.kindai.ac.jp b Present address: Nanotechnology Research Institute, AIST. c Present address: Advanced Device Laboratory, RIKEN. a good precursor for atomically aligned linear carbon ar- rays confined in a cylindrical nanospace [15]. In this work, we produced polyyne-SWNT composite materials for size- selected longer polyyne molecules, C 2n H 2 of n = 4–8, and characterized those by Raman spectroscopy. 2 Experimental Polyynes were formed by laser ablation of graphite powder suspended in hexane [5,8] and separated by high perfor- mance liquid chromatography (HPLC) [9,10]. The SWNTs were produced by laser ablation of metal/carbon compos- ite rods under argon gas flow in a furnace [16]. For encap- sulation, a sheet of SWNTs was sintered into a solution of hexane that contained size-separated polyynes, and kept at 80 ◦ C for 48 h. The SWNT sheet was dried in air at 80 ◦ C and Raman spectra were measured [12,13]. For the present work, two SWNTs were prepared, one with metal catalysts of Rh/Pt at 0.6/0.6 atomic% to car- bon and ablated at the furnace temperature of 1350 ◦ C and the other with Ni/Co at 0.6/0.6 atomic% and ab- lated at 1150 ◦ C. The former consists of SWNTs with relatively large diameters (∼1.4 nm) and the latter with moderate diameters (∼1.35 nm) as evaluated by Raman spectroscopy [16]. The purity for the SWNT samples was