Laser ablation of diamond nanoparticles suspended in solvent: synthesis of polyynes Hiroshi Tabata a , Minoru Fujii b , Shinji Hayashi a,b, * a Graduate School of Science and Technology, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan b Department of Electrical and Electronics Engineering, Faculty of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan Received 8 June 2004 Available online 10 August 2004 Abstract Laser ablation of diamond nanoparticles suspended in ethanol has been performed by using the second harmonic of a Nd:YAG laser (532 nm). UV–Vis absorption spectra revealed the formation of polyynes (C n H 2 : n = 8, 10, 12, 14, and 16). The same experiment was performed for graphitic nanoparticles suspended in ethanol. It was found that ablation of diamond nanoparticles results in larger amounts of long polyynes. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction Laser ablation is an effective method to produce car- bon nanostructures such as fullerenes [1] and nanotubes [2]. It is known that ablation of graphite in gas phase yields linear carbon chain structures such as hydrogen- capped polyynes with the general structure H–(C„C) n – H and cyanopolyynes with N„C–(C„C) n –C„N [3]. These linear carbon chain structures are extremely interesting, because they offer a possibility of realizing one-dimensional conducting materials [4]. Furthermore, the polyynes are considered to be the precursors in the for- mation of fullerenes [5,6] and carbon soot [7]. They are also possible carriers of unidentified interstellar bands [8,9]. Recently, Tsuji and co-workers have reported success- ful formation of hydrogen-capped polyynes by laser ablation of graphite [10] or fullerene [11] particles sus- pended in organic solvents. Polyynes produced in solu- tion were very stable at room temperature and the amount of them was sufficient to carry out several kinds of analysis including optical measurements. They studied the correlation of the amount of polyynes and the chain length distribution of individual polyynes with experi- mental conditions. They found that the amount and the distribution considerably depend on the experimental condition, in particular the kind of starting material and the laser wavelength. Although they suggested the importance of photochemical process in the polyyne for- mation, detailed mechanism is not yet well understood. Very recently, Cataldo [12–14] has reported that polyy- nes can also be synthesized by an electric arc generated between two graphite electrodes submerged in an organic solvent. He has performed a detailed study of the elec- tronic absorption spectra of individual polyynes and examined the chemical properties of the polyynes solu- tions (hydrogenation and oxidation). The mechanism of the polyynes formation by arc discharge in a solvent may be very similar to that by laser ablation in a solvent, but little is known at present about this point. In order to further explore the correlation between the products of laser ablation in liquids and the kind of target material, we have carried out laser ablation experiments by using diamond nanoparticles 5 nm in diameter suspended in ethanol. The ablation of the dia- 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.07.063 * Corresponding author. Fax: +81 78 803 6073. E-mail address: hayashi@eedept.kobe-u.ac.jp (S. Hayashi). www.elsevier.com/locate/cplett Chemical Physics Letters 395 (2004) 138–142