A path to larger yields of multishell fullerenes

Abstract

Multishell fullerenes were foreseen by Kroto et al. [1] as it allows flexible control of different key parameters of the early as in 1988, i.e. shortly after his pioneering discovery process. of the basic buckminster fullerene C [2]. Unlike classical The purpose of the present work was to find an efficient 60 fullerenes, which have a cage structure and are known to synthetic route to multishell fullerenes by use of laser have been synthesized in a variety of sizes (C , C , C , vaporization method. 60 70 84 C , etc.), multishell fullerenes have a cage-inside-cage For laser vaporization, a KrF excimer pulse laser (l5 102 concentric structure such as double-shell C @C or 248 nm) was used. Typical laser fluence and repetition rate 60 240 triple-shell C @C @C . Multishell fullerenes are the 60 240 560 smallest among other multishell carbon clusters such as bigger, graphitic onions [3,4] or multishell nanotubes [4,5]. The first observation of several double-shell and tripleshell molecules was however reported only recently [6,7]. In Refs. [6,7], the double-shell C @C , double-shell 60 240 C @C and triple-shell C @C @C were found 240 560 80 240 560 in the products of 30008C high temperature treatment of laser pyrolysis carbon blacks. The content of multishell fullerenes was less than 0.01%, while most of the material was dominated by hollow graphitic particles of |20 nm size and ordinary, single-shell fullerenes. Though the multishell fullerenes possibly possess interesting and attractive properties [7], no measurement could have been done until these fullerenes were isolated in milligram amounts, at least. So the first priority of the research in this field was to find an efficient synthetic route to production of multishell fullerenes. It is hard to improve the method of high temperature treatment of laser pyrolysis carbon black [7]. Also, it seems reasonable to suggest that actual growth of additional shells around C cores took place not during 30008C 60 treatment but during cooling down after the heat treatment. If this suggestion is correct, a successful synthetic route should comprise at least two steps: (1) formation of carbon vapour which contains many C molecules; and (2) 60 cooling down at the appropriate substrate. A hypothetical growth sequence is shown in Fig. 1. We realized that the method of laser vaporization would meet the above conditions. Another attractive feature of this method is that Fig. 1. Hypothetical growth sequence of multishell fullerene evolving from: (a) a fullerene molecule and a fullerene /nanotube fragment through (b) and (c) in which the shell fragment deposited *Corresponding author. Tel.: 181-44-813-7830; fax: 181-44onto a fullerene forms an embryo in which the second shell is 813-7233. forming. The sequence leads in a natural way to multishell E-mail address: vladimir@icmr.co.jp (V.Z. Mordkovich). fullerenes.