Selective Co-catalysed growth of novel MgO ®shbone fractal nanostructures Y.Q. Zhu a ,W.K.Hsu a , W.Z. Zhou b , M. Terrones a , H.W. Kroto a , D.R.M. Walton a, * a Physics and Environmental Sciences, School of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, UK b School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK Received 16 May 2001 Abstract Novel MgO ®shbone- or fern-like nanostructures, and Al 2 O 3 ®bre networks, have been generated for the ®rst time fromanAl 2 O 3 matrix containing MgO and SiO 2 . The signi®cance of the selective Co-catalysed growth of the elegant three-dimensional fractal ®shbones is discussed. We have adopted the vapour±liquid±solid V±L±S) and nucleation± aggregation N±A) mechanisms, which take eect equally during the heating process, to account for the formation of these uniquely stacked fractal structures. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction During the past decade, various types of one- dimensional nanometer-scale materials have been generated. Examples include: C, BN, MoS 2 and WS 2 nanotubes[1±4],SiCandGaNnanorods[5,6] and carbon-coated Pb and Sn nanowires [7,8]. These materials often possess unique chemical, mechanical and physical properties, and some of them promise to be key components in the next generation of nanoscale optical and electronic de- vices [9,10]. Magnesium oxide has been used widely in steel manufacturing because it is highly corrosion-re- sistant. Refractory MgO micro-®bres were pro- duced half a century ago and pure single MgO crystals have been obtained by epitaxial growth. MgO is an excellent catalyst and its crystals are valuable, e.g., as in optical transmitters and as substrates for thin ®lm growth. Recently, MgO whiskers have been used to reinforce supercon- ductingcomposites[11],howeverMgOnano®bres and nanowires have yet to be prepared. In this Letter we describe the use of a modi®ed Co-ca- talysed vapour±liquid±solid V±L±S) process [12], to generate MgO nano®bres, assembled in elegant ®shbone fractal arrays. Signi®cantly, the selective fractalgrowthoftheMgO®shbonestakesplacein anAl 2 O 3 matrix,whereastheAl 2 O 3 grownin®bre or network forms contain no Mg. 2. Experimental The apparatus was similar to that employed to generate SiO x nano¯owers [13], except that an Al 2 O 3 plate 10  5  1mm 3 ; Al 2 O 3 > 96%) was 26 October 2001 Chemical Physics Letters 347 2001) 337±343 www.elsevier.com/locate/cplett * Corresponding author. Fax: +44-1273-677196. E-mail address: d.walton@sussex.ac.uk D.R.M. Walton). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00939-3