Article

Applied Physics A

, Volume 88, Issue 1, pp 21-26

Nanostructure size evolution during Au-catalysed growth by carbo-thermal evaporation of well-aligned ZnO nanowires on (100)Si

  • P. PreteAffiliated withUnità di Lecce, Istituto per la Microelettronica e Microsistemi (IMM) del CNR Email author 
  • , N. LovergineAffiliated withCNISM, Unità di Lecce, and Dipartimento di Ingegneria dell’Innovazione, Università di Lecce
  • , L. TapferAffiliated withDipartimento di Tecnologie Fisiche e Nuovi Materiali (FIM), Centro Ricerche di Brindisi, Ente per le Nuove Tecnologie, l’Energia e l’Ambiente (ENEA)

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Abstract

We report the structural and morphological properties of well-aligned ZnO nanowires grown at 750 °C on Au-deposited and annealed (100)Si substrates using carbo-thermal evaporation. As-grown nanowires are made of wurtzite ZnO, have cylindrical shape and carry droplet-like nanoparticles (NPs) at their tips, as expected for vapour–liquid–solid (VLS) growth. Grazing incidence X-ray diffraction measurements demonstrate that the NPs are made of pure fcc Au. No secondary Au/Zn alloy phases were detected. Bragg diffraction patterns confirmed that the nanowires were grown with their crystal c-axes parallel to the [100] direction of Si (i.e. normal to the substrate surface), while Au NPs are mostly (111)-oriented. The diameter distribution of ZnO nanowires mimics that of the Au NPs at their tips. A quantitative study of the nanostructure size distribution after sequential annealing and growth steps evidences the occurrence of three nanoscale processes: (i) Ostwald ripening and/or coalescence of Au NPs before nanowire nucleation, (ii) Au-catalysed VLS nucleation and axial growth of ZnO nanowires and (iii) radial growth of nanowires by a vapour–solid process. These processes originate the NP and nanowire size evolution during the experiments. The present findings are interpreted in terms of Zn vapour pressure changes during carbo-thermal evaporation.