Several chemical and physical methods are used to grow different types of ZnO-NWs. One-dimensional (1D) nanostructure ZnO in the form of nanowires (ZnO-NWs) is very desirable in many important practical applications and is extensively studied because of its geometrical conﬁguration, electron conﬁnement properties, large surface-to-volume ratio, and polar nature. ZnO is a highly attractive material due to its availability, ease of fabrication, non-toxicity, low cost, and high transmittance in visible region, etc.

Introduction Zinc oxide (ZnO) is an n-type IIeVI wurtzite semiconductor with a wide direct band gap of 3.7 eV and an excitation binding energy of 60 meV. These ﬁndings suggest that the use of intermittently pumped carrier gas is one of effective control parameters that promote the nucleation and growth of nanomaterials using thermal evaporation method. Results showed that the proposed method facilitates epitaxial nucleation and growth of high density vertically aligned ZnO nanowires with length of several micrometers and that have a smaller diameter compared to that of ZnO nanowires fabricated by traditional continuous pumping described in the literature under the same growth condition. The structural, morphological, and optical properties of the nanowires were analyzed by ﬁeld emission scanning electron microscopy, X-ray diffraction, UVevis spectroscopy, and photoluminescence spectroscopy. We report the growth mechanism of ZnO nanowire balls by thermal evaporation under intermittently pumped carrier gas as a new and simple nucleation method.

School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia Institute of Nano-Optoelectronics Research and Technology (INOR), Universiti Sains Malaysia, 11800 USM, Penang, MalaysiaĪrticle history: Received 21 December 2016 Received in revised form 24 March 2017 Accepted 26 March 2017 Optical Materials journal homepage: Growth mechanism of seed/catalyst-free zinc oxide nanowire balls using intermittently pumped carrier gas: Synthesis, characterization and applications Forat H. Contents lists available at ScienceDirect

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