Materials Science and Engineering B 174 (2010) 55–58 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Effect of Pb-doping on the morphology, structural and optical properties of ZnO nanowires synthesized via modified thermal evaporation Mashkoor Ahmad, Caofeng Pan, Wang Yan, Jing Zhu ∗ Beijing National Center for Electron Microscopy, The State Key Laboratory of New Ceramics and Fine Processing, Department of Material Science and Engineering, Tsinghua University, Beijing 100084, China article info Article history: Received 25 August 2009 Received in revised form 16 March 2010 Accepted 16 March 2010 Keywords: ZnO Pb-doped Crystalline Photoluminescence abstract Pb-doped ZnO nanowires (NWs) have been synthesized by modified thermal evaporation method. Effect of Pb-doping on the morphology, structure, and optical properties of as deposited NWs have been inves- tigated. The TEM images show that the doped NWs consist of cantilever-like with diameter in the range of 20–150 nm. It has been found that the doped NWs are single crystalline grown along [1 0 1] direction. The composition and valence state of Pb ions have been investigated through energy dispersive spec- troscopy (EDS) and X-ray photospectroscopy (XPS), which demonstrate that the Pb ions are uniformly doped into each NW and are in +2 oxidation state. In addition, photoluminescence spectra exhibit an increased amount of defects with increasing Pb, which leads to a red shift in the UV region. Furthermore, the band gap tailoring in Pb-doped ZnO NWs makes their potential for optoelectronics devices. © 2010 Elsevier B.V. All rights reserved. 1. Introduction ZnO is one of the most promising materials because of a direct wide band gap E g = 3.37 eV and large exciting binding energy 60 meV at room temperature. It has been found useful in many applications such as optoelectronic devices, surface acoustic wave devices, field emitters, piezoelectric, transparent conduct- ing materials and solar cells [1–7]. Recently, intensive research has been focused on fabricating one-dimensional (1D) ZnO nanos- tructures such as nanotubes, nanowires (rods), and nanobelts (rings) due to their shape induced novel properties and potential applications [8–10]. The synthetic methods reported of 1D ZnO nanowires and nanorods include chemical vapor deposition [11], low-temperature wet-chemical methods [12], thermal evaporation [13], and hydrothermal syntheses [14,15]. On the other hand, doping of semiconductor with selective ele- ments [16,17] offers an effective approach to adjust the electrical, optical and magnetic properties, which is crucial for their practical applications. Although a mass of research has been done on nanos- tructure doping, it still remains a challenge to achieve high quality crystalline with excellent optical and electrical properties in doped one-dimensional ZnO nanostructures. Furthermore, although some groups already focused their work on Pb-doping in ZnO [18,19], however, the detailed study of Pb-doping is still required to under- stand the role of Pb in ZnO NWs. As the ionic radius of Pb 2+ (1.19 Å) ∗ Corresponding author. Fax: +86 10 62771160. E-mail address: jzhu@mail.tsinghua.edu.cn (J. Zhu). is larger than Zn 2+ (0.74 Å), Zn is more active in chemical reaction then Pb. In vapor reaction Pb can be easily substituted by Zn and become Pb-doped ZnO nanomaterial. The main focus of the present work is to investigate the effect of Pb-doping in ZnO NWs for the future optoelectronics applications. 2. Experimental Synthesis of un-doped and Pb-doped ZnO NWs were carried out in a horizontal quartz tube furnace via thermal evaporation method, where the temperature, pressure and flow rates of working gases are well controlled. In this process, a crucible containing the mixture of metallic Zn powder (3 g) and Pb 2 O 3 (99.998%, Aldrich) powders (0, 0.5, 1, 2 g) were respectively added, placed in the cen- tral region of the quartz tube furnace and heated to 550 ◦ C for 3 h. Ar carrier gas with an O 2 content of 5% flows through the quartz tube at a rate of 150 standard cubic centimeter/min (sccm). A Si substrate cleaned carefully, followed by supersonically in acetone, alcohol and de-ionized water for 30 min and mounted downward region of the furnace where the temperature was 450 ◦ C. Two sam- ples were prepared in our experiments, i.e. ZnO nanowires with or without Pb-doping. After the reaction completed, the as-prepared products were examined by X-ray diffraction (XRD) with Cu K radiation,  = 1.5418 Å, scanning electron microscope (SEM-6301F operated at 15 kV), high resolution transmission electron micro- scope (HRTEM-JEM2011 operated at 200 kV), energy dispersive spectroscopy (EDS) and X-ray photospectroscopy (XPS). PL mea- surement was conducted at room temperature using the 325 nm line of a He–Cd laser as the excitation source. 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.03.039