Materials Chemistry and Physics 127 (2011) 174–178 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Conducting ZnO thin films with an unusual morphology: Large flat microcrystals with (0 0 0 1) facets perpendicular to the plane by chemical bath deposition Xiaoheng Liu a , Mohammad Afzaal b , Tom Badcock c , Phil Dawson c , Paul O’Brien d,∗ a Key Laboratory for Soft Chemistry and Functional Materials, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China b Center of Research Excellence in Renewable Energy, King Fahd University of Petroleum and Minerals, P.O. Box 1292, Dhahran 31261, Saudi Arabia c Photon Physics Group, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK d School of Chemistry and School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, UK article info Article history: Received 4 June 2010 Received in revised form 14 December 2010 Accepted 24 January 2011 Keywords: ZnO Crystals Photoluminescence Microplatelets abstract Gelatine has been employed to modify the growth of ZnO in a chemical bath deposition (CBD). The poly- mer profoundly affects crystal growth and leads to films of high-density which are composed of vertically aligned hexagonal ZnO microplatelets. This morphology is in stark contrast to the [0 0 0 1] orientated rods most often seen in CBD. These crysatllites are well defined, relatively uniform in diameter, thickness and shape. The height of the ZnO platelet in the film is ∼2.0 m (as is the measured film thickness). The films present near perfect linear current–voltage (I–V) curves and have a very characteristic Raman resonance. Near band-edge emssion is observed in the low temperature photoluminescence (PL). Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction Zinc oxide (ZnO) is an important material with many useful properties. It is a wide band gap semiconductor that has found use in optical [1–3], electronic [4–6], catalytic [7,8] and sensing [9,10] devices. Many methods [2] have been used to obtain high quality films of ZnO including: chemical bath deposition (CBD) [11], pulsed laser deposition (PLD) [12], sputtering [13], chemi- cal vapour deposition (CVD) [14], metal organic chemical vapor deposition (MOCVD) [15], and chemical vapor transport (CVT) [16]. Wet chemical techniques such as CBD are potentially econom- ical, and can operate at low-temperatures using relatively benign aqueous chemistry [11,17]. The method has been extensively used for ZnO deposition onto glass, silicon, plastic and other substrates [5,11,18–23], a range of different morphologies (shape, size and packing of ZnO particles) have been obtained in such films and some of the morphologies obtained are shown in Fig. 1 [24–34]. The morphology of the ZnO within a film is largely dependent on the conditions of the deposition reaction (which include ligand, stabilizer/growth modifier, pH, metal counter-ion, ionic strength, reaction time, reaction temperature, crystal growth seed, sub- ∗ Corresponding author. E-mail address: paul.obrien@manchester.ac.uk (P. O’Brien). strate). We have reported in some detail of the plethora of factors affecting the growth of ZnO in work principally aimed at producing highly z-axis orientaed rods with the familiar hexagonal exter- nal geometry in which the polar family of faces predominates. In this work, we have in contrast sought to produce flattened struc- tures bound to a substrate mirrorring our recent work in producing [0 0 0 1] cleaved flat ZnO structures [35]. The morphology of ZnO can depend on the ligand used in the bath with different results being obtained with: hexam- ethylenetetramine, citrate, ethylenediamine, triethanolamine and other small organic molecules have been successfully used in CBD [11,18,20–22]. The influence of these components is often indirect and supersaturation and pH are of especial importance in control- ling the nature of the material deposited, e.g. as in rods vs granular. To date, there has been limited study on ZnO films by CBD in the presence of a polymeric stabilizer [33,35] such additives pro- foundly influence the nature of final material formed. In contrast, several different polymers have been used during the synthesis of isolable nanomaterial [36,37]. Our [38,39] and other groups [40,41] have successfully used gelatine for the microstructural control of inorganic nanomaterials. In the present work, we use gelatine, a natural macromolecule, to modify the growth of ZnO in CBD and obtained films with unusual morphologies and properties. We note in particular that adherent films in which plates are bound to a substrate by their edges are ununsual if not unique and potentially technologically important. 0254-0584/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.01.054