Full length article Impact of annealing on the structural and optical properties of methylene green nanostructure films prepared by drop casting E.M. El-Menyawy a , A.A.A. Darwish b,c,n , I.T. Zedan d a Solid State Electronics Laboratory, Solid State Physics Department, Physical Research Division, National Research Centre, 33 El-Bohouth St., Dokki, Giza 12622, Egypt b Department of Physics, Faculty of Education at Al-Mahweet, Sana’a University, Al-Mahweet, Yemen c Department of Physics, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia d Basic Science Department, High Institute of Engineering and Technology, El-Arish, North Sinai, Egypt article info Article history: Received 17 August 2015 Received in revised form 9 November 2015 Accepted 3 December 2015 Keywords: Organic compounds X-ray diffraction Optical properties abstract The methylene green (MG) powder was found to be polycrystalline with the triclinic system. MG films were deposited by drop coating technique. X-ray diffraction and scanning electron microscopy showed that the MG films have nanostructure nature. It is found that the crystal size is increased by annealing. Optical properties of nanostructured MG films were performed in the spectral range from 200 to 2500 nm to determine the optical constants (n and k). The absorption coefficient of the as-deposited film revealed a two indirect allowed optical band gap with values of 1.90 and 3.11eV, which increased by annealing to 2 and 3.48 eV, respectively. The dispersion of n was discussed in terms of the single os- cillator model. The high frequency dielectric constant and the lattice dielectric constant were estimated and found to decreased by annealing. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction It is interesting to search for new materials with promising performance characteristics as well as the improvement in device fabrication. Compounds classified as heterocyclic probably con- stitute the largest and most varied family of organic compounds Carbocyclic compounds may in principle be converted into a col- lection of heterocyclic analogy by replacing one or more of the ring carbon atoms with different elements. The dyes usage in the industries has been increased such as: plastic, textile, dye, dyestuffs, rubber, paper, leather, cosmetics, food, carpet and printing wastewater extensively [1,2]. Methylene green (MG), with its molecular structure depicted in Fig. 1, is a heterocyclic aromatic chemical compound. It is a basic dye used as a chromatin stain, a differential stain for RNA and DNA, and a tracking dye for DNA in electrophoresis [3]. It is used commonly with bright-field microscopes to dye the chromatin of cells so that they are more easily viewed. MG has also been recommended as a suitable dye for the metachromatic demonstration of amyloid [3]. MG has been studied spectrophotometrically, electrochemically and cyclicvoltammetry [4], but physical studies of MG are rare. The study of the optical constants of materials is very interesting for many reasons. Firstly, the use of materials in optical devices re- quires brief knowledge of their optical constants over a wide range of wavelengths. Secondly, the optical absorption measurements are used to obtain information concerning the band structure of the organic semiconductor thin films. Thus, it is important to re- veal the properties of MG as a new semiconductor material for electronic device applications. In this work, we studied the influ- ence of the annealing temperature on the structure and the optical parameters of MG thin films deposited by drop casting technique. 2. Experimental details 2.1. Films preparation The MG powder was obtained from Fluka Company. Thin films of MG were fabricated using a drop casting technique at room temperature (300 K). A 2 mg of MG powder was dissolved in 25 mL of methyl alcohol. The mixture was magnetically stirred for 5 min for obtaining a homogenous coating solution. Simple, two drops of this solution were dropped onto 2 Â 2 cm 2 optically flat quartz substrates, which were previously cleaned. The whole surface of the substrate was covered by a homogeneous layer of MG film. Film thickness was checked by an interferometric Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology http://dx.doi.org/10.1016/j.optlastec.2015.12.006 0030-3992/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author at: Department of Physics, Faculty of Education at Al- Mahweet, Sana’a University, Al-Mahweet, Yemen. E-mail address: aaadarwish@gmail.com (A.A.A. Darwish). Optics & Laser Technology 79 (2016) 158–163