Topological, morphological and optical properties of Gamma irradiated Ni (II) tetraphenyl porphyrin thin films M.M. El-Nahass a, ⁎, H.M. Abd El-Khalek b , Ahmed M. Nawar b a Thin Film Laboratory, Physics Department, Faculty of Education, Ain Shams University, Heliopolis, Roxy, Cairo, Egypt b Thin Film Laboratory, Physics Department, Faculty of Science, Suez Canal University, Ismailia, Egypt abstract article info Article history: Received 11 June 2011 Received in revised form 27 November 2011 Accepted 1 December 2011 Available online 15 December 2011 Keywords: NiTPP thin film Gamma-irradiation Optical dispersion Roughness parameters Thermal evaporation technique was used to prepare NiTPP Thin films at room temperature. The prepared films were divided into two groups; the first group was as-deposited films, and the second group was irradi- ated in gamma cell type 60 Co source at room temperature with total absorbed dose of 150 kGy in air. All films were identified by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) before and after ex- posed to gamma radiation. The spectrophotometric measurement of transmittance and reflectance were used to investigate the optical properties at normal incidence of light in the wavelength range 200–2500 nm for as-deposited and gamma-irradiated films. Optical constants (refractive index n, and ab- sorption index k) of as-deposited and irradiated films have been obtained in the wavelength range 200–2500 nm for all the samples. The single oscillator energy (E o ), the dispersion energy (E d ), the high fre- quency dielectric constant (ε ∞ ), the lattice dielectric constant (ε L ) and the ratio of the free charge carrier con- centration to the effective mass (N/m ⁎ ) were estimated for each group. The absorption analysis has been also performed to determine the type of electronic transition and the optical energy gap. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Porphyrins are representative of photofunctional organics, and they show a remarkable photo-, electro- and biochemical property that con- tributes to light harvesting by their strong absorption in photosynthesis [1,2]. The architectures of meso/nano-scaled porphyrin assemblies or particles are expected to be promising candidates for use in photonic devices [3–6]. In order to exploit the properties of porphyrins and metalloporphyrins, they can be deposited as thin films by using several techniques such as solvent casting, Langmuir–Blodgett, spin coating, high vacuum evaporation and glow discharge induced sublimation [7–9]. In order to fabricate organic nano-architectures composed of por- phyrins, it should be recognized that Van der Waals intermolecular and hydrogen-bonding interactions as well as the electrostatic attraction are responsible for the specific electronic/optical properties that are funda- mentally different from those of inorganic metals or semiconductors [10–16]. The presence of π-electrons diminishes the probability of a lo- calization of excitation energy at a specific bond. In turns, the excitation energy will spread over the whole carbon ring and de-excitation is more likely to occur through processes such as collisional transfer rather than by dissociation. The aromatic ring is considered as the dominant com- ponent in porphyrins, which is mostly responsible for the strength, the high temperature and radiation resistance of the material [17]. Porphyrins and metalloporphyrins exhibit an intensive absorption band called the Soret band in visible region, and at longer wavelength, there is another series of absorption band called the Q-band. Using fea- tures in color, porphyrin and related compounds can be applied to opti- cal memory [18,19]. The interaction of gamma-rays with material, mainly, occurs by means of electronic excitation, electronic ionization, and, primarily, atomic displacement of the orbital electrons [20]. The in- fluence of radiation on the material depends on dose rate and the pa- rameters of the films, including their thickness and composition. The degradation is more severe for the higher dose and the thinner films [21,22]. Numerous efforts have recently been made to investigate the influence of gamma radiation on thin films and thin film structures of different metal oxides and polymers, in order to find out the suitability of using thin films and thin film structures of different metal oxides and polymers as gamma radiation dosimeters [22–24]. The present work, aims to study in detail the induced changes in the topological and the morphological nanostructures of NiTPP thin films and estimate the re- lated optical and dispersion parameters of these films before and after exposed to gamma radiation of dose 150 kGy. The change in exposure time and exposure intensity have not considered because they were not one of the objective of this study. 2. Experimental procedures A dark purple crystalline powder 5, 10, 15, 20-Tetraphenyl-21H, 23H-porphine nickel (II) NiTPP was purchased from Aldrich Chem. Optics Communications 285 (2012) 1872–1881 ⁎ Corresponding author. Tel.: + 20 124168621. E-mail address: prof_nahhas@yahoo.com (M.M. El-Nahass). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.12.019 Contents lists available at SciVerse ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom