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a b s t r a c tInvestigations of the structural, morphological and electrical properties of multilayer ZnO/TiO 2 thin films deposited by sol-gel technique on glass substrate. Sol-gel is a technique in which compound is dissolved in a liquid in order to bring it back as a solid in a controlled manner. TiO 2 solution was obtained by dissolving 0.4 g of TiO 2 nano powder in 5 ml ethanol and 5 ml diethylene glycol. ZnO solution was obtained by dissolving 0.88 g zinc acetate in 20 ml of 2-methoxyethanol. X-ray diffraction (XRD) (PW 3050/60 PANalytical X'Pert PRO diffractometer) results showed that the crystallinity is improved when the number of ZnO/TiO 2 layers increased. Also it shows the three phases (rutile, anatase and brookite) of TiO 2 . Surface morphology measured by scanning electron microscopy (SEM) (Quanta 250 fei) revealed that Crakes are present on the surface of ZnO/TiO 2 thin films which are decreased when the number of ZnO/TiO 2 layers increased. Four point probe (KIETHLEY instrument) technique used to investigate the electrical properties of ZnO/TiO 2 showed the average resistivity decreased by increasing the number of ZnO/TiO 2 layers. These results indicated that the multilayer thin films improved the quality of film crystallinity and electrical properties as compared to single layer. Ó 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). IntroductionThe electrical and optical properties of semiconductors can be increased by the coupling of two semiconductors than a single semiconductor [1][2][3][4][5][6][7][8][9][10][11]. Titanium dioxide (TiO 2 ) is an important semiconductor having vast applications in photocatalysis, solar cells and photonic devices [1,[12][13][14]. It has rutile, anatase and brookite phases [15][16][17][18][19][20]. The presence of any one or more than one phases in the material can effect on the micro-structural, optical and electrical properties of the material. Among these phases rutile is a stable phase while the other two phases are metastable which are difficult to synthesize and are continuously studied [21]. In many publications the stability of these phases are discussed [19,[22][23][24][25]. Zinc oxide (ZnO) is abundant, non-toxic and a low cost attractive material having vast applications because of its high optical and electrical properties [26][27][28][29][30][31][32][33][34][35]. Both zinc oxide (ZnO) and titanium oxide (TiO 2 ) materials are abundant, and nontoxic, with wide band gap ceramic materials and have been widely applied in the electronic and optoelectronic products because of their unique optical and electronic properties [36]. ZnO has a high electron mobility than TiO 2 and both ZnO and TiO 2 have a similar band gap energy [37]. A negative shift is present in the valence and conduction bands of ZnO as compared to those of TiO 2 . Also it is claimed that the photodegradation mechanism of organic dyes in ZnO has been similar to that of TiO 2 . As a c...

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