Influence of reactive oxygen ambience on the structural, morphological and optical properties of pulsed laser ablated potassium lithium niobate thin films V. Jayasree a , R. Ratheesh b , V. Ganesan c , V.R. Reddy c , C. Sudarsanakumar d , V.P. Mahadevan Pillai a, ⁎, V.U. Nayar a a Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram 695 581, Kerala, India b Centre for Materials for Electronics Technology, Athani P. O, Thrissur, Kerala, India c UGC-DAE Consortium for Scientific Research, Indore Centre, Madhya Pradesh, India d School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, Kerala, India abstract article info Article history: Received 10 October 2007 Received in revised form 7 June 2008 Accepted 6 July 2008 Available online 17 July 2008 Keywords: Potassium lithium niobate Nonlinear optic materials Ferroelectric Tungsten bronze materials Electro-optic materials Pulsed laser deposition Transmittance spectra Optical band gap The effect of oxygen ambience on the structure and properties of potassium lithium niobate (K 3 Li 2 Nb 5 O 15 : KLN) films prepared on glass substrates by pulsed laser ablation technique (PLD) are studied. The influence of annealing on the properties of vacuum deposited films is also investigated. The Gracing Incidence X-ray Diffraction (GIXRD) data suggests the tetragonal structure for the KLN film whose grain sizes increase on thermal annealing. The Atomic Force Microscopic (AFM) analysis reveals the four-fold symmetric nature of the grains in the films. Self assembly of grains in the form of rings and rods are observed in AFM images of the films deposited in an oxygen ambience of 2 Pa. The films deposited at higher oxygen ambience show a blue shift in optical band gap. The direct current (DC) resistance measurement on the films deposited at non-reactive ambience reveals resistivity in the range of kΩ m. © 2008 Elsevier B.V. All rights reserved. 1. Introduction As a class of compounds, ferroelectric oxides have very attractive and potential properties such as wide band gap (N 3 eV), large electro- optic and nonlinear optic coefficients and have the possibility of sustaining the spontaneous polarizations [1]. Ferroelectric tungsten– bronze crystals with general formula (A 1 ) 2 (A 2 ) 4 C 4 (B 1 ) 2 (B 2 ) 8 O 30 have generated much interest, especially for nonlinear optical applications and for their large optical damage threshold originating from their crystal structure [2]. Potassium lithium niobate (K 3 Li 2 Nb 5 O 15 : KLN) with a completely filled tungsten–bronze type structure is a very promising material for various optical applications owing to its large electro-optic, nonlinear optic, piezoelectric and pyroelectric proper- ties [3] However the growth of large single crystals of KLN is still a challenging problem as they crack easily while cooling down through paraelectric to ferroelectric phase. Moreover the crystallographic and dielectric properties are severely affected by the Nb 2 O 5 content in the melt. Hence, the growth of epitaxial thin films of KLN is of particular interest, as high quality thin films of KLN are suitable for many of its applications. Different thin film depositions technique such as epitaxial growth by melting [4], RF magnetron sputtering [5,6] on substrates like potassium bismuth niobate [5] and sapphire have been used for the epitaxial or polycrystalline growth of KLN thin films. However, preparation of KLN thin film using pulsed laser deposition technique has not yet been reported. Pulsed laser deposition (PLD) is an effective tool for the growth of quantum structures with high chemical purity and controlled stoichiometry. In PLD, one can control size distribution in nanocrystals by varying the parameters like target to substrate distance, laser fluence, background gas pressure etc. This paper presents a report of preparation of KLN thin film using pulsed laser deposition technique in non-reactive and reactive atmosphere. The as-deposited films prepared under vacuum condition, the films annealed in air atmosphere and the as-deposited films prepared under different reactive oxygen pressures, are characterised using Gracing Incidence X-Ray Diffraction (GIXRD), Atomic Force Micro- scopy (AFM), UV–Vis spectroscopy and direct current (DC) resistance measurements to study the effect of annealing and that of background oxygen pressure on the properties of the films. 2. Experiment 2.1. Preparation of stoichiometric target for PLD operation Stoichiometric composition of K 2 CO 3 , Li 2 CO 3 and Nb 2 O 5 (Aldrich, purity 99.99%) is mixed well in an agate mortar for an hour using Thin Solid Films 517 (2008) 603–608 ⁎ Corresponding author. E-mail address: vpmpillai9@rediffmail.com (V.P.M. Pillai). 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.07.004 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf