Analysis of the electronic configuration of the pulsed laser deposited La 0.7 Ca 0.3 MnO 3 thin films C.N. Borca a, * , S. Canulescu a , F. Loviat a , T. Lippert a , D. Grolimund a , M. Do ¨beli b , J. Wambach a , A. Wokaun a a Paul Scherrer Institut, CH-5232 Villigen, Switzerland b Paul Scherrer Institut c/o ETH Zu ¨rich, CH-8093 Zu ¨rich, Switzerland Received 13 September 2007; received in revised form 18 September 2007; accepted 18 September 2007 Available online 22 September 2007 Abstract The electronic properties of La 0.7 Ca 0.3 MnO 3d thin films grown by the pulsed reactive crossed beam laser ablation method are investigated. The effects of post-deposition annealing of epitaxial La 0.7 Ca 0.3 MnO 3d thin films have been investigated using X-ray photoelectron spectroscopy (surface sensitive) and hard X-ray absorption spectroscopy (bulk sensitive). The films deposited in the high vacuum are oxygen deficient and contain mostly Mn 3+ . High temperature annealing in a flowing oxygen atmosphere partially changes the Mn oxidation state from +3 towards +3.4. These changes should favor a metal-like conduction and a ferromagnetic double exchange transport mechanism in the annealed thin films. # 2007 Elsevier B.V. All rights reserved. Keywords: Pulsed laser deposition; Thin films of manganates; X-ray photoemission spectroscopy; X-ray absorption spectroscopy 1. Introduction The perovskite system L 1x A x MnO 3 (L, lanthanide; A, alkaline earth doping element) has been widely studied due to interesting electronic and magnetic properties [1]. The CMR effect (change in the resistivity with the applied magnetic field) observed in the lanthanum-doped compounds can be used for industrial applications, such as low field magnetic sensors or magnetoresistive reading heads [2]. The La 1x Ca x MnO 3 manganite materials exhibit a transition from an insulator-paramagnetic to metallic-ferromagnetic phase, with the maximum CMR effect at the transition temperature point [1]. The double exchange (DE) interaction is used as a main mechanism to explain the CMR effect. The DE interaction is related to the double exchange of e g electrons between the Mn 3+ –O 2 –Mn 4+ network, which is possible due to the overlap between 3d orbitals of Mn species and 2p orbitals of O species. A second mechanism emphasizes the importance of polaron formation due to the Jahn–Teller effect in compounds with Mn 3+ ions in the perovskite structure [3]. The presence of oxygen vacancies in the manganites can dramatically affect the transport properties of the materials. Moreover, when the material is processed as thin film, the crystal structure and chemical composition at the surface can have a significant influence. In the present work, we analyze the surface composition of the La 0.7 Ca 0.3 MnO 3d manganite thin films using X-rays photoelectron spectroscopy (XPS) as well as the bulk electronic configuration using X-ray absorption spectroscopy (XAS) of the Mn K-edge spectra. A detailed comparison between the as- deposited and O 2 annealed thin films is performed. 2. Experimental The La 0.7 Ca 0.3 MnO 3d (LCMO) thin films were grown on (1 0 0) LSAT [(LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 ] substrates, using the pulsed reactive crossed beam laser ablation (PRCLA) method [1]. A cylindrical target of LCMO with high purity (99.9%) was ablated with a KrF excimer laser (l = 248 nm, n = 10 Hz) using a laser fluence of 5.5 J/cm 2 and 30.000 pulses for the films growth. During the deposition process, two different oxidizing sources were used, i.e. O 2 as background gas (at a pressure of 8  10 2 Pa) and N 2 O for the gas pulse ( p = 200 kPa, duration 400 ms). The overall pressure in the chamber during the www.elsevier.com/locate/apsusc Available online at www.sciencedirect.com Applied Surface Science 254 (2007) 1352–1355 * Corresponding author. Tel.: +41 56 310 4076; fax: +41 56 310 2688. E-mail address: thomas.lippert@psi.ch (T. Lippert). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.09.049