Comparison of Sol-Gel Derived and Pulsed Laser Deposited Epitaxial La 0.67 Ca 0.33 MnO 3 Films for IR Bolometer
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Comparison of Sol-Gel Derived and Pulsed Laser Deposited Epitaxial La0.67Ca0.33MnO3 Films for IR Bolometer Rickard Fors,1 Annika Pohl,2 Sergey Khartsev,1 Alexander Grishin,1 and Gunnar Westin2 1 Department of Condensed Matter Physics, Royal Institute of Technology, SE-164 40 Stockholm-Kista, Sweden 2 Department of Material Chemistry, Ångström Laboratory, Uppsala University, SE-751 21 Uppsala, Sweden ABSTRACT Epitaxial La0.67Ca0.33MnO3 films have been prepared on LaAlO3 crystals by pulsed laser deposition (PLD) and by a novel all-alkoxide sol-gel technique. Different out-of-plane lattice parameters are found for the as-prepared films, and scanning electron microscopy shows a more porous structure for sol-gel films as compared to PLD films. These differences are largely removed by post-annealing at 1000 °C. Transport measurements show maximum temperature coefficient of resistivity of 8.2 % K-1 at 258 K (PLD) and 6.1 % K-1 at 241 K (sol-gel) and colossal magnetoresistance at 7 kOe of 35 % at 263 K (PLD) and 32 % at 246 K (sol-gel). INTRODUCTION The perovskite manganites with the general formula La 1+-x3 A +x2 MnO 3 are very interesting both from a fundamental physics standpoint and due to their promise for potential application in various devices such as un-cooled infrared (IR) bolometers and field effect transistors (FET) [16]. Spin-dependent transport close to the para-to-ferromagnetic transition (semiconductor-tometallic) temperature, Tc, causes the resistivity to strongly depend on magnetic field (colossal magnetoresistance) and temperature. As figures of merit it is suitable to introduce the temperature coefficient of resistivity (TCR) and the magnetoresistance (MR) to determine the materials performance as an IR bolometer and as a semiconductor channel material for FET, respectively. A high TCR and low excess noise in La 0.67 Ca 0.33 MnO 3 (LCMO) thin films on Si have recently been demonstrated as a prototype of an IR bolometer [6], and the challenge now lies in moving the applications out of academia and into industry. To date, most perovskites engineered towards applications are grown by pulsed laser deposition (PLD) which is not an industrially viable technique since there is almost no possibility of large area deposition. Sol-gel derived thin films do not suffer this drawback and represent a cheap and fast route to industry scale production. High quality sol-gel derived, epitaxial LCMO have been demonstrated [7-8], but a comparison of transport, quality of epitaxy and surface morphology to PLD-grown films is to the best of our knowledge lacking. We present results on the characterization of both pulsed laser deposited and all-alkoxide sol-gel derived LCMO on LaAlO3 (LAO) single crystal substrates with and without post-annealing EXPERIMENTAL DETAILS The processing technique for sol-gel films is described in detail in [10] and only a brief outline will be included here. Precursor solutions were prepared according to [9] and mixed in stoichiometric ratio and gel films were deposited on the (001) LaAlO3 s
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