Pulsed Laser Deposition of Chromium Oxides: Substrate Effects
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0998-J05-06
Pulsed Laser Deposition of Chromium Oxides: Substrate Effects Helia Jalili, Nina Heinig, and K. T. Leung Departments of Physics and Chemistry, University of Waterloo, Waterloo, N2L 3G1, Canada ABSTRACT Pulsed Laser Deposition (PLD) was used to grow chromium oxides (CrOx) on MgO(100), Al2O3(0001), SrTiO3(100), LaAlO3(100), and Si(100) under different growth conditions, including substrate temperature, O2 pressure, and laser fluence. SEM, AFM and XRD measurements show that various phases of CrOx films with different morphologies could be obtained on different substrates under the same growth conditions. Half-metallic CrO2 needle-like nanostructured films were only observed on MgO(100) under a special set of conditions. INTRODUCTION Chromium oxides are interesting materials because of their technological applications as catalysts, gas sensors, dehydrogenation and protective layers for preventing oxidation [1,2,3,4]. In the case of CrO2, its special magnetic and electrical properties have attracted a lot of recent attention. CrO2 is ferromagnetic at room temperature, with a Curie temperature TC=395 K. Band structure calculations indicate the half-metallic character of CrO2 [5]. Spin- and energyresolved photoemission data further show nearly 100% spin polarization for electrons with binding energies of 2 eV below the Fermi energy [6], suggesting CrO2 as a promising candidate for spintronic applications [7,8,9]. Furthermore, in order to achieve the higher magnetic switching ratio by using the spin effects, it is crucial to prevent scattering during extraction of polarized spins. The development of preparation methods for defect-free multilayer films with high-quality interfaces is therefore of special importance to the fabrication of spintronic devices. The metastable nature of CrO2 at room temperature makes its synthesis difficult. Thermal decomposition of CrO3 under a high oxygen pressure and chemical vapour deposition (CVD) methods are commonly used to grow CrO2 films, with successful epitaxial growth demonstrated only on single-crystalline TiO2 substrates [10,11,12,13,14]. PLD is a particularly powerful film growth technique because it enables the formation of metastable phases under non-equilibrium thermodynamic conditions. Furthermore, multilayer films and complex materials can also be obtained in situ by using different targets and feed gases, which is an important advantage in device fabrication. In the present work, we investigate the use of the PLD technique for the growth of a single-phase CrOx film (particularly CrO2), with focus on the nature of the resulting nanostructured films grown on different substrates, including MgO(100), Al2O3(0001), SrTiO3 (100), LaAlO3(100), and Si(100). Our goal is to develop a set of optimized growth conditions for producing a high-quality film by systematically varying the substrate temperature, the O2 pressure, the laser fluence, and the target-to-substrate distance. Unlike the previous PLD studies that did not produce a single-phase CrOx film [15,16], the present
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