Reflection High Energy Electron Diffraction and Atomic Force Microscopy Studies of Mn x Sc (1-x) Alloys Grown on MgO(001
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Reflection High Energy Electron Diffraction and Atomic Force Microscopy Studies of MnxSc(1-x) Alloys Grown on MgO(001) Substrates by Molecular Beam Epitaxy
Costel Constantin,1 Abhijit Chinchore,2 Arthur R. Smith,2 1
Department of Physics and Astronomy, James Madison University, Harrisonburg, VA 22801 Nanoscale & Quantum Phenomena Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 2
ABSTRACT
The combination of the molecular beam epitaxy growth method with the in-situ reflection high energy electron diffraction measurements currently offers unprecedented control of crystalline growth materials. We present here a stoichiometric study of MnxSc(1-x) [x = 0, 0.03, 0.05, 0.15, 0.25, 0.35, and 0.50] thin films grown on MgO(001) substrates with this growth method. Reflection high energy electron diffraction and atomic force microscopy measurements reveal alloy behavior for all of our samples. In addition, we found that samples Mn0.10Sc0.90 and Mn0.50Sc0.50 display surface self-assembled nanowires with a length/width ratio of ~ 800 – 2000. INTRODUCTION
Due the fact that manganese is a sulfur-fixing agent and thus helps increase the corrosion resistance in steel production, there is a significant interest in alloying it with iron, vanadium, chromium, and aluminum [1-6]. To date, very few groups have explored the possibility of alloying manganese with scandium [e.g., Ref. 7]. Buch et al. [7] reported that the Mn2Sc alloy enhances the creep resistance of magnesium alloys only above 450 oC. The increase in the creep resistance found in this study has been attributed to a semi-coherent precipitation formed by the Mn2Sc inside the magnesium alloy grains. The phase diagram for Mn-Sc alloys have been reviewed recently [8, 9], with the conclusion that the Mn23Sc6, Mn2Sc, and MnSc4 were the most stable; however, only Mn2Sc melted congruently, while the other two formed peritectic reaction. Mn-Sc alloys are usually synthesized in bulk by normal crucible melting and levitation melting methods [10]. This material has never been synthesized by radio-frequency molecular beam epitaxy (rf-MBE). We show here that MnxSc(1-x) thin films can be grown with this method with a stoichiometry range from x = 0 to x = 0.5. We present here a preliminary analysis of the way in which different stochiometries influence surface properties, including growth of surface selfassembled nanowires. EXPERIMENT
We performed the growth of Mn-Sc alloys using a homemade rf-MBE growth chamber [11, 12] and we employed Knudson effusion cells for manganese and scandium metallic sources. Before we loaded the MgO(001) substrates into the rf-MBE chamber, we ultrasonically cleaned them with acetone and isopropanol. Inside the chamber the substrates were deoxidized by heating and nitridation at a temperature of 900 °C for 30 minutes, by keeping the N2 flow rate to 1.1 sccm (Pchamber = 9 × 10-6 Torr) and rf-plasma power of 500 W. All the films were grown with
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a thickness of ~ 50 nm each, and at a substrate temperature of Ts ~ 450 oC. Th
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