Chromium Oxide Sub-Micron Particles Fabricated by a Unique Technique: Laser-Induced Solution Deposition
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Chromium Oxide Sub-Micron Particles Fabricated by a Unique Technique: Laser-Induced Solution Deposition Zhenchen Zhong Institute for Micromanufacturing and Physics Program, Louisiana Tech University, Ruston, LA 71272, U.S.A. and Department of Physics, Grambling State University, Grambling, LA 71245, U.S.A. ABSTRACT We have demonstrated that well-dispersed sub-micron chromium oxide particles can be fabricated by laser-induced solution deposition (LISD) from the solution of CrCl2 solute dissolved in organic solvents containing THF and cyclohexane. The particles are uniform in composition and contain little contamination. The distribution of the particles is narrow in three sizes: 230 nm, 350 nm and 400 nm. We have discussed the kinetics of forming these three kinds of sub-micron particles and the difficulty in obtaining single-phase chromium oxide. We have successfully shown that LISD is a unique technique for fabricating submicron chromium oxide particles with uniform composition and controllable size with narrow particle size distribution. The kinetics (nucleation and growth mechanism) of forming three sizes of particles is discussed. INTRODUCTION Metallic wires and dots can be obtained by reducing a metallic salt in the pores of a membrane. Electro-deposition processes in nanometer-sized pores of aluminum oxide membranes was reported more than 30 years ago [1]. This is of great interest because magnetic systems of very small dimensions can reveal mesoscopic and quantum effects. Single-electron blocking effects have been evidenced in oxidized STM tips or substrates [2], and similar effects were reported in nanowires smaller than 0.01 µm2 [3]. Making nanoscale particles of ferromagnetic and antiferromagnetic particles is the key to future research in this area. Chromium oxides have attracted much attention recently because of their importance both in science and technology. Band-structure calculations [4] predict that CrO2 is a halfmetallic ferromagnet – a system, which is metallic for one spin direction and insulating for the opposite spin direction. This contention is supported by many experimental measurements. Therefore chromium oxides have been seriously considered as spin-polarized electron injectors to spin-tunnel junctions [5] and other magnetoresistive devices [6,7]. The insulating antiferromagnetic chromium oxide Cr2O3 has a Néel temperature of 307K and is suitable for tunnel junction barrier [8] both below and above the Néel temperature. The ferromagnetic chromium oxide CrO2 with a Tc of 397K [4] has been predicted to be half-metallic (metallic for one spin direction while insulating for the other spin direction) by band structure calculations [4, 9-13], though Kulatov and Mazin found CrO2 to be insulating in both spin-directions [10]. Evidence of close to 100% polarization, consistent with the half metallic character of CrO2, was observed in spin-polarized photoemission [14], vacuum tunneling [15], and Andreev scattering [16] (Though some discrepancies from perfect half metallic character remain unresolve
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