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Article

Microfluidic Synthesis of Cobalt Nanoparticles

Yujun Song,^†^‡ Hartwig Modrow,^§ Laurence L. Henry, Cheng K. Saw, E. E. Doomes,^†^# Vadim Palshin,^† Josef Hormes,^† and Challa S. S. R. Kumar*^†

Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, Physikalisches Institut, University of Bonn, Nussallee 12, D-53115 Bonn, Germany, Department of Physics, Southern University and A&M College, Baton Rouge, Louisiana 70813, and Lawrence Livermore National Laboratory, Livermore, California 94550

Chem. Mater., 2006, 18 (12), pp 2817–2827

DOI: 10.1021/cm052811d

Publication Date (Web): May 20, 2006

†

Louisiana State University.

‡

Current address: Applied Research Centre at Old Dominion University, Newport News, VA 23606.

University of Bonn.

Department of Physics, Southern University and A&M College.

Lawrence Livermore National Laboratory.

Current address: Department of Physics, Southern University and A&M College.

To whom correspondence should be addressed. E-mail: ckumar1@lsu.edu.

Abstract

Co nanoparticles with three different crystal structures were synthesized in a microfluidic reactor through manipulation of reaction times, flow rates, and quenching procedures. Cobalt nanoparticles of face-centered cubic (β) phase were obtained from a high flow rate of the reactants followed by in situ quenching of the reaction. hcp and ε-cobalt nanoparticles were obtained at a low flow rate of the reactants followed by in situ quenching and delayed quenching, respectively. The crystal structures were characterized using Co K-edge X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction (XRD), and selected area electron diffraction (SAED). In situ XANES measurements on Co nanoparticles coming out of the outlet of the microfluidic reactor at different flow rates seem to indicate that the difference in flow rate influences the nucleation process in a critical way and that particle growth occurs mainly outside the reactor. The magnetic properties of the cobalt nanoparticles, measured using a SQUID magnetometer system, showed significant differences among the samples and are consistent with the three different crystal structures.

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