Probing the growth and aging of cobalt nanoparticles

INOR 500

Guangjun Cheng, guangjun.cheng@nist.gov1, Cindi L. Dennis, cindi.dennis@nis.gov2, Robert D. Shull2, and A. R. Hight Walker1. (1) Optical Technology Division, Physics Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Mail Stop 8443, Gaithersburg, MD 20899, (2) Materials Science and Engineering Laboratory, NIST, 100 Bureau Drive, Gaithersburg, MD 20899-8552
We have combined transmission electron microscopy (TEM) and magnetic measurements to characterize the growth of 10 nm cobalt nanoparticles during synthesis and their subsequent stability in air. Cobalt nanoparticles are synthesized by first injecting the cobalt precursor solution into 1,2-dicholorbenenze (DCB) containing surfactants at 120 oC. TEM and magnetic measurements of the solution extracted 10 minutes after the original injection have shown the formation of cobalt nanoparticles and the presence of a paramagnetic component in the solution. Then, the temperature is raised to 180 oC for 10 minutes to complete the synthesis. TEM shows the freshly-prepared cobalt nanoparticles are mono-disperse and magnetization measurements demonstrate the disappearance of the paramagnetic component. Over time, the saturation moment of the cobalt nanoparticles in DCB decreases and a hysteresis loop shift under field-cooled condition is observed, suggesting the formation of an anti-ferromagnetic cobalt oxide shell on the surface of the cobalt nanoparticles with time.
 

Nanoscience - Characterization and Applications
9:00 AM-1:00 PM, Tuesday, April 8, 2008 Morial Convention Center -- Rm. 219, Oral

Division of Inorganic Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008