Sample Investigation
Controlled Large-Scale Synthesis and Magnetic Properties of Single Crystal Cobalt Nanorods
Rohan Bhobe conducted his two Student Inquiry and Research investigations in Engineering/Materials Sciences on nanotechnology at Northwestern University under Professor Vinayak P. Dravid.
This 2005 investigation, described below, builds on Rohan's 2004 Student Inquiry and Research work entitled: ELECTROCHEMICAL FABRICATION OF COBALT NANOROD ARRAYS IN POROUS ALUMINUM OXIDE TEMPLATES. As a result of his 2004 work, Rohan was one of 20 high school delegates sent in August 2004 to represent the United States and present their research during two weeks of scientific collaboration in Beijing, China. Rohan's 2004 project was named Best in Category in Materials Science at the 2004 Illinois Junior Academy of Science regional and state science fairs.
Rohan presented his 2005 work at the 2005 American Junior Academy of Science session of AAAS (American Association for the Advancement of Science) in Washington DC. He was a regional finalist for the 2005 Intel Science Talent Search competition.
Abstract
Nanostructured magnetic materials are drawing considerable attention for their potential applications in ultra high-density magnetic data storage, sensors, and other electronic devices. One-dimensional structures such as nanorods and nanotubes exhibit interesting properties not characteristic of their bulk-material counterparts. Nanorods created from single crystalline ferromagnetic materials have the added advantage of being magnetically polarized in the same direction along the entire length of the nanorod.
We report detailed synthesis studies and a novel procedure for the large-scale fabrication of single crystalline cobalt (Co) nanorods using thermally evaporated gold as a conducting electrode on a nanoporous anodic aluminum oxide (AAO) template. Cobalt was chosen over other ferromagnetic materials because of recommendation by previous literature. Electrodeposition was used to fabricate the cobalt nanorods inside the pores of the AAO membrane, after which a mild hydrofluoric acid (HF) solution was used to dissolve the AAO, yielding a large-scale ensemble of isolated Co nanorods.
A preferred perpendicular anisotropy is observed in these nanorod arrays. Scanning electron microscopy and transmission electron microscopy (SEM and TEM, respectively) examination show clear evidence of single crystal metallic Co nanorods (approx. 100 nm in diameter and 10 µm in length). Superconducting quantum inference device magnetometer (SQUID-M) studies demonstrate ferromagnetic behavior in the cobalt nanorods. Magnetic properties indicate both coercivity and thermal activation volume increase with increasing nanorod length.