Scientists unlock recipe for creating rare cobalt alloy at industrial scale
Researchers have pinpointed how to reliably produce metastable face-centered cubic cobalt—a form that normally doesn't exist in nature—by controlling temperature and processing gas during thin-film manufacturing. The discovery could enable development of cobalt alloys with superior properties for electronics, aerospace, and renewable energy applications.
Originaltitel: Phase formation kinetics of metastable fcc cobalt
<p>The kinetics for phase formation of metastable face-centered cubic (fcc) cobalt is explored using a combination of epitaxial thin film deposition and first-principles calculations. Co layers are deposited by magnetron sputtering while systematically varying the substrate, substrate temperature Ts, and processing gas (Ar or N2). Deposition in N2 results in nitrogen-free fcc Co on amorphous SiO2/Si for Ts &gt;= 300 degrees C but causes residual nitrogen incorporation for Ts &lt;= 200 degrees C. Templating with hexagonal Al2O3(0001) leads to nucleation and growth of epitaxial hexagonal close-packed (hcp) Co(0001) in Ar while N2 causes stacking faults and the formation of a coherent mixed hcp/fcc epitaxial microstructure. MgO(001) substrates facilitate nucleation of metastable fcc Co and growth of epitaxial Co(001)/MgO(001) in both Ar and N2 for Ts &gt;= 100 and Ts &gt;= 300 degrees C, respectively. Density functional calculations support experimental trends, suggesting that nitrogen stabilizes the cubic phase with a predicted hcp-to-fcc transition at 10 at.%N for T = 0 K and 2 at.%N at 300 degrees C. They also indicate a negligible hcp (0001)/fcc(111) phase-boundary energy, facilitating the experimentally observed mixed hcp/fcc microstructure. The overall results demonstrate that N2-assisted Co deposition provides an effective approach to synthesize metastable fcc Co layers.</p>