Hexagonal close-packed Ni nanostructures grown on the „001... surface of MgO

We report the in situ microscopy observation of an unnatural phase of Ni, a highly strained hexagonal close-packed shcpd form which we believe is stabilized by heteroepitaxial growth on the s001d face of MgO. We find that the nanosized hcp nickel islands transform into the normal face-centered cubic structure when the size of the islands exceeds a critical value sabout 2.5 nm thick with a lateral size of ,5 nmd. The structural transition proceeds via a martensitic change in the stacking sequence of the close-packed planes. The formation of hcp Ni nanostructures with an unusually large crystallographic c /a ratio s,6% larger than ideal hcpd is very interesting for spintronic and recording applications where large uniaxial anisotropies are desirable. © 2005 American Institute of Physics. fDOI: 10.1063/1.1890472g