hcp and bcc Cu and Pd Films

Epitaxial hcp and bcc Cu and Pd films were grown on W(100). The epitaxial relation of the hcp films is determined by reflection high energy electron diffraction (RHEED) as $\left(11\overline{2}0\right)\parallel \left(100\right)$ and $\left[0001\right]\parallel \left[011\right]$. The growth of hcp Cu and Pd is attributed to the much smaller misfit for this hcp orientation in either the [ $1\overline{1}00$] or [0001] direction, respectively, than for any fcc orientation. This misfit difference overcomes the energy difference between hcp and fcc crystal structure. The atomic diameter of Pd is near that of W, which also gives a good fit for bcc pseudomorphic Pd. The energy difference between hcp and bcc determines the structure. X-ray photoelectron diffraction measurements show a bcc Pd film, transmission RHEED hcp islands.