Epitaxial hcp and bcc Cu and Pd films were grown on W(100). The epitax
ial relation of the hcp films is determined by reflection high energy
electron diffraction (RHEED) as <(11(2)over bar 0> parallel to (100) a
nd [0001] parallel to [011]. The growth of hcp Cu and Pd is attributed
to the much smaller misfit for this hcp orientation in either the <[1
(1)over bar 00] or [0001] direction, respectively, than for any fee or
ientation. This misfit difference overcomes the energy difference betw
een hcp and fcc crystal structure. The atomic diameter of Pd is near t
hat of W, which also gives a good fit for bcc pseudomorphic Pd. The en
ergy difference between hcp and bcc determines the structure. X-ray ph
otoelectron diffraction measurements show a bcc Pd film, transmission
RHEED hcp islands.