G. Dehm et al., GROWTH AND STRUCTURE OF COPPER THIN-FILMS DEPOSITED ON (0001) SAPPHIRE BY MOLECULAR-BEAM EPITAXY, Philosophical magazine. B. Physics of condensed matter. Structural, electronic, optical and magnetic properties, 71(6), 1995, pp. 1111-1124
The structure of copper films grown on (0001) sapphire by molecular be
am epitaxy at 200 degrees C and 600 degrees C was studied by in situ r
eflection high-energy electron diffraction (RHEED) and transmission el
ectron microscopy (TEM). Both RHEED and TEM confirm that growth is epi
taxial at 200 degrees C, but {111}(Cu) textured at 600 degrees C. Howe
ver, in both instances growth occurs with the copper (111) plane paral
lel-to the interface. In the case of the 200 degrees C films the close
-packed directions of copper lie parallel to the close-packed directio
ns of sapphire in the interfacial plane; these films contain low angle
grain boundaries with the interface normal to the axis of rotation. H
igh resolution and atomic resolution electron microscopy of the interf
ace viewed in cross-section suggest that the atomic structure of the c
opper/sapphire interface is incoherent. The textured growth at 600 deg
rees C and near single crystal growth at 200 degrees C are explained i
n terms of entropy contributions to the free energy of the Cu/Al2O3 in
terface.