Transmission electron microscopy investigation of Co thin films on GaAs(001)

Transmission electron microscopy (TEM) observations of the microstructure of epitaxial Co thin films on GaAs(001) are reported. Cross-sectional TEM confirmed both bcc-Co and hcp-Co exist in a single 345 Angstrom film. During film growth by molecular beam epitaxy, the epitaxial bcc-Co layer forms first at the GaAs interface, and hcp-Co islands subsequently form at the free surface of the bcc-Co layer when it reaches a thickness of about 145 Angstrom. The bcc-Co film is single crystal at early stages of growth, but later may develop into multiple bcc crystals. The final hcp-Co grain size is roughly 15-20 nm, and selected area electron diffraction showed these grains are strongly textured. Four previously unreported variants of the hcp-Co/GaAs orientation relationship were observed in which the c axis of the hcp unit cell lies out of the plane of the film. [S0003-6951(99)02529-2].