Contrasted morphologies in nanostructured Janus W-Cu columns

Janus-like W-Cu films exhibiting a tilted columnar architecture are prepared by GLAD co-sputtering using W and Cu targets. Co-deposition of these two-immiscible metals leads to contrasted morphologies in the columns growth. Observations by scanning electron microscopy reveal different structural features at the micro- and nanoscales as the tilted columns face W or Cu target. In front of the W flux, columns are dense with a saw-tooth profile, whereas a granular and rough aspect is produced for the opposite side receiving Cu atoms. A finer structural analysis by high resolution transmission electron microscopy supports these different morphologies. Growth mechanisms as well as occurrence of diverse crystallographic phases (bcc alpha-W, fcc Cu and even a disordered WxCu1-x alloy despite immiscibility of W and Cu metals) through the cross-section of the columns are discussed.