Martensitic transition during Ni growth on Fe(001): evidence of a precursor phase

Abstract

We report evidence that the body-centered cubic (bcc)–face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main 〈100〉 crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Ni〈211〉 crystallographic directions aligned with the Fe〈110〉 axes. In addition, the martensitic transition is detected not at 6 ML, as previously believed, but above 20 ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc–fcc transition is characterized by the development of Ni mounds oriented along the 〈110〉 directions, as shown by scanning tunneling microscopy.