In situ transmission electron microscopy observations of the fcc-hcp phase transformation in Co Nanowhiskers

One dimensional nanostructures have the prospect to change the properties of materials used in contemporary devices. Recently we reported a process to grow perfect defect and flaw free nanostructures with diameters of several ten nanometers under UHV conditions. Typical diameters of the nanowhiskers are 100 nm and lengths of up to 50 µm are observed.

In the presentation we will address the growth of Co nanowhiskers and the onset of the fcc-hcp phase transformation in those nanostructures. The later was studied by in situ transmission electron microscopy. Compared to the perfect crystal structure of fcc nanowhiskers, those grown for Co exhibit stacking faults parallel to its axis when observed at room temperature. The overall crystal structure is fcc. In situ heating and cooling experiments performed in a high resolution TEM were carried out with the goal to reach the stable hcp crystal structure in Co nanowhiskers. During thermal cycling partial dislocations are nucleated and propagate parallel to the nanowire axis, forming only a local hcp structure, the overall fcc crystal structure however remains.