Determination of the coordination number of Co atoms at the CoSi2(A,B)/Si(111) interface by transmission electron microscopy

The atomic structure of the (111) interface between CoSi2 (type A and B) and Si is investigated by high-resolution transmission electron microscopy, combined with image simulations. Type B interfaces of CoSi2 layers formed by thermal reaction of vapor deposited Co on (111) oriented Si, of Si/CoSi2/Si heterostructures, and of CoSi2 precipitates formed by high-dose Co implantation were examined. The coordination of the Co atoms at all B-type interfaces is found to be eightfold, in accordance with theoretical predictions. Type A interfaces of CoSi2 precipitates and continuous CoSi2 layers, formed by ion implantation and subsequent annealing, showed clear evidence for the presence of sevenfold coordinated interfacial Co.