NODULAR DEFECT GROWTH IN THIN-FILMS

The formation and microstructure of nodular defects in thin films of sputtered Ti and evaporated MgF2 are studied and modelled. Unintentional nodular defects in Ti occurred from growth onto uncleaned substrates whereas nodule growth in MgF2 was initiated by seeding the substrate with polystyrene spheres. Nodules grew in a characteristic shape consisting of a cone with a domed top, and with the nodule separated from the bulk of the film by a low density boundary. Simulation of nodule growth by a ballistic deposition model in two and three dimensions confirmed this nodular shape, but also predicted that a low density region extends into the nodule from the boundary. Further predictions of the minimum seed size required to initiate nodule growth lead to suggestions for a technique for film adatom mobility measurement.