Studies of structural transformations and electrical behaviour of FeSe films

The formation of FeSe alloy films as a result of the co-deposition of Se and Fe thin films has been studied. It has been found that the as-grown FeSe film corresponds to a cubic phase with a = 5.37±0.05 Å. The effect of annealing on this FeSe phase has been investigated. At annealing temperatures ranging between 150° and 200°C, the cubic phase transforms to a hexagonal phase (a = 4.00±0.05 Å, c = 5.88±0.05 Å) which resembles one of the known bulk phases of FeSe. On further annealing in the temperature range 250°–300°C, the hexagonal phase transforms to a tetragonal phase with a = 4.18±0.05 Å, c = 4.73±0.05 Å. All the transformations have been found to be irreversible. The electrical behaviour of the FeSe films at various temperatures has also been studied. Evidence for the phase transformations is provided by the nature of the variation of the electrical resistivity with temperature.