Ion irradiation—a technique providing a criterion to distinguish between amorphous and nanocrystalline In_1−x Pd _x films

Abstract

In_1−x Pd _x films with 0.2≦x≦0.75 have been prepared by vapour quenching at 4.2 K or 77 K, respectively. To test whether amorphous (a-) phases can be obtained in this way, the resistance behavior and the electron diffraction patterns of the as-prepared and annealed films were studied insitu. For films withx=0.25 additional information could be acquired from their superconducting behavior. Combining these results one concludes that a-phases exist for the compositional range 0.2≦x≦0.6, which are stable up to crystallization temperaturesT _x within the range 250 K≦T _x ≦420 K. Irradiation of the crystallized films at low temperatures (4.2 K or 77 K) with heavy ions (350 keV Ar⁺ or Kr⁺) leads to complete re-amorphization. Forx=0.67 corresponding to InPd₂ a nanocrystalline (n-) phase is obtained by vapour quenching at 77 K as inferred from x-ray diffraction. AtT _x =700 K, thesen-films exhibit a drop of the electrical resistance indicating the beginning of significant grain growth. After recooling, Kr⁺ bombardment at 77 K does not restore the high electrical resistance of the as-quenchedn-film. This result can be used as a criterion when studying quenched films withx=0.625 corresponding to In₃Pd₅. In this case, a resistance drop is found atT _x =600 K, but the diffraction techniques do not allow an uniquevocal distinction between amorphous and nanocrystalline. This becomes possible by low temperature ion irradiation after annealing atT>T _x . The bombardment results in resistance changes, which saturate well-below the value of the as-quenched sample implying nanocrystallinity for the latter. Based on this criterion, a ‘phase’-diagram for quenched In_1−x Pd _x is provided with 0≦x≦1 containing the newly detecteda- andn-phases.