The effect of an electric field on the crystallization of gel-derived alumina precursors observed in situ in the TEM

Abstract A method has been devised to enable the observation of structural changes occurring in situ in TEM when an electric field is exerted across a thin-film sample connecting two electrodes. During early observation in the electron microscope, while an electric field is applied, small crystals formed in the alumina precursor gel assumed a preferred orientation yielding electron diffraction spots in a line almost perpendicular to the electric field direction. This phenomenon suggests that dipolar units produced during decomposition and restructuring in the precursor were aligned by the electric field. This behavior is contrasted with that of precursor samples observed in a similar way except without an applied electric field, where no special orientation for the small crystals formed was observed. The orientational effect occured only during the early stages of the structural transformations. Annealed crystalline samples did not exhibit this behavior.