Observation of the early stages of growth of superconducting thin films by transmission electron microscopy

A method for the direct observation of the early stages of growth of superconducting films by transmission electron microscopy (TEM) is reported. The technique uses well-characterized, single-crystal TEM foils as substrates for the deposition process. Ultrathin films of YBa2Cu3O6+x (YBCO) were prepared by pulsed laser deposition from stoichiometric bulk samples directly onto (001) oriented MgO thin-foil substrates. Observation of the film by TEM is possible without any post-deposition specimen preparation. The epitactic nature of the film growth is shown by analysis of the moiré fringe pattern and by selected area diffraction. In addition to an interconnected film, copper oxide particles and stoichiometric ablated clusters were observed.