Microstructural development of thin films grown by pulsed laser deposition

Abstract

Pulsed laser deposition (PLD) of thin films involves conditions that differ substantially from those of other vapor deposition techniques and that may be expected to influence film nucleation and growth mechanisms. In order to study the effect of these conditions on these mechanisms, a series of films was deposited using discrete numbers of laser pulses ranging from 1 to 3000. The films were YBa 2Cu 30 7−δ (YBCO) and Sr 0.5SBa 0.5Ti0 3 (SBT) and the substrates were single-crystal (100) MgO and (100) LaA10 3 (LAO), or YBCO films deposited by PLD on (100) MgO substrates. Substrate temperatures ranged from 675 to 875 °C. Characterization of the surfaces by atomic force microscopy showed that both SBT and YBCO films exhibited an island growth mechanism. For the same number of pulses, SBT films were smoother than YBCO films due to the smaller unit cell height of SBT. X-ray diffraction and cross-sectional transmission electron microscopy showed that the crystal quality of SBT films improved with increasing deposition temperature and was higher for films on LAO substrates than for those on MgO. The LAO substrates were found to be microscopically smoother than MgO substrates. The island growth mechanism observed was similar to that of other vapor deposition techniques and suggests that the high vapor flux and pulsed nature of the PLD flux did not have a substantial effect on the nucleation and growth mechanisms.