Interlayer Transport in Pulsed Laser Deposition of SrTiO₃ Studied by Time-Resolved Surface X-Ray Diffraction

Abstract

Format

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Abstract

Film growth in pulsed laser deposition (PLD) occurs from the energetic plume of material ejected from a solid target by pulsed laser ablation. The plume consists of a complex mixture of neutral and ionized atoms, molecules, and even small clusters with kinetic energies ranging from thermal to a few hundred eV. The extra kinetic energy provides a transient (nonequilibrium) enhancement of surface mobility and is believed to alter the nucleation and growth of thin films. However, the mechanisms by which the transient mobility enhancement affect the growth kinetics are not well understood. We use time-resolved surface x-ray diffraction (SXRD) measurements with microsecond range resolution to study the role of nonequilibrium processes in PLD of SrTiO3. The use of x-ray diffraction greatly simplifies growth kinetics studies because in the kinematic limit the x-ray intensity changes correspond directly to coverage changes. Rather than using a transport model to fit the data, we instead analyze the intensity transients using an approach that allows direct determination of the transient surface coverages from the diffraction intensities [1]. The initial change in the coverage shows the fraction of the pulse instantaneously forming on each layer, and the time evolution of the coverages shows the amount of material transferred from the top of the islands into the growing layer. This analysis reveals that the energy-enhanced interlayer transport occurs on a time scale of microseconds or less and it dominates layer filling in PLD growth. A much smaller fraction of material, which is governed by the dwell time between successive laser shots is transferred by slow, thermally driven interlayer transport processes. [1] J.Z. Tischler, Gyula Eres, B.C. Larson, C.M. Rouleau, P. Zschack, and D.H. Lowndes, Phys. Rev. Lett. 96, 226104 (2006).