Homoepitaxial growth of SrTiO₃ by Pulsed Laser Deposition: energetic vs thermal growth

The role of energetic processes in homoepitaxial growth of SrTiO₃ (STO) by Pulsed Laser Deposition (PLD) was studied via Real-Time X-ray scattering. Two process were developed, an energetic process and a thermal process. Both processes utilized a background gas of 2 mTorr of O₂. The thermal process had an additional 300 mTorr of Helium to act as a buffer gas. Langmuir probe measurements verified the energies of the two process to be between 50-100 electron-volts (eV) and 0.02-0.05 eV respectively. Specular X-ray reflectivity, sensitive to inter-layer transport of material, was the same for both processes. Diffuse scattering, sensitive to the in-plane transport of material, was markedly different. In the thermal process, sharp peaks in the diffuse scattering arise with the growth of each successive layer indicating growth of well correlated islands with a well-defined mean spacing. In the energetic process, diffuse scattering peaks also arise at a similar wavevector, though much weaker and broader. These results suggest an energetic process, such as island breakup, may be responsible for the broadening of the diffuse scattering, in which material from the edges of growing islands is broken off into smaller islands.