Building designer oxide heterostructures one atomic layer at a time
Nanoscale oxide heterostructures have been in the focus of cutting edge scientific and technological research. Reactive MBE and Laser MBE are two effective techniques in the growth of oxide thin films and heterostructures with controls to the atomic level. Using Reactive MBE, stoichiometric SrTiO3 films on SrTiO3 substrate with crystalline perfection have been grown by alternately depositing each atomic layer [see Brooks et al. APL 94, 162905 (2009).] Exceptionally high quality BaTiO3/SrTiO3 superlattices with nanoscale dimensions have been grown by Reactive MBE [see Tenne et al., Science 313, 1614 (2006).] In my lab at Temple University, Laser MBE from separate oxide targets, e.g., growing SrTiO3 films from SrO and TiO2 targets, has been recently developed to fabricate nanoscale oxide thin films and heterostructures with stoichiometry and crystallinity equal to those achieved by Reactive MBE. Sr1+xTiO3 films with various stoichiometry were grown by controlling the numbers of pulses on each target. X-ray diffraction spectra show the same lattice constant in the stoichiometric SrTiO3 film as in the SrTiO3 substrate, while both strontium-rich and strontium-poor Sr1+xTiO3 films show lattice expansion. Having demonstrated the capability of precise controls of growth at the atomic layer level and film stoichiometry of Laser MBE from separate oxide targets, I will present two ongoing research projects to use this technique to fabricate designer oxide heterostructures. One would lead to artificial multiferroics materials, and the other would result in cuprate-like layered materials with possible high temperature superconductivity.