Figure 1. Growth control of homoepitaxial STO films.

(a) Photographs of STO films grown with four different apertures showing a wide variation of color depending on the aperture size. A STO substrate is also shown for comparison. The laser-beam spot sizes on the target are 7.7 (A1), 2.0 (A2), 1.1 (A3), and 0.4 mm² (A4) and require approximately 7, 27, 60, and 200 laser pulses, respectively, to grow one monolayer (~0.4 nm) of STO. (b) Optical absorption spectra for the four STO films. The STO film grown with A4 had an optical transparency identical to that of the bare STO substrate, implying good stoichiometry. (c) Sheet resistance (R_s) data representing conducting (A1–A3) and insulating (A4) STO thin films. The resistance from the A4 sample was too high to measure as it exceeded the instrumental limit.