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(a) The crystal structure of SrLaAlO4 is of tetragonal K2NiF4 type having a = b = 3.75 Å and c = 12.6 Å. Along c-axis, the layered stacking is-AlO2-(Sr,La)O-(Sr,La)O-AlO2-(Sr,La)O-(Sr,La)O-, indicated in the yellow rectangular shaded region. (b) The AFM image of the surface of an as-received sample shows roughness of ∼1 nm. (c) Thermal annealing at 1000 °C for 2 h forms SrO particles of 10–50 nm in size on the surface. (d) These particles are soluble in de-ionized water; after soaking for 10 min, they disappear and nanometer sized holes become visible.
(a) Annealing setup of a SrLaAlO4 substrate surface surrounded with La2O3 powder. (b) AFM image of the surface after annealing at 1000 °C for 2 h reveals terraces and steps. (c) The line profile along the dark line indicated in (b) shows atomically flat step-terrace structure. (d) Annealing setup with LaAlO3 covered. (e) AFM image of the surface after annealing at 1000 °C for 2 h reveals terraces and steps. (f) The line profile along the dark line indicated in (e) shows atomically flat step-terrace structure. The step height corresponds to the half unit cell lattice spacing of 0.63 nm.
The ratio of the Al signal against the sum of the Sr and La signals from AR-MSRI is shown for substrates as they were received (black) and that went through annealing processes in La2O3 (green) and LaAlO3 (pink) environments. The decreased (La2O3 surrounded) and increased (LaAlO3 covered) ratios at ± 45° are indications for A-site and B-site terminations, respectively. Illustrated in the inset is a schematic for time of flight ion scattering and recoil spectroscopy experiments using pulsed potassium (39K) ions. Detectors for AR-MSRI and DRS are indicated in the figure.
Individual cation ratios extracted from the AR-MSRI measurements are shown. (a) The ratio between Al and Sr. (b) The ratio between Al and La. (c) The ratio between Sr and La. These data provide further insight in the cation arrangements of the top layers, and reveal La poor layers for annealed substrates.
Relative intensities from the DRS spectra are shown for potassium scattered off (Sr,La) in (a) and off Al in (b), designated as Ks(Sr,La) and Ks(Al), respectively. The Ks(Sr,La) intensity is significantly higher for the La2O3 surrounded sample than others, indicating (Sr,La)O termination. The Ks(Al) intensity is significantly higher for the LaAlO3 covered sample, indicating AlO2 termination.
AFM images of SrRuO3 films grown on different terminated substrates; (a) (Sr,La)O termination, (b) AlO2 termination. For the film grown on (Sr,La)O terminated substrate, clear nm sized trenches are visible, which are absent for that on AlO2 terminated substrate; this selective growth preference of SrRuO3 confirming different substrate terminations. (c) Resistivity of the two samples showing morphology dependent transport behavior.
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