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M. Riva, G. Franceschi, Q. Lu, M. Schmid, B. Yildiz, U. Diebold:
"Pushing the detection of cation nonstoichiometry to the limit";
Physical Review Materials, 3 (2019), 4; 04380201 - 04380210.

Nanoscale complex-oxide thin films prepared by well-established growth techniques, such as pulsed-laser
deposition or molecular-beam epitaxy, often exhibit compositions that deviate from the ideal stoichiometry.
Even small variations in composition can lead to substantial changes in the technologically relevant electronic,
magnetic, and optical properties of these materials. To assess the reasons behind this variability, and ultimately
to allow tuning the properties of oxide films with precise control of the deposition parameters, high-resolution
detection of the nonstoichiometry introduced during growth is needed. The resolution of current techniques,
such as x-ray diffraction, fluorescence, or spectroscopy, is limited to estimating composition differences in the
percent level, which is often insufficient for electronic-device quality. We develop an unconventional approach
based on scanning tunneling microscopy for enabling the determination of cation imbalance introduced in thin
films with exceptionally small detection limit. We take advantage of the well-controlled surface reconstructions
on SrTiO3(110), and use the established relation between those reconstructions and the surface composition
to assess the cation excess deposited in pulsed-laser grown SrTiO3(110) films. We demonstrate that a <0.1%
change in cation nonstoichiometry is detectable by our approach. Furthermore, we show that, for thin films that
accommodate all the nonstoichiometry at the surface, this method has no fundamental detection limit.