Nonstoichiometry accommodation in SrTiO3thin films studied by positron annihilation and electron microscopy

Abstract

Accommodation of nonstoichiometry in SrTiO 3 pulsed laser deposited (PLD) films was investigated using positron annihilation lifetime spectroscopy and (scanning) transmission electron microscopy. Increasing PLD laser fluence changed the stoichiometry from Ti to Sr deficient. Cation vacancy defects were detected, and the concentration ratio of Sr to Ti vacancies, [V Sr ]/[V Ti ], was observed to increase systematically in the Sr-deficient region, although no change in the electron microscopy lattice images was detected. Increasing Ti deficiency resulted in the accommodation of SrO layers in planar defects, and in the formation of vacancy cluster defects. A change from V Ti to V Sr defect positron trapping was also detected.

Oxygen partial pressure dependence of surface space charge formation in donor-doped SrTiO3

“…Clear RHEED oscillations indicate a layer-by-layer growth of the thin film (S1 of the supplementary material). The stoichiometric growth process of the thin film was optimized by a variation of the laser fluence 29,30 and confirmed by angular dependent X-ray photoelectron spectroscopy in UHV conditions. 31,32 Further sample characterization including surface topography and X-ray diffraction data are provided in the supplementary material S1 and S2.…”

Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3Thin Films Controlled by Defects

“…After deposition the samples were cooled at the same oxygen pressure. The conditions were optimized to obtain layer-by-layer growth, even in films as thick as ≈50 nm (see Supplemental Material [19]).Growing stoichiometric films of STO by PLD is only possible in a very narrow range of laser fluence, oxygen pressure and temperature [15,16,[29][30][31][32][33]. Away from this window, the samples always present a varying amount of cationic and anionic vacancies, which produce a substantial enlargement of the unit cell [29].…”

“…This orbital reconstruction can be intrinsic, to cancel the electrostatic energy of the polar interface [12], but could also be caused by the structural distortions and atomic vacancies which relax the epitaxial strain in these thin-film heterostructures. However, the effect of cationic and anionic vacancies on the transport properties of both STO [13] and LAO/STO interfaces [14] is mostly considered from the point of view of their acceptor or donor nature over the total charge density, although vacancies distribute along the crystal structure expanding the unit cell due to an increased Coulomb repulsion [15]. In the case of epitaxial thin films below a certain critical thickness, this has to be necessarily accommodated purely as an increase of the c-axis parameter, due to the clamping of the in-plane lattice parameters to the substrate [16].…”

Complex behaviour of vacancy point-defects in SrRuO3 thin films

“…Such high concentrations of vacancies on both cation sublattices are expected for films grown by a non-equilibrium process, such as PLD, as evidenced by studies 46,47 of cation defects in PLD thin films of SrTiO 3 . The chemical formula of thin-film strontium ruthenate in its as-deposited state is thus Sr 1Ày Ru 1Àz 0 O 3 , with y o z 0 and z 0 4 z.…”