Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3

Abstract

At the heart of modern oxide chemistry lies the recognition that beneficial (as well as deleterious) materials properties can be obtained by deliberate deviations of oxygen atom occupancy from the ideal stoichiometry. Conversely, the capability to control and confine oxygen vacancies will be important to realize the full potential of perovskite ferroelectric materials, varistors and field-effect devices. In transition metal oxides, oxygen vacancies are generally electron donors, and in strontium titanate (SrTiO3) thin films, oxygen vacancies (unlike impurity dopants) are particularly important because they tend to retain high carrier mobilities, even at high carrier densities. Here we report the successful fabrication, using a pulsed laser deposition technique, of SrTiO3 superlattice films with oxygen doping profiles that exhibit subnanometre abruptness. We profile the vacancy concentrations on an atomic scale using annular-dark-field electron microscopy and core-level spectroscopy, and demonstrate absolute detection sensitivities of one to four oxygen vacancies. Our findings open a pathway to the microscopic study of individual vacancies and their clustering, not only in oxides, but in crystalline materials more generally.

Tuning the electronic effective mass in double-dopedSrTiO3

“…Particularly, clusters of oxygen vacancies can act as localizing sites for such itinerant electrons 25,26 and clustering of vacancies is a common feature in PLD grown STO thin films grown under low pressures. 27 In the case of samples containing 15% La, the low temperature resistivity is best described by ρ ∼ sinh 2 ( 1 T ), characteristic of small polaron conduction. Recently, Liang et al 28 suggested the possibility of small polaron conduction in 15% La doped STO films grown under similar conditions, corroborating our observation.…”

Collapse of electrons to a donor cluster inSrTiO3

“…The vacancies either form along a network of extended defects 6 or assemble together to lower the system's energy 7,8 , probably producing large positively charged donor clusters. Another way to more controllably create such a cluster is to "draw" a disc of charge by the atomic force microscope (AFM) tip on the surface of LAO/STO structure with the subcritical thickness for LaAlO 3 (LAO) 9,10 .…”

Fabrication, Characterization, and Modulation of Functional Nanolayers

“…10.3c. [27] and Nb 4+ /Nb 5+ [28] from previous studies are also plotted for comparison. Reprinted with permission from [22].…”

“…Figure 10.4 shows the EELS spectra acquired around the Ti L (c) and O K edges (d). The reported EELS spectra of Ti 3+ /Ti 4+ [27] and Nb 4+ /Nb 5+ [28] are plotted for comparison. In the Ti L edge spectrum (c), t 2g and e. g. peak splitting is clearly observed for Ti L 3 , indicating that the dominant valence state of Ti is 4+.…”