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Surface Termination Conversion during SrTiO3 Thin Film Growth Revealed by X-ray Photoelectron Spectroscopy.

Baeumer C, Xu C, Gunkel F, Raab N, Heinen RA, Koehl A, Dittmann R - Sci Rep (2015)

Bottom Line: Currently, these quantities have to be measured separately with different sophisticated techniques.Fitting the experimental angle dependence with a simple analytical model directly yields both values.We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film.

View Article: PubMed Central - PubMed

Affiliation: Peter Gruenberg Institute and JARA-FIT, FZ Juelich, D-52425 Juelich, Germany.

ABSTRACT
Emerging electrical and magnetic properties of oxide interfaces are often dominated by the termination and stoichiometry of substrates and thin films, which depend critically on the growth conditions. Currently, these quantities have to be measured separately with different sophisticated techniques. This report will demonstrate that the analysis of angle dependent X-ray photoelectron intensity ratios provides a unique tool to determine both termination and stoichiometry simultaneously in a straightforward experiment. Fitting the experimental angle dependence with a simple analytical model directly yields both values. The model is calibrated through the determination of the termination of SrTiO3 single crystals after systematic pulsed laser deposition of sub-monolayer thin films of SrO. We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film. We show that this termination conversion results in insulating properties of interfaces between polar perovskites and SrTiO3 thin films. These insights about oxide thin film growth can be utilized for interface engineering of oxide heterostructures. In particular, they suggest a recipe for obtaining two-dimensional electron gases at thin film interfaces: SrTiO3 should be deposited slightly Ti-rich to conserve the TiO2-termination.

No MeSH data available.


Related in: MedlinePlus

Characterization of LaAlO3/SrTiO3 thin film heterointerfaces.(a–d) AFM morphology of 10 unit cells heteroepitaxial LaAlO3 thin films grown on the films shown in Fig. 4. Step terraces are of unit cell height (≈4 Å). (e) Carrier density (grey dots) and electron mobility values (black triangles) extracted from Hall measurements as a function of laser fluence. The approximate SrTiO3 stoichiometry is indicated through the top axis. The surface termination is indicated with a color gradient from complete SrO-termination (orange) to complete TiO2-termination (violet). The carrier density and mobility range expected for LaAlO3/SrTiO3 interfaces fabricated with SrTiO3 single crystals is indicated with the shaded area. For the SrO-terminated SrTiO3 films, the sheet resistance of the resulting heterostructures is above the measurement limit, which inhibits the extraction of quantitative values for the carrier density and mobility.
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f5: Characterization of LaAlO3/SrTiO3 thin film heterointerfaces.(a–d) AFM morphology of 10 unit cells heteroepitaxial LaAlO3 thin films grown on the films shown in Fig. 4. Step terraces are of unit cell height (≈4 Å). (e) Carrier density (grey dots) and electron mobility values (black triangles) extracted from Hall measurements as a function of laser fluence. The approximate SrTiO3 stoichiometry is indicated through the top axis. The surface termination is indicated with a color gradient from complete SrO-termination (orange) to complete TiO2-termination (violet). The carrier density and mobility range expected for LaAlO3/SrTiO3 interfaces fabricated with SrTiO3 single crystals is indicated with the shaded area. For the SrO-terminated SrTiO3 films, the sheet resistance of the resulting heterostructures is above the measurement limit, which inhibits the extraction of quantitative values for the carrier density and mobility.

Mentions: To demonstrate the strong impact this surface termination conversion has upon the properties of oxide heterostructures, we fabricated LaAlO3/SrTiO3 interfaces on each of these SrTiO3 films shown in Fig. 4 through the deposition of 10 unit cells of LaAlO3via PLD. The surface morphology for each film is shown in Fig. 5(a–d). For each film, layer-by-layer growth mode was observed and the surface structure of the underlying SrTiO3 film is well preserved. For the films grown on (partially) SrO-terminated SrTiO3, the vicinal step surface structure of the substrate is still apparent, while the films grown on TiO2-terminated SrTiO3 do not show these step edges. However, these films are still fairly smooth with a root-mean-square roughness below 0.34 nm.


Surface Termination Conversion during SrTiO3 Thin Film Growth Revealed by X-ray Photoelectron Spectroscopy.

Baeumer C, Xu C, Gunkel F, Raab N, Heinen RA, Koehl A, Dittmann R - Sci Rep (2015)

Characterization of LaAlO3/SrTiO3 thin film heterointerfaces.(a–d) AFM morphology of 10 unit cells heteroepitaxial LaAlO3 thin films grown on the films shown in Fig. 4. Step terraces are of unit cell height (≈4 Å). (e) Carrier density (grey dots) and electron mobility values (black triangles) extracted from Hall measurements as a function of laser fluence. The approximate SrTiO3 stoichiometry is indicated through the top axis. The surface termination is indicated with a color gradient from complete SrO-termination (orange) to complete TiO2-termination (violet). The carrier density and mobility range expected for LaAlO3/SrTiO3 interfaces fabricated with SrTiO3 single crystals is indicated with the shaded area. For the SrO-terminated SrTiO3 films, the sheet resistance of the resulting heterostructures is above the measurement limit, which inhibits the extraction of quantitative values for the carrier density and mobility.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507138&req=5

f5: Characterization of LaAlO3/SrTiO3 thin film heterointerfaces.(a–d) AFM morphology of 10 unit cells heteroepitaxial LaAlO3 thin films grown on the films shown in Fig. 4. Step terraces are of unit cell height (≈4 Å). (e) Carrier density (grey dots) and electron mobility values (black triangles) extracted from Hall measurements as a function of laser fluence. The approximate SrTiO3 stoichiometry is indicated through the top axis. The surface termination is indicated with a color gradient from complete SrO-termination (orange) to complete TiO2-termination (violet). The carrier density and mobility range expected for LaAlO3/SrTiO3 interfaces fabricated with SrTiO3 single crystals is indicated with the shaded area. For the SrO-terminated SrTiO3 films, the sheet resistance of the resulting heterostructures is above the measurement limit, which inhibits the extraction of quantitative values for the carrier density and mobility.
Mentions: To demonstrate the strong impact this surface termination conversion has upon the properties of oxide heterostructures, we fabricated LaAlO3/SrTiO3 interfaces on each of these SrTiO3 films shown in Fig. 4 through the deposition of 10 unit cells of LaAlO3via PLD. The surface morphology for each film is shown in Fig. 5(a–d). For each film, layer-by-layer growth mode was observed and the surface structure of the underlying SrTiO3 film is well preserved. For the films grown on (partially) SrO-terminated SrTiO3, the vicinal step surface structure of the substrate is still apparent, while the films grown on TiO2-terminated SrTiO3 do not show these step edges. However, these films are still fairly smooth with a root-mean-square roughness below 0.34 nm.

Bottom Line: Currently, these quantities have to be measured separately with different sophisticated techniques.Fitting the experimental angle dependence with a simple analytical model directly yields both values.We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film.

View Article: PubMed Central - PubMed

Affiliation: Peter Gruenberg Institute and JARA-FIT, FZ Juelich, D-52425 Juelich, Germany.

ABSTRACT
Emerging electrical and magnetic properties of oxide interfaces are often dominated by the termination and stoichiometry of substrates and thin films, which depend critically on the growth conditions. Currently, these quantities have to be measured separately with different sophisticated techniques. This report will demonstrate that the analysis of angle dependent X-ray photoelectron intensity ratios provides a unique tool to determine both termination and stoichiometry simultaneously in a straightforward experiment. Fitting the experimental angle dependence with a simple analytical model directly yields both values. The model is calibrated through the determination of the termination of SrTiO3 single crystals after systematic pulsed laser deposition of sub-monolayer thin films of SrO. We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film. We show that this termination conversion results in insulating properties of interfaces between polar perovskites and SrTiO3 thin films. These insights about oxide thin film growth can be utilized for interface engineering of oxide heterostructures. In particular, they suggest a recipe for obtaining two-dimensional electron gases at thin film interfaces: SrTiO3 should be deposited slightly Ti-rich to conserve the TiO2-termination.

No MeSH data available.


Related in: MedlinePlus