The surface structure of SrTiO3 at high temperatures under influence of oxygen

Hesselberth, M.B.S.; Molen, Sense Jan van der; Aarts, J.

doi:10.1063/1.4864186

Cited by 9 publications

(6 citation statements)

References 27 publications

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“…1a for bare SrTiO 3 . The starting surface shows clear diffraction spots and a 2 × 1 reconstruction, in line with earlier observations 25 . From the diffraction images, the peak intensity and full-width-halfmaximum (FWHM) of the specular spot were recorded and are shown in Fig.…”

Section: Resultssupporting

confidence: 90%

“…The LaAlO 3 /SrTiO 3 interfaces are grown and studied in an aberration corrected low-energy electron microscope (LEEM) at Leiden university, called ES-CHER [21][22][23][24] . The LEEM technique has been used before to study SrTiO 3 25 and LaAlO 3 26 separately. We now also developed a pulsed laser deposition (PLD) system inside the system to allow for analysis during growth, which was already used to study the growth of SrTiO 3 on SrTiO 3 18 .…”

Section: Experimental Setup and Sample Preparationmentioning

confidence: 99%

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Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Torren

Liao

Xu³

et al. 2017

Phys. Rev. Materials

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The two-dimensional electron gas occurring between the band insulators SrTiO3 and LaAlO3 continues to attract considerable interest, due to the possibility of dynamic control over the carrier density, and the ensuing phenomena such as magnetism and superconductivity. The formation of this conducting interface is sensitive to the growth conditions, but despite numerous investigations, there are still questions about the details of the physics involved. In particular, not much is known about the electronic structure of the growing LaAlO3 layer at the growth temperature (around 800 • C) in oxygen (pressure around 5 × 10 −5 mbar), since analysis techniques at these conditions are not readily available. We developed a pulsed laser deposition system inside a low-energy electron microscope in order to study this issue. The setup allows for layer-by-layer growth control and in-situ measurements of the angle-dependent electron reflection intensity, which can be used as a fingerprint of the electronic structure of the surface layers during growth. By using different substrate terminations and growth conditions we observe two families of reflectivity maps, which we can connect either to samples with an AlO2-rich surface and a conducting interface; or to samples with a LaO-rich surface and an insulating interface. Our observations emphasize that substrate termination and stoichiometry determine the electronic structure of the growing layer, and thereby the conductance of the interface. arXiv:1709.02583v1 [cond-mat.mtrl-sci]

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Section: Resultssupporting

confidence: 90%

Section: Experimental Setup and Sample Preparationmentioning

confidence: 99%

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Torren

Liao

Xu³

et al. 2017

Phys. Rev. Materials

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Section: Introductionsupporting

confidence: 75%

“…Specifically, the sign of the surface potential difference between regions initially consisting of nominally pure single terminations (SrO and TiO 2 ) is reversed. Whereas instability of STO surface under UHV conditions at elevated temperatures had been already reported [15], the present results emphasize chemical and electrostatic implications of surface reconstruction signaling a narrower temperature window of surface stability. EXPERIMENTAL (001)STO single-crystalline substrates from CrysTec GmbH were thermally treated at high temperature (≈1150 °C) in air for 2 h in a dedicated tubular furnace: in the following these samples are labeled "as-prepared".…”

Section: Introductionsupporting

confidence: 75%

Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO₃ Surfaces

et al. 2015

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ABSTRACT:The (001)SrTiO 3 crystal surface can be engineered to display a self-organized pattern of wellseparated and nearly pure single-terminated SrO and TiO 2 regions by high temperature annealing in oxidizing atmosphere. By using surface sensitive techniques we have obtained evidence of such surface chemical self-structuration in as-prepared crystals and unambiguously identified the local composition. The contact surface potential at regions initially consisting of majority single terminations (SrO and TiO 2 ) is determined to be Φ(SrO) <Φ(TiO 2 ), in agreement with theoretical predictions, although the measured difference ΔΦ ≤ 100 meV is definitely smaller than theoretical predictions for ideally pure single-terminated SrO and TiO 2 surfaces. These relative values are maintained if samples are annealed in UHV up to 200 °C. Annealing in UHV at higher temperature (400 °C) preserves the surface morphology of self-assembled TiO 2 and SrO rich regions, although a non-negligible chemical intermixing is observed. The most dramatic consequence is that the surface potential contrast is reversed. It thus follows that electronic and chemical properties of (001)SrTiO 3 surfaces, widely used in oxide thin film growth, can largely vary before growth starts in a manner strongly dependent on temperature and pressure conditions. INTRODUCTIONElectronic redistributions at solid interfaces occur to reduce the chemical potential gradients, and the energy cost to bring electrons in/out across these interfaces is strongly influenced by the intrinsic properties of materials involved, namely, the work function (Φ) in metals and the electron affinity (χ) and the ionization potential (IP) in intrinsic semiconductors and insulators.The work function of metals and degenerated semiconductors depends on the electron density and surface dipoles formed at the corresponding free surface. Similarly, the IP of insulators and intrinsic semiconductors depends on the crystallographic plane considered. Modulation of the substrate work function, as required in most common planar electronic devices or active surfaces, can be achieved by changing the carrier concentration by chemical or electrostatic doping, or by chemically engineering the surface. A beautiful example is the LaAlO 3 −SrTiO 3 interface, where a high mobility two-dimensional electron gas (2DEG) can be formed only if the STO surface is TiO 2 terminated [1]. Although, following the pioneering work by Kawasaki et al. [2], TiO 2 singleterminated (001)SrTiO 3 (STO) single-crystalline surfaces can be prepared, as-received crystals display

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“…At present, however, the surface of hybrid-grown STO films is poorly understood, making research on such complex heterostructures difficult to pursue. In spite of decades of studies, the stability of various STO surface terminations and reconstructions is still a matter of great debate [25][26][27][28]. In most SrTiO3 MBE film growth, in situ reflection high energy electron diffraction (RHEED) has been applied to monitor the growth in real time domain, though in-vacuo X-ray photoelectron spectroscopy (XPS) studies have never been reported.…”

Section: Introductionmentioning

confidence: 99%

Correlating surface stoichiometry and termination in SrTiO3 films grown by hybrid molecular beam epitaxy

Thapa

Provence

Jessup

et al. 2021

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Hybrid oxide molecular beam epitaxy (hMBE), a thin-film deposition technique in which transition metal cations are delivered using a metal-organic precursor, has emerged as the state-of-the-art approach to the synthesis of electronic-grade complex oxide films with a stoichiometric growth window. However, numerous questions remain regarding the chemical mechanisms of the growth process and the surface properties of the resulting films. To examine these properties, thin film SrTiO3 (STO) was prepared by hMBE using a titanium tetraisopropoxide (TTIP) precursor for Ti delivery and an elemental Sr source on annealed STO and Nb-doped STO substrates with varying TTIP:Sr flux ratios to examine the conditions for the reported stoichiometric growth window. The grown films were transferred to an appended x-ray photoelectron spectroscopy (XPS) system under ultrahigh vacuum to study the surface elemental composition in the STO samples. Low energy electron diffraction and microscopy (LEED/LEEM) measurements were also performed to correlate the XPS data with the surface termination. Also, samples were examined using x-ray diffraction (XRD) in order to compare our surface sensitive results with previously reported measurements of the bulk of the films in the literature. We find that a surface exhibiting a mixture of SrO and TiO2 termination, or a full SrO termination is necessary to obtain stoichiometric adsorption-controlled step-flow growth. These results indicate that surface Sr is necessary to maintain chemical equilibrium These results can open new opportunities for the study of interfacial structures synthesized via hMBE.

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The surface structure of SrTiO3 at high temperatures under influence of oxygen

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Cited by 9 publications

References 27 publications

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO₃ Surfaces

Correlating surface stoichiometry and termination in SrTiO3 films grown by hybrid molecular beam epitaxy

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The surface structure of SrTiO3 at high temperatures under influence of oxygen

Abstract: Articles you may be interested in

Cited by 9 publications

References 27 publications

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO3 Surfaces

Correlating surface stoichiometry and termination in SrTiO3 films grown by hybrid molecular beam epitaxy

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Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO₃ Surfaces