Atomic-resolved depth profile of strain and cation intermixing around LaAlO3/SrTiO3 interfaces

Zaid, Hicham; Berger, Marie‐Hélène; Jalabert, D.; Walls, Michael; Akrobetu, Richard; Fongkaew, Ittipon; Lambrecht, Walter R. L.; Goble, Nicholas; Gao, Xuan; Berger, Pascal; Sehirlioglu, Alp

doi:10.1038/srep28118

Cited by 28 publications

(27 citation statements)

References 57 publications

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“…Such information is recently becoming available from MEIS studies by Zaid et al 2 However, the gradual interdiffusion profile is too complex to treat directly with first-principles simulations. A small concentration in a any given layer would require a much large 2D cell than we here can afford with present computational power.…”

Section: Discussionmentioning

confidence: 99%

“…However it can be controlled by annealing and is assumed to make a negligible contribution for sheet carrier densities of order 10 13 e/cm 2 . There has also been ample evidence for some degree of interdiffusion, most recently through a Medium Energy Ion Scattering (MEIS) study by Zaid et al 2 . The gradual change in c/a ratio observed in these measurements could be well explained by models including a gradually changing interdiffusion model.…”

Section: Introductionmentioning

confidence: 99%

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Effects of structural relaxation, interdiffusion, and surface termination on two-dimensional electron gas formation at theLaAlO3/SrTiO3(001) interface

2015

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First-principles (generalized gradient approximation) calculations are presented for symmetric LaAlO3/SrTiO3/LaAlO3 [001] orientation slab models with varying thickness (3, 4, 5 unitcells) of the LaAlO3 (LAO) layers. The buckling of the layers and their effect on the slope of the layer averaged electrostatic potential and layer projected densities of states are studied. We find the buckling of the LAO layers to increase from the interface toward the surface, while the buckling of the AlO2 layers decreases toward the surface. The critical layer thickness for obtaining electrons in the Ti-d band of the STO is determined to be 4 layers within this model. Beyond this point, the sloped potential is confined to the 4 layers of LAO nearest to the interface. The electrons in the Ti-d states extend throughout the 5.5 layer thick STO region of our calculation. The sheet charge density of electrons in the STO conduction band is determined and found to be of order 1 − 3 × 10 13 e/cm 2 , in fair agreement with experimental values and an order of magnitude smaller than required by the polar discontinuity model. We also find still a significant change in the sheet density between the 4-LAO layer and 5-LAO layer model. It results in only dxy-like states being occupied for the 4-LAO layer case but other t2g bands becoming occupied for the 5-LAO layer case. The effects of H adsorption on surface O and OH adsorption on the surface Al are investigated for a model with 1/8 coverage of H and 1/4 coverage of OH. The former leads to electron doping of the SrTiO3 (STO) layer while the latter leads to a p-type surface. When both together are present, they cancel each other. For high H-coverage, we find that only a certain fraction of the electrons donated by H can be accommodated at the interface while the remaining go to the surface and lead to a reversal of the slope of the potential in the LAO region. Addition of 25 % Ti on Al sites into the first layer of LAO, already leads to a cancellation of the field in the LAO layer. It does not lead to Ti 3+ embedded in the LAO site but rather the Ti donates its additional electron to the interface 2DEG confined to the STO TiO2 layers. A swap of Al with Ti in the layers closest to the interface does not produce a 2DEG because the Al in the TiO2 interface layer provides holes compensating the electron doping from the Ti. Interdiffusion of Sr and La between the layers nearest to the interface does not lead to a 2DEG. These species are just electron donors in their own materials respectively. In a swap compensating dipoles result from the different nuclear charges but the electronic states near the gap are not affected. Thus no 2DEG formation occurs. On the other hand a SrLa placed in the middle of the LAO layer is found to facilitate electron transfer from the surface to the interface and could lead to a 2DEG. However, the latter had only a small sheet density.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of structural relaxation, interdiffusion, and surface termination on two-dimensional electron gas formation at theLaAlO3/SrTiO3(001) interface

2015

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“…7 Novel behavior with the implication to cation intermixing has been observed at the interface of LaAlO 3 /SrTiO 3 heterostructures such as two dimensional metallic conductivity, magnetic scattering and superconductivity. 41 …”

Section: Ba Xmentioning

confidence: 99%

134Ba diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce)

et al. 2017

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Cation diffusion in functional oxide materials is of fundamental interest, particularly in relation to interdiffusion of cations in thin film heterostructures and chemical stability of materials in high temperature electrochemical devices. Here we report on 134Ba tracer diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce) materials. The dense BaMO3 ceramics were prepared by solid state sintering, and thin films of 134BaO were deposited on the polished pellets by drop casting of an aqueous solution containing the Ba-tracer. The samples were subjected to thermal annealing and the resulting isotope distribution profiles were recorded by secondary ion mass spectrometry. The depth profiles exhibited two distinct regions reflecting lattice and grain boundary diffusion. The grain boundary diffusion was found to be 4-5 orders of magnitude faster than the lattice diffusion for all three materials. The temperature dependence of the lattice and grain boundary diffusion coefficients followed an Arrhenius type behaviour, and the activation energy and pre-exponential factor demonstrated a clear correlation with the size of the primitive unit cell of the three perovskites. Diffusion of Ba via Ba-vacancies was proposed as the most likely diffusion mechanism.

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“…Along with numerous physical phenomena, perovskite oxide heterointerface systems boast complexities that rival high-T c superconductors. Oxygen growth pressure 26 27 28 , La/Al stoichometry 29 , and cation intermixing 30 31 are a few of known factors that can affect interfacial conduction in LAO/STO. Recently, scanning probe or scanning electron microscopy techniques showed that crystal domain boundaries in the STO layer of LAO/STO modify the local conductivity of the interface and create regions of striped potential modulations 32 33 34 .…”

mentioning

confidence: 99%

Anisotropic electrical resistance in mesoscopic LaAlO3/SrTiO3 devices with individual domain walls

Goble

Akrobetu

Zaid

et al. 2017

Sci Rep

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The crystal structure of bulk SrTiO3(STO) transitions from cubic to tetragonal at around 105 K. Recent local scanning probe measurements of LaAlO3/SrTiO3 (LAO/STO) interfaces indicated the existence of spatially inhomogeneous electrical current paths and electrostatic potential associated with the structural domain formation in the tetragonal phase of STO. Here we report a study of temperature dependent electronic transport in combination with the polarized light microscopy of structural domains in mesoscopic LAO/STO devices. By reducing the size of the conductive interface to be comparable to that of a single tetragonal domain of STO, the anisotropy of interfacial electron conduction in relationship to the domain wall and its direction was characterized between T = 10–300 K. It was found that the four-point resistance measured with current parallel to the domain wall is larger than the resistance measured perpendicular to the domain wall. This observation is qualitatively consistent with the current diverting effect from a more conductive domain wall within the sample. Among all the samples studied, the maximum resistance ratio found is at least 10 and could be as large as 105 at T = 10 K. This electronic anisotropy may have implications on other oxide hetero-interfaces and the further understanding of electronic/magnetic phenomena found in LAO/STO.

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Atomic-resolved depth profile of strain and cation intermixing around LaAlO3/SrTiO3 interfaces

Cited by 28 publications

References 57 publications

Effects of structural relaxation, interdiffusion, and surface termination on two-dimensional electron gas formation at theLaAlO3/SrTiO3(001) interface

Effects of structural relaxation, interdiffusion, and surface termination on two-dimensional electron gas formation at theLaAlO3/SrTiO3(001) interface

134Ba diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce)

Anisotropic electrical resistance in mesoscopic LaAlO3/SrTiO3 devices with individual domain walls

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