In situ study of redox processes on the surface of SrTiO3 single crystals

Wrana, Dominik; Rodenbücher, Christian; Bełza, Wojciech; Szot, K.; Krok, Franciszek

doi:10.1016/j.apsusc.2017.06.272

Cited by 32 publications

(45 citation statements)

References 29 publications

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“…Therefore, one can only state at this point that the local resistance is higher than 1 PΩ (Peta Ohm). An additional thermal reduction of the crystal enhances the concentration of the oxygen vacancies [48,50,51,53,55,68,222,225,226] along the dislocations, which in turn leads to a further local increase of the electrical conductivity (with dominance of the electronic conductivity). In contrast to the electrical conductivity of dislocations in stoichiometric crystals, LCAFM studies of reduced crystal do indeed show an enhancement of the conductivity of the core of dislocations relative to the surrounding matrix, leading now to values higher than 3-6 orders of magnitude with respect to the background (here notice also from an experimental point of view that the dynamic of the LCAFM measurements can be increased by a parallel investigation of the regions between dislocations using a higher sensitivity of the I/V converter).…”

Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

“…As a result of the electrical stimulus, the electrical conductivity of the whole crystal gets "switched" from insulating to metallic or even superconducting behavior [4] (see Figures 47 and 48). Such transformation, i.e., switching, of the macroscopic crystal into an object with metallic conductivity (see the typical dependence of the resistance as a temperature function, Figure 47 or Figure 49), has been observed for many crystals with perovskite structure (SrTiO 3 [45,51,55,68,225,226,255], see also Figure 49), Nb:SrTiO 3 [227], Fe:SrTiO 3 [58] (see also Figures 50 and 51), La:SrTiO 3 [228,256], BaTiO 3 [257], KTaO 3 [232], NaNbO 3 [233,234], PbZrO 3 [231], BiFeO 3 [235], and binary crystals such as TiO 2 [48,53] (see also Figures 52 and 53). The electrically induced insulator-to-metal transformation is in its character very similar to the above described thermal reduction process (see previous chapter).…”

Section: Role Of Dislocations In Resistive Switching Of Tio 2 and Srtmentioning

confidence: 99%

“…This includes our oxides of choice in this review: TiO 2 [48,53], SrTiO 3 crystals [50,51,55,68,225,226], and doped SrTiO 3 such as Nb:SrTiO 3 [227], La:SrTiO 3 [228], Fe:SrTiO 3 [58], as well as related oxides such as BaTiO 3 [229,230], PbZrO 3 [231], KTaO 3 [232], NaNbO 3 [233,234], and BiFeO 3 [235]. Similar effects have also been observed for thin films, see, e.g., TiO 2 [236], SrTiO 3 , Fe:SrTiO 3 [225,[237][238][239], BaTiO 3 [230,240], HfO 2 [241][242][243][244], and NiO [245].…”

Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

“…For this, we used one piece with a high concentration of dislocations, here around 10 12 /cm 2 in the surface region, which was generated by mechanical polishing, and another piece with the original epi-polished surface (here the concentration of dislocations is of order 10 10 /cm 2 ). These two samples were simultaneously reduced to the minimum of the resistance of the bathtub curve (see, e.g., [45,226]) and subsequently cooled down to room temperature. Under these conditions, the electrical measurements revealed that the temperature dependence of the resistance for the crystal with high concentration of dislocations is typical for a metallic behavior while it exhibits only semiconducting behavior in the case of the epi-polished crystal (see Figure 45).…”

Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

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Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

et al. 2018

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Studies on dislocations in prototypic binary and ternary oxides (here TiO 2 and SrTiO 3 ) using modern TEM and scanning probe microscopy (SPM) techniques, combined with classical etch pits methods, are reviewed. Our review focuses on the important role of dislocations in the insulator-to-metal transition and for redox processes, which can be preferentially induced along dislocations using chemical and electrical gradients. It is surprising that, independently of the growth techniques, the density of dislocations in the surface layers of both prototypical oxides is high (10 9 /cm 2 for epipolished surfaces and up to 10 12 /cm 2 for the rough surface). The TEM and locally-conducting atomic force microscopy (LCAFM) measurements show that the dislocations create a network with the character of a hierarchical tree. The distribution of the dislocations in the plane of the surface is, in principle, inhomogeneous, namely a strong tendency for the bundling and creation of arrays or bands in the crystallographic <100> and <110> directions can be observed. The analysis of the core of dislocations using scanning transmission electron microscopy (STEM) techniques (such as EDX with atomic resolution, electron-energy loss spectroscopy (EELS)) shows unequivocally that the core of dislocations possesses a different crystallographic structure, electronic structure and chemical composition relative to the matrix. Because the Burgers vector of dislocations is per se invariant, the network of dislocations (with additional d 1 electrons) causes an electrical short-circuit of the matrix. This behavior is confirmed by LCAFM measurements for the stoichiometric crystals, moreover a similar dominant role of dislocations in channeling of the current after thermal reduction of the crystals or during resistive switching can be observed. In our opinion, the easy transformation of the chemical composition of the surface layers of both model oxides should be associated with the high concentration of extended defects in this region. Another important insight for the analysis of the physical properties in real oxide crystals (matrix + dislocations) comes from the studies of the nucleation of dislocations via in situ STEM indentation, namely that the dislocations can be simply nucleated under mechanical stimulus and can be easily moved at room temperature.

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Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

Section: Role Of Dislocations In Resistive Switching Of Tio 2 and Srtmentioning

confidence: 99%

Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

Section: Electrical Properties Of the Dislocations In Tio 2 And Srtiomentioning

confidence: 99%

See 2 more Smart Citations

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

et al. 2018

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“…Previous studies via LC-AFM have revealed inhomogeneously distributed spots with strongly enhanced nanoscale conductivities within a less conductive matrix on the sample surface as terminating points of this conductive network 5,34 . The concentration of conductive spots is reported to be of the order of 10 11 cm −2 .…”

Section: Resultsmentioning

confidence: 91%

In-situ four-tip STM investigation of the transition from 2D to 3D charge transport in SrTiO3

Leis

Rodenbücher

Szot

et al. 2019

Sci Rep

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The electrical properties of SrTiO 3 (100) single crystals were investigated in-situ at different stages of thermal reduction by means of a 4-tip STM. Using the tips of the STM as electrical probes, distance-dependent four-point measurements were performed at the surface of the crystal at room temperature after reduction by thermal treatment. For annealing temperatures T ≤ 700 °C, charge transport is confined to a surface region <3 μ m below the surface. For reduction at T ≥ 900 °C a transition from a conducting 2D sheet with insulating bulk to a system with dominant 3D bulk conductivity is found. At an intermediate reduction temperature of T = 800 °C, a regime with mixed 2D/3D contributions is observed in the distance-dependent resistance measurements. Describing the depth-dependent conductivity with an analytical N-layer model, this regime of mixed 2D/3D conductivity is evaluated quantitatively under the assumption of an exponentially decaying conductivity profile, correlated with the previously observed depth-dependent dislocation density in the sample. A non-monotonous temperature dependence of the 3D conductivity in the respective conducting layer is found and possible underlying mechanisms are discussed, particularly with regard to non-intrinsic material properties depending on details of the sample preparation.

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Tailoring Work Functions of Heterostructures by Varying the Depth of a Buried Monolayer

Whittles,

Parks,

Wang

et al. 2024

Adv Materials Inter

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The work function is a critical parameter for device design and understanding of materials properties, but contemporary experimental literature on tailored work functions is rather scarce. This paper presents a promising new approach to work function design that uses pulsed laser deposition (PLD) growth with unit cell precision. It is shown that a monolayer buried within a material can influence the work function as a function of the layer depth. This method can preserve properties of the original material's surface, and furthermore, a sensitive material can be used as the monolayer, both of which are beneficial for device design. Proof of concept is demonstrated by inserting a nominal monolayer of barium oxide (BaO) into strontium titanate (SrTiO3) (001) at different depths, revealing a previously unknown work function trend. Density functional theory (DFT) calculations, surface characterization, and scanning transmission electron microscopy (STEM) studies verify the quality of the heterostructures and help to understand how charge transfer, slight barium diffusion, and termination effects account for the observed work function trends. This work function tunability is a promising approach for future devices that require a tailored work function, which can easily be extended to a wider variety of materials.

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In situ study of redox processes on the surface of SrTiO3 single crystals

Cited by 32 publications

References 29 publications

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

In-situ four-tip STM investigation of the transition from 2D to 3D charge transport in SrTiO3

Tailoring Work Functions of Heterostructures by Varying the Depth of a Buried Monolayer

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