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Visible-light-accelerated oxygen vacancy migration in strontium titanate.

Li Y, Lei Y, Shen BG, Sun JR - Sci Rep (2015)

Bottom Line: There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies.Tuning the kinetics of oxygen vacancies is then highly desired.This effect provides a feasible approach towards the modulation of the anionic processes.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter &Institute of Physics, Chinese Academy of Sciences, Beijing 100190, Peoples' Republic of China.

ABSTRACT
Strontium titanate is a model transition metal oxide that exhibits versatile properties of special interest for both fundamental and applied researches. There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies. Tuning the kinetics of oxygen vacancies is then highly desired. Here we reported on a dramatic tuning of the electro-migration of oxygen vacancies by visible light illumination. It is found that, through depressing activation energy for vacancy diffusion, light illumination remarkably accelerates oxygen vacancies even at room temperature. This effect provides a feasible approach towards the modulation of the anionic processes. The principle proved here can be extended to other perovskite oxides, finding a wide application in oxide electronics.

No MeSH data available.


Related in: MedlinePlus

Effect of combined electrical and optical stimuli on the structure of STO.(a) A sketch of the experimental setup for x-ray diffraction. (b) XRD spectra of the 002 reflection of (001)-STO, recorded right upon the application of an electrical field along the [001]-axis. The duration of each ϑ–2ϑ scanning is 180 s. Shaded area marks the difference of the two XRD spectra with and without light illumination. The inset sketch shows the field direction with respect to the axes of the unit cell. (c) A reciprocal mapping of the 103 reflection of STO, measured under the conditions of VG = −500 V and P = 100 mW. The downward tail of the main reflection marks the c-axis lattice expansion. (d) Structural changes for a constant light illumination but different gate fields. Positive gate bias produces no effect on structure even aided by illumination. Arrows mark the positions of the Bragg reflections. (e) Structural changes with light power while gate voltage is kept constant. (f) Distribution of structural deformation on VG-P plane, showing the combined effect of the electrical stressing and light illuminating. Light wavelength adopted here is λ = 532 nm. In all cases the leakage current is lower than 10 nA. All measurements were conducted at room temperature.
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f1: Effect of combined electrical and optical stimuli on the structure of STO.(a) A sketch of the experimental setup for x-ray diffraction. (b) XRD spectra of the 002 reflection of (001)-STO, recorded right upon the application of an electrical field along the [001]-axis. The duration of each ϑ–2ϑ scanning is 180 s. Shaded area marks the difference of the two XRD spectra with and without light illumination. The inset sketch shows the field direction with respect to the axes of the unit cell. (c) A reciprocal mapping of the 103 reflection of STO, measured under the conditions of VG = −500 V and P = 100 mW. The downward tail of the main reflection marks the c-axis lattice expansion. (d) Structural changes for a constant light illumination but different gate fields. Positive gate bias produces no effect on structure even aided by illumination. Arrows mark the positions of the Bragg reflections. (e) Structural changes with light power while gate voltage is kept constant. (f) Distribution of structural deformation on VG-P plane, showing the combined effect of the electrical stressing and light illuminating. Light wavelength adopted here is λ = 532 nm. In all cases the leakage current is lower than 10 nA. All measurements were conducted at room temperature.

Mentions: As schemed in Fig. 1a, samples are (001)-orientated STO substrates of the dimension of 5 × 5 × 0.5 mm3. As electrodes, two Ti layers were deposited respectively on the top and bottom surfaces through magnetron sputtering in an Ar atmosphere of 0.5 Pa. A gate voltage, VG, between −200 V and 200 V was applied to the back gate of STO while the top surface was grounded. In all cases, the leakage current is lower than 10 nA at the ambient temperature, which rules out the effect of Joule heating. Fig. 1b presents the x-ray diffraction (XRD) spectra of the 002 Bragg reflection of STO, recorded in the presence or absence of light. Without illumination, a bias voltage up to ±200 V produces negligible effects on the structure of STO. This can be ascribed to the low mobility of oxygen vacancies (~8 × 10−12 cm2/Vs at room temperature20).As recently reported, the structural deformation only occurs for STO accompanying the electro-migration of VOs6. It is easy to calculate the time required for the VOs to drift out of the interfacial layer, and it is ~6200 s under the gate bias of −200 V if layer thickness is ~2 μm, well beyond the time window of the ϑ–2ϑ scanning (~180 s). Aided by light, however, a gate bias of −200 V is high enough to cause sizable structural deformation. As shown in Fig. 1b, an obvious shoulder appears beside the main reflection when illuminated by a light of P = 100 mW (λ = 532 nm), indicating a lattice expansion along [001] axis. Since the unchanged phase can be clearly seen, the deformed phase could be much thinner than the penetration depth of x-ray in STO (~6 μm), appearing in an interfacial layer. According to reciprocal space mapping of the 103 reflection, fascinatingly, this new phase has an elongated c-axis lattice constant but a unchanged a-axis one (Fig. 1c). In contrast, positive biases produce no effect on lattice even aided by illumination, which means that the field-induced lattice expansion only appears underneath anode (Fig. 1d).


Visible-light-accelerated oxygen vacancy migration in strontium titanate.

Li Y, Lei Y, Shen BG, Sun JR - Sci Rep (2015)

Effect of combined electrical and optical stimuli on the structure of STO.(a) A sketch of the experimental setup for x-ray diffraction. (b) XRD spectra of the 002 reflection of (001)-STO, recorded right upon the application of an electrical field along the [001]-axis. The duration of each ϑ–2ϑ scanning is 180 s. Shaded area marks the difference of the two XRD spectra with and without light illumination. The inset sketch shows the field direction with respect to the axes of the unit cell. (c) A reciprocal mapping of the 103 reflection of STO, measured under the conditions of VG = −500 V and P = 100 mW. The downward tail of the main reflection marks the c-axis lattice expansion. (d) Structural changes for a constant light illumination but different gate fields. Positive gate bias produces no effect on structure even aided by illumination. Arrows mark the positions of the Bragg reflections. (e) Structural changes with light power while gate voltage is kept constant. (f) Distribution of structural deformation on VG-P plane, showing the combined effect of the electrical stressing and light illuminating. Light wavelength adopted here is λ = 532 nm. In all cases the leakage current is lower than 10 nA. All measurements were conducted at room temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4588568&req=5

f1: Effect of combined electrical and optical stimuli on the structure of STO.(a) A sketch of the experimental setup for x-ray diffraction. (b) XRD spectra of the 002 reflection of (001)-STO, recorded right upon the application of an electrical field along the [001]-axis. The duration of each ϑ–2ϑ scanning is 180 s. Shaded area marks the difference of the two XRD spectra with and without light illumination. The inset sketch shows the field direction with respect to the axes of the unit cell. (c) A reciprocal mapping of the 103 reflection of STO, measured under the conditions of VG = −500 V and P = 100 mW. The downward tail of the main reflection marks the c-axis lattice expansion. (d) Structural changes for a constant light illumination but different gate fields. Positive gate bias produces no effect on structure even aided by illumination. Arrows mark the positions of the Bragg reflections. (e) Structural changes with light power while gate voltage is kept constant. (f) Distribution of structural deformation on VG-P plane, showing the combined effect of the electrical stressing and light illuminating. Light wavelength adopted here is λ = 532 nm. In all cases the leakage current is lower than 10 nA. All measurements were conducted at room temperature.
Mentions: As schemed in Fig. 1a, samples are (001)-orientated STO substrates of the dimension of 5 × 5 × 0.5 mm3. As electrodes, two Ti layers were deposited respectively on the top and bottom surfaces through magnetron sputtering in an Ar atmosphere of 0.5 Pa. A gate voltage, VG, between −200 V and 200 V was applied to the back gate of STO while the top surface was grounded. In all cases, the leakage current is lower than 10 nA at the ambient temperature, which rules out the effect of Joule heating. Fig. 1b presents the x-ray diffraction (XRD) spectra of the 002 Bragg reflection of STO, recorded in the presence or absence of light. Without illumination, a bias voltage up to ±200 V produces negligible effects on the structure of STO. This can be ascribed to the low mobility of oxygen vacancies (~8 × 10−12 cm2/Vs at room temperature20).As recently reported, the structural deformation only occurs for STO accompanying the electro-migration of VOs6. It is easy to calculate the time required for the VOs to drift out of the interfacial layer, and it is ~6200 s under the gate bias of −200 V if layer thickness is ~2 μm, well beyond the time window of the ϑ–2ϑ scanning (~180 s). Aided by light, however, a gate bias of −200 V is high enough to cause sizable structural deformation. As shown in Fig. 1b, an obvious shoulder appears beside the main reflection when illuminated by a light of P = 100 mW (λ = 532 nm), indicating a lattice expansion along [001] axis. Since the unchanged phase can be clearly seen, the deformed phase could be much thinner than the penetration depth of x-ray in STO (~6 μm), appearing in an interfacial layer. According to reciprocal space mapping of the 103 reflection, fascinatingly, this new phase has an elongated c-axis lattice constant but a unchanged a-axis one (Fig. 1c). In contrast, positive biases produce no effect on lattice even aided by illumination, which means that the field-induced lattice expansion only appears underneath anode (Fig. 1d).

Bottom Line: There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies.Tuning the kinetics of oxygen vacancies is then highly desired.This effect provides a feasible approach towards the modulation of the anionic processes.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Laboratory for Condensed Matter &Institute of Physics, Chinese Academy of Sciences, Beijing 100190, Peoples' Republic of China.

ABSTRACT
Strontium titanate is a model transition metal oxide that exhibits versatile properties of special interest for both fundamental and applied researches. There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies. Tuning the kinetics of oxygen vacancies is then highly desired. Here we reported on a dramatic tuning of the electro-migration of oxygen vacancies by visible light illumination. It is found that, through depressing activation energy for vacancy diffusion, light illumination remarkably accelerates oxygen vacancies even at room temperature. This effect provides a feasible approach towards the modulation of the anionic processes. The principle proved here can be extended to other perovskite oxides, finding a wide application in oxide electronics.

No MeSH data available.


Related in: MedlinePlus