Irradiated SrTiO3 Research Articles

Understanding the role of structural distortions on the transport properties of Ar ion irradiated SrTiO3 thin films: X-ray absorption investigation

We report the evolution of structural distortions on the pulsed laser deposited SrTiO3 (STO) thin films irradiated by 1 MeV Ar ion beam and their response in the electrical and thermoelectric properties correlated with their electronic structures. The structural studies reveal a modification in the crystalline nature resulting in the synergistic enhancement of resistivity and the Seebeck coefficient due to ion irradiation-induced oxygen vacancies and augment the power factor to ∼17 μW m−1K−2, which is 2.5 times higher than the pristine STO. An in-depth analysis of the conduction mechanism using various theoretical models implies the role of band conduction and Mott-variable range hopping. Further, the changes in the local electronic structures are reflected in the variation in the Ti–O bond length and the density of unoccupied states that alter the spectral intensities and chemical shifts and are responsible for the observed enhancement in the thermoelectric properties. The above results indicate the significance of the ion beams to tune the electrical and thermoelectric properties.

Symmetry degeneration and room temperature ferroelectricity in ion-irradiated SrTiO3

Polar phonon modes associated with room temperature ferroelectricity are observed in SrTiO3 single crystals irradiated with Ti ions. Quantitative strain analysis reveals that irradiation-induced out-of-plane strain drives the centrosymmetric cubic SrTiO3 to a tetragonal-like structure in the maximum damaged region. Energy transfer from ions to electrons during ion irradiation yields defects in SrTiO3 that also plays an important role for the room temperature ferroelectricity. Different from thin film techniques, the ferroelectricity in the ion irradiated SrTiO3 can occur for much larger thicknesses, depending on the energy and type of ion.

Ultrasound assisted fabrication of SrTiO3 nanopowders: Effect of electron beam induced structural and luminescence properties for solid state lightning and high temperature dosimetry applications

Strontium titanate (SrTiO3) nanopowders are prepared by ultrasound assisted sonochemical route using Polyethylene glycol as a surfactant. The obtained product is irradiated with 8 MeV electrons with electrons dose strength of 2 kGy, 4 kGy, 6 kGy and 8 kGy. The powder X-ray diffraction studies reveals well indexed cubic structure in both pristine and electron beam irradiated samples. Morphological results evidence the spherical shaped nanopowders. The energy band gap was found to be decrease with increase of electron beam irradiation strength. The photoluminescence emission spectra of pristine and electron beam irradiated samples exhibit defects related peaks at ∼424, 444, 460, 483 and 520 nm. Upon electron beam irradiation, the Commission International de I'Eclairage color coordinates are engineered from deep blue color to cyan color. A single thermoluminescence glow peak is recorded at ∼213 °C in all the electron beam irradiated samples up to given dose range 2 kGy, 4 kGy, 6 kGy and 8 kGy. The trapping parameters (E, s) are calculated by employing various methods. Linear dose response, less fading and high reproducibility of electron beam irradiated SrTiO3 samples broadly indicated its suitability for thermoluminescence dosimetry applications.

Effect of the Gamma-Ray Irradiation on the Electric and Optical Properties of SrTiO3 Single Crystals

We investigated the visible emission property of SrTiO3 (STO) single crystals irradiated with gammy-ray (γ-ray) at various total doses up to 900 kGy. The electric and optical absorption properties of the irradiated STO samples were hardly changed with the γ-ray irradiation, compared with those of un-irradiated STO. In contrast, the visible emission near 550 nm increased with the γ-ray dose increasing. While the development of the visible emission was indicative of the increase of oxygen vacancies inside STO by the γ-ray irradiation, the newly generated oxygen vacancies were not significantly harmful to the electric and optical properties of STO. We concluded that the STO single crystal should have a good tolerance against the damage by the γ-ray irradiation.

Publisher's Note: Current-induced nonuniform enhancement of sheet resistance in Ar+ -irradiated SrTiO3 [Phys. Rev. B 95 , 245303 (2017)

Publisher's Note: Current-induced nonuniform enhancement of sheet resistance in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>Ar</mml:mi></mml:mrow><mml:mo>+</mml:mo></mml:msup></mml:math> -irradiated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>SrTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> [Phys. Rev. B <b>95</b> , 245303 (2017)

Current-induced nonuniform enhancement of sheet resistance in Ar+ -irradiated SrTiO3

The sheet resistance Rs of Ar+ irradiated SrTiO3 in patterns with a length scale of several microns increases significantly below 40 K in connection with driving currents exceeding a certain threshold. The initial lower Rs is recovered upon warming with accelerated recovery around 70 and 160 K. Scanning superconducting quantum interference device microscopy shows local irreversible changes in the spatial distribution of the current with a length scale of several microns. We attribute the observed nonuniform enhancement of Rs to the attraction of the charged single-oxygen and dioxygen vacancies by the crystallographic domain boundaries in SrTiO3. The boundaries, which are nearly ferroelectric below 40 K, are polarized by the local electrical field associated with the driven current and the clustered vacancies which suppress conductivity in their vicinity and yield a noticeable enhancement in the device resistance when the current path width is on the order of the boundary extension. The temperatures of accelerated conductivity recovery are associated with the energy barriers for the diffusion of the two types of vacancies.

Role of oxygen vacancies on light emission mechanisms in SrTiO3 induced by high-energy particles

Light emission under MeV hydrogen and oxygen ions in stoichiometric SrTiO3 are identified at temperatures of 100 K, 170 K and room-temperature. MeV ions predominately deposit their energies to electrons in SrTiO3 with energy densities orders of magnitude higher than from UV or x-ray sources but comparable to femtosecond lasers. The ionoluminescence (IL) spectra can be resolved into three main Gaussian bands at 2.0 eV, 2.5 eV and 2.8 eV, whose relative contributions strongly depend on irradiation temperature, electronic energy loss and irradiation fluence. Two main bands, observed at 2.5 eV and 2.8 eV, are intrinsic and associated with electron–hole recombination in the perfect SrTiO3 lattice. The 2.8 eV band is attributed to recombination of free (conduction) electrons with an in-gap level, possibly related to self-trapped holes. Self-trapped excitons (STEs) are considered suitable candidates for the 2.5 eV emission band, which implies a large energy relaxation in comparison to the intrinsic edge transition. The dynamics of electronic excitation, governs a rapid initial rise of the intensity; whereas, accumulated irradiation damage (competing non-radiative recombination channels) accounts for a subsequent intensity decrease. The previously invoked role of isolated oxygen vacancies for the blue luminescence (2.8 eV) does not appear consistent with the data. An increasing well-resolved band at 2.0 eV dominates at 170 K and below. It has been only previously observed in heavily strained and amorphous SrTiO3, and is, here, attributed to transitions from d(t2g) conduction band levels to d(eg) levels below the gap. In accordance with ab initio theoretical calculations they are associated to trapped electron states in relaxed Ti3+ centers at an oxygen vacancy within distorted TiO6 octahedra. The mechanism of defect evolution monitored during real-time IL experiments is presented. In conclusion, the light emission data confirm that IL is a useful tool to investigate lattice disorder in irradiated SrTiO3.

Antiferromagnetism of two-dimensional electronic gas on light-irradiated SrTiO3 and at LaAlO3/SrTiO3 interfaces

To gain an insight into the origin of tunable two-dimensional (2D) electronic liquid at the interfaces of transition-metal oxides, we address properties of a conducting layer on the light-irradiated surfaces of SrTiO3; the energy spectrum of the latter is known and consists of the titanium dxz/dyz and dxy bands. Recently, Santander-Syro et al (2014 Nature Mater. 13 1085) revealed that the dxy bands actually comprise two chiral branches with the Kramers degeneracy at the zone center lifted in the absence of a magnetic moment. We suggest that interacting electrons on the irradiated SrTiO3 go over into a magnetic phase as the result of one of the instabilities of the 2D Fermi liquid with exchange interactions, and point out the concrete antiferromagnetic order parameter. Large energy scales of the order of Fermi energy ∼0.1 eV inherent in this mechanism warrant stability of the magnetic ground state against ever-present effects of disorder. Arguments are given that electrons at the irradiated SrTiO3 surface and at the LaAlO3/SrTiO3 interfaces undergo a kind of first-order transformation into one and the same phase of the 2D electronic Fermi liquid with reduced magnetic symmetry.

Photocatalytic reduction synthesis of SrTiO3-graphene nanocomposites and their enhanced photocatalytic activity.

SrTiO3-graphene nanocomposites were prepared via photocatalytic reduction of graphene oxide by UV light-irradiated SrTiO3 nanoparticles. Fourier transformed infrared spectroscopy analysis indicates that graphene oxide is reduced into graphene. Transmission electron microscope observation shows that SrTiO3 nanoparticles are well assembled onto graphene sheets. The photocatalytic activity of as-prepared SrTiO3-graphene composites was evaluated by the degradation of acid orange 7 (AO7) under a 254-nm UV irradiation, revealing that the composites exhibit significantly enhanced photocatalytic activity compared to the bare SrTiO3 nanoparticles. This can be explained by the fact that photogenerated electrons are captured by graphene, leading to an increased separation and availability of electrons and holes for the photocatalytic reaction. Hydroxyl (·OH) radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and were found to be produced over the irradiated SrTiO3 nanoparticles and SrTiO3-graphene composites; especially, an enhanced yield is observed for the latter. The influence of ethanol, KI, and N2 on the photocatalytic efficiency was also investigated. Based on the experimental results, ·OH, h+, and H2O2 are suggested to be the main active species in the photocatalytic degradation of AO7 by SrTiO3-graphene composites.PACS61.46. + w; 78.67.Bf; 78.66.Sq

RBS/C, HRTEM and HRXRD study of damage accumulation in irradiated SrTiO3

Damage accumulation in argon-irradiated SrTiO3 single crystals has been studied using a combination of Rutherford backscattering/channeling (RBS/C), high-resolution transmission electron microscopy (HRTEM) and high-resolution X-ray diffraction (HRXRD) techniques. The RBS/C spectra were fitted using McChasy, a Monte Carlo simulation code that allows for a quantitative analysis of amorphous-like and dislocation-like types of defects. The results were interpreted by using a multi-step damage accumulation model under the assumption that the damage accumulation occurs in a series of structural transformations that are triggered by lattice stress caused by formation of a free volume in the irradiated crystal. This assumption has been confirmed by HRTEM and HRXRD.

Irradiation study on Srn+1TinO3n+1 Ruddlesden‐Popper phases synthesized by hot‐forging

AbstractThe hot‐forging technique was used to obtain both the n = 2 (Sr3Ti2O7) and n = ∞ (SrTiO3) members of Ruddlesden‐Popper phase Srn+1TinO3n+1. Pure phase and high density (&gt;95% theoretical) materials were achieved using this technique. These polycrystalline samples were irradiated with 200 keV He ions to a fluence of 2×1021 ion/m2 (corresponding to a peak dose at 5 dpa) at room temperature to study radiation damage effects. Microstructural investigation on pristine and irradiated samples was performed using grazing incidence X‐ray diffraction (GIXRD) and transmission electron microscopy (TEM). Three phenomena are revealed upon comparing prisXtine versus irradiated samples. First, both compounds interplanar lattice spacings increased after irradiation. Second, peak broadening possibly suggests incredibly small grain due to irradiation. Third, experiment results revealed an amorphization in the irradiated Sr3Ti2O7, while no amorphization was observed in irradiated SrTiO3. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Characterization of irradiation damage distribution near TiO2/SrTiO3 interfaces using coherent acoustic phonon interferometry

We apply ultrafast coherent acoustic phonon interferometry to characterize the distribution of the radiation damage near the TiO2/SrTiO3 interfaces. We show that the optical and mechanical properties of anatase TiO2 remain unaffected by the radiation dosages in the 0.1÷5 dpa (displacements per atom) range, while the degraded optical response indicates a significant defect accumulation in the interfacial region of SrTiO3 at 0.1 dpa and subsequent amorphization at 3 dpa. Comparison between the theoretical simulations and the experimental results reveals an almost threefold reduction of the sound velocity in the irradiated SrTiO3 layer with peak damage levels of 3 and 5 dpa.

Photoluminescence spectra of perovskite oxide semiconductors

We report photoluminescence (PL) spectra of typical wide-gap perovskite semiconductors, SrTiO3, KTaO3, BaTiO3, LiNbO3, and LiTaO3. In SrTiO3, KTaO3, and BaTiO3, undoped crystals show no PL at room temperature, while broad PL bands appear by Ar+ irradiation. The room temperature PL properties of SrTiO3, KTaO3, and BaTiO3 are very similar to each other, but are different from those of LiNbO3 and LiTaO3. At low temperatures, only Ar+-irradiated SrTiO3 crystals show sharp band-edge PL, corresponding to the band-to-band radiative recombination of free electrons and holes. Unique PL behaviors in SrTiO3 are discussed, compared to other perovskite oxides.

Noise and electric field characterization of irradiated SrTiO3

SrTiO3 (STO) is a band insulator with a perovskite crystallographic structure, widely used as substrate for the deposition of other perovskite materials, for instance manganites or cuprates. STO surface becomes conductive under Ar+ ion irradiation, exhibiting similar properties to STO/LaAlO3 interface or bulk reduced STO. We report the transport and noise properties as function of temperature and electric field of Ar+ irradiated STO exhibiting at its surface a high mobility electron gas. This system shows metallic properties with low charge densities allowing mobility measurements. The low frequency 1/f noise presents an unexpected linear dependence with the mobility which cannot be described by the usual Hooge model. The effect of the electric field at a given temperature on the mobility, magnetoresistance and low frequency noise is also presented.

Evidence of the primary-color photoluminescence in ion (H+,H2+,C−) irradiated and thermal annealed SrTiO3

We have measured photoluminescence (PL) spectrum of (1) thermal-annealed SrTiO 3 /Si thin film and undoped SrTiO 3 single crystal; (2) SrTiO 3 single crystal irradiated by high energy (3 MeV) proton, deuterium, and He ion beams and (3) SrTiO 3 single crystal irradiated by low energy (60 keV) H + and C − ions. Two PL emissions are induced in (1) and (2) at visible frequencies 3 and 2.45 eV, while another PL peak is induced at 2 eV in (3). When compared with our previous PL experiments on high-temperature annealed SrTiO 3 /SiO 2 /Si thin film and 3 MeV proton (H + ) irradiated STO single crystal, these results confirm that the three PL emissions with blue (3 eV), green (2.45 eV), and red-orange (2 eV) frequencies originate indeed from SrTiO 3 . These primary-color PL effect induced at room-temperature makes STO a strong candidate material for future oxide-based optoelectronic application.

Photoluminescence of high energy Ar+-irradiated SrTiO3 single crystal

Abstract We report the structural and photoluminescence characteristics of a high energy Ar + -irradiated SrTiO 3 single crystal. High resolution X-ray reciprocal space mapping, cross-section scanning electron microscopy and photoluminescence measurements suggest that thick amorphous and oxygen-deficient SrTiO 3 layers are formed after irradiation. Due to the highly accelerated Ar + (∼100 keV), electrical conductivity of the oxygen-deficient SrTiO 3 layer seems to be highly reduced, which results in the absence of 440 nm (blue-light) emission at 300 K, and broad and weak 380 nm emission at 20 K.

Blue luminescence from electron-doped SrTiO3

Blue-light emissions from electron-doped SrTiO3 single crystals at room temperature were observed. Substituting La3+ for Sr2+ and Nb5+ for Ti4+ in SrTiO3 provides electron carriers in Ti 3d conduction bands; these carriers are responsible for the room-temperature blue-light emission. This blue-light emission is essentially the same as that observed in Ar+-irradiated oxygen-deficient SrTiO3. This blue luminescence is independent of the defect type. The chemical substitution of La3+ for Sr2+ changes the temperature of the structural phase transition from cubic to tetragonal symmetry. The relation between the photoluminescence properties and the structural phase transition is also discussed.

Blue-light emission at room temperature from Ar+-irradiated SrTiO3

Oxide-based electronic devices are expected to have fascinating properties, unlike those made from conventional semiconductors. SrTiO3 (STO) is a key material for this new field of electronics1,2,3,4,5,6,7,8,9,10,11. Here we report on blue-light emission at room temperature from Ar+-irradiated, metallic STO. The irradiation introduces oxygen deficiencies to a depth of ∼20 nm from the crystal surface. These deficiencies generate conduction carriers and stabilize a hole level in a self-trapped state. We propose a model by which the doped conduction electrons and the in-gap state produce a radiative process that results in blue-light emission. The emitting region can be patterned into any size and shape with conventional microscopic fabrication techniques.

Thermal annealing of disorder in Pb-ion irradiated SrTiO3

Attention was paid to thermal annealing of defects in the SrTiO3 lattice preliminary irradiated by Pb2+ ions which were used to simulate the recoil-nuclei during α-decay events in actinide waste forms. Two different types of defect depending upon Pb2+ irradiation fluence and annealing temperature were characterized with their activation energy and a prefactor related to the fraction recovered per second. Such thermal annealing data are necessary to predict the matrix behaviour under the storage conditions. Additional informations were obtained on the defect structure using Rutherford backscattering spectrometry in channeling condition. The measurement of the de-channeling yield along different axes and planes in the crystal has permitted to analyse partially the isolated defect structure.

Thermal annealing of disorder in Pb-ion irradiated SrTiO3

Attention was paid to thermal annealing of defects in the SrTiO3 lattice preliminary irradiated by Pb2+ ions which were used to simulate the recoil-nuclei during α-decay events in actinide waste forms. Two different types of defect depending upon Pb2+ irradiation fluence and annealing temperature were characterized with their activation energy and a prefactor related to the fraction recovered per second. Such thermal annealing data are necessary to predict the matrix behaviour under the storage conditions. Additional informations were obtained on the defect structure using Rutherford backscattering spectrometry in channeling condition. The measurement of the de-channeling yield along different axes and planes in the crystal has permitted to analyse partially the isolated defect structure.