| 1. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Cationic Disorder and Phase Segregation in LaAlO3/SrTiO3 Heterointerfaces Evidenced by Medium-Energy Ion Spectroscopy
- 2009
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 103:14, s. 146101-
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Tidskriftsartikel (refereegranskat)abstract
- Medium-energy ion spectroscopy (MEIS) has been used to study the depth profile and deduce the distribution of possible cationic substitutions in LaAlO3/SrTiO3 (LAO/STO) heterointerfaces. Analysis of La and Sr peaks in aligned and random MEIS spectra indicates that the surface layers of LAO on an STO substrate are not homogeneous and stoichiometric if the film thickness is less than 4 unit cell layers. This is possibly caused by a redistribution of La and Sr at the interface. Kelvin probe force microscopy reveals an inhomogeneous distribution of the surface potential in a 4 unit cell LAO film, indicating micrometer-sized regions of different compositions. Our findings provide a novel view on the microstructural origin of the electrically conductive interfaces.
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| 2. |
- Chakalov, R, et al.
(författare)
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Fabrication and investigation of YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 thin film structures for voltage tunable devices
- 1998
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Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 308:3-4, s. 279-288
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature superconducting/ferroelectric thin film structures were deposited by laser ablation. Three types of voltage tunable devices were fabricated and investigated-trilayer capacitor, planar interdigital capacitor and coplanar waveguide. As ferroelectric the solid solution BaxSr1-xTiO3 was chosen with barium content x = 0.05 because its Curie temperature is close to the liquid nitrogen boiling point (77 K). Temperature and voltage dependences of the Ba0.05Sr0.95TiO3 dielectric constant epsilon(r,BSTO) were studied. High epsilon(r,BSTO) values were determined-up to 3000 at 75 K, 20 GHz and zero de bias. Efficient voltage tunability was demonstrated (up to 40%) at loss level tan delta=0.01-0.1. Compact YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 coplanar waveguide with as narrow gap as 18 mu m was tested as electrically tunable phase-shifter and field-induced phase shifts of more than 180 degrees were obtained by 35 V de bias at 20 GHz. This improvement was attained by proper choice of the ferroelectric material, accomplished epitaxial growth of the films and decrease of the specific dimensions. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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| 3. |
- Boikov, Iouri, 1949, et al.
(författare)
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Atomic rearrangements at the TiO2-terminated (001)SrTiO3 surface and growth of thin LaMnO3 films
- 2013
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 102:5
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Tidskriftsartikel (refereegranskat)abstract
- SrTiO3 is commonly used as a substrate for growth of various oxide films. Different reconstructions at the SrTiO3 surface have been claimed. A question is whether these survive subsequent depositions of thin films and influence film properties. Medium energy ion scattering (MEIS) was used to probe structure and composition of the surface layer of a TiO2-terminated (001) SrTiO3 single-crystal substrate and 1-4 unit cell (u.c.) thick LaMnO3 epilayers. Aligned spectra indicate enrichment of Ti at the surface and a TiO2 double-layer (DL) configuration. The DL arrangement survives pulsed-laser deposition of LaMnO3 in a background of high oxygen pressure (5 x 10(-2) mbar) while it is destroyed at lower oxygen pressure (10(-4) mbar). Simulations of random MEIS spectra indicate substantial interdiffusion and La doping of the substrate surface but all interfaces are nevertheless insulating.
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| 4. |
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| 5. |
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| 6. |
- Boikov, Iouri, 1949, et al.
(författare)
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Dielectric response of Ba0.05Sr0.95TiO3(110) films to variations in temperature and electric field
- 2015
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Ingår i: Physics of the Solid State. - 1063-7834 .- 1090-6460. ; 57:5, s. 957-961
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Tidskriftsartikel (refereegranskat)abstract
- Three-layer epitaxial heterostructures, in which a 1000-nm-thick intermediate layer of Ba0.05Sr0.95TiO3 is integrated with strontium ruthenate conducting electrodes, have been grown by laser evaporation. Using photolithography and ion etching, film parallel-plate capacitors SrRuO3/Ba0.05Sr0.95TiO3/SrRuO3 are formed based on the grown heterostructures. A sharp maximum in the temperature dependence of the capacitor capacitance is observed at T ≈ 75 K. At T 250 K and the measuring signal frequency of 1 kHz, the dielectric loss tangent of the film capacitors increases exponentially with increasing temperature.
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| 7. |
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| 8. |
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| 9. |
- Boikov, Iouri, 1949, et al.
(författare)
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Reactance of the n-Au/p-La0.67Ca0.33MnO3 film contact
- 2006
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Ingår i: Technical Physics. - 1063-7842 .- 1090-6525. ; 51:8, s. 1097-1100
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Tidskriftsartikel (refereegranskat)abstract
- The responses of the resistance and reactance of Au/(20 nm)La 0.67Ca0.33MnO3 film heterostructures to temperature variation and magnetic field (f = 100 kHz) are investigated. At T = 300 K, the capacitance per unit area of the interface between a gold contact and the Au/(20 nm)La0.67Ca0.33MnO3 epitaxial film is found to be about 1 μF/cm2. The maximum value of the negative magnetoreactance (≈60% at μ0 H = 0.4 T) of the heterostructures is almost twice as high as the extremal value of the active magnetoresistance at T ≈ 235 K. The effective depth of magnetic field penetration into the manganite film on the side of the gold contact deposited on its surface is about 3 nm at room temperature. © Pleiades Publishing, Inc., 2006.
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| 10. |
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| 11. |
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| 12. |
- Boikov, Iouri, 1949, et al.
(författare)
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Strain enhanced anisotropy of in-plane resistivity of YBa2Cu3O7-delta films
- 2013
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 26:11
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Tidskriftsartikel (refereegranskat)abstract
- Highly bi-axially stressed, thin epitaxial films of YBa2Cu3O7-delta were deposited on mismatched, orthorhombic (001) YAlO3 substrates. Strain may be used to enhance anisotropy and affect spin and charge ordering in cuprate superconductors. The resistivity was anisotropic along the a and b axes and the ratio rho(a)/rho(b) approximate to 2 agreed well with that for untwinned single crystals. rho(a)(T), but not rho(b)(T), peaked sharply at a temperature closely above the superconducting transition temperature, while the latter estimated from rho(b)(T) exceeded the one determined from rho(a)(T). The height of the peak Delta rho(a) in rho(a)(T) decreased with increased bias current and applied magnetic field. The behavior may be explained by partly relaxed regions, preferably aligned along the b axis, but may also depend upon spin/charge ordering.
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| 13. |
- Boikov, Iouri, 1949, et al.
(författare)
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Strain-enhanced phase separation affecting electro- and magnetotransport in La0.67Ca0.33MnO3 films
- 2004
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Ingår i: Journal of Applied Physics. ; 96:1, s. 435-442
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Tidskriftsartikel (refereegranskat)abstract
- Biaxial strain during nucleation influences phase separation into ferromagnetic (metallic) and nonferromagnetic (insulating) regions and that, in turn, markedly affects the electric transport of a manganite film. A 40-nm-thick La0.67Ca0.33MnO3 film, coherently constrained by a (001)LaAlO3 substrate, possesses a noticeably contracted unit cell volume (Veff[approximate]56.70 Å3) as compared with that of a stoichiometric bulk sample. It corresponds to a higher relative concentration (45%) of tetravalent manganese ions in the manganite layer than that in the target (33%). The resistivity rho(T) curve of the strained film peaks twice in the range 4.2300 K. The charge transport of strained La0.67Ca0.33MnO3 films is non-ohmic at T
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| 14. |
- Boikov, Iouri, 1949, et al.
(författare)
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Variations in the electrical resistivity of La0.67Ca0.33MnO3 films and induced interconversions of ferromagnetic and nonferromagnetic inclusions in their bulk
- 2011
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Ingår i: Physics of the Solid State. - 1063-7834 .- 1090-6460. ; 53:10, s. 2168-2173
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Tidskriftsartikel (refereegranskat)abstract
- A significant (similar to 1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion (a (aSyen)/a (aEuro-) a parts per thousand 1.04) and reduction in the volume of the unit cell of La(0.67)Ca(0.33)MnO(3) films (15 nm) quasicoherently grown on the (001) surface of a LaAlO(3) substrate. The films consist of single-crystal blocks with the lateral size of 30-50 nm. The atomically smooth LaAlO(3)-La(0.67)Ca(0.33)MnO(3) interphase boundary has no misfit dislocations. At T = 4.2 K, the transformation of nonferromagnetic phase inclusions into ferromagnetic ones in a constant magnetic field H is accompanied by a stable reduction in the electrical resistivity rho of manganite films with time, so that the curve rho(t) is well approximated by the relationship rho(t) similar to rho(1)(t - t (0))(1/2), (where t (0) is the time for establishment of the specified value (mu(0) H = 5 T) of the magnetic field and rho(1) is a coefficient independent of H). The magnetocrystalline anisotropy due to the elastic deformation of films by the substrate and stratification of electronic phases are the reasons of the distinct hysteresis in the dependences rho(mu(0) H, T 0 -> -5 T -> 0 -> 5 T. At T = 50 K and mu(0) H = 0.4 T, the magnetoresistance MR = 100% [rho(mu(0) H) - rho(mu(0) H = 0)]/rho(mu(0) H = 0) of LCMO films attains 150%.
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| 15. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Cation stoichiometry and electrical transport properties of the NdGaO 3 /(0 0 1)SrTiO 3 interface
- 2015
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:25, s. Art. no. 255004-
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Tidskriftsartikel (refereegranskat)abstract
- The interface formed between two wide band-gap insulators, NdGaO3 and SrTiO3 renders metallic behavior, similar to the LaAlO3/SrTiO3 interface. The interface conductivity depends strongly upon oxygen pressure during growth of the NdGaO3 film and subsequent annealing in oxygen. The conductivity of a (10uc) NdGaO3/SrTiO3 film, pulsed laser deposited at low (pO2=10-4mbar) oxygen pressure, vanishes after annealing at 600 C in oxygen atmosphere. For a similar interface formed at high oxygen pressure (pO2=0.3mbar), the metallic conductivity remains also after post annealing. Medium energy ion spectroscopy (MEIS) in random (non-channeling) direction showed that a substantial part of Ga is missing in films deposited at low pressure, while optimal stoichiometry is approached in films deposited at high pressure. Aligned (channeling) MEIS likewise show that the Ga/Nd ratio approaches the stoichiometric value as the pressure is increased from 10-4 to 0.3mbar. This is interpreted as due to gallium desorption from a growing film at high temperature and low oxygen pressure while the re-evaporation of gallium is considerably suppressed at higher pressure. We discuss the possible role of stoichiometry on electrical transport properties.
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| 16. |
- Schoofs, F., et al.
(författare)
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Optimized transport properties of LaAlO3/SrTiO3 heterointerfaces by variation of pulsed laser fluence
- 2011
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:30
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Tidskriftsartikel (refereegranskat)abstract
- We show the influence of pulsed laser deposition fluence on the transport properties of the LaAlO(3)/SrTiO(3) (LAO/STO) heterointerface. Structural characterization by x-ray diffraction and medium energy ion spectrometry enables us to deduce that the electronic behaviour is extremely sensitive to the stoichiometry of the LAO layer as well as the structural quality of the STO surface. An optimum balance of these two quantities is demonstrated for an intermediate laser fluence.
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| 17. |
- Serenkov, I.T., et al.
(författare)
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Structural distortions induced during stress relaxation affecting electrical transport of nanometer-thick La0.67(Ba,Ca)0.33MnO3 films
- 2010
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 404:23-24, s. 5234-5236
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction (XRD) and medium-energy ion scattering (MEIS) were used to clarify distortions induced during mechanical stress relaxation in nanometer-thick epitaxial La0.67Ba0.33MnO3 (LBMO) and La0.67Ca0.33MnO3 (LCMO) films fabricated by pulsed laser deposition. It follows from measured XRD and MEIS spectra that LBMO films grown on mismatched LaAlO3 were partly relaxed in the main part of the film, leaving about 4 nm heavily strained portion close to the interface. The critical thickness of LCMO films grown on LaAlO3 substrates was several times larger than that of LBMO due to a better match in lattice parameters. Electro- and magneto-transport parameters of nanometer-thick manganite films grown on mismatched substrates differed markedly from those of LBMO and LCMO layers nucleated and grown on well-matched ones because of non-stoichiometry, biaxial mechanical stresses, and phase separation. The resistivity ρ of manganite films grown coherently at a substrate with small mismatch obeyed the relation ρ=ρ1+ρ2(H)T4.5 at temperatures well below the Curie point. Parameter ρ1 was temperature T and magnetic field H independent while ρ2 was temperature independent but decreased linearly with increasing H.
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