| 1. |
- Aurino, Pier Paolo, 1985, et al.
(författare)
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Nano-patterning of the electron gas at the LaAlO3/SrTiO3 interface using low-energy ion beam irradiation
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:20, s. 201610-
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Tidskriftsartikel (refereegranskat)abstract
- The quasi-two dimensional electron gas formed at the interface between LaAlO3 (LAO) and SrTiO3 (STO) shows fascinating properties, such as two-dimensional superconductivity, giant electric field effect, and the possible co-existence of ferromagnetic and superconducting phases. In this work, we demonstrate that the conducting LAO/STO interface can be made insulating after short irradiation by a beam of low energy Ar+ ions. The irradiation process does neither result in physical removal of the LAO film nor produces oxygen vacancies in the STO layer. Using electron beam lithography and low ion beam energy irradiation, we fabricated conducting nano-structures in the LAO/STO interface with dimensions down to 50 nm. Such a reliable and robust method of nano-patterning may be a prerequisite for future electronic applications of the LAO/STO interface.
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| 2. |
- Aurino, Pier Paolo, 1985, et al.
(författare)
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Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer
- 2016
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO) offers a unique playground to study the interplay and competitions between different ordering phenomena in a strongly correlated two- dimensional electron gas. Recent studies of the LAO/STO interface reveal the inhomogeneous nature of the 2DEG that strongly influences electrical-transport properties. Nanowires needed in future applications may be adversely affected, and our aim is, thus, to produce a more homogeneous electron gas. In this work, we demonstrate that nanostructures fabricated in the quasi-2DEG at the LaAlO3/SrTiO3 interface, capped with a SrCuO2 layer, retain their electrical resistivity and mobility independent of the structure size, ranging from 100 nm to 30 mu m. This is in contrast to noncapped LAO/STO structures, where the room-temperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. High-resolution intermodulation electrostatic force microscopy reveals an inhomogeneous surface potential with "puddles" of a characteristic size of 130 nm in the noncapped samples and a more uniform surface potential with a larger characteristic size of the puddles in the capped samples. In addition, capped structures show superconductivity below 200 mK and nonlinear currentvoltage characteristics with a clear critical current observed up to 700 mK. Our findings shed light on the complicated nature of the 2DEG at the LAO/STO interface and may also be used for the design of electronic devices.
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| 3. |
- Aurino, Pier Paolo, 1985, et al.
(författare)
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Reversible metal-insulator transition of Ar-irradiated LaAlO3/SrTiO3 interfaces
- 2015
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:15
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Tidskriftsartikel (refereegranskat)abstract
- The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAlO3 (LAO) and SrTiO3, can be made completely insulating by low-energy, 150-eV, Ar+ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation.
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| 4. |
- Baek, S. J., et al.
(författare)
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Electrical conduction of palladium-decorated multi-layered graphene oxide effected by hydrogen dissociation
- 2015
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Ingår i: Synthetic Metals. - : Elsevier BV. - 0379-6779. ; 199, s. 74-78
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Tidskriftsartikel (refereegranskat)abstract
- Multi-layered graphene oxide (MGO) and palladium-decorated MGO (PdGO) are electrically evaluated as a function of H-2 pressure up to 20 bar to elucidate an interaction between molecular hydrogen and PdGO. As H-2 pressure increases, the electrical conductance (G) of MGO also increases while that of PdGO decreases. Using atomic force microscopy, X-ray photoelectron spectroscopy, and Fourier transform-infrared spectroscopy analysis, we found that MGO reduction due to H-2 accounts for the increase in G of the MGO. For PdGO, an increase of OH groups was observed, which shows that PdGO was oxidized when exposed to high H-2 pressure. The PdGO oxidation can be explained by a hydrogen spillover effect and the decrease of G may be due to this behavior.
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| 5. |
- 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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| 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. |
- 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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| 8. |
- 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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| 9. |
- Boikov, Y. A., et al.
(författare)
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Degradation of the SrRuO3/SrTiO3 Interface Capacitance Induced by Mechanical Stresses
- 2014
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Ingår i: Physics of the Solid State. - : Pleiades Publishing Ltd. - 1063-7834 .- 1090-6460. ; 56:12, s. 2446-2450
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Tidskriftsartikel (refereegranskat)abstract
- Trilayer epitaxial heterostructures in which a 700-nm-thick SrTiO3 interlayer is integrated with two SrRuO3 electrodes have been grown by laser ablation. In the top electrode, twenty contact pads (S approximate to 0.1 mm(2)) have been formed using photolithography and ion etching. The bottom SrRuO3 electrode grown on a MgO(001) substrate is common for all film capacitors on the chip. As the temperature decreases in the range of 300-50 K, the capacitance C of the capacitors increases by a factor more than two due to an increase in the permittivity epsilon of the interlayer. At T = 4.2 K, as the bias voltage of +/-2.5 V is applied to the oxide electrodes, the capacitance C decreases by similar to 40%. In the temperature range of 100-300 K, the ratio epsilon(0)/epsilon increases almost linearly with increasing temperature (epsilon(0) is the permittivity in vacuum). At T > 250 K, the dielectric loss tangent of the SrTiO3 interlayer increases exponentially with increasing temperature and substantially depends on the bias voltage applied to the oxide electrodes.
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| 10. |
- Boikov, Y. A., et al.
(författare)
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Elastically strained and relaxed La0.67Ca0.33MnO3 films grown on lanthanum aluminate substrates with different orientations
- 2016
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Ingår i: Physics of the Solid State. - : Pleiades Publishing Ltd. - 1063-7834 .- 1090-6460. ; 58:12, s. 2560-2566
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Tidskriftsartikel (refereegranskat)abstract
- Structure of 40-nm thick La0.67Ca0.33MnO3 (LCMO) films grown by laser evaporation on (001) and (110) LaAlO3 (LAO) substrates has been investigated using the methods of medium-energy ion scattering and X-ray diffraction. The grown manganite layers are under lateral biaxial compressive mechanical stresses. When (110)LAO wafers are used as the substrates, stresses relax to a great extent; the relaxation is accompanied by the formation of defects in a (3-4)-nm thick manganite-film interlayer adjacent to the LCMO-(110)LAO interface. When studying the structure of the grown layers, their electro- and magnetotransport parameters have been measured. The electroresistance of the LCMO films grown on the substrates of both types reached a maximum at temperature T (M) of about 250 K. At temperatures close to T (M) magnetoresistance of the LCMO/(110)LAO films exceeds that of the LCMO/(001)LAO films by 20-30%; however, the situation is inverse at low temperatures (T < 150 K). At T < T (M) , the magnetotransport in the grown manganite films significantly depends on the spin ordering in ferromagnetic domains, which increase with a decrease in temperature.
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