| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Boikov, Yu A., et al.
(författare)
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Structure and magneto-transport parameters of partially relaxed and coherently grown La0.67Ba0.33MnO3 films
- 2013
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Ingår i: Physics of the Solid State. - 1063-7834 .- 1090-6460. ; 55:10, s. 2043-2050
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction (XRD) and medium-energy ion scattering (MEIS) have been used to reveal distortions in the crystal lattice of La0.67Ba0.33MnO3 (LBMO) films formed in relaxation of mechanical stresses. The LBMO films 25 nm thick have been prepared by laser deposition. The XRD and MEIS data obtained suggest that biaxially and mechanically elastically stressed LBMO layers grow coherently on LSATO substrates, whose crystal lattice parameter differs only weakly from the corresponding LBMO parameter, whereas in the bulk of manganite films grown on LaAlO3 substrates, stresses relax partially. Stresses do not relax in the LBMO interface about 4 nm thick adjoining LaAlO3. The electro- and magneto-transport parameters of partially relaxed LBMO films have been compared with those obtained for coherently grown manganite films with approximately the same tetragonal distortion of the lattice cell (a (aSyen)/a (aEuro-) = 1.024-1.030; a (aEuro-) and a (aSyen) are the unit cell parameters in the substrate plane and normal to it, respectively). At temperatures substantially lower than the Curie temperature, the electrical resistivity rho of LBMO films fits the relation rho = rho(0) + rho(1) T (2) + rho(2)(H)T (4.5); the coefficients rho(0) and rho(1) do not depend on temperature T and magnetic field, and rho(2) does not depend on temperature but almost linearly decreases with increasing magnetic field strength H. The coefficient rho(2) for partially relaxed LBMO films is substantially larger than that for coherently grown manganite layers.
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| 5. |
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| 6. |
- Han, Kyoo-Hyun, et al.
(författare)
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Proton bombardment of Hard Carbon
- 2006
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Ingår i: Fullerenes, Nanotubes and Carbon Nanostructures vol. 14 issue 2&3. - : Informa UK Limited. ; , s. 381-384
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Konferensbidrag (refereegranskat)
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| 7. |
- 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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| 8. |
- 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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| 9. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Electrical and structural properties of ABO3/SrTiO3 interfaces
- 2012
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Ingår i: Materials Research Society Symposium Proceedings. - Warrendale, Pa. : Springer Science and Business Media LLC. - 0272-9172. - 9781605114316 ; 1454, s. 167-172, s. 167-172
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Konferensbidrag (refereegranskat)abstract
- Electrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2 terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.
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| 10. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Improved cationic stoichiometry and insulating behavior at the interface of LaAlO3/SrTiO3 formed at high oxygen pressure during pulsed-laser deposition
- 2011
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- Medium-energy ion spectroscopy, MEIS, and scanning transmission electron microscopy, STEM, were used to correlate the atomic structure of LaAlO3/SrTiO3 interfaces with their electrical properties. Interfaces were prepared at high (5x10(-2) mbar) and low (10(-4) mbar) oxygen pressure by pulsed-laser deposition. The high-oxygen-pressure heterostructures were insulating for all thicknesses while the low-oxygen-pressure ones became metallic for thicknesses above 4 unit cells. MEIS data show enhancement of the Sr surface peak and suppression of the La one in interfaces prepared at low oxygen pressure, which is interpreted as a La-Sr intermixing. The effect was considerably smaller in high-oxygen-pressure samples. Analysis of high-angle annular-dark-field STEM images of the LAO films also indicates intermixing between La and Sr in low-oxygen-pressure samples, supporting MEIS data. Our results reveal the important role of oxygen pressure on the formation of the interface electron gas. Copyright (C) EPLA, 2011
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