3 results
Tunability of Artificial Interface Phases in LaAlO3/SrTiO3 Heterostructures
- Mark Huijben, Jeroen Huijben, Guus Rijnders, Dave H.A. Blank, Alexander Brinkman, Hans Hilgenkamp
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1000 / 2007
- Published online by Cambridge University Press:
- 12 July 2019, 1000-L05-02
- Print publication:
- 2007
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This is a copy of the slides presented at the meeting but not formally written up for the volume.
AbstractResearch into new concepts for oxide-electronic devices has been enriched by the emerging field of functional interfaces. A high control of the materials down to the atomic level enables the improvement of existing oxide devices, like magnetic tunnel junctions, but also the formation of new artificial interface phases. Previous work revealed the existence of a metallic electron gas at the interface between the two band-insulators, LaAlO3 and SrTiO3, for a certain atomic arrangement [1,2]. Several studies on single epitaxial connections between LaAlO3 and SrTiO3 have revealed them to be either high-mobility electron conductors or insulating, depending on the atomic stacking sequences. An important point to take into account is the formation of oxygen vacancies for low deposition pressures (<10-5 mbar). For this growth regime the transport properties are fully dominated by the presence of the oxygen vacancies. In this talk we will show a detailed investigation of the controllable electronic properties of coupled interfaces in SrTiO3-LaAlO3-SrTiO3 heterostructures. Recently we reported a critical separation distance of 6 perovskite unit cell layers (~23 Å) for the electronic coupling of closely-spaced complementary interfaces in SrTiO3/LaAlO3 multilayer structures [3]. We showed that a decrease of the interface conductivity and carrier density occurs when the LaO:TiO2 and AlO2:SrO interfaces are brought closer together. Interestingly, the high carrier mobilities characterizing the separate conducting interfaces were found to be maintained in such coupled structures down to sub-nanometer interface spacing. Here, we will explain in more detail the electronic properties of the closely spaced LaO:TiO2 and AlO2:SrO interfaces below the critical separation distance. The carrier density at room temperature for dLAO5 is similar to a single LaO:TiO2 interface and has a value of ~1.5X1014 cm-2, corresponding to ~0.23 electrons per unit cell area on the LaO:TiO2 interface. In this, the contribution by the AlO2:SrO interface to the sheet carrier density is neglected, due to its much lower conductivity. When both interfaces are brought closer to each other the electronic coupling between them is increased and the charge density at room temperature is reduced to 0.15, 0.11 and 0.07 electrons per unit cell area for a spacing of respectively 3, 2 and 1 unit cells. However, for lower temperatures the sheet carrier density decreases and becomes constant for all coupled heterostructures at temperatures below 10 K. This constant low temperature carrier density has a value of 2.0×1013 cm-2 and corresponds to 0.003 electrons per unit cell area. These results show the ability to control the electronic properties in SrTiO3 heterostructures and to vary the carrier density homogeneously over the interface.
Monitoring oxide thin film growth with in-situ atomic force microscopy
- Joska Broekmaat, Frank Roesthuis, Alexander Brinkman, Horst Rogalla, Dave H.A. Blank, Guus Rijnders
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- Journal:
- MRS Online Proceedings Library Archive / Volume 967 / 2006
- Published online by Cambridge University Press:
- 11 June 2019, 967-U04-02
- Print publication:
- 2006
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This is a copy of the slides presented at the meeting but not formally written up for the volume.
AbstractComplex oxides exhibit various physical properties such as ferromagnetism, dielectricity, and superconductivity. The nature of these physical properties is determined by very small characteristic length scales. Future heteroepitaxial devices based on such oxides have great potential for applications provided that the growth can be controlled on an atomic level.Currently, in-situ growth morphology characterization is mostly performed by diffraction techniques such as Reflection High Energy Electron Diffraction (RHEED). We have now realized a system, in which Atomic Force Microscopy (AFM) can be performed during Pulsed Laser Deposition (PLD). Deposition and force microscopy are performed in one vacuum chamber and via a fast transfer (in the order of seconds) the surface of a sample can be scanned. In our system we take advantage of the pulsed deposition process, because microscopy measurements can be carried out between the pulses. This provides real-time morphology information on the microscopic scale during growth. The transfer mechanism allows switching between microscopy and deposition with a re-position accuracy of ±500 nm which gives new opportunities to study growth processes. This system is especially useful to study crystal growth, phase transitions, diffusion processes and nanoparticle formation. Furthermore, it will provide information if RHEED is not possible, for example during amorphous and polycrystalline growth. In this contribution, we will present the results obtained with a few model systems on oxide surfaces. We have used treated SrTiO3 (001) oxide substrates with 0.4 nm high substrate steps which are ideal for these experiments. Several materials are currently investigated, such as Au, SrRuO3, PbTiO3 and transparent conducting indium tin oxide. The in-situ AFM has been used to study the initial growth of these materials at various deposition conditions. The physical properties of these materials are correlated with the growth conditions, such as deposition pressure, fluency and substrate temperature. Besides showing the growth results obtained with the AFM, the latest equipment developments will be presented. To scan at elevated temperatures, small heaters have been developed. These small thermal mass heaters are designed in such a way to obtain stable monitoring settings at temperatures >973K in a high pressure environment or even ambient pressure. With high temperature microscopy, growth characterization at typical deposition conditions of complex oxides becomes feasible.
Peculiar Features of the Dielectric Response in Lead Scandium Tantalate Pb(Sc1/2Ta1/2)O3 Thin Films
- Kyle Brinkman, Alexander Tagantsev, Vladimir Cherman, Yongli Wang, Nava Setter, Stanislav Kamba, Jan Petzelt
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- Journal:
- MRS Online Proceedings Library Archive / Volume 966 / 2006
- Published online by Cambridge University Press:
- 26 February 2011, 0966-T07-37
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- 2006
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An examination of the low temperature (20 K) dielectric permittivity revealed dispersion between the MHz and THz frequencies in both disordered and ordered Pb(Sc1/2Ta1/2)O3 (PST) thin films. The difference between the lattice contribution in the THz regime and that measured in the MHz regime at extremely low temperatures points to the peculiar contribution of polar regions which maintain their mobility on cooling. Experiments measuring the permittivity upon cooling under an electric bias field revealed an additional peculiar feature of polar regions in disordered PST thin films: the application of a DC field of 30kV/cm failed to induce a phase transition to a long range polar state.