Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D37: Focus Session: Complex Oxide Thin Films -- Oxide 2DEGs and Devices |
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Sponsoring Units: DMP GMAG Chair: Amlan Biswas, University of Florida Room: E147-E148 |
Monday, March 15, 2010 2:30PM - 3:06PM |
D37.00001: Observation of fractional quantum Hall effect in MgZnO/ZnO based heterostructures Invited Speaker: ZnO has been recognized as one of the key materials in Oxide Electronics, enabling UV emitters [1], thin film transistors, self-organized nanostructures, and spintronics. Among them, two-dimensional (2D) electron system at the MgZnO/ZnO heterointerfaces has attracted much attention for the device application of transparent field-effect transistors. The 2D electron gas (2DEG) at the interface is spontaneously generated by the polarization mismatch between MgZnO and ZnO layers. The first quantum Hall effect in oxides was observed for the 2DEG with an electron mobility of 5,500 cm$^{2}$V$^{-1}$s$^{-1}$ in pulsed-laser-deposition (PLD) grown MgZnO/ZnO [2]. The density of 2DEG could be tuned by the electrostatic field-effect [3] as well as the built-in Mg content [2]. By employing molecular beam epitaxy (MBE), the electron mobility could be enhanced to 20,000 cm$^{2}$V$^{-1}$s$^{-1}$ and detailed characteristics such as effective spin susceptibility were revealed [4]. The talk will cover the materials aspect, control of the 2D transport, enhancement of electron mobility over 100,000 cm$^{2}$V$^{-1}$s$^{-1}$, and quantum transport as well as fractional quantum Hall effect at low temperatures. This work has been carried out under the collaboration with the groups of M. Kawasaki, H. Ohno, and M. Shayegan. \\[4pt] [1] A. Tsukazaki \textit{et}.\textit{ al}., Nature Mater. \textbf{4}, 42 (2005). \\[0pt] [2] A. Tsukazaki \textit{et}.\textit{ al}., Science \textbf{315}, 1388 (2007). \\[0pt] [3] A. Tsukazaki \textit{et}.\textit{ al}., Appl. Phys. Lett. \textbf{93}, 241905 (2008). \\[0pt] [4] A. Tsukazaki \textit{et}.\textit{ al.}, Appl. Phys. Express \textbf{1}, 055004 (2008)., Phys. Rev. B \textbf{78}, 233308 (2008). [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D37.00002: Metal-insulator transitions in LaTiO$_{3}$ / CaTiO$_{3}$ superlattices Sung Seok A. Seo, Ho Nyung Lee Strongly correlated electrons at an interface of complex oxide heterostructures often show interesting behaviors that require an introduction of new physical concepts. For example, the metallic transport behavior found in the superlattices of a Mott insulator LaTiO$_{3}$ and a band insulator SrTiO$_{3}$ (STO) has established the concept of interfacial electronic reconstruction. In this work, we have studied the transport property of a new type of Mott/band insulator LaTiO$_{3}$/CaTiO$_{3}$ (LTO/CTO) superlattices grown by pulsed laser deposition (PLD). In order to rule out concerns about the PLD plume-triggered oxygen vacancies generated in STO substrates, which might influence transport measurement, and to investigate the effect of epitaxial strain, we have used insulating NdGaO$_{3}$ substrates. While both LTO and CTO single films are highly insulating, we have observed intriguing metal-insulator transitions (MIT) in the LTO/CTO superlattices depending on the global LTO/CTO thickness ratio and temperature. (Note that LTO/STO superlattices are metallic at all temperatures (2-300 K)). In this talk, we will discuss the origin of the MIT in the scheme of self compensation mechanism of $d$-electrons at the hetero-interface between LTO and CTO. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D37.00003: Two-dimensional electron gas at LaAlO$_{3}$/ SrTiO$_{3}$ heterointerfaces grown on silicon Jae-Wan Park, Daniela F. Bogorin, Cheng Cen, Christofer Nelson, Yi Zhang, Wung Bark, Chad Folkman, David Felker, Mark Rzchowski, Xiaoqing Pan, Jeremy Levy, Chang-Beom Eom Reversible nanoscale control over the metal-insulator transition in a two-dimensional electron gas (2DEG), formed at the heterointerface between LaAlO$_{3}$ and SrTiO$_{3}$, raises the possibility to develop ultrahigh-density oxide nanoelectronics. Prerequisites to the development of new technologies are integration with existing electronics platforms and scaling to a commercially available large wafer process. Here, we demonstrate the viability of 2DEGs formed at LaAlO$_{3}$/SrTiO$_{3}$ heterointerfaces grown directly on Si. We observe 2DEG behavior only when growth of LaAlO$_{3}$ layer occurs on post-annealed TiO$_2$-terminated SrTiO$_{3}$ template on (001) Si substrate. The ability to form reversible conducting nanostructures below ~10 nm-scales highlights the viability of this materials synthesis route for commercial device applications. Atomic-scale control of the surfaces of quasi-single-crystal SrTiO$_{3}$ templates on Si substrates also inspires the development of new oxide electronics using novel interfacial phenomena. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D37.00004: Rewritable superconducting nanostructures at the LaAlO$_{3}$/ SrTiO$_{3}$ interface Daniela F. Bogorin, Cheng Cen, Jeremy Levy We describe efforts to control the superconducting-insulator transition in LaAlO$_{3}$/ SrTiO$_{3}$ using a conducting AFM writing technique.\footnote{C. Cen, S. Thiel, K. E. Andersen, C. S. Hellberg, J. Mannhart, and J. Levy, Nature Materials \textbf{7}, 2136 (2008).}$^,$\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} Low temperature superconductivity of nanowires created at the 2DEG has been observed, corresponding to carrier densities $\approx$ 5x10$^{13}$ cm$^{-2}$. The ability control superconductivity in this fashion paves the way for new classes of superconducting devices. Support from DAPRA Seedling (W911NF-09-10258) and ARO MURI (W911NF-08-1-0317) and NHMFL is gratefully acknowledged. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D37.00005: Nanoscale rectification at the LaAlO$_3$/SrTiO$_3$ interface Adam Burch, Daniela F. Bogorin, Cheng Cen, Jeremy Levy, Jae-Wan Park, Chang-Beom Eom We report nanoscale electrical rectification in nanowires formed at the interface between LaAlO$_{3}$ and SrTiO$_{3}$. Using an AFM writing technique\footnote{C. Cen, S. Thiel, K. E. Andersen, C. S. Hellberg, J. Mannhart, and J. Levy, Nature Materials \textbf{7}, 2136 (2008).}$^,$\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} it is possible to create conducting nanoregions with a precision that approaches the atomic scale. Here we demonstrate how controlled asymmetries in the in-plane potential profile along a nanowire lead to controlled electrical rectification, similar to that observed in Schottky diodes. [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D37.00006: Low temperature Study of Oxide Nanostructures Ricki Garden, Cheng Cen, Jeremy Levy Nanoscale control of the metal-insulator transition at the interface between LaAlO$_{3}$ and SrTiO$_{3}$, which utilizes a conducting atomic force microscope (AFM) probe to define conducting and insulating regions, combines the precision and control of top-down lithographic approaches with the special quality resembling self-assembly of the material itself$^{1}$. Recently, a sketch based transistor (SketchFET) device was created with characteristic dimensions as small as 2 nm$^{2}$. Here we describe the low temperature transport measurement carried out on SketchFET devices with different structural modifications. Activation energies under different gating conditions is extracted from temperature dependent measurement. At low temperature, sharp peaks of tunneling current are observed and attributed to structural phase transitions in SrTiO$_{3}$. With an additional nanoisland in the middle, SketchFETs exhibit hysteretic and nonlinear behavior which is attributed to hysteretic charging in the nanoisland. [1] C. Cen, S. Thiel, K. E. Andersen, C. S. Hellberg, J. Mannhart, and J. Levy, Nature Materials \textbf{7}, 2136 (2008). [2] C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009) [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D37.00007: Energy dissipation of nanotransistors formed at the LaAlO$_{3}$/SrTiO$_{3}$ interface Patrick Irvin, Cheng Cen, Jeremy Levy, Jae-Wan Park, Chang-Beom Eom Nanoscale control of the metal-insulator transition at the interface between LaAlO$_{3}$ and SrTiO$_{3}$ can be used to create transistors with dimensions below projected limits for CMOS.\footnote{C. Cen, S. Thiel, K. E. Andersen, C. S. Hellberg, J. Mannhart, and J. Levy, Nature Materials \textbf{7}, 2136 (2008).}\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} In order to help determine the scalability of such transistors, we are attempting to characterize the dissipation mechanisms in transistor designs. Such a determination must distinguish power dissipated by the transistor from power dissipated in the oxide nanowire leads. We discuss noise cross correlation measurements designed to elucidate the mechanism for transistor switching, and attempt to quantify dissipation mechanisms during switching. [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:30PM |
D37.00008: Mechanism for writing and erasing nanostructures at the LaAlO$_{3}$/SrTiO$_{3}$ interface using vacuum AFM Feng Bi, Jeremy Levy, Daniela F. Bogorin Nanoscale control of the metal-insulator transition in LaAlO$_{3} $/SrTiO$_{3}$ heterostructure can be achieved using local voltages applied by a conducting AFM probe. One proposed mechanism for the writing process (C.S. Hellberg, unpublished) involves adsorbed H$_{2}$O which dissociates into OH$^{-}$ and H$^{+}$ which are then selectively removed by a biased AFM probe. To test this mechanism, writing and erasing experiments are performed in a vacuum AFM ($2\times10^{-5}$ Torr) using various gas mixtures. We find that it is not possible to write nanostructures in vacuum or in the presence of several gas mixtures that do not contain H$_{2}$O. [Preview Abstract] |
Monday, March 15, 2010 4:30PM - 4:42PM |
D37.00009: The effect of top LaAlO$_{3}$ surface treatment on the q-2DEGs at the LaAlO$_{3}$/ SrTiO$_{3}$ interface Shan Hu, Jeremy Levy, Cheng Cen, Daniela F. Bogorin We investigate the effect of various adsorbates on the ability to create and erase nanostructures at the LaAlO$_{3}$/SrTiO$_{3}$ interface. Our results show that when the top LaAlO$_{3}$ surface is made hydrophobic, the conductivity of nanostructures decays much slower than for hydrophilic treatments. This dependence provides further support that H$_{2}$O plays an important role in the writing and erasing process. [Preview Abstract] |
Monday, March 15, 2010 4:42PM - 4:54PM |
D37.00010: Rewritable nanoscale photodetector at the LaAlO$_{3}$/ SrTiO$_{3}$ interface Yanjun Ma, Patrick Irvin, Daniela Bogorin, Cheng Cen, Jeremy Levy It has been demonstrated by Cen. et al that a conducting nanowire can be written or erased at the interface between LaAlO$_{3}$ and SrTiO$_{3}$, using a conducting AFM writing technique.\footnote{C. Cen, S. Thiel, K. E. Andersen, C. S. Hellberg, J. Mannhart, and J. Levy, Nature Materials \textbf{7}, 2136 (2008).}$^,$\footnote{C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science \textbf{323}, 1026 (2009).} We show two-terminal and three-terminal junctions can behave as nanoscale photodetectors. Two-terminal nanowire junctions and three-terminal SketchFETs are excited locally with visible-IR light, and the photoconductive response is measured as a function of position and wavelength. The spatial sensitivity appears to be diffraction-limited, and the photoconductive response extends into the NIR. Both the mechanism and possible applications for this class of devices will be discussed. [Preview Abstract] |
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