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The physics of conducting interfaces in insulating heterostructures

Applicant Willmott Philip
Number 146015
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Material Sciences
Start/End 01.05.2013 - 30.04.2014
Approved amount 56'740.00
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Keywords (7)

strongly correlated electron-systems; oxide electronics ; synchrotron radiation; complex metal oxides; interfacial physics; pulsed laser deposition ; surface x-ray diffraction

Lay Summary (German)

Lead
Der Struktur und die chemische Zusammensetzung von SrTiO3-Duennschichten, die auf SrTiO3 Einzelkristall-Substrate gewachsen sind werden mittels Synchrotronlicht und die komplementaren Methoden "low-energy ion scattering" (LEIS) und "Rutherford backscattering" (RBS) untersucht, um besser zu verstehen, wie Abweichungen von ein idealen Chemie und Kristallinitaet die physikalische Eigenschaften beeinflussen.
Lay summary

Die Grenzflaeche zwischen die zwei isolatoren SrTiO3 (STO) und LaAlO3 (LAO) ist  leitend. Der Grund fuer die Enstehung dieser sehr duennen Schicht ist nach fast 10 Jahren immer noch unklar. Es gibt aber zwei weitere und verwandte Resultate, naemlich 1) est ist niemanden gelungen, mehr als ein leitende Schicht uebereinander zu wachsen; und 2) wenn mehr als 3 oder 4 Monolagern von STO abgeschieden sind, bevor man die LAO darauf abscheidet, ist die Grenzflaeche nicht mehr leitend. Man meint, dass wenn diese Phaenomene verstanden sind, wird auch der Grund fuer die Leitfaehigkeit an der STO/LAO-Grenzflaeche klar. 

Diese Arbeit probiert das Wachstum von STO auf STO-Kristallen (sogenannte "Homoepitaxie") zu untersuchen, und wie dieses Wachstum die nachfolgende Abscheidung von LAO darauf beeintraechtigt. Um dieses zu realisieren werden die folgende Techniken verwendet: Oberflaeche-Roentgenbeugung (SXRD), "low-energy ion scattering" (LEIS), "Rutherford backscattering" (RBS), und "atomic-force microscopy" (AFM). Falls das Wachstum von STO auf STO doch perfekt kontrolliert werden kann, werden auch Multischichten von STO und LAO (d.h. STO/LAO/STO/LAO, usw.) gewachsen werden, um Leitfaehigkeit von mehreren Grenzflaechen zu demonstrieren.  

Direct link to Lay Summary Last update: 26.03.2013

Lay Summary (English)

Lead
The structure and chemical composition of SrTiO3 thin films grown on top of a nominally identical SrTiO3 single-crystal substrate will be investigated using synchrotron x-ray diffraction techniques, plus complementary methods such as low-energy ion scattering (LEIS) and Rutherford backscattering (RBS) in an attempt to understand deviations from perfect crystallinity and chemistry during film growth.
Lay summary

The interface between the two insulating materials SrTiO3 (STO) and LaAlO3 (LAO) has been shown to be conducting. The reason for the formation of this very thin metallic layer is still disputed. Two peculiar results are 1) when attempts are made to grow several of these layers on top of each other (i.e., STO/LAO/STO/LAO, etc), only the bottom interface is conducting; and 2) when more than three or four monolayers of STO is grown on top of STO before the first layer of LAO is grown, conductivity is suppressed. It is thought that if these phenomena are understood, this will contribute significantly in understanding the physics of this intriguing interface. 

This proposal attempts to discover why this is so by investigating the structure of STO grown homoepitaxially on STO, plus how this added layer affects the subsequent growth of LAO. This will be performed using synchrotron-based surface x-ray diffraction, low-energy ion scattering (LEIS), Rutherford backscattering (RBS), and atomic-force microscopy. If control of the film properties can be perfected, multilayer conductivity will be attempted and the transport properties investigated using four-point conductivty measurements. 

Direct link to Lay Summary Last update: 26.03.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Chemistry and structure of homoepitaxial SrTiO3 films and their influence on oxide-heterostructure interfaces
Reinle-Schmitt ML, Cancellieri C, Cavallaro A, Harrington GF, Leake SJ, Pomjakushina E, Kilner JA, Willmott PR (2014), Chemistry and structure of homoepitaxial SrTiO3 films and their influence on oxide-heterostructure interfaces, in Nanoscale, 6, 2598-2602.
Cluster method for analysing surface X-ray diffraction data sets using area detectors
Leake SJ, Reinle-Schmitt ML, Kalichava I, Pauli SA, Willmott PR (2014), Cluster method for analysing surface X-ray diffraction data sets using area detectors, in Journal of Applied Crystallography, 47, 207-214.
Doping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission
Cancellieri C, Reinle-Schmitt ML, Kobayashi M, Strocov VN, Willmott PR, Fontaine D, Ghosez P, Filippetti A, Delugas P, Fiorentini V (2014), Doping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission, in Physical Review B Rapid Communications, 89, 121412.

Collaboration

Group / person Country
Types of collaboration
Andrea Cavallero/Imperial College Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Professor Jean-Marc Triscone/University of Geneva Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Dr. Vladimir Strocov/Paul Scherrer Institut Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Associated projects

Number Title Start Funding scheme
126901 The physics of conducting interfaces in insulating heterostructures 01.05.2010 Project funding (Div. I-III)
117615 Interfacial properties of perovskite thin films 01.10.2007 Project funding (Div. I-III)

Abstract

Since its discovery in 2004, the phenomenon of the formation of 2-dimensional conducting layers at the interface between two insulating metal oxides has been the subject of intense research. The reason for the enormous interest these systems have provoked is due to their possible application in novel and highly versatile electronic applications and circuitry based on metal oxides, for which a very broad range of physical properties exist, despite their often very similar crystallographic structures. However, in 2009, there remain many fundamental questions, as new and unexpected results are reported. One of the problems in investigating such systems is that the regions of interest, that is, the interface, is by its very nature embedded in a solid. This makes electronic studies such as photoelectron spectroscopy very problematic (and is further exacerbated by the fact that the conducting interface lies between insulating layers), while scanning probe techniques such as scanning tunneling microscopy or atomic force microscopy are completely excluded. On the other hand, structural studies using x-rays provide a very powerful probe, as x-rays can penetrate deeply into material, and their wavelengths are such that sub-atomic resolution is provided. The Swiss Light Source at the Paul Scherrer Institut provides highly brilliant x-radiation, ideal for such investigations. At the Surface Diffraction station of the Materials Science beamline at the SLS (of which the applicant is the Beamline Manager), a unique combination of experimental equipment exists, whereby surface x-ray diffraction (SXRD) can be performed on these interfaces and, importantly, this can be done as the interface is being fabricated, such that the change in the structure can be monitored in steps well under a single monolayer of growth. This has been made possible on the one hand by a custom-made and dedicated growth chamber, with exactly this application in mind, and on the other, on the availability of a novel photon-counting 2-D x-ray pixel detector, a development which has revolutionized SXRD in the last three to four years. Very recent results by the group of the applicant for this grant have demonstrated that a novel and as yet unconsidered process is responsible for the formation of 2-dimensional conductivity. It is the goal of this project to investigate this using SXRD and the available facilities at the Surface Diffraction station of the SLS, both to probe the growth dynamics and surface/interfacial chemical kinetics, and to provide a detailed structural model at all stages of the formation of the conducting interface.
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