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Retention of Electronic Conductivity in LaAlO3/SrTiO3 Nanostructures Using a SrCuO2 Capping Layer
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0001-8199-5510
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0001-8534-6577
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2016 (English)In: PHYSICAL REVIEW APPLIED, ISSN 2331-7019, Vol. 6, no 2, article id 024011Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society , 2016. Vol. 6, no 2, article id 024011
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-193441DOI: 10.1103/PhysRevApplied.6.024011ISI: 000381486000002Scopus ID: 2-s2.0-84994620464OAI: oai:DiVA.org:kth-193441DiVA, id: diva2:1034597
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Institute
Note

QC 20161012

Available from: 2016-10-12 Created: 2016-10-03 Last updated: 2018-09-26Bibliographically approved
In thesis
1. Probing nonlinear electrical properties at the nanoscale: Studies in multifrequency AFM
Open this publication in new window or tab >>Probing nonlinear electrical properties at the nanoscale: Studies in multifrequency AFM
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanostructured materials promise great advances in diverse and active research fields such as energy harvesting and storage, corrosion prevention and high-density memories. Electrical characterization at the nanometer scale is key to understanding and optimizing the performance of these materials, and therefore central to the progress of nanotechnology. One of the most versatile tools for this purpose is the atomic force microscope (AFM), thanks to its ability to image surfaces with high spatial resolution.

In this thesis we present several multifrequency techniques for AFM. Intermodulation electrostatic force microscopy (ImEFM) measures the potential of a surface with low noise and high spatial resolution. In contrast to traditionally available methods, ImEFM does not use a feedback-controlled bias to measure the surface potential, and is therefore suitable to measurements in liquid environments. Removing feedback allows the applied bias to be used for investigating charge injection and extraction on nanocomposite materials. Intermodulation conductive AFM (ImCFM) measures the current-voltage characteristic of a sample at every point of an AFM image. ImCFM is able to separate the galvanic and displacement contributions to the measured current, improving the measurement speed by four orders of magnitude compared to previously available methods. We finally demonstrate an alternative approach to pump-probe spectroscopy, which allows the AFM to measure electrical charge dynamics with a time resolution approaching the nanosecond range.

These techniques are based on intermodulation spectroscopy, and they demonstrate the power and flexibility of measuring and analyzing nonlinear response in the frequency domain. The nonlinearity of the tip-surface force is used to concentrate response in a narrow band around the resonance of the AFM cantilever, where force measurement sensitivity is at the thermal limit. In this narrow band, we perform coherent measurements at multiple frequencies by exploiting the stability of a single reference oscillation. The power of the multifrequency approach is nicely demonstrated in a general method for measuring and compensating background forces, i.e. long-range linear forces that act on the body of the AFM probe. This compensation is necessary to reveal the the true force between the surface and the AFM tip. We show the effect of the compensation on soft polymer materials, where the background forces are typically strongest.

Abstract [sv]

Nanostrukturerade material utlovar stora framsteg inom olika forskningsområden som till exempel energiutvinning och lagring, korrosionförebyggande beläggningar och högdensitetsminnen. Elektrisk karakterisering på nanometerskalan är nyckeln till förståelse och optimering av ett materials prestanda, och därmed central för utvecklingen av nanoteknik. Ett av de mest mångsidiga verktygen för detta ändamål är atomkraftmikroskopet (AFM), tack vare dess förmåga att avbilda ytor med hög spatial upplösning.

I denna avhandling presenteras flera multifrekvenstekniker för AFM. Intermodulationselektrostatiskkraftmikroskopi (ImEFM) mäter en ytas ytpotential med lågt brus och hög upplösning. Till skillnad från traditionellt tillgängliga metoder behöver ImEFM inte någon återkopplingsstyrd spänning för att mäta ytpotentialen och är därför lämplig att använda för mätningar i vätska. Genom att ta bort återkopplingen kan den applicerade spänningen istället användas för att undersöka laddningsinjektion och extraktion hos nanokompositmaterial. Intermodulationsström AFM (ImCFM) mäter ström-spänningsegenskaperna hos ett prov vid varje punkt i en AFM-bild. ImCFM kan särskilja galvanisk- och förskjutningsström i mätningar, vilket förbättrar mäthastigheten med fyra storleksordningar jämfört med tidigare tillgängliga metoder. Vi visar slutligen ett alternativ till pump-probespektroskopi, som gör att AFM kan mäta elektrisk laddningsdynamik med en tidsupplösning som närmar sig nanosekunder.

Alla dessa tekniker bygger på intermodulationsspektroskopi, och de visar kraften och flexibiliteten med att mäta och analysera olinjära signal i frekvensområdet. Icke-linjäriteten hos kraften mellan en AFM-spets och en yta används för att koncentrera svaret i ett smalt frekvensband runt AFM-cantileverens resonans, där känsligheten för att mäta kraft är termiskt begränsad. I detta smala band utför vi koherenta mätningar vid flera frekvenser genom att utnyttja stabiliteten hos en enda referensoscillator. Fördelen med denna multifrekvensmetod demonstreras i en allmän metod för att mäta och kompensera bakgrundskrafter, linjära krafter som verkar över långt avstånd på hela AFM-cantilevern. Denna kompensation är nödvändig för att avslöja den sanna kraften mellan ytan och AFM-spetsen. Vi visar effekten av kompensationen på mjuka polymermaterial, där bakgrundskrafterna typiskt är starka.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 82
Series
TRITA-SCI-FOU ; 2018:38
Keywords
Atomic Force Microscopy, Nonlinear dynamics, Multifrequency, Contact potential difference, Conductance, Fast dynamics
National Category
Condensed Matter Physics Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-235315 (URN)978-91-7729-952-3 (ISBN)
Public defence
2018-10-26, FB42, Albanova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20180927

Available from: 2018-09-27 Created: 2018-09-26 Last updated: 2018-09-27Bibliographically approved

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