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Fast multifrequency measurement of nonlinear conductance
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0001-8199-5510
Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden.
Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden.ORCID iD: 0000-0003-2935-1165
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0001-8534-6577
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Low noise measurement of small currents in nanometer-scale junctions is of central importance to the characterization of novel high-performance devices and materials for applications ranging from energy harvesting and energy conversion to topological materials for quantum computers. The high resistance of these junctions and the stray capacitance of their measurement leads impose speed limitations (tens of seconds) on the traditional methods of measuring their nonlinear conductance, making detailed investigations of change with external fields or maps of variation over a surface impractical, if not impossible. Here we demonstrate fast (milliseconds) reconstruction of nonlinear current-voltage characteristics from phase-coherent multifrequency lock-in data using the inverse Fourier transform. The measurement technique allows for separation of the galvanic and displacement currents in the junction and easy cancellation of parasitic displacement current due to the measurement leads. We use the method to reveal nanometer-scale variations in the electrical transport properties of organic photovoltaic and semiconducting thin films. The method has broad applicability and its wide-spread implementation promises advancement in high-speed and high-resolution characterization for nanotechnology.

National Category
Condensed Matter Physics Nano Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-235359OAI: oai:DiVA.org:kth-235359DiVA, id: diva2:1250403
Note

QC 20180927

Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2018-09-27Bibliographically 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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arXiv:1809.07671 [cond-mat.mes-hall]

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