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Intermodulation electrostatic force microscopy for imaging surface photo-voltage
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: 0000-0003-0675-974X
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0002-4331-6940
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 14, p. 143113-Article in journal (Refereed) Published
Abstract [en]

We demonstrate an alternative to Kelvin Probe Force Microscopy for imaging surface potential. The open-loop, single-pass technique applies a low-frequency AC voltage to the atomic force microscopy tip while driving the cantilever near its resonance frequency. Frequency mixing due to the nonlinear capacitance gives intermodulation products of the two drive frequencies near the cantilever resonance, where they are measured with high signal to noise ratio. Analysis of this intermodulation response allows for quantitative reconstruction of the contact potential difference. We derive the theory of the method, validate it with numerical simulation and a control experiment, and we demonstrate its utility for fast imaging of the surface photo-voltage on an organic photovoltaic material.

Place, publisher, year, edition, pages
2014. Vol. 105, no 14, p. 143113-
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-156990DOI: 10.1063/1.4897966ISI: 000344343900057Scopus ID: 2-s2.0-84908006009OAI: oai:DiVA.org:kth-156990DiVA, id: diva2:769072
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20141205

Available from: 2014-12-05 Created: 2014-12-04 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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