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Note: The intermodulation lockin analyzer
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.ORCID iD: 0000-0002-5923-0279
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.
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2011 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 2, 026109- p.Article in journal (Refereed) Published
Abstract [en]

Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.

Place, publisher, year, edition, pages
2011. Vol. 82, no 2, 026109- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-31596DOI: 10.1063/1.3541791ISI: 000287813400082Scopus ID: 2-s2.0-79952143423OAI: oai:DiVA.org:kth-31596DiVA: diva2:406373
Funder
Swedish Research Council
Note

QC 20110325

Available from: 2011-03-25 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Reconstructing force from harmonic motion
Open this publication in new window or tab >>Reconstructing force from harmonic motion
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High-quality factor oscillators are often used in measurements of verysmall force since they exhibit an enhanced sensitivity in the narrow frequencyband around resonance. Forces containing frequencies outside this frequencyband are often not detectable and the total force acting on the oscillatorremains unknown. In this thesis we present methods to eciently use theavailable bandwidth around resonance to reconstruct the force from partialspectral information.We apply the methods to dynamic atomic force microscopy (AFM) wherea tip at the end of a small micro-cantilever oscillates close to a sample surface.By reconstructing the force between the tip and the surface we can deducedierent properties of the surface. In contrast, in conventional AFM only oneof the many frequency components of the time-dependent tip-surface forceallowing for only qualitative conclusions about the tip-surface force.To increase the number of measurable frequency components we developed Intermodulation AFM (ImAFM). ImAFM utilizes frequency mixing ofa multifrequency drive scheme which generates many frequencies in the response to the nonlinear character of the tip-surface interaction. ImAFM,amplitude-modulated AFM and frequency-modulated AFM can be considered as special cases of narrow-band AFM, where the tip motion can bedescribed by a rapidly oscillating part and a slowly-varying envelope function. Using the concept of force quadratures, each rapid oscillation cycle canbe analyzed individually and ImAFM measurements can be interpreted as arapid measurement of the dependence of the force quadratures on the oscillation amplitude or frequency. To explore the limits of the force quadraturesdescription we introduce the force disk which is a complete description of thetip-surface force in narrow-band AFM at xed static probe height.We present a polynomial force reconstruction method for multifrequencyAFM data. The polynomial force reconstruction is a linear approximativeforce reconstruction method which is based on nding the parameters of amodel force which best approximates the tip-surface force. Another classof reconstruction methods are integral techniques which aim to invert theintegral relation between the tip-surface force and the measured spectraldata. We present an integral method, amplitude-dependence force spectroscopy (ADFS), which reconstructs the conservative tip-surface force fromthe amplitude-dependence of the force quadratures. Together with ImAFMwe use ADFS to combine high-resolution AFM imaging at high speeds withhighly accurate force measurements in each point of an image. For the measurement of dissipative forces we discuss how methods from tomography canbe used to reconstruct forces that are a function of both tip position andvelocity.The methods developed in this thesis are not limited to dynamic AFM andwe describe them in the general context of a harmonic oscillator subject to anexternal force. We hope that theses methods contribute to the transformationof AFM from a qualitative imaging modality into quantitative microscopy andwe hope that they nd application in other measurements which exploit theenhanced sensitivity of a high-quality factor oscillator.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. v, 91 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:21
Keyword
oscillator, force spectroscopy, atomic force microscopy, intermodulation, multifrequency, inverse problem, high quality factor
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-122583 (URN)978-91-7501-792-1 (ISBN)
Public defence
2013-06-14, FA31, Albanova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20130527

Available from: 2013-05-27 Created: 2013-05-23 Last updated: 2013-05-27Bibliographically approved

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Platz, DanielForchheimer, DanielHaviland, David B.

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