Cantilever properties and noise figures in high-resolution non-contact atomic force microscopy

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Titel: Cantilever properties and noise figures in high-resolution non-contact atomic force microscopy
Autor(en): Lübbe, Jannis Ralph Ulrich
Erstgutachter: Prof. Dr. Michael Reichling
Zweitgutachter: Prof. Dr. Ernst Meyer
Zusammenfassung: Different methods for the determination of cantilever properties in non-contact atomic force microscopy (NC-AFM) are under investigation. A key aspect is the determination of the cantilever stiffness being essential for a quantitative NC-AFM data analysis including the extraction of the tip-surface interaction force and potential. Furthermore, a systematic analysis of the displacement noise in the cantilever oscillation detection is performed with a special focus on the thermally excited cantilever oscillation. The propagation from displacement noise to frequency shift noise is studied under consideration of the frequency response of the PLL demodulator. The effective Q-factor of cantilevers depends on the internal damping of the cantilever as well as external influences like the ambient pressure and the quality of the cantilever fixation. While the Q-factor has a strong dependence on the ambient pressure between vacuum and ambient pressure yielding a decrease by several orders of magnitude, the pressure dependence of the resonance frequency is smaller than 1% for the same pressure range. On the other hand, the resonance frequency highly depends on the mass of the tip at the end of the cantilever making its reliable prediction from known cantilever dimensions difficult. The cantilever stiffness is determined with a high-precision static measurement method and compared to dimensional and dynamic methods. Dimensional methods suffer from the uncertainty of the measured cantilever dimensions and require a precise knowledge its material properties. A dynamic method utilising the measurement of the thermally excited cantilever displacement noise to obtain cantilever properties allows to characterise unknown cantilevers but requires an elaborative measurement equipment for spectral displacement noise analysis. Having the noise propagation in the NC-AFM system fully characterised, a proposed method allows for spring constant determination from the frequency shift noise at the output of the PLL demodulator with equipment already being available in most NC-AFM setups.
Schlagworte: non-contact atomic force microscopy; NC-AFM; cantilever; eigenfrequency; resonance frequency; spring constant; stiffness; Q-factor; quality factor; thermal excitation; noise; mounting loss; tip mass; ambient pressure; feedback loop; filter; noncontact atomic force microscopy; spectral analysis; PLL; FM-AFM
Erscheinungsdatum: 3-Apr-2013
Lizenzbezeichnung: Namensnennung 3.0 Unported
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Publikationstyp: Dissertation oder Habilitation [doctoralThesis]
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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