TY - JOUR A1 - Krivcov, Alexander A1 - Junkers, Tanja A1 - Möbius, Hildegard T1 - Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single superparamagnetic nanoparticle resolution JF - Journal of Physics Communications N2 - The detection of superparamagnetic nanoparticles by magnetic force microscopy (MFM) at the single particle level faces difficulties such as superposition of nonmagnetic signals caused by electrostatic interactions as well as reaching the resolution limits due to small magnetic interactions. In MFM the magnetic force is measured at a certain distance to the substrate following the topography measured in a first scan to avoid an influence of short range forces (lift mode). In this work we showed that performing MFM on superparamagnetic nanoparticles the increase of the tip-substrate distance above the nanoparticle in lift mode scans leads to a reduction of the electrostatic forces resulting in a positive phase shift in contrast to the negative phase shift of the attractive magnetic force. Identifying the electrostatic force in MFM on nanoparticles as a capacitive coupling effect between tip and substrate the origin of often seen topography mirroring in phase images of nanoparticles in general is theoretically explained and experimentally proved. Minimization of the capacitive coupling by adjusting the work function difference between tip and substrate as well as using an optimized tip allows the magnetic visualization of single 10 nm superparamagnetic iron oxide nanoparticles (SPIONs) at ambient conditions with and without an external magnetic field. KW - Electrostatic forces KW - Capacitive coupling KW - Magnetic force microscopy Y1 - 2018 U6 - https://doi.org/10.1088/2399-6528/aad3a4 SP - 2 EP - 13 ER - TY - JOUR A1 - Möbius, Hildegard A1 - Fuhrmann, Marc T1 - Influence of dielectric layer thickness and roughness on topographic effects in magnetic force microscopy JF - Beilstein Journal of Nanotechnology N2 - Magnetic force microscopy (MFM) has become a widely used tool for the characterization of magnetic properties. However, the magnetic signal can be overlapped by additional forces acting on the tip such as electrostatic forces. In this work the possibility to reduce capacitive coupling effects between tip and substrate is discussed in relation to the thickness of a dielectric layer introduced in the system. Single superparamagnetic iron oxide nanoparticles (SPIONs) are used as a model system, because their magnetic signal is contrariwise to the signal due to capacitive coupling so that it is possible to distinguish between magnetic and electric force contributions. Introducing a dielectric layer between substrate and nanoparticle the capacitive coupling can be tuned and minimized for thick layers. Using the theory of capacitive coupling and the magnetic point dipole–dipole model we could theoretically explain and experimentally prove the phase signal for single superparamagnetic nanoparticles as a function of the layer thickness of the dielectric layer. Tuning the capacitive coupling by variation of the dielectric layer thickness between nanoparticle and substrate allows the distinction between the electric and the magnetic contributions to the MFM signal. The theory also predicts decreasing topographic effects in MFM signals due to surface roughness of dielectric films with increasing film thickness. KW - Capacitive coupling KW - Electrostatic effects KW - Magnetic force microscopy KW - Nanoparticles KW - Superparamagnetic iron oxide nanoparticle (SPION) Y1 - 2019 U6 - https://doi.org/10.3762/bjnano.10.106 IS - 2019/10 SP - 1056 EP - 1064 ER - TY - JOUR A1 - Möbius, Hildegard A1 - Fuhrmann, Marc T1 - Magnetic Imaging of Encapsulated Superparamagnetic Nanoparticles by Data Fusion of Magnetic Force Microscopy and Atomic Force Microscopy Signals for Correction of Topographic Crosstalk N2 - Encapsulated magnetic nanoparticles are of increasing interest for biomedical applications. However, up to now, it is still not possible to characterize their localized magnetic properties within the capsules. Magnetic Force Microscopy (MFM) has proved to be a suitable technique to image magnetic nanoparticles at ambient conditions revealing information about the spatial distribution and the magnetic properties of the nanoparticles simultaneously. However, MFM measurements on magnetic nanoparticles lead to falsifications of the magnetic MFM signal due to the topographic crosstalk. The origin of the topographic crosstalk in MFM has been proven to be capacitive coupling effects due to distance change between the substrate and tip measuring above the nanoparticle. In this paper, we present data fusion of the topography measurements of Atomic Force Microscopy (AFM) and the phase image of MFM measurements in combination with the theory of capacitive coupling in order to eliminate the topographic crosstalk in the phase image. This method offers a novel approach for the magnetic visualization of encapsulated magnetic nanoparticles. KW - Atomic force microscopy KW - Magnetic force microscopy KW - Hybrid nanoparticles KW - Polystyrene KW - Data fusion Y1 - 2020 U6 - https://doi.org/10.3390/nano10122486 IS - 10 SP - 1 EP - 11 ER -