Dynamic magnetic characterizations at the nanoscale: A new mode for AFM imaging with magnetic sample modulation (MSM-AFM)

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© 2014 by Nova Science Publishers, Inc. Magnetic sample modulation combined with contact mode atomic force microscopy (AFM) provides a sensitive way to detect the vibration of magnetic nanomaterials at the level of individual nanoparticles or ferroproteins. Rather than using a coated AFM probe as a magnetic sensor, our strategy is to use a non-magnetic probe for contact mode AFM to characterize the vibration of superparamagnetic nanomaterials responding to the flux of an AC electromagnetic field. We refer to this hybrid imaging and measurement mode as magnetic sample modulation AFM (MSM-AFM). An alternating electromagnetic field induces the actuation of magnetic and superparamagnetic nanomaterials that are attached to surfaces, and the AFM tip is used to detect the sample vibration. For MSM-AFM, an oscillating magnetic field is produced by applying an AC current to a wire coil solenoid placed under the sample stage. The AFM is configured for contact mode imaging, and the probe is scanned slowly across the vibrating samples. Selected parameters of frequency and magnetic field strength can be tuned to study dynamic changes in the vibrational response of samples. The MSM-AFM imaging mode has been used successfully to detect the vibration of nanomaterials with dimensions less than 1.0 nm, and has been applied for measurements with ferritin, an iron-containing protein. Dynamic measurements can be accomplished by changing the modulation frequency and the strength of the applied electromagnetic field. With MSM-AFM, responses of both the amplitude and phase signal along with spatial maps of the topography channel can be collected simultaneously. The hybrid approach of combining MSM with contact mode AFM provides nanoscale characterizations for detecting the changes in vibrational resonance signatures, differences in vibrational amplitude versus size, and coupling effects of the magnetic response due to the proximity of adjacent magnetic nanomaterials.

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Atomic Force Microscopy (AFM): Principles, Modes of Operation and Limitations

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