The force modulation microscopy (FMM) mode of scanning probe microscopy is often used to characterize hard and soft regions of heterogeneous polymer films. The FMM mode can acquire information of the mechanical properties of samples along with information of topography. Phase and amplitude images are acquired simultaneously with topography frames that sensitively disclose fine details of the surface morphology. For FMM, the scanner is operated in contact-mode while the sample stage is driven to vibrate. For our investigations, a home-built FMM sample stage was constructed with a piezoactuator located underneath the sample to drive the sample vibration. The magnitude and frequency of vibration can be controlled according to selected parameters of the driving AC signal. As the tip is scanned in contact with the vibrating surface, the force applied by the probe is modulated according to the hardness or softness of sample domains. When characterizing core-shell nanoparticles of cobalt encapsulated within a film of polystyrene, we found that the hard core of the metal nanoparticles could be sensitively imaged using FMM at resonant frequencies. Essentially, FMM enabled discrimination of subsurface features of polymer-coated cobalt nanoparticles. Particle lithography was applied for preparing samples to organize the arrangement of nanoparticles into circular rings on surfaces of Si(111). Successful FMM characterizations were achieved reproducibly for nanoparticle samples with exquisite resolution at the level of individual nanoparticles measuring 30 nm in diameter. 

Subsurface imaging of the metal cores of polymer coated cobalt nanoparticles with force modulation microscopy

247th National Meeting (2014)

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