Articles you may be interested inControlled manipulation of ethen molecules and lead atoms on Cu(211) with a low temperature scanning tunneling microscope

We present measurements of the nanoscale elastic and viscoelastic properties of samples of poly(methylmetacrylate) (PMMA)/rubber nanocomposites. For these studies we have used a new technique based on atomic force microscopy (AFM) with ultrasonic excitation, heterodyne force microscopy (HFM), which provides a means of testing the viscoelastic response of polymeric materials locally (in tip-probed regions) at MHz frequencies. Phase-HFM contrast distinguishes local differences in the dynamic response of PMMA/rubber composites. Comparison of HFM with other AFM-based techniques (ultrasonic force microscopy, friction force microscopy and force modulation microscopy), while imaging the same surface region, emphasizes the unique capabilities of HFM for these kinds of studies, and reveals key nanostructural characteristics of the composites. Some of the toughening particles appear to be broken down, with areas of PMMA detached from the surrounding matrix.

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We have manipulated raw and functionalized gold nanoparticles (with a mean diameter of 25 nm) on silicon substrates with dynamic atomic force microscopy (AFM). Under ambient conditions, the particles stick to silicon until a critical amplitude is reached by the oscillations of the probing tip. Beyond that threshold, the particles start to follow different directions, depending on their geometry and adhesion to the substrate. Higher and lower mobility were observed when the gold particles were coated with methyl- and hydroxyl-terminated thiol groups, respectively, which suggests that the adhesion of the particles to the substrate is strongly reduced by the presence of hydrophobic interfaces. Under ultrahigh vacuum conditions, where the water layer is absent, the particles did not move, even when operating the atomic force microscope in contact mode. We have also investigated the influence of the temperature (up to 150 degrees C) and of the geometrical arrangement of the particles on the manipulation process. Whereas thermal activation has an important effect in enhancing the mobility of the particles, we did not find differences when manipulating ordered versus random distributions of particles.