Using a home-built frictional force microscope that is able to detect forces in three dimensions with a lateral force resolution down to 15 pN, we have studied the energy dissipation between a tungsten tip sliding over a graphite surface in dry contact. By measuring atomic-scale friction as a function of the rotational angle between two contacting bodies, we show that the origin of the ultralow friction of graphite lies in the incommensurability between rotated graphite layers, an effect proposed under the name of ''superlubricity'' [M.
Graphite is known to be a good solid lubricant. The low-friction behavior is commonly ascribed to the low resistance to shear. Using a home-built frictional force microscope that is able to detect forces in three dimensions, we have studied the energy dissipation between a tungsten tip sliding over a graphite surface in dry contact. By measuring atomic-scale friction as a function of the rotational angle between two contacting bodies we show that the origin of the ultra-low friction of graphite lies in the incommensurability between rotated graphite layers, an effect proposed under the name of ‘superlubricity’.
Adhesion forces between a gold sphere and flat gold substrate are studied using atomic force microscopy in different environments. The pull-off force measured in a vacuum is found to be a small fraction of that in ambient air or nitrogen atmosphere. Calculations of capillary condensation forces, including the effects of elastic deformation of the contacting bodies and of adsorption layers, reveal that the meniscus force is the dominant source of the observed difference in pull-off forces. The experimental data show that nitrogen purge does not eliminate the meniscus contribution to the pull-off force.
This chapter outlines procedures for sample preparation and the determination of nanoparticle size using atomic force microscopy (AFM). Several procedures for dispersing gold nanoparticles on various surfaces such that they are suitable for imaging and height measurement via intermittent contact mode, or tapping mode, AFM are first described. The methods for AFM calibration and operation to make such measurements are then discussed. Finally, the techniques for data analysis and reporting are provided. The nanoparticles cited are National Institute of Standards and Technology (NIST) Au nanoparticle Reference Materials RM 8011 (nominally 10 nm particles), RM 8012 (nominally 30 nm), and RM 8013 (nominally 60 nm).
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