No abstract

This paper has investigated the dynamic behavior of a cylindrically shaped DNA nanoparticle during its displacement on a rough substrate by an atomic force microscope. Due to the cylindrical geometry of the DNA nanoparticle, two multi-asperity models have been considered for the adhesion between nanoparticle and rough substrate. The two selected models for the contact between smooth and rough surfaces have been further developed for cylindrical geometries. One of these models is analytical and based on uniform asperities and the other one is based on random asperities. Also, in each of these models, the real area of contact between particle and rough substrate has been calculated based on the number of asperities in contact. Then, a 3D dynamic model for the manipulation of cylindrical nanoparticle on rough substrate has been developed and simulated. The maximum difference between the results obtained from the two multiasperity models is \5 %, indicating a good agreement between the two models. The comparison of critical forces indicates that the critical force necessary for moving a particle is smaller for rough substrates than for smooth substrates and larger compared to the critical force obtained from the Rabinovich model, which is singleasperity model. Finally, the surface roughness parameters were estimated from the topographic images, and the manipulation process was simulated for these substrates by developing the relevant equations. The obtained results indicated that the critical force for a substrate with a higher root-mean-square roughness is smaller and particles can be moved easier on such a substrate.

The exact positioning of micro/nanoparticles is essential in the construction of micro/nanoscale structures. Of course, the shape of a particle and the external force application location on it influence the type of behavior exhibited by that particle during its displacement on a surface. In former works, biological and non-biological particles have been modeled as cylindrical or spherical particles, while the shape of many such particles is a combination of these two geometries. In this paper, the driving and displacement of particles with circular crowned roller geometry on a substrate by means of an AFM cantilever tip have been modeled three-dimensionally. For a more realistic modeling of actual particle conditions, the Cooper model has been developed for this geometry and the effects of surface roughness have been incorporated into the model. By using the presented model, the forces applied on particle during the manipulation process, the deformations induced in the AFM cantilever, the rotation center and the maximum force applied on particle can be computed and the motion modes of particle (sliding, rolling, rotating) at the onset of displacement can be predicted. The findings indicate that the critical forces associated with rough particles are smaller than those for smooth particles. Furthermore, the effects of particle dimensions and roughness parameters such as the radius and height of asperities and also the effect of AFM tip location on a particle on its motion modes have been studied and the suitable conditions for creating different motion modes have been discussed.