No abstract

We examine the competition between diffusion-mediated irreversible nucleation and growth of islands during submonolayer deposition on perfect substrates. We provide a detailed scaling theory for the complete distribution of island sizes and separations, both with the ratio of diffusion to deposition rate and with time. Scaling functions and exponents are obtained by simulation. The leading scaling behavior is independent of details of the island structure. These results are supplemented by an analysis of rate equations for the islandsize distribution whose unconventional form appropriately describes island nucleation and growth mechanisms. The exponents agree with the simulations and the island-size distribution shows qualitative agreement. We further provide simulation results for the scaling of the island-separation distribution, quantifying, in particular, the depletion in the concentration of pairs of islands at small separations. Disciplines Condensed Matter Physics | Physics Comments This article is published as Bartelt, M. C., and J. W. Evans. "Scaling analysis of diffusion-mediated island growth in surface adsorption processes."

No abstract

No abstract

No abstract

No abstract

the contact width, and L is the nanotube length. These quantities are dif®cult to measure independently and calculations are modeldependent. As a guide, we apply a JKR model for the contact of cylinders 25 and ®nd a contact width of 3 nm for a tube radius of 13.5 nm. Our measurements of 0.006 N m -1 for the friction force per unit length is then consistent with a shear stress of 2 3 10 6 Pa. This can be compared with a value of 5 3 10 6 Pa, as inferred from AFM tip/graphite measurements 16 . To compare rolling and sliding in a single tube, we can calculate the force (4 nN for L 590 nm) and that would be needed to slide tube B, which in fact rolls. Finally, we note that the area under the lateral force trace is a direct measure of energy loss in rolling. For tube B, we measure an energy loss of 8 6 3 3 10 2 16 J per revolution. The sliding energy loss expected for this distance (85 nm) can be calculated using the frictional force of 4 nN, yielding 3 3 10 2 16 J.When we compare our lateral force measurements for sliding and rolling cases, we ®nd that the stick peaks in rolling are higher than the lateral force needed to sustain sliding, and that the energy cost for rolling is larger than that of the sliding cases. Why should the nanotubes roll? We speculate that, owing to the size and surface features of the rolling nanotubes, a stick peak for sliding in side-on pushing might exist that is larger than the threshold for rolling. Atomic-scale substrate interactions may also play a roll as we have observed this characteristic rolling only on graphite. Rolling behaviour has been accompanied by a preferential, threefold, inplane orientation that indicates intimate nanotube/graphite contact, and perhaps lattice registry. Rolling may occur only when both the nanotube and the underlying graphite have long-range order. In these cases that there may be a barrier for sliding which is larger than that for rolling and may preclude the direct measurement of sliding friction 7 . M

No abstract