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HW 5.3:

Vladimir Privman's Seminar 21.01.15:

Mechanisms and models of synthesis of uniform colloids, nanoparticles and nanostructures

The reason to focus on the nanoparticles and nanostructures is to understand what is going on in the nano-scale.

They first formed tiny nano crystals and then they grew into colloids.Start with metal ions in salt or chloric acid. The ions reduce into clusters and as they grow they can become aggregated systems or stable nanosystems.

The group is interested in the size distribution. They want to know how do the nanostructures an cristalline particles grow. At this point they cannot see the clusters which are small inough to understand their dynamics.

In order to use a kinetic Monte-Carlo modeling approach a few assumptions are made:

  • They consider isometric nanosize crystals as they grow by relatively fast supply of matter (atoms).

  • They grow in an effective environment: in a ''box'', the boundary of which is used to replenish atoms as needed.

  • The initial seed is crystalline typically of order 30 atoms in diameter.

  • Free atoms diffuse by random bopping in space.

  • If free atoms hop to close to a crystal position, they are attached following the "exact registration" rule.

  • The atoms are allowe to hop to the nearest neighbor sites. If there is no neighbor they detach and go to the diffuser gas.

  • The attached atom dynamics follows localy-thermal-like Bolzmann factor translatioon rules with one energy scale (related to "bulk" binding) for the probability of hopping in the first place, and with another energy scale for which site amongst the neighbors to move to (loosely related to surface entropy or on-surface diffusion coefficient).

    The findings of this approach:

  • They can find reasonable energy scale and range of growth with well defined faces.

  • The shapes are consistent with experimental observations (mostly for metals).

  • Some of the "Wulff" faces are not present. The particle's proportions are different.

    Another project the group is working on is modeling of growth morphology of Core-Shell nanoparticles and they hope to be able to look at biological/ organic particles in the future.

    Dennis Rapaport's website:

    Professor Dennis C Rapaport is currently researching at the Department of Physics in the Bar- Ilan university.

    Currently professor Rapaport is focused on a few researches, one of them is the GPU (graphic processor units) based studies of of emergent phenomena.

    Emergent phenomena are notable for not being obvious outcomes of the design of the systems in which they appear.

    For example: self- assembly, atomistic hydrodynamics and granular segregations.

    Rapaport is using Molecular Dynamics Simulation for studying such phenomena.

    Moreover, Rapaport is using simulations to study statistical and chemical physics including phase transitions, magnetic systems, percolation and polymers.

    Prof. Rapaport's website