Time Resolved Chemical Dynamics on Size Controlled Metal Particles

    Supported metal particles on surfaces are highly interesting model systems for fundamental research on physical and chemical processes. In recent years, there have been a number of approaches used for the synthesis of supported metal particles, among which, the diblock copolymer reverse micelle approach stands out with the ability to control the particle size and interparticle spacing independently.



Figure 1: Polystyrene-block-poly(4-vinylpyridine)


    In this method, a diblock copolymer, like polystyrene-block-poly(4-vinylpyridine), comprised of a hydrophilic block and a hydrophobic block is dissolved in an organic solvent wherein an inverse micelle with a hydrophilic core and a hydrophobic corona is formed. Next, a metal precursor (metal salt) is introduced into the organic solvent. The salt ions segregate to the hydrophilic micelle core. Then the micelles are spin coated or dip coated onto a solid support. The polymer is removed by exposure to oxygen plasma in a reactive ion etcher, and the resultant metal oxide NPs are reduced by heating in vacuum. The interparticle distance and the size of the metal particles can be modulated independently by the molecular weight of the polymer, the metal ion concentration and other factors.


 

Figure 2: Micelle Formation

    With well-defined supported metal particles in the 1 to 100 nm size range on surfaces, we are working to time resolve—on the subpicosecond time scale—the chemical dynamics of adsorbates on the surfaces, and compare and contrast the dynamics with that of adsorbates on extended single crystal metal surfaces.



Figure 3: SEM of Pd Nanoparticles