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e) Nano-Composites: Metal Nano-Particles and Coatings

In the area of nano-composites of metal and polymers, I intend to find out how to metallize colloidal patterns on surfaces.  To achieve this, I utilize both the two-step metal plating technique and particle arraying technique based on polyelectrolyte multilayers as templates to develop metal-coated particle arrays on surfaces.  Controlled and stabilized metal-coated particle arrays on surfaces have a great potential application in optical, electrical, and magnetic sensors and devices, and in photonic, and bio-chip applications.

Electroless metal plating technique is based on the chemical reduction of the metal ions from solution on the surface of the substrate using a chemical reducing agent (Cohen group, MIT).  In this process, the kinetics of the electron transfer should be slow enough to prevent the reduction of the metal ions from occurring in solution.  In addition, it is desirable that the surface act as a catalyst to make sure that reduction of metal ions only happens on the surface, so that metal remains attached to the surfaces.  For this reason, a catalyst is first deposited on surfaces.  Among other catalysts, Pd based catalysts are commonly used for this pretreatment step to direct metal ions to reduce only on surfaces.

Recently, we (the Rubner and Hammond group at MIT) have developed a selective metal-plating process to create, in a very simple fashion, a wide variety of topographically structured surfaces based on polyelectrolyte multilayers with micron-scale control over critical surface features and hence surface functionality[1]-[2].  The new technique includes the controlled and stable particle arrays on surfaces over large area.  The controlled functional particle arrays on surfaces have a lot of potential applications.  Also, the two-step metal plating technique, easier to prepare metal-coated particle arrays on surfaces, which has a great potential for photonic wave guides.

Figure 3. Selective nickel deposition in controlled particle arrays.  Catalyst 1 (Na2PdCl4) was used on b, and catalyst 2 ([NH4]4PdCl2) on a, c, and d [ref 2].

[1]. I. Lee, T. C. Wang, M. F. Rubner, P. T. Hammond, ˇ°Selective Nickel Deposition in Patterned Layer by Layer Thin Films,ˇ± Manuscript in preparation.

[2]. I. Lee, M. F. Rubner, P. T. Hammond, ˇ°Selective Nickel Deposition in Controlled Particle Arrays,ˇ± Manuscript in preparation,ˇ± Manuscript in preparation. 


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