The objective of this work is to outline a new coating technique suitable for surface modification and creation of high ordered array of colloidal particles on a semiconductor surface. Usage of these structures to create biosensor and non-linear optic devices require developing new inexpensive, large area fabrication technique.

    We use electrophoretic deposition (EDP) to produce gold nano-scale structures on a prior patterned silicone surface from colloidal suspension. Two kinds of gold colloids have been used: 1) gold particle suspension deaggregated and stabilized by citric acid and 2) suspension of gold particles covered with a silica shell. Today, nano-particles of gold, as well as a number of chemically modified gold colloids (for example gold particles covered with a silica shell), are commercially available with typical particle sizes in the range 2-50 nm.
    EDP from these colloids has been carried out using patterned semiconductor (n-type Si) or semiconductor covered with a porous metal oxide (Al₂O₃) film.

  Anodizing of thin aluminum film evaporated on silicon surfaces produce a self ordered hexagonal array of cylindrical pores with character size about 20-50 nm. The pore formation process proceeds until it consumes all of the aluminum and stops at the Al/Si interface.
 
 
 
 
 
 

    The initial pore diameter as received is 15-20 nm. The pore diameter can be increased relative to the  pore spacing by an additional phosphoric acid widening etch.
 
 
 
 
 

Crossection of anodized Al film on Si

Crossection of anodized Al film on Si after widening in phosphoric acid

    The self arranged alumina pores array can be used as an etch mask, to produce highly ordered structure on the Si surface. The hexagonal pattern has been transferred to the Si using a three step reactive ion etch.
 
 
 
 
 
 
 
 

    The deposition of nano particles on the metal oxide is difficult due to agglomeration during the deposition process. EDP on a porous alumina surface lead to uncontrolled aggregation and development of spherical aggregates of 5000-15000 particles.
    The nuclei pure gold particles stabilized by citric acid increase in size to form clusters, which are then bridged and converted into dense arrays. These arrays plug the pore mouth.
    Gold particles with silica shells were able to infiltrate the space within the pore. We achieve a good particle packing, producing a structure which adhered to the silicon with extensive heterocoagulation in the nanoscale range.
    Our scanning electron microscopy studies show that we produce aligned gold particle arrays on the silicon surface.