Patterning of metals and metal compounds using ionotropic polymers
Patterning surfaces to create some function is a core technology propelling our technical society. The most important such technology, photolithography, is used to create IC chips with nanoscale features. It is also the most expensive with fab capital costs greater than several billion dollars. Not all surface patterning needs require nanoscale resolution. Soft lithography, pioneered by George Whitesides, can create patterns on a surface in the microscale using a suite of techniques easily carried out in an ordinary lab or factory environment with capital costs in the thousands of dollars. Soft lithography is beginning to be used to make commercial products. The current soft lithography invention is useful for creating patterns of metals and semiconductors on a surface with a resolution on the border of the nano- and microscale.
The invention takes advantage of a property of a polymer like polyacrylic acid (PAA), which is water soluble when its counterion is monocationic (i.e, Na+1) and not crosslinking and insoluble in water when its counterion is a doubly charged and is crosslinking (i.e., Zn+2). A template of surface microfluidic channels, in a desired pattern, is impressed on a soluble PAA layer and Zn+2 solution in the channels converts soluble PAA into insoluble PAA impregnated with zinc ions in the pattern of the microfluidic template. Removing the template and washing with water leaves the zinc ion impregnated PAA in the pattern of the template. Now one can use this patterned surface as a template for chemical conversion to zinc nanoparticles (by reduction) or to form compounds of zinc such as zinc sulfide, a semiconductor. The PAA can be removed by oxygen plasma. Other metals such as Al, Ti, Mn, Fe, Ni, Cu, Pd, La, Gd, Ho, Pb and U can be used. Nanoparticles can be used as nucleation sites for the growth of patterned microstructures. Different channels can carry different metal solutions allowing complex structures with more than one metal to be produced. The microfluidic template is made using well-known and inexpensive soft lithography techniques, such as described in the publication entitled, ''Microfluidic Devices Fabricated in Poly(Dimethylsiloxane)for Biological Studies Electrophoresis'', 2003, 24, 3563-3576.
Intellectual Property Status: Patent(s) Pending
The ability to lay down microscale patterns of these industrially important metals and their compounds on a substrate without the requirement for ''fab-like'' conditions will have many applications. The ability to pattern thin polymer films on substrates is central to microelectronics, optics, MEMS and biochemistry.