Process for mass producing uniform multi-layer non-linear optical polymer thin polar films

Abstract

A process that lends itself to automation for producing multi-layer second-order nonlinear optical polymer (NLOP) thin films by the forming of a polycation layer containing an NLO-active cationic polymer, having non-centrosymmetric chromophores, on a substrate followed by the forming of a polyanion layer, also having non-centrosymmetric chromophores, on the polycation layer. A predetermind number of the polycation and the polyanion layers may be alternated upon the surface as well as one or more buffer layers. An added benefit is the formation of an ultra-smooth surface of the same order of roughness as the substrate upon which the layers are formed.

What is claimed is:  
     
       1. A process for producing a uniform multi-layer second-order nonlinear optical polymer (NLOP) thin film incorporating aligned non-centrosymmetric chromophores, the chromophores each having an electron-donor end and an electron-receptor end, the process comprising: 
       dipping a substrate, having upper and lower surfaces and a thickness, said thickness being in a plane of said substrate roughly perpendicular to said upper and lower surfaces, into a first aqueous solution containing an NLO-active cationic polymer having at least one repeating unit and incorporating positive ions, wherein at least one of said upper and lower surfaces has a net negative charge permanently imposed thereon; removing said substrate from said first solution after a first soak time; cleaning said substrate using a suitable solvent for a first pre-determined cleaning time;  
       drying said substrate for a first pre-determined drying time;  
       wherein said dipping in said first solution, cleaning, and drying results in the forming of a polycation layer of NLOP on at least one of said upper and lower surfaces;  
       dipping said substrate into a second aqueous solution containing an anionic polymer having at least one repeating unit and incorporating negative ions;  
       removing said substrate from said second solution after a second soak time;  
       cleaning said substrate using a suitable solvent for a second pre-determined cleaning time;  
       drying said substrate for a second pre-determined drying time; wherein said dipping in said second solution, cleaning, and drying results in the forming of a polyanion layer on said polycation layer; and  
       repeating said dipping, cleaning, drying processes so that a predetermined plurality of alternating said polycation and said polyanion layers are built up uniformly upon said at least one surface of said substrate. wherein said process is performed in a manner to allow the chromophores within the cationic polymer to align as said cationic and anionic polymers within the structure solidify.  
     
     
       2. The process of  claim 1  wherein said cleaning involves contact with a cleaning solvent selected from the group consisting of: an alcohol, an aromatic, water, and any combination thereof. 
     
     
       3. The process of  claim 1  wherein said cleaning is rinsing with ultrapure water. 
     
     
       4. The process of  claim 1  wherein said drying is carried out in a process selected from the group consisting of: drying in ambient air, drying in inert gas, drying in heated air, drying in heated inert gas, drying in a vacuum, and any combination thereof. 
     
     
       5. The process of  claim 1 , further comprising repeating the forming of each of said polycation and said polyanion layers from about 3 or more times. 
     
     
       6. The process of  claim 1 , wherein said ions are present in a concentration of from about 10 −2  M or less in said first and second aqueous solutions, wherein said first and second aqueous solutions are formed by dissolving said polycation and said polyanion polymers in separate vessels containing first and second fluid solvents, respectively, wherein said first and second fluid solvents are selected from the group consisting of: methanol, dimethylsulfoxide and water. 
     
     
       7. The process of  claim 6 , wherein said ions are present in a concentration of from about 10 −3  M to about 10 −7  M in said first and second solutions. 
     
     
       8. The process of  claim 7 , wherein said ions are present in a concentration of from about 10 −5  molar to about 10 −7  molar in said first and second solutions, 
       wherein said cationic polymer and said anionic polymer are water soluble and  
       wherein said first and second fluid solvents consist mainly of water.  
     
     
       9. The process of  claim 1 , wherein said cationic polymer has an asymmetric sidechain chromophore on each said repeating unit of said cationic polymer, 
       wherein said sidechain chromophore is linked to the main chain by short alkyl spacers.  
     
     
       10. The process of  claim 9 , wherein said short alkyl spacers contain from one to eitht carbon atoms. 
     
     
       11. The process of  claim 9 , wherein said first cationic solution comprises stilbazolium-substituted polyepichlorohydrin. 
     
     
       12. The process of  claim 1 , wherein said second anionic solution comprises an NLO-active anionic polymer. 
     
     
       13. The process of  claim 1 , wherein said second anionic solution contains an NLO-active anionic polymer having an accordion backbone architecture incorporating bridging grousp with said negative ions on every other said bridging group, 
       wherein said NLO-active anionic polymer has the chromophores syndioregic in said backbone with a pendant carboxylate anion tethered to the donor end of each chromophore.  
     
     
       14. The process of  claim 1 , wherein said second anionic solution contains an NLO-inactive polymer. 
     
     
       15. The process of  claim 14 , wherein said NLO-inactive polymer is poly(sodium 4-styrenesulfonate). 
     
     
       16. The process of  claim 13 , wherein said NLO-active anionic polymer is a sodium salt of poly(2-((4-(2- (N-(2-hydroxyethyl)carbamoyl)-2-cyanovinyl)phenyl) (2-((4-(2-(N-methylcarbamoyl)-2 cyanovinyl)phenyl) (carboxymethyl)amino)ethyl)amino)acetic acid). 
     
     
       17. The process of  claim 1 , wherein said first cationic and said second anionic solutions have approximately equal concentrations of said ions. 
     
     
       18. The process of claim l, further comprising repeating the forming of each of said polycation and said polyanion layers from about 8 or more times. 
     
     
       19. The process of  claim 1 , wherein said substrate comprises at least one hydrophobic surface upon said upper and lower surfaces, said hydrophobic surface having substantially zero net charge. 
     
     
       20. The process of  claim 1 , further comprising adding at least one buffer layer on at least one of said alternating polycation and polyanion layers. 
     
     
       21. The process of  claim 1 , further comprising maintaining the pH of said polycation solution in the range from 3.0 to 10.0. 
     
     
       22. The process of  claim 1 , further comprising maintaining the pH of said polyanion solution in the range from 8.0 to 11.0. 
     
     
       23. The process of  claim 1 , wherein said first soak time is in the range from 1 minute to 90 minutes, said second soak time is in the range from 1 minute to 90 minutes, said first and second pre-determined cleaning times are in the range from 5 seconds to 30 seconds. 
     
     
       24. The process of  claim 1 , wherein said process is carried out at a temperature in a range from 5° C. to 90° C. 
     
     
       25. The process of  claim 10  wherein said short alkyl spacers contain one carbon atom. 
     
     
       26. The process of  claim 1 , wherein selection of said cationic and anionic polymers incorporated in said first and second solutions and processing of said substrate is controlled so that the roughness of said alternating layers does not exceed that of said substrate as originally configured. 
     
     
       27. The process of  claim 1  wherein the non-centrosymmetric chromophores of said polycation and polyanion layers are attached as main chain non-centrosymmetric chromophores. 
     
     
       28. The process of  claim 1  wherein said first solution contains an anionic polymer, said second solution contains an NLO-active cationic polymer and said at least one of said upper and lower surfaces has a net positive charge permanently imposed thereon. 
     
     
       29. The process of  claim 28  wherein said first anionic solution comprises an NLO-active anionic polymer. 
     
     
       30. The process of  claim 1  wherein said substrate is physically separated from the multi-layer NLOP thin film. 
     
     
       31. The process of  claim 28  wherein said substrate comprises at least one hydrophobic surface upon said upper and lower surfaces, said hydrophobic surface having substantially zero net charge. 
     
     
       32. A process for producing an electro-optic waveguide, having a core and cladding, wherein the process for making the core comprises: 
       dipping a substrate, having upper and lower surfaces and a thickness, said thickness being in a plane of said substrate roughly perpendicular to said upper and lower surfaces, into a fresh first solution containing an NLO-active cationic polymer having non-centrosymmetric chromophores and at least one repeating unit and incorporating positive ions, wherein at least one of said upper and lower surfaces has a net negative charge permanently imposed thereon;  
       removing said substrate from said first solution after a first soak time;  
       cleaning said substrate using a suitable solvent for a first pre-determined cleaning time;  
       drying said substrate for a first pre-determined drying time; wherein said dipping in said first solution, cleaning, and drying results in the forming of a polycation layer of NLOP, having non-centrosymmetric chromophores, on at least one of said upper and lower surfaces;  
       dipping said substrate into a fresh second solution containing an anionic polymer, having non-centrosymmetric chromophores and at least one repeating unit and incorporating negative ions;  
       removing said substrate from said second solution after a second soak time;  
       cleaning said substrate using a suitable solvent for a second pre-determined cleaning time;  
       drying said substrate for a second pre-determined drying time; wherein said dipping in said second solution, cleaning, and drying results in the forming of a polyanion layer on said polycation layer; and  
       repeating said dipping, cleaning, drying processes so that a predetermined plurality of alternating said polycation and said polyanion layers are built up uniformly upon said at least one surface of said substrate.  
     
     
       33. The process of  claim 32  further comprising adding at least one buffer layer on at least one of said alternating polycation and polyanion layers.