Method for forming conductive film at room temperature

Abstract

A method for forming a conductive film at room temperature is provided and includes steps of: adding AgNO 3 into a first solution of dodecanoic acid; dropping n-butylamine and a diluted aqueous solution of a reducing agent into the first solution in turn, so as to initially obtain the dodecanoate-protected silver nanoparticles as a capping ligand; then using cyclohexane as a solvent to apply the silver nanoparticles onto a surface of a substrate to form a patterned film of silver nanoparticles; and finally immersing the substrate into a high concentrated aqueous solution of a reducing agent to chemically reduce the patterned film of silver nanoparticles into a conductive silver film. Thus, a patterned film or circuit can be conveniently and rapidly formed, and the silver nanoparticles can be applied to flexible substrates with low material cost and temperature sensitivity.

What is claimed is: 
     
         1 . A method for forming a conductive film at room temperature, comprising:
 (a) adding AgNO 3  into a non-polar solvent containing dodecanoic acid to be a first mixture;   (b) dropping n-butylamine into the first mixture as a ligand of silver ions of silver nitrate to be a second mixture;   (c) dropping a diluted aqueous solution of a reducing agent into the second mixture to be a third mixture, wherein the reducing agent reduces silver ion into silver nanoparticles and dodecanoate group of dodecanoic acid is used as a capping ligand to be around and protect the silver nanoparticles;   (d) separating the silver nanoparticles using dodecanoate as the capping ligand from the third mixture;   (e) using cyclohexane as a solvent to mix with silver nanoparticles using dodecanoate as the capping ligand to be a fourth mixture;   (f) applying the fourth mixture onto a surface of a substrate to form a film of silver nanoparticles using dodecanoate as the capping ligand; and   (g) immersing the substrate into an aqueous solution of a reducing agent to chemically reduce the film of silver nanoparticles into a conductive silver film;   wherein the processes in the steps (a) to (g) are all performed at room temperature.   
     
     
         2 . The method for forming a conductive film at room temperature according  claim 1 , wherein in the step (a), the molar ratio of the silver ions of AgNO 3  and the dodecanoate group of dodecanoic acid is 1:2. 
     
     
         3 . The method for forming a conductive film at room temperature according  claim 1 , wherein in the step (a), the non-polar solvent is toluene. 
     
     
         4 . The method for forming a conductive film at room temperature according  claim 1 , wherein in the step (b), the molar ratio of the silver ions of AgNO 3  and n-butylamine is 1:2. 
     
     
         5 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (c), the diluted aqueous solution of the reducing agent is selected from a diluted aqueous solution of hydrazine, ascorbic acid, NaBH 4  or dimethylformamide (DMF). 
     
     
         6 . The method for forming a conductive film at room temperature according to  claim 5 , wherein in the step (c), the diluted aqueous solution of the reducing agent is the diluted aqueous solution of hydrazine, and the molar ratio of the silver ions of AgNO 3  and hydrazine of the diluted aqueous solution of hydrazine is 2:1. 
     
     
         7 . The method for forming a conductive film at room temperature according ti  claim 1 , wherein in the step (c), the range of average particle diameter of the dodecanoate-protected silver nanoparticles is 6.20±0.57 nm. 
     
     
         8 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (d), firstly adding acetone into the third mixture to deposit the dodecanoate-protected silver nanoparticles as the capping ligand, and then adopting methanol and acetone to wash, centrifuge and dry by reduced pressure condensation, in order to obtain the dodecanoate-protected silver nanoparticles. 
     
     
         9 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (e), the fourth mixture is treated by firstly using cyclohexane containing 0.5 wt % dodecanoate acid as a solvent to mix silver nanoparticles in the step (d) into the fourth mixture which has 5.0 to 15.0 wt % silver nanoparticles. 
     
     
         10 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (f), the fourth mixture is selected to apply onto the surface of the substrate by spin-coating or inkjet printing. 
     
     
         11 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (f), the substrate is selected from the group consisting of a flexible plastic substrate, a glass substrate and a silicon wafer substrate. 
     
     
         12 . The method for forming a conductive film at room temperature according to  claim 11 , wherein the flexible plastic substrate is a polyethylene terephthalate substrate. 
     
     
         13 . The method for forming a conductive film at room temperature according to  claim 1 , wherein in the step (f), the aqueous solution of the reducing agent is selected from an aqueous solution of hydrazine, ascorbic acid, NaBH 4  or dimethylformamide (DMF). 
     
     
         14 . The method for forming a conductive film at room temperature according to  claim 13 , wherein in the step (f), the aqueous solution of the reducing agent is an aqueous solution of hydrazine, and the hydrazine concentration of the aqueous solution of hydrazine is between 70 and 90 wt %. 
     
     
         15 . The method for forming a conductive film at room temperature according to  claim 1 , wherein the processes in the steps (a) to (g) are all performed at room temperature in the range between 20 and 30° C. 
     
     
         16 . The method for forming a conductive film at room temperature according to  claim 1 , wherein after the step (g), the method further comprises:
 (g1) applying a heat-treatment to the conductive silver film at 100° C.   
     
     
         17 . The method for forming a conductive film at room temperature according to  claim 1 , wherein after the step (g), the method further comprises:
 (h) repeating the steps (f) and (g) to further stack and form another conductive silver film on the original conductive silver film.   
     
     
         18 . The method for forming a conductive film at room temperature according to  claim 17 , wherein after the step (h), the method further comprises:
 (h1) applying a heat-treatment to two of the stacked conductive silver film at 100° C.