Method and device for promoting adhesion of metallic surfaces

Abstract

An adhesion promoting layer is formed on a metallic substrate by generating a non-thermal plasma in air at atmospheric pressure, and exposing a surface of the metallic substrate to the plasma. The plasma oxidizes the metallic substrate to form metal oxide from metal atoms of the metallic substrate. The metal oxide is formed as a metal oxide layer disposed directly on an underlying bulk metallic layer of the metallic substrate. Alternatively, the plasma nitridizes the metallic substrate to form metal nitride from metal atoms of the metallic substrate. The metal nitride is formed as a metal nitride layer disposed directly on an underlying bulk metallic layer of the metallic substrate.

What is claimed is: 
     
         1 . A method for forming an adhesion promoting layer on a metallic substrate, the method comprising:
 generating a non-thermal plasma in air at atmospheric pressure, the non-thermal plasma comprising monatomic oxygen; and   exposing a substrate surface of the metallic substrate to the non-thermal plasma, wherein:   the non-thermal plasma oxidizes the metallic substrate to form metal oxide from metal atoms of the metallic substrate; and   the metal oxide is formed as a metal oxide layer disposed directly on an underlying bulk metallic layer of the metallic substrate.   
     
     
         2 . The method of  claim 1 , wherein generating the non-thermal plasma comprises generating an electric field in the presence of air. 
     
     
         3 . The method of  claim 2 , wherein generating the electric field comprises applying a voltage between two electrodes in a range from 1 kV to 50 kV. 
     
     
         4 . The method of  claim 3 , wherein the electric field has a field strength in a range from 1 kV/cm to 500 kV/cm. 
     
     
         5 . The method of  claim 1 , comprising generating the non-thermal plasma in a confined plasma-forming region, and flowing air to the plasma-forming region. 
     
     
         6 . The method of  claim 5 , comprising flowing air at an air flow rate in a range from 1 SLM to 5000 SLM. 
     
     
         7 . The method of  claim 1 , wherein the non-thermal plasma has an applied power density in a range from 0.25 kW/cm 3  to 400 kW/cm 3 . 
     
     
         8 . The method of  claim 1 , comprising, before or during exposing the substrate surface to the non-thermal plasma, heating the metallic substrate. 
     
     
         9 . The method of  claim 8 , comprising heating the metallic substrate to a temperature in a range from 0° C. to 400° C. 
     
     
         10 . The method of  claim 1 , comprising:
 generating the non-thermal plasma in a confined plasma-forming region; and   before or during generating the non-thermal plasma, flowing diatomic oxygen gas into the confined plasma-forming region to increase a concentration of diatomic oxygen in the confined plasma-forming region.   
     
     
         11 . The method of  claim 1 , comprising:
 generating the non-thermal plasma in a confined plasma-forming region; and   before or during generating the non-thermal plasma, flowing an auxiliary gas into the confined plasma-forming region.   
     
     
         12 . The method of  claim 11 , wherein the auxiliary gas is selected from the group consisting of: diatomic nitrogen, diatomic fluorine, diatomic chlorine, diatomic bromine, diatomic iodine, a nitrogen compound, a fluorine compound, a chlorine compound, a bromine compound, an iodine compound, a boron compound, a carbon compound, an oxygen compound, a sulfur compound, a phosphorous compound, a silicon compound, a selenium compound, a tellurium compound, and a combination of two or more of the foregoing. 
     
     
         13 . The method of  claim 1 , wherein:
 generating the non-thermal plasma comprises generating the non-thermal plasma in a chamber; and   exposing the substrate surface to the non-thermal plasma comprises flowing the non-thermal plasma from the chamber, through an outlet, and toward the substrate surface.   
     
     
         14 . The method of  claim 1 , wherein:
 generating the non-thermal plasma comprises generating the non-thermal plasma between a first electrode and a second electrode spaced from the first electrode by an open gap, wherein a dielectric barrier is interposed between the first electrode and the second electrode and the non-thermal plasma is generated as a dielectric barrier discharge; and   exposing the substrate surface to the non-thermal plasma comprises positioning the substrate surface in the gap.   
     
     
         15 . The method of  claim 1 , wherein the metal oxide layer comprises an outer oxide surface and has a thickness defined from the underlying bulk metallic layer to the outer oxide surface, and the thickness is on the order of nanometers. 
     
     
         16 . The method of  claim 1 , wherein the metal oxide layer comprises an outer surface having a surface energy higher than a surface energy of the substrate surface prior to the substrate surface being exposed to the non-thermal plasma.