Method for electrochemically depositing carbon film on a substrate
Dense carbon films are deposited on a conductive substrate by placing the substrate acting as anode in a molten salt electrolyte bath containing a source of carbide ion and applying DC current across the substrate and a counter electrode acting as cathode also placed in the molten salt electrolyte bath. The carbide ions are electrochemically oxidized to deposit a carbon film on the surface of the substrate.
1. A method for electrochemically depositing a carbon film on a conductive substrate comprising:
providing a molten salt electrolyte bath selected from the group consisting of: a binary mixture of lithium chloride and potassium chloride, and a ternary mixture of lithium chloride, potassium chloride and calcium chloride;
dissolving calcium carbide as a source of carbide ion in said molten salt electrolyte bath;
placing said conductive substrate and a counter electrode in said electrolyte bath, said conductive substrate being made of metals, said substrate and said counter electrode being electrically connected to a DC current source and acting as anode and cathode, respectively; and
applying DC current across said substrate and said counter electrode through said electrolyte bath whereby said carbide ion is electrochemically oxidized to deposit a carbon film on the surface of said substrate.
2. The method according to claim 1 wherein the DC current is applied at a potential capable of anodically oxidizing said carbide ion.
3. The method according to claim 1 wherein said DC current is applied at a potential in the range between 1.0 V and 3.0 V (vs. Li+/Li).
4. The method according to claim 1 wherein said molten salt electrolyte bath further contains a source of nitride ion dissolved therein.
5. The method according to claim 4 wherein said nitride ion source is lithium nitride.
6. The method according to claim 1 wherein said counter electrode is made of a metal capable of forming an alloy with lithium metal.
7. The method according to claim 6 wherein said metal is aluminum.
8. The method according to claim 1 wherein said molten salt electrolyte bath further contains a metal species capable of forming a liquid phase alloy with lithium at the temperature of said molten salt electrolyte bath.
9. The method according to claim 8 wherein said metal species is tin.
10. The method according to claim 1 wherein said molten salt electrolyte bath temperature ranges between 250° C. and 800° C.
11. The method according to claim 10 wherein said molten salt electrolyte bath temperature ranges between 350° C. and 700° C.
12. The method according to claim 1 wherein said binary mixture comprises 55 to 65 mol % of lithium chloride and 45 to 35 mol % of potassium chloride.
13. The method according to claim 1 wherein said binary mixture is a eutectic mixture of lithium chloride and potassium chloride.
14. The method according to claim 1 wherein DC current is applied to said substrate until a quantity of electricity of about 40 C/cm 2 is applied to said substrate.