Electron emission material, method of manufacturing the same, and electron emission element including the same

Abstract

The present invention provides an electron emission material that is excellent in electron emission characteristics, a method of manufacturing the same, as well as an electron emission element. The method is a method of manufacturing an electron emission material including a carbon material obtained by baking a polymer film. In the method, a polyamic acid solution is prepared in which at least one metallic compound selected from a metal oxide and a metal carbonate is dispersed; the polyamic acid solution thus prepared is formed into a film and then is imidized to form a polyimide film including the metallic compound; and then the polyimide film thus formed is baked to form the carbon material. The electron emission material is formed so that it includes a carbon material, a protrusion having a concavity in its surface is formed at the surface of the carbon material, and the protrusion includes a metallic element.

1 - 6 . (canceled)  
   
   
       7 . An electron emission material comprising a carbon material, 
 wherein a protrusion having a concavity in its surface is formed at a surface of the carbon material, and    the protrusion contains a metallic element.    
   
   
       8 . The electron emission material according to  claim 7 , wherein the electron emission material has an emission current density of at least 1×10 −4  A/cm 2 .  
   
   
       9 . The electron emission material according to  claim 7 , wherein the electron emission material has an emission current density of at least 5×10 −4  A/cm 2 .  
   
   
       10 . The electron emission material according to  claim 7 , wherein the electron emission material has an emission current density of at least 7.2×10 −4  A/cm 2 .  
   
   
       11 . The electron emission material according to  claim 7 , 
 wherein the protrusion has a substantially circular shape or a substantially elliptical shape when viewed from a direction perpendicular to the surface of the carbon material; and    the concavity is formed at a substantial center of the protrusion when viewed from the direction.    
   
   
       12 . The electron emission material according to  claim 7 , wherein the concavity has a depth that is less than the height of the protrusion.  
   
   
       13 . The electron emission material according to  claim 7 , 
 wherein the protrusion has a substantially circular shape or a substantially elliptical shape when viewed from a direction perpendicular to the surface of the carbon material;    the concavity is formed at a substantial center of the protrusion when viewed from the direction: and    the concavity has a depth that is less than the height of the protrusion.    
   
   
       14 . The electron emission material according to  claim 7 , wherein the carbon material is a material obtained by baking a polymer film.  
   
   
       15 . The electron emission material according to  claim 14 , wherein the polymer film is a polyimide film.  
   
   
       16 . The electron emission material according to  claim 7 , wherein the metallic element is at least one selected from an alkali metal element and an alkaline earth metal element.  
   
   
       17 . The electron emission material according to  claim 16 , wherein the metallic element is at least one selected from the group consisting of Ca, Sr, Ba, Li, Na, K, Rb, and Cs.  
   
   
       18 . The electron emission material according to  claim 7 , wherein the protrusion has a mean diameter in a range of 10 nm to 200 nm when viewed from a direction perpendicular to the surface of the carbon material.  
   
   
       19 . The electron emission material according to  claim 7 , wherein the carbon material comprises a graphite structure.  
   
   
       20 . The electron emission material according to  claim 7 , 
 wherein the carbon material includes a void therein; and    the metallic element additionally is disposed on a surface of the carbon material facing the void.    
   
   
       21 . An electron emission element, comprising: 
 an electron emission layer including an electron emission material; and    an electrode that is disposed so as to face the electron emission layer and that allows a potential difference to be generated between the electron emission layer and itself,    wherein the electron emission material includes a carbon material, a protrusion having a concavity in its surface is formed at a surface of the carbon material, and the protrusion includes a metallic element.