Method for controlled density growth of carbon nanotubes
Described is a method for preparation of carbon nanotubes (CNTs) with medium to low-site density growth for use in field emission devices (FEDs). The method involves the deposition of a non-catalytic metal layer (interlayer), preferably a metallic conductor, onto the surface of a substrate, prior to the deposition of a catalytic layer (overlayer). The interlayer allows for only partial (sparse) growth of CNTs on the substrate, and helps to prevent resist layer “lift-off” when photolithographic processing is employed.
1. A method for fabricating a carbon nanotube array having a low site-density growth, which method comprises:
providing a substrate;
forming a non-catalytic metal interlayer on the substrate, the non-catalytic metal interlayer having a thickness of from about 0.6 nm to about 2.0 nm;
forming a catalytic metal overlayer on the non-catalytic metal interlayer, the catalytic metal overlayer having a thickness of from about 1.0 nm to about 5.5 nm and defined by a plurality of separate pads disposed on the surface of at least a portion of the non-catalytic metal interlayer; and
forming the plurality of carbon nanotube structures on the substrate in the presence of the catalytic metal overlayer, the carbon nanotube structures having a density of no more than 10 10 nanotubes/cm 2 .
2. The method of claim 1 , wherein forming the plurality of carbon nanotube structures comprises forming a plurality of carbon nanotubes on each of the separate pads.
3. The method of claim 1 , wherein the non-catalytic metal interlayer comprises a non-catalytic metal selected from the group consisting of chromium, aluminum gallium, indium, tin, and lead.
4. The method of claim 3 , wherein the catalytic metal is chromium.
5. The method of claim 1 , wherein the catalytic metal overlayer comprises a catalytic metal selected from the group consisting of iron, cobalt, nickel, molybdenum, palladium, and platinum.
6. The method of claim 5 , wherein the catalytic metal is iron.
7. The method of claim 1 , wherein forming the non-catalytic metal interlayer comprises forming the non-catalytic metal interlayer using a physical vapor deposition (PVD) process.
8. The method of claim 1 , wherein forming the catalytic metal overlayer comprises forming the catalytic metal overlayer using a physical vapor deposition (PVD) process.
9. The method of claim 1 , wherein forming the non-catalytic metal interlayer and forming the catalytic metal overlayer comprises forming the non-catalytic metal interlayer and the catalytic metal overlayer wherein a ratio of a thickness of the non-catalytic metal interlayer to a thickness of the catalytic metal overlayer is in the range of about 1:1 to about 1:8.
10. The method of claim 9 , wherein the ratio of thickness is from about 1:3 to about 2:3.
11. The method of claim 1 , wherein the density of carbon nanotube structures is not more than 10 8 nanotubes/cm 2 .
12. The method of claim 1 , which method further comprises:
depositing a layer of a resist material on one or more of the substrate, non-catalytic metal interlayer, and catalytic metal overlayer;
patterning the resist layer; and
removing a portion of the resist layer according to the pattern of the underlying substrate, non-catalytic metal interlayer, or catalytic metal overlayer.
13. A carbon nanotube array, comprising:
a substrate;
a non-catalytic metal interlayer disposed over at least a portion of the substrate; and
a plurality of catalytic metal overlayer pads disposed on the surface of at least a portion of the non-catalytic interlayer, a plurality of carbon nanotubes disposed on each pad with a density of no more than 10 10 nanotubes/cm 2 ; wherein
the non-catalytic metal interlayer has a thickness of from about 0.6 nm to about 2.0 nm, and wherein the catalytic metal overlayer pads have a thickness of from about 1.0 nm to about 5.5 nm.
14. The carbon nanotube array of claim 13 , wherein the density of carbon nanotubes on each pad is no more than 10 8 nanotubes/cm 2 .
15. The carbon nanotube array of claim 13 , wherein the pads are arranged in a regular array.
16. A field emission display, comprising:
a cathode;
an anode;
a carbon nanotube array disposed on the cathode, the carbon nanotube array comprising
a non-catalytic metal interlayer disposed over at least a portion of the cathode; and
a plurality of catalytic metal overlayer pads disposed on the surface of at least a portion of the non-catalytic interlayer, a plurality of carbon nanotubes disposed on each pad with a density of no more than 10 10 nanotubes/cm 2 ; wherein
the non-catalytic interlayer has a thickness of from about 0.6 nm to about 2.0 nm, and wherein the catalytic metal overlayer pads have a thickness of from about 1.0 nm to about 5.5 nm.
17. The field emission display of claim 16 , wherein the density of carbon nanotubes on each pad is no more than 10 8 nanotubes/cm 2 .
18. The field emission display of claim 16 , wherein the plurality of pads are individually addressable.