CONTACT METALLIZATION OF CARBON NANOTUBES

• US 20080241755A1
• Filed: 02/01/2008
• Published: 10/02/2008
• Est. Priority Date: 02/01/2007
• Status: Active Grant

• Current Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: MASCHMANN, MATTHEW R., FRANKLIN, AARON D., FISHER, TIMOTHY S., SANDS, TIMOTHY D.
• Granted Patent: US 9,487,877 B2
• Time in Patent Office: Days
• US Class Current: 430/296
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: C01B 2202/02 Single-walled nanotubes
• CPC Class Codes: C01B 2202/08 Aligned nanotubes
• CPC Class Codes: C01B 32/162 characterised by catalysts
• CPC Class Codes: C01B 32/168 After-treatment
• CPC Class Codes: C25D 11/045 for forming AAO templates
• CPC Class Codes: C25D 5/02 Electroplating of selected surface areas
• CPC Class Codes: C25D 5/605 Surface topography of the layers, e.g. rough, dendritic or nodular layers
• CPC Class Codes: C25D 7/00 Electroplating characterised by the article coated

Abstract

In one embodiment, SWNTs are synthesized from an embedded catalyst in a modified porous anodic alumina (PAA) template. Pd is electrodeposited into the template to form nanowires that grow from an underlying conductive layer beneath the PAA and extend to the initiation sites of the SWNTs within each pore. Individual vertical channels of SWNTs are created, each with a vertical Pd nanowire back contact. Further Pd deposition results in annular Pd nanoparticles that form on portions of SWNTs extending onto the PAA surface. Two-terminal electrical characteristics produce linear I-V relationships, indicating ohmic contact in the devices.

Claims

1. A method of metallizing an array of carbon nanotubes, comprising:

fabricating a template having a layer of aluminum covering a catalyst layer separating the aluminum from another aluminum layer that is supported on a conductive material;

anodizing the template to form porous anodic alumina;

synthesizing at least one single walled carbon nanotube from the catalytic layer in each of a plurality of pores;

placing the porous template in a solution containing metallic ions after said synthesizing; and

electrodepositing a quantity of metal in each of the plurality of pores sufficient to establish electrical contact from the nanotube to the conductive material.

2. The method of claim 1 which further comprises removing a quantity of alumina from the bottom of a pore prior to said electrodepositing.

3. The method of claim 1 wherein said removing is by exposure to a plasma with a reducing agent, by reverse anodic anodization, or by ion milling.

4. The method of claim 1 which further comprises dissolving the template.

5. A method of metallizing an array of carbon nanotubes, comprising:

providing a plurality of nanopores in an array, each nanopore having first and second ends interconnected by a chamber;

forming a carbon nanotube in each nanopore, a first end of each nanotube contacting the wall of the chamber intermediate of the first and second ends of the chamber, the second end of the nanotube being proximate one of the first or second ends of the chamber;

providing a first electrical contact of a first polarity at the other of the first or second ends of the chamber;

placing the array and nanotubes in a solution containing metallic ions;

providing a second electrical contact of an opposite polarity in the solution; and

applying a plurality of electrical pulses between the first and second electrical contacts, said pulses being either of a predetermined waveform of current or a predetermined waveform of voltage.

6. The method of claim 5 wherein the carbon nanotube is a single walled carbon nanotube.

7. A method of metallizing an array of carbon nanotubes, comprising:

providing a plurality of nanopores in an array;

forming a carbon nanotube in each nanopore;

providing a first electrical contact of a first polarity within each nanopore;

placing the array and nanotubes in a solution containing metallic ions;

providing a second electrical contact of an opposite polarity in the solution;

applying a plurality of input electrical pulses between the first and second electrical contacts, said pulses being either a predetermined waveform of current or a predetermined waveform of voltage;

measuring the corresponding output pulses of the other of current or voltage;

detecting either a monotonic increase or monotonic decrease in the ratio of input pulse to output pulse during a first sequence of pulses;

detecting the other of a monotonic increase or monotonic decrease in the ratio of input pulse to output pulse during a second sequence of pulses following the first sequence; and

stopping said applying in response to said detecting the second sequence.

8. The method of claim 7 which further comprises electrodepositing a nanoparticle of electrically conductive material at an end of at least one of the nanotubes.

9. A method of metallizing an array of carbon nanotubes, comprising:

fabricating a template of substantially porous anodic alumina;

synthesizing a single walled carbon nanotube in each of a plurality of pores;

placing the porous template in a solution containing metallic ions after said synthesizing;

electrodepositing a nanowire of metal in each of the plurality of pores, each nanowire being in electrical contact with one end of the corresponding nanotube; and

electrodepositing a nanoparticle of metal on the other end of at least one of the nanotubes.

10. The method of claim 9 wherein the pulses during said electrodepositing a nanowire are substantially constant in current.

11. A method of metallizing an array of carbon nanotubes, comprising:

fabricating a template of first and second layers of aluminum separated by a catalytic layer, at least a portion of one outer surfaces of a layer of aluminum having an electrically conductive material deposited thereon;

anodizing the template to form porous anodic alumina;

removing a portion of alumina in the bottom of a pore;

synthesizing at least one carbon nanotube from the catalytic layer in the pore;

placing the porous template in a solution containing metallic ions after said synthesizing; and

electrodepositing a quantity of the metal in the pore.

12. The method of claim 11 which further comprises removing a portion of the nanotube extending beyond the external surface.

13. The method of claim 11 wherein said fabricating includes a third layer of aluminum separated from the second layer of aluminum by a second catalytic layer.

14. The method of claim 13 which further comprises synthesizing a second carbon nanotube in the pore from the second catalytic layer.

15. A method of metallizing an array of carbon nanotubes, comprising:

providing a plurality of aligned, generally cylindrical nanopores in an array, each nanopore having first and second apertures interconnected by a chamber, the first aperture extending to an external surface of the array;

forming a carbon nanotube in each nanopore, a first end of each nanotube connecting to the wall of the chamber intermediate of the first and second ends of the chamber, the second end of the nanotube extending to the surface and beyond the first end of the chamber; and

removing the portion of the nanotube extending beyond the surface.

16. The method of claim 15 wherein said removing is by mechanical polishing, by milling by an ion beam, or by etching with oxygen plasma.

17. A method of producing a nanoporous array, comprising:

providing a film of aluminum;

applying to a surface of the aluminum a layer of resist material sensitive to an electron beam;

exposing the layer to an electron beam at a plurality of sites in a predetermined pattern;

etching the surface of aluminum under each of the sites to create a corresponding pattern of defects;

removing the layer;

anodizing the etched aluminum; and

creating a pore from each defect by said anodizing.

18. The method of claim 17 wherein the sites have a characteristic size less than about twenty nanometers and the spacing between adjacent sites are less than about one hundred nanometers.

19. The method of claim 17 which further comprises creating a pattern of voids in the layer by developing the exposed resist material.