Methods for the fabrication of graphene nanoribbon arrays using block copolymer lithography
Methods of fabricating patterned substrates, including patterned graphene substrates, using etch masks formed from self-assembled block copolymer films are provided. Some embodiments of the methods are based on block copolymer (BCP) lithography in combination with graphoepitaxy. Some embodiments of the methods are based on BCP lithography techniques that utilize hybrid organic/inorganic etch masks derived from BCP templates. Also provided are field effect transistors incorporating graphene nanoribbon arrays as the conducting channel and methods for fabricating such transistors.
1. A method of fabricating a graphene nanoribbon array, the method comprising:
forming a graphoepitaxy channel over a graphene substrate, the channel comprising side walls and a floor;
depositing a layer of a surface-modifying copolymer on the side walls and the floor of the channel;
depositing a block copolymer in the channel and subjecting the block copolymer to conditions under which spatial confinement of the block copolymer by the channel induces the block copolymer to self-assemble into a plurality of domains, such that the self-assembled block copolymer layer defines a striped pattern over the graphene substrate, wherein the stripes in the striped pattern are oriented parallel with respect to the graphene substrate surface and perpendicular with respect to the channel side walls; and
transferring the striped pattern into the graphene substrate to provide the graphene nanoribbon array.
2. The method of claim 1 , wherein the surface-modifying copolymer is a random copolymer of styrene and methylmethacrylate, the block copolymer is a block copolymer of styrene and methylmethacrylate and the domains are lamellar domains.
3. The method of claim 1 , further comprising depositing a layer of wetting material in the channel prior to depositing the layer of a surface-modifying copolymer.
4. The method of claim 3 , wherein the surface-modifying copolymer is a random copolymer of styrene and methylmethacrylate, the block copolymer is a block copolymer of styrene and methylmethacrylate and the wetting material is silicon oxide.
5. The method of claim 3 :
wherein the graphene substrate is disposed on a support substrate comprising a gate dielectric overlying a gate electrode;
wherein the graphoepitaxy channel is defined by a source electrode and a drain electrode separated by a gap and disposed on the graphene substrate, such that the inner side edges of the source and drain electrodes provide the channel side walls and the surface of the graphene substrate provides the channel floor;
wherein the layer of wetting material is a layer a silicon oxide; and
wherein the method further comprises removing the surface-modifying copolymer and the block copolymer after the striped pattern has been transferred into the graphene substrate to form a field effect transistor in which the graphene nanoribbon array provides a conducting channel region.
6. The method of claim 1 , wherein the average width of the nanoribbons in the array is no greater than about 20 nm.
7. The method of claim 1 , further comprising removing the surface-modifying copolymer and the block copolymer after the striped pattern has been transferred into the graphene substrate.
8. The method of claim 1 , wherein the graphene substrate is a single sheet of graphene.
9. The method of claim 1 :
wherein the graphene substrate is disposed on a support substrate comprising a gate dielectric overlying a gate electrode;
wherein the graphoepitaxy channel is defined by a source electrode and a drain electrode separated by a gap and disposed on the graphene substrate, such that the inner side edges of the source and drain electrodes provide the channel side walls and the surface of the graphene substrate provides the channel floor; and
wherein the method further comprises removing the surface-modifying copolymer and the block copolymer after the striped pattern has been transferred into the graphene substrate to form a field effect transistor in which the graphene nanoribbon array provides a conducting channel region.
10. The method of claim 1 , wherein the plurality of domain are lamellar domains in which lamellae are oriented perpendicular with respect to the graphene substrate surface and perpendicular with respect to the channel side walls.
11. The method of claim 1 , wherein the plurality of domains are cylindrical domains in which the cylinders are oriented parallel with respect to the graphene substrate surface and perpendicular with respect to the channel side walls.
12. A method of fabricating a patterned graphene array, the method comprising:
depositing a block copolymer over a graphene substrate and subjecting the block copolymer to conditions that induce it to self-assemble into a plurality of polymeric domains, such that the domains define a pattern over the graphene substrate;
converting polymeric domains in the self-assembled block copolymer into inorganic domains comprising a metal oxide, such that the inorganic domains define a pattern over the graphene substrate, by exposing the self-assembled block copolymer to metal-containing precursor molecules that coordinate selectively with a set of the polymeric domains to form initiating sites for an atomic layer deposition process and sequentially exposing the self-assembled block copolymer to oxygen-containing precursor molecules and metal-containing precursor molecules in an atomic layer deposition process, whereby metal oxide domains are grown from the selectively coordinated polymeric domains; and
transferring the pattern of the inorganic domains into the graphene substrate to provide the patterned graphene array.
13. The method of claim 12 , further comprising selectively coordinating the set of polymeric domain with precursor-coordinating molecules that increase the domains' selectivity for the metal-containing precursor molecules prior to exposing the self-assembled block copolymer to the metal-containing precursor molecules.
14. The method of claim 12 , wherein the block copolymer is a block copolymer of styrene and vinylpyridine and the polymeric domains comprise cylindrical domains oriented parallel with respect to the graphene substrate surface.
15. A method of fabricating a patterned graphene array, the method comprising:
depositing a block copolymer over a graphene substrate and subjecting the block copolymer to conditions that induce it to self-assemble into a plurality of polymeric domains, such that the domains define a pattern over the graphene substrate;
converting the polymeric domains in the self-assembled block copolymer into metal domains, such that the metal domains define a pattern over the graphene substrate, by selectively protonating a set of the polymeric domains; exposing the protonated polymeric domains to a solution comprising a metal salt, wherein the protonated polymeric domains become loaded with the metal salt via electrostatic interactions between the protonated polymeric domains and the anions of the salt; and exposing the metal salt-loaded domains to an oxidizing plasma, whereby a metal is formed from the metal salt; and
transferring the pattern of the metal domains into the graphene substrate to provide the patterned graphene array.
16. The method of claim 15 , wherein the block copolymer is a block copolymer of styrene and vinylpyridine and the polymeric domains comprise cylindrical domains oriented parallel with respect to the graphene substrate surface.