Inventor(s): Jeffrey A. Bowers, Roderick A. Hyde, Muriel Y. Ishikawa, Jordin T. Kare, Clarence T.

Tegreene, Tatsushi Toyokuni, Richard N. Zare SUMMARY

In one aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property {e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first defined region is chemically functional ized with a first dopant species and the second defined region is chemically functional ized with a second dopant species.

The difference in the at least one electronic property may be a consequence of the functionalization. The first and second defined regions may form a

semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include interconnects electrically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The first and second regions may be adjacent, and either or both may be remote from an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from the first and second defined regions, which may be functional ized with a third dopant species. The graphene substrate may be disposed on a base substrate {e.g., graphite or a crystal containing a noncarbon component). The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first region is chemically functionalized with a first dopant species and is remote from any edge of the graphene substrate.

The second defined region may be chemically functionalized with a second dopant species, which may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern on the graphene substrate, or number density. Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same.

The difference in the at least one electronic property may be a consequence of the functional ization. The first and second defined regions may form a

semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include interconnects electrically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The first and second regions may be adjacent, and either or both may be remote from an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from the first and second defined regions, which may be functionalized with a third dopant species. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second defined region may be chemically functionalized with a second dopant species including a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the composition of the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, an electronic circuit includes a graphene substrate including a first device and a second device. The first device includes a first defined region and a second defined region differing in at least one first electronic property (e.g. , Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region, wherein the first region is chemically functionalized with a first dopant species. The second device includes a third defined region and a fourth defined region differing in at least one second electronic property {e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the third defined region, wherein the third region is chemically functionalized with a second dopant species.

The first and second dopant species may be the same or different. The first and second devices have substantially the same electronic character. The circuit may further include a fifth defined region of the graphene substrate that functions as an interconnect between the first and second devices. The at least one first electronic property and the at least one second electronic property may include a common electronic property. The difference in the at least one first electronic property may be a consequence of the functionalization of the first and second defined regions, or the difference in the at least one second electronic property may be a consequence of the functionalization of the third and fourth defined regions. The first and second defined regions, or the third and fourth defined regions, may form a semiconducting junction. The first or second device may be a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect.

The graphene substrate may include a single layer or a multilayer. The first defined region and the second defined region, or the third defined region and the fourth defined region, may be adjacent. The first or second defined region may not include an edge of the graphene substrate. The graphene substrate may be disposed on a base substrate {e.g., graphite or a crystal containing a noncarbon component). The first dopant species and the second dopant species may functionalize a common surface of the graphene substrate or opposing surfaces, and the first device and the second device may be positioned on opposing surfaces of the graphene substrate. The first or second dopant species may include at least one of an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group. The second dopant species may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density. Any of the dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, a method of forming an electronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species, and functionalizing a second defined region of the graphene substrate with a second dopant species. The functionalized first region differs in an electrical property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the functionalized second defined region.

Functionalizing the first defined region may include selectively exposing the first region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or . introducing a defect into the graphene substrate. The first defined region and the second defined region may be functionalized simultaneously, or the first defined region may be functionalized before the second defined region. The second defined region may overlap the first defined region. Functionalizing the second defined region may include co-depositing the second dopant species with the first dopant species. The first dopant species may exclude the second dopant species from depositing on the graphene substrate. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

In another aspect, a method of forming an electronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species. The functional ized first region differs in an electrical property {e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from a second defined region (which may or may not be functionalized) and is remote from any edge of the graphene substrate.

Functionalizing the first defined region may include selectively exposing the first region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or introducing a defect into the graphene substrate. The first defined region and the second defined region may be functionalized simultaneously, or the first defined region may be functionalized before the second defined region. The second defined region may overlap the first defined region. Functionalizing the second defined region may include co-depositing the second dopant species with the first dopant species. The first dopant species may exclude the second dopant species from depositing on the graphene substrate. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

In another aspect, an optoelectronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electro-optical property {e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from the first defined region. The first region is chemically functionalized with a first dopant species and the second defined region is chemically functionalized with a second dopant species. The difference in the at least one electro-optical property may be a

consequence of the functionalization. The first and second defined regions may be parts of a component such as laser, a light-emitting diode, a plasmon waveguide, an optical waveguide, an optical grating, a fluorescent device, a light-absorbing device, a photoelectron converter, a phaseshifting device, a interferometer, an optical coupler, or a plasmon coupler, and the optoelectronic device may be nonlinear or be a plasmonic device. The device may further include interconnects optically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electro-optical property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, an optoelectronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electro-optical property (e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from the first defined region. The first region is chemically functionalized with a first dopant species and does not include an edge of the graphene substrate.

The second defined region may be chemically functionalized with a second dopant species, which may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern on the graphene substrate, or number density. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electro-optical property may be a function of a property of the free moiety. The second defined region may be chemically functionalized with a second dopant species including a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the composition of the first and second bound moieties may be the same or different. The optoelectronic device may include a laser, a light-emitting diode, a plasmon waveguide, an optical waveguide, an optical grating, a fluorescent device, a light-absorbing device, a photoelectron converter, a phaseshifting device, a interferometer, an optical coupler, or a plasmon coupler, and the optoelectronic device may be nonlinear or be a plasmonic device. The difference in the at least one electro-optical property may be a consequence of the

functionalization. The device may further include interconnects optically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region. In another aspect, an optoelectronic circuit includes a graphene substrate including a first device and a second device. The first device includes a first defined region and a second defined region differing in at least one first electro-optical property (e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from the first defined region, wherein the first region is chemically functionalized with a first dopant species. The second device includes a third defined region and a fourth defined region differing in at least one second electro-optical property (e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from the third defined region, wherein the third region is chemically functionalized with a second dopant species.

The first and second dopant species may be the same or different. The first and second devices have substantially the same electro-optical character. The circuit may further include a fifth defined region of the graphene substrate that functions as an optical interconnect between the first and second devices. The at least one first electro-optical property and the at least one second electro-optical property may include a common electro-optical property. The difference in the at least one first electro-optical property may be a consequence of the functionalization of the first and second defined regions, or the difference in the at least one second electro-optical property may be a consequence of the functionalization of the third and fourth defined regions. The first or second device may be a laser, a light-emitting diode, a plasmon waveguide, an optical waveguide, an optical grating, a fluorescent device, a light-absorbing device, a photoelectron converter, a phaseshifting device, a interferometer, an optical coupler, or a plasmon coupler.

The graphene substrate may include a single layer or a multilayer. The first defined region and the second defined region, or the third defined region and the fourth defined region, may be adjacent. The first or second defined region may not include an edge of the graphene substrate. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first dopant species and the second dopant species may functional ize a common surface of the graphene substrate or opposing surfaces, and the first device and the second device may be positioned on opposing surfaces of the graphene substrate. The first or second dopant species may include at least one of an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group.

The second dopant species may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density. Any of the dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electro-optical property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, a method of forming an optoelectronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species, and functionalizing a second defined region of the graphene substrate with a second dopant species. The functional ized first region differs in an electro-optical property (e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from the functionalized second defined region.

The first dopant species and the second dopant species may be selected to confer a first electro-optical property and a second electro-optical property on the first defined region and second defined region, respectively. Functionalizing the first defined region may include selectively exposing the first region to a chemical solution, lithographically masking the graphene substrate, or applying a spatially patterned electrical potential to the graphene substrate.

In another aspect, a method of forming an optoelectronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species. The functionalized first region differs in an electro-optical property (e.g., optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy) from a second defined region and is remote from any edge of the graphene substrate.

The first dopant species may be selected to confer a first electro-optical property on the first defined region. Functionalizing the first defined region may include selectively exposing the first region to a chemical solution, lithographically masking the graphene substrate, or applying a spatially patterned electrical potential to the graphene substrate.

In another aspect, an electronic device includes a graphene substrate including a junction between an n-type defined region and a p-type defined region. The n-type region is chemically functionalized with a first dopant species and the p-type defined region is chemically functionalized with a second dopant species.

The graphene substrate may further include a neutral region (e.g. , an insulator, a semiconductor, or a metal) having substantially fewer free carriers than either the n- type defined region or the p-type defined region. The n-type and p-type defined regions may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include interconnects electrically connected to the n-type and p-type defined regions. The graphene substrate may include a single layer or a multilayer. Either or both of the n- type and p-type regions may be remote from an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from the n-type and p-type defined regions, which may be functionalized with a third dopant species.

The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and may be the same or different. The first dopant species may include at least one of an amine, an imine, an organic free radical, or an aromatic molecule, and the second dopant species may include at least one of an aromatic molecule, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, and an alkyl group. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the n-type or p-type defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property (e.g., free carrier population) may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first or second dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first or second dopant species may vary in concentration or attachment pattern within the n-type or p-type defined region. The p-type defined region may surround the n-type defined region, or the n-type defined region may surround the p-type defined region.

In another aspect, an electronic device includes a graphene substrate including a first defined region chemically functional ized with a first dopant species. The first dopant species has a concentration that varies across the first defined region (e.g., stepwise across the defined region or smoothly across the defined region).

The device may have at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) that varies across the first defined region, for example as a consequence of the functionalization of the first defined region. The first region may be part of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include an interconnect electrically connected to the first defined region. The graphene substrate may include a single layer or a multilayer. The first region may be remote from an edge of the graphene substrate. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first dopant species may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may vary in attachment pattern to the graphene substrate.

The first dopant species may include a plurality of intermixed dopant subspecies. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate.

In another aspect, an electronic circuit includes a first device and a second device. The first device includes a first junction between a first n-type defined region and a first p-type defined region, wherein the first n-type region is chemically functionalized with a first dopant species and the first p-type defined region is chemically functionalized with a second dopant species. The second device includes a second junction between a second n-type defined region and a second p-type defined region, wherein the n-type region is chemically functionalized with a third dopant species and the p-type defined region is chemically functionalized with a fourth dopant species.

The first and third dopant species, or the second and fourth dopant species, may be the same, and the first and second devices may have substantially the same electronic character. The circuit may further include a fifth defined region of the graphene substrate that functions as an interconnect between the first and second devices. The first or second device may be a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The graphene substrate may include a single layer or a multilayer.

The first n-type or first p-type defined region may not include an edge of the graphene substrate. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first dopant species and the second dopant species may functionalize a common surface of the graphene substrate or opposing surfaces, and the first device and the second device may be positioned on opposing surfaces of the graphene substrate. The first dopant species may include at least one of an amine, an imine, an organic free radical, or an aromatic molecule, and the second dopant species may include at least one of an aromatic molecule, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group.

The second dopant species may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density. Any of the dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first or second dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first or second dopant species may vary in concentration or attachment pattern within the first n-type or p-type defined region, respectively. The first p-type defined region may surround the first n-type defined region, or the first n- type defined region may surround the first p-type defined region.

In another aspect, a method of forming an electronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species selected to confer an n-type character on the first defined region, and functionalizing a second defined region of the graphene substrate with a second dopant species selected to confer a p-type character on the second defined region.

Functionalizing the first or second defined region may include selectively exposing the first defined region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or introducing a defect into the graphene substrate. The first defined region and the second defined region may be functionalized simultaneously or sequentially. The second defined region may overlap the first defined region. Functionalizing the first or second defined region may include co-depositing the second dopant species with the first dopant species. Either or both of the dopant species may exclude the other from depositing on the graphene substrate. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

In another aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property {e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first region is chemically functionalized with a first dopant species on a first surface of the graphene substrate, and the second region is chemically functionalized with a second dopant species on a second surface of the graphene substrate. The second surface opposes the first surface.

The first region may be chemically functionalized on opposing surfaces of the graphene substrate. The difference in the at least one electronic property may be a consequence of the functionalization of the first and second defined regions. The first and second defined regions may form a semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include a first interconnect electrically connected to the first defined region and a second interconnect electrically connected to the second defined region. The graphene substrate may include a single layer or a multilayer. The first defined region and the second defined region may be adjacent, and either may not include an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from each of the first defined region and the second defined region. The third defined region may be chemically functionalized with a third dopant species. The first or second dopant species may includes at least one of an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be the same or different. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first region is chemically functional ized with a first dopant species and a second dopant species on opposing surfaces of the graphene substrate.

The difference in the at least one electronic property may be a consequence of the functionalization of the first and second defined regions. The first and second defined regions may form a semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include a first interconnect electrically connected to the first defined region and a second interconnect electrically connected to the second defined region. The graphene substrate may include a single layer or a multilayer. The first defined region and the second defined region may be adjacent, and either may not include an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from each of the first defined region and the second defined region. The third defined region may be chemically functional ized with a third dopant species. The first or second dopant species may includes at least one of an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be the same or different. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region.

In another aspect, a method of forming an electronic device on a graphene substrate includes functionalizing a first defined region of the graphene substrate with a first dopant species on a first side of the graphene substrate, and functionalizing a second defined region of the graphene substrate with a second dopant species on an opposing second side of the graphene substrate. The first defined region and the second defined region differ in at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character).

Functionalizing the first or second defined region may include selectively exposing the first defined region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or introducing a defect into the graphene substrate. The first defined region and the second defined region may be functionalized simultaneously or sequentially. The second defined region may overlap the first defined region. Either or both of the dopant species may exclude the other from depositing on the graphene substrate. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

In another aspect, a method of making an electronic device includes applying a first functional group to a graphene substrate in a first predetermined pattern, and applying a second functional group in a second predetermined pattern to the graphene substrate patterned with the first functional group. The second predetermined pattern is at least partially determined by the application of the first functional group.

The method may further include removing at least a portion of the first functional group from the graphene substrate subsequent to applying the second functional group. The first or second predetermined pattern may be aligned in a predetermined relationship to a crystal direction of the graphene substrate. Applying the first functional group may include selectively exposing the first defined region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or introducing a defect into the graphene substrate. Either or both of the functional groups may exclude the other from depositing on the graphene substrate.

In another aspect, a method of making an electronic device includes applying a first functional group to a graphene substrate, and applying a second functional group to the first functional group in a predetermined pattern.

The second functional group may bonds to or exchange with the first functional group. After application of the second functional group, the graphene substrate may include a first region and a second region differing in at least one electrical property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character). The predetermined pattern may be aligned in a predetermined relationship to a crystal direction of the graphene substrate. Applying the first functional group may include selectively exposing the first defined region to a chemical solution, lithographically masking the graphene substrate, applying a spatially patterned electrical potential to the graphene substrate, or introducing a defect into the graphene substrate. Either or both of the functional groups may exclude the other from depositing on the graphene substrate.

In another aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first region is chemically functionalized with a first dopant species and the second defined region is chemically functionalized with a second dopant species, and the first defined region has a border aligned with a crystal direction of the graphene substrate.

The difference in the at least one electronic property may be a consequence of the functionalization. The first and second defined regions may form a

semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include interconnects electrically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The first and second regions may be adjacent, and either or both may be remote from an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from the first and second defined regions, which may be functionalized with a third dopant species. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same. The first and second dopant species may differ in concentration, attachment pattern to the graphene substrate, or number density.

Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second dopant species may include a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

In another aspect, an electronic device includes a graphene substrate including a first defined region and a second defined region differing in at least one electronic property (e.g., Fermi level, band structure, carrier populations, mobility, tunneling behavior, or conductive character) from the first defined region. The first region is chemically functional ized with a first dopant species, has a border aligned with a crystal direction of the graphene substrate, and is remote from any edge of the graphene substrate.

The second defined region may be chemically functional ized with a second dopant species, which may differ from the first dopant species. The first and second dopant species may differ in concentration, attachment pattern on the graphene substrate, or number density. Either or both dopant species may include a plurality of intermixed dopant subspecies, which may include the same or different subspecies, and which may differ in attachment pattern or relative concentration from one another. One or more dopant subspecies may vary in concentration within the first defined region. The first and second dopant species may functionalize a common surface of the substrate or opposing surfaces, and either or both may include an amine, an imine, an organic free radical, an aromatic molecule, nitrogen, boron, gold, bismuth, antimony, bromine, iodine, a diazonium salt, hydrogen, or an alkyl group, and may be different or the same.

The difference in the at least one electronic property may be a consequence of the functionalization. The first and second defined regions may form a

semiconducting junction, and may be parts of a component such as a diode, a transistor, a switch, a resistor, a capacitor, an inductor, a sensor, or an interconnect. The device may further include interconnects electrically connected to the first and second defined regions. The graphene substrate may include a single layer or a multilayer. The first and second regions may be adjacent, and the second region may be remote from an edge of the graphene substrate. The device may further include a third defined region differing in at least one electronic property from the first and second defined regions, which may be functionalized with a third dopant species. The graphene substrate may be disposed on a base substrate (e.g., graphite or a crystal containing a noncarbon component). The first dopant species may include a first bound moiety affixed to the graphene substrate and a first free moiety removably attached to the first bound moiety, in which case the difference in the electronic property may be a function of a property of the free moiety. The second defined region may be chemically functional ized with a second dopant species including a second bound moiety affixed to the graphene substrate and a second free moiety removably attached to the second bound moiety, in which case the composition of the first and second bound moieties may be the same or different. The first dopant species may be adsorbed onto the graphene substrate (e.g., chemisorbed or physisorbed), chemically bound to the substrate (e.g., covalently bound), or intercalated in the graphene substrate. The first dopant species may vary in concentration or attachment pattern within the first defined region. The second defined region may surround the first defined region, or the first defined region may surround the second defined region.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of a graphene-based electronic device.

FIG. 2 is a schematic of a graphene-based capacitor.

FIG. 3 is a flow chart describing a process for forming a graphene-based electronic device.

FIG. 4 is a schematic of a two-sided graphene-based device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

Graphene, a freestanding monolayer of graphite, exhibits unique electronic properties, including very high conductivity and unusual quantum effects (e.g., zero effective mass charge carriers with low scattering). Graphene sheets may be manufactured by flaking off of graphite (e.g. , highly oriented pyrolytic graphite (HOPG)), by growing as an epitaxial layer on other crystals and chemically etching to remove the graphene, or by reducing graphite oxide. See, e.g. , Li, et al, "Large-area synthesis of high-quality and uniform graphene films on copper foils," Science

324: 1312-1314(2009); Geim, et al, "The rise of graphene," Nature Mat 'Is 6: 183- 191 (March 2007); Benayad, et al, "Controlling work function of reduced graphite oxide with Au-ion concentration," Chem Phys Lett, 475: 91 -95 (2009), each of which is incorporated by reference herein. Either before or after removal from the graphite or heterogeneous substrate, graphene may be chemically functionalized to produce electronic devices. While the description that follows focuses on monolayer graphene, chemical functionalization of oligolayers may also yield interesting electronic properties.

FIG. 1 is a schematic of a graphene-based electronic device. In the illustrated embodiment, graphene sheet 10 includes three doped regions 12, 14, 16. Region 12 is functionalized with a species that renders it n-type relative to pristine (pure) graphene. Region 14 is functionalized with a species that renders it p-type relative to pristine graphene, and region 16 is functionalized with a species that renders it more insulating than pristine graphene. Regions 18 may be undoped, functionalized with a conductive species, or functionalized with a species that renders the underlying graphene more conductive than region 16, to form interconnects. In the illustrated embodiment, the device functions as a simple p-n junction diode. By analogy with silicon-based semiconducting devices, other arrangements of p-type and n-type regions may be used to construct transistors, switches, and other electronic components. Further, dopant species and/or concentrations may be varied in some regions to produce other components, such as resistors, capacitors, inductors, sensors, or interconnects. For example, FIG. 2 illustrates a graphene-based capacitor.

Interdigitated conductive regions 30 and 32 are separated by dielectric region 34 in a two-dimensional analog of a typical capacitor design. In other embodiments, conductive regions may form opposing T-shapes or double spirals, for example. A spiral configuration may also be used to form an inductor, for example. A method of forming a device like that in FIG. 1 is illustrated in FIG. 3. In the illustrated embodiment, a pure graphene sheet is masked (using conventional lithographic methods) to expose only region 12, which is then exposed to a chemical that forms an n-type region. For example, exposure of graphene to NH ₃ gas at elevated temperatures will tend to form an n-type region by covalent bonding, particularly at edges and defect sites, as described in Wan, et al, Science

32 _. 4(5928):768-771 (May 2009), which is incorporated by reference herein. N-doped graphene may also be formed by chemical vapor deposition of a mixture of NH ₃ and CH ₄ gas, or by arc discharge of carbon electrodes in the presence of H ₂ /pyridine or H ₂ NH ₃ . See, e.g. , Wei, et al, "Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties," Nano Lett. 9(5): 1752- 1758 (2009);

Panchakarla, et al, "Synthesis, Structure, and Properties of Boron and Nitrogen Doped Graphene," Adv. Mat., 21(46):4726-4730 (Aug. 2009), each of which are incorporated by reference herein. Other suitable electron-donating agents which may be adsorbed onto the graphene surface include organic free radicals {e.g., 4-amino- TEMPO), aromatic molecules with electron-donating groups, or electron-donating macromolecules such as poly(ethylene imine). See, e.g., Choi, et al, "Chemical Doping of Epitaxial Graphene by Organic Free Radicals," J. Phys. Chem. Lett.

2010(1 ):505-509 (2010); Dong, et al, "Doping Single-Layer Graphene with

Aromatic Molecules," Small 5(12): 1422-1426 (June 2009); Farmer, et al, "Chemical Doping and Electron-Hole Conduction Asymmetry in Graphene Devices," Nano Lett., 9(l):388-392 (2009), each of which are incorporated by reference herein. In the illustrated embodiment, the region 12 is remote from any edge of the graphene sheet {i.e., far enough away from the edge that electrical properties imparted by the donor species are no more than minimally affected by the existence of the edge). In some embodiments, the borders of region 12 may be aligned with a crystal direction of the graphene, while in other embodiments, the borders may be at any angle to the crystal axis. In some embodiments, application of the functional group may include applying an electric potential to the graphene substrate, e.g., a patterned electric potential.

In an embodiment, it may be desirable to introduce one or more defects into the region before exposure to NH ₃ (or other dopants), which is believed to be chemically reactive at defect sites. For example, a focused electron beam may be used to introduce one or more defects into the graphene lattice at region 12 before exposure, or the masked region may be exposed to an oxygen plasma. (In an embodiment, simultaneous n-doping and reduction of oxidized graphene may be achieved by exposure to an oxygen plasma. See, e.g., Li et al, "Simultaneous Nitrogen-Doping and Reduction of Graphene Oxide," J. Am. Chem. Soc,

131(43): 15939- 15944 (2009), which is incorporated by reference herein.) Very precisely placed defect sites may also be introduced by use of an atomic force microscope. In an embodiment, with sufficiently well-controlled introduction of defects and chemical functionalization, it may be possible to eliminate the need to mask the region, defining the doped region by selective introduction of defects into the graphene lattice. In an embodiment, it may be possible to anneal or otherwise heal such defects after doping.

Once region 12 has been formed, the substrate may be cleaned and remasked according to standard lithographic techniques, then exposed to a different electron donor species to form p-type region 14. For example, substitution of boron into the graphene backbone will tend to form a p-type region, as will adsorption (or intercalation in graphene oligolayers) of bromine, iodine, aromatic structures including electron-withdrawing groups, or diazonium salts {e.g., 4-bromobenzene diazonium tetrafluorate), or deposition of gold, bismuth, or antimony (in some embodiments, followed by annealing). See, e.g., Panchakarla, et al, "Synthesis, Structure, and Properties of Boron and Nitrogen Doped Graphene," Adv. Mat.,

21(46):4726-4730 (Aug. 2009); Jung, et al, "Charge Transfer Chemical Doping of Few Layer Graphenes: Charge Distribution and Band Gap Formation," Nano Lett., 9(12):4133-4137 (2009); Dong, et al, "Doping Single-Layer Graphene with

Aromatic Molecules," Small 5(12): 1422-1426 (June 2009); Farmer, et al, "Chemical Doping and Electron-Hole Conduction Asymmetry in Graphene Devices," Nano Lett., 9(l):388-392 (2009); Gierz, et al, "Atomic Hole Doping of Graphene," Nano Lett. 8(12):4603-4607 (2008), each of which are incorporated by reference herein. For any of these species, in some embodiments, it may be preferable to introduce defects into the graphene as described above. Once region 14 has been formed, the substrate may be cleaned and remasked, then exposed to a different to form region 16. For example, exposure of graphene to atomic hydrogen (e.g., as a plasma) will tend to form an insulating region

("graphane"). (P-type regions may also be produced by annealing of graphane regions formed by exposure to hydrogen plasma.) See, e.g., Elias, et al., "Control of Graphene's Properties by Reversible Hydrogenation: Evidence for Graphane,"

Science 323:610-613 (2009), which is incorporated herein by reference. In general, selective rehybridization of graphene's carbon atoms from an sp ² state to an sp ³ state will tend to open a band gap, thus producing semiconducting or insulating regions. For example, alkylation or arylation may also produce semiconducting or insulating regions. Optionally, after formation of region 16, regions 18 may also be formed by lithographic methods. Alternatively, regions 18 may consist essentially of pristine graphene. It will be understood that the steps of forming the different regions may occur in any convenient order. For example, if the conditions required to produce an n-type region might tend to degrade a p-type region on the same sheet, then it may be preferable to firm produce the n-type region(s), and follow with production of the p- type region(s).

One challenge in nanolithography is registration when successive masks are used on the same substrate. In an embodiment, registration "marks" may be placed on the graphene substrate in the form of easily detectable functional groups (which may or may not have any function in a final electronic device). For example, electroluminescent polymers (e.g. , oligomers) such as poly(p-phenylene vinylene) may be well suited to be used as markers, forming large, rigid structures which may be detected by their photon emission. In an embodiment, X-ray emitters may be placed on the substrate, but caution is needed to avoid degradation of the final product by the emitted X-rays.

In an embodiment, rather than individually functionalizing each region of a graphene sheet with a different dopant species as described above, it may be desirable to functionalize the entire sheet (or a portion of the sheet) with a species, and then to lithographically create the desired regions, either by swapping the whole functional molecule, or by adding new functionality (as a free moiety attached to a bound moiety affixed to the substrate) that confers the desired properties. In an

embodiment, graphene circuits may be made partially or fully rewritable by such methods. For example, carbon nanofibers have been modified with electrochemically active ferrocene groups by the Cu(I)-catalyzed azide-alkyne cycloaddition reaction ("click" chemistry). See, e.g., Landis, et al, "Covalent grafting of redox-active molecules to vertically aligned carbon nanofiber arrays via 'click' chemistry," Chem. Mater. , 21(4):724-730 (2009), which is incorporated by reference herein. This approach is expected to be applicable to modification of graphene functionalized with azide, as well. In an embodiment, functional groups may be adsorbed (e.g. , physisorbed or chemisorbed) onto the graphene surface, rather than covalently bonded. Some dopant species may also intercalate in oligolayers of the graphene substrate.

While the above methods have been described in connection with production of a single p-n junction surrounded by an insulator, more complicated geometries, for example including many interconnected devices, may be produced by following the same steps, for example by using masks that include a plurality of openings to form many regions having each desired carrier density. In general, most any two- dimensional arrangement of doped regions for silicon devices is expected to have a graphene analog.

Further, the above methods are described with reference to deposition of a single dopant species in each region. In some embodiments, multiple dopant species may be applied to a single region. These may co-deposit (in a spontaneously ordered, partially ordered, or random configuration), or the deposition of one species may exclude the bonding of another to the graphene surface. In the latter case, the exclusion effect may be used to improve registration of multiple regions. For example, if an electron donor dopant species also has the property of excluding an electron acceptor dopant species, then p-type region 14 might be produced first.

Subsequent masking to produce region 12 would not need to be precisely aligned at the border between regions 12 and 14, but could form some degree of overlap, and the exclusion of the acceptor species would produce two adjacent but not overlapping regions. Certain species are known to deposit on graphene in ordered patterns that depend on the character of their bond with carbon and also on steric considerations. These effects may be used in sequential reactions to deposit other species in an ordered fashion at less than full saturation. For example, it has been calculated that optimum coverage of phenyl groups on graphene is at 2 phenyl groups per unit cell of 18 graphene carbon atoms, for a coverage density of 1 1%. See, e.g., Bekyarova et al, Phys. Status Solidi RRL, 3(6): 187-189 (2009), which is incorporated by reference herein. A graphene substrate may be covered with phenyl groups at this density, and then subsequently exposed to a physically smaller dopant species {e.g., a metal or a halide), which is expected to deposit in between the phenyl groups. Finally, the phenyl groups may optionally be removed, leaving behind the smaller dopant species at a less than fully saturated concentration. In an embodiment, the phenyl groups may be adsorbed, rather than covalently bonded to the graphene, to facilitate removal. More complicated multistep processes for doping may also be envisioned, for example following the removal of the phenyl groups with doping with another small dopant species that does not displace the first non-saturated small dopant species, thereby achieving a patterned co-deposited layer. These techniques may also be used, for example to produce a graphene substrate including two doped regions which are each doped with the same intermixed co-dopants, but in different concentrations, number density, or attachment pattern. Dopants may also be deposited in a gradient concentration across a region, a random concentration, or in any other suitable pattern in which concentration varies with in a region. A mixture of dopants may also be simultaneously co-deposited in a single region, in which case the dopants may deposit randomly, in a partially ordered fashion, or in a fully ordered fashion {e.g., by spontaneous self assembly into an ordered array).

In an embodiment, one or both sides of a free graphene sheet may be functionalized. For example, in the embodiment shown in FIG. 4, region 40 is functionalized with a first dopant species, and region 42 is functionalized with a second dopant species on the opposite side of the graphene sheet. Region 44

represents an overlap area between the functionalized regions which is expected to have different electronic properties than either of the non-overlapping functional ized regions.

In an embodiment, instead of or in addition to lithographic masking of the substrate, deposition may be controlled by applying a patterned electric or magnetic field in the vicinity of the substrate.

In one example, a p-n junction in the configuration of FIG. 1 is formed as follows. A pristine graphene substrate is formed by flaking from HOPG. The substrate is masked with a lithographic mask exposing region 16 and exposed to a cold hydrogen plasma (0.1 mbar 10% hydrogen-90% argon mixture at 30 cm for 2 hr) to form graphane in the region. (See, Elias, et al, supra The mask is then removed.

The substrate is masked with a water- and alcohol-compatible lithographic mask that exposes region 14, and then immersed in a 1 mM solution of 4- bromobenzenediazonium tetrofluoroborate in a 1 : 1 water/methanol mixture at 300 K for 2 h and rinsed with water and methanol, thereby doping the region with diazonium to produce a p-type region. (See Farmer et al , supra.) The lithographic mask is then removed.

Finally, the substrate is then masked with a lithographic mask that exposes regions 12 and 14. The surface is dosed using a direct doser (controlled by means of a variable leak valve) with azidotrimethylsilane (ATS), which adsorbs via nitrene radical onto the graphene surface. (See Choi et al , supra.) The already-doped region 14 excludes the ATS, so only region 12 is doped to produce an n-type region. The mask is then removed. Regions 18 have not been exposed to any of the graphene- modifying procedures in this example, and thus remain pristine metallic or semiconducting graphene.

In another example, an epitaxially grown graphene layer on a nitrogen-doped

SiC substrate has an intrinsic n-type character. The graphene is masked to expose region 14 and gold is deposited using a nudsen cell at room temperature. The substrate is then annealed at 700°C for 5 min, which simultaneously allows the gold to bond to the graphene layer (forming a p-type region) and decomposes the resist. (See, Gierz et al, supra.) The layer is then remasked to cover regions 12 and 14 and expose region 16 and exposed to a solution of 4-nitrophenyl diazonium tetrofluoroborate, which forms an insulating region. {See Bekyarova et al, supra) The resist is then removed, leaving a p-n junction surrounded by an insulating region.

In an embodiment, dopants may be selected to adjust other electronic properties of graphene besides the carrier populations described above, such as Fermi level, band structure, mobility, tunneling behavior, or conductive character. For example, effects of adsorbates on Fermi level and Fermi velocity are discussed in Khomyakov, et al, "First-principles study of the interaction and charge transfer between graphene and metals," Phys Rev B, 79: 195425 (2009); Giovannetti, et al, "Doping graphene with metal contacts," Phys Rev Lett, 101:026803 (2008); Benayad, et al, "Controlling work function of reduced graphite oxide with Au-ion

concentration," Chem Phys Lett, 475:91-95 (2008); and Tapaszto, et al, "Tuning the electronic structure of graphene by ion irradiation," Phys Rev B, 78:233407 (2008), each of which is incorporated by reference herein.

In an embodiment, rather than or in addition to adjusting charge carrier populations as discussed above, dopant species may be selected to modify optical or electro-optical properties of graphene, such as optical gain, transmissivity, reflectivity, permittivity, permeability, refractive index, or anisotropy, for example to form plasmonic devices (lasing or passive) or other nonlinear electro-optical devices. Pristine graphene is found to absorb πα = 2.3% of incident white light despite having a thickness of one atom (where a is the fine structure constant, approximately 1/137). Disruption of the graphene's sp ² network {e.g., by sp ³ bond formation) reduces the transparency as observed in graphene oxide. See, e.g., Nair, et al., "Fine structure constant defines visual transparency of graphene," Science, 320: 1308 (2008); Kim, et al, "Large-scale pattern growth of graphene films for stretchable transparent electrodes," Nature, 457:706-710 (2009); U.S. Published Application No.

2009/01461 1 1 to Shin et al; Rao, et al., "Some novel attributes of graphene." J Phys Chem Lett; 1:572-580 (2010), each of which is incorporated by reference herein. Those of skill in the art will recognize how to use these optical or electro-optical properties to construct various graphene-based optoelectronic devices by analogy with silicon-based or other known devices, such as lasers, light-emitting diodes, plasmon waveguides, optical waveguides, optical gratings, fluorescent devices, light- absorbing devices, photoelectron converters, phaseshifting devices, interferometers, optical couplers, or plasmon couplers.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art based on the teachings herein. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and

modifications as are within the true spirit and scope of this subject matter described herein.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

It will be understood that, in general, terms used herein, and especially in the appended claims, are generally intended as "open" terms (e.g. , the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of introductory phrases such as "at least one" or "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a functional group" should typically be interpreted to mean "at least one functional group"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, it will be recognized that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two functional groups," or "a plurality of functional groups," without other modifiers, typically means at least two functional groups). Furthermore, in those instances where a phrase such as "at least one of A, B, and C," "at least one of A, B, or C," or "an [item] selected from the group consisting of A, B, and C," is used, in general such a construction is intended to be disjunctive (e.g. , any of these phrases would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, and may further include more than one of A, B, or C, such as Ai, A ₂ , and C together, A, Bj, B ₂ , Ci, and C ₂ together, or B) and B ₂ together). It will be further understood that virtually any disjunctive word or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Moreover, "can" and "optionally" and other permissive terms are used herein for describing optional features of various embodiments. These terms likewise describe selectable or configurable features generally, unless the context dictates otherwise.

The herein described aspects depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively

"associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality. Any two components capable of being so associated can also be viewed as being "operably coupleable" to each other to achieve the desired functionality. Specific examples of operably coupleable include but are not limited to physically mateable or interacting components or wirelessly interacting components.

What is claimed is: