Monolayer and/or Few-Layer Graphene On Metal or Metal-Coated Substrates
Graphene is a single atomic layer of sp 2 -bonded C atoms densely packed into a two-dimensional honeycomb crystal lattice. A method of forming structurally perfect and defect-free graphene films comprising individual mono crystalline domains with in-plane lateral dimensions of up to 200 μm or more is presented. This is accomplished by controlling the temperature-dependent solubility of interstitial C of a transition metal substrate having a suitable surface structure. At elevated temperatures, C is incorporated into the bulk at higher concentrations. As the substrate is cooled, a lowering of the interstitial C solubility drives a significant amount of C atoms to the surface where graphene islands nucleate and gradually increase in size with continued cooling. Ru(0001) is selected as a model system and electron microscopy is used to observe graphene growth during cooling from elevated temperatures. With controlled cooling, large arrays of macroscopic single-crystalline graphene domains covering the entire transition metal surface are produced. As the graphene domains coalesce to a complete layer, a second graphene layer is formed, etc. By controlling the interstitial C concentration and the cooling rate, graphene layers with thickness up to 10 atomic layers or more are formed in a controlled, layer-by-layer fashion.
1 . A graphene layer comprised of a two-dimensional hexagonal array of carbon atoms, the graphene layer substantially free of defects.
2 . The graphene layer of claim 1 comprising mono crystalline domains whose lateral dimensions are greater than about 20 μm along at least two orthogonal directions within the two-dimensional plane.
3 . The graphene layer of claim 1 wherein the two-dimensional hexagonal array of carbon atoms is one atomic layer thick.
4 . The graphene layer of claim 1 wherein the two-dimensional hexagonal array of carbon atoms is two atomic layers thick.
5 . The graphene layer of claim 1 wherein the two-dimensional hexagonal array of carbon atoms is three atomic layers thick.
6 . The graphene layer of claim 1 wherein the graphene layer is less than about ten atomic layers thick.
7 . The graphene layer of claim 6 further comprising a substrate and wherein the graphene layer is formed on a surface of the substrate.
8 . The graphene layer of claim 7 wherein the substrate comprises a transition metal.
9 . The graphene layer of claim 8 wherein the transition metal comprises a thin film.
10 . The graphene layer of claim 8 wherein the transition metal comprises a bulk material
11 . The graphene layer of claim 8 wherein the surface of the substrate is Ru(0001).
12 . The graphene layer of claim 9 wherein the thin film of the substrate is polycrystalline Ru.
13 . The graphene layer of claim 9 wherein the thin film of the substrate is epitaxial Ru.
14 . The graphene layer of claim 7 , wherein the substrate is planar.
15 . The graphene layer of claim 7 , wherein the substrate exhibits curvature having a radius greater than 100 μm.
16 . The graphene layer of claim 7 , wherein the substrate exhibits curvature having a radius smaller than 100 μm.
17 . An electronic device comprising a graphene layer comprised of a two-dimensional hexagonal array of sp 2 -bonded carbon atoms consisting of monocrystalline domains whose lateral dimensions are greater than about 20 μm along at least two orthogonal directions within the two-dimensional plane, the graphene layer substantially free of surface defects.
18 . A sensor comprising a graphene layer comprised of a two-dimensional hexagonal array of sp 2 -bonded carbon atoms consisting of monocrystalline domains whose lateral dimensions are greater than about 20 μm along at least two orthogonal directions within the two-dimensional plane, the graphene layer substantially free of surface defects.
19 . A method of forming graphene comprising:
heating a transition metal to about 0.5(T M ) under vacuum and maintaining this temperature for several seconds to several minutes;
exposing the transition metal to a hydrocarbon gas at a pressure of about 10 −8 to 10 −5 torr; and
cooling the transition metal to 0.3 to 0.4(T M ) at a rate of about 20° C./minute or less;
wherein T M is the melting temperature of the transition metal.
20 . The method of claim 19 wherein the hydrocarbon is ethylene.
21 . The method of claim 19 wherein the graphene forms on a surface of the transition metal.
22 . The method of claim 21 wherein the transition metal is a bulk single crystal.
23 . The method of claim 21 wherein the transition metal is a polycrystalline thin film.
24 . The method of claim 21 wherein the transition metal is an epitaxial thin film.
25 . The method of claim 19 wherein a region near a surface of the transition metal is enriched with interstitial carbon atoms.
26 . The method of claim 19 , wherein the transition metal has a surface consisting of atomically flat terraces separated by steps.
27 . The method of claim 21 , wherein the surface of the transition metal has a hexagonal crystal structure which is lattice-matched to graphene within about 15%.
28 . The method of claim 27 , wherein the transition metal is ruthenium and the surface comprises a (0001) plane.
29 . The method of claim 19 wherein the graphene layer comprises less than about ten atomic layers of graphene.
30 . The method of claim 26 wherein the graphene layer is a monolayer of graphene.
31 . The method of claim 26 wherein the graphene layer comprises two atomic layers of graphene.
32 . The method of claim 26 wherein the graphene layer comprises three atomic layers of graphene.
33 . The method of claim 19 further comprising isolating the graphene layer from the transition metal.
34 . The method of claim 33 wherein isolating the graphene layer comprises etching the transition metal.
35 . The method of claim 33 wherein isolating the graphene layer comprises weakening the interaction between the transition metal and graphene.
36 . The method of claim 35 further comprising transferring the graphene layer to a solid support.
37 . The method of claim 36 wherein the support is an electrical insulator.
38 . The method of claim 33 wherein isolating the graphene layer comprises intercalating a substance between the transition metal and a first atomic layer of the graphene layer covalently bonded to the transition metal, and removing all atomic layers comprising the graphene layer.
39 . A mirror comprising:
a substrate, the substrate having a surface exhibiting a curvature operable to focus an incident beam onto a focal plane; and
a graphene layer conformally adhering to the substrate, the graphene layer operable to protect the substrate surface from degradation due to the incident beam and an ambient environment.
40 . The mirror of claim 39 , wherein the substrate comprises a thin film of a transition metal deposited on a substrate form.
41 . The mirror of claim 40 , wherein the substrate form comprises a fused silica form.
42 . The mirror of claim 39 , wherein the incident beam is chosen from the group consisting of an electromagnetic beam, an electron beam, a neutral atomic species beam, and a neutral molecular species beam.
43 . The mirror of claim 42 , wherein the incident beam is a beam of helium.
44 . The mirror of claim 42 , wherein the incident beam is a beam of hydrogen.
45 . The mirror of claim 39 , wherein the curvature is elliptical.
46 . The mirror of claim 39 , wherein the curvature is spherical.
47 . The mirror of claim 39 , wherein the graphene layer comprises less than ten atomic layers of graphene.
48 . The mirror of claim 47 , wherein the graphene layer is a monolayer of graphene.
49 . The mirror of claim 47 , wherein the graphene layer comprises two atomic layers.
50 . The mirror of claim 47 , wherein the graphene layer comprises three atomic layers