Monolayer and/or Few-Layer Graphene On Metal or Metal-Coated Substrates

Abstract

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