Evidence of Nanocrystalline Semiconducting Graphene Monoxide during Thermal Reduction of Graphene Oxide in Vacuum

Abstract

As silicon-based electronics are reaching the nanosize limits of the semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning the properties of carbon-based materials. Chemical functionalization is a proposed route, but syntheses of graphene oxide (G-O) produce disordered, nonstoichiometric materials with poor electronic properties. We report synthesis of an ordered, stoichiometric, solid-state carbon oxide that has never been observed in nature and coexists with graphene. Formation of this material, graphene monoxide (GMO), is achieved by annealing multilayered G-O. Our results indicate that the resulting thermally reduced G-O (TRG-O) consists of a two-dimensional nanocrystalline phase segregation: unoxidized graphitic regions are separated from highly oxidized regions of GMO. GMO has a quasi-hexagonal unit cell, an unusually high 1:1 O:C ratio, and a calculated direct band gap of ∼0.9 eV.

Overcoming the Phase Inhomogeneity in Chemically Functionalized Graphene: The Case of Graphene Oxides

“…As the typical values of x in CO x in the current experiments are usually smaller than 0.5, we can understand that inhomogeneous phase generally exists in almost all the GO samples. Our calculations explain quite well the recent experimental discovery that thermally reduced GO is separated into unoxidized graphene regions and high-oxidized GO regions that have a quasi-hexagonal unit cell with an unusually high 1:1 O:C ratio [20].…”

“…We find that the miscibility temperature of GO even at quite low oxygen concentration (x ≤ 0.05) is around 4000 K, which is rather high and close to the melting point of graphite [31]. The calculated phase diagram clearly demonstrates that it is impossible to get homogeneous GOs by the conventional Hummers methods under the typical temperature for preparing thermally reduced GOs [6,8,9,15,20,21].…”

“…However, the hydroxyl groups are less stable, so after annealing to produce the thermally reduced GOs, most of the hydroxyl groups are removed and the epoxy groups play the dominant role in GOs [20]. Moreover, recent experimental progress also shows that it is possible to produce GOs with only epoxy groups [20,21], e.g., by using atomic oxygen as dopant [21]. Therefore, in this study, we will focus on GOs with only epoxy groups.…”

“…1a. In the ground state of CO 1 , epoxy pair chains are aligned along zigzag direction and the C-C bonds under epoxy pairs are broken [17,20]. Compared with graphene (D 6h symmetry), the magnitude of the lattice vectors of CO 1 (D 2h symmetry) is increased from 2.46Å to 3.02Å and the angle between them is 129.5 o versus the 120 o of an ideal hexagonal lattice.…”

A Review on Reducing Graphene Oxide for Band Gap Engineering

“…A recent study showed graphene monoxide production having a band gap of ~0.9 eV with a thermal reduction (~500-700°C) of GO in vacuum. Intercalated water in GO demonstrated an unobserved atomic structure and morphology, which is a phase segregation resulting in graphitic regions with little or no oxidation after annealing (Mattson et al, 2011). It was also found that water molecules from the ambient or at the SiO 2 /graphene interface can split into H + and OH -with further attaching to graphene and generating a band gap (Echtermeyer et al, 2008).…”