Oh, the places you'll go with graphene.

Since the first reported isolation of graphene by peeling graphite with cellophane tape in 2004, there has been a paradigm shift in research. In just nine years, graphene has had a major impact on fields ranging from physics and chemistry to materials science and engineering leading to a host of interdisciplinary advances in nanotechnology. Graphene is attractive because it possesses many extraordinary characteristics that are a direct consequence of its unique atomic structure, as discussed here. For over a decade, our group has been exploring new routes to synthesize graphene so that this potentially important material can be scaled up for use in practical applications. We have made several significant discoveries starting with the synthesis of few-layer graphene from intercalation/exfoliation reactions that upon sonication produce carbon nanoscrolls. Next, we developed high-throughput methods for producing chemically converted graphene from graphene oxide using either aqueous or anhydrous hydrazine. Recently, we introduced an inexpensive process that uses the laser in an optical drive to deoxygenate graphite oxide layers to create laser scribed graphene. The impetus of this Account is to discuss both synthetic routes to graphene and their applications. The first part highlights both our top-down and bottom-up routes to graphene, which includes intercalation/exfoliation, chemical reduction with hydrazine and other organic reagents, chemical vapor deposition, and laser scribed graphene. In the later part, we emphasize the significance of these contributions to the field and how each approach has afforded us unique opportunities to explore graphene's properties. This has resulted in new applications such as practical chemical sensors, flash memory storage devices, transparent conductors, distributed ignition, and supercapacitors.

Chemical vapor deposition of graphene on copper from methane, ethane and propane: evidence for bilayer selectivity.

To study the effects of hydrocarbon precursor gases, graphene is grown by chemical vapor deposition from methane, ethane, and propane on copper foils. The larger molecules are found to more readily produce bilayer and multilayer graphene, due to a higher carbon concentration and different decomposition processes. Single- and bilayer graphene can be grown with good selectivity in a simple, single-precursor process by varying the pressure of ethane from 250 to 1000 mTorr. The bilayer graphene is AB-stacked as shown by selected area electron diffraction analysis. Additionally propane is found to only produce a combination of single- to few-layer and turbostratic graphene. The percent coverage is investgated using Raman spectroscopy and optical, scanning electron, and transmission electron microscopies. The data are used to discuss a possible mechanism for the second-layer growth of graphene involving the different cracking pathways of the hydrocarbons.

Continuity of graphene on polycrystalline copper.

The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with graphene's perfect carbon honeycomb lattice. Our observations suggest that growth models including a stagnant catalytic surface do not apply to graphene growth on copper. Contrary to current expectations, these results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure.

Low-temperature solution processing of graphene-carbon nanotube hybrid materials for high-performance transparent conductors.

We report the formation of a nanocomposite comprised of chemically converted graphene and carbon nanotubes. Our solution-based method does not require surfactants, thus preserving the intrinsic electronic and mechanical properties of both components, delivering 240 ohms/square at 86% transmittance. This low-temperature process is completely compatible with flexible substrates and does not require a sophisticated transfer process. We believe that this technology is inexpensive, is massively scalable, and does not suffer from several shortcomings of indium tin oxide. A proof-of-concept application in a polymer solar cell with power conversion efficiency of 0.85% is demonstrated. Preliminary experiments in chemical doping are presented and show that optimization of this material is not limited to improvements in layer morphology.

Graphene flash memory.

Graphene's single atomic layer of sp(2) carbon has recently garnered much attention for its potential use in electronic applications. Here, we report a memory application for graphene, which we call graphene flash memory (GFM). GFM has the potential to exceed the performance of current flash memory technology by utilizing the intrinsic properties of graphene, such as high density of states, high work function, and low dimensionality. To this end, we have grown large-area graphene sheets by chemical vapor deposition and integrated them into a floating gate structure. GFM displays a wide memory window of ∼6 V at significantly low program/erase voltages of ±7 V. GFM also shows a long retention time of more than 10 years at room temperature. Additionally, simulations suggest that GFM suffers very little from cell-to-cell interference, potentially enabling scaling down far beyond current state-of-the-art flash memory devices.