Graphene Transfer: A Physical Perspective.

Graphene, synthesized either epitaxially on silicon carbide or via chemical vapor deposition (CVD) on a transition metal, is gathering an increasing amount of interest from industrial and commercial ventures due to its remarkable electronic, mechanical, and thermal properties, as well as the ease with which it can be incorporated into devices. To exploit these superlative properties, it is generally necessary to transfer graphene from its conductive growth substrate to a more appropriate target substrate. In this review, we analyze the literature describing graphene transfer methods developed over the last decade.

Transfer of printed electronic structures using graphene oxide and gelatin enables reversible and biocompatible interface with living cells.

We present a low-cost, easy-to-implement platform for printing materials and interfacing them with eukaryotic cells. We show that thermal or chemical reduction of a graphene oxide thin film allows water-assisted delamination of the film from glass or plastic. The chemical and physical properties and permeability of the resulting film are dependent on the method of reduction and deposition of the graphene oxide, with thermal reduction removing more oxidized carbon functionality than chemical reduction.

Protection from Below: Stabilizing Hydrogenated Graphene Using Graphene Underlayers.

We show that dehydrogenation of hydrogenated graphene proceeds much more slowly for bilayer systems than for single layer systems. We observe that an underlayer of either pristine or hydrogenated graphene will protect an overlayer of hydrogenated graphene against a number of chemical oxidants, thermal dehydrogenation, and degradation in an ambient environment over extended periods of time. Chemical protection depends on the ease of oxidant intercalation, with good intercalants such as Br demonstrating much higher reactivity than poor intercalants such as 1,2-dichloro-4,5-dicyanonbenzoquinone (DDQ).

Surface fouling as a mechanism for chemotaxis in isotropic catalytic swimmers.

We present microscopic models for surface fouling of an isotropic spherical catalytic microswimmer at and away from equilibrium and show how a foulant gradient can induce chemotactic behavior. Our simulations establish that the presence of foulant manifests itself in two ways: as a braking effect on propulsive particle motion, and as a drift term which probes the foulant concentration gradient. Our results suggest that, while foulant gradients are unlikely to be directly useful for chemotactically directed particles, they nevertheless exert a non-negligible influence on particle motion under a wide range of conditions.

Transfer of Chemically Modified Graphene with Retention of Functionality for Surface Engineering.

Single-layer graphene chemically reduced by the Birch process delaminates from a Si/SiOx substrate when exposed to an ethanol/water mixture, enabling transfer of chemically functionalized graphene to arbitrary substrates such as metals, dielectrics, and polymers. Unlike in previous reports, the graphene retains hydrogen, methyl, and aryl functional groups during the transfer process. This enables one to functionalize the receiving substrate with the properties of the chemically modified graphene (CMG).

Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature.

Direct mechanochemical cleavage of functional groups from graphene.

Mechanical stress can drive chemical reactions and is unique in that the reaction product can depend on both the magnitude and the direction of the applied force. Indeed, this directionality can drive chemical reactions impossible through conventional means. However, unlike heat- or pressure-driven reactions, mechanical stress is rarely applied isometrically, obscuring how mechanical inputs relate to the force applied to the bond.

Patterning magnetic regions in hydrogenated graphene via e-beam irradiation.

Partially hydrogenated graphene is ferromagnetic and may be patterned by electron-beam irradiation. Sequential patterning produces a patterned magnetic array. Removal of the hydrogen atoms also can convert electrically insulating fully hydrogenated graphene back into conductive graphene, enabling the writing of chemically isolated, dehydrogenated graphene nanoribbons as narrow as 100 nm.

Chemical stability of graphene fluoride produced by exposure to XeF2.

Fluorination can alter the electronic properties of graphene and activate sites for subsequent chemistry. Here, we show that graphene fluorination depends on several variables, including XeF2 exposure and the choice of substrate. After fluorination, fluorine content declines by 50-80% over several days before stabilizing.

Theoretical studies of CH4 inside an open-cage fullerene: translation-rotation coupling and thermodynamic effects.

Molecules trapped inside fullerenes exhibit interesting quantum behavior, including quantization of their translational degrees of freedom. In this study, a theoretical framework for predicting quantum properties of nonlinear small molecules in nonsymmetric open-cage fullerenes (OCFs) has been described along the lines of similar theories which treat small molecules inside C(60) and clathrate cages. As an example, the coupled translational-rotational energy structure has been calculated for the case of CH(4) inside a known OCF.

Methane in an open-cage [60]fullerene.

An endohedral methane complex of a fullerene derivative is first synthesized by insertion of a methane molecule through the opening of an open-cage C(60) derivative. The trapped methane is confirmed by NMR spectroscopy and mass spectrometry. Both methane carbon and protons show remarkable upfield shifts in NMR, characteristic of a chemical species in a fullerene cage.

Putting ammonia into a chemically opened fullerene.

We put ammonia into an open-cage fullerene with a 20-membered ring ( 1) as the orifice and examined the properties of the complex using NMR and MALDI-TOF mass spectroscopy. The proton NMR shows a broad resonance corresponding to endohedral NH 3 at delta H = -12.3 ppm relative to TMS.