Deposition and Characterization of Graphene from Solid Carbon Sources

The near-room temperature thermal conductivity of graphene was recently measured to be between 4.84 - 103 to 5.30 - 103Wm−1K−1.
These measurements, made by a non-contact optical technique, are in excess of those measured for carbon nanotubes or diamond. It can be shown by using the Wiedemann-Franz law, that the thermal conduction is phonon-dominated. Despite its 2D nature, graphene has 3 acoustic phonon modes. The two in-plane modes (LA, TA) have a linear dispersion relation, whereas the out of plane mode (ZA) has a quadratic dispersion relation. Due to this, the T2 dependent thermal conductivity contribution of the linear modes is dominated at low temperatures by the T1.5 contribution of the out of plane mode. Some graphene phonon bands display negative Grüneisen parameters. At low temperatures (where most optical modes with positive Grüneisen parameters are still not excited) the contribution from the negative Grüneisen parameters will be dominant and thermal expansion coefficient (which is directly proportional to Grüneisen parameters) negative. The lowest negative Grüneisen parameters correspond to the lowest transversal acoustic ZA modes. Phonon frequencies for such modes increase with the in-plane lattice parameter since atoms in the layer upon stretching will be less free to move in the z direction.
This is similar to the behavior of a string which is being stretched will have vibrations of smaller amplitude and higher frequency. This phenomenon, named "membrane effect", was predicted by Lifshitz in 1952.
Graphene’s unique electronic properties produce an unexpectedly high opacity for an atomic monolayer: it absorbs - 2.3 of white ligh. Based on the Slonczewski-Weiss-McClure (SWMcC) band model of graphite, the interatomic distance, hopping value and frequency cancel when the optical conductance is calculated using the Fresnel equations in the thin-film limit. This has been confirmed experimentally, but the measurement is not precise enough to improve on other techniques for determining the fine-structure constant. The optical response of graphene nanoribbons has been shown to be tunable into the terahertz regime by an applied magnetic field. [...] Graphene appears to be one of the strongest materials ever tested.
Measurements have shown that graphene has a breaking strength 200 times greater than steel, a bulk strength of 130 GPa. Using Atomic-Force Microscopy (AFM), the spring constant of suspended graphene sheets has been measured. Graphene sheets, held together by Van der Waals forces, were suspended over SiO2 cavities where an AFM tip was probed to test its mechanical properties. Its spring constant was in the range 1–5N/m and the Young’s modulus was 0.5 TPa, which differs from that of the bulk graphite. These high values make graphene very strong and rigid. These intrinsic properties could lead to using graphene for nanoelectromechanical systems (NEMS) applications such as pressure sensors and resonators. As is true of all materials, regions of graphene are subject to thermal and quantum fluctuations in relative displacement. Although the amplitude of these fluctuations is bounded in 3D structures (even in the limit of infinite size), the Mermin-Wagner theorem shows that the amplitude of long-wavelength fluctuations will grow logarithmically with the scale of a 2D structure, and would therefore be unbounded in structures of infinite size. Local deformation and elastic strain are negligibly affected by this long-range divergence in relative displacement.
It is believed that a sufficiently large 2D structure, in the absence of applied lateral tension, will bend and crumple to form a fluctuating 3D structure. Researchers have observed ripples in suspended layers of graphene, and it has been proposed that the ripples are caused by thermal fluctuations in the material. As a consequence of these dynamical deformations, it is debatable whether graphene is truly a 2D structure.