This review examines the properties of graphene from an experimental perspective. The intent is to review the most important experimental results at a level of detail appropriate for new graduate students who are interested in a general overview of the fascinating properties of graphene. While some introductory theoretical concepts are provided, including a discussion of the electronic band structure and phonon dispersion, the main emphasis is on describing relevant experiments and important results as well as some of the novel applications of graphene. In particular, this review covers graphene synthesis and characterization, field-effect behavior, electronic transport properties, magnetotransport, integer and fractional quantum Hall effects, mechanical properties, transistors, optoelectronics, graphene-based sensors, and biosensors. This approach attempts to highlight both the means by which the current understanding of graphene has come about and some tools for future contributions.

We demonstrate a combination of micro four-point probe (M4PP) and non-contact terahertz time-domain spectroscopy (THz-TDS) measurements for centimeter scale quantitative mapping of the sheet conductance of large area chemical vapor deposited graphene films. Dual configuration M4PP measurements, demonstrated on graphene for the first time, provide valuable statistical insight into the influence of microscale defects on the conductance, while THz-TDS has potential as a fast, non-contact metrology method for mapping of the spatially averaged nanoscopic conductance on wafer-scale graphene with scan times of less than a minute for a 4-in. wafer. The combination of M4PP and THz-TDS conductance measurements, supported by micro Raman spectroscopy and optical imaging, reveals that the film is electrically continuous on the nanoscopic scale with microscopic defects likely originating from the transfer process, dominating the microscale conductance of the investigated graphene film.

The electrical performance of graphene synthesized by chemical vapor deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles, and tears. In this study, we experimentally investigate and compare the nano- and microscale electrical continuity of single layer graphene grown on centimeter-sized single crystal copper with that of previously studied graphene films, grown on commercially available copper foil, after transfer to SiO2 surfaces. The electrical continuity of the graphene films is analyzed using two noninvasive conductance characterization methods: ultrabroadband terahertz time-domain spectroscopy and micro four-point probe, which probe the electrical properties of the graphene film on different length scales, 100 nm and 10 μm, respectively. Ultrabroadband terahertz time-domain spectroscopy allows for measurement of the complex conductance response in the frequency range 1-15 terahertz, covering the entire intraband conductance spectrum, and reveals that the conductance response for the graphene grown on single crystalline copper intimately follows the Drude model for a barrier-free conductor. In contrast, the graphene grown on commercial copper foil shows a distinctly non-Drude conductance spectrum that is better described by the Drude-Smith model, which incorporates the effect of preferential carrier backscattering associated with extended, electronic barriers with a typical separation on the order of 100 nm. Micro four-point probe resistance values measured on graphene grown on single crystalline copper in two different voltage-current configurations show close agreement with the expected distributions for a continuous 2D conductor, in contrast with previous observations on graphene grown on commercial copper foil. The terahertz and micro four-point probe conductance values of the graphene grown on single crystalline copper shows a close to unity correlation, in contrast with those of the graphene grown on commercial copper foil, which we explain by the absence of extended defects on the microscale in CVD graphene grown on single crystalline copper. The presented results demonstrate that the graphene grown on single crystal copper is electrically continuous on the nanoscopic, microscopic, as well as intermediate length scales.

Using very uniform large-scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D + D peak corresponding to a double-phonon process involving both an inter-and intravalley phonon.

Strain can be used as an alternate way to tune the electronic properties of graphene. Here we demonstrate that it is possible to tune the uniform strain of graphene simply by changing the chemical vapor deposition growth temperature of graphene on copper. Due to the cooling of the graphene on copper system, we can induce a uniform compressive strain on graphene. The strain is analyzed by Raman spectroscopy, where a shift in the 2D peak is observed and compared to our ab initio calculations of the graphene on copper system as a function of strain.

Absence of hyperfine effects in 13C-graphene spin-valve devices Wojtaszek, M.; Vera-Marun, I.J.; Whiteway, E.; Hilke, M.; Wees, B.J. van Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The carbon isotope 13 C, in contrast to 12 C, possesses a nuclear magnetic moment and can induce electron spin dephasing in graphene. This effect is usually neglected due to the low abundance of 13 C in natural carbon allotropes (∼1%). Chemical vapor deposition (CVD) allows for artificial synthesis of graphene solely from a 13 C precursor, potentially amplifying the influence of the nuclear magnetic moments. In this work we study the effect of hyperfine interactions in pure 13 C-graphene on its spin transport properties. Using Hanle precession measurements we determine the spin relaxation time and observe a weak increase of τ s with doping and a weak change of τ s with temperature, as in natural graphene. For comparison we study spin transport in pure 12 C-graphene, also synthesized by CVD, and observe similar spin relaxation properties. As the signatures of hyperfine effects can be better resolved in oblique spin-valve and Hanle configurations, we use finite-element modeling to emulate oblique signals in the presence of a hyperfine magnetic field for typical graphene properties. Unlike in the case of GaAs, hyperfine interactions with 13 C nuclei influence electron spin transport only very weakly, even for a fully polarized nuclear system. Also, in the measurements of the oblique spin-valve and Hanle effects no hyperfine features could be resolved. This work experimentally confirms the weak character of hyperfine interactions and the negligible role of 13 C atoms in the spin dephasing processes in graphene.

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Highly dendritic graphene crystals up to 0.25 mm in diameter are synthesized by low pressure chemical vapor deposition inside a copper enclosure. With their sixfold symmetry and fractal-like shape, the crystals resemble snowflakes. The evolution of the dendritic growth features is investigated for different growth conditions and surface diffusion is found to be the growth-limiting step responsible for the formation of dendrites. The electronic properties of the dendritic crystals are examined down to sub-Kelvin temperatures, showing a mobility of up to 6300 cm 2 V −1 s −1 and quantum Hall oscillations are observed above 4T. These results demonstrate the high quality of the transport properties despite their rough dendritic edges.The advent of large-scale graphene grown by chemical vapor deposition (CVD) on transition metals opens a viable and promising route towards the commercialization of graphene-based electronics. 1-3 The growth of graphene on copper has attracted considerable interest due to the simplicity, scalability, affordability, and homogeneity of the synthesized film. While this method solves the obvious problem of small-scale production associated with exfoliated graphene, it often results in a graphene film with lower electronic performance.