C. N. Lau

Extremely high thermal conductivity of graphene: Prospects for thermal management applications in nanoelectronic circuits

The authors reported on investigation of the thermal conductivity of graphene suspended across trenches in Si∕SiO2 wafer. The measurements were performed using a noncontact technique based on micro-Raman spectroscopy. The amount of power dissipated in graphene and corresponding temperature rise were determined from the spectral position and integrated intensity of graphene’s G mode. The extremely high thermal conductivity in the range of ∼3080–5150W∕mK and phonon mean free path of ∼775nm near room temperature were extracted for a set of graphene flakes. The obtained results suggest graphene’s applications as thermal management material in future nanoelectronic circuits.

Gate-tuning of graphene plasmons revealed by infrared nano-imaging

Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such medium—graphene—is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage. Here, using infrared nano-imaging, we show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and the wavelength of these plasmons by varying the gate voltage. Using plasmon interferometry, we investigated losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene. Standard plasmonic figures of merit of our tunable graphene devices surpass those of common metal-based structures.

Phase-Coherent Transport in Graphene Quantum Billiards

As an emergent electronic material and model system for condensed-matter physics, graphene and its electrical transport properties have become a subject of intense focus. By performing low-temperature transport spectroscopy on single-layer and bilayer graphene, we observe ballistic propagation and quantum interference of multiply reflected waves of charges from normal electrodes and multiple Andreev reflections from superconducting electrodes, thereby realizing quantum billiards in which scattering only occurs at the boundaries. In contrast to the conductivity of conventional two-dimensional materials, graphenes conductivity at the Dirac point is geometry-dependent because of conduction via evanescent modes, approaching the theoretical value 4e2/πh (where e is the electron charge and h is Plancks constant) only for short and wide devices. These distinctive transport properties have important implications for understanding chaotic quantum systems and implementing nanoelectronic devices, such as ballistic transistors.

Thermal contact resistance between graphene and silicon dioxide

The thermal contact resistance between graphene and silicon dioxide was measured using a differential 3ω method. The sample thicknesses were 1.2 (single-layer graphene), 1.5, 2.8, and 3.0 nm, as determined by atomic force microscopy. All samples exhibited approximately the same temperature trend from 42 to 310 K, with no clear thickness dependence. The contact resistance at room temperature ranges from 5.6×10−9 to 1.2×10−8 m2 K/W, which is significantly lower than previous measurements involving related carbon materials. These results underscore graphene’s potential for applications in microelectronics and thermal management structures.

Electronic doping and scattering by transition metals on graphene

We investigate the effects of transition metals (TM) on the electronic doping and scattering in graphene using molecular-beam epitaxy combined with in situ transport measurements. The room-temperature deposition of TM onto graphene produces clusters that dope

Spatially resolved spectroscopy of monolayer graphene on SiO2

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Variable temperature Raman microscopy as a nanometrology tool for graphene layers and graphene-based devices

type for all TM investigated (Ti, Fe, and Pt). We also find that the scattering by TM clusters exhibits different behavior compared to

Electrical detection of spin precession in single layer graphene spin valves with transparent contacts

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Electron-Hole Asymmetry of Spin Injection and Transport in Single-Layer Graphene

Coulomb scattering. At high coverage, Pt films are able to produce doping that is either

Effect of cluster formation on graphene mobility

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