Controlling the type and density of charge carriers in graphene is vital for a wide range of applications of this material in electronics and optoelectronics. To date, chemical doping and electrostatic gating have served as the two most established means to manipulate the carrier density in graphene. Although highly effective, these two approaches require sophisticated graphene growth or complex device fabrication processes to achieve both the desired nature and the doping densities with generally limited dynamic tunability and spatial control. Here, we report a convenient and tunable optical approach to tune the steady-state carrier density and Fermi energy in graphene by photochemically controlling the concentration of adsorbed molecular O 2 , a p-dopant in graphene, using femtosecond pulsed laser irradiation in the UV range. As an all-optical approach, it allows spatial control over doping levels. Combined terahertz (THz) spectroscopy and electrical device measurements reveal that the Fermi level in laser-illuminated graphene can be controllably and reversibly tuned between p-and n-type in a large range (over ∼600 meV from −420 to +180 meV) by readily tuning the peak intensity and the duration of the laser irradiation treatment. Furthermore, we demonstrate that our photochemical approach for doping of graphene allows one to optically write doping structure with spatial control. Given the ease, effectiveness, and simplicity of the method, this photochemical doping mechanism offers a simple, reversible approach to control the steady-state electronic and optical properties of graphene.

The addition of Nitrogen as a dopant in monolayer graphene is a flexible approach to tune the electronic properties of graphene as required for applications. Here, we investigate the impact of the doping process that adds N-dopants and defects on the key electronic properties, such as the mobility, the effective mass, the Berry phase and the scattering times of the charge carriers. Measurements at low temperatures and magnetic fields up to 9 T show a decrease of the mobility with increasing defect density due to elastic, short-range scattering. At low magnetic fields weak localization indicates an inelastic contribution depending on both defects and dopants. Analysis of the effective mass shows that the N-dopants decrease the slope of the linear bands, which are characteristic for the band structure of graphene around the Dirac point. The Berry phase, however, remains unaffected by the modifications induced through defects and dopants, showing that the overall band structure of the samples is still exhibiting the key properties as expected for Dirac fermions in graphene.

We present an overview of charge transport in selected one-, two-and three-dimensional carbon-based materials with exciting properties. The systems are atomically defined bottom-up synthesized graphene nanoribbons, doped graphene and turbostratic graphene micro-disks, where up to 100 graphene layers are rotationally stacked. For turbostratic graphene we show how this system lends itself to spintronic applications. This follows from the inner graphene layers where charge carriers are protected and thus highly mobile. Doped graphene and graphene nanoribbons offer the possibility to tailor the electronic properties of graphene either by introducing heteroatoms or by confining the system geometrically. Herein, we describe the most recent developments of charge transports in these carbon systems.