Negative differential resistance: gate controlled and photoconductance enhancement in carbon nanotube intraconnects.

Intraconnects, as-grown single-walled carbon nanotubes bridging two metal electrodes, were investigated as gated structures. We show that even with a seemingly "ohmic" contact at zero gate voltage one observes negative differential resistance (NDR) at nonzero gate bias. Large differential photo conductance (DPC) was associated with the NDR effect raising hopes for the fabrication of novel high-speed optoelectronic devices.

Micro-Raman spectroscopy as an enabling tool for long-term intracellular studies of nanomaterials at nanomolar concentration levels.

Given the importance of nanomaterials for medicine, health and biological sciences, a method for reliable intra-cellular tracking of nanocarbon materials at ultra-low concentrations was investigated. Namely, hyperspectral imaging of DNA-functionalized single-walled carbon nanotubes inside neural stem cells was demonstrated, over several mitosis cycles, also in a 3D z-stacking mode.

Size quantization of Dirac fermions in graphene constrictions.

Quantum point contacts are cornerstones of mesoscopic physics and central building blocks for quantum electronics. Although the Fermi wavelength in high-quality bulk graphene can be tuned up to hundreds of nanometres, the observation of quantum confinement of Dirac electrons in nanostructured graphene has proven surprisingly challenging. Here we show ballistic transport and quantized conductance of size-confined Dirac fermions in lithographically defined graphene constrictions. At high carrier densities, the observed conductance agrees excellently with the Landauer theory of ballistic transport without any adjustable parameter. Experimental data and simulations for the evolution of the conductance with magnetic field unambiguously confirm the identification of size quantization in the constriction. Close to the charge neutrality point, bias voltage spectroscopy reveals a renormalized Fermi velocity of ∼1.5 × 10(6) m s(-1) in our constrictions. Moreover, at low carrier density transport measurements allow probing the density of localized states at edges, thus offering a unique handle on edge physics in graphene devices.

Raman spectroscopy as probe of nanometre-scale strain variations in graphene.

Confocal Raman spectroscopy has emerged as a major, versatile workhorse for the non-invasive characterization of graphene. Although it is successfully used to determine the number of layers, the quality of edges, and the effects of strain, doping and disorder, the nature of the experimentally observed broadening of the most prominent Raman 2D line has remained unclear. Here we show that the observed 2D line width contains valuable information on strain variations in graphene on length scales far below the laser spot size, that is, on the nanometre-scale. This finding is highly relevant as it has been shown recently that such nanometre-scaled strain variations limit the carrier mobility in high-quality graphene devices. Consequently, the 2D line width is a good and easily accessible quantity for classifying the crystalline quality, nanometre-scale flatness as well as local electronic properties of graphene, all important for future scientific and industrial applications.