We show that strong photoluminescence (PL) can be induced in single-layer graphene using an oxygen plasma treatment. The PL is spatially uniform across the flakes and connected to elastic scattering spectra distinctly different from those of gapless pristine graphene. Oxygen plasma can be used to selectively convert the topmost layer when multilayer samples are treated.

Abstract:We observe the angular radiation pattern of single carbon nanotubes' photoluminescence in the back focal plane of a microscope objective and show that the emitting nanotube can be described by a single in-plane point dipole. The near-field interaction between a nanotube and an optical antenna modifies the radiation pattern that is now dominated by the antenna characteristics. We quantify the antenna induced excitation and radiation enhancement and show that the radiative rate enhancement is connected to a directional redistribution of the emission.

We report on near-field optical imaging of single-walled carbon nanotubes (SWNTs), observing photoluminescence (PL) quenching at nanotube ends and defects. The extension of reduced PL reflects the exciton diffusion length of about 100 nm, which can be directly visualized with our technique. Additionally, we model the complete imaging process, including exciton diffusion and tip-induced rate enhancement, for a deeper understanding of the experimental data and the determination of, e.g. diffusion length and tip enhancement from near-field PL images.

Down to the wire: High‐resolution photoluminescence (PL) and Raman images of CdSe nanowires were obtained using tip‐enhanced near‐field optical microscopy. They show that the optical properties of the CdSe nanowires vary significantly within a few nanometers leading to strong spatial fluctuations in both PL intensities and energies (see picture).

We review recent experimental studies on single-walled carbon nanotubes on substrates using tip-enhanced near-field optical microscopy (TENOM). High-resolution optical and topographic imaging with sub 15 nm spatial resolution is shown to provide novel insights into the spectroscopic properties of these nanoscale materials. In the case of semiconducting nanotubes, the simultaneous observation of Raman scattering and photoluminescence (PL) is possible, enabling a direct correlation between vibrational and electronic properties on the nanoscale. So far, applications of TENOM have focused on the spectroscopy of localized phonon modes, local band energy renormalizations induced by charge carrier doping, the environmental sensitivity of nanotube PL, and inter-nanotube energy transfer. At the end of this review we discuss the remaining limitations and challenges in this field.