Bulk ZnO samples, epitaxially grown ZnO layers, and ZnO nanostructures frequently exhibit a characteristic emission band at 3.31-eV photon energy whose origin is controversially discussed in the literature. Partly, this omnipresent band is ascribed to ͑e , A 0 ͒ transitions of conduction band electrons to acceptors, which are abundant in relatively high concentrations but have not positively been identified. The band is, in particular, often reported after intentional p-type doping of ZnO, preferentially with group V species. In the present work, we study the 3.31-eV band by low-temperature cathodoluminescence ͑CL͒ with high spatial resolution, by scanning electron microscopy, and by transmission electron microscopy ͑TEM͒. Line shape analyses at different temperatures give clear evidence that the band originates from an ͑e , A 0 ͒ transition where the acceptor binding energy is ͑130Ϯ 3͒ meV. The 3.31-eV luminescence is exclusively emitted from distinct lines on sample surfaces and cross sections representing intersections with basal planes of the wurtzite hexagons. Correlating monochromatic CL images with TEM images, we conclude that the localized acceptor states causing the 3.31-eV luminescence are located in basal plane stacking faults.

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Besides its interesting physical properties, graphene as a two-dimensional lattice of carbon atoms promises to realize devices with exceptional electronic properties, where freely suspended graphene without contact to any substrate is the ultimate, truly two-dimensional system. The practical realization of nano-devices from suspended graphene, however, relies heavily on finding a structuring method which is minimally invasive. Here, we report on the first electron beam-induced nano-etching of suspended graphene and demonstrate high-resolution etching down to ~7 nm for line-cuts into the monolayer graphene. We investigate the structural quality of the etched graphene layer using two-dimensional (2D) Raman maps and demonstrate its high electronic quality in a nano-device: A 25 nm-wide suspended graphene nanoribbon (GNR) that shows a transport gap with a corresponding energy of ~60 meV. This is an important step towards fast and reliable patterning of suspended graphene for future ballistic transport, nano-electronic and nano-mechanical devices.

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The time-resolved photoluminescence (PL) characteristics of single CdSe/ZnS nanoparticles, embedded in a PMMA layer is studied at room temperature. We observe a strong spectral jitter of up to 55 meV, which is correlated with a change in the observed linewidth. We evaluate this correlation effect using a simple model, based on the quantum confined Stark effect induced by a diffusing charge in the vicinity of the nanoparticle. This allows us to derive a mean distance between the center of the particle and the diffusing charge of approximately 3.3 nm on average, as well as a mean charge carrier displacement within the integration time. The distances are larger than the combined radius of particle core and shell of about 3 nm, but smaller than the overall radius of 5 nm including ligands. These results are reproducible, even for particles which exhibit strong blueing, with shifts of up to 150 meV. Both the statistics and its independence of core-shell alterations lead us to conclude that the charge causing the spectral jitter is situated in the ligands.